counterbore/countersink Plastic Injection 1

[NathanLee]

Does anybody have any experience/direction with this question. Regarding DFM, design for manufacturing, would a plastic injection operation w/ glass nylon have an easier time spitting out widgets with counterbores or countersinks if it otherwise made no difference. Are the holding power between comparable holes the same between c-sink and c-bore? i would guess c-bore as the tool won't require the sloped surface but I haven't the experience/education to tell me the answer. any help would be greatly appreciated!! thnks!!

 

[Barry1961]

As far as the die goes it won't make enough difference in cost to matter. The counterbore will have a slight taper/draft also.

If you use counterbore make sure the contact area between the bottom screw head and the lip of hole is large enough not to yield the material. This is mostly a problem when using SHCS and oversized holes.

If you use countersink ensure your tolerance stack is close enough not to allow unwanted loading when screws are torqued.

It really depends on the part and what the part connects to. You might need counterbore with room for steel washers.

Barry1961

 

[ornerynorsk]

You will have greater ejection force on a counterbore than a countersink. Not a big deal unless you have a fragile part.

 

[MikeHalloran]

DFM teaches that the ideal number of screws in an assembly is zero. You therefore should not waste your time screwing around with screws, but should concentrate on replacing them with tabs, slots, snap fits and other self- fixturing and self- retaining features.

Assuming you have done that, and must have screws for political reasons ....

Counterbores and countersinks are both produced by core pins, and it is usually a simple matter to modify or replace core pins in a given mold, so you can try it both ways if you wish.






Mike Halloran
NOT speaking for
DeAngelo Marine Exhaust Inc.
Ft. Lauderdale, FL, USA