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IndustryArena Forum > MetalWorking Machines > Shopmaster/Shoptask > Shopmaster Mill Turn rebuild and control conversion
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  1. #1
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    Shopmaster Mill Turn rebuild and control conversion

    I have had a Mill Turn since 2016. I bought it thinking I would get into a machining hobby as I was planning on retiring in a few years. I was also looking a a Tormach 1100 and a stand alone lathe. There was a lot of difference in the cost so I went with the Shopmaster. I was always pretty disappointed in what little I had used the machine. The controls were not stable with lots of random resets,... The machine was not accurate or ridged at all. It was more of an expensive toy to tinker with than a tool. I was used to using some pretty nice CNC routers with ATC,... and this was just not the same game. I got distracted doing some consulting and it has just been sitting collecting dust. Over the years, I've been collecting stuff to "some day" upgrade it. With the Pandemic going on this year, our Christmas was going to be pretty quite and now that I am more like a retiree, I decided to spend a few weeks and take on rebuilding this thing and seeing if I could make a tool out of it. I knew it would never be a ridged production machine, but felt I should be able to get it where it could do light work with reasonable precision and at least have control stability. I had already purchased much larger drives of the hybrid servo type as missing steps was one of the real nuisances of the machine. I had also bought the CNC4PC Ether 300, their interface boards, and their software license. Back when I bought these controls, it looked like their milling software was pretty complete but the lathe package was quite lacking. I figured that would come along by the time I needed it or I could run MACH3 for lathe work. Now, years later, that I was ready to do the conversion, I decided to take a quick look at where conversion controls were and if that was still a good choice for the upgrade. I was impressed with what I saw in the Centroid Acorn product and both their lathe and milling versions of CNC12 looked pretty good. Also, they had a lot of good reviews. They have an active forum for support. Also, thye build complete machines so I thought their knowledge depth would be valuable. I aborted on the CNC4PC and went that route. I've been pleased with that decision.

    I attached the machine to the wall and put some sand bags in the base enclosure for stability. I spent a good bit of time going through alignments and determining how badly warped the table was. I had about .017" of warp as you would drive the table around under a dial indicator in the spindle. That just wasn't going to do it so I had the table ground. A really nice shop in Houston did it for me and when he found out it is a hobby, didn't even charge me. Now I can run the dial around and get about .0005" deviation which is more than good for me. I spent a good bit of time getting the tram set up and the spindle square.... Finally, it was pretty true. Still not real ridged so that means light passes but that's OK.

    It was time to take on the controls and fortunately, I have a decent background in that area. I left the VFD mounted where it was and basically stripped everything else electric/electronic off. I didn't need the storage space in the cabinet so I partitioned off part of that space for my control enclosure. I went with the Centroid Acorn, a new touch screen PC, 8.5NM hybrid servo drives, encoders for both spindles for threading, inductive home switches, wireless MPG,... I used line filters on all the power circuits and shielded cable on all inputs and outputs. I have also built a power draw bar using a converted impact wrench. It works, but I think an air cylinder with bellville spring would be better and plan to change to that path. I have been real happy so far with the CNC12 software. I have tow configurations installed (one for mill and one for lathe). I have redone the panel and gotten rid of most switches. When the machine is booted up as a lathe, it automatically selects which spindle the VFD is driving and which spindle encoder to use.

    This post is getting too long so I'll stop there. However, attached is a quick video tour of the machine and me cutting my first lathe part.

    https://www.youtube.com/watch?v=b4H1LM3mKkw&t=37s

  2. #2
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    Re: Shopmaster Mill Turn rebuild and control conversion

    Also, here is my first attempt at cutting threads on a lathe. Not any commentary in this video. Before I started cutting, I got a proper sized nut to check the fit. At the end of cutting, I could not find the nut anywhere, so you don't see me screw it on. It turns out that the MPG in my hand has a magnet on the back of it and as you can see, it had picked up my test nut 8?) It is just a s well though as it was too tight to screw on. I had to tweak the thread cutting tool's offset a couple of time to dial that in and make it fit. Not sure why I had to go so much but that's to figure out later.... I have never done this kind of threading, so I didn't have a feel for feeds and speeds. I probably went too light but figured that was better than too heavy.

    https://www.youtube.com/watch?v=hxwg1GT6rU0&t=6s

  3. #3
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    Re: Shopmaster Mill Turn rebuild and control conversion

    Very impressive conversion. I was noting your limit switch setup. Could I get a few photos of what you did? Also a photo of the mill spindle encoder, if you wouldn't mind? I've collected everything to convert to an Ethernet Smooth Stepper driver including a rugged touch screen laptop, but you carried it many steps further. I appreciate your trailblazing and the supporting posts. Very beneficial and thought provoking. Have you seen the old posting regarding the external framework to reinforce the mill top support? Might be of interest.

  4. #4
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    Re: Shopmaster Mill Turn rebuild and control conversion

    Quote Originally Posted by gahux View Post
    Very impressive conversion. I was noting your limit switch setup. Could I get a few photos of what you did? Also a photo of the mill spindle encoder, if you wouldn't mind? I've collected everything to convert to an Ethernet Smooth Stepper driver including a rugged touch screen laptop, but you carried it many steps further. I appreciate your trailblazing and the supporting posts. Very beneficial and thought provoking. Have you seen the old posting regarding the external framework to reinforce the mill top support? Might be of interest.
    Thanks for the feedback. You're welcome to anything I've done here. First off, I was pretty limited on number of inputs without buying an expansion board so I wired the limit switches to share an input. I was only going to home the Z axis so I brought that switch in separately. I used inductive prox switches and they seem to work well. The pic of the carriage shows the +/- Y switches. They detect the motor and bearing plates. Note, I swapped the table around so the motor was in the back. The hybrid servo is much longer than the original motor and since I have an MPG, I didn't need access to a crank handle. I had to relocate the ball nut in order to swap the table end for end. Since the machine can be a mill or a lathe with different tooling installed, I wanted to make the X limits adjustable. The photo shows the X switch mounted to the carriage. There a split collars on the rod that allow adjusting where it stops. I did the limit wiring for the carriage in the carriage so a single small cable was all that was needed back to the panel. I mounted a cable chain to manage the carriage wiring.I'll explain later why this wasn't really needed but I didn't realize it at the time. The pic of the top of the machine shows the proximity switch mounted through the idler support bracket. This is the Z+ home position. There is another pic of the Z- limit.

    So, what I learned after working with the machine a few days.... It was very unhandy having to manually home the X & Y axis and red0 zeros every time powered up. I decided it would always be safe to home the z axis up, the table to the front in y and then the table left in X. I then set the software limits of travel relative to the home switches so now only have soft limits. That has worked on my industrial CNC routers for 20 years so I figured it would be good enough for this machine. I do want some kind of limits as the bigger drives are much more powerful and could break something (or me!). I haven't really tested max speed on the axis. They don't have any problem with 200 ipm and that's too fast for me on this small machine. I have them set at a limit of 120. It is SO nice with the bigger hybrid servos to not have to worry about missed steps.

    l definitely want to try to find the thread you referred to about the frame stiffening. After receiving the machine initially, I immediately realized it would never be more than a hobby toy. However, now I have it where I can do pretty accurate machining. I have to take light passes, but I'm not doing production. I hope the accuracy is stable over time. I'll respond to your question about the spindle encoder separately.

  5. #5
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    Re: Shopmaster Mill Turn rebuild and control conversion

    Thanks! Look for the headingCUSTOMER MODS ON MILL TURN BENCH

    this has photos where someone created an external structure to support the mill bridge at the top. I believe this is where this design has its weakness. The rods supporting the bridge can allow a deflection under load manifesting itself as a twisting motion between upper and lower rod support planes. Note that the newest version of this design has increased the diameter of these support shafts in an effort to control this twist. Just food for thought......

  6. #6
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    Re: Shopmaster Mill Turn rebuild and control conversion

    Wow, that should make a difference. I would love to have that mod, but it would be a lot of work to tear the machine down that far again. Might be worth it though. Attaching it to the wall helped a good bit but I'm sure nothing like this. Needed a concrete wall ;?)

  7. #7
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    Re: Shopmaster Mill Turn rebuild and control conversion

    An external frame like this would go a long way to minimizing a twisting effect. Would move the torque reaction to the base plate the machine is bolted thru. Ever think about the fact that the stiffeners for that base plate are located on the outer edge and to allow fork lift use underneath? Look where the base plate mounts to the base and the machine bolts to the base. What actually ties these points together? 1100 pounds of mass with any kind of arm length creates a sizable force. Tying the base of the machine itself to the upper plane as rigidly as possible is the goal. I was thinking to try additional wall supports to the plane of that base plate and see if that significantly dampens the reaction. Could use the lower framework to base plate bolt mounting points.

  8. #8
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    Re: Shopmaster Mill Turn rebuild and control conversion

    Quote Originally Posted by gahux View Post
    An external frame like this would go a long way to minimizing a twisting effect. Would move the torque reaction to the base plate the machine is bolted thru. Ever think about the fact that the stiffeners for that base plate are located on the outer edge and to allow fork lift use underneath? Look where the base plate mounts to the base and the machine bolts to the base. What actually ties these points together? 1100 pounds of mass with any kind of arm length creates a sizable force. Tying the base of the machine itself to the upper plane as rigidly as possible is the goal. I was thinking to try additional wall supports to the plane of that base plate and see if that significantly dampens the reaction. Could use the lower framework to base plate bolt mounting points.
    Agree. I have a large enough piece of 1 1/2" thick granite left from a kitchen remodel. I think if I did the upper support, I would also build a substantial base with the granite on it.

  9. #9
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    Re: Shopmaster Mill Turn rebuild and control conversion

    Quote Originally Posted by gahux View Post
    Very impressive conversion. I was noting your limit switch setup. Could I get a few photos of what you did? Also a photo of the mill spindle encoder, if you wouldn't mind? I've collected everything to convert to an Ethernet Smooth Stepper driver including a rugged touch screen laptop, but you carried it many steps further. I appreciate your trailblazing and the supporting posts. Very beneficial and thought provoking. Have you seen the old posting regarding the external framework to reinforce the mill top support? Might be of interest.
    Attached are a few pics of the mill spindle encoder. It is a medium duty 1000PPR from automationdirect.com. That gives the controls 4000 pulses per revolution and it has a z output for timing threads. The brackets had to be a bit weird only because I had previously installed a pneumatic power draw bar that was in the way of the easier options. I purchased 40 tooth XL timing belt pulleys. I had to bore the one on the spindle to 25mm and machine a recess for the spindle nut. The exposed spindle threads required the recess on the pulley. I did my first rigid tapping with it today and it worked as planned. With the encoder, you can re-enter the hole and the threads stay aligned. I'm not a machinist, but I guess the spindle encoder would normally be more important for a lathe than a mill. Since I was doing the upgrade, I just went ahead and did them both. Here is a short video of the tapping I did.

    https://www.youtube.com/watch?v=XFwU6jTstmg

    Since the power draw bar is in the pics, I'll comment about it as well. I did it several years ago when I got the machine. today if I were doing it, I would use the air cylinder and Bellville washer approach that Thormach does. Chicago Lathe offers one for this machine as well, but the encoder is in the way. I would like to fabricate my own but haven't had any luck coming up with the Bellville washer or spring. Mainly, I would just like to know the force required for a good grip, but haven't come up with that yet. Here is a video about the good and bad of this design and a bit more detail is in the description.

    https://www.youtube.com/watch?v=0GAA0-9ysrk


    Let me know if you need any other info....

  10. #10
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    Re: Shopmaster Mill Turn rebuild and control conversion

    Here are schematics of my build in case someone is interested...
    Attached Files Attached Files

  11. #11
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    Re: Shopmaster Mill Turn rebuild and control conversion

    Thanks for the info. I have been thinking about the drawbar situation and looking at the Tormach setup. I ordered a set of Bellville washers from them to play with. Their setup applies pressure between the top of the spindle and the air cylinder. No loading of the spindle bearings occurs. Judging by your earlier comments, you already know that. If a custom spindle nut was made that was tall and flanged at the top you could accomplish the same thing. Looking at your current setup you may be able to float an air cylinder with attached lower capture plate to your current rods. Applying air pressure would push the air cylinder rod to contact the drawbar and raise the air cylinder. The attached lower capture plate would contact the spindle flange and compress the Bellville washers. Tormach uses 3 stage 4" cylinder @ 60 psi that should generate ~2261 pounds of force. I was actually considering a design using ramps and captured rollers to accomplish the same thing by pulling a lever. I'll keep you posted on that. The older I get the more I like automation......

  12. #12
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    Re: Shopmaster Mill Turn rebuild and control conversion

    JT sent me pics of a new model that is available that uses one cylinder mounted on the bridge and a 3:1 lever so it only requires a single cylinder. Price is $499. See attached. He said they did the calcs on the bearings they use and there is a large safety factor for end loading the bearings. Says they have tested on an active machine for 3 years.... I asked him about buying a set of washers from him, but he only has one set and it is with a kit. He gave me the name of the source (not part numbers), but doesn't know the specs of the washers used. Said he just stacked them up until it worked.

    I sure would like some numbers on how much force it takes to hold the cutter in the collet. Sounds like from what you have found that 2200 does it. I wonder what numbers JT used for his bearing calcs? He may be getting tired of me pestering him. He's always been great at supporting me. I don't mind supporting them and buying their accessories, but what they have won't work with my modified machine.

    Was it any issue buying the washers from Tormach? Is the ID OK for our bar? What did they cost? Automationdirect.com has 100mm bore cylinders fro $155. There are probably other sources for less.

  13. #13
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    Re: Shopmaster Mill Turn rebuild and control conversion

    I looked up the info from Tormach. Power drawbar spring #31319. Cost are $2.96 @ and they use 8 of them stacked alternately. OD 1.180, ID .454, .087 thick, overall height .120. I have a question about the software you use with the Acorn. I see they have a basic included package for lathe and/or mill but offer an upgrade for either lathe or mill. What are you running?

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    Re: Shopmaster Mill Turn rebuild and control conversion

    Thanks for the spring info. Amazingly inexpensive.... Sounds like the proven way to go.
    I m running the PRO version of the software. I think it's the same program and the license just unlocks additional features. I just went ahead in the beginning and upgraded. It wasn't that much money.... I can't remember for sure what all the difference is but I wanted to use the wireless MPG and that required the upgrade. Also, it opens up the file size. I was going to do some graphic engraving and those files can get pretty large.

    Their support forum is very good. You might take a look if you haven't. I find their products much more solid than most of the hobby market and I didn't have the greatest experience with stability of Mach3. wwwcentroidcncforum.com

    Have you sourced the 100mm cylinders yet?

    I think my next step will be to create a good CAD model of the top of the bridge and see how I can best fit the draw bar and encoder in. I recently tried a little ridged tapping with the encoders. It worked! I could run the tap in and out multiple times and the threads stayed in sync.

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    Re: Shopmaster Mill Turn rebuild and control conversion

    In going thru my notes on the drawbar analysis I had done some testing to see how tight I normally tighten the drawbar. Number I came up with were 22-25 ft/lbs consistently and that's using the TTS collet and toolholder. McMaster sells an equivalent washer #9712K436 in a 6 pack. Their product information for that washer is very informative and shows ~1860 pounds working force for the alternate stacked setup. So back to the software, did you have to buy a Pro version for both of the versions (lathe / mill) or a single version to cover both? On the 4" cylinder sourcing, I bought a double stack cylinder used months ago. My thoughts then were to use the double with a higher air pressure since my machine is about 3' away from my 80 gallon 2 stage compressor. Was going to use the tee shaped top spindle nut and free float the air cylinder with a lower clamp plate attached to it per Tormach setup. Looked over that setup getting washer info and realized they have to swing the cylinder out of the way to change belt locations for the spindle. Probably not to remove load on the bearing. Still got that Gecko 540 gathering dust somewhere?

  16. #16
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    Re: Shopmaster Mill Turn rebuild and control conversion

    Loved your lathe videos. Are you going to do any for the mill part?

  17. #17
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    Quote Originally Posted by gahux View Post
    Loved your lathe videos. Are you going to do any for the mill part?
    I haven’t, but will be happy to in a few days.

  18. #18
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    Re: Shopmaster Mill Turn rebuild and control conversion

    Quote Originally Posted by gahux View Post
    Loved your lathe videos. Are you going to do any for the mill part?
    Here are a few clips that will give you a feel for it. When I made them, I wasn't intending to upload them so they aren't real complete and don't have dialog. I did them initially for troubleshooting in case something "turned dirty brown".

    https://www.youtube.com/watch?v=8t8xGe8FfDM

    https://www.youtube.com/watch?v=5SmR-eCLt90

    https://www.youtube.com/watch?v=YrK8ooANuxA

    https://www.youtube.com/watch?v=1c0MqkMbMm4

    Also, here is a review of the pneumatic power draw bar I just completed.

    https://www.youtube.com/watch?v=P188_Xuwogw

    Let me know if you have any questions.

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