Springing and brakes for a Grande Vitesse van

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Guy Rixon
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Springing and brakes for a Grande Vitesse van

Postby Guy Rixon » Fri Jan 15, 2021 11:05 pm

I'm building another of the Roxey kits for SECR Grande Vitesse vans, and in this one I wanted sprung suspension. The kit doesn't help here, being designed for either rigid suspension or a rocking axle in inside bearings.

Nobody does a sprung axleguard of exactly the right profile for the SECR stock, but the GWR-coach kind in the Bedford range is reasonably close to the right shape. The trick is to mount them into the Roxey chassis, getting them right in all three axes.

First thing is make up the axleguard units (no need to do the spring carriers and bearings at this stage) and to fix their relative position. I did this with a brass bar across the centre of each axleguard-pair. It's 0.8 mm K&S strip, and it has to go on the inside of the "U" of the axleguard unit because I don't know, at this stage, how much space is needed between the axleguard unit and the floor of the van. Here's the strip soldered into one axleguard-unit by eye and I'm checking that the alignment is OK-ish. It doesn't need to be perfectly square or central, which is a help.
IMG_8086.JPG

The strip is cut about as long as the length over spring mounts. The bits that stick out at the ends do nothing for the suspension, but they are there to locate the brake bits later.

Now the second axleguard pair is located using a wheelbase gauge. It's a Bill Bedford gauge, which leaves the top of the model open to admit the soldering iron. You can't easily do this with the Brassmasters gauge because it blocks out the iron. 2.0 mm drill-bits stand in for axles.
IMG_8089.JPG

In fact, I've jigged this up the wrong way round in the photo and should have the end of the jig with the bigger opening where I'm soldering.

Now I need to align this sub-chassis with the main chassis. Measuring with my dial callipers suggests a 1.6mm gap between each axleguard and the solebar etch, so I wedged it in with some fragments of 1.6 mm wood.
IMG_8092.JPG

This holds it moderately firmly but still allows me to slide the sub-chassis along the main chassis to get it central. I centred it up with calliper measurements. The axleguards foul one of the brake-shaft hangers, which is a problem for later. (Its deferrable because I don't fix the sub-chassis permanently at this stage.)

I could now solder the sub-chassis into the main chassis, but it would probably give the wrong buffer height. I'm expecting about 0.5 mm of packing will be needed between the two, but I can't check that until I put the headstocks on the main chassis. For now, I want to preserve the alignment while still being able separate the two assemblies. Therefore, I drill both for 10BA securing screws.
IMG_8094.JPG

I did this in with the pillar drill because it was easiest and the clamps on the drill table were convenient for holding down the bar between the axleguards. It could be down well enough with a hand drill. Neither screw hole is perfectly centred in the bar, but it doesn't matter. Clearance size for 10BA is supposed to be 1.75 mm, but I wanted minimal slop, so I drilled 1.70 mm and broached the holes until the screws would just pass.
IMG_8096.JPG

The screws are nearer the centreline than the nearest spring-attachments, so I know that they will clear the brake assemblies on the two axles. I've moved one of them to clear the brake-shaft hangers too.

Total time to this point: about 2.5 hours, including head-scratching time. I could probably do it faster next time. Next task is to set up the buffer height.
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Guy Rixon
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Re: Springing and brakes for a Grande Vitesse van

Postby Guy Rixon » Sat Jan 16, 2021 9:16 pm

I got the headstocks on and checked the buffer height. Surprisingly, it was too high rather than too low.
IMG_8108.JPG

The body and the chassis bits added so far weigh about 40 grams. When weighted up to 60 grams it settles to the right height, so that's OK.

Time so far: about 4 hours, but an hour of that was cursing the headstocks into place (not a very friendly design in this kit) and not related to the suspension.
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Guy Rixon
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Re: Springing and brakes for a Grande Vitesse van

Postby Guy Rixon » Sun Jan 17, 2021 9:01 pm

Having established that no packing was needed under the axleguards, I could have soldered the sub-chassis permanently into the main chassis and had done. However, I quite liked the ability to take the sensitive bits away to safety during the messiness of painting the solebars and brutality of fitting the step-boards. Further, the brake rigging is easier to complete when there is full access from all directions. The brake-shaft hangers needed to shift anyway to clear the axleguard, so I moved them onto the sub-chassis.

First I cut a baseplate from scrap etch --- from the axleguard fret, so it's the same thickness as the axleguards --- and soldered it to the spine of the sub-chassis.
IMG_8110.JPG

I drilled through from the main chassis a hole to locate the brake cylinder, then separated sub from main.

I bent up the V-hangers on the main chassis and soldered in the brake shaft of 0.7mm wire (remembering to add the centre crank and brake-cylinder crank, which is better than I usually manage). This fixed the spacing and alignment of the two V-hangers. I cut one hanger away from the chassis (an act of felony-grade tool-abuse I won't detail) and bent the other one back and forth until I got a fatigue fracture. This gave me an assembly to transfer to the sub-chassis, where I fixed them with lower-melting-point solder than that used on the brake-shaft joints. The assembly was positioned using the brake cylinder and its crank as a guide.

Finally, I soldered in the brake cylinder and added its piston rod from 0.7mm wire.
IMG_8114.JPG


Cumulative time to this point: about 5.5 hours, of which about 3 is incurred by me complicating the chassis and the rest is inherent.

If you look closely, you'll see that the centre crank is one-sided, the brakes of both axles being worked by the same arm. It follows that one set of brakes are pulled on and the others push on. This is real, apparently, backed up by the Ashford GA for these vans, a similar GA for contemporary 4-wheeled coaches, and the only photo of the GV van that I can find. It seems to have been an SER and SECR peculiarity.

FWIW, chopping up the etch scrap was greatly helped by these:
IMG_8111.JPG

Despite filling the workbench like a megaladon in a goldfish pond, they actually cut very neatly, and they don't curl the metal.

Next step is to paint the sub-chassis and to fit the brakes.
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Winander
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Re: Springing and brakes for a Grande Vitesse van

Postby Winander » Sun Jan 17, 2021 11:31 pm

Hello Guy,

Are they the shears with the serrated jaws?

Whilst I'll never probably have to do anything like this it is useful to see the techniques used and motives behind them. I'm enjoying the read.

best wishes
Richard Hodgson
Organiser Scalefour Virtual Group. Our meeting invitation is here.

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Guy Rixon
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Re: Springing and brakes for a Grande Vitesse van

Postby Guy Rixon » Mon Jan 18, 2021 8:44 am

Yes, these snips have serrated jaws and the serrations leave fine marks on the edge of the cut. That didn't matter for what I was doing here. For other work I might use the snips to rough out the shape and then file to final size, removing the marks.
IMG_8115.JPG
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Guy Rixon
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Re: Springing and brakes for a Grande Vitesse van

Postby Guy Rixon » Thu Jan 21, 2021 9:07 am

IMG_8128.JPG

Brakes are now completed on the sub-chassis. The blocks, hangers, etc. around each wheelset are prints. The push-rod to the axle nearest the brake shaft is a bit of waste etch, filed down at one end to fit the 0.5 mm hole in the print and CA'd to the centre crank at the other. The pull-rod for the other axle is 0.5 mm wire, fitted the same way.

The wheels are in for good now. Before assembly, I painted the "wooden" bits in body colour (didn't bother with the backs of the wheels) and blackened the bright tyres with a Posca paint-pen. This is easier to do with the wheels in one's hand.

The brake prints are fixed, to the spine of the sub-chassis, with "tacky" PVA at this stage. This allows for slight adjustments, and I could lever the brake-prints off altogether if I needed to get the wheels out. I may lock them in place permanently with CA or epoxy when all is done.

Time to this point: about 8 hours cumulative, including an hour and a half of painting, which is always time-consuming. Actually fitting the brake assemblies took about 15 minutes. C.f. the 5-hour cuss-fest, followed by a lie down in a dark room, to fashion brakes from etched bits.

I can now build, paint and varnish the main chassis with the sub-chassis safely tucked away. The varnishing is significant, since I want a satin finish on the black solebars and headstocks (they look grotty and wrong in matt off-black), whereas the bits below solebars need to stay matt. Much masking is avoided by separating the parts.
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Guy Rixon
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Re: Springing and brakes for a Grande Vitesse van

Postby Guy Rixon » Thu Jan 21, 2021 12:33 pm

I now realize that I'm ahead of myself and have assembled out of order. What I should have done was to fix the axlebox castings before trapping the wheels with the brakes. That would have allowed me to fold the bearing carriers down, out of harm's way. I may dismantle the brakes to allow this; they are easy to refit and I have spare prints if I damage the first set.

If I'd really thought about it, I might have fitted the castings before painting, so they could be soldered. But I am not very good at soldering whitemetal, so prefer to glue castings when they have no hidden, non-cosmetic surface to take the solder.

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Guy Rixon
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Re: Springing and brakes for a Grande Vitesse van

Postby Guy Rixon » Sat Jan 30, 2021 1:57 pm

The chassis assemblies, and therefore the van, are now almost done.
IMG_8135.JPG


On the main chassis, I have attached the upper steps as per the kit design. They have tabs that fit behind the solebars and "fingers", representing the vertical parts of the supports for the lower steps, that fit in front.

The lower steps are supported by lengths of 0.5mm wire, formed into "U" shapes. Initially, I formed the wire into "L"s and soldered them under the lower step. Then, using a jig made of scrap wood to set the height, I formed the top bends. When all was done, for the step on one side, I soldered the step assembly to the underside of the top step. I did it this way to leave the backs of the solebars clear to accept the axlebox/spring castings. In fact, having a bend in each wire under the top step seems to strengthen the support; perhaps the brass is being work-hardened? This will be my preferred way of doing step supports from now on, at least where there are brass top-steps.

The man chassis was sprayed off-black and then I varnished and lettered the solebars. The final finish on the solebars is semi-gloss because they look wrong in matt off-black. The steps were masked and not varnished.

Buffers are my home prints discussed elsewhere on this forum. Normally, I paint and assemble sprung buffers before fitting them. This time, I thought I'd be clever and fit the guides then assemble the moving parts in situ; this lets me adjust the seating and angle of the guides, the home prints not being as clean and flat at the back as the Shapeways prints. Mistake! It's difficult to set up the buffer action with the guides in the chassis and I ruined two in the process. Luckily the home prints are almost free and I had spares. There are cases where the buffers do need to be set up in situ, to do with anti-rotation devices for oval buffer-heads, but these need more engineering (in process) before they become easy.

The clunking great 8BA screws that hold the body on foul the motion of the buffers and had to have their heads filed down. If I do more Roxey kits, I shall have to re-drill the body-fixing holes in a better place.

The only remaining items of note (apart from couplings) are the axleboxes, springs and spring mounts. The castings in the kit have two big problems. Firstly, they put the axleboxes too near the solebars to cover the bearings, the camber cast into the springs being too little and the spring mounts modelled too short. Secondly, they have the kind of large, square-cornered axleboxes sometimes called "C type", whereas my only decent photo of these vans shows the older and smaller design of box inherited from the SER. Therefore, I need replacements and shall print them. I could use Branchlines' castings with my printed spring-supports, but hollowing the castings for bearing movement is difficult in these small boxes.

Time spent so far is about 13.5 hours, including two hours to make the steps, an hour painting and two hours fighting the buffers.
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Guy Rixon
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Re: Springing and brakes for a Grande Vitesse van

Postby Guy Rixon » Tue Feb 02, 2021 11:41 am

IMG_8138.JPG

Spring and axlebox prints achieved, I think, after a couple of tries.

The boxes are nearly scale width; I measured 5.75 inches wide from the drawing and mine are expanded to 6 inches in order to clear the bearing tip and have some thickness of wall left. The previous version fitted beautifully into the chassis, but tended to print with holes in the side. This one is tweaked to print fully and I hope it still fits. The axlebox-sides are extremely thin and successful printing seems to depend on surface tension in the resin.

The bottom of the axlebox is unrealistically hollowed out, to win a little more movement for the bearing. It doesn't seem to show with the van on the track. The opening lets me slide the assembly into place with the wheels and bearings in situ, and avoids the needs to remove brakes, wheels etc. for fitting.

There should be a small stalk (oil-filler tube?) on the top of the axlebox, but it won't print survivably and I shall probably leave it off.

The bar at the bottom of the print is designed to be glued either to the top of the axleguard, or to the solebar. In this way, I avoid having glue near the moving parts.

These assemblies are probably suitable for the outer axles of a SECR brake van that I have in progress; if not, the CAD can be adapted. I need a variant with J-hangers for the centre axle. They may also be right for the 27' coaches I'm building, but there are worries about the correct length of the springs, since the GA specifies one length in writing and shows another on the drawing.
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Guy Rixon
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Re: Springing and brakes for a Grande Vitesse van

Postby Guy Rixon » Thu Feb 04, 2021 9:47 pm

PHOTO-2021-02-04-21-09-10.jpg

It's finished. It took another two prints of the springs and axleboxes, one to unbung the real springs by increasing the camber of the cosmetic ones by 0.5mm, and one print run because I broke two prints while trimming them.

Remember when I moved the brake-shaft hanger toward the solebar to clear the BB suspension? Of course, I moved it too far and it now fouls the cosmetic spring-hanger, the latter having to be savagely pruned to fit, hence the breakage. When I do repeats of this chassis (two new vans to build and chassis refits for the two I already have), I'll need to find a better way. But for now, all is in place and all the moving bits still move freely.

Total time to assemble this chassis has come out at ~ 15.5 hours, plus ~ 7 hours to design and print the replacement parts. About 15 hours extra work, above the time to build the kit as designed, was caused by me adding the sprung suspension, sprung buffers, and replacement details. Was it worth it? Definitely.
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