Sunday, April 01, 2007

Fitting the wheels

I've been thinking about how to fit the wheels for some time ("putting it off" might be more accurate). Seems that people have their own methods, and the instructions touch on this only briefly. I've looked at the design for a jig that fits wheels (and does the quartering) by tightening it a vice. But an Association member who builds his own locos successfully with relatively simple tools has described his method for fitting and quartering wheels which I plan to follow.

First file a chamfer on the end of each wheel axle

I'd already opened up the muffs with a 1.5mm drill. Now I need to drill a 1mm hole through the centre of the muff. This is to allow release of air as the tight-fitting axles are pushed in.

A final check that the chassis sides are still electrically separate, then I fit the first axle by turning each wheel by hand with gentle pressure inwards.

I've put a small washer on this axle to reduce sideways play.

I'd previously calculated that I needed a 0.45mm gap on each side between the wheels and chassis and now I need some spacers.

simple styrene sheet spacer

The key dimension is the distance between the back of the wheel rim and the chassis side. So the gap in the spacers has to be big enough to go around the small raised section visible around the axle, allowing the spacer to lie flat against the wheel. I cut some from 0.5mm thick styrene sheet.

Now with the spacers in place I can gently twist both wheels inwards until they are tight against the spacers. The first axle turns freely so I do the same with the central axle.

spacers on central axle

Now the gears are locking. Even though they had previously been running smoothly, I have to spend quite a while running the wheels along the test track by hand to loosen them up again.

Next to add the final axle, tighten the wheels to 8.5mm back-to-back (or just over) and turn the wheels so that the balance weights are aligned on both sides, with a quarter-turn difference between sides.


Anonymous said...

I've been following your progress with great interest. I am a HOn2/HOn30 modeler from the US. I scratchbuild most of my locomotives, so I understand what you are going through.

With all that has been talked about in the scratchbuilding circles of 2mm and 4mm scale modelers, I have a hard time understanding how some modelers shy away from driving rod driven locomotives with the connecting rods vs gearing.

It seems to me that gearing only one axle, and using properly quartered drivers would be easier than trying to align all the gears, counterweights and cranks properly in a gear driven chassis. I think it would be easier to use a purpose built, chassis specific simple fixture to quarter all the driver sets for a given chassis.

Great work! I look forward to seeing your completed locomotive and have thoroughly enjoyed following your progress.

Best regards,

West Hartford, CT USA

Gram said...


Many thanks for your kind words. To be honest, I had no idea anyone else was reading this, apart from a few helpful 2mm members.

I’m not sufficiently confident to believe that I could make those flimsy axlepins power a (relatively) heavy engine. Chunky gears seem more reassuring, although I have had some problems setting them up. I think I’ll have a better view of the relative merits once I’ve fitted the connecting rods.

The 2mm Association has a quartering jig in the pipeline. I’m waiting to hear more details before I decide how to do my quartering. The point has been made that I can “get away” with larger holes to accomodate my axlepins, but I’d like to see how accurately I can do it, for future reference perhaps.

Like you I’m also looking forward to seeing my completed locomotive, but meantime I’m enjoying the challenges and the minor victories.

Best wishes


Anonymous said...

Hi Graham,

Yes, I've been following your blog quite regularly. I check it about every other day.

I can understand your reservations on quartering such small crankpins. After looking at the 2mm Stores site, finding crankpins and their size, I realized how small they are!

Though with the proper fixture and use of a retaining compound (Loctite "Green"), it could probably be manageable.

Even though I am a US narrow gauge modeler, I love the 08/09 "Gronk" shunters... At some point I plan on purchasing one of the Bachmann OO 08's for the HO scale layout I'm building for my sons.

Keep up the great work! I look forward to the next update.


Anonymous said...

Really for JeffB if he's still reading rather than Gram..

I've got an inside track on this loco kit as I'm on the Association Committee, so saw the designs and test builds.

For locos with crankpins direct from the wheel, crank driven drive is the normal arrangement for 2mm locos; every chassis kit I know, and almost all scratchbuilders I know, use that method.

You mention a quartering tool; there is one about to hit the Association shop, though designed to quarter wheels with crankpins fitted, not outside frame locos (though could be made to quarter outside frame locos, but would need a simple part to hold the crank).

The original design for the 08 Gram is building included the option for crank-driven drive, as an alternative to gear driven.

But, in test builds it looked far to flimsy to work reliably. Yes, the test design worked, but it was very awkward to set it up. Much more difficult than with the crank pins on the wheels (for a loco with inside frames). So, the decision was taken to recommend an all-geared build in the instructions, and to supply all the parts for that.

- Nigel

Anonymous said...

Oh, comment for Gram.

Quartering jig probably not a sensible buy for the 08. It is expensive (cos its superbly engineered), and you'd need extra bits to quarter the 08. And its really meant to squeeze the wheels into the muffs and achieve quartering - something you don't need to do here.

Quarter by eye. John Greenwood wrote it up, April 1995 if memory correct on the backnumber CD/DVD (and if you don't have the backnumber DVD its a better buy than the quartering jig !).

- Nigel

Anonymous said...

Hello Nigel and Gram,

Thanks for the information on the 08 kit development Nigel. I could see where outside cranks on a 2mm scale locomotive would be cause for concern. I can't imagine that the laminated cranks are much more than 0.5mm thick, making for tricky assembly/quartering.

The 2mm Association have put together one of the best designed kits I've ever seen. That the kit included fold up assembly/alignment fixtures is brilliant! My hat is off to all involved with its conception and design.

Thanks for the information... I look forward to seeing the Association's new quartering fixture.

Gram, please keep up with the blog on your kit, you are doing great work and I really enjoy reading and seeing your progress!

Best Regards,


Gram said...


I’ll second what you say about this kit. It’s great for a first-timer. I’ve also benefited from our very helpful Yahoo group where a number of members have been building this kit recently.

You mentioned that you’ve done a bit of scratch-building. Is there anything on the web that I could check out?

Best wishes


Anonymous said...

Hi Gram,

I used to have a website, but pulled it down. I can send you photos if you can give me an E-mail address or some sort of forum to post them on.

Admittedly, I'm more of a chassis builder than anything else. I don't finish a lot of locomotive superstructures. I build chassis' for existing locomotives or for friends to scratchbuild their own bodies onto my chassis.

I'm currently working on a freelance HOn30 (9mm gauge) 0-6-0 diesel mechanical. It's somewhat inspired by the 08's.

Let me know the best way to share pictures and I'll gladly do so...

Keep up the great work... Best regards,


Assembly Fixtures said...

Yes, it is true that the key dimension is the distance between the back of the wheel rim and the chassis side.