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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Another Mill Choice Dilemma
- Thread starter ptrotter
- Start date
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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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.
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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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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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.
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.
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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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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
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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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:
Still on the fence.
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:
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.
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- Mar 16, 2017
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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.