Concentricity on Gears

You can find it in DIN 3961. It depends of the piece diameter, the module and the general quality you want to have.

Concentricity on plastic parts can be affected in several ways. Parting line mismatch may casue parts to be misaligned (look for flash or raised parting line). To measure the concentricity, you might use the proper pin for the pitch diameter and rotate the part on the shaft over Top Dead Center giving you a measure of the shaft to gear concentricity. Another thing that you may wish to look at is any drags or pulls on the mating parts. This is often caused by a lack of polish on the die and the part sticks at ejection. The part is still somewhat plastic and can distort. If I can help, let me know.

best

It depends on whether the plastic is cast with formed teeth, or the teeth are added later by machining. I presume the former.

The A.G.M.A. standards cover all series, DP, CP, MP in all of their forms. Each numerical value of the standard indicates index error, pitchline runout, accuracy of tooth involute curvature, axial runout, etc. and takes all of the errors of these components into the numerical value, i.e. A.G.M.A. 12 is made to closer tolerances than A.G.M.A. 10 and is classified as a precision gear with ground teeth, whereas the teeth of the A.G.M.A. gear may be produced with a gear hobber that is in excellent condition.

The accuracy of all gears is covered by this set of standards for gears made and used in the U.S.A. In other countries, either the I.S.O. or D.I.N. standards will apply.

Aside from purchasing an expensive Fellowes gear tester, there are some other testers on the market that will provide a quick determination of pitchline runout through the mating of a master gear that is connected to a precision test indicator. But this only measures pitchline runout, and will not measure "wobble" unless the master gear is moved across the face.

In short, you need to determine the quality of the gears that you need, and assign a standard and designation that will ensure this quality is maintained. Myself, for a moulded gear I would examine the cooling cavities of the mold in order to determine whether there is uneven colling and therefor even, yet not shape-consistent shrinkage.

Ing. Robert Forbus

You could try speaking with Mike Stiglanese of Dimension Molding.

Mike is an expert in molding gears. He has done a great job for me in the past. You can have the best quality tool available, but with the wrong gates and design you will finish with a bad part.

http://www.dimensionmold.com

630 628 0777