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ID Grinding help for a NEWBIE

lethal375

Aluminum
Joined
Oct 16, 2017
I have some parts that will need final ID grinding after heat treating.

4140 55RC .625 bore with .005 tapper 2 inches deep.
.002-.003 grind stock
Customer says needs best surface finish possible, No surface finish specified. The better the surface finish the more they will pay.
I can and will polish after grinding.

Never ID ground anything this small.
Did some test pieces with a few old wheels I had (.560 dia.) with good results but the wheels have no identification so not sure what I am using.

Any recommendations on wheel size, grade/type, speed, wet/dry, etc?

Thanks for any help
 
Assume you have a cylindrical grinder with ID capability, use a CBN quill 3/8 diameter with coolant.

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Yes I have a couple of Heald Grinders and do a little grinding as needed but never this small.
I literally got hundreds of stones/wheels when I purchased these grinders but most have no markings

I have arbors small enough and long enough that take a wheel

I also have a head that has collet for mounted/bonded with .250 stem

Can do wet

Was searching info on ratio of bore to wheel size, assuming there is an ideal range for ID grinding?
Part rotation same as wheel or opposite?
Part rotation speed?
Wheel speed?

Been reading about CBN, but again no experience with it.
I gather that CBN will hold its size better?


Just been winging it on most things with good results but nothing this precise till now.
 
I have been doing some simple ID grinding in the past months, so don't have much experience. But I have been reading a lot about the topic.

Was searching info on ratio of bore to wheel size, assuming there is an ideal range for ID grinding?
Part rotation same as wheel or opposite?
Part rotation speed?
Wheel speed?.

Wheel size should be as large as possible, up to 80% ID. I would use 1/2" for your 5/8" bore.
Arbor/mount should also be as large as possible, for 2" depth 3/8" would be better than 1/4". What sort of grinding spindles do you have? Here in Germany it's common to use "Fischer UJ" spindles and mounts. You want the shortest possible arbor/mount that will fit through you hole. Is it a through hole or blind hole?
As with OD grinding part rotation opposite wheel if possible.
Wheel rotation speeds should be FAST, you want surface speeds of 20-40 meters/sec which is 4-8000 feet per minute. So if you have a 1/2" wheel (circumference 1.6 inches) this means 30-60,000 rpm. Do you have spindles that can do this?
Part rotation speed and traverse speed are linked, I would start at 100 rpm rotation speed and experiment with the traverse.
If you are going to be doing any reasonable number of these I would call a wheel vendor (Norton for example) and ask them for advice about the wheel for this particular material and hardness. 0.002-3" is a lot of material to remove. That plus the 2" depth are a challenge. I hope it's a through hole not blind.
 
I spent several years grinding tooling for cold formers. Mostly M4, HSS and Carbide. One tip I will give you is that when you dress your wheel to grind HSS make sure that you have a sharp diamond dresser. Look at it under a magnifying glass and if it doesn't come to a point get a new one. With a mandrel in an ID grinder you get some spring and if you are trying to rub the material out instead of cut it you will be there a long time and get unwanted taper.

As to getting a mirror finish, use a high speed grinder with a felt bob on it. Add some lapping compound and work from coarse to fine and you can get a mirror finish. I've done it literally thousands of times.
 
Assume you have a cylindrical grinder with ID capability, use a CBN quill 3/8 diameter with coolant.

Sent from my moto z3 using Tapatalk

In my somewhat limited experience vitrified will give a lot better surface finish than CBN. The material is not difficult to grind.
 
I found an arbor that is .500 and just long enough to reach
Final bore is .600 on the small end

I can bore larger and have less grind stock but not sure about distortion during heat treat?
1.25 OD 3in long

Bore is the only critical dimension/surface
 
Here is one of the arbors
Not sure what type/model?

WIN_20201102_12_26_39_Pro.jpg
 

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Generally, suggested grinding wheel/pin size for I.D. grinding is 80% (4/5) of the bore size when possible. Better to err on the small side than the large. Grind with wheel rotation opposite part rotation if possible. I'd start at 50FPM on the part surface, see how it cuts/looks, increase if necessary. For a .600" bore that'd be around 320 RPM. Grind wet whenever possible.
 
Which Heald ?

I wrote this out once before but ...

Set your stops to traverse maybe 1/4 of the wheel past the hole on both in and out. Traverse is not extremely fast, just a nice calm speed, like a slow wave bye-bye to the great-aunt after she made you eat that damned fruitcake again. Maybe a liitle slower. Andante.

I'm not used to this small a hole, use the fastest red head you've got and I bet it'll still be too slow, so go for a harder wheel, it will act softer from running too slow.

Vitreous is fine, cbn is too expensive.

Wheel and work rotate against each other. Usually wheel away from you, work towards you, grind on the back side.

I usually like to go about 2/3 bore size with the wheel, get more coolant in there but 80% sure, why not.

You need coolant, it keeps the temp down and washes the swarf out.

Make sure to use a blotter, and you know you have to dress every new wheel before you use it, right ? You can just run your finger over it after you dress, you can feel any non-roundness in the wheel that way, plus you can rob a bank that night, no fingerprints :) If I was going on a date I'd always smooth off the fingers on a wheel, that way you don't get yelled at for running her stockings. Machinist fingers :(

For so few parts I'd just manually drive it, no point in setting up all the auto stuff -- pull the wheel back clear of the diameter then bring it into the hole, now touch off while the table is reciprocating, set the amount to go on the handwheel (you had to measure the part first), kick it in one notch (.0002") at the end of each out stroke, or with such a small hole you may need to let it reciprocate twice between infeeds, grind until you are maybe a half thou away from finish on this small a hole (bigger hole I'd do a thou or even two), retract the wheel from the hole, dress, come back in, touch off, reset the handwheel to account for what you dressed, let it spark out or just reciprocate a few times, you better not be seeing sparks anyhow, retract, measure, set the handwheel for how much there really is to go, then grind to finish size. You'll want to dress for each part.

Retract is just pulling the table out, don't move the infeed of the wheel or you'll never know where you are. You can set a stop for the feed control lever so it will come back to the same place every time between rapids.

On bigger holes I always wanted .010" grind stock, heat treat always makes the parts go wonky and for the stuff I normally did, they wouldn't clean up until you took out three or four thou at least. But those were bigger, inch and a half or larger.

Still, it's easier to grind out more than to find the deposit tool and put material back on.

You can mess with the workhead speed to change how hard or soft the wheel grinds - faster makes the wheel softer - but I don't think you're going to be able to pull much info from the charts, cuz unless you have a very high-speed red head, your wheel speeds are going to be way slow. So just try then modify. I bet you'll have to run the workhead slower than the numbers say.

It should make a nice whoosh whoosh whoosh noise, that's the best way to tell.

After the first few parts it'll be fun. Healds are cool. Just do everything exactly the same on each part, they respond to that.
 
Heald 72A
One is manual feed and the other is hyd auto feed

I have several heads and one is rated for 15,500 max rpm
So 15k is my ceiling
Looks like about half of what I should be running?

The same old story
A whole shop full of equipment and still dont have what I need:willy_nilly:
 
When I seen this post I assumed 32K rpm for this size wheel?
Emanuel, made mention of Heald heads not having enough speed?
Heald made Red Heads that are faster than 15,000, I had a 17-5 one, but what you'd want for 1/2" is way high. I'm not sure they even built belt-drive heads that fast, at some point they turned to built-in motors and complicated lube systems that pump oil-laden air through the bearings.

Almost forgot, be sure to wear earplugs, that high-pitched scream will give you tinnitus. E above middle C right now, many years later :(

Anyway, not a hugely big deal, slower speeds will just make the wheel act soft; compensate by running the hardest wheel you have and slowing down the workhead. You aren't doing thousands of parts, right?

I'd choose the hydraulic machine, never ran a mechanical one, them's older than the hills :)

When you first fire it up, run the table all the way back and forth a few times to get the air out of the cylinders or she'll jump at the end of the stroke. You won't be able to get it all the way in, probably, because the part's in the way but ya just do the best you can.

You can just throw the handle over and let her fly in rapid on the outstroke to measure, the table won't come off or anything (embarrassing story not going to be told there). Just kick up the trip dog to escape, there's even a little handle for that.

Do you have the manual ? You almost need it for those, unless you have someone there to show you everything. They are more complicated than an o.d. grinder.

p.s. That arbor's pretty long but oh well. Don't forget the blotters. Probably be a bit of a bitch to change it if another one has been left in the head for a long time. Clean that one for sure first, and oil it ?

Dresser should be on a stand on the back side, in front of the workhead (duh !) a little ways. Sharp single diamond, and you don't need it on auto, just pull it down by hand when you go to dress. If you've got the cross-feeding workhead, it's easier to set the work relative to the dresser. If not, well, damn, do it the hard way :)

You might want to grind something bigger and longish to get the taper out before you go to the small stuff ? Normally people don't swivel the head around but you never know what the last user was doing with the machine, unless the last user was you .... kinda like tramming a Bridgeport before you go boring any accurate holes or facing something.
 
50 FPM at .600" diameter is 320 RPM... What kind of math are you doing? This is the part RPM, not the wheel.... Why I said 50 FPM on the part surface, not the wheel surface.


Sorry, my bad, I though you were talking about the grinding wheel RPM not the part RPM.
 
This is a very good thread.
Full of information about ID grinding.
I have some interest, as some time ago,
I bought an ancient HEALD model 70 ID grinder.
It looks to be from the lineshaft era, having
been adapted with some motor conversions, with
the typical haphazard bracketry. Anyhow, I have
not had time to go through it yet, as in completely
take it apart and make sure no dirt is in the ways
or in the gears. It does have some large oil wells
with wicks in the table, so that is a good thing.
All the mechanical powerfeed gearing is still there
and nothing is broken.
The grinding head says PARKER, wondering if it is
the same PARKER-MAJECTIC company that I have heard of.
It is a dovetail slide in mount, my thinking is the
RED HEAD spindles will fit. Some of those for reasonable
money on Ebay, but I don't want to spend money before I
to a take apart of the machine and make sure the ways are
at least somewhat is good condition.
But the machine is very heavy built. Worth saving in my
opinion, even though it is quite old. My thinking is the
1930s range of being old. I have zero ID grinding experience.
I do have a Brown Sharpe #13 and a Covel 512. The Covel even
has the swing down PREECISE ID grinding attachment, but I have
not played with it yet.
I believe I have seen one member here that has a HEALD model 70
and has posted pictures of it. His was nice and clean, painted
grey, but had the powerfeed stuff either removed or missing.
So there is at least one out there.
So anyhow, thank you for the information in this thread.
I will keep an eye open to see how this job in question turns out.

--Doozer
 








 
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