We’ve been fighting the fit of two parts. The shaft is purchased, and the part it fits into is machined. The real problem is that the size of the shaft is all over the place, but we can’t control that.
I’ve invested a bunch of time trying to come up with a tolerance I thought would be the best compromise. I also invested a decent amount of money in tight tolerance go / no go gages to check the fit. The difference between the low number and the high number is 0.0005"
A batch of parts arrived on Friday, and the machine shop provided the following after inspecting them.
“I inspected them with the pin gages. They all look good to me.”
To which I replied:
“The no go gages drop right in.”
Machine shop:
“I added 3 tenths because I’m tired of the assembler telling me they are too tight.”
Me:
“So you made that call on your own, without discussing it with me?”
Machine shop:
“I added 0.0003”, that is 3/10,000ths, to the hole to try and help your parts fit.
Fun fac: If you divide a human hair over 13 times, that’s .0003"
I was talking with a machinist once who was explaining that he was off by 0.005", but that it was only the thickness of a hair. We then measured one of the hairs off my head and confirmed that I do have fine hair. It was 0.003". The 0.005" that the part was off was not a problem for that application.
i wouldve lit that guy up… fun fac you dont change anything without approval. return all the parts to them, cancel payment and send them to Triangle Tool where management will tell the assemblers ‘shut up and put them together’ (although we have seasoned tool makers that love doing that stuff)
I wish. More like trying to make enough in the years I have left to cover the debt that I’m partially responsible for if/when this place goes belly up. I’m trying real hard not to think about the salary I left behind in exchange for “equity.” Even if the company were healthy and sales strong, the company is only worth what someone else is willing to pay for it, and that was never going to cover what I walked away from. Live and learn.
The relationship with the machine shop is a mess. All of the principals in the company, and the owner of the machine shop worked together at a previous company. (I went racing for almost 20 years, the rest stayed until that company was bought out by MTS and the NC location shut down.)
Our company purchased the building, and a couple of worn out CNC machines that were in the building. The machine shop rents space in our building, and is buying the Fadal’s as well as paying rent.
The president decided that he can’t be bothered, so the machine shop is in charge of purchasing all machined parts, regardless of whether the in house machine shop makes them or orders them from another supplier (which was the case with the parts in question.) Also, the president absolutely hates any type of confrontation, and certainly isn’t going to make an issue with someone he has been friends with for 30 years.
Going from manufacturability issues to supply chain issues. The hair supply from the top of my head has been in rapid decline over the past decade with no projected recovery as the problem appears to be spreading. As you mentioned, the alternate supply from the jaw region fails consistency requirements; in terms of quality as well as production stability.
