jcardi2890
Plastic
- Joined
- Apr 10, 2014
- Location
- Pasadena, CA
Hi All, I'm having a problem where I'm not getting flat surfaces when machining plates of 6061 that are 2" x 7" and 0.5" thick. I don't have enough experience to gauge right off the bat whether this is thin enough to warrant residual stress / warping an issue. Here is some information that may be useful:
1) First I square and finish the stock surfaces using a fly cutter, the subsequent milling operations are light slots, the heaviest cut being 0.045" DOC, 0.05" WOC with an 1/8" EM.
2) When I mate the surfaces of the two parts by just laying them on top of each other, they make zero gap contact along the middle ~4" of the 7" long plate, while the ends are visibly not making contact. I measured a 0.006" max gap at the ends with a feeler gauge.
3) I'm using a glacern 4" vise with hard jaws to clamp the plate. The area of contact with the stock per jaw is 4" x 0.25".
I'm thinking that the problem is that the plate bows when clamped in the vise, (this is not visible by eyesight by the way), and I clamp with full force and then lead hammer down onto parallels. The bowed ends get surfaced to the same level as the middle of the plate, at which point I probe with an indicator to verify the surface is flat along its 7" length to <0.001". When the machining operation is finished and I unclamp the part, the plate must bow back to its original state, hence the visible gap (0.006") when attempting to mate the top surfaces of the two plates.
I don't have this problem when I machine 9" long blocks that are 1" thick, so that's why I'm thinking the limiting factor in this problem is the thickness of the plate.
To solve the problem I am considering setting up two vises next to each other (as long as the jaws are aligned well there's no problem with doing this correct?), and in the long term considering getting a nice iron fixture plate and using mitee-bite clamps or something similar. Or perhaps I should switch from 6061 to a harder alloy
Do you guys have experience with this problem? Am I in the right track? Any other suggestions for solutions?
Thanks!
1) First I square and finish the stock surfaces using a fly cutter, the subsequent milling operations are light slots, the heaviest cut being 0.045" DOC, 0.05" WOC with an 1/8" EM.
2) When I mate the surfaces of the two parts by just laying them on top of each other, they make zero gap contact along the middle ~4" of the 7" long plate, while the ends are visibly not making contact. I measured a 0.006" max gap at the ends with a feeler gauge.
3) I'm using a glacern 4" vise with hard jaws to clamp the plate. The area of contact with the stock per jaw is 4" x 0.25".
I'm thinking that the problem is that the plate bows when clamped in the vise, (this is not visible by eyesight by the way), and I clamp with full force and then lead hammer down onto parallels. The bowed ends get surfaced to the same level as the middle of the plate, at which point I probe with an indicator to verify the surface is flat along its 7" length to <0.001". When the machining operation is finished and I unclamp the part, the plate must bow back to its original state, hence the visible gap (0.006") when attempting to mate the top surfaces of the two plates.
I don't have this problem when I machine 9" long blocks that are 1" thick, so that's why I'm thinking the limiting factor in this problem is the thickness of the plate.
To solve the problem I am considering setting up two vises next to each other (as long as the jaws are aligned well there's no problem with doing this correct?), and in the long term considering getting a nice iron fixture plate and using mitee-bite clamps or something similar. Or perhaps I should switch from 6061 to a harder alloy
Do you guys have experience with this problem? Am I in the right track? Any other suggestions for solutions?
Thanks!