[BTP]

I guess I got no idea what the need for a collet or adapter is. But I do have a suggestion for the draw bar. I personally don't think the little hardened balls are going to work for pulling in the pull stud. I started out with that very same idea, but now have work toward gripper fingers instead. My problem with the balls was one of accuracy. In order to keep from pushing the pull stud out of alignment with the spindle center line, they would need to contact the ramp on the pull stud in exactly the same place. I felt a lot had to be right for that to happen with little room for error. With fingers, or pedals as I hear them called, I think they are more forgiving as they provide a means to turn the holding feature all in one operation yielding a uniform ramp to match the ramp on the pull studs. In addition, they add way more contact area than any number of balls ever could.

It doesn't take much web searching to find stated problems with the ball type grippers, and that was what started my rethinking them. I was able to keep the outer cylinder that had the ball cage inside it and use the ramp in it to close the fingers on drawing in the tool holders, so the only changes I made was to replace the ball cage and balls with he fingers and add a shoulder bolt to the bottom of the draw bar to array the fingers around.

Attachment 262580

Bob

Just out of curiosity, what material are you using for the gripper fingers? Heat treating will be necessary for longevity and reliability so material choice will be crucial. I've done both Cat-R8 and BT30 with the ball stud gripper which worked very well. My component were made from 304 SS and seemed to work quite well.

[RustedOut]

D2 for the gripper fingers, the rest of the parts in that area are from 01. And yes, heat treated. I have my own oven for that.

What I really don't like about the balls is the contact area or lack of it. Just doesn't seem right to me. The wear points are so small they have to wear faster than something with more contact.

Bob

[RustedOut]

I've been working on my Cat R8 tool holders and have one end of 15 or so of them done and about a third of those nearly done with the end mill bores finished. I had to work out the process to be able to turn them 100% on my lathe and that's working well. I'm getting low runout numbers on the actual tools sticking out of the tool holders with the worst being .0004" tir 3.5" from the gauge line of the longest tool holder. I'm measuring half that or less as they get shorter, so I'm pleased with that.

But one thing has been bothering me as I get these finished. That is how far the actual cutting end of the end mills are ending up from the gauge line. I wish I had made the tapered ends longer so the pull stud could be farther up from the gauge line so I could shift the end mill bores up into the taper. Mine all start at the gauge line as the end of the pull stud ends there. And there's nothing in the spindle that would prevent that other than my spindle sleeve. My sleeve is a exact copy of Mr Decaussins other than changing what was needed for my selection of pull studs and fitting it to my draw bar diameter. There is inches above the gripper area that could have been used. But I don't think inches were needed, maybe just 1/2" shift on the pull stud. That could have been accomplished by just making the taper longer and the spindle sleeve shorter. You can see in one of my shortest tool holders the large diameter flat at the top of the taper. No real reason for that other than following what Dave did in his design. There wouldn't be any more engagement of the taper as there is no more taper in the spindle.

Attachment 268072

That being said, I'm wondering lately how tough it would be to modify an existing NMTB 30 spindle to make the features needed to to make gripper fingers function. That's probably above my pay grade though. I don't think I'd want to be modifying any existing NMTB 30 tapered tool holders either to shorten them and add the pull stud there unless I was turning the rest of the tool holder features afterward. I'm cutting my tapers first along with the gripper section of the tool holders, then flipping the tool holders and holding them by the taper in my lathe spindle with a heavy draw bar through the spindle. So, in theory, if I could have modified an existing NMTB 30 spindle, then made the custom tool holders to fit that with the shift of the pull stud and end mill bores as mentioned above, there would be more taper to be engaged. That would be a good thing. But I'm not changing course on what I'm doing, just thinking out loud about the results.

So native34, how goes the design of the ATC? You get any further than a concept? Not that I'm going to build one, just always interested in what others are doing with these mills. I got my hands full with the Cat R8 stuff for now.

Bob

[native34]

I haven't been able to do much on it lately, as I'm working fulltime and back in school fulltime as well. I'm hoping to get some more accomplished on this over the spring break and have a working prototype done by June/July.

[CNC4XR7]

Hi Bob,
I am interested in the CAT R8 tool holders I ordered a couple from DD and wondered how yours are coming along can you give me any information as to which size pull stud your using?
The amount of Bellville's needed, and if you have experienced any slippage etc.
Are you grinding the tool holders after Heat treating? etc.

Any info would be helpful. Also if your running Mach3 I have developed a ATC Screen set and Macro unlike anything else Ive seen.

Be Safe Sam
www.cnc4xr7.com