[davidperry3]

How much pressure is on the Bellvill washers in the PDB?
How far are they compressed?

[Steve Seebold]

The manual says to tighten your draw bar finget tight or until the collet holds a TTS Tool Holder, then go two more turns. I went 2 1/2, and I have virtually no slippage.

[nitewatchman]

I tighten mine until the PDB will not release the tool and slowly back off until the tool will release. I try to do this with the pressure dropping to the compressor start pressure.

As soon as time allows I intend to pipe this into my 80gal shop compressor. Usinf this system there should be virtually no pressure sag in operation.

nitewatchman

[GJeff]

How much pressure is on the Bellvill washers in the PDB?
How far are they compressed?

I'm curious to know this as well. You thinking about making your own belleville tensioned system with a manual release lever?

[BAMCNC.COM]

I'm way past 2.5 turns, but I have a different drawbar for ATC I believe. My Tormach came with 3 drawbars, all different lengths if I remember right.

[davidperry3]

I'm curious to know this as well. You thinking about making your own belleville tensioned system with a manual release lever?

Bingo!
It cant be that hard.

[SCzEngrgGroup]

Properly retaining TTS tooling requires upwards of 2500# of drawbar tension, which means your release mechanism needs to be capable of well over 3000#. Even the Tormach PDB seems to suffer from pull-out, judging from the number of problems cited here over the last several months. My solution is a motor-driven drawbar, driving through a high ratio (50:1) planetary gearbox. This allows me to properly, and very consistently, torque the drawbar to 25 ft-lbs, and has the added advantage of allowing me to use R8 tools just as easily as TTS tools. This system has worked flawlessly for me, for the last year.

Regards,
Ray L.

[BAMCNC.COM]

Torque? So your spinning the drawbar?

[davidperry3]

Properly retaining TTS tooling requires upwards of 2500# of drawbar tension, which means your release mechanism needs to be capable of well over 3000#. Even the Tormach PDB seems to suffer from pull-out, judging from the number of problems cited here over the last several months. My solution is a motor-driven drawbar, driving through a high ratio (50:1) planetary gearbox. This allows me to properly, and very consistently, torque the drawbar to 25 ft-lbs, and has the added advantage of allowing me to use R8 tools just as easily as TTS tools. This system has worked flawlessly for me, for the last year.

Regards,
Ray L.

I am currently using an air ratchet, it works great and I have never had pull out. Still a simple lever that compresses spring washers would be even faster. The little bit of research I have done says you can stack as many of these washers as you need for the force required. If you need more travel you can invert some of them in the stack. It would seem to me that the travel you would need would be slight to get the collet to release.

[Don Clement]

Even the Tormach PDB seems to suffer from pull-out, judging from the number of problems cited here over the last several months.

For someone who has never seen a Tormach or Tormach PDB, the use of the words "seems to suffer from" is appropriate.

[SCzEngrgGroup]

Torque? So your spinning the drawbar?

Yes, I spin the stock drawbar. With my current PDB, driven by a 400 oz-in stepper motor, I have more than enough torque on-tap (~100 ft-lbs) to easily twist the drawbar completely off. I have it set to about 25 ft-lbs when tightening, about 35 ft-lbs when loosening. As I said, it has worked absolutely flawlessly since the first day I put it into service about a year ago. No pull-out, ever, even on the most aggressive cuts.

Regards,
Ray L.

[GJeff]

Looks like there are far fewer washers on the actual Tormach one:


Appears to be 8 in a ()()()() configuration but an actual owner should be able to tell you. Wouldn't be very much travel required for the lever especially since they're already partially compressed before you compress them further to release the tool. Each washer's full range of compression at that size is probably no more than 0.050 using LeeSpring.com as a reference. So you're talking 0.4" maximum travel, realistically you only need to move <0.2" (if that) at 3000 lbs which seems very do-able.

[Scott_M]

Hey David
I am sure you are aware of my Manual Drawbar http://www.sdmfabricating.com/LOD.html I use 12 Bellevilles and compress them quite a bit, they pull on the drawbar with about 2600 lbs. This is about equal to tightening the stock drawbar to about 35 ft lb. When it is all loaded up it only needs about .035" travel to release a tool from the collet. The amout of distance your preload requires is strictly dependent on the type and number of Bellevilles you use.


Scott

[davidperry3]

Hey David
I am sure you are aware of my Manual Drawbar http://www.sdmfabricating.com/LOD.html I use 12 Bellevilles and compress them quite a bit, they pull on the drawbar with about 2600 lbs. This is about equal to tightening the stock drawbar to about 35 ft lb. When it is all loaded up it only needs about .035" travel to release a tool from the collet. The amout of distance your preload requires is strictly dependent on the type and number of Bellevilles you use.


Scott

Yours is what got me thinking. I thought I might take a crack at the design and see if I could figure a way around modifing the motor base casting.

[SCzEngrgGroup]

Yours is what got me thinking. I thought I might take a crack at the design and see if I could figure a way around modifing the motor base casting.

Why would you need to modify the casting for ANY PDB, beyond finding/making two threaded holes to hold it in place? I've build PDBs using impact wrenches, Belleville springs, and various kinds of motor, and never needed anything more than two threaded holes, which can be located almost anywhere. The PDB should not be heavy, and should not be transmitting a large force through its attachment points.

Regards,
Ray L.

[davidperry3]

Why would you need to modify the casting for ANY PDB, beyond finding/making two threaded holes to hold it in place? I've build PDBs using impact wrenches, Belleville springs, and various kinds of motor, and never needed anything more than two threaded holes, which can be located almost anywhere. The PDB should not be heavy, and should not be transmitting a large force through its attachment points.

Regards,
Ray L.

Can you post one of your spring washer DB designs?

[SCzEngrgGroup]

Can you post one of your spring washer DB designs?

Not really. That was years ago, and I don't have any decent pictures of it.

Scott's is by far the most elegant Belleville design I've ever seen. If I were to go that route again, I'd do it very much like he did.

Regards,
Ray L.

[davidperry3]

Not really. That was years ago, and I don't have any decent pictures of it.

Scott's is by far the most elegant Belleville design I've ever seen. If I were to go that route again, I'd do it very much like he did.

Regards,
Ray L.

Which requires modifying the casting.

[SCzEngrgGroup]

Which requires modifying the casting.

I think you don't understand how Scotts PDB works.... The "magic" all happens in the piece that mounts directly to the spindle. The rest you can replace with a small-ish air cylinder (or even a linear actuator), and there is not a lot of force involved in that part of it, so you can likely use existing bolt holes for mounting the air cylinder. Even with his "manual" setup, the only "modifications" to the casting is drilling a few holes for mounting bolts.

Regards,
Ray L.

[rowbare]

How many washers are you guys using on your PDB? Mine came with 6 but I see pictures where they are using 8. I know mine drags a bit when removing the holder so perhaps the 8 washer configuration is to make life easier for the tool changer?

bob