Hi all,
I'm trying to design a 28 teeth POM gear for an education project. We'll need about 3,000 units, so we decided injection moulding is probably the best way to go. I have several questions:
1) The injection moulder's draft angle is 4 degrees - is it too big for POM gears?
2) I have produced a drawing sheet, but I can't seem to specify the draft angle. Is it typically acceptable to specify the draft angle as a note?
3) Usually, what tolerances are acceptable for POM gears? Is 0.05mm (linear? angular?) too tight?
4) Are tolerances usually specified for each dimension or stated as a note on the sheet?
5) Are fillets needed around the teeth?
Here's the sheet so far:
Does it look adequate for manufacturing?
Any help appreciated.
**EDIT:**
A 4 degree draft angle is too big, so I'll find a manufacturer that can do 0.5 degree.
You make part of my point regarding the draft.
Toolbox gears are only crude representations and are not at all suitable for actual use unless your gears are going to be made from the specifications (which you don't have on your drawing) instead of the geometry (as the molder would want to use to start with). Toolbox gears only have arcs to represent the tooth profile instead of actual involute curves.
Here is a link to a parametric file for a true involute gear profile that you can use: Does Anyone have a Parametric Bevel Gear Model to Share? Just go to the Design Table and set the module, pressure angle, and number of teeth.
0.7 module is a non-standard module. How did you arrive at this? Modules of 0.8 and 0.6 are standard.
You still have not mentioned the pressure angle.
What about the mating gear? Model the mating part and add your draft to see what effect it has on the mesh of the teeth.
You really must do more research on specifying gears or else you will end up buying 3k worth of parts and a mold that do not serve your purpose.