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Thread: Slot Drill Size
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2nd Jul 2020, 04:52 PM #1Golden Member
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Slot Drill Size
I just did a job using a new 2-flute solid carbide slot drill in 6061 aluminium on my CNC mill.
A quick check with a caliper said about 3.85 mm, so I "assumed" it would cut 4 mm.
Not so, it actually cut like a 3.85mm - duh !
So, measured carefully the flutes, also 3.85 mm.
5/32" is 3.97 mm, 9/64" is 3.57 mm, so it does not appear to be imperial.
Is it normal for cutters like this, probably purchased cheap somewhere, to be somewhat smaller than the expectation ?
I will start checking actual cutter dimensions for future jobs.
Keep well,
John
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2nd Jul 2020, 06:00 PM #2Gear expert in training
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Just had a look through the Guhring catalogues and their tolerance on flute diameter is generally h10 or e8, which would make a 4mm endmill 3.952 - 4.000mm or 3.962 - 3.980 respectively.
Some tolerance is to be expected, but 0.15 under is waaay not acceptable.
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2nd Jul 2020, 07:14 PM #3Senior Member
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I've found cheap Chinese carbide is sometimes under size by a far amount. I assume they are starting with a nominal size blank and then grinding a bit off.
Not a big issue for me using CNC so long as I remember to check actual cutter size...
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11th Jul 2020, 11:10 PM #4Senior Member
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Back in the olden days HSS slot drills always had a (-) tolerance whereas endmills always had a (+) tolerance but agreed -0.15 on 4mm is a bit gross. Hardly the end of days tho'.
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12th Jul 2020, 12:10 AM #5
Hi Guys,
I think I would prefer undersized slot drills to oversize ones, at least you can always take a finishing cut !Best Regards:
Baron J.
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13th Jul 2020, 06:53 PM #6Senior Member
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- Jun 2016
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- Sydney
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Dear me. Where did that come from???
But yes, if it is undersize you can handle that. In fact, I often prefer to do it that way, after micing the cutter carefully.
Cheers
Roger
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