Gear cuting

[Roger HulettParticipant @rogerhulett83124]

[Roger HulettParticipant @rogerhulett83124]

I need to make 4 small identical spur gears. Is it better to mount each blank separately on the mandrel (it is a horizontal mill) between the rotary table and tailstock, or, mount a sufficient length of material to cut all four in one go and then part off ? Thankyou

[Phil PParticipant @philp]

Make four blanks and mount them on a common mandrel and cut all the teeth at one go.

Dont try parting off finished gears.

Phil

[Roger HulettParticipant @rogerhulett83124]

Thankyou very much for such a prompt reply. Will take your advice.

[Roderick JenkinsParticipant @roderickjenkins93242]

Well, I think it depends on both the size of the gears and your parting arrangements. These 2 chaps were cut on the same blank and then parted off using the rear toolpost on my S7. No problems but they are only 48DP. Clearly there could be issues with an interrupted cut with a large, coarse gear but I have successfully parted off square stock before now.

Cheers,

Rod

Edited By Roderick Jenkins on 07/08/2015 23:32:49

[JasonBModerator @jasonb]

The companies that sell pinion stock may well agree with you Rod

If you are going to put them all on a mandrel make sure they are tight, I remember someone posting where they had done similar and the gears had slightly rotated on the mandrel giving a very slow helix

[Nigel McBurney 1Participant @nigelmcburney1]

If the method of stacking multiple gears on a mandrel is used,the faces of each gear must be parallel within close limits otherwise the mandrel will bow when the securing nut is tightened, I make gears for full size stationary engines and very often make multiple gears,best method is to turn one end of length of bar (steel /brass) to make say three or four gears ,cut the teeth, in the dividing head ,mount in the lathe and part off, then if the no of teeth is a multiple of 3 they are held in the 3 jaw chuck ,bored to size,and parted off , size -up to 2 .5 inches dia and 10 dp, for accuracy I use a newish 3 jaw kept for this type of work ,for odd numbers of teeth ,they are held in soft jaws. Providing one is careful there should be no problem with parting off provided the lathe used is up to the job . The problem of gears rotating slightly on the mandrel is usually due to the cutter teeth on one side of the cutter being blunt due to hitting a tough spot on a previous job .a problem when buying used cutters from a boot sale. The blunt side of the cutter tends to push the work to one side.The multiple cutting does save time during the dividing tooth /cutting stage as the bar is solid and heavier cuts can be taken .For cast iron gears I use sawn blanks as the cast bar is rough and far from round.

[Neil WyattModerator @neilwyatt]

When I've done this, I turned the blank with the bosses in place, rather like a camshaft with no lobes. It means a lot less work for the cutter and you can tidy up the edges of the gears easily.

In many ways it depends on your ability to accurately bore the centre hole for all the gears while they are still on a stick.

Neil

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