hugh.radkins@LIGO.ORG - posted 17:49, Friday 13 January 2012 - last comment - 13:17, Tuesday 17 January 2012(2044)
BSC8 SEI Stage0 Modified to SUpport ACB Install
JimW, ScottS, Hugh See the attached which is a zoom in of D0900894 sht2. The upper right cloud area is the SW corner of the SEI ISI Stage0(+Y,-X) looking up. We tapped and helicoiled the three holes in the right cloud and one of the 'A' holes in the left (not exactly sure which) to accommodate the planned mounting of the ACB dog clamp and alignment pushers. These holes were vent holes and were never planned to be tapped. We were lucky in that they were close enough in size to only lose maybe 25% of the thread holding in the aluminum--plenty fine for the 200lb ACB. The story is this clamp and these pushers can be removed as there is another clamp on the mounting plate. And we could swap out the hardware later with vented bolts.
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Below is Actual entry before system logged me off and I thought all was lost. Jonathan showed me the drafts and it was saved there. Thanks! The Arm Cavity Baffle crew this morning reported holes that were not tapped/helicoiled for the dog clamp & pusher attachment. These were in the bottom of Stage0. See D0900894 if you want to follow along or see the attached. On the attached drawing, I've zoomed in and highlighted the areas of interest. The cloud circled area to the right is the SW corner(+Y,-X) of the SEI Stage0 looking up. This is grid area H6 of Sheet 2 of D0900894. The three holes in vertical alignment on the left with the center one labeled A and the other two unlabeled are the three holes that were planned to connect a custom dog clamp to Stage0. Problem is only holes marked C are actually tapped and helicoiled for use. The 'A' hole is the bottom thru vent for the 1/2-13 Stage0 Bottom/Top clamping bolts. The unmarked holes are the '2' holes called out on sheet 3. These are fully thru Stage0 Bottom venting the 5/8-11 bolts clamping the Stage0 Spring Post to the Stage0 Top along with a few other things. The right most 'A' hole in the cloud area was planned to be used with the lower 'C' hole to clamp on an ACB alignment pusher. On the left side of my zoom-in drawing in the ellipse highlight area, one of the outboard 'A' holes (not sure which) was planned to mount the other pusher in combination with a 'C' hole. We got very lucky. Both the A & 2 holes were drilled 0.41" and are plenty deep (inches). The drill diameter for a 3/8-16 helicoil tap is 0.397". So we started with a hole 13mils oversized. The helicoil OD is 0.450". So we lost 13 of 53mils (assuming the helicoil diameter is the tap OD, which it likely isn't.) Still we assumed this and figured we lost some 25% of the nominal thread holding in the Stage0 Aluminum. Since the ACB weighs less than 200 lbs, any one of these even weakened holes can likely hold the entire ACB and it will actually be held by at least four. So we went to John Worden with this info and he gave us approval to use these thru/vent holes. So we tapped the 4 holes on the right and 1 on the left for 3/8-16 2D helicoils. We did this in-situ holding a chip catch under the tap. I can't lie, I'm sure there are some tap chips that made it under the flooring of the BSC but we did the best we could to catch all the chips. We swapped out our chip catch for each hole and had no spills. As the hole was oversized, the tapping wasn't too bad and we flushed the hole with IPA again catching the effluent. We then ran the cleaned tap into the hole again, flushed the hole again, and then inserted the helicoil. We tested the holes and then mounted the Pushers. The right middle 'A' hole must have gotten a little chip under the helicoil but the bolt wasn't too bad going in--it starts fine and threads a few turns before tightening up for just a little bit, then it is fine. Finally--These vent holes are now not vented and there is a fairly large trapped volume--~20"x.41dia. Fortunately, the pushers AND the right clamp can come off as there is another clamp in the middle. And we have a chance to get vented bolts and replace them if needed.