Two months ago we completed our thermocouple connector design and sent it off to the sheet metal factory. They said we would have prototypes by mid June. As expected, they were about one week late, which is pretty normal. Then they wanted more time. We pushed the factory to give us prototypes before the Dragon Boat Festival in late June. Liberties were taken with our specifications and we received a nightmarish batch of thermocouple connector prototypes. A few nail-biting weeks later, we now have proper connector prototypes.
The original design was fairly precise. It's not called out on the specification sheet, but our manufacturer said they could make the connectors better than +/- 0.1 mm tolerance. We were pretty shocked and terrified to see what they handed us. You can see this crusty flap of metal looks nothing like the renderings or the specification sheet.
The second batch is rather pleasing. The connectors are properly coated and all the bend angles are correct.
It looks like the factory had partial tooling complete. The original parts look like they were cut with a stamping tool. The entry tabs and PCB mount tab look like they are bent with tooling. The other bends, however, look like they were done by hand.
Let's do a side by side comparison of the first and second batch of prototypes.
You can see the first photo looks like a sliver from a crusty old tin can. The two internal surfaces mate with the male thermocouple connector and should be parallel. The second prototype can still be improved, but it is not distressing to look at.
The ten connectors int he first batch varied in size considerably. The first picture show the two extremes. Definetly not the +/- 0.1 mm we agreed on. The new connectors look have a consistent size.
The upper and lower surfaces that contact the male connnector are designed to be parallel. In the first picture you can see that they are off by at least a few degrees. This would give pretty terrible thermal contact. The new connectors look precise.
Never pay in full before seeing prototypes. When you have all your corwdfunding money sitting in an account it is temping to pay thing in full and get that out of the way. I know from my past manufacturing experiences to never trust anyone. Companies can fold over night. Charismatic people are willing to take your money and deliver nothing. Just look at experiences of Voltset
. We payed for 70% of the tooling cost for the factor to get started making the tooling. This was a great comfort when we received the first prototypes.
Get it all in writing. I worked with someone to write a contract in both Chinese and English, so the agreement between the factory and Pax Instruments is explicit. When a factory spends more time on a project than they estimated they may decide their work is good enough. It's nice to have a document that defines what is actually good enough.
Own the tooling. We worked it out in the contract that Pax Instruments owns the physical tooling and can remove it from the factor without notice. We had to pay a little bit more for the parts the factory would normally recycle into another set of tooling. It is good to have the ability to grab your tooling and walk away from a bad factory.
Make datasheets. If a picture is worth a thousand words, a datasheet is worth a thousand dollars. Your datasheets are the most important part of your agreement. Datasheets are what defines your product and is the standard for determining if the factory did its job. In this case it was easy to show the factory boss that they handed us crap.
The new parts look good. Once I get back to Shenzhen in mid July I can examine the connectors and begin quality testing. We'll work with the factory to improve any deficiencies or make any changes.
Learn more at: http://paxinstruments.com/thermocouple-connector-prototypes/