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

[vmax549]

OK Now for the $10 story on atc toolchangers with R8 tool holders and a impact drawbar system.

IF you are not rigidly aligned with the small key slot in the R8 a large mess is in the works as if the alignment is off a hair the collet WILL pull up with the key NOT aligned in the slot and cause one heck of a mess. AND it will do it sooner or later (;-)  ASK me how I know.  I would never use the R8 in an ATC for this reason. THe machine does not know IF the slot is not aligned and there is little room for error.

IF you are going to do a production capable ATC do yourself a favor and find a QC30 spindle with teh center hole for the drawbar.  Change out the lugs and fit it with Cat30 holders and a impact drawbar.  YES it takes a different drawbar as you have to match the thread in the cat30 holder and it is best to use the splined nut on top.  Now you have holders that are more common AND have the slots for the ATC fingers. I have seen this type of arrangement run for years without problems.

Just a thought, (;-) TP

[vmax549]

NOW for the rest of the story (;-)  how are you going to index the spindle to the correct position each time. NO easy feat on a BP type machine. The mechanism is quiet simple but fitting it in a manner that works well is not.

Was not a problem with teh tormach style of holders BUT(;-) any style with a keyed holder it is vital.

Just another though, (;-) TP

[HimyKabibble]

NOW for the rest of the story (;-)  how are you going to index the spindle to the correct position each time. NO easy feat on a BP type machine. The mechanism is quiet simple but fitting it in a manner that works well is not.

Was not a problem with teh tormach style of holders BUT(;-) any style with a keyed holder it is vital.

Just another though, (;-) TP

Terry,

The short answer is:  You don't.  You MUST remove the pin from the spindle.  I can't for the life of me understand why that pin is there anyway.  It serves no useful purpose.  If the tool is too loose, it'll just shear the pin off.

Regards,
Ray L.

[vmax549]

It is there for a reason, To hold the toolholder until the drawbar tightens up enough to finish tightening or you run the risk of spinning the holder in the spindle instead of tightening.  We tried it without , did not always go well. (;-)  Might not be a problem BUT(;-)

(;-) TP

[Hood]

The dog pin and R8 has been argued over many times on many forums, all I can say is on all Bridgeports I had and any I have seen the pin has been removed and I have never had an issue with a collet spinning whilst tightening the drawbar, both manually and with a power drawbar.

Hood

[panaceabeachbum]

This seems similar to this system.
www dot mach-1tooling dot com

I have used it and it works extremely well. Very rigid and accurate. Quick tool changes too.

Kenny

Kenny,

I find that system fascinating.  The pullstud mechanism is precisely what I had in mind for a future "upgrade" to my setup, and proves that it CAN be done.  What really surprises me is the very low drawbar tension - apparently only 600#?  After my testing the last few weeks, I'm amazed that's enough to securely hold an endmill in a collet.  Do you by any chance have a means of measuring (even crudely) how much torque it takes to make a 1/2" endmill slip in a collet using that setup?  I was able to do it by clamping a vise grip on a scrap endmill, and using a $5 hardware store "fish scale" to pull on the handle, then calculate the torque based on the fishscale reading and the length of the vise grip. That would be invaluable in helping me correctly calibrate my drawbar.

I'm going to read their patents and see what I can learn....

Regards,
Ray L.

The reason their system works with such low tension is they are using endmill holders which rely on a set screw that fits in the recess in the side of the endmill, unlike collets they dont rely on friction. The 600lbs of force hold the pull stud fingers up inside a collar. My milltronics uses a spring loaded fingers , marqaurt and a number of other companies have the "gripper" assemblies .


Here is the patent number for an interesting system. 5846037   here is a link to the patent office search page  http://patft.uspto.gov/netahtml/PTO/srchnum.htm  i attached one of the drawings from the patent below that shows their simple sytem of gripping the pullstud , they use balls wich have a tiny contact surface , some of the finger types have alot more bearing surface

 I dont know anybody doing any production work that uses collets over tool holders for the simple reason that you have to measure tool length everytime you change a tool with collets, and the obvious tool slipage problem . The tormach sytem utilizes a collet to hold the tool holders that overcome that one issue but as noted it has limitations and is for light duty use. Expecting to take a 1" depth of cut pass with a half inch endmill may be great as a sales tool but isnt practical in the shop .  

[panaceabeachbum]

The dog pin and R8 has been argued over many times on many forums, all I can say is on all Bridgeports I had and any I have seen the pin has been removed and I have never had an issue with a collet spinning whilst tightening the drawbar, both manually and with a power drawbar.

Hood

I agree , the pin isnt present in either of mine and we have never had one spin while using the impact type power drawbar, also never had a cross thread or thread stripping issue , although we use tool holders intead of collets so they really dont kneed to be that tight.

Another thought might be to swap to a cat 30 spindle if avail for your machine , I know acra has them for their bridgeport clones and tool holders are fairly cheap

[vmax549]

HOOD were you running the R8 with a ATC or installing them by hand(;-) IF by hand then YOU know IF the toolholder is enganed and tightening up ok you will hold on to the tool holder and FEEL it.

On an atc the machine cannot feel the holder tightening up and can just spin the holder in the spindle. Seen it happen years ago when "WE" were going to perfect and sell  the AUTOCHANGE R8 ATC for the BP (;-) LOL

With a bt/ct/nmtb holder the holder is held in the fingers with the index slot so it has a grip on the hoilder that will not allow it to rotate in the finger.(;-)

(;-) TP

Never had a crossthread either(;-) That part always worked well.

[simpson36]

Well, I got some time to catch up on this thread . . . . interesting new ideas presented . . . BUT

We old engineers have a saying "you can't polish a turd"

All of the problems are the result of relying on friction alone to transmit torque. That's the turd.

My original solution is still the best, methinks. Positive drive = end of problem. Easily accomplished with a dog drive on the end of the spindle as I mentioned previously, and since I now see that the plan was to make new tool holders anyway . . zero added cost except for the dog for the spindle nose, which could be a simple bolt-on. 

Ultimately, I would prefer Vmax' solution of a new spindle (although I would build it differently) as a rugged and permanent high performance solution, but the current scheme could be made to function, I believe.

[Hood]

Never had an ATC but I also know I didnt grip them, I normally offered them up with two fingers underneath and certainly never had to stop them roatating, granted if you have crap threads on the collets or the drawbar then it may be a problem.
 The matchmaker I referred to earlier had the dogs removed from the spindle nose so that spindle orientation wasnt required so in effect the same as it would be with a R8.
I would however imagine if you were thinking of an ATC with the R8 then it would probably be best to have some form of modification to the holder, the one earlier where a sleeve went over the collet and a nut closed the collet would be very simple to make up and probably get over a lot of problems associated with R8 and ATC. Obviously there will be a patent out so no chance of selling them but cant see anyone being able to do much if you make them for yourself.
Hood