Advice on building a compensated chassis

[hayfield]

I want to build a compensated chassis, fixed rear wheel drive and rocking beam on the front two axles

 

 

I am building this Southeastern Finecast LNER J69 chassis

 

 

Am I correct in thinking I remove the 2 sets of springs

Then cut out both slots

Finally use the hole midway between the two axles and modify the L shaped frame spacer to a flat bar or just use the rocker bar as the central frame spacer

 

Rather than a central bar would two independent rocker bars be better

 

Thanks

[jamieb]

Try and leave the springs intact then you can use them as bearing retainers.

Cut diagonally through the axle holes on the hornblocks then you can gently bend the etch back and forth to cleanly snap them off

[hayfield]

jamieb

 

Thank you just the type of advice I need

 

A bit more information, years ago (somehow) I built a Percy compensate chassis (which still works) without a chassis jig. These days I have a Hobby Holidays chassis, but only used it for rigid chassis to date

[Captain Kernow]

Don't do two independent bars unless the third axle is also to rock, on it's own central pivot. This would be twin beam compensation. 

 

The single beam system should be fine.

 

[Captain Kernow]

You can also  (carefully) remove the springs and re-attach them to a removable plate  (eg. copper-clad). Depending on your chosen hornblocks, this would enable removal of each of the leading and centre wheelsets.

 

[Izzy]

I don’t find single beam compensation to be totally stable so when not using springing of the axles by some means always use twin beams. Normally I just allow the other axle a bit of downward movement. As you will I presume be using a HL gearbox having axle movement on the rear axle won’t be a problem. I also always allow the axles to drop out of the chassis. This makes mounting/quartering press fit Gibson/Sharman/Ultrascales so much easier.

 

 Bob

[Barclay]

Any thoughts on hornblocks? I can recommend the MJT type from Dart castings and the High Level ones. London Road Models make a cast one which does away with the need to assemble. I have some but haven't used them yet.

 

When setting the square bearings up in the units always keep them in the same unit and the same way up. A small x scribed onto the bottom of the bearing makes sure you always put it in the same way. This is to ensure that manufacturing tolerances don't throw out the wheelbase very slightly if you put one back in a different orientation.

 

When fitting up the bearings they sometimes need a rub on the finest abrasive until they run smoothly up and down, but don't overdo this. I always switch to Brasso when I'm getting close - flood the thing with it and work the bearing up and down until it is smooth enough to drop under its own weight.

[Pierview]

If you don't already have it I would recommend  Iain Rice's  book "Locomotive Chassis Construction in 4mm". Like all his books it is very readable and has a  chapter on compensation. It certainly helped me to understand what i had previously thought to be a dark art!

 

Barry 

[hayfield]

8 minutes ago, Barclay said:

Any thoughts on hornblocks? I can recommend the MJT type from Dart castings and the High Level ones. London Road Models make a cast one which does away with the need to assemble. I have some but haven't used them yet.

 

When setting the square bearings up in the units always keep them in the same unit and the same way up. A small x scribed onto the bottom of the bearing makes sure you always put it in the same way. This is to ensure that manufacturing tolerances don't throw out the wheelbase very slightly if you put one back in a different orientation.

 

When fitting up the bearings they sometimes need a rub on the finest abrasive until they run smoothly up and down, but don't overdo this. I always switch to Brasso when I'm getting close - flood the thing with it and work the bearing up and down until it is smooth enough to drop under its own weight.

 

Barclay

 

Thanks for the tips re hornblocks

 

I do have quite a range to choose from in my spares box

Perseverance, Exactoscale (+springs) Alan Gibson, MJT, London Road Models, High Level and Maygib

 

I have tried both Maygib and Alan Gibson without any luck, but many years ago I used Perseverance which worked in 00 gauge

 

Suggestions welcome, my own thoughts are for Perseverance as I have had success before, I have heard London Road Models and High Lever to be very good and also heard good reports about MJT

[hayfield]

5 minutes ago, Pierview said:

If you don't already have it I would recommend  Iain Rice's  book "Locomotive Chassis Construction in 4mm". Like all his books it is very readable and has a  chapter on compensation. It certainly helped me to understand what i had previously thought to be a dark art!

 

Barry 

 

Barry 

 

Thanks I have 3 of his books on loco construction, Locomotive kit chassis construction in 4 mm scale and both etched and whitemetal loco construction  (I seem to have all the gear and no idea!!)

[Brassey]

I tend to build the chassis rigid on the Hobby Holidays jig first. That way I’ve got a better chance of getting it square and the axles parallel.  Don’t forget the hole for the beam first. 
 

i cut out  the horn guides after. We’ve had this discussion before but High Level hornblocks are by far the best 

 

use the rods to set the jig for the hornblocks. Obviously need to be jointed

[Captain Kernow]

5 hours ago, Izzy said:

I don’t find single beam compensation to be totally stable so when not using springing of the axles by some means always use twin beams.

I won't disagree with this notion but I've always found single beam systems to work satisfactorily, ie. the locos run smoothly and don't derail.

 

Single beams also have the advantage that (unless they are part of the kit) they are easier to fabricate and 'get right' (fewer moving parts). 

 

There are different ways of doing twin beam compensation, eg. using the chassis hornblocks and providing beams that act on the bearings or mounting the actual bearings (front and middle) in the beams themselves.

 

I did read a very interesting suggestion in one of the recent MRJs (sorry, can't recall but if it's important I'll check) that you can improve on single beam systems by arranging the single beam pivot further forward, so that there is more weight on the leading drivers. This makes sense to me and I am planning to try it in due course.

 

One or two of my P4 locos are rigid, however, where an existing RTR chassis is used (eg. in a recent pannier I did, currently featured in S4News 226). Provided the track is OK, you should have no derailments. Having said that, if going to the trouble of building a chassis kit, it makes sense to put some kind of compensation or springing in, if only to improve electrical pick up.

 

 

[MarkC]

I'm another one who likes the single beam "Flexichas" arrangement, a la Mike Sharman, if I'm installing compensation myself, as opposed to twin beam as supplied in many kits these days.

 

It's what I started with; must be a bit too "set in my ways" to change 

 

Having said that, both systems have their merits 

 

Mark

[Jeff Smith]

My P4 chassis had all been beam compensated until I decided to use the Comet sprung hornblocks for a GWR Mogul.  Absolutely superb but requires a heavy body to function at their best.  I did this because I wanted to drive the centre axle but would recommend whichever one was being driven.

 

Hornblocks, whichever type you use, need to have enough play when sliding to allow the axle to tilt slightly.

[hayfield]

17 hours ago, Captain Kernow said:

I won't disagree with this notion but I've always found single beam systems to work satisfactorily, ie. the locos run smoothly and don't derail.

 

Single beams also have the advantage that (unless they are part of the kit) they are easier to fabricate and 'get right' (fewer moving parts). 

 

There are different ways of doing twin beam compensation, eg. using the chassis hornblocks and providing beams that act on the bearings or mounting the actual bearings (front and middle) in the beams themselves.

 

I did read a very interesting suggestion in one of the recent MRJs (sorry, can't recall but if it's important I'll check) that you can improve on single beam systems by arranging the single beam pivot further forward, so that there is more weight on the leading drivers. This makes sense to me and I am planning to try it in due course.

 

One or two of my P4 locos are rigid, however, where an existing RTR chassis is used (eg. in a recent pannier I did, currently featured in S4News 226). Provided the track is OK, you should have no derailments. Having said that, if going to the trouble of building a chassis kit, it makes sense to put some kind of compensation or springing in, if only to improve electrical pick up.

 

 

 

 

One of the reasons I chose EM gauge is its more forgiving

 

An interesting thought about moving the beam forward, presumably you need a loco with a decent weight ?

[hayfield]

17 hours ago, MarkC said:

I'm another one who likes the single beam "Flexichas" arrangement, a la Mike Sharman, if I'm installing compensation myself, as opposed to twin beam as supplied in many kits these days.

 

It's what I started with; must be a bit too "set in my ways" to change 

 

Having said that, both systems have their merits 

 

Mark

 

I guess its a bit simpler than making a twin beam loco

[hayfield]

14 hours ago, Jeff Smith said:

My P4 chassis had all been beam compensated until I decided to use the Comet sprung hornblocks for a GWR Mogul.  Absolutely superb but requires a heavy body to function at their best.  I did this because I wanted to drive the centre axle but would recommend whichever one was being driven.

 

Hornblocks, whichever type you use, need to have enough play when sliding to allow the axle to tilt slightly.

 

Jeff

 

A spanner in the works, I have got a High Level CSP measuring tool but its a bit advanced at the moment

[hayfield]

 

Another related question, at what point do you paint the chassis. The last thing you want is for the paint to glue everything together

[MarkC]

1 hour ago, hayfield said:

 

I guess its a bit simpler than making a twin beam loco

Oh it is, John. Easier to adjust ride height too, of course.

 

Mark

[Captain Kernow]

3 hours ago, hayfield said:

An interesting thought about moving the beam forward, presumably you need a loco with a decent weight ?

Yes, I would say so.

 

[Captain Kernow]

3 hours ago, hayfield said:

Another related question, at what point do you paint the chassis. The last thing you want is for the paint to glue everything together

Provided I can remove the wheelsets at any stage (either unscrew Markits types or drop whole Gibson or Ultrascale types out), then I would probably wait for the chassis to be completed, clean any oil or flux residue etc. from it and then spray it with primer and then black (although I sometimes put a weathered dirt finish straight onto the red oxide primer).

 

If for any reason I can't remove any wheelsets (eg. fixed axle and Gibson or Ultrascale wheels and can't drop it out of the chassis), then I would certainly (hand) paint the area behind the wheels with primer and then black, before finally fixing the wheels in place.

 

In such circumstances, where there is one or more wheelset permanently fixed to the chassis, I would then brush paint everything, from the primer to the main colour (whether black and then weathering or weathering mix straight on to the primer).

 

If wheelsets can be dropped out or otherwise removed, I cut circular holes in a piece of card the exact diameter of the wheel (or possibly 0.5mm less) and then press each wheel into the card and use that as a basis for spraying the primer and top coat onto the wheel.

 

Wheel treads are then cleaned, once the final coat of weathering has hardened off, by using cotton buds dampened (but not soaked) in cellulose thinners. This is easier with Markits type wheels, as each wheel in turn can be attached to an axle and spun in an electric drill, while your other hand carefully holds the cotton bud against the tread.

 

Tempting though it might be to spray the entire chassis while it is 'under power', I am uneasy about this and feel that the extra work in terms of painting it as per the above is worth it, as compared to the risks of gumming the whole thing up with paint.

 

[Jol Wilkinson]

On 04/02/2022 at 11:46, Barclay said:

Any thoughts on hornblocks? I can recommend the MJT type from Dart castings and the High Level ones. London Road Models make a cast one which does away with the need to assemble. I have some but haven't used them yet.

 

When setting the square bearings up in the units always keep them in the same unit and the same way up. A small x scribed onto the bottom of the bearing makes sure you always put it in the same way. This is to ensure that manufacturing tolerances don't throw out the wheelbase very slightly if you put one back in a different orientation.

 

When fitting up the bearings they sometimes need a rub on the finest abrasive until they run smoothly up and down, but don't overdo this. I always switch to Brasso when I'm getting close - flood the thing with it and work the bearing up and down until it is smooth enough to drop under its own weight.

Good advice.  I now only use the LRM cast hornguide/turned bearing. Partly because I have a good stock of them and partly because I had some issues with MJT, etc. mainly with solder getting in the wrong places. The LRM version may need a bit of fitting as there may be  some shrinkage in the casting process but a couple of minutes work with a good quality needle file will soon take care of that, then number marking with a small punch so that they always go back together and in the same orientation. 

 

Like Captain Kernow I have found the single beam/fixed driven axle the easiest approach. I've also been able to readily assemble chassis with just the taper end axle jigs, starting with the fixed axle as  the datum.

 

Provided you have well laid track without changes of rail height at rail joints, crossing vees, switch rails etc. (check with your finger, you can detect differences as little as .001"), then movement of the fixed axle won't be evident. Any derailments will be the result of incorrect B2B, wobbly wheels or the track not being made to controlled standards.

[hayfield]

1 hour ago, Jol Wilkinson said:

Good advice.  I now only use the LRM cast hornguide/turned bearing. Partly because I have a good stock of them and partly because I had some issues with MJT, etc. mainly with solder getting in the wrong places. The LRM version may need a bit of fitting as there may be  some shrinkage in the casting process but a couple of minutes work with a good quality needle file will soon take care of that, then number marking with a small punch so that they always go back together and in the same orientation. 

 

Like Captain Kernow I have found the single beam/fixed driven axle the easiest approach. I've also been able to readily assemble chassis with just the taper end axle jigs, starting with the fixed axle as  the datum.

 

Provided you have well laid track without changes of rail height at rail joints, crossing vees, switch rails etc. (check with your finger, you can detect differences as little as .001"), then movement of the fixed axle won't be evident. Any derailments will be the result of incorrect B2B, wobbly wheels or the track not being made to controlled standards.

 

Joel

 

Thanks for the advice, I think for the first one I will use a set of Perseverance, firstly as I have used these before, secondly I have quite a few compensated Perseverance chassis in stock. However I do want to try both the London Road models and High Level hornblocks I have.

[Guest WM183]

Re: single beam compensation

 

So the axles make contact with the beam. Does this lead to wear on the beam at all, or to noise or squeaks due to the rubbing of the axle on the beam?

[Jol Wilkinson]

I have only seen a minimal amount of wear, as in a polishing of the axle at the contact point and never heard of a noise problem,  Unless the model is doing high mileage (such as the locos at Pendon) noticeable wear is unlikely with properly installed axles and bearings. Steel axles in plastic bearings, etc.  is a different matter