Whats on your 2mm Work bench

[Richard Hall]

Rather inevitably it has all gone wrong, but not for the reasons I expected.  As mentioned above I had to relocate the first stage gear assembly so that it would drive the rear axle rather than the centre one.

 

What I should have done: look up the gear meshing data, precisely mark the new bearing location and carefully drill it out in small steps.

 

What I actually did: measure the hole centres as best I could with a Vernier caliper, then spotted an etched hole on the chassis in roughly the right place (probably intended for brake gear), said "that'll do" and very carefully drilled and reamed the new bearing holes about 0.2mm too close to the axle, so when I fitted the 1st stage gear I got a load of tight spots.  To make matters worse, for some reason I thought I must have disturbed the rear axle quartering and spent ages fiddling around to no avail.  Finally I took the rear rods off and found that the rear wheelset still locked up once every revolution.

 

It's not dead yet, but the odds just lengthened.

 

Richard

[Richard Hall]

Rescue operation under way.

 

 

Things weren't quite as bad as I thought, it started to free up quite quickly and after half an hour's running there is only one small sticky spot left.  If this doesn't quite clear it I have a small pot of jewellers rouge at work doing nothing useful so I might try that.

 

Motor is a Chinese 8 x 15 flat can, first one I have used from this batch and it seems very nice, quiet and plenty of torque for its size. 

 

Richard

[Richard Hall]

Last post on my experimental chassis for the moment.  It now has the smoothest, sweetest motor and geartrain that anyone could wish for, but despite endless fiddling I couldn't get it to run without binding up and lifting the centre axle, even after using Association quartering plates.  After much measuring I think I have found the problem: one of the wheels has a crank throw 0.2mm less than the other five. I've measured the throws several times in half a dozen ways and always come back to the same result: left hand rear wheel is different to the others.  Probably a bit late to send them back (I think I bought them in 2002), so I'll order up some Mk 5s and see if that cures the problem.

 

Richard

[Nigelcliffe]

On 02/10/2022 at 21:04, Richard Hall said:

....one of the wheels has a crank throw 0.2mm less than the other five. I've measured the throws several times in half a dozen ways and always come back to the same result: left hand rear wheel is different to the others.  Probably a bit late to send them back (I think I bought them in 2002), so I'll order up some Mk 5s and see if that cures the problem.

 

There were some duff brass centred wheels way back, with the crankpins in the wrong place.  I recall Bill Blackburn took those that were spotted in hand, drilled out, filled with some brass bar/rod, turned to smooth, then re-drilled the crank pin hole in the right place.   Could be done by someone determined with decent workshop facilities.   

 

 

- Nigel

 

 

[Richard Hall]

10 hours ago, Nigelcliffe said:

 

There were some duff brass centred wheels way back, with the crankpins in the wrong place.  I recall Bill Blackburn took those that were spotted in hand, drilled out, filled with some brass bar/rod, turned to smooth, then re-drilled the crank pin hole in the right place.   Could be done by someone determined with decent workshop facilities.   

 

 

- Nigel

 

 

Thank you for confirming that I wasn't just imagining that the crank throws were out.  I should have worked it out when one wheelset didn't fit snugly into the quartering press.  I'll stick the errant wheels in a box and wait for the day when I have a decent mill/drill machine.  Never throw anything away.

 

Richard

[richbrummitt]

The sides need some further tweaking - when I find the 3/4 view photos again - but this will add some variety to the livestock train that’s in progress (for over a year). 

 

[bradfordbuffer]

55 minutes ago, richbrummitt said:

The sides need some further tweaking - when I find the 3/4 view photos again - but this will add some variety to the livestock train that’s in progress (for over a year). 

 

Can't get over how good end strapping is...well done in cad stage pays off in printing

[tapdieuk]

Progress of sorts, a hybrid tiebar on the rest track easitrak point I damaged. With hind sight it could have been a bit thinner/neater. Testing locos though the points, showed up a couple of tight back to backs on both locos. All sorted and running with no bumps though the point work. Time for scenic work.

 

 

 

The M7 has the motor attached, after the first attempt moved while the glue was setting. 

The back to backs on this were tight. But it's running thought point work now. Weighting the body and springing the rear pony the main bits left to do  for running ,along with tidying up the body detail which has been damage with all the handling. 

 

 

[Ian Smith]

1 hour ago, tapdieuk said:

 

 

The M7 has the motor attached, after the first attempt moved while the glue was setting. 

The back to backs on this were tight. But it's running thought point work now. Weighting the body and springing the rear pony the main bits left to do  for running ,along with tidying up the body detail which has been damage with all the handling. 

 

 

I’ll say the body has been damaged. Looks like all of the boiler furniture has been knocked off and it may be sitting a little high 🤣

[John57sharp]

Joy of joys a running 08 chassis! 
 

It runs one way fine, but rough and jamming after a few seconds the other way.

 

Investigations showed that one wheel (stub axle ) rotates in the muff, so I’ll fix that first…

 

Video shows how it all is, any comments/observations welcome.

 

Revised YouTube link

 

thanks all

John

Edited October 16, 2022 by John57sharp
Link update

[tapdieuk]

I got fed up with the M7 it runs, but it a bit of a fiddle, more tweaking is needed and the body tidying up.

So I dung out the Terrier chassis, and in-between working on a wagon chassis fitted the motor. I had found a off cut of roofing lead. So the space under the motor was packed out after insulating with Rizzla. The worm shorten and Loctited to the motor shaft. I have already Loctited one motor solid! I put the tiniest dab of Peco power lube on the motor front bearing to diswade any Loctite if it gets there. 

The motor was attached in the crude cradle with quick setting Araldite. I resisted the temptation to test before it had fully cured.

There is still some work to do on the steps to stop the crank pins catching and how the body sits but it runs.

2 strips of lead were shaped to sit in the side tanks. Giving it quite a good chunky feel, better than the M7.

It quite pleasing when it comes together and works!

 

PXL_20221019_091457347 by tapdieuk, on Flickr

 

 

 

I had a couple of days away, so threw together a simple tool kit for putting a couple of etched chassis together. It all fitted in a ice cream/sandwich sized box. 

This was based around the USB soldering iron I picked up in the summer and a bright Traveling LED desk light.

I used cored solder with a flux pen, to save faffing with solder balls and flux. 

I only got as far as soldering the top hat bearings in 3 wagon etches. The soldering It's not great, but it's not bad. A different tip on the iron and a better flux would help. But it proves the point.  There is no excuse not to get some modeling done when I am away now!

 

PXL_20221015_231108574 by tapdieuk, on Flickr

 

 

 

 

 

Edited October 19, 2022 by tapdieuk
Links for photos

[Richard Hall]

Quick update on the compensation experiment.  Now fitted with a shiny new set of Mk 5 wheels (thanks Jon for excellent service as always) and with an old Farish Pannier body dumped on top for a bit of weight, it runs very smoothly indeed.  It steps neatly over a bit of 0.5mm wire laid over one rail, and all is rosy in my 2mm garden except for one problem - poor conductivity between the axles and the U-shaped guides that take the place of axle bearings. 

 

I was expecting problems here. I can't use conventional Simpson springs (apart from the driven axle, where I have already fitted them) as they would interfere with the vertical movement of the axles. I think I'll be looking at some kind of scraper pickup, as fine and light as possible, most likely mounted vertically to bear on the back of the flanges. I foresee much fiddling with 0.3mm phosphor bronze wire: fortunately I have lots of this.  

 

Whether all this effort is worthwhile, I know not at this stage.  It will be interesting to see what kind of load the Pannier will handle, compared to my other two 2mm locos. Right now I'm just pleased the thing runs at all.

 

Richard

[Richard Hall]

Things are starting to get interesting.  I fitted vertical scraper pickups to the leading wheelset which work beautifully, and tried a simple adhesion test, gradually raising one end of my test plank until the Pannier slipped to a halt. This little engine will tackle a 1 in 4 gradient! The benefits of distributing weight evenly across all the driving wheels seem fairly plain.

 

The only problem I have now if a tendency to lift each centre driver alternately under heavy loads.  Because each wheel is only bearing one-sixth of the weight, the drive from the rear axle through the rear coupling rods can be enough to push one wheel upwards clear of the track.  That little 8 x 15 flat can motor has a lot more poke than I expected. Not a problem in 4mm where (all other things being equal) you have eight times the weight on each wheel. Adding more weight to the body would help, but this chassis was only intended as a rough prototype for the compensated "03" that I actually want to build, which will be much lighter.  Incidentally the Pannier runs sweetly and without hesitation as a bare chassis, in which form it weighs about the same as a sweet wrapper, but the wheel lifting is very evident at anything above walking pace. I tried fitting lightly sprung wires bearing downwards on the centre wheelset but it seemed to run worse.

 

Richard

[Izzy]

Hi Richard,

 

Are you using split/pivoting rods? That could be the issue if there is too much slop between the front and rear portions. I’ve hit this problem a few times in the past, enough to move over to using solid/non-pivoting ones with a bit of slop over the crankpins. This I found was more than enough to allow the compensation/springing to work. It’s especially beneficial if the drive is off an outer axle rather than a central one, which evens out the coupling rod forces to a great extent.

 

Bob

[2mm Andy]

There is a set of 3 articles in the 2mm Magazine (circa 2000) by Stephen Harris on the subject of compensation. Worth a read as they seem to cover some of the points raised above (they are accessible via the member's area of the 2mm website). The loco he fitted the compensation to was an '08' shunter.

 

Andy

[Richard Hall]

7 hours ago, Izzy said:

Hi Richard,

 

Are you using split/pivoting rods? That could be the issue if there is too much slop between the front and rear portions. I’ve hit this problem a few times in the past, enough to move over to using solid/non-pivoting ones with a bit of slop over the crankpins. This I found was more than enough to allow the compensation/springing to work. It’s especially beneficial if the drive is off an outer axle rather than a central one, which evens out the coupling rod forces to a great extent.

 

Bob

Thanks for that Bob. Yes, it does have split rods.  I'm with you in thinking most compensated chassis have far too much articulation, you probably only need 0.1mm above and below the centre line to get most of the benefits, unless your tracklaying is especially wonky.  The problem for me at least is building the thing square enough to achieve that tiny amount of axle travel equalised over four wheels. Having said which, your suggestion is basically using the rods to restrict travel and I can see that might work.  One other thought I have had is to move the pivot point for the compensating beam, so as to increase the proportion of total weight borne by the centre wheelset.  I haven't seen that done but it will be easy enough to see if it works.

[Richard Hall]

Not quite sure whether moving the pivot point was worth the effort.  I think my first compensating beam was a fluke: much harder to get it central on the axles and the ride height correct, second time around.  I'm now getting an oscillation at certain speeds which rapidly increases until the loco derails. So it still needs a bit of fettling, but here are a couple of bad videos for now. First up, the naked chassis, completely unweighted.  If the low speed control looks a bit unimpressive, bear in mind that the controller is an H&M Clipper.

 

https://www.youtube.com/watch?v=z9q4UrAFsJE

 

And secondly the same chassis with Pannier body tackles a ridiculous gradient.  1 in 5, maybe a bit steeper.

 

https://www.youtube.com/watch?v=r9QM0VtImxM

 

Still not 100% sure all this will end up leading anywhere useful, but it's fun.

 

Richard

[Donw]

Climbing that gradient looks insane. I dont think the Snowden Mountain Railway is that steep. I am not convinced compensation works with auch lightly loaded models but interesting.

 

Don

 

[DavidLong]

30+ years ago I built a chassis for a J94 with twin compensation beams from an idea by Don Boreham in 'Narrow Gauge Railway Modelling. The beams were drilled at the same time as the coupling rod blanks and the frames with the pivot hole in the centre between the axle holes. I think that the beams were from some thickish brass and the only bearings were on the rear driven axles. It had 65:1 gearing with a 1013 Sagami can in the cab and split rods. It ran like a dream and even won the Chairman's Trophy. Sadly, at an exhibition, a friend decided that the wheels needed cleaning which did for the quartering and I never got it right again!

These days it's DCC + Stay-alive + coreless motor + 30:1 gearing + rigid rods = faultless running and a lot less effort.

 

David

[Chris Higgs]

16 hours ago, Richard Hall said:

Not quite sure whether moving the pivot point was worth the effort.  I think my first compensating beam was a fluke: much harder to get it central on the axles and the ride height correct, second time around.  I'm now getting an oscillation at certain speeds which rapidly increases until the loco derails. So it still needs a bit of fettling, but here are a couple of bad videos for now. First up, the naked chassis, completely unweighted.  If the low speed control looks a bit unimpressive, bear in mind that the controller is an H&M Clipper.

 

https://www.youtube.com/watch?v=z9q4UrAFsJE

 

And secondly the same chassis with Pannier body tackles a ridiculous gradient.  1 in 5, maybe a bit steeper.

 

https://www.youtube.com/watch?v=r9QM0VtImxM

 

Still not 100% sure all this will end up leading anywhere useful, but it's fun.

 

Richard

 

A point I have seen made is that compensation  keeps all the wheels on the track, but not in the same way the prototype does (or at least normally does). Hence don't expect it to ride like the real thing. If you want that, you probably have to spring it. Certainly my fully sprung 4mm CCTs glide along compared to my compensated wagons.

 

Chris  

[Izzy]

The problems I've encountered with sprung or compensated chassis have arisen when the torque involved, the mechanical advantage, overcomes the weight of the loco or the springing. This is what I think Richard has encountered. Solid rods was one of the methods I have used to try and overcome the problem along with twin beams when compensation is used. The single centre beam design is where I had the most issues arise, and especially when combined with drive off an outer axle which they require. I've also found what works one time doesn't always the next if the loco spec is materially different.

 

It's all a learning curve isn't it?

 

Bob

[Richard Hall]

52 minutes ago, Izzy said:

The problems I've encountered with sprung or compensated chassis have arisen when the torque involved, the mechanical advantage, overcomes the weight of the loco or the springing. This is what I think Richard has encountered. Solid rods was one of the methods I have used to try and overcome the problem along with twin beams when compensation is used. The single centre beam design is where I had the most issues arise, and especially when combined with drive off an outer axle which they require. I've also found what works one time doesn't always the next if the loco spec is materially different.

 

It's all a learning curve isn't it?

 

Bob

 

The torque from my 50 pence Chinese can motor is ridiculous, I wish I had bought twenty of them rather than just ten.  I think part of the problem here is that the Farish Pannier body carries most of its weight high up.  I also managed to mount the motor slightly lopsided so that it catches on the body and stops it sitting entirely square on the chassis, which combined with my slightly off-centre compensating beam is making the whole thing a little unstable.  All fixable, and it will be interesting to see how I get on with applying the principles to a nice new chassis rather than a much-bodged one. Mike Sharman's ideas continue to provoke debate and experimentation: I suspect he would have been delighted.

 

Couple of random thoughts: firstly, wondering if I can get a very small vertical slide for my very small lathe.  Then I can mill the frame bushes into slots.  I tried doing this with a file but the results were horrid.  Secondly, the compensating beam might benefit from a couple of guide slots to keep it dead central in the frames. Or even just one slot at the forward end. 

 

Richard

[Izzy]

1 hour ago, Richard Hall said:

  I think part of the problem here is that the Farish Pannier body carries most of its weight high up.  I also managed to mount the motor slightly lopsided so that it catches on the body and stops it sitting entirely square on the chassis, which combined with my slightly off-centre compensating beam is making the whole thing a little unstable.

 

That's where twin-bean compensation scores, stablitiy, at the risk of not being 'true' 3-point compensation. That worries some. It also allows drive on the middle axle, probably not applicable in 2mm since you need a floating gearbox. It all depends what you want.

 

Bob

[Richard Hall]

39 minutes ago, Izzy said:

 

That's where twin-bean compensation scores, stablitiy, at the risk of not being 'true' 3-point compensation. That worries some. It also allows drive on the middle axle, probably not applicable in 2mm since you need a floating gearbox. It all depends what you want.

 

Bob

 

A six coupled chassis built on Sharman principles has some of the dynamics of a Reliant Robin, which is not a good thing I feel.  In the same way that a three-wheeler handled better with a couple of bags of cement in the boot, I suspect part of the trick here is to get the C of G back towards the fixed (driven) axle. The Sharman system is delightfully simple but has its quirks as I am now finding out. The twin beam system is intriguing though trickier to build.

 

Richard

[Michael Edge]

Have a look at compensating beams on full size locos and see where they are - I don’t think you’ll find any on the axle centres.