The Art and Science of drilling the perfect hole...Need help from the folder makers

McMaster sells Lapping Paste that comes in different grit - from 90 to 8000.
Different grit also comes in different abrasives Silicon Carbide, Aluminum Oxide, Corundum Aluminum Oxide, Alumina, Chrome Oxide Alumina.

Which would you use?
 
I've talked to Ralph Darrel and he recommended to go with diamond compound and 400 grit.
 
Kevin Wilkins said:
I ream all of my folder pivot holes in the hardened blade after heat treating and final surface grinding. I use a Gühring carbide reamer ...
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Since carbide reamers are quite expensive can I get away with just lapping the hole after HT?

Thanks,
Alex
 
alexmin said:
Since carbide reamers are quite expensive can I get away with just lapping the hole after HT?

Thanks,
Alex
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You're going t need a really rigid set up to use carbide cutters anyway. Carbide cutters often disintegrate in, say, a drill press. You'll need a mill.

You can/should lap after HT.

I prefer honing (on a honing machine such as a Sunnen) after HT. If you're going to sweat a ten-thousanth or two, you'll find it's a highly accurate, repeatable and potentially affordable method---especially if you're going to do a bunch at a time.
You don't get bell-mouthed, conical or oval holes or 6 blades ranging from say .1872 to .1877 from the same set up as can happen with other methods.

If you're just doing a couple pieces and don't have access to a mill or honing machine, you'll probably be happy with a barrel lap and some Clover 400 compound.

My 2 cents, take it for what it's worth:) .
 
You don't have to ream if your going to hone. Cut the hole a bit undersize with an endmill, HT and hone to final. The small Dia. Sunnen honing mandrels for hardened stainless are something like $2.60 each. We're able to do about 12 blades (+or-) per mandrel.
Again, this is probably something you'll want to approach with a good number of blades. If you're paying someone to do the honing, they're probably not going to want to set up for just a couple blades, but you never know...
 
Joe,

can you give me specific size for drill bit if I want to have a hole for slip fit 0.250" bushing? I am guessing "C" drill bit before HT and then honing to 0.251" after HT. Am I right?

Thanks,
Alex
 
I've just indicated my HSS reamers. Damn! Practically all of them have run-out at the cutting end 0.005"-0.007" (Run-out measured on test drill rod is just 0.0005)
Even my brand new reamers have some run-out. Are they still usable? Does the long reamer length is suppose to minimize effect of runout so reamer wont bellmouth a hole?

Thanks,
Alex
 
alexmin said:
Joe,

can you give me specific size for drill bit if I want to have a hole for slip fit 0.250" bushing? I am guessing "C" drill bit before HT and then honing to 0.251" after HT. Am I right?

Thanks,
Alex
Click to expand...

When it comes to close-tolerance holes, it's best not to trust cutters/drill bits/reamers size indication at face value.
Rather than drill, you should plunge or interpolate with an endmill in some scrap material of the same kind and condition you're going to use, then check the hole with the gage pins adjusting program or cutter size as needed. If you're going to hone them, try to get the hole within about .001 undersized.
Assuming the bushing is .250 on the button, a plunged hole at .249 or .2495 so should be fine. You're probably going to like to see .2503 to .2505 after honing, I would think but that's where you're going to have to dial in the tolerance to what you're after.
+.001 will probably be too much if I understand what you're after.
 
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