Wheel and Pinion Depthing

[Steve CrowParticipant @stevecrow46066]

Hello, I have been trying out my newly made depthing tool with a variety of Mod 0.3 wheels and pinions.

On measuring across the runners, the distance is consistently 0.2mm more the theoretical (sum of pitch circle radii). Any less and they bind. Plus 0.25mm gives a good mesh.

I expected it to be more than theoretical but not that much. Am I missing something here or does this seem normal.

By the way, the tooth form is involute.

Cheers

Steve

[Steve CrowParticipant @stevecrow46066]

[duncan webster 1Participant @duncanwebster1]

When I made a slave clock using bought in gears I just drilled the spindle centres at the theoretical pitch and they meshed fine.

[Martin KyteParticipant @martinkyte99762]

I think your post and Duncan's has just about summed up the entire operation. Duncan was using a pair of bought gears which I assume to be correct so theoretical pitch results in a correct mesh. You have cut your own gears (I assume) and have found a good mesh using a depthing tool which suggests that the gears are maybe a little off from theoretical dimesions. The whole point of depthing is to get the best running mesh with the gears you have.

regards Martin

[Michael GilliganParticipant @michaelgilligan61133]

I hesitate to mention this, Steve, but … when I admired your depthing tool, it did cross my mind that the numbers on the micrometer screw might lead you down a path that you do not need to take.

The inclusion of fine adjustment is an excellent idea, but the numbers are irrelevant to the traditional usage of a depthing tool.

As I presume you already know, the process is to optimise the depth of each pair ‘by feel’ and then use the points to scribe an arc on the plate … this accommodates any minor errors in the making of the wheels and pinions.

It is not necessary to know the dimension, you simply mark-out directly from whatever it happens to be.

MichaelG.

[Martin posted whilst I was typing]

Edited By Michael Gilligan on 11/09/2022 18:38:46

[Martin KyteParticipant @martinkyte99762]

The next iteration of the conventional depthing tool is the kind that will allow the pivots for the wheels to be exchanged for drilling bushes so allowing the pivot holes to be very accurately placed. Don't attribute this to me it's from Dick Stephen's 30 day Vienna Regulator design. As Michael and I have already pointed out when you have made your own wheels and pinions depth of cut is generally done by allowing a witness to remain on the blank so exact theoretical sizing cannot be assumed.

regards Martin

[Sam StonesParticipant @samstones42903]

Hi Steve,

Judging from the quality and precision of your work and the expertise from others, should have been enough for me to keep my trap shut.

However, back in April 2019, I was the likely cause of ‘much wailing and gnashing of teeth’, mostly my own I suspect.

I’d spent a considerable amount of time in CAD, attempting to discover more about meshing. It was also unfortunate for many that I was only interested in cycloidal tooth profiles. In my wildest dreams, I wouldn’t (couldn’t) have tackled involutes.

When I started my one and only clock, I knew nothing about all this meshing/depthing stuff, and drilled the pivot holes first. Maybe I was lucky but my clock worked in a fashion.

Keep up the good work.

Sam

Still chilly in Melbourne.

[Steve CrowParticipant @stevecrow46066]

Thank you for all the replies.

I realise that it is a transfer tool rather than a measurement tool and that is how I intend to use it.

I was just interested in what the best distance actually was. I'm glad I did as the accumulation of extra 0.2mm's on the wheel train meant I had to change my design a bit.

I'm happy with the meshing but would like to understand why there is such a big discrepancy. the blanks were all turned to within 0.01mm of textbook and DoC the same.

Steve

[Martin KyteParticipant @martinkyte99762]

It did occur to me that gears are generally intended to be used with the pinion as the driver and it's perfectly possible (although I haven't looked too closely at the geometry) that wheels driving pinions as is normal for clocks may cause a wedging action especially with involutes and cause increased friction. The optimum centre distance may then be greater than theoretical when driven in this manner.

regards Martin

[Steve CrowParticipant @stevecrow46066]

Hi Martin, with my project, it's going to be mainly pinions driving wheels for a calendar and a lunar train.

I am wondering if my tooth profile is ok.

I put my wheels on the scanner and set the dpi to 1200 and got quite good results. Here are 4 different wheels, 73, 64, 60 and 48. All but the 48 crossings are part filed to shape.

Can anyone see any fault with the profile?

Steve

[roy entwistleParticipant @royentwistle24699]

They don't look deep enough to me. I would like to see one depthed with a pinion

Roy

[Steve CrowParticipant @stevecrow46066]

Posted by roy entwistle on 12/09/2022 12:48:29:

They don't look deep enough to me. I would like to see one depthed with a pinion

Roy

I'll try to take a photo.

Ivan Law quotes a DoC of 0.65mm for Mod 0.3. Other sources told me 0.675mm. I went for 0.67mm.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Steve Crow on 12/09/2022 13:00:06:

Posted by roy entwistle on 12/09/2022 12:48:29:

They don't look deep enough to me. I would like to see one depthed with a pinion

Roy

I'll try to take a photo.

Ivan Law quotes a DoC of 0.65mm for Mod 0.3. Other sources told me 0.675mm. I went for 0.67mm.

.

I suspect that the pinions might be part of your problem … especially if they are low count

A detailed photo or two would help a lot

MichselG.

[Michael GilliganParticipant @michaelgilligan61133]

Not sure how widely-known this article is … but it’s packed with useful guidance: **LINK**

https://www.geartechnology.com/ext/resources/issues/1084x/back-to-basics.pdf

MichaelG.

[roy entwistleParticipant @royentwistle24699]

Thorntons quote 2.95 x Module up to and including 0.45. Which I work out to be 0.885mm Using Thornton cutters of course. How accurate is the OD of the wheel. No teeth + 2.76 x Mod

Roy

[Steve CrowParticipant @stevecrow46066]

Posted by roy entwistle on 12/09/2022 13:20:26:

Thorntons quote 2.95 x Module up to and including 0.45. Which I work out to be 0.885mm Using Thornton cutters of course. How accurate is the OD of the wheel. No teeth + 2.76 x Mod

Roy

Aren't Thornton cutters cycloidal? I'm using involute.

[Martin KyteParticipant @martinkyte99762]

Posted by Steve Crow on 12/09/2022 13:23:56:

Posted by roy entwistle on 12/09/2022 13:20:26:

Thorntons quote 2.95 x Module up to and including 0.45. Which I work out to be 0.885mm Using Thornton cutters of course. How accurate is the OD of the wheel. No teeth + 2.76 x Mod

Roy

Aren't Thornton cutters cycloidal? I'm using involute.

Yes

[Steve CrowParticipant @stevecrow46066]

This site quotes 2.25 x Mod for involute gears.

[Michael GilliganParticipant @michaelgilligan61133]

This … from ‘Gears for Small Mechanisms’ well-illustrates why I was interested in the profile of your pinions, Steve

.

.

Note: __ I find it a little disturbing that figs 1.4 and 1.5 are presented at different scales … must get around to doing a proper overlay sometime.

MichaelG.

Edited By Michael Gilligan on 12/09/2022 14:27:48

[roy entwistleParticipant @royentwistle24699]

Sorry yes they are cycloidal. It was just that yours don't look like wheels that I'm used to.

Still like to see it depthed with a pinion

Roy

[Steve CrowParticipant @stevecrow46066]

Posted by roy entwistle on 12/09/2022 14:29:03:

Sorry yes they are cycloidal. It was just that yours don't look like wheels that I'm used to.

Still like to see it depthed with a pinion

Roy

Camera battery just died! Will get photos later.

[Steve CrowParticipant @stevecrow46066]

Ok, I've took some meshing pictures. It wasn't easy. I had to take dozens to get two adequate pics.

These ar at the tightest mesh that still allows free running. In practice, I'd probably increase it by a couple of thou.

By the way, 12T pinion, 73T wheel.

Steve

[Steve CrowParticipant @stevecrow46066]

This close up photography does not flatter the finishing on my tools!

For scale, the runners are 2mm diameter.

[derek hall 1Participant @derekhall1]

By the look of those photos the wheel tooth form is all wrong for a clock

A good reference book is Michael Wild clock wheel and pinion cutting, it's expensive but the definitive book on the theory and practice of cutting wheels and opinions for clocks.

Good photos though !

Regards

Derek

[Michael GilliganParticipant @michaelgilligan61133]

Good photos, Steve … but I don’t like the look of that meshing

If you send me your eMail address by personal message here, I have a PDF of chapter1 of Gears for Small Mechanisms, which you might find of interest.

The book is excellent, but rather dated … grab a copy if you see it cheap, but I doubt you would need most of it.

MichaelG.

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