dlaery, on 06 February 2012 - 01:37 PM, said:
That's interesting. Do you have any sloop when fit together? I have been milling with a 3/16" bit to .250' and then use a reamer. I like the way the smaller pins fit the 2 halves better. With the 1/8" dia. and the 3/16" pin sticking out. Now, I have not made anything with the 1/8, I was looking at a mold that belonged to someone else. I got my pins and reamers today. I am going to try the smaller ones to see.
I like the sound of your method, but I think I want it smaller.
I just use drill bits on my drill press. I center spot the screw and pin locations on the mill, but because the spindle is so fast its not great for drilling.
I could pocket like you do, but its faster to drill the halves after I take them off the mill. As to slop. Yeah, a few thousandths. Not really critical with plastics. With a lead mold it might be better to get tighter tolerance if you can, but you have to remember that the aluminum will shrink and swell and distort some with heating and cooling. Its also not as predicatable now that its not uniform thickness from you making a mold out of it. If you get it to close with your tolerances you may not be able to get the molds together or apart easily.
One thing I have learned about machining is that a successful process works. Its not necessarily a perfect/exact/precise fit/cut. It works for the job intended and produces a satisfactory result.
A couple tips. Chamfer or lightly counter sink the pin holes and screw holes. This will make insertion faster and easier even with realitevelyt square end pins. Also, use a tapered or rounded (one end) pin if you can. That's why I am considering making my own pins out of precision rod in the future. I can grind a lathe bit to round and part off in one operation.
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