parts .025" off size

DMF_TomB · Jul 21, 2016

had some little parts made and i notice no way they will fit. they measure .775 rather than .750 diameter
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i can only assume machinist mistakenly read micrometer wrong. even cheap HF digital micrometer has numbers to read then read barrel for .001 and .0001
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i am assuming machinist used a old Starrett mic the old ones with no digital counter on them. not saying machinist did not make a mistake. still kinda annoying to setup big part weighing over a ton on big machine and i cannot install little parts only 1.5" long
.
to me it would be cheaper for boss to buy digital or electronic micrometers. no excuse to make bad parts cause machinist misreads micrometer .025". and no i have no interest in getting a machinist fired who made a mistake. like who does not every make any mistakes ? still very annoying as i will have to probably remove 1 ton part and 1 ton fixture already setup. last time took a month to get little parts.

Atomkinder · Jul 21, 2016

1) Okay?

2) If the guy gets fired for screwing up one part, maybe it's more than one part.

3) Did you check the parts before you set up for the assembly?

DMF_TomB · Jul 21, 2016

Atomkinder said:
1) Okay?

2) If the guy gets fired for screwing up one part, maybe it's more than one part.

3) Did you check the parts before you set up for the assembly?

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12 little parts all consistently around .775 and not .750, at least he is repeating
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no i did not check parts before setting up. normally they vary +/-.001
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in hind sight yes i should have checked them before setting up. that is something new for me checking for gross out of tolerance parts. learn something new every day i guess.

HuFlungDung · Jul 21, 2016

Yep, I've done that a time or two. Now I always quick check my progress with a digital caliper to make sure I'm in the right ballpark, then to the micrometer.

yardbird · Jul 21, 2016

A lot of times I will throw some calipers on a part I'm measuring with a mic just so that doesn't happen.

Maybe he did that job right after a liquid lunch?

Brent

DMF_TomB · Jul 21, 2016

HuFlungDung said:
Yep, I've done that a time or two. Now I always quick check my progress with a digital caliper to make sure I'm in the right ballpark, then to the micrometer.

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yes i carry a $20 4" electronic digital caliper on me for quick checks. sure might get reading .001" off but it tells me quick if i am in the ballpark. machinist has i believe a dial caliper too but must have just used the micrometer

Porschefix · Jul 21, 2016

Digital schmigital, I'd guess anyone who could make a mistake on a dial micrometer could make the same mistake on a digital. Doesn't it really boil down to care, procedure and pride in ones work? You don't know what sort of day the guy was having maybe his child is sick or something, but you're ready to bust his butt for a mistake? Where is the QC dept., if that means you then where were you?

I don't know about you but I'd be real introspect about fault before throwing someone else under the bus. At least you admitted you could have checked the parts. Gotta give you that.

Like my dad used to say, "Did ya learn anything from that?"

DMF_TomB · Jul 21, 2016

the part is threaded .750-16
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not sure how he used a thread die even on a lathe with parts measuring .775
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you would think he noticed on a turret lathe the die resisting starting threads

Larry Dickman · Jul 21, 2016

Sounds like a dial caliper that skipped a tooth.

Chip Chester · Jul 21, 2016

Always good to check the drawing the part was made from... all good there?
Their outbound QC? Your timely inbound QC?
I know it can be challenging to set aside the time for stuff that's regular and low-buck, but here's why it's still important...

Chip

HuFlungDung · Jul 21, 2016

Porschefix said:
Digital schmigital, I'd guess anyone who could make a mistake on a dial micrometer could make the same mistake on a digital.

Highly unlikely. The error with a digital could be anything due to a bad zero, so there would be no reason for the error to round off at .025". If you've ever done it, you'd understand that sometimes, most times, you see what you expect to see and not what is actually there.

comstockfriend · Jul 21, 2016

Had a customer QC guy (Fortune 500 company, aerospace, nuclear) oversee me measure some centerless ground electric heaters. All measured on a dial caliper 0.496-0497, right on the money for these elements. He takes the calipers and a handful of elements and proclaims them to be about 0.045 under that. We pass the calipers back and forth once or twice before I see the idiot is measuring in the notch under the measuring anvils. Of course, he's QC, NOT a machinist!

John

Johnny Larue · Jul 21, 2016

been there done that...but have him check that screw on the top of the mic it comes loose sometimes and can throw it off...also I would wipe each anvil and check zero....digital I don't use as you can be off with those without knowing...with a mechanical mic with threads....its all you baby...win or lose...but if its off .025 and its threads that were done in turret lathe with a die...he mighta forgot to click it down to finish cut after the rough pass or touched off with a sharp tool and forgot about the flat on a 3/4-16....without looking it up I think its like .015 or .02...my 2c

Porschefix · Jul 21, 2016

HuFlungDung said:
Highly unlikely. The error with a digital could be anything due to a bad zero, so there would be no reason for the error to round off at .025". If you've ever done it, you'd understand that sometimes, most times, you see what you expect to see and not what is actually there.

I understand what you're saying, I have done it, I admit to being careless (tired, preoccupied, daydreaming, whatever) at times too. The first thing my dad taught me in the machine shop was to read a mike. He always said read what you see, not what you want to see. How is it that you couldn't see .775 when you were supposed to read .750? I'm saying that because I have done it. My point is if you're being careless all bets are off. The more I do this machine shop gig the more I know how important it is to be alert and present at all times Danged if I still don't screw up, just not as badly as I did when I was a young whippersnapper.

Tyrone Shoelaces · Jul 21, 2016

Yeah we've all seen that.

A foreman friend of mine gave a job to a turner when the owner of the company wanted to give the job to a family friend.

The first job the new guy did was to turn 20 really expensive forged rings about 15" dia. He bored them all perfectly 0.025" oversize. Easy miss reading of the inside mike. All bang on every other size but unfortunately they were all scrap !

I found out when I saw my foreman pal sat in his office with his head in his hands !

Of course the owner wanted the new guy fired right away.

My pal saw that every other dimension was bang on and therefore really stuck his neck out for the new guy to be kept on.

The new guy later turned out to be one of the best five turners I ever had the pleasure to work with.

Regards Tyrone.

specfab · Jul 21, 2016

DMF_TomB said:
the part is threaded .750-16
.
not sure how he used a thread die even on a lathe with parts measuring .775
.
you would think he noticed on a turret lathe the die resisting starting threads

So the parts are actually threaded .775-16 instead of .750-16. Much harder to see how you would end up with parts said to be good from the guy that made them. Sounds like absolutely zero checking going on there for the thread functionality. That's not just a mis-reading of a micrometer, that's a full-blown total assumption that "the parts I made are perfect, no reason to check anything".

John Welden · Jul 21, 2016

It's stupid to use anolog mics unless you have to get in small space.

Digital is more efficient and way less prone to mistakes.

steve45 · Jul 21, 2016

DMF_TomB said:
the part is threaded .750-16
.
not sure how he used a thread die even on a lathe with parts measuring .775
.
you would think he noticed on a turret lathe the die resisting starting threads

What makes you think he used a die?

Since it was a screw-up, I think that the shop should move fixing your parts to the front of the line and get them out immediately.

DMF_TomB · Jul 22, 2016

specfab said:
So the parts are actually threaded .775-16 instead of .750-16. Much harder to see how you would end up with parts said to be good from the guy that made them. Sounds like absolutely zero checking going on there for the thread functionality. That's not just a mis-reading of a micrometer, that's a full-blown total assumption that "the parts I made are perfect, no reason to check anything".

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parts done on turret lathe with a thread die the threads are .750-16 although he must have struggled to get die started on .775 diameter
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i prefer mechanical digital mic. in 36 years it has never failed to give a good reading. many common mics the lines are close to either and hard to tell which .025 some times. some mic barrels can shift side ways to better align the barallel lines. i use tri inside mics all the time and it is a simple single set screw and you can put barallel with mic lines any where you want. other micrometers they give special wrench but it turns hard and difficult to shift sideways a small amount to line up lines better

toolsteel · Jul 22, 2016

DMF_TomB said:
.
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parts done on turret lathe with a thread die the threads are .750-16 although he must have struggled to get die started on .775 diameter
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i prefer mechanical digital mic. in 36 years it has never failed to give a good reading. many common mics the lines are close to either and hard to tell which .025 some times. some mic barrels can shift side ways to better align the barallel lines. i use tri inside mics all the time and it is a simple single set screw and you can put barallel with mic lines any where you want. other micrometers they give special wrench but it turns hard and difficult to shift sideways a small amount to line up lines better

Sounds like there is a good chance that there is a screwed up die floating around the shop now too.....
Since its not your responsibility to discipline whoever screwed up, I wouldnt worry about whether the guy gets fired or not......thats his problem, and if he gets fired over 1 mistake then you will be doing him a favor, he should get out. If he has screwed up so many other things that this is the straw that gets him fired.....then you are doing yourself and the company you work for a favor.

parts .025" off size

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Johnny Larue

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