Getting graphite molds to mate

[Mark Roberts]

Hello, recently, I have been machining a lot of graphite molds of a bowl like shape; what would I use to "bench" the halves together? I know with aluminum, you could use prussian blue, but I don't think that this would show up on the graphite. The pieces are of a nature that they don't slide together; they mate straight face to face. When I put the two halves together, they rock a bit. I belive that the problem lies within the model itself, and not the machining; nonetheless, I need to fix it.

Thanks in advance,
Mark Roberts

[packrat]

Not real sure what you mean, pictures would help me, to help you.

cary

[Mark Roberts]

I will try to post some pictures today....Thanks.

[Pandinus]

Just a thought to eliminate a variable...
I'm not sure what type of machine you are using so this might be be pointless or impractical... I sometimes think outside the box...

Try surfacing a single flat face on two pieces of stock and then mate them together, if they mate perfectly then rotate one 90 piece degrees... If they still mate perfectly then your machine should be cutting true, if they rock a little then you might have a slight twist in your machine.

If the later is the case... and your machine has the size necessary for the movements... try rotating one half of the mold 90 degrees in software before cutting...

[Mark Roberts]

Thanks for the reply! I am running a '00 vintage HAAS VF-3, and program using GIBBS CAM. For the machining, I rough with a 1/2" ball, and finnish with a 1/4" BEM at 90 degrees to the first cut. Comparing a few measurable dimensions on the part to what the model says it should be, they were off by less than 0.0005"; I really think that the issues are within the model itself. Sorry no pictures yet.

Mark