# Another Mill Choice Dilemma



## ptrotter (Sep 14, 2020)

I have decided that it is time to finally get a mill . I have been very happy with my PM1340GT lathe but am getting to the point where I am limited in what I can do.

For no particular reason, I have always wanted a Bridgeport style knee mill but I don't have the space, and in reality don't really need, a full size mill.  I seriously considered the PM935TS but decided that I want to do a CNC conversion and I think that is more difficult on a knee mill. Also, giving more thought to my use case, a decent bench type mill will be more than enough.  So now comes the dilemma.

I think if I were to design my perfect mill, it would have a 2 speed belt drive, maybe 3:1 and 1:3 ratios, with a 3 phase 1800rpm
inverter duty motor.  This would allow a good top speed and also pretty good power at lower RPMs.  Of course that doesn't exist so I have to look at what is available and decide what compromises I can live with.

I have read pretty much every post discussing the pros and cons of the various mills out there and still can't make up my mind.  I have a couple of required features and a few desired features:

Required:

1. Commercially available CNC conversion kit.  I can handle all the electronics and steppers, but I don't want to deal with the ball screws and motor mounts.

Desired:

1. 3 phase.  Almost a requirement, but could probably convert to 3 phase if not available initially.
2. Taiwan quality.
3. Decent low speed power
4. High speed maybe around 3000 to 5000 RPM.  I'm not looking at a true high speed CNC ATC spindle.
5. Decent size work envelope
6. Decent weight and therefore rigidity.

I think this boils down to 3 possible choices:

PM940M
PM833T
PM833TV

PM940M Pros

-Heaviest
-Largest work envelope
-CNC conversion available

PM940 Cons

-Chinese quality  - Replacing the lead screw with ball screws will offset some of this but still dealing with the casting quality.
-Gear drive - Limited high speed
-Only available in single phase.  Should not be too difficult to change to a 3 phase motor.  Would require either turning down the motor shaft or making an adapter to match the original shaft size and lifting the motor up to accommodate this.  This would also allow for higher speeds within the capability of the bearings.

PM833T Pros

-CNC conversion available
-Taiwan quality

PM833T Cons

-Gear drive - Limited high speed.
-Only available in single phase.  Should not be too difficult to change to a 3 phase motor.  Would require either turning down the motor shaft or making an adapter to match the original shaft size and lifting the motor up to accommodate this.  This would also allow for higher speeds within the capability of the bearings.
-Lighter weight than the PM940 but much of the difference may be in the 940's stand so the rigidity may not be much different.
-Slightly smaller work envelope than the 940.

PM833TV Pros

-Taiwan quality
-3 phase. 
-Higher speed
-CNC conversion available

PM833TV Cons

-Lower power at low RPM.  I'm not sure how much of an issue this is in a CNC machine.
-Built in VFD. I'm not fond of the built in VFD as I don't know what it is but this could be replaced to give more access to the VFD programming.  This is useful if I want to control spindle RPM through the CNC programming.

As can be seen, all the machines have good points.  I could go with a 940M or 833T and consider changing the motor and maybe eventually converting it to a belt drive.  This would get closest to my ideal machine but requires a lot of work.  I could go with the 833TV and get most of what I want on day one.  My problem is that I over think things and also think I need more than I do.  I am always scared that if I make any compromises, I will be mad about it in the future.

After typing all this and thinking about it, I am thinking my best option is to just go with the 833TV.  It has almost everything I want and I will probably never run into its limitations.  Not needing the axis powerfeeds and DRO pretty much offset the cost of the CNC conversion.

I am interested in everybody's thoughts on this.  I need to do something soon before I drive myself crazy.

Paul


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## markba633csi (Sep 14, 2020)

Seems like you are more than halfway there already, you've narrowed it down to one supplier!
-Mark


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## parshal (Sep 14, 2020)

I have the 833TV.  The low-end power hasn't caused me an issue yet.  However, I haven't worked with much other than aluminum right now.


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## 7milesup (Sep 14, 2020)

I am assuming that you have seen --> this conversion done by Dr. D-flo. He does a nice job in my opinion, especially with the electronics end of it. I am very interested myself in doing this conversion on my 833T. My hesitation is spending that nearly $1000 on just motor mounts and ball screws. I that Heavy Metal gets their ball screws from VXB which I don't think are very high quality. I could be wrong on that though. If I had the dimensions of the motor mounts I would just make them myself.


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## mksj (Sep 14, 2020)

Reviewing the information, it probably comes down to how much travel and drive system speed you need and less so about Chinese vs. Taiwan. Another factor would be available kits if you do not plan (or have the ability) to mill the parts to convert to CNC. I would probably go with the PM-940V-BASICw/HRDWYS, it is basically setup for conversion to CNC, it is a 2 speed Low 100-1640 RPM, High 350-5000 RPM variable speed head. Probably beyond 5000-6000 RPM the bearing would need to be switched out and change the pulley ratios. It has an option for hardened beds, you would want to add an automatic oiler. Seems to be a number of CNC kits available, this was also can include Clear Path or DMM servos. I had looked into DMM servos in the past and they have some very nice drives/controllers. If going with the PM-833, the TV seems to be a more logical choice for reliability and convert the head to a 2 speed pulley belt system. In both mills you are already starting out with a VFD rated motor and drive, the downside would be if there is any provision for interfacing its control with a CNC system. You could interface a control relay to turn on/off the drive. You also could check if any of the CNC retrofit vendors have something in the works for the PM-833TV.  Both mills are close to the same price, but for a CNC conversion project I think the PM-940V has a bit more going for it.


			PM 940M CNC conversion Kits


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## chipping (Sep 14, 2020)

Ptrotter - excellent summary of the options.

I am also considering a path to CNC.  What I would love to see is Precision Matthews offering a stripped-down mill, as referenced by davidpbest in the other thread: https://www.hobby-machinist.com/threads/pm1340gt-mods.86651/post-776456

What I envision is the frame (base and column) and table with precision ballscrews and mounts for NEMA motors.  But no motors, head/spindle, controllers, or software.  That way the end-user can customize based on cost, quality, features, and materials to be milled.

The Dr. Flo video referenced by 7milesup is excellent, but shows the complexity of the conversion.  (And PM needs to stop gluing the column to the base with paint.)  Converting to CNC is more complex, time-consuming and expensive than necessary because of the extra work that went into making it a manual mill.

Bonus points if the 833 is offered with an iron cast base - perhaps the PM-940 one, although it might need new mounting holes.

[And if PM ever wanted to offer a CNC-only machine, then the design choices open up.  But I acknowledge that is a lot more design/engineering/manufacturing/customer support, so I am opting for what seems to me the simplest path.]


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## Skowinski (Sep 14, 2020)

After 3 months of wandering back and forth through the entire PM lineup from the 727's to the 935, I ended up with an 833TV.  There's always some tradeoff it seems.  I was a bit concerned about low RPM power with this mill.  But, decided that the better high end RPM was worth the tradeoff, and anyway I'm not likely to go much down below 200-300 RPM for my intended uses.  

For awhile I was about to buy an 833T and put a VFD and 3-phase motor on it, but the expense and possibility of exploding the gearbox if I pushed the RPMs too high worried me.

I figured if the proprietary VFD that comes on the 833TV fizzles out I can just replace it with a mainstream Hitachi or Teco VFD.  At least I have the 3-phase motor already.

I have wondered if a 2 step pulley could be adapted to the 833TV?


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## davidpbest (Sep 14, 2020)

chipping said:


> Ptrotter - excellent summary of the options.
> 
> I am also considering a path to CNC.  What I would love to see is Precision Matthews offering a stripped-down mill, as referenced by davidpbest in the other thread: https://www.hobby-machinist.com/threads/pm1340gt-mods.86651/post-776456
> 
> What I envision is the frame (base and column) and table with precision ballscrews and mounts for NEMA motors.  But no motors, head/spindle, controllers, or software.  That way the end-user can customize based on cost, quality, features, and materials to be milled.



If you’d be interested in a stripped down 940 for CNC conversion, I would be as well.  If we could get a handful of people interested, maybe we could talk Matt into sourcing such a configuration.  

My interest in doing a CNC conversion is increasing rapidly - I need a new project to sink teeth into.  The 940 with hardened ways looks like the most desirable path so far in my research.   Assuming the ways are hardened, the China versus Taiwan quandary strikes me as nearly irrelevant if in the conversion process the positioning guts are all replaced, the spindle is upgraded in some manner to achieve 5k RPM.   I’m still intrigued with the idea of using some kind of replacement spindle more suitable for CNC work rather than upgrading the OEM head, but haven’t done much digging on the replacement spindle options.  I’d love to hear more on this aspect from others who have deeper experience than I do.   Mark suggested the 940V with a hint toward retaining the OEM spindle/motor, and while that sounds like an expedient path, for me at least it causes the ”China v Taiwan” question to pop up again.  

I’m also not sure that 350 pound cast base is ideal if the intent is to ultimately have an enclosure.  I think I’d rather fabricate my own stand with better facilities for chip evacuation below.    My experience building my own platform for the 1340 lathe was both gratifying, and the end result superior to the option offered by PM.


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## Watchwatch (Sep 14, 2020)

I’d be interested in a stripped down PM Taiwan bench top mill for CNC conversion. No motor, ball screws installed, no motor, axis and motor mount options.


Check out Clough42 spindle upgrade for his Grizzly. Very impressive what a $3000 12k spindle can do on a benchtop mill. That video series, actually the test cuts, really made me want a CNC.


Sent from my iPhone using Tapatalk


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## mksj (Sep 14, 2020)

davidpbest said:


> OEM spindle/motor, and while that sounds like an expedient path, for me at least it causes the ”China v Taiwan” question to pop up again.



You get a 3 year warranty, it either holds up or fails. If you want a higher speed spindle or worried about longevity there are better bearings. If the motor eventually fails, then replace it with vector motor, and if you want power tapping add an encoder.  I worked with a number of individuals that went with the PM-932 in the past (before a 940 was available) and they added a Marathon Black Max 3 Hp motor. More recently there have been some AB (same as Baldor) vector motors that one person went with a 3 Hp in his mill and another a 5 Hp 130lb brute in his lathe.


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## ptrotter (Sep 14, 2020)

mksj said:


> Reviewing the information, it probably comes down to how much travel and drive system speed you need and less so about Chinese vs. Taiwan. Another factor would be available kits if you do not plan (or have the ability) to mill the parts to convert to CNC. I would probably go with the PM-940V-BASICw/HRDWYS, it is basically setup for conversion to CNC, it is a 2 speed Low 100-1640 RPM, High 350-5000 RPM variable speed head. Probably beyond 5000-6000 RPM the bearing would need to be switched out and change the pulley ratios. It has an option for hardened beds, you would want to add an automatic oiler. Seems to be a number of CNC kits available, this was also can include Clear Path or DMM servos. I had looked into DMM servos in the past and they have some very nice drives/controllers. If going with the PM-833, the TV seems to be a more logical choice for reliability and convert the head to a 2 speed pulley belt system. In both mills you are already starting out with a VFD rated motor and drive, the downside would be if there is any provision for interfacing its control with a CNC system. You could interface a control relay to turn on/off the drive. You also could check if any of the CNC retrofit vendors have something in the works for the PM-833TV.  Both mills are close to the same price, but for a CNC conversion project I think the PM-940V has a bit more going for it.
> 
> 
> PM 940M CNC conversion Kits



Mark,

Somehow I seemed to miss the 940V completely. I swear it wasn't on their website this morning. This looks like it could be a good option. I was leaning toward the 940M but didn't like the gearbox so I was thinking the 833TV but this changes things. I'm not sure how they do the variable speed on the 940V though.  The specs say it is a single phase motor but that could be a misprint held over from the 940M specs.   Hopefully it is actually a 3 phase motor.  If the column and the bed is the same as the 940M, the ArizonaCNCKit conversion would work.  I'll call PM in the morning and find out more.  ArizonaCNCKits is suppoedly coming out with a belt drive conversion for the 940M as well but he hasn't started on it yet.  I believe it will be a 2 speed unit which would be great.  I already have a sherline mill set up for CNC with a Centroid Acorn board so all I would need to do is put in the appropriate stepper or server motors and bigger motor drivers and I will be set.  The electronics are the easy part for me.  I know nothing about ball screws and nuts so that is why I am looking for that as a kit.

Paul


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## davidpbest (Sep 14, 2020)

Yea, I referenced James’ spindle in *the other thread.*   If the conversion is essentially eliminating everything except the castings, then the insistence on Taiwanese-made seems to me to be largely irreverent.


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## ptrotter (Sep 14, 2020)

Watchwatch said:


> I’d be interested in a stripped down PM Taiwan bench top mill for CNC conversion. No motor, ball screws installed, no motor, axis and motor mount options.
> 
> 
> Check out Clough42 spindle upgrade for his Grizzly. Very impressive what a $3000 12k spindle can do on a benchtop mill. That video series, actually the test cuts, really made me want a CNC.
> ...



The Clough42 videos are great.  I think I have watched all of them, including his ATC spindle conversion.  His videos are what prompted me to get moving on getting a mill.


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## ptrotter (Sep 14, 2020)

mksj said:


> You get a 3 year warranty, it either holds up or fails. If you want a higher speed spindle or worried about longevity there are better bearings. If the motor eventually fails, then replace it with vector motor, and if you want power tapping add an encoder.  I worked with a number of individuals that went with the PM-932 in the past (before a 940 was available) and they added a Marathon Black Max 3 Hp motor. More recently there have been some AB (same as Baldor) vector motors that one person went with a 3 Hp in his mill and another a 5 Hp 130lb brute in his lathe.



Mark,

Do you know how the person who put the Black Max motor on the PM-932 dealt with the shaft size differences?  I assume the PM uses metric shaft motors, but maybe I am wring.

Paul


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## davidpbest (Sep 14, 2020)

ptrotter said:


> Mark,
> 
> Somehow I seemed to miss the 940V completely. I swear it wasn't on their website this morning. This looks like it could be a good option. I was leaning toward the 940M but didn't like the gearbox so I was thinking the 833TV but this changes things. I'm not sure how they do the variable speed on the 940V though.  The specs say it is a single phase motor but that could be a misprint held over from the 940M specs.   Hopefully it is actually a 3 phase motor.



The 940V didn’t hit my radar screen until early this afternoon.  I will be interested to hear what you find out from PM.  You’d think that when they introduce a new product, they’d blast out a post or email with more details.

My bet is that the machine has a two-speed, 3-phase motor, and the electronic controls switch the VFD output between the different windings to achieve low and high speed.  My RF45 (sold when I got my PM935) had a two-speed, 3-phase motor, and even without a VFD would operate the spindle at 3,100 RPM.  Assuming the motor is of sufficient quality, it’s easy to see how 5K is within reach with the VFD putting out ~100Hz.  

My questions are more about what’s been done to the gear train and spindle bearings to actually handle 5k RPM on a consistent basis - especially since this is from China and not Taiwan.  One thing is for sure - it going to be loud.  

Please let us know what you find out.


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## ptrotter (Sep 14, 2020)

davidpbest said:


> The 940V didn’t hit my radar screen until early this afternoon.  I will be interested to hear what you find out from PM.  You’d think that when they introduce a new product, they’d blast out a post or email with more details.
> 
> My bet is that the machine has a two-speed, 3-phase motor, and the electronic controls switch the VFD output between the different windings to achieve low and high speed.  My RF45 (sold when I got my PM935) had a two-speed, 3-phase motor, and even without a VFD would operate the spindle at 3,100 RPM.  Assuming the motor is of sufficient quality, it’s easy to see how 5K is within reach with the VFD putting out ~100Hz.
> 
> ...



David, I'll see what I can find out.  Looking at the picture closer, it has a 2 speed belt drive and the motor looks like a 3 phase motor.  If so, I think it would be a great choice , it pretty much matches what I had described in my initial post as ideal for me.  I would probably replace the VFD and the control panel to match my needs but that is not a big deal.

Paul


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## addertooth (Sep 14, 2020)

I would toss in that the brushless motors are inherently 3 phase.  Which is why with their small HP figures they have rather good torque. 
They have the bonus of not needing your shop wired for 3 phase power. An example would be the PM 728VT, which has a peak RPM of 4000 as well. It is a two speed belt drive. So it is quieter than many of the gear-drive bretheren.


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## davidpbest (Sep 14, 2020)

ptrotter said:


> David, I'll see what I can find out.  Looking at the picture closer, it has a 2 speed belt drive and the motor looks like a 3 phase motor.  If so, I think it would be a great choice , it pretty much matches what I had described in my initial post as ideal for me.  I would probably replace the VFD and the control panel to match my needs but that is not a big deal.
> 
> Paul


Bingo!   I see it now.   Kipp lever to release belt tension, handle to swing the motor, clear markings on the face of the head.  Ugh  -  not what I was hoping for or how I would have spec’d it.  Worse than the backgear on a J-head.   Fine for manual mill I guess, but you aren’t going to find any G-code that will change that belt position from a CNC controller.     Too bad they didn’t put this two-belt position setup on the 833TV - that would have resolved my issue about low end torque on that model.

My thinking is still more in the camp of using the ATC spindle James is putting on his Grizzly mill - or something similar. That seems like a viable alternative to using the OEM spindle and upgrading bearings, Black Max motor replacement and a PDB and still stuck with R8. But I’ve been back and forth more than a dozen times.


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## ptrotter (Sep 15, 2020)

davidpbest said:


> Bingo!   I see it now.   Kipp lever to release belt tension, handle to swing the motor, clear markings on the face of the head.  Ugh  -  not what I was hoping for or how I would have spec’d it.  Worse than the backgear on a J-head.   Fine for manual mill I guess, but you aren’t going to find any G-code that will change that belt position from a CNC controller.     Too bad they didn’t put this two-belt position setup on the 833TV - that would have resolved my issue about low end torque on that model.
> 
> My thinking is still more in the camp of using the ATC spindle James is putting on his Grizzly mill - or something similar. That seems like a viable alternative to using the OEM spindle and upgrading bearings, Black Max motor replacement and a PDB and still stuck with R8. But I’ve been back and forth more than a dozen times.



Maybe not optimal, but then how often do you have to change the speed enough on a single setup that you would need to change the speed range.  Still better than a gear box. At least it should be reasonably quiet.  Why would you have liked this on the 833TV but not on the 940 except that the 833 is Taiwanese?

For my use case this is probably a good alternative.  Large work envelope, good speed, and decent low speed power with minimal upgrades required.  Assuming the castings are the same as the 940M, the CNC upgrade using the ArizonaCNCKit conversion is fairly simple.  Perhaps a future motor upgrade and new VFD, but that would not be necessary anytime in the near term.

I wonder what kind of low speed torque you get with the ATC spindle that James is using?  I do like the ease of tool change though.

Thanks for your comments. your insight is appreciated.

Paul


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## mksj (Sep 15, 2020)

I do not know the specifics as to the PM-940V, but I would assume it is akin the the PM-833TV vs. the M. Belt drive, and in the PM-940V it has a more desirable 2 speed belt drive. It is purposely built for CNC conversion, I see no reason for QMT to add more customization when there are other individuals already offering decent conversions. Often individuals want different build specs. such as the ball screws, so better to allow people to outsource these components then try to carry all the options. Give QMT a call and you should be able to get more details.

So an old thread on a full CNC conversion of the PM-932, I think a lot of it was based off of conversion that JBOLT did. In most of these builds the old gear box is removed and a belt drive is implemented. I can't recall if JBOLT also went with a Marathon motor. TomS pretty much milled all new hardware for a 2 speed belt drive. Since the vast majority of CNC involved small cutters, I think the need to change the belts speed would be infrequent. Even when I run face mills, in steel for a 2.5" I run 600-1000 RPM, aluminum 2-3X that speed. Shouldering in steel, still in the 600-800 RPM range. Inverter/Vector motors have full torque almost to 0 RPM and you can easily dial up the VFD's to 180-200% overload for up to a minute. Given that they top out at 6000 RPM it gives a very wide operating window.  Some industry people will even push the vector motors 10-20% over the max RPM w/o issue, but I see no practical reason to do so in this application. If one wants to be in the 8-12K spindle speed region, then going with a more purposely built CNC mill like the Tormach 1100MX will take you to 10K RPM.  The pricing on the 3 HP ATC ISO spindles I saw listed was pushing 3K and then one needs to adapt it to your mill head, there are some Chinese variants for less, and back to long term reliability.








						Taking the CNC Plunge
					

you jumper them at the plug just like X and Y, they will fit in the connector housing. Steve




					www.hobby-machinist.com
				




The PM-940V is single phase input, i.e. but the variable speed motor is not single phase. I am assuming that the motor is an inverter style, it may be a TEBC from the pictures, which is what I have on my mill. These typically operate from 15-20Hz to 200 Hz, so a much wider usable speed range. The approach one would take depends on the the end point of the conversion and how deep your pockets are. One can take as basic approach, that the drive system is at least good to 5000 RPM, and longevity wise should last a long time. At least as a starting point.  Arizona CNC seems like they will put together all the parts, and do some customization as to drive components. Their pricing seems very reasonable and they offer different build levels as to the drives selected, and in some cases priced below market pricing. Also may provide post sales support.


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## davidpbest (Sep 15, 2020)

ptrotter said:


> Maybe not optimal, but then how often do you have to change the speed enough on a single setup that you would need to change the speed range.  Still better than a gear box. At least it should be reasonably quiet.  Why would you have liked this on the 833TV but not on the 940 except that the 833 is Taiwanese?



I do a lot of work in stainless and 4140, so I need low end torque for tapping and drilling.  It would be a real PITA to have to change belt positions in the middle of machining a part that was otherwise fully automated via automatic tool changes.  If your standing there changing tools with a drawbar hammer between operations, then of course a belt change is a minor irritant.  

The spindle James is putting on his Grizzly Is 4 pole, or two-speed, so it can run at slower speeds without giving up so much torque using a sensor less vector VFD.  Some specs are *here*.

Have a look at *this video* showing that spindle working in steel.

As for my comment on the 833, let me clarify.   The 833TV most obvious drawback is lack of low end torque because at 100 RPM the VFD is putting out maybe 10Hz.  So a two position belt would have been ideal on that machine for use as a manual mill.   The fact that the 940V has a two position belt is great - provided its used as a manual mill.  I’m glad PM didn’t try to span 50-3200 RPM without a belt change on the 940V, like they do on the 833TV.  But both machines could just as easily been done with two-speed motors and no belt change to get similar benefit (but this would probably cost more).  Not a big deal for manual machining to change belts, but pretty disruptive to change belts in a series of CNC operations that include an ATC. 

I‘m not in disagreement with you about the utility of the 940V given your desire to do as little as possible for the conversion. It looks ideal, assuming the right things have been done with motor, VFD, spindle bearings for 5K RPM duty. Being from mainland China I am a bit suspicious. But as Mark points out, it does have 3 year warranty. Do think about a power drawbar - I spent the better part of a week on a Tormach without a PDB and it was excruciating.

In my case, I’m open to more substantial conversion efforts to attain perfection.   Can the “Best & Jacobs full Custom CNC” be that far off?    LOL


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## davidpbest (Sep 15, 2020)

mksj said:


> If one wants to be in the 8-12K spindle speed region, then going with a more purposely built CNC mill like the Tormach 1100MX will take you to 10K RPM. The pricing on the 3 HP ATC ISO spindles I saw listed was pushing 3K and then one needs to adapt it to your mill head


1100mx is ~$20K now.   Just saying.


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## ptrotter (Sep 15, 2020)

I'm going to try to get more info from PM tomorrow on the 940V particularly regarding the motor and VFD. This could be a good choice for me.  I don't think I am likely to need to do much outside of its capabilities.  I'm going to spend some time doing research on servo/stepper motors and drives to see what makes sense from a cost vs performance/accuracy perspective.  I have been playing around with some recently to get some basic knowledge.  

The ArizonaCNC stuff looks pretty good.  I sent him an email yesterday with a couple of questions and he responded fairly quickly. When I get a little closer, I might ask him for some recommendations as to which servo/stepper motors to use, he seems to offer several choices.

Is there any value to a PDF on a CNC machine?  It is an option on the 940V and I am wondering if it is worth it if I am going go CNC.  My milling knowledge is somewhat limited at this time.  I suppose there might be times I just want to bore a single hole and don't want to bother programming it.

I need to stop analyzing this and just buy something.


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## ptrotter (Sep 15, 2020)

davidpbest said:


> I do a lot of work in stainless and 4140, so I need low end torque for tapping and drilling.  It would be a real PITA to have to change belt positions in the middle of machining a part that was otherwise fully automated via automatic tool changes.  If your standing there changing tools with a drawbar hammer between operations, then of course a belt change is a minor irritant.
> 
> The spindle James is putting on his Grizzly Is 4 pole, or two-speed, so it can run at slower speeds without giving up so much torque using a sensor less vector VFD.  Some specs are *here*.
> 
> ...



I see your point on the speed change but I need to draw the line somewhere or I will never get anything.  Even the 940V or 833TV is much more than I probably need.  I am looking at them more for the work size, particularly the X axis, than anything else.  If changing belts becomes and issue, I guess I could always change the motor to a 2-speed motor and leave the belt in 1 position.

That ATC spindle is quite impressive.  If Matt could get a Taiwanese casting without a head that might be an interesting way to go. Of course you need a mill to make the parts to do that.

I do expect to see a full blown CNC version from you at some point, probably with automatic tool changing as well.  I once started a project to rebuild an old Southbend lathe.  I took it all apart and started cleaning and painting the pieces.  That was about 8 years ago and it is still in pieces in the corner of my shop.  I now know better than try that again.   I'm better at making small incremental improvements that don't interrupt the use of the tool for too long like the one shot oiler on my lathe.  I also have an airplane in my shop that I started building about 15 years ago that is 90% done that I need to finish.  I don't need another major project but I will watch yours with great interest.


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## davidpbest (Sep 15, 2020)

ptrotter said:


> Is there any value to a PDF on a CNC machine?  It is an option on the 940V and I am wondering if it is worth it if I am going go CNC.  My milling knowledge is somewhat limited at this time.  I suppose there might be times I just want to bore a single hole and don't want to bother programming it.



To me, a mill without a PDB is like a lathe without a QCTP - even worse.   Watch *this video*.    Then *watch this typical milling sequence*, noticing the tool changes, and imagine dealing with the drawbar every tool change.


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## ptrotter (Sep 15, 2020)

davidpbest said:


> To me, a mill without a PDB is like a lathe without a QCTP - even worse.   Watch *this video*.    Then *watch this typical milling sequence*, noticing the tool changes, and imagine dealing with the drawbar every tool change.



David, I was questioning the need for a Power Down Feed for CNC, I definitely see the need for a Power Draw Bar.

Paul


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## mksj (Sep 15, 2020)

No reason to have a PDF on a CNC machine. I think David is referring to an ATC or some form of quick change system. I might be missing something in CNC of stainless, you are still using an RPM in the 1-2K range for 1/4-1/2" end mills. Tapping requires very little power for smaller sizes and would require some form of positional control (encoder) for the motor. I do not see a motor/spindle designed to spin in the 10-12K+ range having enough low speed power for tapping unless it was significantly oversized. I also do not see the advantage of a 2/4 pole motor when a 4 pole motor can spin to 6K RPM or more, which is much higher than a 2P 60Hz motor. I was interested in the DMM drives in the past because they were AC servo and there was no issue with generation if using a mill in a manual mode (although this is probably not a factor in a full CNC conversion).


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## ptrotter (Sep 15, 2020)

So I spoke with Matt at PM at length about the PM-940V.  It sounds like they had it built for those who want to do a CNC conversion.  It has the same casting as the PM-940M, just a different head.  The head has a 2 speed belt drive and a new spindle and 3 phase motor.  Matt says he has run it at high speed for 24 hours and the bearings only get a little warm.  The VFD is a Delta VFD so it should be possible to get the programming information if one wants to change anything or add CNC spindle speed control.  It looks like a good choice for my needs.  It comes in at the same price as the 833TV w/stand but is heavier, has a larger work envelop and a higher top speed.  It also looks like the CNC conversion is easier on the 940 than the on the 833.  They have already sold a couple so I guess I need to get my order in soon.  I'll probably drive down to their warehouse and pick it up.


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## chipping (Sep 15, 2020)

I agree - the motor is a reasonable choice.  I'd extrapolate it is running from about 15 Hz to about 225 Hz at high speed.  Maybe the upper limit is capped by the bearings, in which case the maximum rpm would be at a lower frequency.  Not sure what the torque curve is like, but it seems reasonable that you could keep to one of the two belt speed options when milling a part (the speed choice governed by the material being milled).

As for making it ATC-capable, the R8 might not be optimal.  But you can leverage manual mill tooling.  So, also a reasonable choice for non-production.  (Don't think I want to venture into ATC quite yet.)

The question of Chinese vs Taiwanese remains.  But if you have to swap in the ballscrews, then you are disassembling and reassembling every part of the machine.  There is still risk in the finish of the surfaces that matter, and the precision in holes.

Finally, I think that an oiler system would be either a requirement or very highly desirable in CNC.  I don't see that the 940 comes with it.


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## davidpbest (Sep 15, 2020)

ptrotter said:


> David, I was questioning the need for a Power Down Feed for CNC, I definitely see the need for a Power Draw Bar.
> 
> Paul


Sorry I misread your question.   No need for PDF on a CNC machine.   If you plan to use the machine as a manual mill for some time prior to cnc conversion, and you intend to work with a boring head, you'd want PDF.

Thanks for the update about the 940V.  

I spent many hours yesterday digging into CNC control software - Mach3, Mach4, LinuxCNC.  These bring a bewildering complexity that I do not want in my life.  EVER!   So I will be exploring alternatives that actually are well supported, or I will give up on the idea of doing a CNC conversion and go with Tormach.


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## ArmyDoc (Sep 15, 2020)

davidpbest said:


> If you’d be interested in a stripped down 940 for CNC conversion, I would be as well.  If we could get a handful of people interested, maybe we could talk Matt into sourcing such a configuration.





Watchwatch said:


> I’d be interested in a stripped down PM Taiwan bench top mill for CNC conversion. No motor, ball screws installed, no motor, axis and motor mount options.





ptrotter said:


> Is there any value to a PDF on a CNC machine?  It is an option on the 940V and I am wondering if it is worth it if I am going go CNC.  My milling knowledge is somewhat limited at this time.  I suppose there might be times I just want to bore a single hole and don't want to bother programming it.
> 
> I need to stop analyzing this and just buy something.



I would be interested in the 940M for an eventual CNC conversion, especially if there was a discount for multiple purchasers/group purchase.  Only snags would be a) I wont have my shop up for a couple months and b) I wouldn't want a stripped one because I want to learn on it before converting.  I would either want the #7 option with PDF and hardened ways, or more likely the #8 option with DROs.  I realize it would be redundant/unnecessary  for CNC, but I would definitely want them for manual work until I did the CNC conversion...


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## mksj (Sep 15, 2020)

I have worked with the Delta VFD's in the past, and done some programming. They are decent programmable VFD's, or it can be easily upgraded if needed. So maybe a plus for the 940V as a more traditional VFD implementation. The PM-932 and PM-940 have been around for quite awhile with quite a few CNC conversions, if there were issues with the castings and or other functional issues they would have been mentioned. All you need is good bones for the CNC conversion. Given the weight of the heads and also that you will get uneven wear on the gibs, I would use some form of counterbalance or gas strut system to offset the weight of the head. Add a powered drawbar system, otherwise the manual tooling changes and height changes will be a real PTA. Alternative would be a TTS type system, so all the tool heights are programmed in. Also need a probe system, lot of moving pieces to get it all to work together. I do not know squat about the CNC control software, I leave that to David to figure out.

On the stand, the 940V is cast iron and recommended because of the weight, but I am in agreement with David that one would probably be better off fabricating a stand with enclosure if one has the means. Price wise close enough with the 833TV that it is a matter of choice between the two. Not sure on the type of motor on the 833TV but it needs to cover a very wide speed range, Arizona CNC does have a dual pulley conversion for the 940M and others have made their own dual speed belt drives, so it may be an option for higher CNC speeds.


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## ptrotter (Sep 15, 2020)

Here is a picture of the control box for the 940V that Matt sent me.  The VFD is a Delta VFD015E21 and the manual is online.


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## ptrotter (Sep 15, 2020)

davidpbest said:


> If you’d be interested in a stripped down 940 for CNC conversion, I would be as well.  If we could get a handful of people interested, maybe we could talk Matt into sourcing such a configuration.



I asked Matt about a stripped down version and he said the manufacturers don't want to do it.  It sounds like he looked into at one time.


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## ptrotter (Sep 15, 2020)

mksj said:


> I have worked with the Delta VFD's in the past, and done some programming. They are decent programmable VFD's, or it can be easily upgraded if needed. So maybe a plus for the 940V as a more traditional VFD implementation. The PM-932 and PM-940 have been around for quite awhile with quite a few CNC conversions, if there were issues with the castings and or other functional issues they would have been mentioned. All you need is good bones for the CNC conversion. Given the weight of the heads and also that you will get uneven wear on the gibs, I would use some form of counterbalance or gas strut system to offset the weight of the head. Add a powered drawbar system, otherwise the manual tooling changes and height changes will be a real PTA. Alternative would be a TTS type system, so all the tool heights are programmed in. Also need a probe system, lot of moving pieces to get it all to work together. I do not know squat about the CNC control software, I leave that to David to figure out.
> 
> On the stand, the 940V is cast iron and recommended because of the weight, but I am in agreement with David that one would probably be better off fabricating a stand with enclosure if one has the means. Price wise close enough with the 833TV that it is a matter of choice between the two. Not sure on the type of motor on the 833TV but it needs to cover a very wide speed range, Arizona CNC does have a dual pulley conversion for the 940M and others have made their own dual speed belt drives, so it may be an option for higher CNC speeds.



One advantage of the belt drive is that the head should be lighter.  The head on the 833TV seems to be 150 lbs. lighter than on the 833T, but something to offset the weight would be good.

I have learned a bit about CNC recently and think a TTS tool system would work well as Mark stated, as your tool heights are known.  I think it is actually possible with the right tool height sensor to dynamically determine an set the tool height during the CNC tool change process, but that is probably more trouble than it is worth.

Arizona CNC is looking at doing a dual pulley system for the 940M but has not started on it yet according to an email I got from him a couple of days ago. He did a CNC conversion on his 940M and has some videos of it and he seems pleased with results.  That is how he designed his conversion kit.

It is a toss up between the 833TV and the 940V at this time, but the heavier weight and larger work envelope of the 940V may win.  Matt also said that he feels the 940 is better for a CNC conversion.  Probably a little less accurate and a lousy paint job but it should be good for what I need.  Matt did say that his biggest complaint to the Chinese manufacturers is that they can't for some reason do a decent paint job.

I'll probably pull the trigger this week.


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## chipping (Sep 15, 2020)

> ptrotter: VFD is a Delta VFD015E21


Well, it is well documented.  Speed can be controlled with a traditional 0-10V signal.  So it seems that a controller that can output that analog range can control the speed of the spindle (within the range of one belt setting).  (And getting the software to work is probably the tricky part.)


> I asked Matt about a stripped down version and he said the manufacturers don't want to do it.


I am coming to the conclusion that the (new?) PM-940V is a suitable choice.  As davidpbest mentioned, I also need to do homework regarding the software and controllers.


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## ptrotter (Sep 15, 2020)

chipping said:


> Well, it is well documented.  Speed can be controlled with a traditional 0-10V signal.  So it seems that a controller that can output that analog range can control the speed of the spindle (within the range of one belt setting).  (And getting the software to work is probably the tricky part.)
> 
> I am coming to the conclusion that the (new?) PM-940V is a suitable choice.  As davidpbest mentioned, I also need to do homework regarding the software and controllers.



I have a Centroid Acorn setup on my Sherline mill that seems to work fine and is fairly easy to setup and use.  The other commoin alternatives are Mach3/4 and LinuxCNC.  They all seem pretty similar.  I'll probably use Clearpath servos for the axes.  They have built in motion controllers so all I need is a new power supply and I can hook up my existing Acorn board and I am all set.  I have been doing a lot of reading and video watching.  I have learned a little Fusion360 to do the modeling, but the most difficult part I find is the CAM portion.  You need to set up a lot of info on your tooling, tool length, speed, depth of cut, etc.  You need to model your vise and other hold downs holding your raw stock to make sure you don't hit them.  It gets pretty complex.  3D printing is much easier.


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## ptrotter (Sep 16, 2020)

I pulled the trigger on a PM-940V.  I will pick it up next week probably.  I decided to do the 940V for a couple of reasons.

1. Ease of CNC conversion with an ArizonaCNC kit
2. Higher RPM at 5000
3. 3 phase motor
4. Dual speed belt drive for decent low end power
5. Belt drive should be quieter than a gear box
6. Large work envelope, particularly the X axis
7. Decent weight

I understand the fit and finish will not be as good as the 833 but I can live with that.  Maybe I will strip the paint and redo it like davidpbest does.  I'll have it apart for the CNC conversion anyway.  Since I will be putting in ball screws, any lack of precision in the Chinese lead screws and bearings will be removed.

There are always compromises, but I think this machine gets me closest to what meets my needs.

Now on to the next step, vises, work holding, tooling, etc, etc, etc, another dilemma, it never ends. LOL


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## davidpbest (Sep 16, 2020)

Good for you.   That will be a terrific CNC conversion project.   I hope you document the process here.

Repainting the machine would be a simple task if you're taking it apart for ball screw installation anyway.  I've been through it a few times now, and if you want any help or suggestions on the process let me know.  Get rid of the fragille chalky factory body filler and replace it with Bondo - otherwise your new paint job will chip and flake just like the original from the factory.

I wrote to Matt last night about the 940V saying that if I got one, I would be building my own stand and enclosure, and asking if it can be ordered without the 350 pound factory supplied stand.   Here is his reply:
​


> AS far as the 940V Mill, they only come with the stand, its not available without. The factory will not supply this machine without the stand, they say its necessary to use with the stand, since it has a long Y Axis casting.​​Of course you can do whatever you want, but all we would do is scrap it, the stand and machine is part of a set with the serial numbers and all.​​


​After further research, I have decided that if I do get the 940V and tackle the CNC conversion, I would be using the following components.   The total cost here is within striking distance of a tricked out Tormach 1100MX with 30-taper spindle and full enclosure.  




​Still on the fence.


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## ptrotter (Sep 16, 2020)

davidpbest said:


> Good for you.   That will be a terrific CNC conversion project.   I hope you document the process here.
> 
> Repainting the machine would be a simple task if you're taking it apart for ball screw installation anyway.  I've been through it a few times now, and if you want any help or suggestions on the process let me know.  Get rid of the fragille chalky factory body filler and replace it with Bondo - otherwise your new paint job will chip and flake just like the original from the factory.
> 
> ...



Thanks David.  Your numbers look about right.  I have the Acorn kit, PC and pendant so I am already part way there.  I may not do the CNC build immediately, I'm not sure yet.  It might make more sense to spend the money on tooling first and I am still trying to decide what the best choice of servos/steppers is.  What kind of paint did you use on your lathe rebuild.  I guess I will also need to look into adding a one shot oiler.  I don't know what that needs to do on a mill.  More research.  This should keep me busy for awhile.  I'm going to pick up the mill so I will get a chance to meet Matt and see their operation.

Thanks for all you comments.


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## mksj (Sep 16, 2020)

The PM-940V looks like a great choice for your project. Some nice points in this video as too simple and cost effective CNC conversion. David is also using the Royal TTS system mentioned. Found the video below informative even though I do not plan to go down this path anytime soon.  David, if you add in your hourly rate, you would be over the fence and on the other side. But then you would miss some of the challenge of the build.








						r8 quick change collets
					

So i recently heard about the quick change set up for the r8 collets. My set up now is to use er20 collets in a r8 adaptor. Should i just stay with that design or is the quick change better. Im only a hobby machinist.




					www.hobby-machinist.com
				








						Rotagrip - Quick Change Tooling
					

Rotagrip




					rotagriponline.com
				








						Acorn CNC controller, Step and Direction 4 axis CNC Control board with ethernet communication.DIY CNC kit
					

Acorn Do-it-Yourself CNC control board for Mills,Lathes,Routers,and other Machine tools.  Mach3 replacement CNC controls for new machine tools as well as Retrofits for older NC machinery



					www.centroidcnc.com


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## 7milesup (Sep 21, 2020)

Interesting choice on the NUC.   $800 is pretty spendy for a computer that needs to run G-code.  One could probably utilize a NUC in the $250 range.  $190 for a touchscreen and another $70 for keyboard/mouse.
I know that Dave does his builds in the top shelf way (which is admirable), but for others, the build could probably be done for significantly less.  In fact, I saw a guy use clear shower curtains for an enclosure.  Did it look awesome? No.  But it did the same job.
Also, even after the conversion, the PM 940 will have about 8 or 10 inches more of X travel than the Tormach.
Tormach is designed in Wisconsin but built in China.


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## davidpbest (Sep 21, 2020)

7milesup said:


> Interesting choice on the NUC.   $800 is pretty spendy for a computer that needs to run G-code.  One could probably utilize a NUC in the $250 range.  $190 for a touchscreen and another $70 for keyboard/mouse.
> I know that Dave does his builds in the top shelf way (which is admirable), but for others, the build could probably be done for significantly less.  In fact, I saw a guy use clear shower curtains for an enclosure.  Did it look awesome? No.  But it did the same job.
> Also, even after the conversion, the PM 940 will have about 8 or 10 inches more of X travel than the Tormach.
> Tormach is designed in Wisconsin but built in China.


I agree there are cheaper PC's and NUC's to run the Centroid GUI app that controls their motion controller board.  I was after a configuration that would also run F360 and other apps as well.   Centroid sells a NUC that includes the Windows 10 license and their software already installed and configured for ~$800, but if you want the least expensive PC for this, then one approach ($300) is covered *in this video.*

At this point I'm leaning away from the 940V and debating either a 728VT platform with *BT30F spindle,* or building my own hybrid steel/epoxy-granite mill from scratch similar to the one described *in this video*, but using Acorn controls. If I end up with a shower curtain for the enclosure, it will either be a Gucci or Hermès custom loomed spring fashion edition.


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## 7milesup (Sep 21, 2020)

davidpbest said:


> If I end up with a shower curtain for the enclosure, it will either be a Gucci or Hermès custom loomed spring fashion edition.



Bahaha.   I figured as much!
Before you replied to my post I was looking at Tormach and was unable to determine if they are steppers or servos.  There is a servo upgrade kit for the 1100 at a cost of $2000 but the MX might already be servos.  Their specs are really slim.  
Another thing I found interesting is that the ways are essentially Turcite way material on the Tormach.


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## davidpbest (Sep 21, 2020)

The 1100M is stepper motion controls.   You can upgrade that to servos with their M+ conversion kit costing an additional $2K.   The MX comes with servos (and the BT30 spindle) but the get-started cost is nearly $20K, and they won't supply the MX version without the stand and enclosure.


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## 7milesup (Sep 21, 2020)

I am seriously considering converting my 833T over to CNC, but the head speed is a real issue.  Trying to determine how I can do a belt conversion to get the speed range.


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## davidpbest (Sep 21, 2020)

If you haven't seen *this video,* you should watch it.   Not cheap, but BT30, pull stud actuator, and supposedly good low speed torque driving it with the WJ200 VFD.  Or *there is this.*  That eBay spindle can be seen in action at *this video* - and I'm impressed he's able to hard-mill a 1-2-3 block at 2200 RPM with it. That's a lot of coin, but nice rig.


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## davidpbest (Sep 23, 2020)

ptrotter said:


> What kind of paint did you use on your lathe rebuild.


I have used three different types of paints in my builds.   In all cases, I stripped back to raw castings, filled/sanded with Bondo, then used a rattle-can automotive primer.   The biggest problem with the paint jobs from both mainland China and Taiwan is that they use a chalky brittle body fill to smooth the castings, and any impact against that surface will cause the filler to crumble leaving a nasty wound to the paint.  This is why I strip back and re-fill.  

For the *custom stand *I built for the PM1340, I went with an Industrial polyamide epoxy from Sherwin-Williams called *Macropoxy 646*. The member here Anazi built a stand for his 1340 similar to mine, used the same product and raved about it. It would be best applied with spray if you're looking to get a flat wrinkle-free surface. I rolled it on my lathe stand sicnee I wasn't looking for an "automotive" finish, and the stuff is absolutely impervious once fully cured. It is available in gallons and can be colorized to any color you'd like. It is not cheap, but if you set up a "commercial account" with S-W, the prices is basically half off. Gallon cans is the minimum size and with both parts, you're looking at something like $250 even with a commercial account. It cleans up with VM&P Naphtha.





For the repainting of *my PM1340 lathe*, I used a single-part polyurethane product recommended to me by Tom Lipton (OxTools on YouTube) called *Steel-It.*   It's a clear poly with powdered stainless steel mixed into it.  If you like *the color* ( I do ) then this is a terrific product - almost as durable as the S-W Macropoxy, and a lot easier to use since is single part.  It also flows out better than the S-W products if you're using brush or roller.   It's available in quarts and gallons and rattle-cans.  I love this paint and plan to use it again on my CNC build.  Once fully cured, it has stood up to every solvent I've thrown at it with the exception of Acetone (which will soften this paint). *Contact the manufacturer* to find a distributor - McMaster carries a knock-off product, but it's not as good.




On *my PM935 mill build*, I used another S-W product recommended by Keith Rucker (Vintage Machinery on YouTube) called *Direct-to-Metal Alkyd Enamel*.  This is a high build alkyd enamel available in gallons that can be color matched to anything. It does NOT brush or roll well if you're after a decent flat finish, and it takes several weeks to cure. I tried brushing, stripped that off, tried rolling, stripped that off, and finally pulled out my air-assisted airless Graco which left a nice finish. Light colors will stain when way oil is left on the surface for a few days, and Acetone with soften and dull the finish.




​Of the three, assuming you like the dark warm charcoal color of the Steel-it, that is the product I recommend.   It also comes in a two part epoxy version which I might try using on my CNC build.

Hope this helps.   Anxious to see photos of your 940.


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## ptrotter (Sep 23, 2020)

Thanks David,

I was supposed to pick up the mill today but had to reschedule until Friday due to a tire problem on my truck.   I'll take a look at it and determine if I want to repaint it.  Since I will have it apart to do the CNC upgrade, I might as well do it.  I have spray equipment so I will do it that way, it is faster and better in general.


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