Ho do you measure end mill diameters?

[HankMcSpank]

So I've bought a few used endmills off ebay (I have a habit of snapping them, which hurts when you pay new) ...bit of a lucky dip of 15 end mills/drills.

So how do I establish the true diameter of these - I have digital calipers, but even those end mills I already own & I know the cutting diameter, they measure under - eg 2.00m diameter end mills on my digitial calipers read about 1.86mm (or thereabouts), is it just a case of rounding up?

[blackburn mark]

is it just a case of rounding up?

i wouldnt do that ? you want to be telling your cam software exact sizes

with vernier calipers i use the full length of the faces of the calipers to pinch as much of the cutting section of the tool as i can

i guess makes more sense to use a micrometer but that can be a pain as there are peaks and troughs when measuring with such a small surface aria that micrometers have so in that situation i revolve the tool in the mic until it starts to grip (revolve the tool away from the cutting direction)

youll get a feel for it :smile:

[Jonathan]

I think a micrometer is the best bet as callipers can easily be fooled by positioning it wrong etc. If the cutter has an odd number of flutes then neither will get far...

As they were from eBay the cutters may have been reground, which would make them slightly under the original standard (metric or imperial) dimension. I would start with using the nearest round number (unless it's way off) on something that's not critical, measure the part and compensate from that. It all depends on just how accurate you want to be.

[blackburn mark]

If the cutter has an odd number of flutes then neither will get far...

im pretty sure as long as your flutes have at least one rotation (or just over) the verniers should be as close as verniers are accurate even on a single flute

[Jonathan]

im pretty sure as long as your flutes have at least one rotation (or just over) the verniers should be as close as verniers are accurate even on a single flute

If I'm being pedantic that depends on the helix angle and the length of the flute...

Edit: just noticed you did specify one rotation, so what I said is just repeating that. Oops

[John S]

Nobody has mentioned how many flutes, if it's a three flute you been a vee mice or better still take a cut on some scrap and measure what it actually cuts.

[antsals]

You can buy a micrometer just for this job. I'm sure if you hunt around eBay you should be able to pick some up. The have two faces opposite the anvil. I'll see if I can get a picture of a set.

Ant

[blackburn mark]

cut on some scrap and measure what it actually cuts.

i guess we all do a bit of that in a sense when we are polishing a g-code file

you have the added complication of climb vs conventional and slot cutting flexing tools this way and that.
i do quite a bit with 3.175mm (1/8) tooling (lots of flex) hence the g-code polishing..... on my first run of a complex part i assume it will have small errors that may make assembly a bit of a pain... tune the code run again etc.... usualy my third part is a winner and that g-code file goes into a file reserved for good code :smile:

[HankMcSpank]

Thanks guys....I'll go with the cut/measure option!

[antsals]

Just found one...... http://www.mitutoyo.co.uk/MitProd/mtopr.nsf/UNIDS/5FCE6FB15B0D413A8025693C003E0801!Opendocument but taking a cut in material is also an option I have in the past input the size around nominal knowing the cutter is bigger so dependant what you are doing eg inside slot or outside it would leave metal on the component all over. Then check how bit it all is and adjust the offset accordingly. It means you get a good component first time.

Ant

[AdieR]

2.00mm EM reading 1.86mm?

Not sure what cutters you're measuring (3 or 4 flute), or what you're measuring with (calipers or mic), but one point I'll mention is that it is easy to overdo pressure on your measuring tool (ie pushing a caliper too far or tightening a mic too far) and giving a false reading. I have seen people (even in the trade) tighten mic's like g-clamps (not good, because it twists the frame).

If its a 4-flute, slide it until caliper jaws *just* touch, and rotate it until you get the highest reading - this is your actual size.

You say the cutters are from ebay - in which case they may be worn anyway (not knowing how they've been used / treated).

One other point of note: re-ground cutters can sometimes cut slightly oversize.