Gear cutting with a shaper?

I'm finding this very interesting as I need to make a wormwheel of 1" inch outside diameter but I need to check what TPI and therefor DP I can cut on my Boxford. The wheel then needs a 1/4" Acme thread in the centre but I can cheat on that as I'm waiting for some Acme nuts and threaded rod to arrive and will then silver solder a nut into the wormwheel.

Brian

I just tried an experiment wrapping some Bowden cable inner round my drill pillar 7 times measuring etc. I found that rather than half the cable width compensation it behaved as if the cable was 1.8mm not the 1.54mm measured. Probably a good idea to use thin shim as suggested above

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That's interesting, Bazyle ... and I agree that shim should be the way to go.

I must just mention, though: If you mean flexible [multistrand] Bowden cable ... I very much doubt if it is truly circular in cross-section; so perhaps your result is not so suprising [?]

MichaelG.

Make a 20 tpi silver steel worm and matching tap and you will find that it will make a very nice fitting 60-tooth worm wheel on a 1" blank, if you gash it then free-hob.

Ditto 10 tpi and 2" blank.

I made two dividing heads this way not perfect accuracy, but have served me well.

Neil

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Maag have used this idea for years on their gear grinders which have to have far more accuracy than we can hope to attain in the home shop.

Thanks Neil, I'll have a play at your suggestion and report back later.

Brian

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Just for clarification, John ... "this idea" = shim tape instead of wire [?]

MichaelG.

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Edit: I just found this 20 second video of a Maag grinder in action:

https://m.youtube.com/watch?v=wwn-UMvkcL4

... but it doesn't show how the rotary oscillation is achieved.

Edited By Michael Gilligan on 13/02/2017 23:18:08

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John,

Sorry ... too late to edit my previous post:

If you were actually referring to the general idea described in the 'Base Circle' article ... He does acknowledge that in the second paragraph:

"The idea is to use a shaping machine (in the writer's case, a very old hand-operated machine) and to fit to it a mechanism on the lines of that used in some types of gear-grinding machines, such as the " Maag " or older " Lees-Bradners " to give a rolling motion to the gear blank while being cut. This method, being a true generating method—right back to first principles—results in a correctly formed involute tooth."

MichaelG.

I keep meaning to try this method of shaper gear cutting but haven't got around to it yet...

But Mr C Bamford (from down in the land of Vegemite) describes using the Base Circle shaper method in his ME article "Shaper Cut Gears" dated 20th January 1989. He seems to have had one or two problems with his initial set-up being a bit loose and also his indexing device wasn't spot on to begin with - but he seems to have worked the wrinkles out and made the gears he wanted in the end...

As with all things Shaper - simple tool, easy to sharpen - just need the indexing & wire/tape set-up.

Regards,

IanT

Michael,

Not read that article for many years so not familar with the reference.

I was going on what I'd read in a gear book years ago but as all my books are still at the other house I can't scan the page. From memory it was only like a concept drawing to explain the principle but in true Michael gilligan style will this do ?

**LINK**

The discussion above correctly concludes that the rolling diameter of the centre of the wire must be the gear's PCD (hence disk diameter is PCD less one wire diameter). This applies when the cutting tool is shaped as a matching rack tooth.

Just to complete the record here, the 'Base Circle' ME article of 14th Sept 1950 was followed by some correspondence that discussed the 'pitch circle disk' as opposed to (as two correspondents suggested) the 'base circle'.

12 Oct 1950, K.Horsfell (suggesting base circle)
2 Nov 1950, J. Pearman (suggesting base circle)
2 Nov 1950, 'Base Circle' (replying to Pearman and making (the correct) case for PCD)
23 Nov 1950, A.A. Sherwood (replying to Horsfell, also making case for PCD)

I have scanned copies of all of these letters if wanted, but probably should not post here due to copyright(?).

Rod.

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Yes, that will do nicely, John

Thanks

MichaelG.

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Rod,

I, for one, would be grateful for sight of those letters please.

Neil posted, quite recently, a note explaining his position regarding short items quoted from ME/MEW.

.... I feel very confident that such letters would fall comfortably into the 'acceptable quotation' category.

MichaelG.

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Edit: ... Wow! that took some finding, but I quote from the third post on this page:

http://www.model-engineer.co.uk/forums/postings.asp?th=124306&p=2

"Naturally we are fairly relaxed about material from our own publications (i.e. ME and MEW, but it is nice to be asked first when a significant item (e.g. a whole article) is used."

Edited By Michael Gilligan on 14/02/2017 09:03:23

As promised yesterday, I have modelled the effects of changing the diameter of the index wheel.

This was modelled with a 65mm diameter blank, aimed for 60mm PCD, 50mm diameter root, 1mm wide tool at the root, tool depth 12mm, 29 degree pressure angle, using 1mm traverse steps for the shaper. Three conditions were considered. On the left, the index wheel diameter was 90mm, in the middle, 60mm and on the right, 30mm. No effort was made to make a real gear wheel proportions as the illustration was made oversize to exaggerate the effects.

As correctly pointed out in previous posts, the index wheel diameter needs to be the same as the PCD.

Hope this helps

Richard.

Edited By richardandtracy on 14/02/2017 09:09:45

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Richard,

Many thanks for doing this; but I remain utterly bewildered by your assertion that the diameter of the 'index wheel' is significant.

Before we go much further ... Could I please check that we are both referring to item "D" on the drawing [described as a 120 tooth wheel, salvaged from a magneto].

What you describe is, indisputably, valid for the 'pitch circle disc' "C"

MichaelG.

It seems that posting these extracts will be 'fair use', fitting the purposes of this discussion.
Here then are the letters referred to above [14/2/2017 03:35:10]. Rod.

Hi Richard,

Sorry - my old grey cells are struggling to understand your drawing but in any case, it seems to me that the only effect of the indexing is to change the angular setting of the work - not its 'motion'. So I cannot see how the diameter of the indexing wheel would therefore effect the cut.

I may be wrong in this assumption (and often have been before) and maybe I need an explanation I can better understand. But I'm not convinced at this point...

Regards,

IanT

Ah - Michael beat me to it - takes me a while to type these things...

Regards, IanT

PS Useful to see the letters too RE - thank you

Edited By IanT on 14/02/2017 09:50:18

Rod,

Very useful, thank you.

The response by 'Base Circle' [taken together with his chosen nom de plume] inspires great confidence that he knew exactly what he was doing.

MichaelG

As backed up by MAAG one of the better respected gear companies.