There was some discussion on another thread about adapting a power drawbar to the Mill Turn, and people often ask us if we offer that as an option. We actually built an air butterfly PDB many years ago on our Bridgemill model and it worked great. However back then, there was not as much CNC work as there is now, so we have sort of revived the idea and our factory is working on some ideas for the future. There are as many designs out there as there are machinists, but not too many off the shelf units available. They come in 2 basic types-
1. Air cylinder which compresses a drawbar with a stack of belleville washers to release tension on the collet.
2. The air "butterfly" wrench which loosens and tightens the drawbar threads.
Each has its own advantages and disadvantages.
The compressing air cylinder design is more complex because it has to have a floating design to compress the belleville washers while not putting pressure on the spindle bearings. The air cylinders, valve and air fittings are available, but it takes some engineering calculations to get the proper cylinder etc. And the parts will be more expensive than the butterfly type. However, once engineered it will be a faster and lower maintenance setup. You can buy an off the shelf unit like a Tormach and adapt it to the Mill Turn, but you are looking at 1200.00, which is pretty pricey, considering you could source the parts and make all the components yourself for a few hundred dollars. Here is a simple drawing of how the Tormach unit might look on the Mill Turn.
Attachment 333720 simple idea to attach the Tormach unit
Attachment 333726 Tormach style with belleville washers
Attachment 333728 The Tormach full kit
The butterfly air wrench design is very inexpensive- there are some units on E-bay for 130.00, and one can be built for around 50.00 in parts. The concept is simple, in that the air wrench tightens and loosens the drawbar and with some calculations, it will force the collet down as the drawbar moves up and bottoms out in the socket. Some designs have a lever that you can use to pop the collet loose. However, you will need a better quality drawbar,as the threads are being loosened and tightened a lot. Eventually, the thread on the drawbar and the collet will begin to wear and need replacing. Here are some pictures of variuos styles and a link to a how to build thread.
Attachment 333722 E-Bay unit for 130.00
Attachment 333724 DIY design for 50.00
Here's the link for DIY units
CNC Cookbook: Powered Drawbar for IH Mill