Cutting holes in sheel metal - help needed

I have tried hole saws of the correct size, but have found they have too much runout (hole ends up 1/16 too big), and I can"t slow my drill press down enough to keep them from chattering.

Any suggestions short of cutting the holes smaller and finishing them by hand? I have thought of the "rotabroch" type cutters, but they don"t come in the size of the larger hole ... would an adustable fly type cutter work?

Thanks as always for your help.

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In addition to the other tips on hole saws for a truer hole, you might try using solid round stock [drill rod about $1.25 for a three foot length of 1/4" from Enco] in place of the pilot drill.

I don't think you can get much better size than you are getting with a hole saw. But, clamping the sheet metal between two pieces of 1/2" plywood works well to keep distortion to a minimum and gives a good guide for the saw. Cool with water. Water keeps the cutting edge cooler and steam is much easier to breathe than smoke from oil. No cleanup either.

Not much choice for a typical home shop for accurate holes, .010 or so, but here's what works for be.

First buy a dial indicator, even a cheap one is better than none at all, and adjust your runout on your quill on the drill press. Mine was out .015 and with a brass hammer I knocked it back into .002. So far it has stayed in alignment for several holes, about 50.

Use a piece of scrap piece of 1/4" metal under the 14ga to keep the the pilot bit running true. After you drill the pilot hole then adjust your bit so it rides on the smooth shank of the pilot bit while cutting the large hole.

Clamp your work to the table securely. Once clamped and the pilot hole is cut, do not change the alignment until the final hole is cut for any reason, including adjusting for table hieght.

Next flood the holesaw teeth with cutting oil as you cut. Used/new motor oil works for me.

Adjust your cutting down pressure to remove all chatter.

If you can find the correct size knock out punch that will work well. I only buy Greenlee plug cutter punchs.

You can buy metal punch and dies for just about any hole diameter, costly tho and it would be cheaper having a machine shop cut them for you and more accurate.

T_Bone