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Rant: Customers don't follow their own tolerances

ToolmakerTH

Plastic
Joined
Jul 19, 2022
Just want to rant and get this off my chest because I am dealing with the same shit with multiple customers at this moment.

I have been gaining new works from both old and new customers this past year, so I have been doing alot of sample pieces for them before we go into production. This week, there are 2 cases of rejects from 2 different customers, both are repeat customers.

Case #1 - The sample parts were rejected due to threaded holes being "too loose". They checked with Go NoGo gauges just like I did and they passed the gauge inspection. However, they said they think there is too much slop even if the NoGo gauge can not go in. Well, isn't the point of Go NoGo gauges so you don't have to use your judgement?! What worse was that they cut the part to see the cross section of the thread and saw that the threads were not pointy because I used a roll tap, which they have no idea what the process is. I explained the technical to them and showed them videos of thread rolling. They still didn't care and proceeded to blame the thread rolling process for the "loose" thread. Now, how am I going to measure the threads if I have to go by their "feel"?

Case #2 - This is a very simple pin part. The diameter tolerance is not difficult to machine at all. The part was machined on a cnc lathe and passed all the inspection. Customer's QC gave these parts OK. But their engineer rejected the part. He wants the diameter to have 3 microns straightness and roundness even though there is no callout at all and the diameter tolerance is alot wider than that. I stood my ground and I told them to make revision to their drawing and I would quote it again. The engineer doesn't have authority to make a new design because it came from their oversea headquarter. He still insists on his tolerance though.



Enough ranting for now

How are you guys doing?
 
On your rolled thread is the minor in tolerance? If so, it's to spec. You could try lightly peening the top thread to make it feel tighter.
 
Go / Nogo gages have many different tolerances. Maybe they want you to use a tighter thread.

Classes 1A and 1B are considered an extremely loose tolerance thread fit. This class is suited for quick and easy assembly and disassembly. Outside of low-carbon threaded rod or machine screws, this thread fit is rarely specified.

• Classes 2A and 2B offer optimum thread fit that balances fastener performance, manufacturing, economy, and convenience. Nearly 90% of all commercial and industrial fasteners use this class of thread fit.

• Classes 3A and 3B are suited for close tolerance fasteners. These fasteners are intended for service where safety is a critical design consideration. This class of fit has restrictive tolerances and no allowance. Socket products generally have a 3A thread fit.

I had used the wrong go / no go gage recently and had to order the correct one to make sure I was making good parts. I would have send bad threads out if I went with the gages I had in house.
 
In case 1, I would drill and tap a part to high limit of the specs and send it to them as an example. This may change their thread rolling issue. If they want a certain feel, I would inform them you need a number range to shoot for and they would need to supply thread gages that correlate to that range. You will also need to requote accordingly if it's more of a PITA.

In Case 2, we actually deal with this regularly with a customer. They send a statement of work with the print that will note any additional tolerances/info not on the print. They do this because getting approval to make the print changes for some of the parts is extremely difficult. I'll hand write this on the print and save it for future jobs, then validate each time a new SOW comes in. Of course you will have to adjust your pricing accordingly.

As far as rejecting the parts, I would inform them they are to spec from what was ordered and stand my ground. Then tell them you will need to requote the work and they will need to send a new PO for the changes. Any customer worth keeping will understand this.
 
Alarm bells would be going off in my head over this because I've experienced this before. I don't think it's a coincidence that you've got this from 2 different customers in the same week and we are facing a recession!?
Have they hit you up with a "We'd be willing to accept these defective parts for a discount." yet? I don't know your situation but if you can afford it, play hardball.
 
I will say with roll taps the id can be oversize and it will still make the gage
Make sure the id is good to make sure you are correct, then tell them the gage rules, 'tighter' is not a tolerance

AS mentioned above, requote with a signed not from the engineer, if it doesn't conflict with the drawing[other than being tighter] the price is the only problem
 
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As far as #1 goes If the minor Ø is good and the hole gages good with the thread plug gages. The part is good! If they want a different thread fit they should spec It on the print. We read prints here not freaking minds.

#2, They can't dream shit up after you've quoted and manufactured parts to their print specs. If you want It around here you better have It on the print or don't whine about It. Again we're not freaking mind readers. Put It on the print or forget it!
 
#2, They can't dream shit up after you've quoted and manufactured parts to their print specs. If you want It around here you better have It on the print or don't whine about It. Again we're not freaking mind readers. Put It on the print or forget it!
That's going on right now with one of my customers. Thru hole in (bar stock) part, called out on
drawing as 1-1/8 Drill and it's 9" thru. (Fractions are listed in the tolerance box as +/- 1/64. Part that fits in hole, is 1-1/8 CRS, drawn as a fraction, see above. When the 1-1/8 bar wouldn't fit in the spade drilled hole, they changed the print to 1.133 Dia +.001/ -.000. (Again, 9 inch deep hole) going forward. I guess expecting that at same price as before. Not going to happen on my end. Other features were rejected that convinces me the operative doesn't know what a 'tollerence box' on a drawing is, or what it's for.
 
Other features were rejected that convinces me the operative doesn't know what a 'tollerence box' on a drawing is, or what it's for.

Only somewhat related but "typical", you might think :

Once upon a time I fired a customer politely, because they were nice but also pain in the ass cheapskates and slow pay. So I gave them all the tools and fixtures and even spent an afternoon going over how I made the parts so they could do themselves. Yay, got that money-loser out of my hair.

Went by there a few months later and happened to see what they were doing ... parts did not look as nice. Funny thing -- all that excess finish work that made them look nicer but didn't improve function ? With them doing it, wasn't so important after all :D
 
Another one, different (brief) customer from long ago. Puck shaped part, 2) 1/2-13 threaded blind holes on one of the 'face' sides of the part. Holes are dim'd as +.000 -.005 center to center (on threaded holes).
So I drill & tap like 4 parts on BP mill, send them off. Rejected on C to C distance. So I make studs with a turned dia to mike across, snug threads. They measure .002 wide but within .005. I send them back as 'different' pieces, and I ask how they are measuring the distance......dial calipers. I tell the go-between sales rep who's job it was, that I am confident they are within spec as I've checked with other than dial calipers. A week later he calls and says they'd like me to call them and explain in detail how I am measuring the distance. ......Oh.....hell no, you figure it out, I already have. Next order, wacky engineer now has +.000 -.002 on the drawing. Nope, stop the trolley, here's where I get off ! Customer.....fired.
 
When I started doing this in the 90's I messed up a run of parts for minor diameter being out of spec. I was a rookie and admittedly didn't inspect that.

Now all my thread gage drawers have an accompanying no-go pin to make sure minor dia is not oversized for spot checking. We record actual minor diameter on First Article Inspection sheets.

I have a part-time guy that also works at another shop doing work for big-name semiconductor companies and he tells me they never check minor diameter. Kind of blows my mind.

Are ya'll checking your minor diameters religiously?
 
On your rolled thread is the minor in tolerance? If so, it's to spec. You could try lightly peening the top thread to make it feel tighter.

Yes. This is M14x1.5 thread. Usually, minor diameter would be 12.5mm. I knew this customer's QC likes the Go thread gauge to go in smooth so I even made the thread minor diameter to be 12.3mm (checked with pin gauges). They still feel it's too loose.
Go / Nogo gages have many different tolerances. Maybe they want you to use a tighter thread.

Yea this is Class 2 JIS standard. We even agreed on the model and brand of the thread gauges we would use.
 








 
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