Pinion dimension confusion

[Michael GilliganParticipant @michaelgilligan61133]

Posted by John Haine on 05/11/2022 21:32:43:

For the reason I mentioned above.

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I must be going blind as well as daft, John

… Where ?

MichaelG.

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Edit: __ It’s O.K. John … don’t bother answering … Your words of wisdom are on the other thread:

https://www.model-engineer.co.uk/forums/postings.asp?th=183863&p=2

Edited By Michael Gilligan on 05/11/2022 21:46:43

[ChrisLHParticipant @chrislh]

Michael,

You were wrong but, congratulations, you now have the opportunity to be right !

A pair of involute gears can work "correctly" over a range of centre distances.

"Correctly" here means without change of velocity ratio whatever the rotational position of the gears. Just to make clear, that would not be true if you continuously changed the centres as the gears rotated.

If you needed to maximise the range of centres for some reason, involute gears have been designed that could tolerate a 7% change in centre distance and still work "correctly" at either extreme.

Edited By ChrisLH on 05/11/2022 22:26:52

[duncan webster 1Participant @duncanwebster1]

Posted by Michael Gilligan on 05/11/2022 20:51:43:

I have just spent some time skimming through the archive of the Horological Journal, and I am now convinced that my statement was wrong … every reference that discusses depthing indicates that the Involute form is more tolerant of variations in depthing than the Cycloidal form.

MichaelG.

Well I'm glad I didn't take up Michael's invitation then

[Michael GilliganParticipant @michaelgilligan61133]

Posted by duncan webster on 06/11/2022 16:26:57:

.

Well I'm glad I didn't take up Michael's invitation then

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It was actually a request, not an invitation

but anyway, it’s nice to know you’re happy, Duncan

MichaelG.

Edited By Michael Gilligan on 06/11/2022 18:04:50

[Andrew Knowles 2Participant @andrewknowles2]

Gentlemen

With some embarrassment I have to report that I have solved my pinion cutting issue.

After reading all the advice it appeared that pinion blank size and cutter were correct.

I then realised that the tooth space on the pinion was wider than the cutter teeth. On checking the wheels I had previously cut the cutter fitted perfectly into the tooth space.

On checking the cutter arbour I found it was bent. This must have happened after I finished cutting the wheels.

New arbor made and now the pinions look much better

Once again many thanks to all who replied to my question

Kind regards

Andrew Knowles

[Michael GilliganParticipant @michaelgilligan61133]

Good result, Andrew

… and some of us managed to exercise a few brain-cells on the journey

Win-Win

MichaelG.

[John HaineParticipant @johnhaine32865]

Andrew, did you solve your problem? I'm just composing a PM to you.

[Andrew Knowles 2Participant @andrewknowles2]

Gentlemen (I made this posting on 11/11/22 but it does not show up in this thread but it does in My Postings)

With some embarrassment I have to report that I have solved my pinion cutting issue.

After reading all the advice it appeared that pinion blank size and cutter were correct.

I then realised that the tooth space on the pinion was wider than the cutter teeth. On checking the wheels I had previously cut the cutter fitted perfectly into the tooth space.

On checking the cutter arbour I found it was bent. This must have happened after I finished cutting the wheels.

New arbor made and now the pinions look much better

Once again many thanks to all who replied to my question

Kind regards

Andrew Knowles

[Andrew Knowles 2Participant @andrewknowles2]

And after the posting above the original now appears

Very strange

Andrew

[roy entwistleParticipant @royentwistle24699]

Considering that the hole in a Thorntons cutter is 7mm, how on earth have you managed to bend the arbor?

Roy

[Andrew Knowles 2Participant @andrewknowles2]

Hi Roy

I have no idea but bent it is. I just do not understand as it was fine whilst I was cutting the wheels.

The mill has no power feeds so not that.

I will post some photos of the results with the new arbor. I would be most grateful for any comments

Kind regards

Andrew

[Andrew Knowles 2Participant @andrewknowles2]

Hello All

I have been meaning to post a picture of my pinion cutting set up for the last few weeks

I have now managed to produce some reasonable ( in my opinion ) results with the help of all the comments I have received. Today I have got the going train completed and it runs !!!

Many thanks for all the help

Andrew

Just realised I do not know how to insert an image but I will find out and post the picture in a minute

[Andrew Knowles 2Participant @andrewknowles2]

That was not so hard was it

[John HaineParticipant @johnhaine32865]

Andrew, I like that v-groove "tailstock" support.

[Sam StonesParticipant @samstones42903]

And the direction of cut, even if the spindle is running in reverse!

Or are my eyes deceiving me Andrew?

Sam

[Andrew Knowles 2Participant @andrewknowles2]

Sam. Well spotted I run the spindle in reverse so I can have the cutter in front of the work to make it easier to see what is going on.

Easy to do on the BCA just put the belt on the motor the other way around

Andrew

[HopperParticipant @hopper]

Nice to see a GH Thomas versatile dividing head being used in anger too. I have been meaning to set mine up with ER collet holder like that for several years now. Must get a round tuit. Looks right handy.

[Sam StonesParticipant @samstones42903]

It wasn’t so much the running in reverse Andrew, it was more to do with the possibility that the bolt would unscrew, and perhaps why the arbour was bent.

Speaking of running machinery in reverse, as an apprentice a very long ago time ago, one task I was given was turning up a tapered blank from a piece of HSS. It was the starting point for a 2.5deg reamer.

The flutes of the reamer were milled before the hardening shop did their bit. Finally, it went to the cutter grinder for finishing.

All went well except the (rather accident-prone) miller had cut the flutes left handed.

You get where I’m going?

Actually, the finished reamer came back to me since I had the job of using it to clean up the tapered bore of a sprue bush (look up injection moulding).

Fortunately, the rather clapped out (apprentices) lathe was flat-belt driven from an overhead counter-shaft. The belt had enough slack/stretch to be twisted and the lathe run in reverse. Some of you will cringe at this especially when I reveal that the chuck was screwed onto the end of the lathe spindle and could unscrew.

Under the supervision of the equally anxious foreman, applying plenty of oil I gingerly reamed the bush to a point where it was ready for polishing, as is the custom for reliable mould release.

All went well although I think the miller got some stick for his LH oversight.

Keep safe,

Sam

[ChrisLHParticipant @chrislh]

Andrew,

An incident in my own workshop which may have some relevance to your bent spindle.

I was getting set up to hob some gears using a bought in hob. The hob spindle was very carefully turned between centres and checked for runout. However when the hob was mounted and nutted up, it had a very distinct wobble.Once the hob was removed, the spindle again checked out true. Conclusion, the relevant face of the hob was not perpendicular to its bore. Fortunately, in my case this error was not big enough to bend the shaft permanently and a pair of interposed washers with mating 45 degree faces cured the problem by acting as a crude spherical, self aligning mounting.

[Author]

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