Well i really wasnt expecting that , i think i just hit the quote tag a shade after you hit the edit tag.

I was just about to say nice link MichealG, ( thats not to say it isnt any more ) its just the timing of the edit really

caught me out

pgk post jogged the memory about gear cutting on the shaper , i had look for it but not found it by using the search engine , cant remember what topic it was under

sorry not much help really…………….b

PGK is talking about the same method that Neil use to cut the gears on his 'oriible 'orrery

A concentric hob rather than stacked cutters.

If that's all you have to do then feel free………………………….

PGK although this uses a shaper action you can see the rack form of the cutter, you would jusy need to replicate that profile on your hob, the central tooth will do most of the work and then the outer ones just round over the corners of the next tooth out from center.

Sizes for making the rack can be found on the net, such as this one, Minnie would have used 14.5PA

Edited By JasonB on 30/12/2016 07:57:14

pgk pgk,

Getting back to your original question.

If you want to have gears with properly formed teeth using involute cutters then you must use the correct cutter for the number of teeth required. Involute cutters are sold in sets of cutters for cutting the whole range of gears from 12 teeth to rack. If it were possible to cut all numbers of teeth properly using just one involute cutter as you suggest then there would be no need for the set of eight. This would imply that all makers and users of sets of involute cutters are wrong and have been for years. Clearly not so.

A simple solution is often to make a single tooth cutter to the profile of the nearest gear that you have or use Ivan Laws “button method”. I made a 26 tooth change wheel for my Myford lathe using the 25 tooth standard gear as template for the single tooth cutter.

If the application is for a low speed, low load application then a certain amount of licence can be taken in producing a gear tooth form. For example a change wheel for a lathe. However if the gear is to be used at high rpm and transmit power for long periods as in a vehicle gearbox then the forms must be spot on then the gears will run quietly, absorb minimum power and have along life.

Have look at Len Mason’s excellent book Using the Small Lathe which explains simply about cutting gears in chapter 16.

Michael the shaper link does not have a geometric similarity to the hob method PDK is thinking of using as it shows a single point tool that is moved to several positions and the blank rotated a full turn in each position. It would be similar to the method in his second paragraph where a single profile tool is moved to a new position and the blank rotated again for several positions

The hob only needs the blank rotated once and the tool is not repositioned as it cuts several teeth at onece.

For example the first cut looks like this

Then the next cut starts to shape the previously cut ones as well as start the next

Then when you have gone full circle you get something looking like a gear

This method does give a slightly facetted gear tooth but would probably do on a traction engine.

In theory you could use a rack shaped cutter in a shaper and just rotate the blank once but that is different to the linked method.

Edited By JasonB on 30/12/2016 09:22:14

Jason,

Lovely pictures, but may I suggest you read the article that I linked.

MichaelG.

Michael you may have missed my edit where I added that the method you linked to was the same as PGKs second paragraph in his opening post.

If the drawing showing the 3 passes in your link were turned on its side that would be exactly the same as PGK was thinking about so as you say geometrically the same just a spinning tool rather than one on a shaper. Only down side with this method would be potential for more errors as you have to index the blank round several times as well as the slightly longer time taken.

Off into the workshop now but I may draw it out later with the single profile tool in the 3 or 5 positions needed and should get the same result as the "hob" one.

.

Thanks, Jason

… I have now said all I wish to say on the matter, except to mention for JS's benefit that:

(a) an Adept No.2 shaper can be purchased for less than the Minnie gear set, or the set of cutters.

(b) adopting the principle of operation [as pgk pgk has already deduced] does not demand purchase of a shaper.

MichaelG.