Draw bar issues on PM833TV

[ahazi]

Have you removed or checked the interference for the dog-point set screw that meshes with the slot in the side of the R8 collets? I removed mine completely. But if that set screw is in too far, or has a point that's too wide, it will contribute to the "stickiness" of the R8 not dropping free.

https://www.precisionmatthews.com/wp-content/uploads/2017/01/What-do-you-do-if-your-R8-tooling-will-not-go-in-to-the-spindle.pdf

I removed the set screw. It is not really needed with the small electric impact wrench.

 

[ahazi]

Here's an example of a DIY PDB that has a pneumatic actuator that pushes down on the drawbar during operation (part 4 of 4).

Thanks David!

I guess the only way I will know is to just finish my build and see if it works.

I am not sure if the pneumatic cylinder is just for convenience or it actually bumps the head of the drawbar with an impact that releases the R8 collet especially when the release is done in pulses as it looks like in the videos:
1st pulse pushes the wrench into the drawbar and turns it CCW
2nd pulse after the drawbar is not tightly holding the R8 collet the actuator is hammering the drawbar down and releases the collet from the quill

 

[ptrotter]

Why not go with the air cylinder version of the PDB like Priest Tools sells? I built one for my PM-940V and it works great. Since it pushes down on the drawbar to release the collet, the tool just drops into my hand. It was very easy to build and is fast to operate. Probably a little more expensive though.

 

[davidpbest]

Why not go with the air cylinder version of the PDB like Priest Tools sells? I built one for my PM-940V and it works great. Since it pushes down on the drawbar to release the collet, the tool just drops into my hand. It was very easy to build and is fast to operate. Probably a little more expensive though.

The Priest Tools system is not an R8 power drawbar. It’s a TTS pneumatic tool changer. Yes, it does install into an R8 spindle, but all tooling must be mounted on TTS-style tool holders rather than R8 shanks. In that sense, it is functionally more akin to something like the Royal EasyChange QC tool system.

 

[parshal]

David, I discovered exactly that after I installed Priest Tools' system on my 833TV. I should've known what I was installing. LOL

 

[davidpbest]

David, I discovered exactly that after I installed Priest Tools' system on my 833TV. I should've known what I was installing. LOL

I actually think Priest and Tormach should stop calling it a Power Drawbar. It’s a TTS pneumatic collet closer. It has the advantage of consistent and precise tool offsets and the ability to support an automatic tool changer which are both important in the CNC arena. But it does require all tools to be mounted on TTS spindles, and compared to R8 tooling is less suitable for aggressive milling situations.

 

[ptrotter]

You are right David, I am so used to using my TTS tool holders that I forget that It only works with 3/4" tool shanks.

 

[Lucas E]

On the pneumatically actuated butterfly units the cylinder holds the socket against the drawbar while it unscrews. In a manual one you pull down on the handle which holds it against the drawbar.

You need to make sure you use a shallow socket so the drawbar bottoms out in it. When the drawbar hits the back of the socket it stops going up and if you continue to unscrew it will eject the collet. You don't need a separate hammering action of the air cylinder. Just the force of it holding down is enough to create a backstop for the drawbar to run in to.

On a manual one you'll need to pull down on the handle to put pressure on the top of the drawbar with the back of the socket. This is the reason it doesn't seem like a good idea to mount a handle directly to the butterfly valve. In the video I posted you can see there is a vertical bar supporting the handle. That way the downward pulling force isn't trying to jerk the pivoting handle off the impact wrench.