Since I got good answers asking about the servos on my new-old Milltronics Partner mill, I thought I'd ask a few more about the whole power drawbar system. This has a 40-taper spindle with a large air piston which presses down on a drawbar. The drawbar has a stack of cone (belleville) washers which I believe get compressed, allowing the drawbar to move downward and release the tool via a retention knob (like the quick connects on air tools.)

Here are my questions:

1) What size retention knob do I need for the tool holders?

2) How are the cone washers assembled and how do I know how many I need? As a guess, I figure they alternate small to large so as to be able to compress.

3)Do I need to provide compressed air to both sides of the piston assembly, or is it enough just to valve air to the side that pushes the piston down onto the drawbar?

There are 90 bellville washers. They are stacked 3 x 3. Start with 3 down (crown up) then stack 3 (crown down) then 3 and keep alternating until you get to the top. Like this,
)))((()))((()))((()))((()))((()))((()))((()))(((

You should end with 3 facing up when your done.
Your retention knobs will depend on what tool holder. Cat 40 Or BT 40
I can tell you the Cat 40 one, it's a Command RB4E-0002
My drawbar cylinder has 2 lines going to it.

Hope this helps,
Dave

Thanks Dave! Your diagram was especially helpful. Now if I can just figure out which spindle this machine has!

Well, 40 taper is 40 taper BUT, the way the pulls studs are is a different story. Both tool holders will work in the spindle but only one will only work in your turret. The only reason I know this is, a buddy of mine has all BT tooling for his Milltronics, I have Cat 40. He got a bunch of Cat 40 tooling but couldn't use it, he thought he could use the studs so he kept them. He called a week later and said I could have them because his were different. Cat 40 is a V- flange,,,, BT is more round. My turret uses 2 spring pins to hold the tool in it. Maybe you should call Milltronics with the model and serial number, they might be able to tell you what spindle it has in it. If you want, I can take a picture of what I have and how it's held in the turret.
Dave

To install the draw bar back into the machine. I stack the washers (grease them well) and put the top bushing and nut on real loose. Snug the setscrew on top. Drop the assembly in the hole, install the ball cage from the bottom up. Tighten the cage against the shoulder on the draw bar and sung the setscrew. You will need a 1/8 thk. piece of flat bar 1 in wide to do this. Then, remove the free play from the washer stack using the top nut and tighten 4- 4 1/2 turns and snug the set screw on the top nut and your good to go.
Hope this makes sense,

Dave