Gear Cutters

[kiwi2]

Hi all,
I need to cut a gear which rotates eccentrically inside a ring gear. The gears are shown in the pictures.
The gears are module 0.3 with the ring gear having 119 teeth and the inside gear 107 teeth.
My question is - Should I use an involute gear cutter to cut a new inside gear?
Regards,
Alan C.

 

[SmithDoor]

Ring/ID gear is cut on a gear shaper
Can also be done using shaper

On the OD gear need check to see if it is a using involute gear
Gear Tooth Gages
http://www.mscdirect.com/product/details/93732642?rItem=93732642
Dave

 

[kiwi2]

Thanks Dave. The teeth are so small it would be difficult to see if their profiles matched a gauge. I guess what I need to know is whether a gear which meshes with a 119 tooth ring gear has the same tooth form as one which meshes with a 119 tooth external gear.
Regards,
Alan C.

 

[goldstar31]

I'm different. In another world and in another appication, I might agree about mini sized modules and wishing that I'd not scrapped my old shaper. Not here. It looks -to me- like a nylon moulding and it will cost more to mend it than replace the whole item.

So one could probably mend it- with a small soldering iron.

 

[///]

Goldstar, I don't think Alan want's to mend it, I believe he wishes to replace it, hence the question whether an involute cutter would have the correct profile.

Alan, I briefly researched cutting internal gears (like your ring gear) for a project that ultimately got shelved.
From what I could find(and I could very well have it wrong!) the inside spur gear has a 'normal' involute profile. It is the internal gear profile that is made to suit the spur (with undercuts etc). I could never find how to make a single point cutter with the correct profile for cutting the internal gear, hence the project's shelving. One day I will return to it.

As your internal gear is fine and you only need to replace the spur gear, if you are 100% certain it is a MOD 0.3 gear set, you should have no issue mating a new spur to the internal.

Besides, if you cut a Nylon or preferably Acetal(Delrin) gear, you could test it for fit and feel and it would be very unlikely to damage the brass internal gear one bit.

 

[goldstar31]

Point or some of it, taken but once one gets to' over 100' teeth, the cutter is virtually one for rack! However, as it is soft material, - and so small, who is really bothered?

However, Simon, You CAN cut a reasonably accurate set of gears with one tool- with rack or truncated forms. You simply grind a piece of tool steel- at each end. I recall Cleeve- he's the guy that did the screwcutting gubbins being tossed about here by doing a transposing gear of 127 which should have been 20DP but it would have fouled his lathe tray.

The trick is to use a magnifying glass where some of the greats show something else- and forget to explain the surrounding circumstances.


My wife once bought a house- using my watchmaker's loup on the advert.

I now use a pair of surgeons binoculars- because she wore the loup hinges out.

One reason why I cannot be arsed to take photographs- I watch too many things!

 

[kiwi2]

Thanks Simon - that's what I wanted to know. The gears are the fine focus adjustment on a Nikon microscope from the 1970s. Spare parts aren't available for it any more so I either need to repair the broken gear or make a new one. The existing plastic gear was moulded onto a diamond knurled brass ring fixed to the outside of the ball race. I'm not sure I can get it seated properly into the diamond knurling but I'll try.
If I can't I'll have a go at aralditing a piece of phosphor bronze onto the brass ring and cut a new gear.
Thanks for the comment Goldstar. I was tempted to use a flycutter to cut the gear but I can get a proper cutter from CTC tools for about $10 plus shipping.
Thanks all,
Alan C.

 

[goldstar31]

There is a case to make a new ring out of dental acryllic which is jokingly a way to fixing teeth. I recall my first decent drill had a guard made from it. So I married a dentist

 

[tornitore45]

119 teeth has practically no "profile", pretend is a rack an cut with a trapezoidal tool.
At 0.3 modulus is hard to take precise measurements.