gears

[PDM1]

Hi Monty, you are always asked about gear ratios, but this is a different gear question.

How many different types of tooth profiles are there?

In other words, what brand of gears will work with other brands?

I've noticed that GT1 spurs seem to mesh only with GT1 pinions. What about Sonic, Faas, etc.

Thanks for your help.
Paul

[Monty @ B.O.W.]

Paul,

This is getting pretty deep, even for experienced machinists, but you are right: There are differing tooth profiles. The parameter that changes is the 'pressure angle', and conceiveably the range is infinite if the difference in angle is small. I have seen p.a. 's of 14 to 20 used on slotcar gears.

For gears that are 'cut' to manufacture (most metallic gears), the angle is set in the cutting tool, or hob. The apparent angle will change, however, if the gear diameter is purposely fudged to maintain a maximum tooth count in a given pitch. This is common in slot gears. For instance, some 39 tooth 64 pitch gears will give legal clearance with .750" tires, and some won't because some manufacturers alter the pitch slightly to allow a greater range of gearing. Similarly, for ease of manufacture, a smaller gear may be made on a larger blank. Either change makes a small difference in both pitch diameter and pressure angle (the two move so a gear with compressed p.d. has thinner teeth) Pinion size may also be messed with to allow for say, 7 teeth in 64 pitch without grinding the motor shaft down.

Injection molded gears may be a different case, since the mold may be made either by casting around an existing gear or by various CADCAM processes.

In general, one would hope that each manufacturer tries to make his product compatible with itself at least. I know this is the case where I once worked (Sonic). I often use GT1 pinions with Slick 7 spurs, but Faas and Sonic pinions are also compatible. Camen pinions were always my 'gold standard' for Gr. 7 racing. I suspect that plastic molded spurs are much more tolerant than metallic spurs in meshing with different pinion makes.

The safest course of action would be to use a single manufacturer in creating your gearing pairs.