It would be simpler to use belleville washers and an air cylinder to apply
pressure to release the tooling.
https://hackaday.com/2020/01/11/stacks-of-spring-washers-power-the-drawbar-on-this-cnc-mill-conversion/
On Sunday, July 18, 2021, 5:39:23 PM MDT, John Dammeyer
<jo...@autoartisans.com> wrote:
A long long time ago I read an article in Home Shop Machinist written by Rick
Sparber on what he called a WUT.
https://rick.sparber.org/Articles/drawbar/Drawbar.htm
Although I couldn't make mine exactly as his I was able to at least create a
thick hex washer so that I could tighten the draw bar while holding the WUT
with a wrench. Testing with a torque wrench can actually reach the 20 inch
pounds as the maximum suggested for the Tormach Tooling. In reality I don't
come close to that amount of torque and so far I haven't run into issues with
anything slipping.
I also paid for the instructions from homeshopaccessories for the power drawbar
that uses a small butterfly air impact wrench.
http://home.insightbb.com/~joevicar3/cheap_drawbar.htm
In playing around with the power tapping project I also tried using the
butterfly wrench to tighten and loosen the TT Tools. First, the wrench has to
work really hard to reach 20 inch lbs. And it has to work really hard to
loosen the drawbar if the torque wrench was used to bring it to 20 inch lbs.
The more normal value is around 12 inch pounds which seems more than adequate.
However, and there's the issue. Like any air impact wrench it chugs away until
it breaks the nut loose and then spins up fast. Fast enough to completely
uncouple the draw bar from the R8 holder and the whole works drops out. If it
does that then there's no real point to the TT tools other than repeatability;
which is an advantage..
My question is about controlling the reverse on the butterfly wrench to limit
it to two turns. I'm sure I could connect an encoder on the wrench shaft to
count a number of edges per turn and after two turns shut off the air valve.
But how fast does an air system react? By the time you reach two turns is it
already spinning so fast that it releases the R8 before the air pressure is
gone?
Is there some sort of mechanical approach to allow it to turn two turns and
then prevent further turns? This can't be fixed in stone because there will be
times where more than two turns are required for removing the R8 collet.
So I think LCNC with the MESA interface can count an encoder. It can probably
even switch off a valve within a few milli-seconds of N encoder counts. So
the HAL file would read in input for UnloadTool. Clear the encoder counter and
assert an output to open the air valve. On encoder_count = X close the air
valve.
Actually I'd probably just program a separate micro-processor to do this and
produce a done signal on the request input. I either case though is there a
way to limit the distance the butterfly turns?
John
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