Quartering driving wheels

[David Holman]

 A technical question for those with an engineering background:

 Have managed, after much messing about, to get the outside cranks on my Swilly 4-6-0T, sort of, quartered. However, having got the drivers to go smoothly, I then discovered they are not at 90 degrees, but more like 45.

 Is this going to be a problem? Seem to remember that there were examples of drivers set at 135 degrees, but would be interested to know what the technically minded of you think.

[Tullygrainey]

I know the received wisdom is that the actual angle doesn't matter so long as it's the same on all the axles but I'm not sure how far you can stray from 90 degrees before it starts to affect the running. If your drivers are running smoothly David, then I'd say you don't have a problem but it's an interesting question.

[Horsetan]

Do you not have a quartering jig?

[David Holman]

Don't need one for 7mm scale HT, as Slater's axles and wheels have square ends which takes care of the problem. Not sure a jig would help with outside cranks, so used the old school method of simply setting the first pair as the datum, then added the second pair, with the rods, quartered these as an 0-4-0, before adding the third pair of cranks and doing the same. Had got it all running nicely when I noticed one crank wasn't pushed in far enough and in correcting that bollixed the whole thing up, breaking a golden rule of stopping for a break beforehand. The cranks are soldered to the axles, by the way.

 The cranks are home made from 2mm brass strip, drilled in a jig for the axle ends and crank pins. Have used the Slater's set up for the latter, with 12BA bolts soldered in for the pin and top hat bearings on the coupling rods so pins can be fixed with nuts and washers. By leaving the bearings off, there is enough slop to quarter the wheels in pairs.

 However, my High Level motor gear box has now arrived, so I"m going to need to remove the centre axle to fit it, so might as well move it all to 90 degrees anyway. Am also thinking that that, with the keeper plate giving me a small amount of vertical movement, I might as well make the coupling rods jointed and fit a bit of springing to the outer axles.

 One of the problems of scratchbuilding is the lack of instructions and because I haven't built a loco for a couple of years, it is all to easy to forget some of the conventions. With at least two more outside framed locos to build, I must write myself an aide memoir for future reference, once I've got this one working properly!

 Hopefully a report and pictures soon.

[Northroader]

The cranks are set at 90 degrees so that as the side rods on the one side are at front or back dead centre, t’other side is exerting the full torque to turn the wheels, but I fancy you know this already. If the angle is less than 90 degrees, the effort will be diminished as the wheels rotate, but you should still be getting some torque all the time. If the angle gets too low, the rods will bind up. So, I would think try fitting the motor and see what happens. You might get a little hitch on each revolution rather than a smooth turning which will become annoying and you’ll want to rework the job, maybe they will turn well enough to leave it. Good luck with it. In the past using slaters axles I’ve put the largest diameter drivers I’ve got on the axle and scribed a mark on the tip of the tyre in line with the crank pin, then lined up by eye looking across the wheels, but I’m not sure if this would work how you’re doing it.

[Angus]

Hi David, I am trying to figure out in my head why the quartering would work at 45 degrees but not 90. Something feels wrong there, but not sure what? Are the axles themselves straight and true? Or one driver mounting hole not straight and true? 

It suggests a lack of concentricity somewhere. 

Edited December 9, 2023 by Angus

[David Holman]

Sorry Angus, 90 is fine, 45 not quite. Must be the way I tell it! Fingers crossed, sorted now, though am sure there are other things yet to bite me...

[Angus]

Ah! Sorry misunderstood. 

 

[Mayner]

I used Branchlines Multibox gear boxes for recent builds as they are less fiddly to assemble that High Level Boxes as the effects of age on my eyesight and fingers. Although I have successfully used High Level gearboxes for over twenty years, I recently began to struggle to fit the intermediate gears and the final drive grub screw.

Branchline's have the advantage of lovely old fashioned printed catalogues/leaflets and Irish and Manx models in 4 and 7mm scales

[Horsetan]

On 10/12/2023 at 8:23 AM, Mayner said:

....Branchlines have the advantage of lovely old fashioned printed catalogues/leaflets and Irish and Manx models in 4 and 7mm scales

Available in PDF form, at no charge.

[Mayner]

1 hour ago, Horsetan said:

Available in PDF form, at no charge.

Printed Branchlines catalogues/leaflets were supplied 'free' when I ordered some motors and gearboxes about 12 months ago.