An Experiment with compensation (take 2)

[petermeyer]

So on my first post on this subject http://www.scalefour.org/forum/viewtopic.php?f=89&t=7896&hilit=experiment I thought I was being clever powering the front driver of this LNWR Experiment 4-6-0. I also declared that the articulated chassis was working. However, as things moved on although I found it worked fine as an 0-6-0, but with the bogie on and with some bodywork attached thus changing the balance, it began to derail on my somewhat sharp curves.

This I put down to 1) the bogie 2) lack of side play of the front driver. I always follow the High Level instructions which is to have no side play on the gearbox axle. So, as I may end up with even tighter curves on the layout, to resolve the problem, I reverted to my tried and trusted method of powering the rear axle. Here's a reminder of what the thing looks like:

byzantium (2).jpg

As can be seen the rear axle is completely under the cab floor. So I needed a drive stretcher to get the gears under there. I also changed the HL RoadRunner+ to a LoadHauler+ giving more height which allows for a 1628 motor. The gearbox was soldered up at right angles:

loadhauler.jpg

In rebuilding the chassis I had the opportunity to fit the ashpan profiles which I'd missed first time and conveniently they hide the gearbox/driverstretcher mostly from view:

chassis.jpg

I retained the "rubbing plate" but now non-functioning on the front of the chassis to act as a spacer as this helps to achieve the correct buffer height. The articulated front of the chassis has now been soldered up solid and a slide added to accommodate the bogie:

slide.jpg

The hornblock guides have been soldered back in into their new forward positions and a compensation beam has been added between the front 2 drivers. Next stage is back into the paint shop before I can fit the wheels and brakes again to see if anything has improved. Fingers crossed...

[Winander]

I always follow the High Level instructions which is to have no side play on the gearbox axle.

I don't know where you read that instruction but section J in the hints and tips https://www.highlevelkits.co.uk/_files/ ... 5f7eb6.pdf specifically documents sideplay on the gearbox axle.

[petermeyer]

I always follow the High Level instructions which is to have no side play on the gearbox axle.

I don't know where you read that instruction but section J in the hints and tips https://www.highlevelkits.co.uk/_files/ ... 5f7eb6.pdf specifically documents sideplay on the gearbox axle.

I've been building these gearboxes for some time and my memory goes back to some instructions that must pre-date the hints and tips. On digging these out they state: "You may need to fit washers between the gearbox sides and frames in order to prevent the gearbox moving sideways on the axle. It is also advisable to fit washers behind the wheels on this axle to eliminate any sideplay."

If these instructions have been superseded then I missed that.

I did take advice on the decision to change the driven axle from the Area Group and some did say I could have sideplay on the driven axle. but I was also was prompted by a Finney Duke I recently completed. This has twin beam compensation and all wheels move. However, when I compared that running with a City which has a fixed rear driven axle and a Sharman style beam on the bogie and leading axle, that City runs smoother. So I chickened out and reverted to what I knew worked.

Sideplay was discussed on the recent Society Virtual Forum and the view was that sideplay should be 0.5mm each side or a total of 1mm. The driven axle on this loco has a large motor that also rests on a spacer designed for the purpose. Bearing in mind the axle and motor have to both move sideways in that situation, I'm not sure there was enough room in the boiler space to allow this anyway. I've not fixed it yet on the Experiment but the majority if not all my other LNWR locos have a fixed rear axle with no sideplay and some are my best runners. We''l see...

[Winander]

If it works then stick with it. The motor doesn't have to move, just don't pack the axle so it is able to move independently of the gearbox. You could build it with some sideplay and if you think it would be better without, then push fibre washers onto the axle with a bit cut out - less than the axle diameter so they don't fall out. If there's sideplay on the other axles, then you probably don't need any on the rear as long as it reverses OK.

[Eastern]

I would suggest it perhaps depends on the age of the gearbox. The High Level gearbox detailed designs have been updated from time to time. For example, I have an older version of the Highflier which includes the advice to take steps to reduce side play to a minimum, whereas I then have a newer version which does not. The newer one also came with a copy of the hints and tips sheet. However, I also have an older Roadrunner Gearbox where there is a specific instruction to prevent sideplay to maintain a clearance gap between the 1st stage nylon gear and the final brass gear to prevent wear on the nylon gear. I therefore suggest it is best to follow whichever instruction came with the gearbox you are using.

[Will L]

High level gear boxes, lets be clear about side play and where it could occur.

There should be none between the final drive gear and the gear box frame, and the gear box is set at at a fixed point on the driving axle.

There may be side play between the gearbox frame and the chassis sides, not much with some designs its true. So side play on the driven axle is possible. Its up to you to ensure there is the desired clearance between the wheels and the chassis, and clearance in the body work to allow for the side to side movement of the motor. Generally the amount of side play is set by washes between driving wheels and the chassis, but i suppose putting them between gearbox frame and the chassis sides is a possibility.

See high levels own hints and tip sheet

[davebradwell]

You really don't normally want significant sideplay on leading or trailing coupled axles, regardless of whether they're driven, as it enables the loco to yaw. This allows the front to swing out more and actually means the bogie must travel even further and you'll never get a non-load bearing bogie to guide the loco, especially on sharp curves. In any case, sideplay brings the wheel flange closer to the back of the brakes - potential short - or in the other direction the coupling rod closer to the end of the pin in the centre of the brake block - potential clout. Suggest being wary of using a standard amount.

Your motor restraint should allow motor to move sideways a little, even if you think there's no sideplay. There's no reason why a fixed driven axle should give better a running chassis than a moving one without some other factor coming into play - clearance in extra axlebox affecting the jigging operation perhaps? Poor motor restraint? In fact the rigid axle just follows the shape of the track which is directly reflected in the motion of the body rather than averaging out the bumps with the other axles. You should still be able to fettle your Duke to achieve perfection.

If there's insufficient side movement in the bogie you should be able to feel if chassis is jamming in the curve.

DaveB

[petermeyer]

Thanks all for the helpful replies.

I will respond in detail in due course when I get back to my workbench. But to cut a long story short, here’s the guidance from the HL tips and hints:

“ If you need any more sideplay on the driven axle than the design of the box will allow, then you’ll need to arrange for the gearbox to move sideways with the axle, or, allow more sideplay on non-driven axles.”

I elected for the latter. Details of the specific arrangement to follow.

[petermeyer]

Success: LNWR Experiment negotiates 3 foot curve on test plank.

[petermeyer]

When I started to paint the wheels on my LNWR C1, I found still sat in the paint queue box, a LNWR Precursor class chassis that was waiting for a final coat. Looking at the dates on this thread, it must have been languishing in there for about a year as I am building the Brassmasters Precursor in tandem with the Brassmasters LNWR Experiment! I am in the habit of painting the wheels and chassis before assembly. As I am approaching the stage of having a layout that will accommodate a decent length train in the fiddle yard, an express loco has moved up the todo list for testing purposes. So the Precursor chassis was given a coat of dirty black when I had the airbrush going and the chassis put back on the workbench when dry.

I am using a LRM Precursor Tank (4-4-2) chassis for this loco for which I lopped off the end of the frames with my trusty metal shears to produce a 4-4-0. I do have a Precursor Tank to build so that is likely to get the Brassmasters chassis. These kits do share a common history as I am told that the LRM Precursor Tank initially used the BM chassis.

Here is the current state of play. As can be seen there has been some minor surgery for which the scars are still showing, The long 10ba screw at the front is used to go through the running plate and up into and to attach the boiler which is currently removable. Motor is a Mashima 1424 with a High Level RoadRunner Compact gearbox in the underslung fashion.

IMG_1802.jpg

I am currently doing battle with the tenders for these two Brassmasters locos, one of which is short of the Whale conversion cast whitemetal tender top. (see appeal elsewhere in the wants section). As these kits have become mingled, I'm not sure which one had the missing part but both were supposed to have the Whale tender conversion. If all else fails, the Experiment will end up with an early Bowen-Cooke tender which came out in 1911 so just in time for my period...

[Jol Wilkinson]

Hi Peter,

I built my LNWR Precursor with an etched set of frames based on the LRM Precursor Tank frames I designed. The attached pdf shows the profile I used for compensation on the leading coupled axle and with the LRM bogie as used in the LRM LNWR 4-4-0 kits.

Precursor one off.pdf

I had built my LRM Precursor Tank with the Brassmasters chassis as originally supplied but when they became uneconomic for John Redrup to buy in, designed the new frames. Although not listed as a separate kit, I am sure John would supply the etches, etc. if asked.

Ref your Wanted advert for a BM Whale tender conversion I have had a search and found one excess to requirements in my BM LNWR Experiment kits boxes. It contains the cast top and two sets of brass etches. I have two BM Experiment kits, the original I bought (untouched) plus a part built one from the estate of Tony Osmond. I'll probably complete that one when get my hand/eye in again to building kits and sell off the other. Contact me re the Whale tender conversion.

Jol

[petermeyer]

Hi Peter,

I built my LNWR Precursor with an etched set of frames based on the LRM Precursor Tank frames I designed. The attached pdf shows the profile I used for compensation on the leading coupled axle and with the LRM bogie as used in the LRM LNWR 4-4-0 kits.

Precursor one off.pdf

I had built my LRM Precursor Tank with the Brassmasters chassis as originally supplied but when they became uneconomic for John Redrup to buy in, designed the new frames. Although not listed as a separate kit, I am sure John would supply the etches, etc. if asked.

Jol

Thanks Jol

Yes I was very much inspired by your build on RM WEb and followed that closely but could not produce my own frames. BUT the Precursor Tank chassis is available and indeed listed as a separate kit on the LRM site:

CHAS5 LNWR 4-4-2 Precursor Tank Chassis £43.00

and this is what I bought (a while ago at a show) and took my shears to in order to create a profile pretty much the same as yours.

As your designed kit for the tank has a radial truck I have kept that to use on my Precursor Tank which will use a Whitemetal GEM bodyline kit and the BM chassis kit for the rest. The Tanks had smaller driving wheels (the same size as the Experiment) and I also bought a set of Sharmans from John at the time for the tank.

Thanks very much for the offer of the Whale tender conversion and I will PM you about that. The Whale tender also had curved springs but the Bowen-Cooke ones supplied in the kits are straight. I have asked BM about that but had no reply. Looking at your build on RM web it looks as though you have used the straight springs as supplied.

THIS PICTURE IS NOT OF MINE BUT OF JOL'S PRECURSOR FOR REFERENCE WHICH I "BORROWED" FROM RM=WEB BEFORE THE BIG CRASH

Brassmasters-LNWR-Precursor.jpg

Cheers

Peter

[Jol Wilkinson]

Hi Peter,

I looked at the LRM website but missed that the Precursor Tank chassis kit was on there.

The BM Whale conversion kits that I have and also the one I used had the cast top but no other castings so I used the springs that were supplied with the loco/Bowe Cooke tender kit.

Precursor 34RS.jpg

My Precursor Tank is modelled on the earlier batch with the 6' 9" driving and 3' 9" carrying wheels.

Precursor Tank on LR.jpg

I'll send a PM about the BM Whale tender conversion kit.

Jol

[petermeyer]

Success: LNWR Experiment negotiates 3 foot curve on test plank.

Well that was a bit premature because on the completed layout the loco would go round the curves but otherwise would not run and was many that suffered from my bogie problems.

I'd fixed the articulated front end of the frames solid to the main chassis and inserted a screw/nut as pivot. I put a fairly substantial "slide". But try as I might, this and the LNWR Precursor would not run on my roundy. I'd virtually given up on these and put them on the highest shelf in the cabinet of shame well out of view. But having resolved the running on my GWR 4-4-0's I thought I'd give these a try too; and lo and behold it worked. So a simple washer saved the loco.

It now runs as seen here on a small passenger. Towards the far end of the transition the curve on this inner (down) line is at 900mm (3ft). It's using the only Whale tender I have which it currently shares with the LNWR Precursor which also recovered with the same treatment.

[petermeyer]

Well I've surprisingly managed to resolve my search for another LNWR Whale tender. The dilemma is that it came with another loco kit so my kit mountain has grown by one!

I didn't know Mercian did 4mm kits but I've acquired a Super D (G1/G2) which comes with both Whale and Bowen Cooke tenders. The box says Belpaire with BC tender but it contains both tenders and round top option.

The G1 was introduced at the beginning of my period (1912) so just about makes it. Oddly, as this was under Bowen Cooke, the G1 (later referred to as Super D) was launched with a BC top tender though later the tenders would have been swapped around. The un-superheated "G" was a Whale engine (and new Whale Tender introduced for his Precursor) ordered in 1910 just as he retired and I am wondering whether I can backdate the kit to a G. I guess the difference would be in the size of the smokebox to accommodate the superheating. Got to get another set of H spoke wheels now which will need drilling for the crankpins.

Anyway, in the meantime I now have a Whale Tender for my Precursor which actually has the correct curved axlebox springs too. Better build that first.