fitting small driving wheels

andrewnummelin
Posts: 374
Joined: Mon Jul 21, 2008 9:43 am

fitting small driving wheels

Postby andrewnummelin » Sat Nov 23, 2019 7:26 pm

As a change from doing more complicated things I thought I'd have a go at a couple of 0-4-0ST kits - expected to be straightforward but life doesn't seem to work that way!

In both cases I'm using Gibson wheels and crankpins and the chassis were assembled with an Avonside Chassis2 jig so I'm pretty confident that the axles are square and spaced identically to the coupling rods.

First chassis reached the stage of wheels, coupling rods, connecting rods, crossheads and gear box fitted and running just about OK. Put aside to do other things and on starting up again it was binding badly for no apparent reason. Eventually I decided to take it apart bit by bit to find what was sticking. The crankpin nuts had been secured with Loctite and this proved to be too strong - first nut came off OK, second and third ones could not be moved easily and the last one came off by simply fracturing the crank pin! I managed to remove the crankpin and fit a new one but in doing so I've damaged the hole in the wheel and the pin wobbles. Loctite failed to hold it so does anyone know of a way to fix the pin, or is it a case of buying a new wheel? I'd prefer not to do that as it's fitted with a shorting strip for a split chassis.

Second problem is because of picking a loco with small wheels (11mm) and a tiny crank-throw (2.5mm). I'm having difficulties in starting the axles into the wheels and I suspect the wheel centres may have been distorted by the countersunk head to the crankpin screw. Assembling of the wheels onto the axles using the GW wheel press & quartering jig is not going to work as the crank throw is too small to fit the jig. Quartering by eye is a problem too as almost none of the wheel is visible below the frames (or axleboxes) and it is complicated by the wheel having 9 spokes so there's no obvious guide for alignment. Any suggestions?
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Regards,

Andrew Nummelin

nigelcliffe
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Joined: Mon Jul 21, 2008 8:31 am

Re: fitting small driving wheels

Postby nigelcliffe » Sat Nov 23, 2019 8:46 pm

Wobbly crankpin:
bodge+hope method - devise method to hold pin in correct orientation (or as near correct as you can get) and use either retaining compound (eg. Loctite 603) if the gap isn't overly big, or expoxy resin (araldite type stuff, but pick your grade carefully) to secure pin.
engineering method - remove wheel from axle, bore out crankpin hole to a new size. Put in turned crankpin to fit new hole. May require lathe to make the crankpin, may require mill or precision drill to do the drilling.

Quartering:
by-eye, I find a split screwdriver to put into the spokes helps a lot (like a giant Romford wheel nut tool). Make using a grinder to cut up something suitable (such as a cheap big screwdriver!).
if by-eye doesn't work, do you have a lathe available ? If so, then a press, using the lathe to do most of the work, isn't overly difficult to devise. May be possible on a drill press with various items "turned" using a minidrill to hold them - the press tools could be wooden.

davebradwell
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Re: fitting small driving wheels

Postby davebradwell » Sat Nov 23, 2019 9:43 pm

Why not ring up Colin Seymour and beg a new plastic wheel centre. Push into old tyre and vow you'll never Loctite nuts in place again....or put Loctite anywhere near moving parts. Perhaps a large order for something else might grease the process but Colin's a fine sort.

Looking at your photo there appears to be a burr on the inside edge of the axle hole - perhaps investigate and remove. Suggest, if possible, you file wheel bosses flush with face of tyre to improve clearance behind crosshead.

With 4 coupled chassis you should achieve quartering by simple trial and error, especially if rods and axle centres match. Put far side on bottom centre and tweak near side wheels until rod horizontal. By repeating at top and bottom centres and looking at both sides it's possible to determine whether error is quartering or rod length - think about it. OK it takes great care to get the last gnats but it can work. You can watch the acrobatics of the coupling rods on some locos and see there's an error from a mile away. The limit appears to be inability to twist wheels a small amount, apparently due to give in the plastic.

I'm sure you'll agree we need an improved choice of industrial wheels.

DaveB

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grovenor-2685
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Re: fitting small driving wheels

Postby grovenor-2685 » Sat Nov 23, 2019 10:06 pm

Looking at your photo there appears to be a burr on the inside edge of the axle hole - perhaps investigate and remove.

Same goes for the axle end, needs cleaning up with files and emery paper, aim for a very slight bevel on the end, no more than a qurter mm.
A countersink bit twisted in the fingers should clean up the back of the wheel bore, don't be tempted to use a drill bit, even used in the fingers they can dig in and remove to much.
Rgds
Regards
Keith
Grovenor Sidings

David Thorpe

Re: fitting small driving wheels

Postby David Thorpe » Sun Nov 24, 2019 10:04 am

I di very much sympathise with you in this. Some years ago I bought and built a High Level industrial loco that has tiny driving wheels - smaller than coach wheels. Needless to say the kit and detailed chassis went together beautifully but I have been quite unable to get the loco to run properly and eventually got so exasperated that it went back into its box for later attention and has remained there ever since.

The problem was the small driving wheels. As in your case, the crank throw was so small that they wouldn't fit in my GW wheel press. I couldn't line them up accurately by eye as once assembled very little of the wheel is visible through the chassis, and moreover once the wheels were assembled and in the chassis their small size and close presence to the frames made it very difficult indeed to twist them with any degree of accuracy. Basically, very similar problems to yours and I haven't resolved them. I shall therefore follow this thread with interest.

For fixing crankpins, might I suggest a threadlocker such as Loctite 243 (medium strength) or 222 (low strength)?

DT

davebradwell
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Re: fitting small driving wheels

Postby davebradwell » Sun Nov 24, 2019 10:28 am

Apparently some Sharman wheels can still be obtained - ask around - can't remember where I picked that up but you need to find the part number first.

It seems we need a miniature version of the gadget for getting the lids off jars so we can tweak our wheels.

Suggest you wait until you find your crankpins keep falling off before resorting to any Loctite. Any not in the joint stays liquid and migrates over a period. Never found the need in years of running.

DaveB

Philip Hall
Posts: 1947
Joined: Mon Aug 10, 2009 7:49 pm

Re: fitting small driving wheels

Postby Philip Hall » Sun Nov 24, 2019 10:48 am

My method of checking quartering, when I can’t use the GW press, is a small turntable. I bought a little paint spraying one years ago, about 6” diameter, and it sits on a tripod stand about 4” tall. You can get things like this from cake decorating suppliers, I believe, mine came from a tool supplier at a show. I never use it for paint spraying!

Anyway, the technique is simply to place the chassis on the turntable and line up all the wheels on one side. I use a rule or a square to check all the spokes are exactly in line. Then I revolve the turntable and look at the other side, where any discrepancy should be easy to spot. Correct as required and check again. Because the wheels are all on the surface as the table is turned they don’t move in relation to one another.

If the wheels are very tight on the axles wearing a thin neoprene glove might help with grip.

Philip

John Palmer
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Joined: Fri Jul 15, 2011 11:09 pm

Re: fitting small driving wheels

Postby John Palmer » Sun Nov 24, 2019 11:10 am

Using a wheel that has a wobbling crankpin sounds to me like a sure recipe for long term frustration. Whilst I dare say the wheel concerned can be corrected and made wobble free, I question whether the time and trouble spent doing so can be justified relative to the alternative of buying a replacement wheel.

I would be interested to see the shorting arrangement. I have yet to be convinced that the 'etched ring and spoke' approach to this is the best solution, (a) because electrical continuity depends on a thin edge contact between ring and axle and (b) because achieving a sufficiently tight fit of the ring to overcome problem (a) increases the difficulty in mounting the wheel squarely and correctly quartered. On carrying wheels my preference is to bush the wheel bore and make the axle an interference fit in the bush. I make the shoulder on the bush the full diameter of the wheel's boss so that it remains concealed from view but provides an ample jointing surface to which a shorting wire can be soldered and led down the back of a spoke to the rim. To date I haven't applied the technique to driving wheels but see no reason in principle why it should not work. I do appreciate, however, that this approach is available because I have a lathe for turning the bushes required, so it's not for everybody.

I note that since this is a nine-spoke wheel the crank lead angle cannot be 90 degrees, so any quartering jigs designed to achieve that lead angle are unlikely to provide an acceptable solution (unless you are prepared to accept the wheel spokes on one side being out of alignment with those on the other). In my admittedly limited experience it's never proved impossible to achieve a sightline that enables me to line up the spokes on one side with those on the other, and I have obtained acceptable results from doing so. The photograph suggests that this approach could be applied successfully.

I understand that nail varnish can be used as an alternative to thread locking compound, and that the lock can be released by application of acetone (nail varnish remover!)

davebradwell
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Joined: Fri Jan 18, 2019 3:48 pm

Re: fitting small driving wheels

Postby davebradwell » Sun Nov 24, 2019 12:47 pm

I shorted out some wheels once using a method described in (probably) a single digit MRJ: solder thin piece of copper wire across back of wheel on a diameter - heat sinks will prevent damage to plastic centre. A recess can be created in tyre for this with file or saw. Cut in centre where it crosses the axle hole and just push onto axle.

That was the one and only split framed 4mm loco I ever built. Although the electrical pick-up is better than any others, all the mechanical arrangements are compromised - I like a proper set of frame stays for example. It just swaps one problem for a number of others. In larger scales the axleboxes can be insulating with power collected from a metal bush with the frames dead and this is a better arrangement. No, I'm not going to be drawn into discussion on this - I'll stick to the wheel shorting.

DaveB

David Thorpe

Re: fitting small driving wheels

Postby David Thorpe » Sun Nov 24, 2019 4:00 pm

Thanks, Philip, that's helpful. The only trouble is - will I remember it next time I find myself in that position?

DT

andrewnummelin
Posts: 374
Joined: Mon Jul 21, 2008 9:43 am

Re: fitting small driving wheels

Postby andrewnummelin » Sun Nov 24, 2019 4:34 pm

Gents,
Many thanks for all the interesting and useful responses.

crankpins
First shot will be epoxy - should know in a couple of days if that has worked.
If that fails, it will be buying a new wheel as I'm not happy with Nigel's engineering bodge. If I were to go down the route of doing it properly, I'd start with a steel bar, drills, saws, files and make a wheel from scratch... but pigs flying is more likely!

quartering
I'd looked at the wheels with a magnifying glass but hadn't noticed the burr: photos are very useful for spotting things the eye sometimes glosses over. I have already treated the axle ends so I'll now do the wheels as advised.
I do like Dave's suggestion on quartering, but doing things by eye is very likely not to work for me - I have a reputation for putting up pictures, shelves etc at a slope, even when using a spirit level. So I'll start by trying to make a simple press/jig and get the lathe out - I hardly ever use it so my skill level is pre-beginner...

nut fixing
I know the dangers of Loctite. I have a chassis in bits for rebuilding - it was OK till I tried it (in public) a day or two after finishing it, whereupon the DCC chip literally went up in smoke. I'm pretty sure Loctite used for fixing outside cranks migrated to the wheel bearings.
My wife supports the idea of using nail varnish - it's her remedy for fixing almost anything!
I suppose an engineering approach would be to use a split pin to retain the nut but I don't fancy my chances of drilling a hole through a nut and crankpin! And as for following prototype practice...
Untitled-1.jpg

Top left is the current prototype. The others are on my hit list.
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Regards,

Andrew Nummelin

decauville1126
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Joined: Tue Mar 12, 2013 8:50 am

Re: fitting small driving wheels

Postby decauville1126 » Sun Nov 24, 2019 9:03 pm

I always deburr the axle ends, and pass the axle into then back out of the wheel after a quick wipe round the back of the axlehole with a scalpel at an angle. And I lick the axle end just before fitting. Then when final assembly and quartering is to take place I know they will go together.

Some 1/8" diameter stock I have had was too close to it's upper limit for comfort, and the thought of split hubs .... But the ground stuff from Ultrascale is leaded EN1a and is superb and a dream to machine.

The die pins when the centres are moulded can also wear with use, giving a very-slight undersized bore. Hence why I always do a part pre-assembly. Tyres sometimes come adrift with over-handling but can be easily refitted with a dab of Loctite. Which neatly leads me to suggest using threadlock such as that from Screwfix instead of Loctite for retaining crankpins in the wheel (which I've run a 1mm tap through - or use a 14BA if you have one instead - and countersunk the back) and the nuts when assembled.

Enigma
Posts: 533
Joined: Tue Aug 13, 2013 2:49 pm

Re: fitting small driving wheels

Postby Enigma » Mon Nov 25, 2019 12:03 am

I screw the crankpin into the wheel after cs'ing the hole and then back it out third/half way, put a tiny drop of Loctite 601 just below the head and quickly screw it back in. Any excess Loctite will be around the screw head and can easily be wiped of as 601 only goes off when starved of air (or something like that!). I also make all my wheelsets removable which could possibly help in quartering if the GW wheelpress isn't available or won't work. On a 4-coupled chassis only one wheel needs adjusting as if the other 3 are set as close as possible in the initial fit, the 4th wheel is the one that will determine smooth running.

davebradwell
Posts: 1174
Joined: Fri Jan 18, 2019 3:48 pm

Re: fitting small driving wheels

Postby davebradwell » Mon Nov 25, 2019 10:32 am

Still can't see any reason for adding Loctite, or whatever, and especially 601 which is supposed to be permanent. If you fit the crankpins according to the instructions they're a tight fit, won't ever come loose and can be removed. Perfect. It was the Loctite that caused the problem that led to this plea for help. Doesn't Iain Rice point out in his book that if nuts keep coming off, they're gripping the rods too tightly.

Yes, you need a countersink at the rear for the screwhead, you'll almost certainly need to file the boss flush with the tyre if it's an outside cylinder, non-GW loco and you might consider that the accurate crankthrow dimension should be at the front of the wheel so take care not to compromise this. Running a tap in from rear has dangers, for example and it's not unknown for the hole to be out of square to the wheel on old stock, either. Haven't we recently done crankpins on another thread?

DaveB


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