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Holding +-.0001” on 7/8 bore with cnc lathe

Ianagos

Stainless
Joined
Sep 23, 2014
Location
Atlanta
Hey so the title sums it up pretty well. I have a quote where I need to hold +0 -.0002” on a roughly .875” bore 1.5” deep. Material is 316 stainless

I’ve been able to hold these tolerances on external features but internal features may be a little harder. Qty on the parts is low about 25parts quarterly.

should also mention the machine positions to .00001”

I was thinking 5/8 solid carbide bar for semi finish Would let me hold a few tenths but to inure I hit that +-.0001” I was consider other options.

Internal grinding is one option but the part has almost no way to be refixtured to go on to my cylindrical grinder and I don’t have a high rpm internal head either way.
I did consider grinding on the machine. It has a 12k spindle only though and for the 1/2 or maybe 5/8 stone required I don’t see that really being optimal.

Next thought was finishing to within a few tenths on the lathe then setting up a hone of some sort. But trouble with this comes in the form of no space to setup a sunnen hone although I do see them for sale every few months and also absolutely no experience at all with honing and whether I can even hold those tolerances on a hone. I have drill press I could stick a hone in?


Parts will be checked with a 3point digital bore mic checked against a master ring gauge. I may also pick up a .0001” bore gauge for some additional gauging.

So that’s my thoughts. I know there are some folks that hit these tolerances all day on the forum.

What do you guys recommend?
 

Mechanola

Stainless
Joined
Mar 21, 2011
Location
Äsch
Typical hone job in my understanding

Proper hone oil and air gauge. Of course will a Sunnen find room, if the job runs well on it.
 

FredC

Titanium
Joined
Oct 29, 2010
Location
Dewees Texas
You might try these guys for a single pass diamond hone. Di-Coat Corporation
800-637-9194

I have 2 of their units and they work quite well for me.
 

Dan from Oakland

Titanium
Joined
Sep 15, 2005
Location
Oakland, CA
Hone it, but bigger question is how ya going to measure it? I would imagine that just holding it in your hand might well use up your tolerance. Sunnen mechanical gages to 50 millionths if your part is not too large to get it on the gage.
 

modelmakerblue

Aluminum
Joined
Sep 9, 2005
Location
Dunstable, UK
Hone it, but bigger question is how ya going to measure it? I would imagine that just holding it in your hand might well use up your tolerance. Sunnen mechanical gages to 50 millionths if your part is not too large to get it on the gage.

This has got to be a honing job, obviously in a temperature controlled environment & checked with decent measuring equipment.
Tony
 

barbter

Diamond
Joined
Oct 27, 2007
Location
On Tour...
...should also mention the machine positions to .00001”

:blink:
:blink:
:willy_nilly:

And a 3 point digi mic isn't accurate enough for this (IMHO).
A Diatest bore gauge would probably be (and you can also "feel" the bore with these, but an Air gauge is what i'd be using for a repeat job.
Also, a temperature controlled environment is obviously a biggie, as you're using the ring as a master etc.
 

michiganbuck

Diamond
Joined
Jun 28, 2012
Location
Mt Clemens, Michigan 48035
I think a decent reamer for -.0003, a Sunnen hone, an air gauge, and so a master need be bought. Likely hard to re-coup on a 25 piece order.

I once met a guy who made a small fortune bidding on building a fixture, perhaps another grinder, buying gauges and everything on a thousands pieces repair order on a government small part. He said he didn't event want to take the job because he was full-up so bid way high. He found the parts were all near dead on at -.0003 or so and ran them on a Sunnen machine for like a 1234 (or what) swipes to make good the part.
I forget now but I think he said he was making a thousand or thousands an hour on the job.
 

Ianagos

Stainless
Joined
Sep 23, 2014
Location
Atlanta
Well seems like honing is the recommended way.

This is a repeat job but seems as though it may not be worth it. 125pcs/year

I figured the digital 3 point mic would be accurate enough to measure it as it reads in .00005” but maybe not.

Seems like an air gauge is the appropriate tool. Anybody got one for sale?


Can the honing be done on the cnc machine possibly? Or setup in a drill press. I really do not want a sunnen hone for this one job…
 

Ianagos

Stainless
Joined
Sep 23, 2014
Location
Atlanta
:blink:
:blink:
:willy_nilly:

And a 3 point digi mic isn't accurate enough for this (IMHO).
A Diatest bore gauge would probably be (and you can also "feel" the bore with these, but an Air gauge is what i'd be using for a repeat job.
Also, a temperature controlled environment is obviously a biggie, as you're using the ring as a master etc.

Hey it positions to that not necessarily accurate to .00001”.

Took me several days of settling and a .0001” per 10” level to get this thing setup… probably time to check it again

I’ve held +-.0001” on od of parts before but it’s really a pain. Thermals in the machine means I can’t trust it to do better than .0003” without verification.


Also shop is reasonably temperature controlled. Stays 68-75 degrees. On real hot day if door is open a lot ac can struggle.
 

gappmast

Cast Iron
Joined
May 13, 2007
Location
California
You will need to hone it twice to hold size because of heat, even if it doesn't feel warm it will shrink. I would make sure you are on the same page with your customer when it comes to size and measuring. It doesn't natter what you measure their measurement it what will sign the pay check.

Sunnen has the PG800 gage that will measure down to 50 mill it should do the job and they lease it won't break the bank, give them a call and check the lease price.
 
O

otrlt

Guest
should also mention the machine positions to .00001”

Nothing in existence positions to .00001, you also have another problem; assuming that you can position to .00001, can you repeat within .000005?
 

HuFlungDung

Diamond
Joined
Jan 19, 2005
Location
Canada
I find it easier sometimes to do a precision bore on the cnc mill, using this tooling:

Micron Precision Boring Head Set MariTool

The boring head has .002mm adjustment capability, and it seems to actually be capable of such very fine adjustments. I was in fact boring 35mm bearing bores in 316 SS today, and after getting it dialed in to what I wanted, I never noticed any diameter variation in a dozen parts. But, that is my particular combination of tool and mill, so it might not work out for a different machine.
 

Ianagos

Stainless
Joined
Sep 23, 2014
Location
Atlanta
You might try these guys for a single pass diamond hone. Di-Coat Corporation
800-637-9194

I have 2 of their units and they work quite well for me.

Gonna give them a call here but what does pricing look like on these units? And will yours hold these kinds of tolerances?
 

Kallam

Cast Iron
Joined
Feb 11, 2006
Location
South Carolina
Try ball sizing Balltec sells crome steel and carbide balls
in .0001 increments.I had a job to hold a bore .0002 .750 dia
with a 32 micro inch finish. I would bore to about .0005 undersize and press the balls thru the hole each one a little bigger until it was in spec. It also produced a mirror finish.

Bal-tec - Report On Ball Sizing
 

Conrad Hoffman

Titanium
Joined
May 10, 2009
Location
Canandaigua, NY, USA
If the part lends itself to honing, it will be almost trivial with a decent Sunnen hone and an air gage and some setting rings. Not cheap for 25 parts unless you job it out to somebody who does that sort of thing, but you'll still pay for the gage head and rings. It's the measuring that's the killer. No experience, but I suspect it could be done on the lathe if you found the right insert, but lots of ways to go wrong. With the Sunnen you just sneak up on it.
Honing
 

Milland

Diamond
Joined
Jul 6, 2006
Location
Hillsboro, New Hampshire
Try ball sizing Balltec sells crome steel and carbide balls
in .0001 increments.I had a job to hold a bore .0002 .750 dia
with a 32 micro inch finish. I would bore to about .0005 undersize and press the balls thru the hole each one a little bigger until it was in spec. It also produced a mirror finish.

Bal-tec - Report On Ball Sizing

The issue with ball sizing is the ball can drift a bit side-to-side depending on local hardness. So even if you measure to spec, you could have unseen "wander" in the cylinder, which is likely a no-no here.

I'm with the honing crowd, ditto those that say check with the customer as to how they plan on measuring the parts. You'll need to copy their method.
 

Mechanola

Stainless
Joined
Mar 21, 2011
Location
Äsch
Roller burnishing is another method that might be appropriate. You can reach down to almost full depth of the bore which is not the case with balls and honing stones which actually need to overrun somewhat.
 








 
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