# New PM-940V



## ptrotter (Sep 27, 2020)

I pulled the trigger on a new PM-940V to convert into a CNC machine.  I drove down to PM to pick it up.






At the PM warehouse.





My machine in the warehouse




Loaded into my truck




Part way uncrated




Out of the crate.

So far everything looks ok.  Fit and finish is as expected for a Chinese product.  I'll decide when I have it apart if I want to repaint it.  I plan on doing the CNC conversion soon so I will not be placing it on the stand until that is done. I will be taking it completely apart to do so and will try to document the process at least to some extent.  At this point, I plan to go with an ArizonaCNC kit for the CNC with Clearpath servos.

The people at PM were very friendly, I got a tour of the warehouse from John and then spent a half an hour with Matt.  A long day, a 6 hour drive each way, but I avoided dealing with common carriers.  I guess now the adventure starts.


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## 7milesup (Sep 27, 2020)

Congrats!   Looking forward to your build thread documentation.


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## Kiwi Canuck (Sep 27, 2020)

Paul, that's great that you got to go pickup your machine.

I would do the same if they were that close to me just for the experience, but I also love long road trips.

Did you pick up anything else while you were there? accessories or tooling?

David.


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## ptrotter (Sep 28, 2020)

I didn’t pick up anything else. I thought about it but decided I wasn’t sure about what I want yet. It will be awhile before I have it up and running so I have some time to figure out what I need.


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## davidpbest (Sep 28, 2020)

Hey Paul, good for you.  I’d love to hear your thinking on how you plan to control the beast (I’m planning on Acorn) and what if anything you’re thinking about on spindle improvements.  Looking forward to your follow on posts about this project.


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## Skowinski (Sep 28, 2020)

Congrats on the new machine!


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## Janderso (Sep 28, 2020)

Good for you. I hope all goes well with your new PM


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## ptrotter (Sep 28, 2020)

David,  I've been playing around with Acorn on my little Sherline mill.  It seems to work fine but like anything, there is a learning curve.  There seems to be pretty good community support for it in their forums.


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## ptrotter (Oct 3, 2020)

I'm starting to move along slowly.  I have ordered the CNC conversion kit from ArizonaCNC, the Clearpath servos, a power supply for the servos, as well as the connectors to make up the servo power and control cables.  I have most of the rest of the components.  I need to figure out where I will put the power supply and the Acorn components.

My first step is to determine how much CNC control I want.  If I go full CNC, I can remove all the manual controls and their associated relays and control everything via the computer, including spindle on/off, direction and speed.  This simplifies the wiring considerably as all control is done via signals from the Acorn board to the VFD.  This frees up a lot of space in the control box for the power supply and Acorn board. The downside of this is that it makes it much more complex to do simple things as I would have to do everything via the computer.  The current manual controls uses a number of relays and a few things I'm not sure what are so I'd kind of like to simplify it. The wiring diagram in the manual is very cryptic, I may post a picture of it for amusement.  Since I will need to use the computer to move the axis, I guess there is no reason not to go full CNC.  I am curious as to what others have done in their conversions.

I am starting to break down the machine in preparation for the ball screw installation.  So far I have just taken off the motor and will probably remove the head tomorrow.  The picture below shows the motor and you can see the belt drive.  I'm not sure what the 2nd connection to the motor is for, maybe a temperature sensor as it is up in the fan housing.  I'll have to trace it out.  I'm going to see if I can figure out how to put an encoder on the spindle so I can send rpm info to the Acorn.


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## mksj (Oct 4, 2020)

The motor is most likely a TEBC, they have an electric fan that often runs continuously on 240VAC (mine is connected to two power legs before the VFD). I have a TEBC motor on my mill, I ended up putting a timer on my fan so it runs only when the motor is operating and for about 2 minutes after stopping  and then turns off. Might be interesting to see the motor plate and at some point dig into the VFD parameters.


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## ptrotter (Oct 4, 2020)

I think you are right Mark, although the fan does not show up on the wiring diagram.  Below are pictures of the motor, motor plate and the 2nd connection.















I have finally figured out the wiring diagram, however there is one component I don't understand.  There is are 2 devices called "H3Y" that seem to be a time delay relays that are in the FWD/REV circuits and seem to add about a .5 second delay in the FWD and REV connections to the VFD.   I'm not sure why these are needed.  Maybe someone has seen this before and know why they are needed. The wiring diagram is below.  The components in question at KT1 and KT2. For some reason they are installed in different locations on the FWD and REV circuits but look like they have the same effect.  This is the diagram that comes with the machine from China, not a PM updated diagram.




On another note, I am moving along with the disassembly.  I haven't decided whether I will repaint it or not.  After I get it all cleaned up I'll make that decision.  It shouldn't be too hard as there are only about 7 parts.  The hardest thing to take off is the box with all the electronics.  This requires removing the panel where everything is mounted to get to the screws.  I'm not sure this can be done without disconnecting wires inside the box and I don't really want to do that unless I decide to remove it all and control everything via the Acorn board.


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## mksj (Oct 4, 2020)

Single phase 240VAC fan blower motor. Motor nameplate I assume is the for the fan. I have to say that the paint job on these machines is pretty bad, but I guess at the end of the day it isn't going to matter. On the control cabinet, you may end-up not using the control relays if directly interfaced with the CNC control system to the VFD, but if that is later then you may want to get it all up and running and then take that step. Meed to be careful with electrical noise issues and wiring. Looks like you are moving along.


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## ptrotter (Oct 4, 2020)

Nameplate says 3 phase and you are right about the paint job.  I'll probably keep the existing controls for now in order to get it up quicker.  If I go the other way I can get rid of everything in the cabinet except the VFD.  That would give me plenty of room for the motor power supply and Acorn board.  As it is now, I will need to put the motor power supply somewhere else.  Any idea why they have the time delay relays in the FWD/REV inputs to the VFD?  At some point I will power up the VFD and look at the programming.


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## mksj (Oct 5, 2020)

The schematic does not give any description of the components, just seems like a number of interlocks. If there is a particular component then maybe post a photo of it. The schematics are also quite lacking as well as the part descriptions. Only figured mine out by tracing everything. My mill has a main power relay, it cannot be energized if the for/rev switch is not in the stop position. Most VFD's will not run if say the for/rev input are both activated, but I still use 2-3 levels of interlocks in case a switch fails closed. The motor cooling fan looks to be single phase 240VAC, runs off of the R and S terminals and there is a start/run capacitor.

Just read you comment on the time delays of 0.5 seconds, not sure what that is about. A VFD will ramp down and then reverse if given an opposite run command.


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## ptrotter (Oct 5, 2020)

It took me awhile to understand the wiring diagram but it ended up making sense.   There is a main contactor that is energized by the power button that provides power to the VFD and to the other relays.  The FWD/REV buttons energize relays that latch and lock out the opposite direction, pretty standard interlock.  There is a stop button that de-energizes both direction relays, also straight forward.  What I don't understand is the need for time delay relays.  These are part number H3Y-ST6P which can be googled.  There are in series with the FWD and REV inputs to the VFD and are set for about .5 seconds.  As I think about it, they may be to provide a slight delay in the directional input to the VFD to ensure that the relay for the opposite direction has had time to open.  If one were to push the opposite direction button while the spindle was running, it could send signals to both inputs of the VFD if the relays were a little slow to open.  Actually kind of elegant.


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## mksj (Oct 5, 2020)

With a relay interlock, one relay has to completely release to provide power to the other relay (break before make). It may be the timers have something to do with the motor blower.  Most VFD's have a hierarchy as to input controls and which override other controls, if F/R are both active the VFD would not run until one went open, not aware that it would generate a fault condition.  There is an issue with relays in that as the coil snaps open that it generates a significant voltage spike that can feed back into the control system wiring, typically these are dealt with an AC snubber network or reverse diode for DC. On a 24VDC control systems I use, the spikes can be in the order of 160VDC, which can damage other electronics shared with the same power supply. So if you used the same 24VDC to trigger the VFD inputs they could be damaged. I use reverse diodes to prevent this and also if someone connects the power supply backwards, the diode will present as a dead short and prevent damage to the other components. This is a common practice, but the diode needs to be sized so it will not be damaged if this was to occur and also handle the peak spike voltages. Possibly the relay delays have something to do with the voltage spikes and the relay release, don't know.


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## ptrotter (Oct 5, 2020)

Hi Mark, The time delays are not in the motor blower circuit. They simply seem to add .5 second delay in energizing the FWD and REV inputs to the VFD.  On the diagram above, they are labeled KT1 and KT2.  You might be right about the relay release, this would allow time for any transient to dissipate before connecting to the VFD inputs.  On the reverse side, the delay contact is directly in series with the REV relay contact in the VFD input.  Since both relays are energized at the same time, the timer contact closes slightly after the other contact, adding a little delay.  On the FWD side the delay contact is in series with the power to the FWD relay so it adds a little delay to the closure of the FWD contact.  Same effect, but odd that they would do it differently.  I guess it works so I won't worry about it so this is just curiosity as to why they did this.  I expect at some point I will remove everything but the power button and the main contactor and do it all through CNC control of the VFD.


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## ptrotter (Oct 12, 2020)

I have gotten my new mill pretty much taken apart in preparation for the CNC conversion.






I think I will strip and repaint it since it is apart.  It has surprisingly little painted surface, probably less than 15 sq. ft.  The head will be a little tricky to paint as I really don't want to take it all apart, so we'll see how that goes. I am having a little issue with removing the Z axis lead screw. It has an odd nut on the bottom that looks somewhat like this:




I'm not sure what to use to remove it as I have to get at it from the bottom of the column.

I haven't decided what paint to use on it.  I'll probably wait until I get it striped to see how it looks, probably some kind of epoxy or polyurethane. 

I think I will use the existing spindle motor controls for now and use the CNC system for the axes, then in the future convert those to use the CNC for control.  I plan to build out a new control box with everything for the CNC except for the VFD.  Initially I will need both boxes hooked up, but when I am ready, I will put a VFD in the new box and I will be able to remove the old control box completely.  I received my Clearpath servos so I have almost everything I need, just waiting on the CNC conversion kit for ArizonaCNC. 

Lots of fun so far.


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## davidpbest (Oct 12, 2020)

*This thread* might be useful to you in paint choice.

That nut would perplex me as well.   Can you get into there with a brass drift and hammer on the notches?

I'm toying with what direction to head with my own CNC mill build.  I've considered everything from a simple conversion of the 833 or 940, to epoxy-granite stiffening of the same mills, to a ground up granite slab or molded E-G build.   I was about to pull the trigger on the same 940 you have, but the "mainland China" paranoia kept me from it.   Even Matt at PM cautioned "the 940-V is not up to the standards of the Taiwanese machines" I am accustomed to.  I must admit, by the time I get done, I'd basically be after a set of castings with hardened and ground ways, and if the spindle needs rebuilding to gt better speed/performance, that can't be that difficult.   So I'm following your build with interest.  Very curious about your reaction to the build quality of the 940-V, particularly with my comments in mind.


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## ptrotter (Oct 12, 2020)

David,  The build quality looks ok when you get past the paint.  I have very little experience with this type of equipment so I am not a good judge but while the castings look a little rough, the machining looks ok.  I think the Chinese do a lot of manual work in building these machines such as using jigs and hand drilling and tapping holes rather than CNC machines.  After looking at your lathe and mill rebuilds, I think you would see a significant difference in the quality of this machine vs the Taiwanese machines you have.  It is fine for me, but you would probably be a little frustrated with it judging from the quality of the equipment you list in your signature.  We'll have to wait until I have it back together to really see how it looks as I will be replacing most of the parts that are not as well finished.  With the new ball screws, bearings and motor mounts, about all that is left are the main castings and tables so it might end up better than expected.  I think the poor paint work makes it look a lot worse than it is.  I'm not a big fan of the Chinese electronic control system.  Although the components seem to be good quality, it just has a kind of shoddy feel to it.  When I am done, I will have replaced this completely so I am not worried about it for now as it seems to work.

I think I will use the Steel-It paint.  There is so little surface area to paint that I can do it with their rattle can version which will make it quite easy.  The Steel-It paint does not seem to do well with the HVLP spray equipment I have and I don't want to buy new spray equipment.  No equipment cleanup either with the rattle can.  I'll probably start the paint striping process in the next day or so.

Now it is time to see what to do about removing that Z lead screw.


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## B2 (Oct 15, 2020)

Hi,

I have one of the last PM 940M CNC machines that I think PM sold.  I purchased it around the fall of 2017.  I live in Pittsburgh, PA and so have been to PM facility  several times.  So, if you have questions about how my machine is constructed maybe I can help.  I might even has some thoughts on things not to do!  One of my findings is that with the motor, housing, gears, oil, etc the head is too heavy for the stepper to hold when powered down.  I figure it weights in at about 250#s or so.  So the Z-axis stepper needs to be bigger than is actually required to move the assembly up and down.  I think this is really due to the fact that the Z-axis lead screw is too long for the mountings that it uses.  Maybe your belt drive system will not be so heavy!  Since you have it all apart maybe you could just weight the parts and let me know how heavy it is?

It came with some version of n-motion controller and code for a Mach3 setup.   It has worked fine for me, but I know a some folks are frustrated by not having decent documentation on the Chinese n-motion.    Earlier I posted the owners manual, which contains some circuits including the spindle motor control.  It has a Delta VFD which seems to be decent and pretty standard.  Attached is a photo of the spindle motor.  Similar to yours.  I will say the cooling fan is pretty loud! 






Dave


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## ptrotter (Oct 15, 2020)

Hi B2, Yes, the motor looks similar.  I haven't run it yet but may hook it up on the floor just to see how it runs.  I'll try to weigh some of the parts while it is still apart.

I finally got it all apart, including the Z lead screw.  I decided to paint it so I started to strip everything.  Fortunately, there is not much painted area.  They used more bondo than I expected. The column has pretty much a full skim coat of bondo over the entire surfaces.  The Z axis saddle has up to 1/16" in some places to fair it out.  When I get it all stripped, I'll decide how much I will put back on.  They must have a full team of bondo guys in the factory.


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## mksj (Oct 15, 2020)

So looks like it is a vector motor based on the nameplate, i.e. 2-200 Hz motor rating. It would appear the base speed on the motor is 50 Hz based on the r/min of 1390. I use a timer on my blower so it shuts off, with a TENV motor it is not an issue. As far as the bondo......


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## B2 (Oct 15, 2020)

Hi P
Yes, Bondo everywhere.   You are also going to find that the castings are not great material.  The steel is very porous.   I found that when I went to drill and tap the column that the casting just sort of broke down into sand. Not a nice clean hole at all. You'll not find any thing like a steel cut, chips nor pigtail cuttings.  Just sandy particles.  So if you want to tap into it I suggest you use an undersized drill for the tap.  You can do it successfully but you need to take care.  I took my very large CNC electronics cabinet off of the back of the column and made new holes on the side of the column and in the steel cabinet and mounted it by the side so that I could open the doors from the front. 

mksj, Love that PIG!  
Also the picture I posted is of my 940M motor not P's motor.  His photo was of the fan motor part so I do not know if his motor is exactly the same as mine.  Mine does not have a separate motor lable for the fan part.  I would have to go back and look, but I do not think the fan motor was running on 3 phase.    I have never found the spindle motor to get all that hot unless I am running it under a heavy cutting load for a long time.  Then it does get hot even with the fan on.  I could probably put the fan on a small mechanical thermal switch but have just never bothered to do so.  

Dave


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## ptrotter (Nov 14, 2020)

I am moving along on the CNC conversion for my PM-940V.  As I stated above, I divided to refinish the mill while I had it apart.  While I think it will look good when I am done, I am not sure it is worth it.  It is taking quite a bit of effort to do this.  In order to get a decent finish on the cast iron parts, the factory puts a skim coat of body putty over the entire thing, in some places almost 1/8" thick.  To do this right, I had to remove and redo the skim coat prior to painting.  Th following pictures show the raw base casting with the body putty removed.












And the column before and after painting.









I should have the ArizonaCNC conversion kit in about 2 weeks and I can start to put it back together.

I have also been working on the control system with a Centroid Acorn CNC board and should have that done about the same time.


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## davidpbest (Nov 14, 2020)

It's looking great.   Keep posting please.


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## ptrotter (Nov 15, 2020)

davidpbest said:


> It's looking great.   Keep posting please.



I blame you for all the extra work I am doing to repaint the mill   Looking at all your beautiful repainting work on your mill and lathe got me into this. Joking of course, but if it comes out anywhere as nice as yours I'll be happy.


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## ptrotter (Nov 23, 2020)

I'm moving along with my CNC conversion.  I have most of the mill repainted and ready to put back together when I receive the conversion kit.  In the meantime I have almost completed the new CNC control system based on a Centroid Acorn board.  So far I have the Acorn controlling the VFD for spindle speed and direction at least as far as I can tell without the motor hooked up.  Next step is to hook up a servo and see how that goes.  This is how it looks so far.






Next step is to put the panel in the enclosure and work out all the cable connections.


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## 7milesup (Nov 23, 2020)

That is so awesome!   Keeping an eye on this.  Do you have pictures of the mill after the paint?


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## ptrotter (Nov 24, 2020)

A little more progress.  This is how the control board looks inside the enclosure.  My biggest issue right now is figuring out where to mount the enclosure.  It weighs around 78 lbs so it needs a fairly sturdy mounting location. The original enclosure was mounted on the back of the mill column but that requires too much space behind the mill so the door can open. It will probably have to go beside the base somehow. 






All the cables going to control board including the control panel, drive cables, limit switches , etc. will have Molex connectors mounted on panels on the side of the enclosure.  The Clearpath drives use Molex connectors to I just stuck with them for everything else.  If I change something and need new holes, I can replace the panel and not end up with extra hole in the enclosure.  I will have these panels cut and labeled by Front Panel Express and will install as shown here:





	

		
			
		

		
	
,


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## ptrotter (Nov 27, 2020)

Starting to put it back together.


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## 7milesup (Nov 27, 2020)

Love the color.  
What is that O-360 attached to?


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## ptrotter (Nov 28, 2020)

7milesup said:


> Love the color.
> What is that O-360 attached to?



IO-360 actually.  On a Vans RV-8.


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## ahazi (Nov 28, 2020)

ptrotter said:


> IO-360 actually.  On a Vans RV-8.


Very cool!
I cannot bring my IO-360 and the attachment to my shop...

Ariel


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## kcoffield (Nov 28, 2020)

What does that big Toroid filter/do?

Best,
Kelly


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## ptrotter (Nov 28, 2020)

kcoffield said:


> What does that big Toroid filter/do?



That is the transformer for the servo power supply.


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## 7milesup (Nov 28, 2020)

ptrotter said:


> IO-360 actually.  On a Vans RV-8.


Sweet. Never had the pleasure of flying in any of the Rans aircraft.  Good friend built an RV-7.


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## ptrotter (Dec 22, 2020)

I am getting a little further with my PM-940V CNC conversion.  I have built a new control system around an Acorn board.  So far it seems to be working properly during bench testing.  I totally replaced the OEM system.  I received part of my Arizona CNC conversion kit today, hopefully the rest will arrive tomorrow and I can start to assemble it.  The control enclosure is shown here:















Also attached is the schematic of my control system.


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## ptrotter (Feb 17, 2021)

I have not posted anything for awhile but I have been hard at work on the PM-940V CNC conversion. I am not very good at taking progress photos but here are some:

I made a mobile dolly so that I could move the mill if necessary.  It is a piece of 1/2" steel with 4" steel wheels and adjustable feet.  The next pictures show the stand on the dolly and putting the mill base on the stand.  I have an I beam in my shop with a chain hoist on it that make lifting the heavy parts quite easy.


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## ptrotter (Feb 17, 2021)

More pictures:

I put the column on then the XY table and finally the head.


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## ptrotter (Feb 17, 2021)

I used the ArizonaCNC conversion kit for the PM-940.  I was very impressed with the kit.  Everything fit perfectly and it was easy to install.  The fit was impressive considering the Chinese casting are somewhat rough.  I had to put a small shim on the Y Axis ball nut holder where it mounted to the saddle as the casting was slightly off, but that was the extent of my adjustments.  I had a few other minor glitches that were my fault, such as accidently running the ball nut off the ball screw which allowed me to learn how to pack the balls into a ball nut.  It is actually quite easy.  In addition to a great fit, Dave at ArizonaCNC provides great support for his product.  As I knew very little about Ball screws and CNC machines, I had a number of questions and he talked me through everything.  I highly recommend his products.

I used Clearpath servos and they mounted up to the ball screw mounts perfectly.  Clearpath has a servo tuning program that runs on a PC that is used to test and tune the servos.  After a little tweaking of the gibs and adjusting the servo mounts to ensure that everything was straight, the tuning program ran nicely and show that nothing was binding.

This picture shows the Z axis mount and servo.


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## ptrotter (Feb 17, 2021)

I finished putting everything back together, mounted my control enclosure to the side of the column and connected the drives and spindle motor to my Acorn system and added limit switches.  

X axis limit switches.


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## ptrotter (Feb 17, 2021)

Here are a few pictures of the completed mill:


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## 7milesup (Feb 17, 2021)

Very nice!


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## ptrotter (Feb 17, 2021)

The Acorn system seems to run fine.  All the servos work fine and the spindle is controlled by Acorn as well.  Although the castings are typical Chinese, I was pleased with the finish of the ways, they seem to be pretty good.  I now need to tram the column and the head to the table and  tune the Acorn system.  I'll probably add a Fogbuster system like I have on my lathe. I'll also need to get some basic tooling.

The next step is to try to find something to make with it.


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## Janderso (Feb 17, 2021)

Pretty darn impressive if you ask me.


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## davidpbest (Feb 17, 2021)

Looks great.  Have you checked the spindle?  Curious TIR.


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## Tipton1965 (Feb 17, 2021)

Looks great!  That Z axis mount is sweet looking!!


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## Kiwi Canuck (Feb 19, 2021)

2 Kurt vises, nice, are they DX-6's


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## arizonavideo (Feb 19, 2021)

ptrotter said:


> Here are a few pictures of the completed mill:
> 
> View attachment 355958
> View attachment 355959
> View attachment 355960




Nice work on everything. I'm surprised you took on the job of painting it, its a lot more work than you think.  Whats you plans for chip containment?


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## ptrotter (Feb 19, 2021)

Thanks Dave,

As I said earlier, your conversion kit is excellent.  I figured since I had it apart, I would paint it. It does look better but I don’t think I would do it again, I was a lot of work.

I’m not sure about chip containment at this point. I will not be using flood coolant initially. I’ll talk to you more about this in the future.


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