Back to the J10
Posted: Fri Sep 10, 2010 10:37 pm
So let’s look at what we have got to be getting on with.
The Existing Loco
This time I remembered to take a photo of the loco before I started taking it apart, something I forgot with the tender. This is a DJH kit which was built mumble mumble years ago in OO to run on a previous exhibition layout. My intention is to replace the OO chassis with a completely new one suitable for P4. The body is very likely to need attention underneath to provide clearance for the wheels. It will also need a cosmetic update above the footplate. You will note that the body comes apart at footplate level which should make fitting the footplate to the chassis a lot simpler when we get there.
Bits for the new Chassis
I noticed that Gibson did profile milled chassis frames for the J10. I decided to base the new chassis on these. So I wrote off to Gibson's for the chassis frames, 6 of the wheels closest to the prototype and a universal 6 wheel connecting rod etch. I had hornbock components from HighLevel (on the left) and Exactoscale (on the right) in stock. When I took the picture I hadn't decided which ones I was going to use.
Drive will be through a HighLevel LoadHauler+ gearbox with a DriveStretcher. This should enable the motor to be mounted pointing forward on, or close to, the boiler centre line without the need for the existing visible cut out in the bottom of the boiler. The drive train will be down through the firebox and the drive on the rear wheels under the cab floor.
The choice of gearbox is important as it has implications for the choice of hornblocks. The DriveStretcher is 9.8mm wide which doesn’t leave a lot of room for chucky bearing blocks. The Gibson frames are 0.75mm thick and a standard HighLevel hornblock mounted inside the frame projects 3mm. With a frames width of 16mm, a little arithmetic will tell you that there is only 8.5mm left for the gearbox.
So I considered doing something with the Exactoscale hornblocks which, with a little effort, could be mounted flush with the outside face of the frames. These have bearing blocks 3.2mm thick, which could be reduced if necessary and would just allow enough space to get the gearbox in. However they don’t fit the frame cut outs in the Gibson frame, and though I have planned out a way to get them in, it was going to be labour intensive and I would have to do six.
So back to the Highlevel blocks. It is possible to mount a standard round top hat bearing in the carrier. This gives you a much thinner result and will fit with the gearbox, so that is the way I am planning to go. More details of how it is done later.
Sorting out the Fulcrum Points
I used my spread sheet to produce the fulcrum plot below. I got a perfectly acceptable result using the auto calculate option with fulcrum points rounded to the nearest 0.5mm. I.e. all I had to tell the spread sheet was the wheelbase.
Building Considerations
Looking at the Gibson frame sides, you will notice that these accurately reflect the prototype profile. This isn’t going to work with the cast metal footplate, so we must assume I am going to have to saw a fair chunk off the top. If I started again it might well be just as easy to make my own frames from scratch, but as I’ve got them I’ll use them.
Then there is the question of the Gibson universal coupling rods. These are all very well, but I tend not to believe in rods jointed on the centre crank pin. So the first thing I’m going to have to do is convert the bits of the universal rods into a properly jointed set. When I started this thread I was expecting just to do a blow by blow on fitting CSB’s, but somehow I keep on being diverted into other associated things. As the rods are key in constructing the frames , I’m afraid making jointed rods is going to be another such diversion, and that’s what I will cover in the next post.
The Existing Loco
This time I remembered to take a photo of the loco before I started taking it apart, something I forgot with the tender. This is a DJH kit which was built mumble mumble years ago in OO to run on a previous exhibition layout. My intention is to replace the OO chassis with a completely new one suitable for P4. The body is very likely to need attention underneath to provide clearance for the wheels. It will also need a cosmetic update above the footplate. You will note that the body comes apart at footplate level which should make fitting the footplate to the chassis a lot simpler when we get there.
Bits for the new Chassis
I noticed that Gibson did profile milled chassis frames for the J10. I decided to base the new chassis on these. So I wrote off to Gibson's for the chassis frames, 6 of the wheels closest to the prototype and a universal 6 wheel connecting rod etch. I had hornbock components from HighLevel (on the left) and Exactoscale (on the right) in stock. When I took the picture I hadn't decided which ones I was going to use.
Drive will be through a HighLevel LoadHauler+ gearbox with a DriveStretcher. This should enable the motor to be mounted pointing forward on, or close to, the boiler centre line without the need for the existing visible cut out in the bottom of the boiler. The drive train will be down through the firebox and the drive on the rear wheels under the cab floor.
The choice of gearbox is important as it has implications for the choice of hornblocks. The DriveStretcher is 9.8mm wide which doesn’t leave a lot of room for chucky bearing blocks. The Gibson frames are 0.75mm thick and a standard HighLevel hornblock mounted inside the frame projects 3mm. With a frames width of 16mm, a little arithmetic will tell you that there is only 8.5mm left for the gearbox.
So I considered doing something with the Exactoscale hornblocks which, with a little effort, could be mounted flush with the outside face of the frames. These have bearing blocks 3.2mm thick, which could be reduced if necessary and would just allow enough space to get the gearbox in. However they don’t fit the frame cut outs in the Gibson frame, and though I have planned out a way to get them in, it was going to be labour intensive and I would have to do six.
So back to the Highlevel blocks. It is possible to mount a standard round top hat bearing in the carrier. This gives you a much thinner result and will fit with the gearbox, so that is the way I am planning to go. More details of how it is done later.
Sorting out the Fulcrum Points
I used my spread sheet to produce the fulcrum plot below. I got a perfectly acceptable result using the auto calculate option with fulcrum points rounded to the nearest 0.5mm. I.e. all I had to tell the spread sheet was the wheelbase.
Building Considerations
Looking at the Gibson frame sides, you will notice that these accurately reflect the prototype profile. This isn’t going to work with the cast metal footplate, so we must assume I am going to have to saw a fair chunk off the top. If I started again it might well be just as easy to make my own frames from scratch, but as I’ve got them I’ll use them.
Then there is the question of the Gibson universal coupling rods. These are all very well, but I tend not to believe in rods jointed on the centre crank pin. So the first thing I’m going to have to do is convert the bits of the universal rods into a properly jointed set. When I started this thread I was expecting just to do a blow by blow on fitting CSB’s, but somehow I keep on being diverted into other associated things. As the rods are key in constructing the frames , I’m afraid making jointed rods is going to be another such diversion, and that’s what I will cover in the next post.