Slant gears?

I am rebuilding a 1914 petrol engine that has twin cams. One of the timing gears is missing. I need to make a replacement, I have measured them and they appear to be cut at an angle of 14 1/2 degrees but are straight not helical.

I assume I can cut the gear the same as straight spur gear but at the correct angle.

Anyone has come across this type of gear before?

Yes, but I made it myself. Works well as a wormwheel on a dividing head, meshed with an Acme thread of suitable pitch. I made it just as you say, same as a straight spur gear but mount the blank at the suitable angle. No idea how it would go meshing with another gear rather than a worm.

If they are cut AT AN ANGLE of 14 1/2 degrees then regardless they are helical

Can you put us a close up photo of the gear in question please.

I doubt very much it will be an angled gear as you describe and think it probably is a helical gear, but I would be very interested to see it all the same.

If teeth were cut at an angle across a gear blank, they would be shallower at the sides and deeper in the middle, I don't think that would make for a very good gear if it has to mesh with another one the same.

The only time I have seen this type of gear in use, is as an alternative to a true worm gear on a cheap dividing head, but in that application it is only the centre of the teeth that have contact with a worm and you can sort of get away with it.

Phil

PS. Hopper and JS both type a lot faster than me !!

Edited By Phil P on 16/02/2017 22:21:18

I will post some pictures tomorrow. They are cut in a straight angle ( I have clocked them to confirm this) rather than a helix and they alternate lefthand - righthand so that they mesh. But because of the angle they have thrust washers on all the gears.

It's a bit like 20 questions isn't it ?

That is a helical gear.

I'd suggest that you get hold of a copy of Ivan Laws fine book Gears and Gearcutting, No 17 in the Workshop practice series and all will become clear.

Will do, thank you.

Now tell us what the engine is ! Alfa?  , Peugeot

Edited By Hacksaw on 17/02/2017 22:50:19

White and Poppe / Dennis Brothers Motors. Customer cannot get an exact date but we think its a 1914 engine as it has some W+P parts and some Dennis parts. 5 litres, 4 cylinder T head.

I've got a Dennis ..a 36" Blackburn 500cc beast !

There was a post within the last year or two dealing with cutting helical gears. I searched but could not find it.

I responded to it stating that the traditional method was to use a universal mill (table swivels) and a universal dividing head geared to the lead screw. Several members responded with work-arounds devised by model engineers to cut helical gears without the specialized equipment. I searched for that post but was unable to find it. Perhaps another member can post a link. I think you would find it useful.

You might need to search for a commercial gear shop that could do it on a hobber.

Here:

**LINK**

And for reference the 'traditional' way:

And less conventionally on a vertical mill:

Neither of these methods produce the correct tooth form, although for many practical purposes the gears work well.

Andrew