7 1/4 garratt

This topic has 8 replies, 5 voices, and was last updated 23 April 2013 at 13:56 by OuBallie.

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22 April 2013 at 09:12 #117529
craig fowler
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@craigfowler33724
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
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22 April 2013 at 09:12 #22594
craig fowler
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@craigfowler33724
axles boxes
22 April 2013 at 09:14 #117530
craig fowler
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@craigfowler33724
And the same question for connecting rods too!!!!?
22 April 2013 at 09:37 #117533
KWIL
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@kwil
The boxes have curved vertical faces to allow for the tilt, the horns remain truly vertical.
22 April 2013 at 09:55 #117536
craig fowler
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@craigfowler33724
So does that mean theres always some sideways movement between the axle box and horn block then???
22 April 2013 at 14:08 #117548
nigel jones 5
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@nigeljones5
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
22 April 2013 at 14:14 #117550
Clive Hartland
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@clivehartland94829
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
22 April 2013 at 15:38 #117556
craig fowler
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@craigfowler33724
Thanks for your help people!!! I’ll do some test samples first and give it some inspectigation…
23 April 2013 at 13:56 #117616
OuBallie
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@ouballie
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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