Customer Won't Follow Their Own Tolerance | Machine Shop Talk Ep. 83
ฝัง
- เผยแพร่เมื่อ 10 ก.ค. 2024
- You got the customer’s purchase order, made the parts, and sent them out for inspection. Now, the customer is rejecting them for being out of tolerance - but according to the drawing, everything looks just fine.
This is a difficult situation that no machinist ever wants to find themselves in, and on this episode of Practical Machinist’s MACHINE SHOP TALK, Ian Sandusky from Lakewood Machine is back to answer a forum poster who came on with this exact predicament on their hands.
When it comes to tolerances, on paper - everything should be simple. Make the part to the specifications listed. But, what if the customer wants to go based off of ‘feel,’ or changes tolerances after the parts have already been produced? Typically, good communication can help tackle these issues - but if the customer refuses to budge - it can be a difficult situation to rectify. On this episode, we’ll be discussing strategies to work through these problems, and hopefully prevent them on future jobs.
Have YOU ever found yourself in a situation like this? How did you handle it? Let us know in the comments below!
Forum thread: www.practicalmachinist.com/fo...
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You gave me a smile with that story with the log at the gate! We have two small dogs, and one is practically an escape artist, plotting weekly prison breaks and getting into all sorts of mischief. A few months ago, he jumped on some pallets, hit a spade that unlocked one of the horse boxes, and let one of the horses out, I could almost not believe it when I saw it on the surveillance cameras 😂. Meanwhile, his laid-back partner in crime just tags along like, 'Sure, why not?'
Great post! Helping engineers with machining capability, manufacturability, etc……goes a long way with customer appreciation (help them to help you). I asked an engineer if he meant to have a radius on a drawing vs. an internal corner…..explained the difference between cutting with an endmill vs. EDM……”yea, let’s go with an endmill”.
I’m a cnc machinist and my brother is a mechanical engineer, both in our mid/late 20’s. My brother graduated from an engineering college and not once did he have a class or even a lecture on how to make a print. He started at the company he works for as a graduate engineer and they immediately had him design parts and prints on his own. He often times will send me a draft of the print before he releases it to his shop floor. I think all engineers should start out of the floor or in the field so they can understand what a print needs or doesn’t
I worked with a customer that rejected parts similarly to your pin example. Many features critical to function weren't even dimensioned on their drawings. Their engineers were very good at design, but not so much at creating drawings. After some initial headaches, they turned out to be an excellent customer, even though the engineers never did learn how to detail their drawings well.
The P.O. is the top document. In the pin example tell the engineer to update the P.O. to say "make per engineering drawing 123-4567, rev B
except OD of part will have an
After 40 years in manufacturing and tool & die, this brings back so many instances of miscommunication, engineering inexperience or arrogance, all of which could have been avoided. So much time can be wasted because a phone call wasn't made, an email wasn't sent, or important notes on a drawing weren't added.
When it comes to young engineers, I will always remember having a conversation with a new engineer about the lack of tolerance for a 0.2000 ID dimension on a drawing he sent in. He said there wasn't a tolerance. Zero? He said yes, zero tolerance. Not even a millionth? Nope. I liked the kid and I really tried, but after a half hour of trying to explain something that he should readily understand he still insisted it had to be zero. He wanted them perfect. I had a conversation with his manager, and he told me to get them as close as I could. I asked him to please revise the drawing or put that in writing. He refused. I had a good relationship with the VP of this division and just happened to run into him later that week. I told him the story. New drawings arrived soon after.
I am an engineer, now retired. After retirement, I worked part time for a company that had no incoming inspection. Purchasing always went with the lowest bidder. If they could save a few cents by waiving tolerances or material specs they would do so without engineering buy in. In many cases it resulted in parts that would be potentially dangerous if installed or would have greatly reduced the service life. Each time I found a problem part I reported it to my boss who was head of product life cycle management and copied the head of purchasing. All I accomplished was to piss off purchasing. I gave up a lucrative gig because my conscience would not allow me to look the other way on safety issues.
Worked for a large military/defense contractor for 15yrs. When we got busy, we outsourced a lot of stuff. We had a so-called 'incoming inspection department', who mostly just rubber-stamped the source inspections. Often parts would sit for weeks/months in stock until needed for assembly. Then we'd find the discrepancies. Panic time! We had contracted delivery times. And the stuff was going to the war in the sandbox! But how can you go back to the supplier when our incoming inspection signed off and the bills were paid? Lot's of OT doing rework!
@@pb68slab18 I worked for an elevator company. They made their own worm and gear sets. A field service tech decided they needed to change from an 84:4 ratio to 85:4 to provide a "hunting tooth". He and the shop foreman worked out the details and supposedly informed Engineering. I discovered that if the gear set were made to the drawings, the center distance would be 5/6" too large to fit the gear case. I repeatedly told the VP of engineering that there was a problem and that they needed to send sample gear sets to a gear metrology lab to find out what they were really making and update the drawings. It was not done. The company sold off the machine shop and outsourced the worms and gears. None of the outsourced gear sets fit the gear cases.
Hi Ian,
I work at a small precision machine shop specializing in quick-turn precision prototypes. We often have engineers from new clients that aren't familiar with the machining industry. It is my job to "teach them" the how to make an efficient drawing. It often isn't easy, but in the long run you make a great impression by being understanding and asking them their intent. You have to assume that they know nothing about actual machining. Break it down for them and make it simple. If precision machining was easy, everyone would do it. Nice video!
I had a customer bring their parts and print back to tell me they were out of tolerance. Upon inspection with the customer, after converting their tolerances from mm to inch for them, they realized they were wrong. They requested we remake the parts to new tolerances for free. We declined.
How about a customer with serious revision control issues. It's not uncommon to send this customer a first article and they respond with six different versions of a print labeled "Rev B" marked up in various locations. None of the "Rev B" prints match the print they submitted with the purchase order. We then have to kindly beg them to inspect the part to the print they provided. Halfway through a production they will send a solid model and ask to add "features" from the solid model to the machined apart (the model does not match the machined part or any drawing we have ever seen).
Sadly engineers have not been getting deliberate training in machining or manufacturing for a long time. I have been an engineer for almost 40 years. When I was in school in the early 80's, the University dropped the drafting requirement for my class to 1/2 a semester, and the exam was just draw an orthographic drawing with no dimensions. No GD&T or dimensional analysis. This was pre CAD, mind you. There was NO actual machine shop class available in the engineering school at all. In order to take a machining class, I had to look in the teachers college course catalog to get a class for shop teachers. There were machines available in the labs, but what a sadly abused set of machines they were.
Fortunately for me there was a great staff shop where I interned and the machinists were willing to out up with a green engineer who wanted to learn something. I was also required to work in the drafting room for 3 months making drawings.
To illustrate your point about how a machinist can educate an ignorant engineer, I'll relate a story my Grandfather told. He worked as a tool and die maker in the 1950's. He got a drawing once from an engineer requesting a steel block with a square, blind hole with sharp corners. He asked the engineer if the hole could possibly be circular in profile instead of square. The engineer told him that would be great, it was what he really wanted, but he made the drawing a square because he thought it would be easier to make.
threads are a pain in the ass, we had some problems with minor diameters being undersize with a company, The threads UNS with unj speck so major/pitch/minor .003" undersize, we never checked minor just used gauges, as this company just bought a laser measuring machine it picked up the problem, we had their quality manager out telling us how to check the threads, he did admit they had just scrapped £60k of parts from their machine shop for the same problem, he would not listen when i told him i couldn't produce the thread to them dimensions without increasing the route rad, but you can't do that on a unj , parts put on hold till engineering looked at thread data, works out they never reduced the minor on the drawing so drawing was wrong, as rolls royce parts they have been on hold 5 months now for a drawing change, but the funny thing is, really they are right to thread data just wrong to drawing thread data. so i been told heads are rolling as we have made 1000's of these parts over the years and all wrong to drawing but passed inspection. But as for thread forming we have on RFQs from all the aviation companies we do work for no thread forming. sorry i waffle .
I was an operator at a CNC mill when I had a job to do that was similar to this; no stated tolerances. When the lot was rejected, the customer tried to blame me for the bad parts. But I had a good boss to back me up and show the customer my inspection sheets for the job to demonstrate my duty of care for the work. Found out later that we were sent the previous revision of the part and not the current one (was sent Rev C. not Rev. D of DWG). Scared the heck out of me to think I'd messed up and cost my employer big $$$$$.
Too much stress for s trade that will not compete your wage with McDonalds worker wages😂
Most standard drawing 'blanks' have a listing of ''tolerances unless otherwise noted'' in the lower left information block.
We call tolerances that the customer doesn't want us to abide by and yet insist remain on the drawing "emotional support tolerances".
Im grinding some pistons with 0.0 run-out accross multiple dias on a red pen drawing modden by a new engineer, tolerance used to be 0.5..
Just had this happy and they were picking out the smallest little things.
I worked in tool and die before I eventually received my degree in Mechanical Design. As a designer, most Engineers know nothing about design, let alone detailing a drawing. Most of the Engineering interns at work can't even read a print. Hell, our Quality Engineer has a English Degree. I design gages for him because he doesn't know anything about gages.
Spot on as usual. Great advice, Ian.
Thank you very much sir!
Happens all the time when the process is changed but the drawing isn't
Had rejected parts sent back that were right.
Have YOU ever had a situation like this come up? How did you handle it?
Who takes the hit in the end?? Day light robbery.
How about this trade barely competes with restaurant wages 😮
I think that is really just an American thing
Which rev A?