Author Topic: gear selector pinion gear  (Read 1233 times)

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Offline saluki42

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gear selector pinion gear
« on: 15 Jan 2022 at 10:06 »
Hi again I was wondering if anybody can help me with any information regarding the pinion gear which is driven by the rack in my 1934 4 speed gearbox. This is just about the last thing I need to complete the box build.

Chris

Offline Ian Hand

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Re: gear selector pinion gear
« Reply #1 on: 17 Jan 2022 at 00:49 »
Hi Chris,
I have my gearbox apart at the moment. What information do you need. Here are some photo's which might help.  I am missing the kickstart return spring which I have ordered from the Douglas Spares guy Alan.  I am having difficulty with identifying the model of gearbox without pulling it completely apart. I can identify it a a 4 speed box by the number of detents in the selector shaft but when I attach the foot change I can only select 3 speeds. i guess I will need to pull it apart for a positive ID.
Tell me if you need dimensions and specs for the gear. I can pull it out and give you spme close up pics and measurements that a gear cutter will understand.

Offline Doug

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Re: gear selector pinion gear
« Reply #2 on: 17 Jan 2022 at 04:14 »
Chris,

Are you trying to time it? Is it missing?

-Doug

Offline saluki42

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Re: gear selector pinion gear
« Reply #3 on: 17 Jan 2022 at 07:46 »
Hi thanks for the quick replies, unfortunately although I have a collection of gearboxes from the thirties, two rack and pinion selector and three level and slider selection, none of them have that pinion gear either fitted or in the box of parts which came with them.
I have been trying to find a pinion gear for quite some time but without any success so if it comes to it I'll have to see if I can get one made if you could let me have the details Ian.

As far as the timing is concerned Doug I at first wondered what you meant, on reflection of course the pinion and rack have to be set up to synchronies with the gear selector lever and tank plate. I haven't actually got that far yet but now see it's something I'll have to deal with when the time comes.

Thanks again
Chris

Offline Doug

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Re: gear selector pinion gear
« Reply #4 on: 17 Jan 2022 at 16:03 »
There is a center punch dimple on the rack and one of the teeth on the pinion has a small groove cut on it, so timing is pretty easy to read though sometimes takes more than one try to assemble in sync. Not sure if I have a spare pinion, I'll have to look.

-Doug

Offline Dads bike

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Re: gear selector pinion gear
« Reply #5 on: 18 Jan 2022 at 09:27 »
Morning
A picture of the aforesaid.
Note the common failure of this pinion. Brake through the key way.
Cause? possibly over tightening of the retaining nut onto the taper or over enthusiasm in trying to find gears on a static box or maybe both.

Steve



Attachment converted to linked file, aspect ratio fixed - Dave, 18Jan2022
« Last Edit: 18 Jan 2022 at 16:56 by Dave »

Offline saluki42

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Re: gear selector pinion gear
« Reply #6 on: 19 Jan 2022 at 15:32 »
Thanks Steve, that would definitely cause that type of failure. If I manage to find one I'll have to pay attention to any sign of damage before fitting.

Chris

Offline Doug

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Re: gear selector pinion gear
« Reply #7 on: 24 Jan 2022 at 17:05 »
Threw may back out which precluded climbing up on the mezzanine for a few days to have a rummage around. I do not have a spare, but did find one to make a drawing of.



PDF download


-Doug

[Corrections made to drawing table values of addendum and whole depth. 28Jan22 Doug]
« Last Edit: 29 Jan 2022 at 02:58 by Doug »

Offline Hamwic

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Re: gear selector pinion gear
« Reply #8 on: 25 Jan 2022 at 11:57 »
HPC in the UK do 16DP gears

https://www.hpcgears.com/pdf_c33/23.120-23.125.pdf

So certainly worth a look there.

Cheers for now
Doug

Offline saluki42

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Re: gear selector pinion gear
« Reply #9 on: 27 Jan 2022 at 07:28 »
Hi Doug hope your back is feeling better.
Sorry about the delay getting back to you I've been in touch with 'HPC Gears' Hamwic and bought the correct pinion gear, or at least a nearly correct pinion gear, It will need machining to get the lengths right as well as the tapered bore and keyway but the business end fits the drawing provided by Doug and armed with his drawing machining won't take me long.
Anyway thanks again for all your help on this one and hopefully with that help another gearbox complete.

Chris

Offline Ken Rogers

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Re: gear selector pinion gear
« Reply #10 on: 28 Jan 2022 at 08:58 »
I noted the HCP gear was 20 degree pressure angle where as the original is 14.5 degree.

Offline saluki42

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Re: gear selector pinion gear
« Reply #11 on: 28 Jan 2022 at 12:41 »
Hi Ken, I hadn't noticed that. I've had a chat with my engineering design lecturers and they say that although not ideal for medium to high speed operations mixed PAs should be ok for low speed and relatively low loads encountered with gear changes.

Chris

Offline Doug

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Re: gear selector pinion gear
« Reply #12 on: 29 Jan 2022 at 02:48 »
First, a correction. The drawing for part 13240 earlier in this post had errors in the table for the addendum and working depth values. Not an issue for purchasing a gear based on the diametral pitch and number of teeth, but not so good for posterity. A corrected drawing JPG image and PDF doc have been uploaded. (You may need to press F5 to refresh your webpage.)

Mixing a 20 pressure angle gear with a 14.5 rack might work depending on how much backlash Kingswood factored into the mesh. When I tried the pinion against the gauge, there definitely was some cogging when rolled against the side with the 20 pressure angle. Granted, if you buried the mesh deeply enough, it cogged on the 14.5 side also. This is subject to feel, but I did offer up the gauge to the rack where a more accurate comparison could be made and it is 14.5. Also, my understanding is 14.5 was the favored pitch angle back in the day whereas 20 is more common today.



This is a 14.5 pinion meshed with a 14.5 rack, no backlash.



This is the same with a 20 pressure angle pinion.



While the 20 pressure angle makes the pinion tooth tip slimmer and gives it more clearance (not really visible with the heavy line weights) along the pitch circle, the root of the tooth becomes fatter and interferes with the tip of the rack teeth, as indicated in red. Initially I was thinking that if you performed 'topping' as they call it in gear hobbing parlance, you might be able to modify the pinion if you needed more clearance. This involve clipping the tip corners of the pinion teeth. It need not be highly precise as say cutting the gear teeth, as it is just clearance. But it is not the tips of the pinion teeth that are the problem.

Kingswood would have factored in some backlash. Depending on how much, you may not have a binding problem. In the next illustration I shifted the rack 0.005" away from the pinion. The clearance of the slimmer tooth is more readily visible (circled in green). But there is still a slight interference (circled in red). Backlash in the pinion or rack manufacture would achieve the same effect.



Try it and see. If it binds I think I would try to hunt down a supplier of 14.5 pressure angle pinions rather than do something like shave the back side of the rack to allow it to move further away from the pinion. I am not an advocate for irreversible modifications to original parts. Not if it can be avoided.

-Doug





Offline saluki42

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Re: gear selector pinion gear
« Reply #13 on: 29 Jan 2022 at 08:56 »
Thanks Doug, I'm waiting delivery of the pinion I've ordered but when it arrives I'll have to see what the mesh is like. In the box of gearbox parts that arrived with my project I found three racks, though no pinion,all showing differing amounts of wear so Ill which if any is the better fit.

Chris

Offline eddie

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Re: gear selector pinion gear
« Reply #14 on: 30 Jan 2022 at 17:12 »
Chris,
          As you have some spare racks (with some wear), the easy option would be to experiment on one of them and regrind the flanks of the teeth to the 20 degree pressure angle (the teeth on a rack are flat sided, rather than having an involute form). Some trial and error may be required to establish how much material needs removing, but I would expect that the change in angle would only be necessary over the top half of each tooth.

  Good luck,
                  Regards,
                               Eddie.

Offline saluki42

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Re: gear selector pinion gear
« Reply #15 on: 31 Jan 2022 at 16:09 »
Thanks Eddie it was something I was looking at as a possibility.

Chris