Polycarbonate Machining - close tolerances

[Larry1958]

I am in the process of trying to machine unfilled Polycarbonate. This particular part is about 1-1/4" dia x 1-1/8" long. This is a lens barrel and tolerances of dias, seats, and geometric dimensioning of +,-.001, perpendicularity of .0005, wall thickness of finished part is about 1/8", multiple dias., seats. I am getting annealed stock but was wondering if these should be roughed 1st, then stress relieved or let sit for a couple days prior to finish machining. Worrys are thermal expansion and dimensional changes after finishing. Any help with people that have experience with this would be greatly apprciated. Thanks in advance.

[crazy^millman]

When in doubt follow standard practices to give the best results. Now if it was quoted with 1 op taking 5 minutes then good luck. I always approached these jobs with what are all the things that can go wrong. Think about doing everything to ensure I made the best part possible then eliminate steps or operations as I seen they were not needed. Could you get away with a 1st op finish 2nd op done? That is always a tricky question and if I was never sure I would look at my delivery, my time allotted for the job and then make my decisions from there. Most time people quoting jobs have no clue and under bid. Then you are left cutting corners trying to make something bad work. I also looked at it this way a whole lot easier to take material off to make something right then put it back on.

 

HTH

[Teh Bear without Brains kinda idiot]

I am getting annealed stock but was wondering if these should be roughed 1st, then stress relieved or let sit for a couple days prior to finish machining. Worrys are thermal expansion and dimensional changes after finishing. Any help with people that have experience with this would be greatly apprciated. Thanks in advance.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Once I was in need to do roughing of policarbonate two times roughing and semiroughing .

First part broke itself apart from internal stress relieve

HTH

[Jayson Kramer]

I used to actully take it a cook it in a pizza oven for bout 3 hours at about 300 ° from the stock plate. now are use using the the blue stuff or the higher end clear stuff.

Here is some stuff I used to do.

[crazy^millman]

Jay, I never got down the art of Vapor Polish, but Javier that I worked with was the Master at that stuff. I gave it a try and melted 8 hours of work real quick.

[Larry1958]

Thanks Guys,

This is a product that we have outsourced in the past. We dropped the ball on getting order in on time and are forced to make the product in-house this run. Not a prototype part (300pcs) also the color is black so no Vapor Polish is required. From the history from our vendor and receiving inspection we have had multiple issues with non-conformance. Think I am getting in too deep with these parts and may need to consult with Engineering(yuk). Can annealed stock be roughed and then stress relieved? Does anyone know a good source on the web to get this information? Thanks.

[Newbeeee™]

Here's some good info

http://www.boedeker.com/anneal.htm

[Larry1958]

Thank you neebeeee. Good info.