A running chassis, at last!

The gearbox is in, the motor is secured, it's wired up, it's on the rolling road, the power's on and there are NO BINDS! Here's a photo of it in motion:

Here it is static, complete with grubby bits of white insulation for crankpin washers and ridiculous oversized screw holding the gearbox in:

This is what I did to the gearbox. My obsession with it-must-be-able-to-be-dismantled-ability meant that I wasn't happy about having it captive around the driving axles, so I cut a slot into the front of the gearbox which allows it to be fed into the chassis from underneath. It's secured by the screw at the back which makes the mesh adjustable. The axle bearings in the gearbox are just to keep the last two gears in mesh and there's still enough left this way to maintain this properly, and cutting in from the from the front means that it's not affected by up-and-down torque of the box - the only possible movement is fore-and-aft, and the locating screw takes care of this if it's tight enough. I cut the slots VERY carefully with a slitting disc, and was careful to use a bit of scrap 2mm silver steel in the bearing holes while doing it so that I didn't slip and carve a big lump out of the bearing. Even so, I had to file out the final bits and there are a few marks on the bearings, but they look like they'll be OK.

Since doing the photos in the previous post I've cut a small slot in the locating ring nut on the motor to allow it to be tightened. When it came to the crunch this wouldn't tighten up fully, so I've had to add a 6mm inside diameter x 0.5mm brass washer between the motor and the mount - this takes up the thickness of a small boss moulded onto the front of the motor. Yes, I [b][i]know[/i][/b] there's a crack in the solder joint between the gearbox and motor mounting plate (again).

"Linda" - gearbox and motor mount progress

Well, after a long interlude for a holiday in the USA and a few other things, I achieved a smooth rolling chassis. It had a slight bind for a long time which I think was down to:
1. The cranks which I thought were firmly attached, actually weren't. It seems that one of them moved slightly on every revolution. A tiny dab of Loctite B638 retainer solved this.
2. One of the front bearings was slightly too far back in the frames - it was set up with the coupling rod and an alignment jig and pulled forward slightly.

I've now started on the gearbox. I have to confess that I can't actually find the instructions at the moment (that accounts for a lot!) but I think the advice is to glue the motor into the gearbox. I din't like this as I'm more than likely to get it wrong, and it's not adjustable/removable for mesh or maintenance. The little coreless motor has a threaded boss on the front and I'd originally cooked up a rather rough arrangement with a thin nut soldered onto the gearbox etch and the motor screwed into that. I recently stripped down most of the gearbox and replaced it with what you see below.

I've made a small nut (although it doesn't look like one, as it has no flats and concave sides) to attach the motor to the gearbox. The strange shape is because it's dished to only just clear the large idler gear - space is very tight here. It's made from a nut from an old miniature toggle switch, i.e. the nut which is used to clamp the switch into a control panel via a threaded boss. The next photo shows a similar nut and the mandrel I made up from a very mangy old switch to turn down the motor mounting nut. The nut will eventually have a couple of notches to make it easier to tighten up. If you attempt anything similar, beware - these small switches have a wide variety of different thread diameters and pitches, and there doesn't seem to be a standard. I just happened to get lucky and find one with the same thread (I've no idea what standard it is but it's about 5mm diameter).

Lastly, a grainy photo (not sure what happened there) or the motor, nut and the idler shaft. The latter is a bit of 2mm silver steel tapped 8BA at one end and with a head soldered onto the other, to make the whole thing removable. It has a little 1.0mm brass bush to stop the gear wandering sideways out of mesh. 

Backwoods "Linda" Chassis

I've been posting progress on my Backwoods "Linda" project on the NRGM forum, and it only seems fair to add details here for those who aren't members (although it's well worth it if you are a narrow gauge modeller of any sort...)

I've dusted off my own long-stalled Backwoods "Linda" project. I last worked on this about six or seven years ago, and its sojourn in the draw has just gone to prove that you really should take care in removing all the flux, or your kit will fall apart after a few years. It was up to the badly-running chassis stage - the quartering was and out there were several binds, but there were so many problems with the soldering in the chassis I decided to strip it back and start again. The photos below show how far I've got.

Those who have built one of these will notice that the gearbox isn't fitted - I wasn't keen on the captive gearbox idea so I've decided to either adapt the current one to be removable or build a new one. Also, I've made a set of replacement cranks in 1.0mm brass with press-fitted steel crankpins. These aren't perfect but I'm quite pleased with them, although making them - even cutting them together in a batch of four - is a bit of a pain and I don't want to do it again. You may also notice that I've removed the compensation and rebuilt it with rigid bearing - sorry, far too fiddly for me.

At this point I got really ambitious and designed a set to be laser cut, which you can see in a couple of the photos. The eagle-eyed amongst you will notice that I've actually had them cut to completely the wrong size. I've no idea how I managed this since I had a very precise set of dimensions - I'll order up a few new sets and see how they come out. If they're OK, I'll be using some to replace the cranks on my Backwoods "Lancashire" (no, I haven't finished that yet either).

Regards,

Chris

Checking the bearings for parallel

Checking the bearings for parallel and level

First fit of wheels and new cranks

Chassis with unsuccessful laser cut cranks

Close shot of the laser cut cranks. Well, they look nice anyway. The bottom left hand one has had the pilot holes drilled out 0.5mm - the rest are as they come from the cutter