I was under the impression the tormach holderfs/r8 setup only needed a few hundred pounds of upward pressure on the draw bar to be secure. we are running a washer stack that generates 800lbs on the mill and unlocking with a .2" stroke bimba 4" pancake cylinder , cylinder was less than $100 and I havent had a tool slip in the past couple of years of operation . I hadnt thought about the load being applied to the bearings when unlocking , I would imagine they are probably holding up OK but I am now wondering about the severe load on the ballscrew assembly on my quill . I like your idea of the locking mechanism to handle that load .
Please keep us posted on your progress. I am always fascinated by tool changers and related components.
What kind of machine are you running, and where did you get the 800 pound number? What's interesting is NOBODY seems to know what appropriate drawbar tension is. I asked Tormach tech support, and the response amounted to "Beats the hell out of us! If you find out, please let us know!". So, what I did was put a 1/2" tool in the collet, tightened as I usually do manually, then measured the torque required to make the tool slip in the collet - came out to about 30 foot pounds. I then put the new drawbar in, and played with different stacks of bellevilles, and different amounts determined the drawbar tension was about 2000-2500 pounds, so that is what I'm aiming for. The only place I've seen any numbers tossed around, it was on smaller machines, like X2s, which certainly can get by with a lot less than my knee mill. The 2500 pounds is also in line with my initial esitmates, based on torquing the drawbar to 25 foot-pounds, which is what most of the impact-driver drawbars do. I have seen figures for drawbar stretch (0.015"), but don't know how reliable those are.
I do know my current setup can apply about 1500 pounds, and that is NOT enough - I can make the tool slip pretty easily at that tension.
Yeah, 800# seems like an awful big static load to be putting on the bearings or the ballscrews....
Regards,
Ray L.