gear cutters and compatability to cut gears just out of their range

[brickyParticipant @bricky]

I am about to start cutting 4 gears for my engine .the gears are 18/24  32/48  my question is will a No6 cutter 17/20 also do to cut the 24 tooth gear,  and will the No 3 cutter 35/54 cut the 32 gear.

[JasonBModerator @jasonb]

Watch your numbering on the MOD cutters as they work the opposite way to DP cutters.

For the small load and likely small use the timing gears will get it won’t make a lot of difference particularly at the small 0.5MOD size. You may find you need to make a small adjustment to the PCD of the gears once cut or if you already have that fixed by the crankcase then a bit of trial and error with the total depth of cut may be needed to get smooth meshing.

Though given what you can pick up a set of small MOD cutters for I’d buy what is needed or get an equally cheap off the shalf gear for the ones your cutters don’t suit.

I’ll now go and take cover.

 

[brickyParticipant @bricky]

Thanks Jason for your input I do have the two cutters I will need and It will save me buying two more cutters.

Frank

[Julie AnnParticipant @julieann]

An involute gear cutter has the correct tooth form for the smallest tooth count in its range. Consequently as the tooth count rises the tooth form cut has slightly too much curvature.

Using the 17/20 cutter to cut a 24 tooth gear will result in a tooth form that has too much curvature. Using the 35/54 cutter to cut a 32 tooth gear will result in a tooth form that has too little curvature.

The gear with too much tooth curvature will run with higher count gears albeit with some noise. The gear with too little curvature may not run without increasing the centre to centre distance, or more simply, cutting the teeth slightly deeper. The effect of cutting deeper is to increase backlash. I can’t remember the formula but should be easy enough to look it up as an exercise for the student.

Julie

[brickyParticipant @bricky]

Thank Julie Ann for replying and I will use your advice and cut the gears deeper, as these are compond gears for 2-1 reduction from crank to camshaft I am not to bothered about the noise facter as the engine if it runs will not be run often.

Frank

 

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