Gimme Air

[Bilco]

I started a new project this week - a 15" version of the Eimco 401 compressed air loco from the States. There is a great research resource at http://www.narrowgaugechaos.com/RPC/Mat ... oIndex.htm with lots of photos and a GA drawing. All I had to do was print the drawing to the scale I wanted and I was off.

There have been some 7/8ths scale models of these locos - http://www.7-8ths.info/index.php?topic=16682042.0 and http://www.7-8ths.info/index.php?topic=16682024.0 to give me some more ideas and clues on how to model the beast.

I'm powering the loco with the motor unit from a Bachmann inspection car - not the UE version - that Charlie was kind enough to sell to me. It has a nice low profile to fit under the tank, although the wheelbase is a bit long - 34mm where it should be 31mm.

I've started by making the chassis from 1mm plasticard. It's basically 3 boxes, the ones at each end open at the top and the middle one open at the bottom, where the motor unit fits.



A side view of progress so far. On the prototype the bolt heads around the axleboxes are countersunk but I've decided that the 15" version had them sticking out - life is hard enough as it is, without trying to sink holes that close to the edges of the cut-outs in the frames.





A view of the underside, showing how the Bachmann motor unit fits in and is held in position - the right hand end of the unit is built up level with the underside and fits under a little ledge, while the front is held down by the little brass square.

The angled ends to the chassis were a bit fiddly - I had thought I could scribe and bend them, and then glue them to the underneath pieces, but that wasn't too successful, so I built the ends up piece by piece - with all the inaccuracies that produces. The axleboxes are more of those irritating tiny bits of plasticard and rod that disappear as soon as you look away.

I have some PVC pipe that is just about the right diameter for the air tank, so I shall cut a bit to length and start building up the ends from decreasing circles of 2mm plasticard. Just a matter then of sanding them to shape I also have to make up some sort of air engine to fit into the rear compartment - there are good photos on the 7/8ths site to work from.

Hours of fun

[JAMO]

Nice chassis Bill !

I like !

[Bilco]

Many thanks, Jacky. I have progressed a little further - I've cut the length of PVC pipe to form the basis of the air tank and trimmed it to sit at the right height:





I've also cut out the series of circles of plasticard - 14 in all - for the domed ends and stuck them together. Now I need to get down to producing vast quantities of plastic dust to get the smooth shape

[Steve Bennett]

Great start Bill, looking forward to this build, it might motivate me to dig out an Atlas air loco I started years ago
Marty's page is a great resource for anybody interested in building one of these. I think he had a thread about it on here too, but that was quite a while ago.
Which Bachmann chassis is that
I have a couple of their track maintenance vehicles, but they are a lot longer with a 46mm w/b. Looks the same design but shorter.

[ian holmes]

Looking good.
I started one many, many years ago. Your progress prompted has me to look mine out and see what I can do with it...

Ian

[Bilco]

I think the motor unit is from one of these - http://www.ebay.com/itm/Vintage-Trackst ... 588f43bcd8

Charlie will be able to give a bit more info - he just sold me the motor unit without the body.

I got the wheelbase wrong - the motor unit WB is 32mm. I was right about it being too long though

[rue_d_etropal]

does look like one of the shorter units, a much improved one than the vintage one on eBay, which I think only picked up on one axle. The best of these chassis is the longer wheelbase bus/coach which also has bigger wheels and a bit more weight.

[Steve Bennett]

Thanks Bill, I think this might be the one
http://www.ebay.com/itm/POWERED-4x4-MoW ... 53e7527c63

[Broadoak]

Bill I used the motor from an HO Bachmann HI-rail track maintenance van to power my 1/35 scale “Tilly” pick up truck. (I am pretty sure it is the same as yours.)
It has little out rider wheels which also pick up current. They are not really noticeable at normal viewing distances. They do however make the device a bit of a rascal to put on the track.
I added extra weight in any place I could to help it track better. It runs well if a little noisily but this is because I I use a hand held feed back controller I suspect.


A rather poor photograph of the chassis.

Here is “Tilly” at work in Two Sister’s yard.

[Steve Bennett]

It has little out rider wheels which also pick up current. They are not really noticeable at normal viewing distances. They do however make the device a bit of a rascal to put on the track.

The outrigger wheels are very easy to remove Peter, they just clip onto the axles by a kind of C clip. Not so easy to put back on though

Looks like yours is the longer wheelbase version like the ones I have


Same basic design by the look of it, but the longer wheelbase version has an idler gear inboard of the axles, as seen below, which is what threw me with the unit Bill used.


Apologies Bill, we seem to have gone off track here, as usual

[Bilco]

There's a picture of the one I have here http://forum.gn15.info/viewtopic.php?t=4334 on a posting by Paul in NZ.

I think this gets us back on track -ish?

[DCRfan]

That motor bogie is still going stong. Great runner.

[Bilco]

Another tiny step of progress - the discs for the ends glued together, ready to be sanded to shape.




The bolts are not just to clamp the pieces together - I intend to stick them into the 'letric drill and use it lathe-like to do the coarser sanding and shaping - it will depend on how it goes initially before I decide how far to take it. I may have to start cutting out more discs before long.

[JAMO]

Bill I used the motor from an HO Bachmann HI-rail track maintenance van to power my 1/35 scale “Tilly” pick up truck. (I am pretty sure it is the same as yours.)
It has little out rider wheels which also pick up current. They are not really noticeable at normal viewing distances. They do however make the device a bit of a rascal to put on the track.
I added extra weight in any place I could to help it track better. It runs well if a little noisily but this is because I I use a hand held feed back controller I suspect.


A rather poor photograph of the chassis.

Here is “Tilly” at work in Two Sister’s yard.

This railcar is very nice !

[JAMO]

Another tiny step of progress - the discs for the ends glued together, ready to be sanded to shape.




The bolts are not just to clamp the pieces together - I intend to stick them into the 'letric drill and use it lathe-like to do the coarser sanding and shaping - it will depend on how it goes initially before I decide how far to take it. I may have to start cutting out more discs before long.

Excellent system to make these shapes Bilco !

[Steve Bennett]

it will depend on how it goes initially before I decide how far to take it. I may have to start cutting out more discs before long.

Sounds familiar Bill, I usually have spares ready for when I take too much off when turning in the drill
Dont usually need them, but I know if I didnt have spares, i would mess it up

[ian_g_griffiths]

I usually glue the stack of disks to a rod instead of using a bolt. The whole surface can then be profiled and it provides a central mounting spigot, useful for smokebox doors.
Just need to be a little careful not to twist the spigot off in the chuck.

Ian

[Bilco]

Thanks for your tip, Ian - yes, Ill have to fill in the hole, although I'm planning to put tube into the back end to take the pressure gauge.

I've not started on sanding down the discs yet, but I have done some work on fixing the tank to the chassis.




Looking into the tube. I had to cut away part of the underside to fit over the middle 'box'. You can see the white plasticard 'floor' that is fixed inside the tube - there is another piece fitted under it to fill in the gap - and the black piece of plasticard which holds the captive nut. A bolt comes up from the underside of the motor compartment and holds it all together. Should be easier to paint, too.

The big silver nut is not the captive nut It's a bit of weight sitting over the centre of the motor unit - plenty of room for extra weight in the tank!

[skylon]

The big silver nut is not the captive nut Shocked It's a bit of weight sitting over the centre of the motor unit - plenty of room for extra weight in the tank!

I was going to say!

Always enjoy your builds Bill, plenty of ingenuity.

[Bilco]

I did the rough sanding of the piles of discs today - they look reasonable and just need some fine filling and finishing.




This is the Heath Robinson arrangement for the sanding - a drill stand fixed to a base cobbled together from off-cuts of chipboard. The base can be clamped in the WorkMate horizontally or vertically as needed. Also visible are the impliments used to attack the discs - the chisel works well to take the first rough cut, and various grades of sandpaper then come into play.





A before-and-after shot - the first set of discs on the left show how smooth I got.

[Steve Bennett]

Nice jig for holding the drill press Bill, some useful ideas there.
I'm surprised you are able to do the turnings in plastic with the Black & Decker, as I always found it was way to fast and tended to melt the plastic. You obviously have a lighter touch than me

[Bilco]

Well Steve .... funny you should say that I was quite tentative with the first one, and stopped to check on progress frequently. When I started the second one I thought I knew how much to take off before I needed to check, and held the sanding block against it for a more extended period - and when I did check found that there had been some melting. Fortunately, the melted material tended to fill in the steps rather than distort the discs, so I could continue to sand to get the required profile, but a bit more carefully, and the final result was fine.

As someone said - good judgement comes from experience, experience comes from bad judgement

[ian_g_griffiths]

I have also discovered that it is possible to use a scalpel as a scraper, which removes the plastic more rapidly without melting.
Use a curved blade and stay well away from the pointed end, else it will catch dig in and remove fingers, the edge pointing in the direction of rotation, i.e. at the front and down, and gently shave away the material.
Not tried a mains powered drill but used a battery one running on a slow speed.
Like the quick 'lathe' lash up with the drill stand.

Ian

[Steve Bennett]

I have also discovered that it is possible to use a scalpel as a scraper, which removes the plastic more rapidly without melting.

HAVE TO JUMP IN HERE QUICK, DONT USE A SCALPEL WHEN TURNING WITH A MAINS POWERED DRILL, IT'S A POTENTIALLY LETHAL COMBINATION.
SCALPEL BLADES ARE BRITTLE AND IF THEY CATCH WILL SHATTER WITH BITS OF RAZOR SHARP METAL FLYING THROUGH THE AIR.
Yes, the capitals were intentional.

[ian_g_griffiths]

DANGER DANGER DANGER
Steve is absolutly correct, never use a scalpel with a mains powered drill, you willl have no control there is just too much power.
When I was doing this idiot trick the battery drill was only going very slowly and the shavings were less than 5 thou thick.
The disk was mounted on a polystyrene rod, which woukd easily shear and of course there was no metal bolt head on which to catch the blade.

Before you use any tools, ALWAYS consider the safety aspects.
NEVER put your fingers in front of a cutting edge.
Always wear EYE PROTECTION, even a bit of grit from the sandpaper going in your eye could be disasterous.

Always play safe.
Ian