CSB Without Tears, SN194/Scaleforum 2015

[Will L]

Fascinating article in Scalefour News 194 from Bill Bedford giving a way of estimating the CSB plot without necessarily using any of the available spread sheets. The article is accurate in it description of the nature of CSB solutions and contains a useful table from which you can read off a CSB solution for a wide range of wheel bases. I haven't personally sat down and checked the answers but I can't see any reason to doubt that it does what he claims.

You may have noticed I will be all Scaleforum manning a Demo desk to discuss suspension system, CSB Compensation or otherwise and their implications. I shall have a copy of SN194 with me and I will be happy to discus it with anybody who's interested.

[PeteT]

Bill gave me a very useful estimate when I did an Stanier 0-4-4 tank (covered in the build a loco challenge on RMW) and it runs like a dream. I just need to finish the superstructure... I was flapping about whether/what I needed to account for with the rear bogie, but his rule of thumb worked well.

I look forward to seeing his article.

[PeteT]

Hi Will,

It was good to chat to you on Sunday - but something I didn't take in about the C12 front bogie was the actual bogie pivot. I seem to remember there being a gromit or something between the surfaces, rather than just the top of the bogie against the rubbing plate, so having a bit of an air gap in which the pickup plungers get plunged...

Cheers,
Pete

[Will L]

Hi Will,

It was good to chat to you on Sunday - but something I didn't take in about the C12 front bogie was the actual bogie pivot. I seem to remember there being a gromit or something between the surfaces, rather than just the top of the bogie against the rubbing plate, so having a bit of an air gap in which the pickup plungers get plunged...

Pete

There is a full write up with pictures of that bogie already on the forum, follow this link to see it.

However this too is silent as to the nature of the bogie pivot. It is a top hat bearing like this in section.

top hat.jpg

So you can screw the retaining bolt down hard but leave the bogie free to pivot and rock unimpeded, a habit I picked up from attaching bogies to coaches. I can't remember if the top hat bearing came with the kit or if I manufactured my own. This is something I do quite often, in my lathe free world it is done simply by finding a bit of tube a sliding fit on the bolt I plan to use, soldering a washer of the appropriate size over one end, and cutting it off to the desired length.

[garethashenden]

Hi Will,

It was good to chat to you on Sunday - but something I didn't take in about the C12 front bogie was the actual bogie pivot. I seem to remember there being a gromit or something between the surfaces, rather than just the top of the bogie against the rubbing plate, so having a bit of an air gap in which the pickup plungers get plunged...

Pete

There is a full write up with pictures of that bogie already on the forum, follow this link to see it.

However this too is silent as to the nature of the bogie pivot. It is a top hat bearing like this in section.

top hat.jpg

So you can screw the retaining bolt down hard but leave the bogie free to pivot and rock unimpeded, a habit I picked up from attaching bogies to coaches. I can't remember if the top hat bearing came with the kit or if I manufactured my own. This is something I do quite often, in my lathe free world it is done simply by finding a bit of tube a sliding fit on the bolt I plan to use, soldering a washer of the appropriate size over one end, and cutting it off to the desired length.

Does the bogie just rotate or is there lateral movement as well?

[Will L]

The pivot hole in the bogie stretcher plate, through which the top hat bearing pass, is oval so there is a degree of uncontrolled side to side movement (less than 1 mm). There is no side play available on either driving axle. The bogie had provision for a spring to control side play but I found no way of making this spring light enough to actually work, so it got left off. Presumably there is friction between bogie pick-ups and the ribbing plate, and this seems to be sufficient to ensure there is some degree of steering and the loco runs smoothly with no sign of side to side uncertainly. An alternative would be to have no side play on the bogie pivot and have some side play on the driven axle by the bogie instead. I have a pre - CSB 0-4-4 chassis (compensated) built like this, it works well too. The C12 has the motor driving the leading axle which is why I chose to restrict the side play. In the event I'm not at all sure this was a necessary decision and if I did it again I would probably go for the rigid bogie pivot, even though there is nothing about they way she runs to suggest anything wrong with the current arrangement.

[PeteT]

Thanks Will.

So with the bogie free to rock & roll a bit around yhe top hat, the weight is effectively transferred through the plungers? Or is there a small spring around the pivot too?

I do like the design though - excellently simple yet effective!

[Will L]

So with the bogie free to rock & roll a bit around the top hat, the weight is effectively transferred through the plungers? Or is there a small spring around the pivot too?

No the plunger pick ups carry all the weight

[PeteT]

No the plunger pick ups carry all the weight

Excellent, thanks Will. I'll have a play!

[billbedford]

No the plunger pick ups carry all the weight

Why? There were never any secondary springs on steam loco bogies.

[jim s-w]

They didn't have CSBs either Bill!

Jim

[billbedford]

No, but they had springs. All CSBs do is to take away the skilled and tedious job of setting the spring rates. One of my acquaintances reckoned his gang once took 3-4 to set up the springs on a full-size restored pannier tank.

[Will L]

No the plunger pick ups carry all the weight

Why? There were never any secondary springs on steam loco bogies.

Because it was expedient to do it that way, no better reason. I expect, but don't know for certain, that the sprigs are full compressed when, the loco is static. The resulting bogies does ride well however.