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7 1/4 garratt

axles boxes

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craig fowler22/04/2013 09:12:29
16 forum posts
Hi everyone.

The garratt ive just started building will be the first engine ive made / designed that has a sprung chasis...

Was just wondering, all the axle boxes ive seen so far are just blocks with bored holes for the axle. So why doesnt the axle bind and lock up when only one side moves up.

All help appreciated!!!!

Thanks
craig fowler22/04/2013 09:14:27
16 forum posts
And the same question for connecting rods too!!!!?
KWIL22/04/2013 09:37:11
3681 forum posts
70 photos

The boxes have curved vertical faces to allow for the tilt, the horns remain truly vertical.

craig fowler22/04/2013 09:55:04
16 forum posts
So does that mean theres always some sideways movement between the axle box and horn block then???
fizzy22/04/2013 14:08:21
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1860 forum posts
121 photos

Hi Kwil - Ive made plenty of axle boxes (indeed am in the middle of 4 now) but have no knowledge of any curved surfaces, can you explain please?

Fizzy

Clive Hartland22/04/2013 14:14:11
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2929 forum posts
41 photos

Craig, all you have to do is cut/file and arc curve on both faces of the bearing block as it sits in the horns. This means when the axle is lifted on one side it follows that arc.

Regards side play, you need some side play and about a 1/64 will be enough. With the Garret you are making, its turning radius is quite large so you need some play to take up the curve on the track.

You need to take care that the side play does not let the linkages fowl other parts. Do not make it like a watch to extremely close tolerances, all the parts should rotate easily when assembled.

Clive

craig fowler22/04/2013 15:38:17
16 forum posts
Thanks for your help people!!! I'll do some test samples first and give it some inspectigation...
OuBallie23/04/2013 13:56:09
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1181 forum posts
669 photos

As Clive mentioned, don't make moving parts with too tight a tolerance.
That's why locos with what appear to be totally worn out moving parts/joints work without any problem.
I've heard miniature locos clanking around the track, due to wear, but still performing quite admirably.
Reminds me of a customer who was building an Allchin and who got tolerances so tight, he scraped paint off when doing final assembly.
I don't make sliding/rotating parts a push fit on miniature locomotives, and that philosophy has stood me in good stead over the years.
Too tight a fit could/would induce binding/lockup.
I will be making easy fits on my 4" Little Samson, with exceptions of course.
Geoff - It's sunny!

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