Ride height - CSB

[David B]

I am re-building a 4-4-2 chassis having had some problems with the Gibson hornblocks. I want to use High Level hornblocks and CSB. (This is my first attempt at CSB.)

As there are already the cut-outs for the hornblock, how do I get the new guides in the right vertical position to get the ride height correct? Where do I have the bearing in the hornblock as the weight of the body is going to move the bearing up the guide?

David

[Russ Elliott]

Ask yourself this, David - if this was being built without a CSB, where would you put the hornguides?

[David B]

Ask yourself this, David - if this was being built without a CSB, where would you put the hornguides?

To answer your question, I'd just fit them in the hole I have, but then with the Gibson hornblocks, the bearing rides at the top, springing just working to take out hollows and there is a screw to adjust ride height. The CSB system I understood to operate with springing both up and down, and there is no screw adjustment.

I don't know enough about CSB (which is why I would appreciate some guidance), but I would have thought that the vertical positioning of the hornblock guide is important. If I were starting from an axle hole and cutting out the slots for the guides I would be able to use the High Level jig, but I am not as the slots are already there.

Am I looking for difficulties that don't exist?

David

[Russ Elliott]

David - you need to form an opinion on where the axle datum needs to be on the frame you've got.

The presence or absence of a CSB is not relevant to that process.

[Chris Mitton]

Hi David

If you get Chris Gibbon's CSB jig for drilling the mounting points for the spring beam, it includes adaptor plates for pre-cut hornguide slots and the instructions show how you do it - use (very) short bits of 0.5mm wire soldered into the plate, to form locating pegs so that the plate, complete with bearing, slots into the hornguide slot. Assuming, that is, they are the normal 6 mm wide. Also, I believe most designers put the top of the slots 4 mm above the theoretical axle line that would give the right guide height. See http://www.highlevelkits.co.uk/ for more....

I've set one frame up this very afternoon with the High Level jig and its adapters, slightly fiddly but it works and is as accurate as you want it to be!

Hope this helps,
Regards
Chris

[David Thorpe]

I didn't have one of the High level guides for the last CSB chassis I did, and like you I was a bit bewildered as to how I could establish the correct ride height - again like you, I was rebuilding an old chassis that had all the hornguide slots cut out. But, like Chris, I had been given to believe that most designers put the top of the hornguide slots a uniform height above the theoretical axle line (although I didn't at the time know that was 4mm - had I done so it would have been a lot simpler!). Acting on that premise, I found a hornguide for a rigid axle (ie with a single hole in it - probably an MJT one), put in a 1/8" axle bearing, and put it in place in one of the hornguide slots in the chassis. I then carefully marked on the chassis the centre point of the axle bearing, measured the height of that from the top of the chassis, and then used that measurement to mark out the axle centre line on the whole chassis. I was then able to mark out the chassis for CSBs as per the CLAG recommendations (http://www.clag.org.uk/beam-annex4.html). It worked - the subsequent ride height was fine.

DT

[David B]

If you get Chris Gibbon's CSB jig for drilling the mounting points for the spring beam, it includes adaptor plates for pre-cut hornguide slots and the instructions show how you do it - use (very) short bits of 0.5mm wire soldered into the plate, to form locating pegs so that the plate, complete with bearing, slots into the hornguide slot.

Thanks, Chris . . . So that's what the extra bits on the end of the jig are for! I didn't get any printed instructions and having gone through those on the High Level site not found anything about the 'extras'. Now I know and understand. This is very helpful.

I didn't have one of the High level guides for the last CSB chassis I did, and like you I was a bit bewildered as to how I could establish the correct ride height - again like you, I was rebuilding an old chassis that had all the hornguide slots cut out. But, like Chris, I had been given to believe that most designers put the top of the hornguide slots a uniform height above the theoretical axle line. Acting on that premise . . .

. . . and Davey. I am glad I am not alone in thinking how to get the ride height correct. Your post is reassuring. The cut-outs are my own as the original frames were designed for OO and date from the mid 1980s when rigid chassis were the norm. From the diagrams with the kit and in my reference book I have worked out a line for the axles so I will work from there and set the adaptor plates (that Chris in his post has explained) on that line.

The little light bulb in my head may not be up to 100W yet, but it is getting there with your help. Thank you both, and to Russ.

David

[Will L]

When I was tackling this problem on a set of Gibson precut frames, I came to the conclusion is that for a standard 6mm wide by 7mm deep frame cut out, the answer is that the axle centre line should be 4mm down from the top of the cut-outs. See this post for more details.

Will

[Russ Elliott]

Will - thanks for that post link - I had forgotten the '4mm below the top of the cut-out', but I wonder if frame manufacturers other than Gibson adopted such a custom.

[Will L]

Will - thanks for that post link - I had forgotten the '4mm below the top of the cut-out', but I wonder if frame manufacturers other than Gibson adopted such a custom.

Good question Russ. They must be fairly consistent or the various horn block systems wouldn't work well with them. There again as most chassis kits have rigid axle holes etched in with only half etched horn block cuts outs so the problem doesn't arise because you can measure where the axle centre line will be. The problem only really occurs with Gibson precut chassis sides. The only other non Gibson example I have to hand is a Riceworks/LRM J65, which does have axle holes and half etched horn block cut outs. This had 6mm by 7.5mm cut outs and the axle centres are 4.5mm down from the top. So perhaps the right way to look at this is 3mm up from the bottom edge!

Will

[Jol Wilkinson]

Will - thanks for that post link - I had forgotten the '4mm below the top of the cut-out', but I wonder if frame manufacturers other than Gibson adopted such a custom.

Good question Russ. They must be fairly consistent or the various horn block systems wouldn't work well with them. There again as most chassis kits have rigid axle holes etched in with only half etched horn block cuts outs so the problem doesn't arise because you can measure where the axle centre line will be. The problem only really occurs with Gibson precut chassis sides. The only other non Gibson example I have to hand is a Riceworks/LRM J65, which does have axle holes and half etched horn block cut outs. This had 6mm by 7.5mm cut outs and the axle centres are 4.5mm down from the top. So perhaps the right way to look at this is 3mm up from the bottom edge!

Will

I used the "4mm above axle datum" for the top of the cut-out in the kits I designed for John Redrup of LRM. I think that this is a notional "standard" but clearly each designer can do his own thing and handrawn artwork may create variations, as possibly the case with the Riceworks kits.

The instructions for the LRM CSB/spring etched adaptor fittings stipulate setting the csb datum 4.0 mm above the axle datum, to give .5mm static deflection.

Hornblock spring adaptor dwgs.pdf