[SCzEngrgGroup]

For years, I've been reading posts where many people here and on several other forums state categorically that TTS is only suitable for very light-duty milling, due to "the pull-out problem". I've always disagreed with that position as I've been using TTS for a number of years now, on several machines having 1-3HP spindles, and I have never once experienced pull-out. I have always argued that TTS works very well on machines at least up to 2-3 HP, provided sufficient drawbar tension is provided. Here is some visual back-up for my position:



There are three operations there, all being performed at 6000RPM, using a cheap, low-quality (Interstate brand) 2-flute HSS endmill:

1) Roughing a 1.006" diameter by 1" deep circular pocket - Cut in two steps, each of 1/2" depth. Helical entry at 77IPM, with w/10 degree ramp angle, followed by 110 IPM constant-engagement cutting at 0.050" stepover.

2) Finishing the same pocket - Cut at full 1" depth, at 65 IPM, in two passes of 0.010" each.

3) Roughing a large, odd-shaped pocket - cutting parameters are the same as operation #1, except depth is only 0.325", though I can just as easily cut the same pocket at 0.5" depth - that's just not what this part called for.

Unfortunately, on the fourth operation a programming error caused the spindle to stall, so I had to hit E-Stop. But, despite the fact that much of this was near the spindle power limit of the machine, and the spindle actually stalled at the end due to tool load, there was absolutely NO pull-out of the TTS holder.

Again, the "secret" is simply providing adequate drawbar tension. My power drawbars actually torque the drawbar to 30 ft-lbs, providing a drawbar tension in excess of 3500# - more than can be reasonably achieved using Belleville springs - which is enough to keep the TTS holder in-place under any load a 2-3 HP machine can muster. Many/most TTS users who have experienced pull-out seem to have power drawbars that provide no more than 2000-2500 pounds drawbar tension (many have much less), which is simply not enough to properly retain the toolholder with much more than a 1/4" tool.

Regards,
Ray L.

[waltpermenter]

how are you physically measuring the torque on the drawbar?

[SCzEngrgGroup]

how are you physically measuring the torque on the drawbar?

With an amazing device I found on the Internet: Let me google that for you

[FuriousGeorge]

With an amazing device I found on the Internet: Let me google that for you

It would be nice to see an appropriate answer to a valid question rather than sarcasm, so I'll ask it again.

Could you tell me in a detailed and meaningful way how you measured the torque on your PDB so that I could follow the same procedure to measure mine?

[SCzEngrgGroup]

It would be nice to see an appropriate answer to a valid question rather than sarcasm, so I'll ask it again.

Could you tell me in a detailed and meaningful way how you measured the torque on your PDB so that I could follow the same procedure to measure mine?

I thought use of a torque wrench to do that would be pretty obvious. There is a socket on the PDB, there is a socket on the torque wrench. You simply use a suitable piece of hex stock to connect the two. Could not be simpler. You can also do it even more simply, by using the PDB to tighten the drawbar, then put the torque wrench on it, and see how much torque it takes to get the drawbar to being to tighten further. Either method will get you the same answer, within a couple foot-pounds.

Regards,
Ray L.

[waltpermenter]

how are you checking this with a torque wrench if the power drawbar is doing the tightening? how do you measure the over 3500# tension?

[Hirudin]

I don't want to contribute too much to the pissing contest that is probably brewing, but I would like to say that I'm pretty sure tension is tension. If your power draw bar, which I think looks very good, can provide 3500+ pounds of tension that is fantastic. That 3500# is superior to the 2500# that the Tormach setup provides. That being said: a belleville setup that provides, say, 4000 pounds of tension would be even better - and entirely possible. If someone wanted to they could make a belleville stack that would rip the draw bar in half. Getting it compressed in the first place, particularly while sitting on to of a mill, would be something else entirely.

I guess I think your power draw bar design has real advantages without continuing bellevilles vs. torque debate.

[SCzEngrgGroup]

I don't want to contribute too much to the pissing contest that is probably brewing, but I would like to say that I'm pretty sure tension is tension. If your power draw bar, which I think looks very good, can provide 3500+ pounds of tension that is fantastic. That 3500# is superior to the 2500# that the Tormach setup provides. That being said: a belleville setup that provides, say, 4000 pounds of tension would be even better - and entirely possible. If someone wanted to they could make a belleville stack that would rip the draw bar in half. Getting it compressed in the first place, particularly while sitting on to of a mill, would be something else entirely.

I guess I think your power draw bar design has real advantages without continuing bellevilles vs. torque debate.

Yes, you could build a drawbar to provide virtually any level of tension, but generating the force to RELEASE that drawbar becomes impractical after a certain point, as you'll have to sink an awful lot of money into a multi-stack air cylinder, or air over hydraulic system.

In any case, that is NOT the point of this thread, and I have no intention of engaging trolls. The point is, despite what many seem to believe, toolholder pull-out does NOT have to be an inherent part of life with TTS. TTS is perfectly capable of far greater performance than it is generally given credit for, and certainly capable of handling any load these machines can throw at it. I am trying to de-bunk the persistent myth that it is not.

It's just like the other myth that won't die, that stepper motors ALWAYS lose steps. That one just won't go away, no matter how much evidence there is that it is simply not true. I guess its easier for some people to blame the components than to admit that they did a poor job designing their system. TTS, like stepper motors, works great when used properly.

Regards,
Ray L.

[hoss2006]

I don't want to contribute too much to the pissing contest that is probably brewing, but I would like to say that I'm pretty sure tension is tension. If your power draw bar, which I think looks very good, can provide 3500+ pounds of tension that is fantastic. That 3500# is superior to the 2500# that the Tormach setup provides. That being said: a belleville setup that provides, say, 4000 pounds of tension would be even better - and entirely possible. If someone wanted to they could make a belleville stack that would rip the draw bar in half. Getting it compressed in the first place, particularly while sitting on to of a mill, would be something else entirely.

I guess I think your power draw bar design has real advantages without continuing bellevilles vs. torque debate.

I wonder if any of the Tormach guys have thought of trying a higher psi compressor.
If the air cylinders are rated high enough, be sure to check first, a 200 psi compressor isn't very expensive to perhaps double the pull capability with an upgrade to the bellevilles of course.
No need for a big one, I just got a little 200 psi pancake type that will be just for my drawbar.
I'd suggest checking with Tormach first about safety considerations.
Hoss

[SCzEngrgGroup]

I wonder if any of the Tormach guys have thought of trying a higher psi compressor.
If the air cylinders are rated high enough, be sure to check first, a 200 psi compressor isn't very expensive to perhaps double the pull capability with an upgrade to the bellevilles of course.
No need for a big one, I just got a little 200 psi pancake type that will be just for my drawbar.
I'd suggest checking with Tormach first about safety considerations.
Hoss

Higher pressure is one way to increase capacity, but the problem is the vast majority of consumer-level compressors on the market, and virtually all of the small ones (under 5HP or so), are limited to no more than 100-125 PSI (often limited by the rating on their pressure tanks). Larger compressors often provide higher pressure, but many customers would be justifiably upset if they bought an air-powered product, then found out they had to buy an expensive new compress just to make it work. It's not like an air tool like a sander that you can get by with less pressure if you just work slower. A pneumatic PDB either works or it doesn't - not enough pressure, and it don't work at all. Higher pressure air cylinders are also more expensive - most commodity ones are only rated for 125PSI.

Regards,
Ray L.

[hoss2006]

Higher pressure is one way to increase capacity, but the problem is the vast majority of consumer-level compressors on the market, and virtually all of the small ones (under 5HP or so), are limited to no more than 100-125 PSI (often limited by the rating on their pressure tanks). Larger compressors often provide higher pressure, but many customers would be justifiably upset if they bought an air-powered product, then found out they had to buy an expensive new compress just to make it work. It's not like an air tool like a sander that you can get by with less pressure if you just work slower. A pneumatic PDB either works or it doesn't - not enough pressure, and it don't work at all. Higher pressure air cylinders are also more expensive - most commodity ones are only rated for 125PSI.

Regards,
Ray L.

I said I just got one with 200 psi, only $140 on ebay.
Dewalt make several to 200 psi in a range of tank sizes.
They are out there all over just have to look for them.
I suggested they check with Tormach first but air cyclinders of the type used on theirs are common to 200 psi.
If their air cylinders are capable they don't have to buy new ones, I didn't suggest buying new ones.
I don't own a Tormach just the tooling or I would explore this myself.
Just offering a suggestion if any of the Tormach guys want to look into it.
Hoss

[Hirudin]

To the question above: it seems conceivable that you could attach the torque wrench to the spindle* and watch the needle. Although I'm not sure this exact method would work, I do know that measuring torque is not rocket science.

*Oops, I mean the PDB

[Jabs1542]

Aren't we really concerned with tensile pulling strength? How would one NDT measure that?

[Hirudin]

Letvs all build these!
http://www.cnczone.com/forums/genera...rce_gauge.html

[Jabs1542]

Ok, I buy in on the TTS strength against pullout - I never had a problem when I was manually tightening the drawbar. I saw a screw based power drawbar video (it might have been yours) but unfortunately I have the Tormach belleville based PDB. Now I have tool pullout issues, usually aluminum, usually larger cuts (like the video you posted in this thread). Other than maintaining a well lubed collet shoulder is there anything that can be done to increase the "pull" of the drawbar?

[waltpermenter]

i would still like to know how the 3500# pull that is claimed is measured, theory is just theory until it's proven by physical testing. it would be nice if the procedure for it's testing is described or shown by the claimant so that the same test can be performed on the tormach power drawbar for comparison. i think a more prudent test would be the grip strength on the toolholder as that is what ultimately retains the toolholder.

[johnedward]

i would still like to know how the 3500# pull that is claimed is measured, theory is just theory until it's proven by physical testing. it would be nice if the procedure for it's testing is described or shown by the claimant so that the same test can be performed on the tormach power drawbar for comparison. i think a more prudent test would be the grip strength on the toolholder as that is what ultimately retains the toolholder.

I agree that it would be nice to hear or see the methodology at arriving at 3500 lbs but it's my opinion that it was guesswork not a practical procedure that could be repeated. I would also call the claim about reports "that TTS is only suitable for very light-duty milling" a bit spurious, have never seen that myself here and I've read a lot.
john

[vertcnc]

Ray,

On the stepper subject, are you still using the original steppers or have you changed to servos? I remember you saying you were going to upgrade your Torus Pro. What brand steppers and drives do they use.
Thanks

[SCzEngrgGroup]

Ray,

On the stepper subject, are you still using the original steppers or have you changed to servos? I remember you saying you were going to upgrade your Torus Pro. What brand steppers and drives do they use.
Thanks

I switched over to AC servos a few months ago. The only functional advantage is they are quieter. I still run the machine at the same 350 IPM I ran with the steppers, though the servos are capable of 500 IPM, but I'm just not comfortable with that speed. The stepper drives were, I think, Leadshines, and worked really well. No idea what brand the motors were, but they were NEMA43s - BIG!

Regards,
Ray L.

[johnedward]

Yes but checking drawbar torque is pointless for the tormach drawbar, how did you arrive at the 3500 lb pull force figure? I know how we check ours but would like to hear how you did.
john