I can roughly measure a reground 3-flute or 5-flute cutter using my lathe
as a fixture, measuring the shank, then the diff to the cutting edges.
That works. But I don't own a v-mic in order to do it right. Is there
another 'standard strategy' for measuring odd-number-flutes' diameter?
I've been going through all my old texts, and they all show a v-micrometer
as the preferred method. I was hoping for some old 'shop lore' method.
Quickest way if you don't have a V-mic is to simply run a test cut and
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
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-
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
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.
On Thursday, June 4, 2015 at 8:00:15 PM UTC-4, Lloyd E. Sponenburgh wrote:
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.
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
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.
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
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.
On Fri, 05 Jun 2015 06:12:41 -0500, "Lloyd E. Sponenburgh"
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 takes as much energy to wish as to plan.
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.
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.
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 E. Sponenburgh" <lloydspinsidemindspring.com> fired this volley in
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...
On Tuesday, June 9, 2015 at 8:48:43 AM UTC-7, Lloyd E. Sponenburgh wrote:
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...
"Lloyd E. Sponenburgh"
<lloydspinsidemindspring.com> wrote in message
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
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
same thing, eih? ;>)}
On Thursday, June 4, 2015 at 3:49:56 PM UTC-4, Lloyd E. Sponenburgh wrote:
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.
Polytechforum.com is a website by engineers for engineers. It is not affiliated with any of manufacturers or vendors discussed here.
All logos and trade names are the property of their respective owners.