My RF 31 and I haven't done too much damage to each other, and your
advice has helped me to build some useful items. In particular, the
D-shell panel from hell is ready to enter service. I currently have
some mounting brackets taking up space in my shop, and hope to move on
from them to a small transducer fixture.
One of the mounts brought my flycutter out of "retirement" and I decided
to try one of the import brazed carbide bits that I bought a while back.
With a properly "ground" tool, I was suddenly able to take a lot more
metal in one cut than my own efforts allowed.
I have been reading some old threads and a couple of books, but
sometimes wonder whether I am getting tricked by lathe-specific
instructions?? Are there any good beginner resources on grinding
One thought is to use HSS blanks and my $40 grinder (yell if I need
something better) to try to make a good copy of the carbide tipped
wonder. Some older threads suggest that one should expect to apply some
pressure when grinding HSS. It sounds as though some of you hand-hold
bits for grinding. Being a little cautious, I would prefer a vise grip,
which I have also seen mentioned. Other recommendations are most
welcome should anyone disagree.
What kinds of wheels do you suggest I buy? What should I get to dress them?
My first attempt at grinding a flycutter tool
was to make it like a lathe tool. My second
attempt to make it like what I *thought* a
flycutter tool should look like. Both were
miserable failures. Then I asked an old
retired machinist how to grind one.... No
I handhold it after I wrap 3-4 turns of 3M
high temperature electrical tape on one end
for a handle.
Honestly, no such thing.
A drill is an endmill is a lathe turning tool is a boring tool is a
facing tool, etc.
You have clearance angles and rake angles. Together they make a wedge
Clearance angles prevent the tool from rubbing the work. As your feed
increases, so must your clearance angles. This is tied to the tensile
strength of the material - softer materials have lower strength which
means your tool and feed heavier without breaking. Your edge strength
is reduced as your clearance increases.
Rake is ultimately material specific, but will impact the strength of
your cutting tool as well. Steel ranges from slightly positive to
slightly negative (including neutral). Aluminum would be slightly
positive to very positive.
Tensile strength of steel is reasonably high (sometimes quite high), so
you don't want too much clearance. You can't feed hard enough to make
use of lots of clearance anyway. Rake is roughly neutral. Wedge angle
will be kinda near, but not quite 90=BA. It will get closer to 90=BA for
tough tool steels, and quite a bit smaller than 90=BA for mild steel.
Tensile strength of alumium is low, so use lots of clearance (high
feeds). Rake is quite positive. Wedge angle will be quite "pointy".
Soft cast iron and brass are low/medium tensile, so a fair amount of
clearnace, but not like aluminum. Rake is neutral, if not positive.
Wedge angle will be between steel and aluminum.
Simple, but the above applies to all machining operations, regardless
of the format. Aluminum drills have fast spirals for maximum rake. You
can grind your own agressive clearnace. Drills for brass have very slow
spirals for nearly neutral rake. Same for endmills, same for indexable
If it gets to hot to hold it, you should have already cooled it.
I only hold _small_ bits in a jig.
A white 60 or 80 grit wheel.
A multi-diamond dresser or a dressing wheel. A dressing wheel is sayed
to leave a sharper surface on the wheel.
Nope! Not for offhand grinding, It makes the chore far too difficult,
although the wheel will run very smoothly. Diamond dressing and offhand
grinding to not go well together. The smooth surface cuts hot and slow, and
does not serve the user well at all. As much as I don't like star type
dressers, that's the best surface you can possibly achieve for such
grinding, but you can achieve a surface that is very close by using a
sintered silicon carbide dressing stick. I highly recommend one.
OK---more comments from me, this time not in haste.
Robin, who is working in the industry, has given you some very good
guidelines on grinding toolbits. Truth is, there's very little difference
between a lathe tool and a fly cutting tool, aside from front clearance.
Because the tool rotates in a relatively small circle, front clearance must
be extreme. Rake can be adjusted by grinding proper chip breakers, a very
useful thing to know and understand.
When using a fly cutter, you have options of how the tool can be mounted.
The cutting edge should be on center, even if you have to run the cutter in
reverse. If you don't observe that rule, the front clearance on your tool
will always be wrong for the application unless you grind it accordingly.
Yep, that's true, but it need not be excessive. And yes, your $40 grinder
will work, but it likely has a terrible wheel for the purpose. I already
commented earlier about dressing your wheel with diamond. DON'T DO IT!
Diamond dressed wheels for offhand grinding are a bad idea. The exceedingly
smooth wheel will not cut well, and will cut very hot, burning your tool
instead of removing metal. Buy yourself a sintered silicon carbide
dressing stick from one of the tool supply houses and learn to use it.
They're cheap, less than $5, and will last you a life time in the hobby
shop. The wheel so dressed will come close to rivaling the surface of a
diamond dressed wheel in smoothness, yet still cut quite well. I mentioned
earlier that the wheel will cut very best if dressed with a star dresser,
but they aren't the easiest thing to use without wasting a lot of wheel, and
putting a lot of dust in the air in your shop. They work by fracturing the
grains by hammering, leaving dead sharp grain behind to do the grinding. It
doesn't get better than that. I hate the damned things and don't even own
Unless you have a cutter grinder at your disposal, there IS NO OTHER WAY!
You will never learn to grind toolbits if you use devices that limit your
control. That may not make sense when you strike out, but it will when you
try to hold sizes. Fact is, even a tool rest is a mistake, but it takes
considerable experience before you can free-hand grind toolbits that way.
I grind HSS toolbits exactly as I say-----and can grind pretty much any kind
of configuration imaginable, including gear forms, and chip breakers.
These, of course, are all single point tools, not multiple toothed cutters.
Dressing them has already been addressed, above. The wheels that will
serve you best are aluminum oxide wheels, with a grit spread of 46 to 60.
Don't go finer, although an 80 does a remarkable job of leaving a great
finish. Problem is, they cut hot and slow. My personal choice is a
Norton 38A60K8VBE. I don't necessarily stick to that designation----going
harder (L or M) or even softer (H, I , or J), depending on what's on hand,
and what the job demands. Soft wheels break down quicker, but cut faster
and cooler. You'll eventually come to understand where you get the best
performance for your personal grinding style. It's not the same for
Don't alter course on the bond. Vitrified wheels are the only choice for
offhand grinding. You'll get the very best selection if you'll go out of
your way to make an adapter with proper flanges that will accommodate wheels
that run on surface grinders. Such wheels are 7" (or 8") x 1/2" x 1-1/4"
arbor size. Observe all safety rules---ring the wheels before mounting
them, and don't overdrive them. Don't stand in front of them when you spool
up the grinder. Give it a few moments of top speed operation before
trusting it. That rule applies every time you turn it, or ANY grinder,
on. Also, don't under-drive the wheels.. Slow wheels behave soft and
slough away quickly. They are rated at a given hardness at the proper
speed, not below. Well worn wheels that are reduced in diameter run soft,
but will firm right up if you can get the surface speed back up.
There's more, but this should give you some basics from which you can start.
Probably the easiest way to avoid burning fingertips while hand
grinding HSS, is to grind numerous blanks, laying them down on a plate
of steel (or uhlumium, loonimun) when they get uncomfortable to hold,
then picking up a cool one and doing some grinding on that one until it
gets extra-warm (not scorching).
The room temperature plate will sink heat away from the blanks fairly
I don't care for the visegrip method because the jaws aren't really
gripping the tool blank, since the jaws and the blank are both hardened
materials. The jaws will hold fairly well in one direction, but not too
well when rotated 90 degrees. The plier shape isn't symmetrical and is
not inline with the blank's axis, and obtaining different grinding
angles is a bit tedious and awkward.
A long while ago, I posted a link to one of my old webpages (gone now),
a fairly easy method of making a broached holder for square HSS blanks.
A section of round stock is machined to resemble a deep broach to
accept the square HSS blank.
I haven't seen any commercially-made tools/holders that are made for
this purpose, so they would need to be made by the user AFAIK.
These holders have served me well for "grinding the hell" outta tool
blanks, into the brown heat range without stopping to let them cool. A
good 36 grit wheel will rip that shape down faster than you'd imagine,
compared to holding the blanks with your fingers or other improvised
method. The hloder makes it easy to keep the pressure on, while
vigorously traversing the face of the wheel. The handle is always in
line with the tool blank's axis, and makes handling of the holder easy
at any single or compound angle.
The details that Harold describes will make stock removal nearly
effortless. I have and use a diamond dressers, and also the dressing
"stone" for cleaning/refacing the wheel face at regular intervals.
The basic steps of machining the holder are
Use 1/2" round stock 8-12" long for 5/16" blanks, 5/8" for 3/8" blanks
With a lathe or mill, cut a flat along the stock, creating a sort-of D
shape, a little longer than the length of new tool blanks. Plan your
cuts to keep the square in the center of the diameter.
Cut into the flat face with an endmill (lathe or mill), to create the
broached recess, the same square dimension of the tool blank.. 5/16",
3/8" etc (and the length of the recess about 1/2" longer than the
length of new tool blanks). Remove a little more in depth than the top
of the tool blank's top side will be.
Replace the metal that was cut away to produce the flat with a section
of flat stock and weld in place at both ends, but just the ends.
Rough-in the round shape of the round stock (with a grinder and/or
file), then finish turning the welded-in section round, to match the
round stock's diameter. Cut off the weld at the open end.
This results in a deep broach in a round handle, with one side of the
broach being the piece that was welded in to replace the material that
was milled away.
The trick was to keep a small gap (about .004") between the flat that
was milled away and the flat stock that was added, so that the tool
blank can be securely clamped in the broach with as much of the blank
as you would want sticking out.
Picture a collet for holding square stock, but only one side slitted
The way I attained the small gap was to place pieces of shim stock
between the flat piece of added stock and the machined flat, for the
A locking shaft collar can be slid over the end of broach area for
clamping, or a square block that has been drilled and slitted (with
provisions for a clamping screw).
The square block works well when used on the grinder's tool rest, since
the flat bottom side keeps a reference while the tool blank is ground,
allowing for fine rotational adjustments to be made (to adjust grinding
angles in relatively fine increments while referencing the tool rest).
When you become proficient at grinding cutting tools (not bits), you
will have earned the right to refer to yourself as a Grindor
No self-respecting operator would call himself a grinder..
A note about sharpening cutting tools on belt sander/grinders. The
cloth-backed belt will create a crown in the ground area, creating a
false angle (an arc instad of a flat facet).
If you're good at visualization, sharpen the tool upside-down, so the
arc isn't in the immediate area of the cutting edges.
Otherwise, build a belt grinder that runs the belt backwards, to
sharpen them right-side up. Protect yourself from the sparks and
Bill Schwab wrote:
bill, why spend the time and effort making your own flycutter inserts when
they are so readily available and cheap! i use AR5 replaceable carbide
tipped fly-cutter arms and have found them to work really well, and only
around $10 a piece.
That's certainly a possibility, and it was an even cheaper brazed
carbide toolbit that showed me what I was missing. However, the gang
here tells me (and they have a very good track record) that there is an
advantage to being able to customize angles/shape for a given job.
There is also the opportunity to grind/sharpen tools from $1 blanks vs.
being stuck if something more elaborate breaks.