Spacer width

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Julian Roberts
Posts: 1389
Joined: Sat Jan 09, 2010 11:33 pm

Spacer width

Postby Julian Roberts » Sun Aug 20, 2017 6:06 pm

Hi folks

I'm starting on a Crab Comet replacement chassis for Bachmann model. For a minimum radius of 3ft 6ins I need (I think!) frame spacers of 13.8 for 0.5mm sideplay each side, for 4ft I need 14.2 spacers for 0.3mm sideplay each side. (using Comet hornblocks the thin way outwards on centre axle). Probably 4ft radius will be fine as this takes no account of wheel to rail sideplay and gauge widening, so there will still be some flexibility. The intended layout is 4ft minimum but it might go for a stroll on Allan G's Grayrigg one day if it behaves itself...

I got Comet's EM spacers expecting P4 ones to give insufficient sideplay, but they are 13.1mm. Anyone know how wide the P4 ones are? I read here 14.88 but that is several years ago.

My various spacers are mostly around 13.5, or around 15.0. A Hi Level kit for a much smaller loco provided 3 EM spacers 14.1 (though without central fixing hole), but this gives me no spare. Anyone know of easily obtained ones say 14mm wide?

Yes I could file some wider ones down, but consistency will be a bore if as is all too likely I ball up and have to make several spares (especially getting the fixing hole central). Or I could make do with the 13.5 ones I have which I probably will if no one has any info.

Thanks!

Philip Hall
Posts: 1947
Joined: Mon Aug 10, 2009 7:49 pm

Re: Spacer width

Postby Philip Hall » Sun Aug 20, 2017 10:01 pm

I would use the 13.5mm spacers. I think you would hardly notice the difference in width behind the wheels, and it is much easier to adjust sideplay with washers than to have to squeeze a tiny drop of clearance out of a slightly too-wide chassis. I have never measured sideplay; it is (for me) impossible to measure fractions of a millimetre in such places.

Philip

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steamraiser
Posts: 558
Joined: Thu Dec 31, 2009 4:49 pm

Re: Spacer width

Postby steamraiser » Mon Aug 21, 2017 9:30 am

I take into account:
My back to back gauge is 17.75 mm.
Minus 1mm for the small rim on the back of Gibson wheels.
Minus another 1mm for the outer faces of horn blocks, leaves you 15.75 mm.

From memory Comet frames are thicker than most other etched frames so a dry run using your choosen frame spacers would give you a good indication as to how much side play is available.

Gordon A

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BryanJohnson
Posts: 181
Joined: Wed Jul 23, 2008 7:45 pm

Re: Spacer width

Postby BryanJohnson » Mon Aug 21, 2017 9:45 am

I can't give you a definitive value for the sideplay, but I did a spreadsheet a while ago which takes figures for the dimensions of all the parts between the back of the treads and the inside of the frames. Putting in your required value for sideplay should help you confirm which spacers are the best fit.

The spreadsheet is available at the bottom of the page. http://www.thurstastonp4.uk/downloads.htm

Regards,

Bryan

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Julian Roberts
Posts: 1389
Joined: Sat Jan 09, 2010 11:33 pm

Re: Spacer width

Postby Julian Roberts » Mon Aug 21, 2017 11:11 am

Thanks folks.

I realised I have some perfect NS 0.5mm strip 14mm wide so would just need to create a hole in the middle and fold perpendicularly - not sure it's worth the bother, thanks Phil I think I'll take your advice.

Nice spreadsheet Bryan, the answer was what I expected. The slightly difficult bit is working out the sideplay required, easy enough with the versine calculation (which I think came from Russ originally) at
viewtopic.php?f=20&t=5156&p=49405&hilit=sideplay+required#p49405

Seems to me that each loco needs a different spacer width depending on all the factors (length of wheelbase, minimum radius, frame thickness, wheel boss thickness, minimum hornblock extra width over frame, etc) and the ideal thing would be a range of spacers available in 0.5mm increments between the minimum 00 and maximum P4...?

billbedford

Re: Spacer width

Postby billbedford » Tue Aug 22, 2017 10:07 am

Julian Roberts wrote:Thanks folks.
Nice spreadsheet Bryan, the answer was what I expected. The slightly difficult bit is working out the sideplay required, easy enough with the versine calculation (which I think came from Russ originally) at
viewtopic.php?f=20&t=5156&p=49405&hilit=sideplay+required#p49405


Remembering, of course, that the sideplay is half the versine, unless you want no sideplay behind the slidebars.

Seems to me that each loco needs a different spacer width depending on all the factors (length of wheelbase, minimum radius, frame thickness, wheel boss thickness, minimum hornblock extra width over frame, etc) and the ideal thing would be a range of spacers available in 0.5mm increments between the minimum 00 and maximum P4...?


Go on then.....


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