Our sales department sold a promise that I have been tasked with fulfilling, but I do not have a good idea how to proceed... Hopefully there are some workholding experts here who know an answer...
The machine is an Okuma Horizontal Mill (MB8000H)
The part is 6061-T6 Aluminum.
Finished part is ~200 Lbs, rough block is roughly 30"x40"x8" (1300 lbs)
op 10 is to mill out a 9" through bore, a 23.5" counterbore 6.5" deep, and about 75-80 holes on the front and back of the part. The fixture is pretty straightforward; serrated clamps on 3 sides and a pair of locators on the 4th, with a large opening to give access from the back.
op 20 is the problem... The part will be laid down on the table and machined to a roughly hexagonal shape (op 10 is clamping on/near the corners of the block that are machined away to get the hex shape), each face having a large obround slot that goes through the face into the bore from op 10. And about 20-30 additional holes on each face.
The original intent was to clamp through the 9" through bore from op 10 and clocking the part with a few pins in two of the larger holes on the back side of the part. However, the sales department sold the customer on the idea that the entire part will have a 32rms finish on all faces and will require *zero* hand working to remove and machine marks or clamp marks, and will be completed in two operations. We've had very good luck with a fiber brush we've been testing on a different machine, and are easily getting the required surface finish as well as leaving a uniform-looking surface all over.
Clamping through the large bore will hold the part well enough to machine it, but the concern is that any kind of clamping on the counterbore will leave marks in the finish from op 10, Op 20 will remove roughly 150-200 lbs lbs of chips, so I fully expect to have to clamp pretty tightly to hold it in place, and I also expect the part to do a little moving.
I've gotten the job processed and tooled up , but was only made aware of the "zero hand-working" requirement yesterday. I personally do not believe it is doable, but thought I would ask some experts.
Does anyone have any suggestions on a good way to hold a 200 lb aluminum part in a horizontal without leaving any marks on any surface?