3-flute and 5-flute measuring

Quickest way if you don't have a V-mic is to simply run a test cut and measure it.

Another way if you have a mill with a DRO or known good scales is to take a chunk of scrap. Toss an edge finder in, Bring it in and zero, Now run it out to say .500. Put the unknown cutter in and bring it in till you touch. Check all 3/5/7 flutes. Read the DRO and X2

Or machine up a V adapter like

"Steve W." fired this volley in news:mkqmr5$esd$1 @dont-email.me:

That's essentially what I do on the lathe, now. It's good to within a couple of tenths.

I can do it faster than describe it. But for as small a shop as we are, having four to six different v-anvil mics isn't reasonable, especially since we seldom use re-ground bits for paying work, and only buy good- quality cutters.

I have occasion to measure a re-grind maybe once every two or three months. The tools (and the investment) would just sit in the drawers 99% of the time.

I just took over a CNC router shop and his contracts where almost EVERY bit has been re-ground, because none of his work uses standard sizes ('cept for a few common ones for facing and parting jobs). They aren't re-ground to save money on new cutters. They're ground to make certain sized features.

Among those regrinds, he has otherwise identical bits of different diameters with notes scribbled on the shanks with Sharpie pen. (things like "Big'un", and "Green's job"); and he's too sick now to ask what those 'code' entries mean.

I've characterized a few on the lathe, and etched the measurements onto them with a vibratory marker. Once I measure all of them, I'll just have new ones ground to spec. We have a really good carbide grinding shop up the road about 25 miles. And it IS a router, so a couple of 'tenths' doesn't make much difference, especially in the springy foamboard most of his jobs call for.

Lloyd

Mill a hole and mike it?

Larry Jaques fired this volley in news: snipped-for-privacy@4ax.com:

In my followup, I explained that this is on a router -- cutting structural foam, mostly.

The holes are never the size of the bit. Further (and I didn't mention this), it's a ShopSabre 4896 bed router with a 'best' resolution of one mil. So it's not going to make the same hole twice, even if working only in Z. It's a very sloppy machine, compared to a mill.

Besides... this is a 'learning exercise', not something I absolutely must do. Measuring on the lathe comes out +-0.0002 every time.

I don't want to invest in two whole sets of three-each v-anvil mics -- there are a wide variety of tool diamters, and it will take three micrometers of each anvil angle to span the range of both the 3-flute and

5-flute cutter collections.

I've got to study that, too. It makes no sense to me that he was using

5-flute cutters on foam... But there might have been a reason I don't see, yet.

Lloyd

My first thought was to cob together a jig where the cutter was held between centers and free to rotate (by hand), with a micrometer head positioned to advance perpendicular to the axis of rotation, allowing one to measure how far from the axis the tip of each flute was.

This will probably work well for new cutters, but I think that many regrinding machines hold the cutter in a precision collet (with the cutting end flapping in the breeze), so the original between-centers measurement no longer necessarily applies. Some new cutters are made on collet-based machines as well.

Even so, is the possible error by sticking with the between-centers too much? If so, a collet based jig is needed.

It's hard to beat commercially made ER collets for precision clamping combined with easy mount and dismount of the cutter. One can loosen and tighten the collet to rotate the cutter, but this will cause errors. An ER collet on a spindle would be needed, but these are not easy to make with sufficiently low runout.

Joe Gwinn

That doesn't matter if you're looking for cutter diameter. A spinning bit makes a hole its own size in a harder material (give or take a few tenths, plus runout) right?

So chuck the bit in the mill or lathe and mike the hole?

I'd never even heard of a v-anvil mike until now.

Ayup. What are the chances that "they were cheaper", "they were what I had lying around", or "my buddy gave them to me" came into play? The salesman can't get rid of something so he says "I can make you a really good deal on these blurfls!"

Once I semi-retire, I'll have time (and energy) to finish my Green Monster and start playing with my very own CNC router. I've been putting it off for two years now. Time gets away from you, doesn't it?

Larry Jaques fired this volley in news: snipped-for-privacy@4ax.com:

I'm chucking in the lathe and direct-reading the measurement now. Why do more work?

Lloyd

Gunner Asch fired this volley in news: snipped-for-privacy@4ax.com:

I don't trust my 3-jaw for the sort of accuracy I'd like in this, so I use some ER-16 collet chucks for that.

But, yeah. That's the way I do it. These are not milling cutters, they're router bits.

Unfortunately, many of the 3-flute cutters this guy supplied have 'spurs' in the center of the cutting end (which are, -none-of-them-, centered). So pinning them between centers is out.

I guess, what I've gotten from all of this is that, lacking a whole set of different-sized v-anvil mic's of two anvil angles, I've pretty much hit on the way to do it.

I was just hoping for some ancient 'automatic' technique I couldn't find in my literature.

I'm sure Bonkers could come up with an "instant" way to do it with just smoke and mirrors and his amazing social skills and good looks -- but I wouldn't trust any method he recommended, anyway.

I wouldn't have seen it, anyway. He's in the bucket.

Thanks to the rest of you. At least, my method is exhonerated.

Lloyd

Some times it is cheaper to let a shop that specializes do the work. So you might see what the really good carbide gringing shop would charge to characterise them. Getting a price will not cost anything and it might be the way to go.

Dan

" snipped-for-privacy@krl.org" fired this volley in news: snipped-for-privacy@googlegroups.com:

They can, and they will in future. I didn't need to take an afternoon off and drive 40miles to find out the diameter of a handful of router bits.

Now that I know what sizes they are, I'll let the grinding house take care of both making them that size, and documenting them both on paper and with serial numbers and diameters marked properly on the shanks.

The prior owner kept no documentation except the Sharpie notes written ON the tools, and his g-code files. He didn't even do the CAD/CAM himself!

I've spent the last week taking physical samples of his work, and re-CAD- ing them so that the whole process can be 'in house' again. We've run samples, and the customer approved the parts.

Lloyd

Here's one: Roll the cutter on a flat surface one revolution and measure it. Solve for diameter.

wws fired this volley in news:15a1c7e4-2269-4d0f-9273- snipped-for-privacy@googlegroups.com:

Roll? A three-blade carbide wing drill?

You must be assuming all cutters are helical-flute millers. Not most of these -- "ROUTER BITS".

LLoyd

"Lloyd E. Sponenburgh"

Perhaps by using, OMG, trigonometry? Or plane geometry? horror of horrors... But it may not be accurate to a 0.001 .... phil k.

"Phil Kangas" fired this volley in news:ml6ued $46v$ snipped-for-privacy@dont-email.me:

Phil, all these are methods that might be employed, but all depart from the simplicity of either purchasing a large assortment of v-anvil mics, or just using the lathe/dro as I did.

And to be clear, the v-anvil micrometers would be almost as troublesome to use as the lathe, in the case of cutters like wing drills, where you'd have to rotate the cutter in the anvil, and get a "feel" for when it was properly seated at the 120-degree points.

Like I wrote before, I was hoping there was some old 'lore' about a Q&D method of doing this -- but I couldn't find it in the literature, and nobody's come up with a better way than what we're using, yet.

LLoyd

"Lloyd E. Sponenburgh" fired this volley in news:XnsA4B474DA03346lloydspmindspringcom@216.168.4.170:

To clarify that, the wings are cut with relief, but also are not parallel to the axis of the cutter shaft. So 'fiddling' it to a proper fit in a micrometer would be a bit troublesome (about like measuring a dovetail slotter). Even with the mic', it would require some sort of fixturing...

L

What I ended up doing, with a new dovetail bit, was making a test cut and putting the chunk of wood under a measuring microscope. It was possible to get X-Y coordinates of the cut profile, and size and angles all came out in a blizzard of math...

I would not do it wws's way either. I made a setup for my little surface grinder to resharpen slitting saws 1/8 x 3 and mounted a dial indicator to it to measure run-out only as I'm not concerned about the diameter, just consistant O.D. Spiral flute edges are the most challenging to sharpen. So we are doing basically the same thing, eih? ;>)}

It is not a trivial thing to do. The main thing which makes it more difficult is that with each different diameter, the center moves up or down the V, so the micrometer thimble has to cover a different range while calibrated as something like 1-2" (or something at the small end like .125"-1.000" -- it does not go all the way to zero.)

Now -- if you want another way to do it, set up two Vs of carbide for the two angles (swap in one or the other) , and an electronic sensor which will feed the absolute distance to a computer. Then the computer needs to apply a calibration multiplier to give you a real reading. (A different one for 3-flute and for 5-flute, of course. Zero it from a precise round reference, like the 1.0000" diameter standard provided with some old B&S micrometer sets. A round with a center hole for the 1", and the typical rods for all the greater values

-- except that you need a round zero reference for each size.

Perhaps, if you have a long enough travel electronic sensor, you can make just two -- one for 3-flute from something quite small up to the maximum 3" you say you need, and another for the 5-flute ones.

And -- if you are good with stamp computers or Raspberry Pi, or the like, you could build portable devices with the readout direct. Just add a switch to set it up for 3-flute or 5-flute, perhaps actuated by the installation of the V anvils.

Your accuracy will be a function of the resolution of the sensor, and the precision of the round zero reference. (And, of course, the number of digits in the program in the stamp.

If you do a good job, you may even have a sellable product.

Enjoy, DoN.

Interesting problem. I am sure I am too late to be of any help. But have thought of two solutions that might help someone else in the future. One is to make a couple of V blocks. One 120 degree and the other a 72 degree v block. And then a bit to bolt on to the block to hold a micrometer head . Essentially make a big v mic.

The other is to use a spin index and a dial indicator with a magnetic base. Use a rod of known size to get the dial indicator set up and then put the shank of the cutter in the spin index and do the math to get the diameter of the cutter. But then that is pretty much what you did using the lathe.

Dan