Power Draw Bar build

[mccafferty]

I am interested in building a pneumatic draw bar for a Shopmaster Mill Turn similar to the one offered by Chicago Lathe in the pics attached. I have built one based on a modified air impact wrence, but I think the cylinder one would be better. The price point at $700 for three $20 air cylinders and some bellville washers seems unreasonable to me. The whole cnc machine was only $6000. Has anybody built one similar to this concept? Interested in source for cylinders and specs on the size and number of washers.

Thanks

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[mccafferty]

Found a good thread for this in the Tormach area..... It would still be good if anyone has worked out the correct number and specs for the belleville washers.

Thanks

[jdclark]

I am interested in building a pneumatic draw bar for a Shopmaster Mill Turn similar to the one offered by Chicago Lathe in the pics attached. I have built one based on a modified air impact wrence, but I think the cylinder one would be better. The price point at $700 for three $20 air cylinders and some bellville washers seems unreasonable to me. The whole cnc machine was only $6000. Has anybody built one similar to this concept? Interested in source for cylinders and specs on the size and number of washers.

Thanks

Actually it seems pretty reasonable, considering the Tormach unit which appears to be identical sells for 1295.00.
https://tormach.com/power-drawbar-pcnc-1100-31706.html
You always have to consider that a product is not just the value of the individual pieces, but includes the time involved in design and testing.

[mccafferty]

They have since come out with one that uses only one cylinder and a 3 to 1 lever for $500. However, my machine has a spindle encoder which would get in the way of their device so I would have to rework it anyway. Tormach's unit has a clamping arrangement where it does not load the bearings. This one presses down such that the bearings see the thrust load as the spring is compressed. They say the force is within the range of the bearings, but I would want to verify.

I understand cost of product development,... My machining activities are a post retirement hobby. I get more pleasure making tools and tool accessories than in making stuff to go out the door.

[sharpshooter90]

I spoke to JT about the drawbar upgrade and the bearing load, and he said they have a customer who has used the design for 3 years with no bearing issues. They use a double row high angular contact bearing for the top and bottom of the spindle, and the rated load to release a drawbar is way below the bearing rating. In the automotive industry these type of bearings have replaced the old style tapered roller bearings for their better performance and lower maintenance. For a home garage machine which for most guys gets pretty mild use, I doubt that the bearing load will ever be an issue.

[mccafferty]

I spoke to JT about the drawbar upgrade and the bearing load, and he said they have a customer who has used the design for 3 years with no bearing issues. They use a double row high angular contact bearing for the top and bottom of the spindle, and the rated load to release a drawbar is way below the bearing rating. In the automotive industry these type of bearings have replaced the old style tapered roller bearings for their better performance and lower maintenance. For a home garage machine which for most guys gets pretty mild use, I doubt that the bearing load will ever be an issue.

Thank you for checking this out and responding. I have added a spindle encoder so their package won't fit. I've contacted shopmaster support (which I assume is JT although it doesn't say) about buying the Bellville. They responded that the Bellville won't work on my machine. I've asked for clarification.