Outside diameter divided by (tooth count + two). = MOD

So, 78.5/(57+2) = 1.33

Centre-to-centre of the gears must be correct, too – and every different tooth-count gear of any particular MOD will have a different diameter….

Looking at the PDF I have, the gears are 1 MOD. However I have noticed one gear has the wrong outside diameter.

Regards

Gray,

The large 57T gear on the diff and the gerbox output are a different size to the other Mod1 gears, as said about 1.33MOD. Probably best to start with the PCD and see what you can get to fit.

If you think that is bad take a look at the ones for teh Robey cane crusher that are being published at the moment, all odd gear sizes

So PCD of the two gears is 101.90mm or 4.012"

If you went with 20DP and use 22:58T that would give you a PCD of 4.000". Add a bit of fiddling with depth of cut and you could get away with that if you don't fancy making a cutter to the tooth profile shown in the detail

Just applying simple practical experience

EDIT, as the Gearbox is mounted on slotted holes you don't have to be too worried about exact PCD so if you want to stick with cheap MOD cutters than 1.25MOD and a ratio of say 22:59 would give 101.25 so the 0.65mm difference is easily taken up by sliding the gearbox

PS do check my hurried maths as I'm meant to be off out working.

Edited By JasonB on 12/07/2019 08:17:00

Hi John,

The gear I looked at quickly yesterday morning which for 1 Mod is wrong is Pinion 4-24. Today I see the note "same profile as 3-18", (there is a lot of info on these drawings). These two gears are made using the profile shown in the small drawing on Gear 3-18. From the details given I do not think these gears are of an Involute form. I think they are intended to be a Cycloidal form, the same as the Clock Makers use. Making such cutters to use in a flycutter is simple. Using 1.25 MOD will not give the tooth thickness specified, ie 2.5 mm. From what I have worked out the tooth thickness will be 0.25 mm smaller, but still larger than gap cut by the 1.25 MOD cutter, which is 1.9635 mm.

The gears can be cut using 16 DP as the base but with 16 teeth on the pinion and 48 teeth on the gear. O/D of the pinion will be 28.57 and the gear 79.37 mm, not that far away from what is drawn.

Regards

Gray,

.

Thanks, Jason

Now at least I know that the 57 tooth gear is driven by a 19 tooth

Busy drawings aren't they

MichaelG.

You have two roads that you can follow.

1. One is the make a cutter as per the details on the drawing and cut the 57T & 19T or to another shape and adjust tooth count to suit. Cut the rest with your MOD1 set.

2. If you are ordering a set of cutters then they will have what is needed to do a 25T:77T MOD1 for the two gears in question so you could do them all MOD1

So really upto you if you want to have a go at making a cutter or not. maybe check what tooth numbers you can produce with your indexing/dividing setup and base your decision taking tat into account as it is not worth making a cutter for 19T if you can't get 19 divisions. If the single point cutter doe snot work out you can always fall back to cutting them all MOD1, for the use they are likely to get I can't see the smaller teeth being much of an issue.

Michael, glad I'm not the only one who thinks Julius likes to use as few sheets a possible

Hi John,

I have sent you a PM

Regards

Gray,