Turning a Swedish spark arrester chimney in OO9 - part 1.

A long time ago Charlie asked me if I could turn up a chimney. Not just any old chimney, but a Swedish spark arresting type. These have a peculier bulbous lower section (the actual spark arrester) with a stovepipe top, a nice challenge which I simply couldn't refuse.

I decided that it would need to be made in two sections, the spark arrester and seperate stovepipe, which would slot together once finished. As the lower section would be the hard part I made that first. Actually that's not quite true, the first thing to be made was a flycutter to cut the base of the spark arrester to suit the boiler. I re-scaled the drawing that Charlie provided and found the boiler to be 12mm diameter.

To make the flycutter first a length of 6mm dia. silver steel was cross drilled and reamed 4mm, then the end drilled and tapped M4 for the clamping screw. I then filed the end of a length of 4mm dia. silver steel into a cutter, which could then be sawn off to 11.5mm long. This was then heated to cherry red and quenched in water to harden it with a normal DIY store blowtorch. I didn't bother with tempering, its only going to be used on brass. Here's the cutter;

To set the tool to cut a 6mm radius (to suit a 12mm dia. smokebox) I set the cutter 3mm from the shank of the holder, which as its made from 6mm dia. material will position the cutting edge 6mm from the centre line of the holder (3mm shank radius + 3mm from shank to cutting edge).

For the lower section I chose to use 10mm dia. brass. The first job was to cut the bottom radius so the rod was clamped in a toolholder on the saddle at 90 degrees to the bed. I did this by leaving the toolholder loose, fitting the face/drive plate to the spindle and offering up the bar to the plate then clamping everything up tight;

To set the rod at the correct height I measured from the saddle to the top of the rod. The centre height from the saddle is 12mm, add half of the rod's diameter (5mm) and that measurement should be 17mm. To get that measurement I made a shim from 1mm thick aluminium to sit between the toolholder and the saddle. With the flycutter in the collet chuck the base can now be cut;

Action shot(!);

I set the machine at 1100rpm and took .3mm cuts. Easy work.
Once the base profile was cut I chopped the end of the bar off at 35mm(ish) long to hold in a 3 jaw chuck. Then the bar could be turned down, the smaller diameter is to suit the base flange;

With my compound slide fitted and set to 45 degrees the lower taper was cut along with the smaller flange diameter;

I had to grind up a special left hand turning tool for that operation.
Using the parting-off tool the uppermost flange was turned along with a recess;

The recess is there to make it easier to file the bulbous shape that makes this type of chimney so interesting;

Done with a needle file and finished with a rubbing stick.
The lower flange, where the chimney is attached to the smokebox, is as far as I can tell oval in shape. This needed to be filed but to make a start I milled two flats on the flange;

Note the 2mm dia. hole, this is for the upper section to slot into.
Once I had milled the flats I could start on the hardest part of the entire job, namely filing the lower flange to shape. I'm always slightly nervous when taking a file to a chimney as the shape can be  quite awkward, needing a good eye and steady hand. I'm very aware that one slip of the file, or a lack of concentration, and the job could be ruined. But so far I've not made any mistakes, I work steadily with a decent smooth file and check often with a magnifying glass. Finishing is again done with a rubbing stick.
The base was first filed oval, then the sides were shaped to suit the smokebox. I haven't got any really good photos to work from, just some black and white shots in a Bradford Barton book (European Narrow Gauge Steam volume 2). Once I was happy with the shape I parted the base off, ready for the next operation.
Here it is after parting-off, showing the underside;

And from the front;

Clicking on the photos, which I recommend you do, brings up a larger image. More soon.

Paul.

Rushby's Resins Battery Electric - part 2.

I decided that I wasn't happy with the paint finish, so I rubbed the model down and applied another coat of primer (Hycote white auto acrylic). This crazed, so I ended up doing more rubbing down before re-spraying with Humbrol  A6069 gloss yellow. The finish still isn't great, but I'll just have to live with it. I did consider chemically stripping the bodyshell but an internet search suggested that paint stripper, even Modelstrip, can soften resin.

Once the paint had hardened I applied the wasp stripes, made easy by using gloss paint for the topcoat. These are simply Fox transfers, pack F4303. Whilst one end went without fuss on the other end the transfer broke into three pieces. With care each piece was butted up against its neighbour, aided by a soft brush and a modicum of patience, leaving only the slightest trace of any mishap. A brushload of Carrs Transfix (at least 20 years old!) helps settle things, and a squirt of Testors Dullcoat seals the deal. I did need to do a little touching up with a drop of Revel black paint. Hopefully the striped ends draw the eye away from the cab fronts, which is where the surface finish is at its worst.

I was in two minds whether to paint the window surrounds or not, especially as I'm hardly the tidiest of painters. In the end I decided that picking them out with a touch of Tamiya Nato Black (to represent rubber seals) would add interest. Glazing is cut from the usual 1mm clear sheet, I'm not sure what material it is but its the stuff sold alongside plasticard. Cutting and fitting flush glazing is quite irritating, but the results are worth the effort. A drop of Johnson's Klear run around the edges with a fine brush fixes the panes in place. I have a full bottle of Klear bought when it was mooted as the next best thing since sliced bread, fixing glazing is the only job I use it for. Perhaps I should put it on Ebay...

A black plasticard shelf sits inside the cab, which can be seen in the doorway. Under this is glued additional lead bringing the loco's weight up to 31 grams. In the photo below the shelf is in place but I hadn't yet added the weights;

And with the lead in place;

To hide the motor bogie and that shelf I've made cab doors. I wanted them to look like a local modification made from wooden planks, so I've used .040" plasticard with the planks scribed with an scrawker and grain added using a razor saw blade. Handles are .33mm brass wire suitably blackened. Originally I wanted bare wood, then decided that they might look better painted yellow. So two pairs of doors have been knocked up which can be swapped around until I make my mind up (they're a light push fit). The bare wood pair were primed with my usual Hycote grey acrylic auto paint, then I drybrushed them with first Revel Aqua Color (sic) 378 Dark Grey, followed by Humbrol 5029 Dark Matt Earth and then Revel 75 Stone Grey. A coat of Testors Dullcoat helps blend them in.

At the moment I'm unsure which I like the best so the loco has a yellow door on one side and a bare wood door on the other. I suspect that it'll stay that way for a while...
Weathering can wait.

Paul.

Unimat 3.

Much as I like my Unimat SL it has its limitations. I decided that a compact machine that was more rigid and with a slightly higher capacity would be usefull. It had to be a machine that has a good range of accessories and spares, so I decided that the ideal solution would be a Unimat 3. Mark pointed me towards one on eBay which seemed too good to pass by so I pressed the Buy It Now button.

The U3 has a cast iron bed, which offers far more rigidity than the twin 12mm diameter bed bars of the SL. The spindle has a 10.2mm bore, the spindle bore on the SL is 6.3mm. The swing is greater than on the SL, which means larger diameters can be turned. Spindle and tailstock threads are M14x1 on the U3 and M12x1 on the SL, so swapping chucks from machine to machine is not possible without a threaded adapter. The drive belts on the U3 sit under a plastic cover, which will no doubt be considered safer than the open arrangement on the SL. The lowest speed is 130 rpm, which is only possible on the SL with a special motor bracket.

This one, according to the description, belonged to the vendors grandfather who had an interest in model engineering and clock making (there was also another U3 and an Emco mill for sale from the same vendor). The owner apparently was obsessed with accuracy and had fitted a new cross slide and leadscrew bush. It is sitting on an original Unimat wooden base into which slides a plastic tool tray. Tools included are a 3 jaw chuck, faceplate and drive dog, two Allen keys, two dead centres and a live centre, a Rohm chuch and key, 8/10mm spanner, two tommy bars, six turning tools and a spare set of drive belts. Also included is a manual. At the moment this machine will only be used as a lathe, I'm keeping the SL to use as a mill/drill press (and for a bit of turning no doubt just because I like using it).

It arrived well packaged in a big cardboard box, but not without problems. All of the tools were sent taped to the tray, but the weight of the drill chuck bouncing around cracked the tray. Not a big deal, just a shame. The biggest problem, which I'm sure is the result of a rough shunt on route, was that the steel motor bracket was bent. I think that the package had been dropped, the motor was slightly loose and the weight of the motor bent the 4mm thick bracket and damaged the 6mm bolts holding the bracket to the headstock. I straightened the bracket using a big vise (thanks Stuart) and an 18" adjustable spanner. New bolts finished the repair (luckily the threads in the headstock were not damaged). Should I ever buy another Unimat (any model) I'll ask the seller to remove the motor and send it seperately as a condition of sale unless I can pick up in person. The only other fettling (so far anyway) has been to adjust the gib strips on the cross-slide and tighten a screw in the tailstock.

The machine itself looks to be in very good condition (apart from the usual paint chips). Longitudal and cross travel feels nice and smooth in both directions and the motor is discernably quieter than the SL. I do want to find a few accessories for it (compound slide, quick-change toolpost, collet chuck etc.), but for now it will be used as is. I haven't cut metal on it yet, but that will change soon.

Paul.