What The World's Been Waiting For - Yet Another Power Drawbar Design

[vmax549]

 think a qc30 type spindle could be modified for the claw mechanism and would work just fine. It is ALREADY designed for the machine(lazy me)

I would change the lugs out and go with a cat30 holder to get the grooves for the tool fingers ad ready made toolholders.  Then use a mech on top like ray already has built to actuate the drawbar. You would really only need about max 1000 lbs so it is doable with air ( simple)

I have seen a few qc30 spindles on ebay go for cheap.

The rest would be basic mechanical design for the type of ATC you wanted.  Get the spindle working and the rest will follow.

(;-) TP

[vmax549]

I just took a peak inside of the qc30 cavity and here is a method that could work using the existing parts and spindle without modifying the spindle. Just add in the claw mech and modify the tool holder a bit. It uses the upper part of the toolholder taper to run the claw(;-)

[panaceabeachbum]

pretty far off the original topic of a new power drawbar design , but here is a link to a company that sells the grippers that pull the retention knobs used on cat and bt tool holders. They are avail in a variety of sizes and types

http://www.ortlieb.net/

[simpson36]

I just took a peak inside of the qc30 cavity and here is a method that could work using the existing parts and spindle without modifying the spindle. Just add in the claw mech and modify the tool holder a bit. It uses the upper part of the toolholder taper to run the claw(;-)

If you look back to the photos in Hood's reply #49, this is exactly how his power drawbar works.

Positive drive is the key whether by going with a new CAT spindle or modifying the R8. Either has product potential, methinks. The fast track solution would be a simple modification of the Tormach setup, but in the long run, of all the ideas presented, your spindle solution I think would offer the best perfrormance, and you only have to produce and/or modify one part. The rest are proven off-the-shelf items purpose built for the application.

[vmax549]

THere may be a way (;-) to do a claw type AND use the tormach style holders using a  R8 collet adaptor that has a couple of MODs.  The tormach style would need a stud added to the top and the claw would live inside the R8 adaptor and would work from the drawbar and RAYS mech would operate the drawbar on top.

(;-) TP

[sprockethead]

Ray LOOKS good.   Here is something to consider. The piece that holds UP on the spring pack, the lower plate with the finger that slides under the pack. THis will be tricky to get the spindle in the exact position so the lever can slide under the pack AND still not have any play. ANY PLAY will cause the spindle bearings to load up as the pack is compressed. You might want to consider a push me pull me type of compressor arrangement that floats and as it is compressed both sides of the PACK are compressed at the same time. AND it puts zero load on the drawbar.

Another thought when building a drawbar is the machines always use a long 30deg angle tool holder that does NOT require any of the force of holding in the toolholder to be used to HOLD the bit as well. (;-)

Just a thought, (;-) TP

indeed it would be nice to see that, cylinder incorporated with bolted to base sviwel flange and fork clevis joining with drawbar, both strokes driven using 5/2 1/4" solenoid valve with exhaust regulators, micro plc with hmi is awesome for sorting out things like limits, rpm encoder, safety relay circuit, coolant, ..... its so obvious that tapered shanks dont need holding force anyhow... the cylinder is not pressurised both sides simultaniously!!, 5/2 solenoid valve principle of work clearly indicate its impossible, thats why right stroke here is very important, you can always adjust it winding the clewis onto the rod bit more and properly set up cylinder's cushions you could have, i wonder if it would be possible to drive using 2 Oz carbon dioxide inserts and pressure regulator to eliminate compressor, anyhow i think that you've done an exceptionally good job, ... .. one more... cylinder fitted with reed swith could eliminate any hazards related, micro plc should also controll mains contactor

[cncmill70]

Hi Ray,

I enjoyed reading about your ATC. I'm curious on how it's preforming?  I'm looking into building one for my cnc Bridgeport.

[HimyKabibble]

Hi Ray,

I enjoyed reading about your ATC. I'm curious on how it's preforming?  I'm looking into building one for my cnc Bridgeport.

It isn't....  Never could get it to develop enough force to adequately retain the Tormach holders - over 2000# of drawbar tension is required for maximum retention.  The only practical way to achieve that is with an air over hydraulic system, or a large diameter, multi-stack air cylinder.  The other approach i'd love to try is using a stepper motor, driving a high reduction planetary gearbox to directly spin the drawbar.  This would allow the driawbar to be fully tightened to any desired torque, loosened a controlled about to enable using Tormach tool holders, or the tool released completely.  It's mechanically very simple as well.  You'd want to be able to generate 20-25 foot-lbs for tightening, and about twice that for loosening.

Regards,
Ray L.

[cncmill70]

Sorry to hear this Ray. When I'm using an end mill I typically only take of .030-.040 per pass. After reading through the post it sounds like you possibly taking quite a bit deeper cuts. Would your ATC work with the shallow passes that I'm taking? Thanks again.

[HimyKabibble]

Sorry to hear this Ray. When I'm using an end mill I typically only take of .030-.040 per pass. After reading through the post it sounds like you possibly taking quite a bit deeper cuts. Would your ATC work with the shallow passes that I'm taking? Thanks again.

Yes, for a small machine, taking light cuts, a great deal less force is required.  1000# is not terribly difficult to achieve, and is adequate for most benchtop-class machines, or light-duty work.  I was doing low-volume production work, so needed to be aggressive to get reasonable throughput - my typical roughing pass is up to 1/2" deep with a 1/2" endmill, so keeping the tool where it belongs is pretty important....

Regards,
Ray L.