I usually use Amana end mills, sometimes, Whiteside. They’ve worked really good for me. Bought some 1/8” SpeTool end mills online recently. Excited about how “affordable” they were. A package of 5 pieces. Ran a job today with 6mm slots for mating pieces to fit together. Guess what…the pieces didn’t fit. Checked the slots, they were narrower than designed. Checked the end mills with a digital caliper…they were undersized. A 1/8” end mill should measure 3.175mm, or very close. These measured 2.75-3.0mm. Up to 0.5mm or 0.02” smaller diameter than stated. None were over 3.0mm. The package states “Rigid quality control and extensive testing”. Not. A difference of 0.5mm doesn’t sound like a lot but, of course, with small parts and a need for precision fit, it’s a problem. And having to hand-clean a slot that’s only 6mm wide can be a challenge. So anyway, just letting you benefit from my learnings here. I said to myself “Self, don’t be a cheapskate. Spring for quality end mills.” Don’t assume the actual size of a bit matches the nominal size. Especially from certain sources. I’ve read that here from others, but I guess I just assumed it would never happen to me. Where fit is important, measure the end mill (regardless of source) and use that measurement in your tool settings. Either in your tool database or in the toolpath settings. So you can account this “variance”. TGIF and have a good weekend. Thx, rink
I'm afraid that you should also check "expensive" end mills - they are manufactured to be within tolerances and you cannot expect them to always be spot on. Alex.
Measuring the bit size is a fundamental of CNC router machining and should always be checked and implemented in the CAM program when tool-pathing. I'm not sure how end mills are made, but I always assume that a 6mm blank of tool steel would have slightly smaller cutting edges after the factory machining process. To have the cutting edges match the size of the shank, then, presumably, you would need a blank with a 6mm shank, then a stepped cutting end of maybe 6.05mm to allow for grinding the cut edges - totally impractical for the manufacturers and would be way more expensive. I do think that its an advantage anyway to have a cutting edge which is a few mils under shank {i.e. published size}. The reason for that is, if you use the published size and the cut you make is undersized {likely}, then you have wiggle room to get the size spot on by re-camming using the actual measured bit size and no job will be ruined. Best though, of course, is to measure first - cut once. At the end of the day, it doesn't matter what size the cutting edge is compared to the stated size - the cam program will take care of it with the right dimensions entered.
