Under Springing- rule of thumb?

[brozier]

Hi folks,

Does anyone know if there is rule of thumb for how far the spring guide pins can protrude through the horn keep plates?

I'm thinking of using under springing for Spencer (rather than the suggested Tich style spring pockets above the axle boxes) but being narrow gauge the wheels are relatively small diameter. So any spring pins would probably be lower than the flanges...

Is there a minimum recomended clearance (above sleepers?) or I suppose rail height for 3.5" gauge?

Thoughts anyone?

Cheers
Bryan

[simonwass]

I wouldnt have anything below rail level, you might want to visit a ground level track with points!

[havoc]

AFAIK the spring pins are fixed to the bearing blocks. So they do not move relative to the wheels, they always stay the same height above the rails.

[brozier]

A good point which I hadn't thought of even after drawing it.

It's a 3.5" gauge loco so less likely to run on ground level. What sort of clearance do 2.5" gauge locos use? Baggo?

If I do have to use the "Tich" style springs above the axle boxes. Has anyone used this style springing? I would imagine it is a bit fiddly to get the suspension adjusted.

Cheers
Bryan

[baggo]

Hi Bryan,

Had a quick look at a few drawings and some of them have spring pins extending to an 1/8" above the rails. Clearance shouldn't really be a problem if your only running on raised tracks. On some designs the valve gear eccentrics come very close to rail height! If your running on tracks with 2½" rails as at Whitwick you need to make sure that nothing hangs down low enough to catch the extra rail!

I've never used the spring above the axle box method but I would imagine it's a real pain to get the springing right as the only means of adjustment is to take the springs out every time and either swap or alter them in length. If I decided to use that method I would have to redesign it and provide some means of easy adjustment!

John

[simonwass]

I dont think there would be room under Tich axleboxes, the keeps are only 1/2" or so above the rails so you'd only get 1/4" of spring. Reeves used to sell 'Tich axlebox springs', I guess they were made to suit the expected load assuming the builder made the pockets the correct depth etc!
My Tich must have been close to maxed out as I filled the once usable tanks with lead! It doubled its weight but it still slipped up Chesterfields bank!

[brozier]

I've done a bit more research there is a picture of a Tich with under-springing in the LBSC book.

It's hard to see how low the springs are due to the angle but from the drawings I've done (using TurboCAD) it would have 0.35" from horn plates to the bottom of the flanges when the suspension is fully depressed.

Interestingly it seems like most of the designs I've looked at have just 0.25" of suspension travel.

If I make Spencer's Springs as low as the flanges I would have between 0.44" and 0.690" for the springs - fully compressed and fully extended respectively.

This is compared with 0.1875" and 0.4375" For Tich using over axlebox springing.

I think I'll start with the spring pins the same height as the flanges with a view to shortening them if they foul on anything....

Cheers
Bryan