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Allchin compensating Centre

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Dougie Swan17/02/2022 17:39:41
235 forum posts
53 photos

Hi

I've just machined the centre on the allchin I'm building

It all go's together like it should but at some point it always binds

When I run each side separately against the three idler gears they run smooth as a nut, running them together is the issue

Anybody got any suggestions

Thanks

Dougie

MichaelR17/02/2022 19:01:15
avatar
474 forum posts
76 photos

Dougie, check the three pinion spacings they have to be spot on equal to run smoothly.

MichaelR

noel shelley17/02/2022 19:05:13
1339 forum posts
21 photos

Sounds as though something is not inline ? Would a period of running in help to ease things or is it to bad for that ? This is a difficult assembly to make and requires precision to work well, I would check dimentions and alinement of all parts,may be easing a bit may help. Noel

Clive Brown 117/02/2022 19:26:00
825 forum posts
41 photos

If the mesh is too close, very small inaccuracies will cause tight spots. Try easing the large gears very slightly further apart, I found that a very slight easing of mesh made a big difference. There is a limit to how far this can be taken of course.

Hughes gives quite detailed advice on the machining, including a drilling jig.

Edited By Clive Brown 1 on 17/02/2022 19:29:06

Paul Lousick17/02/2022 20:57:10
2043 forum posts
722 photos

As stated, if the spacing of the planetary gears are not exactly the same, they will bind.

Paul

Dougie Swan18/02/2022 13:01:13
235 forum posts
53 photos

Hi and thanks for all the suggestions

I was thinking about the spacing but if it was incorrect then it would bind when I ran either of the side gears but individually they run sweet, only when I fit both sides do they bind

I will keep trying

Dougie

Clive Brown 118/02/2022 13:30:16
825 forum posts
41 photos

Running with only 1 large bevel is not really a very demanding test. The 3 smaller wheels can each take up their own mesh positions independently of each other.

As I see it, only when the 2nd. large bevel is also in mesh do all 5 bevel gears become interconnected and errors will cause binding.

 

 

Edited By Clive Brown 1 on 18/02/2022 13:36:22

Andrew Johnston18/02/2022 13:32:30
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6601 forum posts
701 photos

With both bevel gears fitted does the centre run smoothly at some points and bind at others? Or does it bind everywhere? If the former then I'd suspect an axial misalignment of the bevel gears rather than radial misalignment of the pinions.

Andrew

Dougie Swan18/02/2022 13:44:46
235 forum posts
53 photos

Hi

Yes, as Andrew said, the gears only bind at one point

Running both bevels against the pinions with one centre removed everything is fine

D

Andrew Johnston18/02/2022 14:18:38
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6601 forum posts
701 photos

I'm not familiar with the detail of the Allchin design, but it seems like one of the bevel gears is not concentric with it's axis. How were the bevel gears manufactured?

Andrew

Dougie Swan18/02/2022 14:26:37
235 forum posts
53 photos

The gears were bought from reeves

Dougie

Andrew Johnston18/02/2022 15:29:23
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6601 forum posts
701 photos

Some pictures of the parts would useful.

Andrew

Dougie Swan18/02/2022 15:42:23
235 forum posts
53 photos

Thanks to all who replied

I've got it sorted

I adjusted the position of the planetary gears out from the centre with a couple of shim washers under each gear

0. 26mm was what it took, I have been at this for a week and was starting to lose the will to live.

The combined knowledge of the members never ceases to amaze me

Thanks again

Dougie

P. S. Sorry for no pics but it's a pain having to load them to the album first then onto the thread

Edited By Dougie Swan on 18/02/2022 15:55:25

Andrew Johnston18/02/2022 15:59:32
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6601 forum posts
701 photos
Posted by Dougie Swan on 18/02/2022 15:42:23:

Sorry for no pics but it's a pain having to load them to the album first then onto the thread

Conversely it's a pain having to second guess about parts with which we're not familiar. smile

Glad it's been fixed, but I suspect the shmming has hidden the original problem rather than solved it. Is the backlash consistent or does it vary as the bevel gear is rotated?

Andrew

JasonB18/02/2022 16:55:38
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Moderator
22747 forum posts
2653 photos
1 articles

The Fowler has a shim washer that sets the spacing between the two halves of the diff which is machined until you have minimal backlash but not too tight to bind, as it uses cast finish gears a little adjustment is needed on each engine.

For Andrew (and others) enlightenment extract from Allchin drawings

diff.jpg

Dougie Swan18/02/2022 17:11:58
235 forum posts
53 photos

Thanks Jason

Dougie

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