Drawbar Action

Jack's Drawbar Wrenches

Jack has a small vertical milling machine. It sits on a bench in his garage. The machine and the bench are each about three feet high. Together they are a tad over six feet. The mill has a vertical shaft that holds a cutting tool. The shaft and the tool spin, the adjustable structure of the machine allows the cutting tool to be brought to bear on the work piece in a controlled manner and so shape the work piece as desired.

Machine tool bit, collet and drawbar assembled within the spindle.

The shaft is not solid, but is a hollow tube called the spindle. The inside of the bottom end of the spindle is tapered.

Set of machine tool collets

A collet is used to hold the actual cutting tool. It acts much like a three jaw chuck, but it only works with one size shaft. The inside of the collet is cylindrical, the outside is tapered to match the inside of the spindle. The back, or top, end of the collet is threaded. The drawbar is threaded to match. To mount a cutting tool in the machine, you insert it in the correct size collet, insert the collet into the spindle, screw the drawbar into the collet and then tighten the drawbar.

With Jack's machine sitting on the bench the hex head on the top end of the drawbar is just over his head. The shape of the machine means he's working by feel everytime he needs to tighten or loosen the drawbar, so he finally decided to dedicate a wrench to the job.

His first attempt was to take a Craftsman deep socket and drill a hole through it so he could mount a handle (center of top picture). Turns out Craftsman sockets are really tough. He was able to drill a small hole through it sideways (after he ground the chrome off), but when he tried to enlarge the hole with a larger size drill bit he got nowhere. Time for some heat treatment to make the steel a little softer, anneal it if you will. Heating it up red hot and then letting it cool down on a bed of sand worked well for one side, the side that was facing the sand, but did nothing for the side facing up. So he heated it up again and then buried it in the sand. Evidently the speed at which steel cools has a big effect on how hard it is. Metallurgical black magic. Now he can drill a hole through the other side. Unfortunately, with all this monkeying around, the two holes are no longer lined up.

Compare this with Mr. Wheels turning down a deep socket on a wood lathe. I can only conclude that Mr. Wheels was dealing with a cheap Chinese made socket.

Ingersoll Rand Impact Wrench

A little reading on the internet reveals that impact sockets (that is, sockets designed to be used with impact wrenches*) are not as hard as regular sockets, so Jack buys one of those and easily drills straight through both sides. Vunderbar!

He uses the holes to attach a handle to the socket (bottom of top picture) and attaches a small piece of brass to the drive end of the socket to use as a hammer. Once the collet has been drawn into the spindle it is pretty well stuck. Tapping on the drawbar will release the collet from the taper so it can be removed. So now he has a single tool to deal with the drawbar.

He revels in his success for a bit, but then he realizes a socket wrench might not be the best choice for this job. You can let go of the handle while the wrench is engaged with the drawbar and it will just sit there. Forget that you left it there and turn on the machine and it will sit there for a bit until the handle gains enough momentum to unbalance it and it is going to be flung at high velocity in some random direction. Not good.

Which brings us to the tool at the top of the top picture. Better to use an open-end wrench that will come off immediately as soon as the tool starts up. Jack just added the brass hammer faces. Two so he can whack it with either side.

* Impact wrenches are what the tire guys use to remove lug nuts when dismounting the wheels from you car.