I'm building some parts where I need to make groves for an oring and
I want to make a prfile. groving tool for the lathe.
I have some Tool steel blanks and a CNC mill that can precisly cut the
profile I want,
The question I have are:
1)Best stratagee to sharpen the tool after the prfile is cut.
2)What if any heat treat should I do?
This will be for cutting aluminum.
Am I completly off base to use the CNC mill to precut the profile?
In my estimation, yes.
Please let me explain.
I am not CNC capable. I was trained as a machinist, starting in '57,
although I had some previous experience, having taken machine shop in high
school, and owning a small lathe that I purchased as a boy.
You will be held captive by your ignorance (I mean that in the kindest way,
so please don't take offense) until you are able to walk up to a bench or
pedestal grinder and fashion, by hand, a cutting tool for a lathe, starting
with a blank piece of HSS. It's not nearly as difficult as it first
appears to be----it just takes some concentration and an understanding of
how tools cut. If you have that knowledge in your head, you can judge the
tool as it evolves at the wheel, and will know where to grind, and how much.
The only thing left is to learn to do it without chopping the tool all to
hell, with multi-facets from the wheel. A person that is skilled at tool
grinding can generally have only one uniform grind on each face, making it
much easier to stone the tool after grinding. The configuration of the
single grind becomes the guide for the stone, and prevents rounding of the
Please give the above advice serious consideration. Unless you have at
your disposal a tool & cutter grinder, or a few accessories that can be used
on a surface grinder to help it act as a tool & cutter grinder, you're more
or less screwed otherwise. You do have one remaining option-----to pay for
insert carbide tooling, which will help keep you in the dark endlessly,
although it will perform well, given the proper machine.
Hand grinding a tool for O rings is a no-brainer. It's nothing more than
a short parting tool, with proper width, side and front clearance, and top
rake if you prefer to enjoy good chip flow and free machining. If you
prefer to take a finish cut on a roughed groove, you can also consider a
tool that is slightly narrower than the desired width, plunge to rough the
groove, leaving a few thou in the bottom, with the undersized groove located
properly, then take a skim cut on the sides and bottom for finish and size
control. On a manual machine, the use of a long travel indicator (Or DRO,
which I do not use) makes that easy. Measure the width of the grooving
tool with a micrometer (very carefully, to not screw up the tool or the
mic), then move the carriage the appropriate amount to achieve the size
I just don't feel comfortable hitting the tolerances specified in the
o-ring grove chart, by hand.
I can hit the width and with some trouble I can get the edge
reasonably square, but getting the edge radius to by 0.3 mm +/-.0 1mm
is byond what I think I can do by hand.
I don't even know how I'd measure that with the tools I have.
I'm really surprised at that .01mm tolerance. I've ground by hand many
O-ring grooving tools. I think that perhaps you have read the spec.
wrong or (more likely) the spec. was printed wrong. The reason for the
edge radii is to prevent cutting of the o-ring during installation.
The radii in the bottom of the groove are for ease of manufacturing
and to avoid stress risers. If the edge radii are too large the o-ring
can extrude into the area defined by the radii and get stuck. If the
o-ring is used in a dynamic situation this can cause the o-ring to
tear. Just gring the tool by hand and use a magnifier to estimate the
radius. A .6mm dia piece of wire can be used next to the radius to
I have years of experience behind me, both defense and aero-space work that
receives intensive scrutiny at the hands of well qualified inspectors, and
have done such thing by hand with no rejections, ever. The idea that a form
tool would be ground to create the corner radius borders on the insane---the
sole exception being high production, fully automated work.
Edge radius in your example, in decimal inch measurement, is .011", with a
tolerance of +/- .0039". You can judge that by eye easily. Don't get an
ulcer worrying about things like this----it's nothing more than routine when
you become familiar with the operation. Again, the radius is not
functional-----it's a safety precaution that sits in the wind. Unless
you're cutting a groove in literally thousands of pieces on a production
basis, you do it with a safe edge file. Do remember, all you're doing is
deburring an edge so it doesn't damage the ring upon assembly.
What this really boils down to is the qualifications of the operator. A
machinist takes it in stride and turns out the work, no problem. The guy
that has no clue and is nothing more than an operator will certainly stumble
a great deal. There's simply no substitute for experience. You get that
by doing the work.
I want teflon o-rings with a backing ring to hold pressure at very low
Its really important to me that the o0ring perfrom to their best
I know that teflon o-rings are very soft, so I'm trying to maximize my
chances by meeting the specification exactly.
I'm a electrical engineer by trade and I'm doing this as a hobby.
I don't have a good machinist mentor and I'm trying to learn by asking
This really is something you can accomplish, exactly as I suggested. Have
a little confidence in yourself and give it a go, even if you have to do a
practice run on some scrap material before attempting the part you need. It
really isn't a big deal----and---sadly, even if you were to have a tool
ground, it wouldn't be any more likely to work than what I've advised.
You didn't mention the material you're trying to machine. If it's mild or
medium carbon steel, you're going to fight a decent finish a lot more than
you'll fight the radius. Can you give us a little more information on what
you're doing, and with what you're working? It's really hard to provide
answers when we have to guess at the bulk of information necessary to
provide good guidance. I checked the link you provided but don't have
enough time, nor the inclination, to read the entire thing and glean enough
information to have it be of assistance.
As I posted in the origional question,
I'm trying to make a tool out of A-1 tool steel.
And I'm cutting Aluminum.
I machined to width on the mill and filed the edges/radius with a
small file and magnifying glass.
I made my fiorst set of o-ring groves and I'll see if they hold
pressure Sunday or christmas.
thanks for the advice.
You didn't mention that it was A-1, but I commend you for your choice if you
choose to heat treat. I'd still start with HSS-----and hand grind the tool.
Without a controlled atmosphere furnace, heat treating can be
challenging----often screwing up surfaces from oxidation. And then there's
always the chance of size change. It's common with heat treat, albeit only
a small amount, either larger or smaller.
Yep-----you did mention that. And folks say I have a short attention span.
Cool! I'm hoping you have success. Be sure to report the outcome.
Wasn't much, eh? It would be far more effective had you been able to
stand in my shop and watch me go about doing it as I suggested. There's no
better way to learn things than by example.
First off we speak american here so stop with the mm crap.
whatever that is in english start practicing. It just takes practice.
30 years ago at school I was the absolute worst at hand grinding but if
I can do it anyone can. Start practicing and then learn to convert your
mm to something I understand
It's called "the world wide web" for a reason , Rosco . I'm not
comfortable working metric , but most of the world uses that system . Get
accustomed to it or you'll be left by the wayside . I just keep in mind that
it takes about 25 mm to equal an inch ... and that serves until I can get my
hands on a calculator to figger it closer .
Thanks, Harold, for a nice essay - a distillation of part of the craft.
Trying to learn tool grinding at school - (practicing on pieces of mild
steel) - its difficult, especially the one grind per face - but I feel
its worthwhile, and I will persist until I am able to make good use of
the box of tool steel I have sitting underneath the lathe. And I need
to eventually upgrade to a decent 8 inch grinder, and get a diamond
dresser for it - the $30 chain store grinder I have is just not up to
Hey Rosco - count yourself lucky you can stay in ONE system of
measurement........I learnt imperial at school here in Australia, and
because of that still think in it. (Lets face it, stuff that was
literally beaten into you at school, well, you don't forget it...)
12 inches 1 foot, 3 feet 1 yard, 22 yards 1 chain, 10 chains 1 furlong,
8 furlongs 1 mile...totally useless now, but its stuck in my head till
About 20 years ago (or something like that) we converted to metric.
Thats fine, I still had my steel tape measures and inch rulers, and for
the work I was doing, that was ok. Bought packets of 1/8th by half inch
Whitworth nuts and bolts for the radio projects I was doing, no
worries. 25.4mm was an inch, and a metre was about 3 and a bit inches
longer than a yard. And 100Km was 60miles. What more did I need?
Then, this year, I signed up for a Trades course in Fitting and
Machining. All metric. all measurements, and instruments, were in
metric. Learning to use precision measuring instruments was taught in
Metric ONLY. They DID cover Imperial measurements as a historical note
due to the "legacy" machines out there still in use (and coping with
the Yanks) - . I wouldn't have a clue how to read a micrometer in thou.
And, this year, bought my first EVER set of Metric drill bits....
So take pity on us mate - stuck between two worlds, trying to translate
measurement on this group to units our instruments can measure, but
still "thinking" in feet and inches. Dont be so quick to condemn, its
only an accident of birth YOU don't have to cope with this.
I have a beaut freeware program called "Convert.exe" on the workshop
PC desktop, and use it frequently to figure out what you guys mean
sometimes....and sometimes, from metric to Imperial so I can get a
mental picture of the size of a thing...
Be a bit conservative with a diamond dresser when dealing with grinding HSS.
Use it to true the wheel if you must, for it will do that faster and better
than any other method, but follow up with a dressing stick, to "rough" the
surface. That creates a surface that cuts free, with less heat generated.
Diamond dressing is, indeed, the ultimate, but not for offhand grinding.
Diamond is so hard that it cuts the individual grains instead of tearing
them loose from the matrix-----leaving the wheel much smoother than might be
desired for such grinding. You soon come to realize that the wheel
requires considerably more pressure in order for it to grind, and grinds
much hotter as a result. The effect is to grind slower, not faster. The
wheel has a perpetual "dull" feel to it.
As much as I'm against their use, a star type dresser is actually the best
of dressing tools for offhand grinding, but they're not as user friendly as
a dressing stick. They tend to be wasteful of the wheel, often requiring
several attempts to get the wheel running true, unlike a diamond or dressing
stick. They also require a work rest, which I don't use.
Star type dressing tools work by impact, so they don't dull the wheel.
With care and skill, a wheel that runs quite true can be achieved with one,
but it's far easier with a diamond, followed by a dressing stick, which, if
properly applied, will yield a wheel that comes very close to rivaling one
dressed with an impact dresser. The one advantage is that the wheel often
runs closer to true than it would with a star type dresser. A bouncing
wheel makes sharpening tools nearly impossible. Because I don't use a
work rest for such grinding, relying solely on the surface of the wheel to
act as a guide, It MUST run true.
Improper use of a dressing stick has the tendency to dull a wheel. A sharp
corner should be applied, never a rounded, dull surface. That dulls the
grinding wheel. Also, the proper dressing stick is one made of bonded
silicon carbide grains, the coarser, the better. The proper wheel for
grinding steel, including HSS, is aluminum oxide, never silicon carbide.
I do suggest a wheel larger than 6", although my pedestal grinder
accommodates wheels that are only 7" x 1/2" x 1-1/4" . Such wheels are
readily available in a myriad of configurations, abrasive types and bond
types due to the wheels being used extensively on cutter and surface
grinders. You are unlikely to find such a grinder, but they're not hard to
build from a 3600 rpm motor with a shaft extending from each end. Mine,
being home made, was constructed accordingly.
When you grind tools well, you end up with a hollow grind, a result of the
radius of the wheel. It's nice to minimize the amount, to preserve heat
transfer from the tool edge to the shank, so the tool holds up better under
adverse conditions. You also maintain greater surface speed, which is
critical for good grinding performance. I have serious doubts about a 6"
or smaller wheel running anywhere near the recommended speeds of wheels.
If you grinder runs @ 3600 rpm, it's woefully under speed, and gets worse
and worse with wheel wear.
Good luck, Andrew.
Bugger. Youve done it to me again, Harold. A comprehensive reply,
leading to more questions....
My experience of dressing grinding wheels has been at school - the
instructor used a diamond dresser, it is a T shaped tool with (diamond
dust) on the face - the face of the tool was flat, so it could be run
across the surface of the wheel to true it up. It made a big
difference - in one exercise (drill sharpening) I was trying to sharpen
a 2 inch drill - moved to the BIG grinder as its face was wide enough
to do one side of the drill in one go - it was hopeless, the drill
bounced and shuddered all over the place. The instructor then dressed
it - no worries, face off beautifully.....
Whats a dressing stick? - are they available from a tool store? I do
have a single point diamond dresser - is that the same thing? - havent
used it as I feel it would not "dress" evenly...
Dont know - havent had the experience to know any better. What I do
know is its a pain when the thing your sharpening starts to get so hot
you have to stop and quench it - you lose the angle you had set up on
the face of the tool...
Is that the thing that looks like a row of metal pointy stars, mounted
on a shaft and bracket held at right angles to the grinding wheel face
via a handle?
Yep, learnt that - the wheel material must be softer than the HSS bit
you are grinding....(correct?)
Yes, I realize that with the bigger diameter wheel, the concavity(??)
in the tool under grind is reduced...(it was in me textbook)
Harold, going to print this out, take it into school next term and ask
for comments - should be interesting. They have already said that some
of the tool profiles illustrated in the South Bend book are wrong
Thanks Harold - I don't need luck, I need to learn enough not to be
relying on the sheer chance of getting it right...yours (and others)