How much axle movement (slop) in a 5" Sweet Pea axle?

I have recently completed a 5" gauge Sweet Pea 0-4-2 chassis and the total amount of side to side movement (slop) in an axle is 80 thou. I am unable to get any definitive advice on whether this 80 thou will be OK.

My feeling is that this might be too much and I have double checked all the drawings and the frames are 11 thou less than they should be. Wheel back to back width is per drawing and 5" Gauge Association specs.

A member of a Sweet Pea forum said 2 thou slop, a respected member of my club said 1/16" which is about 62 thou and another said that his Sweet Pea is 28 thou. I have done a lot of on-line research and there was an old posting on here which said that 1/16" is OK on a 0-6-0 5" Simplex and that too tight a clearance will cause problems on tight curves.

There is a book called "So you want to build your own live steam locomotive" by an American fellow where the calculations are given. The book is quite expensive to buy and I just missed one in EBay last week.

I would appreciate any ideas or suggestions as I don't wish to jeopardise a year's work. Many thanks. Nick

IMHO sideways slop on a 4-wheel fixed wheelbase is not critical. There needs to be enough to allow the axles to tilt without binding when negotiating uneven track, but other than that they only need enough clearance to avoid rubbing. Too much on a 4-wheel chassis and it could allow it to 'waggle' more through the alternating push/pull action of the outside cylinders. On a 6-wheel fixed wheelbase more side play is required in the axles to allow it to traverse curves without binding, as the outer axles will be offset from the centre axle so the wheels will follow the curve. There is an excellent spreadsheet by Warwick Allison on the Australian Model Engineering Magazine website which provides calculations for sideways movement of bogies, pony trucks and multilple axle locomotives in relation to curvature of the track.

Hi Nick,

82 thou in total ie 41 thou either side is quite OK for a Sweet Pea, and unless you have split axleboxes there isnt much you can do about it now anyway.

On some designs clearance between the front crank pin and crosshead can be tight, but from what I remember of Sweet Pea this isnt a problem.

Cheers,

Julian

Geoff & Julian, thank you for your helpful and informative responses which have finally put my mind at rest. I can now crack on with the next phase of the project.

Once again thank you. Nick