[altaic]

Hi all, I'm considering making a pneumatic power drawbar for my mill with a stack of belleville spring washers (in the ballpark of 1000lbs of force) at the top of the spindle (where the head of the threaded drawbar is currently), and a ramped ball-bearing gripper at the bottom to grab the pull-stud attached to the toolholder.

The simplest design involves locking the quill and mashing down on the drawbar assembly with a pneumatic cylinder, compressing the spring washers and releasing the toolholder. However, this also mashes the spindle, which I'm not certain is wise for its bearings. OTOH, the other designs I've seen appear to just mash down like that. (chair)

The "proper" design in my mind is a bit more complicated. The spindle would not be locked by hand (via the quill lock), but instead be supported by an assembly on the top of the mill head. Thus the compression force on the springs from the pneumatic cylinder is transfered to this support on the mill head rather than to the spindle.

So, assuming I want to keep my mill in good repair, is it necessary to support the spindle in this way, or should I mash on the spindle with abandon?

[pete from TN]

However I am getting ready to start on my own tormach system power drawbar setup for my Lathemaster/rf45 cnc mill conversion. I have had some conversations with some clever fellows on here about this and the best Idea I have heard was to create a kind of fork setup on the top of the millhead using a small throw but large force pneumatice cylinder actuating on a dual fork type assembly that uses a scissor action compressing the bellville pack between two large washers . This will allow considerable force and rapid opening of the drawbar to collet link for toolchange yet impose no added force to the spindle bearings. I have yet to build this so it is all pie in the sky right now but it is the best Idea I have seen or heard yet. Another nice feature is that it will also not put any undue force to the millhead itself whereas several designs I have seen require substantial mounts drilled and tapped into the millhead at varying points to allow for counteracting the force applied to the top of the drawbar. It seems like this could be machined into a compact form and be literaly held onto the top of the millhead by a pair of bolts that would only serve to position it and ensure the scissor mechanism retracts adequately to not interfere with the rotation of the spindle. Does that make any sense? Easier to to envision it than to put it into words really...peace

[RICHARD ZASTROW]

You may want to "Google" Kurt Power Drawbar". I believe they also have kits.

Dick Z

[Runner4404spd]

if you do a quick search to mcmaster car you find your spindle bearings. usually a 35-40 mm ID tapered roller bearing. the thrust load rating for this particular bearing is 2000 lbs. more than plenty to support a pneumatic drawbar thats putting out only 1200 lbs of force. ultimately you will have to change them eventually but i bet they don't break down for a long while.

[wwendorf]

I'm working on a drawbar for my X3 as well, and running into the same concerns as you. I've been dreaming up something similar that reaches up and sort of grabs underneath the belleville springs as something presses on the top of the drawbar. I haven't had much time to work on it as i'm finishing a large machining project, but i'm getting close to drawing it out in Alibre.

Wade

[BobWarfield]

So some sort of "pickle fork" (like the auto tool) extends under a shoulder, and force is applied that squeezes between the pickle fork and a lever pressing down on the drawbar?

Hmmm.

That'll certainly keep the forces off the spindle bearings, but there's no feature on the spindle to use as the shoulder. Are you going to be able to afix something tightly enough to withstand the 1100+ lbs? Probably. Needs to be thought through though. That's not a set screw situation I don't think!

Pete, I would think you need to machine your pulley collar to include such a shoulder feature.

I guess I'm starting to wonder with all this panic over stressing bearings whether this isn't just too much trouble. Why not build an impact wrench-style drawbar? True, they're not as nice working with R8 collets, but I hate the collets anyway. I'm going to have to do some repeatability tests on my ER32 collet chucks and the powered drawbar I have.

Cheers,

BW

[wwendorf]

The answer is quite simple really. I have the tormach tooling system, and I want to build tool racks to make an auto tool changer solution for my mill. That being said, an impact wrench style drawbar won't work cause I can't automate it.

My initial drawbar system will be the type where it just presses down on the top of the drawbar and compresses the springs. I need to get something functional now. I will likely work on the design of one with a "pickle fork" as you call it. I'm thinking that a regular washer under the beleville springs (a rather thick and strong one that is) would work more than sufficiently to allow for some upward force. Then I wouldn't have to modify my spindle or quill at all.

Wade


Wade

[wwendorf]

Hmm, now I just had another idea.

Using my idea of a washer, what if I installed a plate on the top of the mill that ended just slightly underneath the level of the washer, like .010" or so. Then, when the arm preseed down on the drawbar from the top, it would just go against the plate?

Something like this:

             ____

            |___|               Top of Bolt

           <      >               Set of Beleville Springs

           <      >               2nd Set of Beleville Springs

          =========           Flat-thick-strong washer

     -------------------

     |                |     THis would be a bar with a U shaped cutout to fit around the 

     -------------------     top of the spindle.

In fact, that bar or base, could even be the base the the pneumatic cyclinder attaches to.

Wade

[BobWarfield]

That being said, an impact wrench style drawbar won't work cause I can't automate it.

The impact wrench automates in exactly the same way as this other style--using air solenoids. It's trivial to do.

Cheers,

BW

[wwendorf]

I realize that, but you run the risk of the R8 collet coming unscrewed. I haven't seen any ATF projects on here that make use of the type of system you are proposing.

The tormach tooling system fits into an R8 collet. There isn't enough control there for me to want to try using it with an automatic tool changer.

If i'm just not understanding, please give a better description of how you propose the whole solution would work?

[BobWarfield]

I realize that, but you run the risk of the R8 collet coming unscrewed. I haven't seen any ATF projects on here that make use of the type of system you are proposing.

The tormach tooling system fits into an R8 collet. There isn't enough control there for me to want to try using it with an automatic tool changer.

If i'm just not understanding, please give a better description of how you propose the whole solution would work?

Go for it Wade, I can see your mind is made up!

Cheers,

BW

[wwendorf]

It's not that my mind is made up, it's just that I don't see how an impact wrench type system would work with the tormach tooling system. I'm totally open to other ideas and if you can show me how it would work, then it's a great way to go.

I've even got the plans at home for making an impact style system, but I didn't go ahead with them because I couldn't see any practical way to make it work with a tool rack or ATC?

I'm always open to ideas.

Wade

[BobWarfield]

You won't be using the powered drawbar system with the TTS. There is no need for TTS if you use endmill holders or collet chucks instead of the R8 collets.

Try the experiment: what is the repeatability in Z of reinserting a collet chuck, endmill holder, drill chuck, etc. with an R8 shank?

I just did it again, just now, takes about 10 minutes. I used a handheld HF impact wrench since my CNC mill doesn't have the powered drawbar. I picked up the first ER32 collet chuck I came across in my shop (a battered chuck I think I originally bought from eBay seller 800watt), got out my Z-axis tool setter, zeroed the tool height in Mach3, and then removed and replaced that collet chuck 5 times. Each time I brought it completely clear of the spindle.

What do you suppose the Z repeatability was? For 5 trials I got
+/- 0.0005". I've done the experiment before with similar results. That is significantly less than the backlash on my Z, so I figure it's pretty good.

This should not be surprising with a solid R8 shank and a tool like the impact wrench that will apply nearly the same torque every time.

I can get a real nice ER32 collet chuck with an R8 shank from Maritool for $75.10 that repeats +/- 0.0005", I can buy cheap ones like my 800watt chuck for as little as $20 with similar Z repeatability (more runout), and points between (I have some Bisons too). It's really nice to have the luxury of so much off the shelf tooling from a standard taper.

Or I can get a TTS ER20 from Tormach for $92.00.

Now, your toolchange time will be ever so slightly slower--the impact wrench takes a little longer than just firing the air cylinder.

However, you don't have to fret over crushing your spindle bearings, nor worry about how much force to apply with the Bellevilles to keep the endmill from slipping on a heavy cut. I've never had a holder slip yet with this setup. If it had, it would've sheared off the little set screw in the R8 taper. Said setscrew would be removed with an ATC for obvious reasons, BTW.

Both systems will work great. You just have to figure out what advantages/disadvantages you want to deal with on either, and what things you want to make versus buy.

Cheers,

BW

[wwendorf]

That's great information. Thanks Bob. I agree with you completely. R8 collets and tool holders are great and work great with the impact wrench, and allow you to maintain z repeatability. I did that for a while myself (minus the impact wrench, which I considered buying).

If I were to make an Automatic Tool Changer using strictly R8 tool holders, how would I go about keeping them so the keyway automatically lines up? My mill doesn't have a servo drive so i'm unable to position the spindle orientation automatically.

Again, my end goal is an ATF. I still haven't seen you mention a way to make an ATF with the R8 toolholders (or collet chucks). I can't imagine removing the keyway from the spindle. Then you just have a collet spinning with nothing to lock it down.

Why would I want to use the TTS ER20 collet for everything when I can use a tool holder than has less than .0002 runout that works for 95% of my tooling? I have one collet chuck from them, and I hardly ever use it. I can make my own tool holders, or buy TTS holders for $23 bucks. Once in a while they have surplus tool holders that they put on EBay and I can get those for $13! Plus, by doing a pneumatic drawbar type system I can put a simple tool rack on the end of my table and have an ATF.

Wade

[BobWarfield]

I'll get around to showing how to do an ATC this way eventually, but I have some other fish to fry at the moment.

I will say that the keyway setscrew is not at all mandatory and is in fact an impediment even when manually machining. I'll be removing mine during the process of converting to a belt drive.

There are quite a few threads around that discuss the ramifications of removing it. It's very coming in shops to find machines where the setscrew was long ago sheared off and never replaced.

As I say, both ways work, it's a matter of your personal evaluation of the trade offs. Just don't assume you have to do it the one way and not the other.

I look forward to seeing you changer. Looks like there will be a lot of them running around before too long. I think that's awesome!

Cheers,

BW

[pete from TN]

I am quite sure that the repeatability of a decent r-8 toolholder is more than adequate enough for my uses on this little mill but I do not see any reason not to go with the same setup that hoss has. It is a proven system and the tormach holders are made to high enough standards for their machine which is pretty good I hear. Another reason is the sheer length of the R-8 tooling would cause you to have a much longer Z travel for each toolchange. It is just too easy to make this non- spindle bearing pneumatic system not to try it. I do not see why you would need a shoulder on the spindle to perform the toolchange. I just see a rather large and thick washer on the drawbar underneath your bellville stack and then the scissor assembly acting on the top of the drawbar and the bottom of the large washer. Once you have this setup you could actually add even tighter bellvilles to ensure better hold on the spindle. The scissor mechanism also imparts another added advantage, due to the lever action of the arms and the pivot point placed appropriately you can actually increase the power of the pmeumatic cylinder so a shorter lighter and smaller unit can be utilized. You might even be able to use a linear actuator if you can find a real stout one...

I have several of the tormach toolholders here as well as a keyless chuck and the tts arbor for it and I am anxious to use it on my machine. I fully intend to create a simple version of Hoss's rack mount toolchanger setup on my Lathemaster mill after I get it running properly and learn how to use the darn thing... Much to do and these belt drive pulleys are taking some time to machine so it will be a while....peace

[Kipper]

Seems a good idea......Give me a long enough lever....Archimedes?

Valve spring compressor from above kind of thing....

[wwendorf]

I'm going to move forward with it. I've been having ideas all day about various methods of getting this to work properly. The more I think about it, I like the idea of having a large washer under the belleville springs. I've got several ideas on mechanisims that will let me compress without putting a ton of stress on the quill or the bearings. I'll just have to see if it works the way I think it will. Time will tell.

Wade

[pete from TN]

Sounds great man, looking forward to the pictures and progress on this. I have some ideas myself as I said but it is a little bit down the road right now as I am still working on the cnc conversion.... good luck to you.....peace..

[wwendorf]

I'm lucky in that I have a Syil X3, so my spindle control is handled. In fact, i'm upgrading the eletronics to the Syil X4 eletronics for even better spindle control.

I'm pretty sure that the route i'm goin to take is the scissor approach so that there is a bit of force pushing up on the springs so I don't wreck the quill or the spindle bearings.

Wade