Injection molding draft

[jonnyton]

I am attempting to setup an injection molding project with polypropylene. I would prefer that the sidewalls be 90 degrees to guarantee a snug on the part I am designing it to fit. However, the design program said that the sidewall should be 92.00 degrees in order to be released from the machine. How true is this? COuld someone elaborate?

[Tech2]

Good question. It's hard to give an exact answer for these types of issues. It depends on the geometry of the part. Generally the rule of thumb we use is that you can get by with 90 deg on walls up to 1/4" high. You can also go 91 but the more you push the limits the more likely there will be problems. If you want to post a 3D image and give the overall size it might help.

Another option for round shapes is to go 92 and add Comments To Machinist to CNC turn the outer wall to 90, but of course that adds cost.

Another option is to add geometry as in a collet which has slots that allow the 92 deg walls to "spring" to 90.

Or to go 92 on the mating part for a taper fit.

[jonnyton]

I don't want to post too much information about the part. However, the main body of the of the item is what I am concerned about. It is a cylinder that has an 18mm outer diammeter and has a height of 20mm (90 degrees sidewall)(z). It is also hollow(90 degrees inner side wall). I can adjust the inner sidewall, but I am really hesitant to adjust the outer. Wht do you think?

[Tech2]

Being round helps and drafting the inner wall helps. It sounds like it might be workable. I recommend to place the order and you will be informed if there are any problems.