Pin gaging tolerance question. HELP

[tay2daizzo8]

So i have a part with a 1.125" bore, 3.00" deep, not a blind hole. total tolerance on the bore is .0005" Also has a surface finish under 8

material is 300 series

Historically we have checked this with a bore micrometer and have had no issues.
Recently the customer has switched from using a CMM to a plug gauge.

IMO a pin gauge is not the way to check this bore. Especially not at this diameter and depth and surface finish.

Im trying to find some information on the class of fit allowable for pin gauges.

I found all the hole and shaft tolerances in the MHB, but nothing that specifically relates to gauging.

they are claiming the bore to be too small, but when reinspected with the bore mics(and setting ring) they all fall in tolerance.

My thinking is there is not enough clearance to get the gauge pin down the bore



thank you

 

[DDoug]

Maybe air gaging ?
air
Air Gages - Precision Gage Co. | Metrology, inspection, calibration & engineering.

 

[michiganbuck]

bore mics and a ring gauge...?

Having a lathe or grinder you can make a 1.1247 (or 1.1248) to 1.125 step gauge as a go/no gauge.
(Yes Lathe made likely soft so care in handling is needed.)

Make/size it by using an indicator and JoBlocks.

Agree air gauges are very accurate but expensive.

An old reamer ground to size between centers makes a long-lasting Go/no gauge.
Cut to a comfortable length after grinding..and shoe off the sharp edge.

$20 and a half hour with the likes of a B&S 13 grinder.

Union Twist Drill Co 1 3/16" Reamer 8 Flutes Straight 12" OAL 6" LOC Used | eBay

RE: the customer has switched from using a CMM to a plug gauge.
*For next to nothing, you can do the same.

You might also ask the customer for the size of his plug gauge.
just goes to show that the customer's CCM did not check as close as a plug gauge.

 

[Cole2534]

Ball gages?

they are claiming the bore to be too small, but when reinspected with the bore mics(and setting ring) they all fall in tolerance.

To my green horned self, this suggests the bore isn't straight. Your mic hits a small ring while their pin hits the a large chunk, if not all, of the bore and is following the hole while their pin does not.

How are you making the hole?

 

[RJT]

Gage pins are normally M+ or M- meaning nominal dimension plus tolerance or nominal dimension minus tolerance (amount of tolerance depending on the class of gage pin). On a perfectly round hole, I find I need at least .0001" clearance to get a gage pin to slip in. Line to line (no clearance) won't go. Are you sure your hole is round? IMHO a pin is a better indication that the hole is not undersize at all points (better functional fit gage). 3 sided tri mics don't find out of round occurrences as well and a 2 point bore gage. I always try to gage my parts the same way the customer is gaging the parts.

 

[Finegrain]

Large pin gages, IME, will rarely go nicely into a bore unless the gage is a few tenths smaller than the bore being measured. I don't know the technical reason, just have given up trying to measure larger bores with pins. ID micrometer, spindle probe, or CMM for that.

It might depend on the 2nd order requirements and/or tolerances. Is there a circularity tolerance given? Is it supposed to be a slip fit or an interference fit? Bore out-of-round by a couple tenths might be (functionally) OK if it's an interference fit, but not a sliding fit.

Regards.

Mike

 

[tay2daizzo8]

Gage pins are normally M+ or M- meaning nominal dimension plus tolerance or nominal dimension minus tolerance (amount of tolerance depending on the class of gage pin). On a perfectly round hole, I find I need at least .0001" clearance to get a gage pin to slip in. Line to line (no clearance) won't go. Are you sure your hole is round? IMHO a pin is a better indication that the hole is not undersize at all points (better functional fit gage). 3 sided tri mics don't find out of round occurrences as well and a 2 point bore gage. I always try to gage my parts the same way the customer is gaging the parts.

when we took the job the customer said they were going to inspect via CMM. the bore mics match what we get on the CMM. obviously we cannot check the part in the machine with the CMM so the mics have proven over years to be a good stand in.

My issue is now they are using a gauge, and while i agree the bore may be a little out of round, its still in spec when rotated.
Mind you the need for a 8 finish screams not to push a gauge down the length of the bore.
there is no roundness or straightness called out

 

[tay2daizzo8]

Large pin gages, IME, will rarely go nicely into a bore unless the gage is a few tenths smaller than the bore being measured. I don't know the technical reason, just have given up trying to measure larger bores with pins. ID micrometer, spindle probe, or CMM for that.

Mike

Exactly my experience this far. the customer has had a bunch of turnover and im afraid this is the consequence.

i dint know if there was a specific spec that said you need .xxxx clearance to make it down the hole.

if they have a M+ gauge and i need .0002" clearance(for example) then i really only have .0001 to hold.

My whole issue is the change in inspection method, had they said from jump they would be using a gauge, then i would have gone that route.

 

[CatMan]

+/- half a thou is pretty tough with a pin gauge.

I'd like to see a dial bore gauge (with master ring) in that application. If it's a steady part, then yes, air gauging would be wonderful (with master ring). And get one of those new electronic air gauges with the different colored lights. No bouncing ball air gauges.

 

[gustafson]

I can see a pin being more fussy, in addition to size it must also be round and straight.

But also more subjective, a tiny bit of oil or something and it doesn't go.

If they want it gauged a way, then maybe they should supply the gage

Sometimes walking in and understanding what they are doing, or what the part is doing can be instructive.

Perhaps they have been having trouble with this part all along and have not communicated it to you because well, the parts measured right.

But of course you cannot tolerate random measurement standards

 

[MCritchley]

The customer sounds like they have no idea how to tolerance a part. No roundness or straightness tolerance on a half thou callout? The customer should also understand any change to the drawing will add cost. So, what are they really after other than a quicker inspection?

 

[Mtndew]

Have them supply the gage and make the bores fit their gages.

 

[Zeuserdoo]

An 8 finish on 300 series huh? After using a gage pin, not anymore. It sounds like the customer has no idea how easy it is to ruin an 8 finish.

 

[tay2daizzo8]

+/- half a thou is pretty tough with a pin gauge.

I'd like to see a dial bore gauge (with master ring) in that application. If it's a steady part, then yes, air gauging would be wonderful (with master ring). And get one of those new electronic air gauges with the different colored lights. No bouncing ball air gauges.

not +/- .0005

its .0005 total( +/-.00025)

 

[Dan from Oakland]

Even at .0005 total, CatMan's post is the place to be IMO.

 

[triumph406]

not +/- .0005

its .0005 total( +/-.00025)

I do a part 1.875 dia, +/-.0002 that gets finished on the hone. I make go/nogo gages on the HLV, on the gages the first 3" are .002" undersize, so by the time the go/nogo part of the gage gets to the bore, it's square to the bore, that way I don't damage the bore by trying to 'wiggle' the gage into the bore, also as it can't tilt in the bore it doesn't get stuck.

I prefer the shop made gages to bore mics everyday of the week.

Using a CMM to measure a bore to +/-.00025 tolerance seems ludicrous to me. That opinion being based on some the people who've worked in inspection at places I've worked and run CMM's.

 

[tay2daizzo8]

I do a part 1.875 dia, +/-.0002 that gets finished on the hone. I make go/nogo gages on the HLV, on the gages the first 3" are .002" undersize, so by the time the go/nogo part of the gage gets to the bore, it's square to the bore, that way I don't damage the bore by trying to 'wiggle' the gage into the bore, also as it can't tilt in the bore it doesn't get stuck.

I prefer the shop made gages to bore mics everyday of the week.

Using a CMM to measure a bore to +/-.00025 tolerance seems ludicrous to me. That opinion being based on some the people who've worked in inspection at places I've worked and run CMM's.

i like the idea of the tapered pin, but i dont have the room at the bottom of the bore for this. there is a smaller thru hole.

air gauge would be nice, maybe ill add it in to the cost and see if they change their mind

 

[michiganbuck]

I have made so many plug gages and GO/NOs even down to 6 to 12 millionths that it seems like apprentice work.
That might be tough on a lathe but on a 13 grinder or the like it is not tough at all.

That is why the OP's customer went to a plug gauge..they are really close.

 

[Conrad Hoffman]

IMHO, print needs more specs. Also, not wanting to read this whole thing again, did anybody mention inspection temperature and how to handle the part? Whenever a pin won't go, and you think the size is OK, it has to be straightness or roundness. With a good hole and good pin, it will drop in at less than 0.0001" diametrical clearance.

 

[Milland]

IMHO, print needs more specs. Also, not wanting to read this whole thing again, did anybody mention inspection temperature and how to handle the part? Whenever a pin won't go, and you think the size is OK, it has to be straightness or roundness. With a good hole and good pin, it will drop in at less than 0.0001" diametrical clearance.

Yup, temperature, and also how the part is being held during cutting. If in a chuck, it could be fine while constrained, then lobular when free.

For this tolerance and finish, I'd want to rough bore, then hone unconstrained to size.