Clamping fixturing with screws only?

[Technics NC]

I am adding fixtures to a new 5 axis trunnion machine. The machine also can turn with the C axis, and uses HSKT type holders. I was going to install a Lang fixture plate using 8X 12MMX1.75 grade 12.9 grade bolts and T-nuts into the existing machine table. Tightened to 108 ft lbs, one bolt should apply 13781 lbs of clamping force. I am debating if I should go through the trouble of keying the plate in to one of the slots? Or just indicate it on center, and tighten to specs I mentioned. Seems like the rotary or linear axis would alarm, far before the fixture would break loose. The machine has 800mm travel in XY axis, and seeing this large table spinning in turning mode is what is making me take pause.

Thank you for any input.

 

[John Garner]

Can't answer your question, because you know your situation far better than I do. But I strongly endorse using 3 "fixture keys" on any fixture that will be removed and reinstalled on a rotary table.

I'll note that I prefer the Jergens-type expanding-plug fixture keys to the Carr-Lane-type fixture key.

In thirty-some years of removing and reinstalling fixtures that are 3 to 7 feet tall x 4 feet diameter every couple of weeks, the fixtures' "Launch Vehicle Acceptance Flanges" centers were found to be within 0.0015 inch of the rotary table axis AND axial runout within 0.0015 inch as-plopped-and-bolted-into-place 95+ percent of the time.

 

[John Garner]

Another thought: If you use fixture keys, put them as far apart as your machine table and fixture plate allow.

 

[Milland]

I would check with the machine vendor as to your torque spec. Even though your stated torque is within the capability of the M12 bolts, the amount of deformation each one will induce on the table may be enough to create machine distortion. It might be better to use more, smaller bolts, or not as tight with the M12's.

In these cases, using keys too may be a good idea.

 

[Technics NC]

Can't answer your question, because you know your situation far better than I do. But I strongly endorse using 3 "fixture keys" on any fixture that will be removed and reinstalled on a rotary table.

I'll note that I prefer the Jergens-type expanding-plug fixture keys to the Carr-Lane-type fixture key.

In thirty-some years of removing and reinstalling fixtures that are 3 to 7 feet tall x 4 feet diameter every couple of weeks, the fixtures' "Launch Vehicle Acceptance Flanges" centers were found to be within 0.0015 inch of the rotary table axis AND axial runout within 0.0015 inch as-plopped-and-bolted-into-place 95+ percent of the time.

Thanks for your input.

I think I will add keys. Another few hours of work, but more security.

 

[Limy Sami]

Use fixture keys, dowels, pegs ''anything'' than just fasteners, ............... + without keys etc, every time you change the fixture you'll have to mess about with DTIs and the like.