Velocette

What's the consensus on the use of a 0.8mod cutter using 32dp specs i.e. depth of tooth and outside diameter on a magneto drive gear for a Velo MAC, alloy engine, 92 teeth?

Cheers

Graham W

They are very, very, close

Assuming of course that the Velo uses 20° pressure angle !!

[which I cannot remember]

MichaelG.

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Can you post a flat-bed scanner image, or a good photo, of a Velocette gear please.

It is 20 degree pa, tried to include a photo but the method eludes me I'm afraid. Understand that 32dp is about 0.794 mod but if I work out the outside diameter on module it equates to 2.961" ((94x0.8) x 0.03937) but  the automatic advance retard unit with tufnol gear i'm looking to replace is 3.055" and have been told previously that the diameter should be 3.063" which is I assume what Velo used way back.

Couldn't find a 32DP cutter at a price I could afford but did find a 0.8mod cutter on ebay hence the question

Edited By Graham Williams 11 on 16/08/2019 12:10:09

I cut a couple last week the other way round eg to 0.8MOD sizes using 32DP cutters as I had the cutters

Are RDG's prices too high?

No Jason, I find RDG an ok supplier but when I last checked they only did 14 1/2 degree pa cutters

Graham,

Sets of gear cutters only produce the true tooth profile for the number of teeth at the bottom end of the range stamped on the cutter but the system works fine. Bearing this in mind I can see no problem in your original plan, I'm sure the gear will mesh adequately. Since Jason is showing off, here's a pair of 0.8 MOD gears I cut for my Farm Boy last week.

I bought my set of cutters from CTC.

Cheers,

Rod

Graham, please let us know how you get on. I have a bit of a collection of knackered tufnol gears.....

Sorry to say no good at all, assuming you are forming rather than generating the gear. These gears need hobbing (generating the tooth form), although not transmitting any great load the formed tooth will probably be quite noisy, defeating Veloce's use of helicals to keep thing quiet.

Why not buy a gear (£59 from the VOC) intended for the manual advance/retard and modify that?

John

Whoa... If we really are talking about helical gears then that's a whole different problem.. Helical gears can be cut using form cutters but it takes a bit of fiddling around to produce the necessary lead on the blank.

Rod

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Arghh ...

Nobody mentioned helical gears 'til now ... did they ?

MichaelG.

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Oops ... 'ere we go : http://velobanjogent.blogspot.com/2008/10/349-cc-mac-velocettethe-so-called-alloy.html

Edited By Michael Gilligan on 16/08/2019 17:09:06

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**LINK**

https://www.model-engineer.co.uk/forums/postings.asp?th=103028&p=1

John. There are quite a few suppliers, Tank Classics, Grove as well as VOC (I'm a member) and they all go for around the same price + P&P and did exactly that for a friend's bike but I just wanted to make my own using my vert. mill, going the manual mag route and made a simple jig to set the mag shaft taper., taper is 11mm to 13mm over 11.5 mm length.EN3 sourced from local machine shop for the price of a pint and disregarding the electric used much cheaper to make and kept me entertained, the cutter cost me £12 delivered from China and trying it today it cuts well. CRT ? in Sheffield want around £90 for the correct cutter and Tap & Die want £120 so more than I wanted to lay out. Bit disconcerting that you suggest there will be a noise problem making it this way, had whines in the past from the timing gears on a Viper but the adjustment on the intermediate gear put that right (thank you Mr. Dodkin). Will have to give it some thought as to completing number 2 methinks.

Wonder what a small gear hobber will cost to make........... where is this going?

Rod. How do you put photo into the post, it's not working for me.

Made a gear today but the 'not' deliberate mistake gave me RH helix, 92 teeth cut, what fun, must pay more attention.. LoL

Graham

As you now have some photos in an album all you do while posting a reply is click the little black camera icon at teh top of the box you are typing in and select the image from there. Michael's link earlier also gives details

Thanks for the 'how to' so put a couple of photos of the one I made (incorrectly) today.

Thanks Jason, just need to find out how to put a comment up with the pictures................. need the grandson here LoL

Graham,

That's a good looking gear and, frankly, I wonder if for a gear with that many teeth and such a shallow angle one would really be able to tell the difference between one that has been cut straight across at an angle and one that has been cut in the correct helical fashion.

Rod

Rod.

In the Velobanjoagent link posted above you can see what Velocette's thinking was at the time, i.e they believed it gave quieter running but that with more modern gear manufacturing methods the same result could be achieved. However having said that they didn't change the gears on any of the singles at all as far as I'm aware once having made the change to helical teeth from the early straight teeth gears. Very quirky bikes are Velocettes, I won't get into the 'famous' clutch as many Velo fans will well know LoL

My thoughts.

You are replacing a tufnol gear with a steel gear? Tufnol might either ‘deform’, ‘run in’ or simply get chewed away in short time if the incorrect tooth form is adopted.

At least the magneto drive is beyond the cam and is, of course, only half engine revs. I think I would be making it in aluminium if it has to be metal - more chance of it ‘conforming’ rather than wearing the cam gear as well.

I’m surprised that the gears are 20 degree pressure angle, but maybe they were introduced long before I thought...

I might be concerned when considering RJ’s comment re straight cut and helical, but I don’t know enough about gears to compromise too much - at least for fast rotating ones. One of our experts (Andrew) is unfortunately ‘on holiday’ from the forum. Might be worth sending him a personal message?

Is the engine ‘safe’ if the cam drive were to fail? Just a thought... ... Likely to go noisy before failure, if it were to wear, I suppose.

Don't know when exactly that Velocette made the change to helical cut gears, it may well have been pre WW2 when the MAC was introduced, I believed the early ones (early 30's) had straight cut gears so that might give a reason for 20 degree pa.

Commercially available mag gears are steel as far as I know no-one has offered Alum gears and think the wear factor s a consideration, Tufnol doesn't seem to wear that badly, the gear usually strips mostly by the kick back when the starting drill is slightly off, that's my experience when Velos were my daily transport anyway, prompting change to manual a/r with steel gear which was the standard for bikes so equipped from the factory, perhaps anodising might toughen them up, just a thought.