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Ian B
12-03-2002, 09:49 AM
I've recently bought a Beaver turret miller with a 40 Int spindle taper. 40 Int tooling has either a 5/8"BSW or an M16 internal thread, but the hole through the Beaver's spindle is only 14mm - ie, I need to make adaptors to reduce the tooling's internal thread size.

Has anyone out there come up with a better solution than simply threading the drawbar all the way in, and then tightening the top nut / wheel? I'm thinking about adaptors with two internal keyways and an annular ring at the bottom, allowing a matching male piece on the end of the drawbar to enter the adaptor, turn about 1/4 turn clockwise and then tighten with one turn of the wheel. Sort of a bayonet fitting.

I know that Bristol Erickson etc make power drawbars, but I don't think I'm likely to find one.

Grateful for any ideas,

Ian

Ragarsed Raglan
12-03-2002, 09:59 AM
Ian,

Are you sure the 14 mm dia is not an ejector shoulder? We have a Thiel mill at work with a fixed drawbar into a 40 INT taper, this passes through, and is retained by a narrowed diameter. The drawbar is 5/8 Whit but is reduced to about 1/2" just behind the threaded portion. When you undo the drawbar the ejector diameter pushes the taper apart.

The drawbar is sleeved and pinned at the top end to retain it in position. Took me ages to figure how to get it out of the machine as some of the new tooling we bought in 40INT was only available with M16 thread, so I had to make a new drawbar for these tools.

RR

Ian B
12-03-2002, 10:18 AM
RR,

When I first tried to get a bit of 5/8" bar down the spindle, I also hoped it was just a reduction sleeve that would come out. So far, no success - I've checked with a few other Beaver owners, they've all ended up making smaller drawbars (I will, however, go and give it a swift clout...)

My drawbar comes out easily, no keyways etc. I can see why an ejection sleeve would be a good idea, though - I was surprised at how well such a steep taper can stick (when you don't want it to, of course).

I think the Beaver mills started their production life with a 30 Int, the 40 Int came later; maybe there wasn't room through the spindle for a bigger hole without a complete redesign?

Ian

Ragarsed Raglan
12-03-2002, 10:34 AM
Ian,

If the spindle size is 14mm all the way through; then I think I would go for the ejector design. The Thiel system is really neat, unlock the drawbar, 3/4 turn then the ejector comes on and 'pop' out drops the tool! The top end can be taper pinned to an oversize nut (this was the bit that I couldn't find on the Thiel, it had been filed dead true to the nut face, and couldn't be seen!). You just need to make sure you've got enough adjustment available on the top side so that you don't bottom out on the tool retainer thread.

RR

Ian B
12-03-2002, 10:58 AM
RR,

You mention 3/4 turn to release the tool (sounds like what I'm after); do you mean first unscrew the drawbar all the way from the tool, 6 to 10 turns and THEN give it 3/4 turn to activate the ejector?

I've made an adaptor with a 5/8"BSW external thread, M10 internal thread and cut an M10 on the drawbar - I first need to hold the tool up, screw the drawbar in about 8 turns, and then tighten it. To remove, I slacken the drawbar by one turn, tap the top of the drawbar to release the taper and then continue unscrewing.

It's the 8 turns to engage about 3/4" of thread that I'm trying to get rid of with the bayonet idea.

Ian

Ragarsed Raglan
12-03-2002, 11:35 AM
Ian,

Unfortunately after the 3/4 turn to release the taper, you still have the 8 or so turns to fully disengage the threads!

I like the idea of a light bulb type bayonet fitting; but, and I never like to pour cold water on someones hot ideas, if you think about the analogy of the light bulb ~ you would have to have some form of spring pressure to allow a tolerence of fits.

Now maybe this is the answer!! If the spring was fitted to the pins of the bayonet rather than in the 40 INT taper......

If this works can we share the Patent rights????

RR

Ian B
12-03-2002, 12:17 PM
The basic idea of the bayonet came to me from my oilfield background - we use something similar (called a J latch) on the end of thousands of feet of tubing to lock the tubing in place.

This should all work without springs - pins sticking out of the bottom end of the drawbar pass freely down the keyways (within reason, fits don't need to be close), until they bottom out in an annular ring space. At this point, tightening the drawbar handle will turn the drawbar (less friction than in the nut at the top), causing the pins to rotate in the annular ring and out of alignment with the keyways.

We have, by this time, already installed a couple of stop pins protruding into the annular ring, to stop the pins spinning endlessly. This is the 1/4 of a turn bit in my first post.

Once against the stops, continue tightening the drawbar wheel - this'll now turn nut against drawbar, pulling it upwards, locking the tool in place. One turn should do it (says he hopefully).

To release, slacken the wheel. The drawbar'll rotate backwards when the tension has gone, the pins will hit the other side of the stop pins (cunningly located to make the drawbar pins now align with the keyways again), give the top of the drawbar a light smack, and tool neatly drops sharp end first onto your newly finished piece of work.

Might work. Snags, anyone?

Ian