Sanderson Beam Gears

I've finally finished my Sanderson beam engine except for the governor drive and governor and have run into a couple of problems. When I bought the castings, I also got the 6 gears from Clarkson's. I didn't check them closely on receipt but now I have found the the teeth on one pair of the mitre gears are cut at an angle to the gear centre line, hence when meshed the shafts are at 90 deg in one plane but are out by about 15 degrees from 90 in the orthogonal plane. Now on setting up the 3:1 drive I find the pinion and bevel gear don't mesh properly. It's as if the two are of different pitches and as they rotate instead of the next tooth falling into the next gap smoothly it is hitting the tooth either side of the gap and jumping into the gap. So I calculated the theoretical pitch circle diameter (PCD ), and OD for both pinion and gear of a 3:1 set 32 DP with 12 and 36 teeth and find that the pinion appears to be right but the gear is too small. Working back from the OD and PCD of the actual gear it works out as about 33.5 DP, which would explain why the teeth don't line up when rotated together. If someone has a set of gears as currently supplied by Blackgates could they measure the OD of the 36 tooth gear and let me know what it is. My calculated OD is 1.14476" and the OD of my gear is only 1.100".
Also on a different note the governor on the original Clarkson's drawings is only an outline with a couple of dimensions on the main shaft, also my drawings have been left out in bright light too long and in that area are barely legible. If anyone has the current Blackgates drawings are all the parts of the governor detailed? If so I will have to consider getting them or engineer the unit from scratch. Thanks.

John

Dare one suggest lapping them together with a good dollop of valve-grinding paste ?

No … I thought not !

Off to bed now … I’m probably safer there.

MichaelG.

Actually, Michael, I had seriously thought of doing that, but after doing the calculations I think that they are too far out for that to be a viable solution. I have done that before to get pairs of gears to run smoother but they have all been the same DP only had some rough edges that the lapping took off.

John

Edited By John Purdy on 08/10/2022 01:21:31

Good morning, John

Pleased to know that you have not branded me ‘unclean’

I wondered whether you might get away with it, simply because they are bevel gears … and with a suitable little jig, you could ‘introduce them to one-another’ quite gradually.

No idea what profile might emerge, but there’s not much to lose [except perhaps your reputation]

MichaelG.

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P.S. __ incidentally, I found some good images of a Sanderson here:

**LINK**

https://www.stationroadsteam.com/sanderson-beam-engine-in-glass-case-stock-code-3781/

and have taken the liberty of snipping these little details to inform any forum discussion:

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Edited By Michael Gilligan on 08/10/2022 06:33:20

I wonder if it's a case of depthing the gears , as the effective DP changes from outer edge to inner edge then moving the pinion towards or away from the ctr line of the larger wheel may allow them to mesh better.

I don't know if the gears supplied were purpose made or stock gears that need some modification such as shortening the bosses to allow the pinion to move and then a final trim of the OD so the look correct. If you mount the larger gear so it is free to spin on a horizontal shaft held in the mill vice the pinion can be held on a shaft in a collet and then you can move the ctrs up/down and sideways to see if you can get a good mesh.

Followed by Michaels suggesting

Edited By JasonB on 08/10/2022 07:11:15

Jason
I think the gears were purpose made (and not very well IMHO ) for the Sanderson either by or for Clarkson's as the bores and hubs required no modification other than drilling and tapping the mitre gears for set screws. As can be seen in the pic below the teeth are not of involute form but are triangular. The top two are the ones where the teeth are cut at an angle to the radial line of the blank. It is most obvious in the top left hand one at about 1 o'clock.

I did try different positions of the pinion relative to the face of the gear to see if if they would mesh better for as you say the effective DP (or more accurately the tooth spacing ) changes from inner to outer edge of both the pinion and the gear. I found if I moved the pinion further out as in the this second pic they rotate fairly well but still roughly. If I have the pinion in what would be the normal position with the two faces matching they lock solid and won't rotate at all. I think I might try your suggestion and mount the crank shaft between centres, so it can rotate freely , on the dividing head on the mill and with the pinion held in the spindle, lap them together while slowly increasing the engagement to see if I can get them to run smoother.

John