CSB Determining spring gauge

[Paul Townsend]

Having built my first CSB loco (ancient MPD body on Bill Bedford CSB chassis kit) I need to select the best spring wire gauge. I dislike trial and error so it seemed appropriate to use the spreadsheets to determine the wire gauge.

In part this is to gain familiarity with the Sshts and build confidence.
This is in effect using the SShts backwards as fulchrum positions are preset by Bill ( and seem to be correct in that the Cof G and wheel loadings seem good.)

Bill's kit includes .011 wire but that is too thin because I have added a fair bit of lead, carefully maintaining the C of G near the centre drivers. The weight of 142gm input is the gross weight of 177gm less the unsprung weight of motor, gearbox and wheelsets.

I have attached both Ssht versions here with the relevant data inserted being the same in each case. Original SSht suggests .014" wire for average wheel deflection of 0.5mm

Original spreadsheet was attached here and now removed as causing confusion. Se Russ below and the updated version on CLAG site which should stop others following my mistake!

but "combined SSht v 1.17" gives .012"

CSB sheet - Combined version - v1.17.xls

I will try both gauges and see which performs best but am mystified that the two spreadsheets give quite different answers and am wondering why.

When I have tried both wires I will report back later this week but hope the theoreticians will debate this apparent discrepancy.

PS
A minor observation is that the latest combined Ssht doesn't save properly if using Open Office ( it does save but when reopened the file doesn't work properly) but is Ok in Excel.

[Will L]

Paul

I approve the approach, I like working backward to find the right wire size too. But I'm afraid you have fallen down the wheel/axle trap.

Alan's spread sheet, and mine which you haven't used, both specify weight per axle. Roger's original specifies weight per wheel. If you half the weights allocated (W1,W2 and W3 on Roger's sheet) to give wheel weights, you will find that they all but agree, and that the perfect answer is 11.8 thou. So Bills 11thou wire should be OK but you might like to try 12 thou if the loco sits a a trifle low.

Will

P.S. Must admit I though Russ had us all standardizing on axle weights, I'm a little surprised Roger's is still working in wheel weights.

[Paul Townsend]

Paul

But I'm afraid you have fallen down the wheel/axle trap.

Excellent.

Now I don't need to faf around with .014"

For your reward here is your version:

CSB 2 3 or 4 axle auto calc v3-2.xls

I put in the unrounded fulchrum positions ( which Alan's version doesn't allow ) and note that the centre axle bias is now green; this goes a bit too high with the rounded figures.

It shows me, as does Alan's, that I ought to move the CofG about .5mm backwards for perfection!

Good to see consistency again, TVM

[Russ Elliott]

P.S. Must admit I though Russ had us all standardizing on axle weights, I'm a little surprised Roger's is still working in wheel weights.

I did insist on a harmonised approach for the spreadsheets. Paul was still using the pre-November 2011 version of Roger's sheet, which used wheel weights. The updated axleweight version is available from the CSB page, or as a direct download.

[Russ Elliott]

Paul - it would be helpful if you could delete the "Roger's original" spreadsheet attachment in your OP to prevent it being downloaded further.

[Paul Townsend]

In response to Russ' request I have removed the undesirable sheet in my OP.

I hope the 10 bods who had downloaded it have now realised it was misleading and won't use that pre Nov'11 version.

This entire thread has been a waste of space except to ......

a) correct my mistake
b) hopefully help others avoid it
c) enhance our faith that the three versions of spreadsheets, both "original Roger version amended for axle weights" and Will's enhanced version for 2,3,4 axles and latest "combined version" from Alan all give the same answers even when "used backwards" to determine wire gauge from known fulchrum positions.

[Will L]

This entire thread has been a waste of space except to ......

d) reassure people that help and advice is only a post away

Will

[Alan Turner]

My spreadsheet isn't used "backwards" to give wire gauge, it's an integral part of my calculations to give the correct gauge of wire to achieve the desired deflection.

regards

Alan

[Will L]

My spreadsheet isn't used "backwards" to give wire gauge, it's an integral part of my calculations to give the correct gauge of wire to achieve the desired deflection.

That's true of all of them, but, as we often start out not knowing what the weight will be, we have to guess and that guess affects the calculated wire gauge. It makes sense to go back after the event, plug in the correct weight, and read off the correct wire gauge. The thing than needs to stay constant is the CofG location.

Will