Re: Tim V's workbench - latest shenanigans

[Tim V]

The story so far.

With my previous conversion under my belt, I came to this one knowing the pitfalls. Matching the wheelbase length to the coupling rod centres is crucial to good running. As can be seen in the picture I've used some jigs - I think they came from London Road. They are turned aluminium, with tapered ends. I have clamped them into the axle slots. Although they are 1/8", they sit well into the slots. I made sure they all stuck out the same distance.

Close examination of the fireman's side under a watchmakers glass reveals the front and back holes are slightly too close. But the middle hole is way out. I'm going to have to file the hole out forwards to accept a new bush. I will also fit bushes into the other two holes, as they are oversize, and they will then all match.

The driver's side will have to wait for me to reset the clamps.

[Brinkly]

I must admit I had a really good running 45xx in 00 and couldn't get it to run smoothly in P4 using Gibson wheels. So decided to put it back and build either a Comet chassis, or wait for High Level, which might not happen, and replace the whole thing.

Regards,

Nick

[Tim V]

The other one I've done is a really good runner - in front line service on Clutton.

[Tim V]

I found these Exactoscale bushes in my box.

IMG_3991.JPG

Popped them on the jigs, made sure they were at equal height and level in all planes.

IMG_3992.JPG

And with the rod put on ready for soldering.

IMG_3993.JPG

The pin in the coupling rod was in good condition, so I'm not going to disturb it.

[Dave K]

Been busy with another Bachman 45xx.
Discovered the wheels I'd bought only had 9" crank throw, as opposed to the 12" they should have. As this was supposed to be a "quickie", I baulked at £62 for Ultrascales, and decided to modify the Gibson's I'd bought. I won't show the jig I made.

Tim,

I've got a couple of sets of Gibson 4' 7" wheels for a couple of High Level 57xx kits (which are the same wheels as the 45xx) and looking at the Gibson web site it states the GW standard 4' 7" wheel had its crank throw at 9 1/2". The wheel I've got do not have the crank pin holes drilled out as I believe they are from the old Studioleth pattern.

I was told that the crank pin throw should br halt the cylinder stroke. What is the right answer?

I must admit I had a really good running 45xx in 00 and couldn't get it to run smoothly in P4 using Gibson wheels. So decided to put it back and build either a Comet chassis, or wait for High Level, which might not happen, and replace the whole thing.

Nick,

I remember speaking to Mr High Level at last years S4urm and he said he would not be doing a 45xx chassis as David Geen sells the Churchward one.

[grovenor-2685]

I was told that the crank pin throw should be half the cylinder stroke. What is the right answer?

With very very few exceptions this is true for outside cylinders, to have anything else you have to have eccentric crankpins.
However for inside cylinders the throw of the inside cranks will be half the cylinder stroke, the outside cranks for the coupling rods can be and often are different, often less as it may reduce the centrifugal forces and hence the balance weights. This is where the Sharman wheel book comes in.
Regards
Keith

[Tim V]

Dave, I see you've asked this question in "other" places!

Critically, as you've found out, the answer is 10". Perhaps you should look for a Mike Sharman "Wheel specifications for the modeller" book. The second edition is better to get hold of, as a lot of mistakes from the first edition were removed. Have a look around at Scaleforum, they often appear on second hand stalls.

Turning to your wheels, I would not, under any circumstances, rely on the countersink to guide the drill. There are various jigs produced over the years to ensure that critical dimension of crankpin throw is EXACTLY the same over all wheels. If it's out, you will never get good running.

The wheels I had bought were new current stock from Gibson, and didn't have drilled out holes, which is why I was easily able to change their throw. The jig I made involved use of a lathe - mention of which seems to bring some people on this forum out in a rash, so I won't show it here.

I have a set of untouched Studiolith pannier wheels, their crank pin holes are moulded in. They also have the brass centres and tapered axles. I'm keeping them as mementos.

[Paul Townsend]

The jig I made involved use of a lathe - mention of which seems to bring some people on this forum out in a rash, so I won't show it here.

Please show it elsewhere next Tuesday!

[martin goodall]

I suspect that lathe ownership is more widespread within this Society than elsewhere, so I don't think Tim need be shy about describing the jig in this thread. Quite frankly, if it gives anyone a fit of the vapours, it's purely their problem and no-one else's. So go on, Tim - spill the beans and let's all see the beast.

[Mike Garwood]

Yep. I'll second those sentiments...let the dogs see the rabbit!

Mike

[rule55]

Yes, please show the jig - I'd love to see it. It would be a good first project for us lathe beginners.

Tony

[LesGros]

Tony wrote:

Yes, please show the jig - I'd love to see it. It would be a good first project for us lathe beginners.

Hear hear; but perhaps on a new thread for such things, best we don't hijack Tims master class .

[Tim V]

It's part of my workbench - so it can stay in!

Well I'm pleased this has provoked such a positive response. I bought my lathe back in '88, a decision I have never regretted. This particular jig was made on my second lathe, but could have been made on the Unimat.

Here is the jig, as you can see, it's just a disc with a hole, which fits the wheel rim. In the centre is a 2.9mm stub, representing the axle, for the 3mm wheels I was using. To left and right (at 3 and 9 o'clock) are small holes, used for pushing pins through to extract the wheel. Just above the stub axle is the hole for the crankpin. At above 3 o'clock is some dirt! At 5 o'clock is a pin, used to locate between spokes. to its left at 7 o'clock is a hole drilled for a pin I wasn't satisfied with. At 12 o'clock is a filed mark to line up the boss with.

IMG_3994.JPG

Here is the jig with a wheel inserted. This particular one has a 1/8" hole. The jig is turned up the other way, a spare rim is used to press the wheel firmly into the jig, before a drill is run through the crankpin hole. Simples!

IMG_3995.JPG

[LesGros]

It's part of my workbench - so it can stay in!

More than fair enough Tim

[rule55]

Many thanks for the detailed description of the crankpin drilling jig. I shall be building a fairly close imitation when I get my hands on a suitable lump of brass.

[grovenor-2685]

An alternative version was described on here, http://www.scalefour.org/forum/viewtopic.php?f=20&t=2019&start=50#p18358 just a few days ago.
another way of skinning the cat, and would cover a larger range of wheel sizes.
Regards
Keith

[Paul Townsend]

An alternative version was described on here, http://www.scalefour.org/forum/viewtopic.php?f=20&t=2019&start=50#p18358 just a few days ago.
another way of skinning the cat, and would cover a larger range of wheel sizes.
Regards
Keith

Only just caught up to that one.....and then there was Alan Goodwillie's chassis Masterclass here a couple of years ago with another set of jig designs.

We are now spoilt for choices of design!

I wonder why no-one has yet produced a set of wheel-fettling jigs commercially? Come on entrepreneurs, I know you are there

[Tim V]

After a bit of fiddling with the front crankpins fouling the slide bars, it works! Needs the pickups tweaking, and a decoder now.

[Paul Townsend]

After a bit of fiddling with the front crankpins fouling the slide bars,

By bending slidebars, moving cylinders or filing crankpin nuts?

[Horsetan]

...I wonder why no-one has yet produced a set of wheel-fettling jigs commercially? Come on entrepreneurs, I know you are there

Sounds like something GW Models could make...

[martin goodall]

After a bit of fiddling with the front crankpins fouling the slide bars, it works! Needs the pickups tweaking, and a decoder now.

You're not going to get a way with it that easily! What else did you have to do to sort out the mismatch between the axle slots in the chassis block casting and the etched rods, for example? Give us the sordid details.

[Russ Elliott]

Martin - I think Tim's methodology was:

- keep the chassis block machining unaltered;
- using the tapered axle jigs, examine the Bachmann rods to see which rod holes needed altering;
- file offending rod holes accordingly;
- using the tapered axle jigs again, place rods onto bushes and solder rods to bushes, thereby ensuring bush centres align with chassis block centres.

I think my only comment is that Bachmann rods often have quite a bit of slop in their knuckles, so maybe the method will work correctly only for those rods that do not have such slop. (Tim noted that his knuckle pin was "in good condition".)

[Horsetan]

You're not going to get a way with it that easily! What else did you have to do to sort out the mismatch between the axle slots in the chassis block casting and the etched rods, for example? Give us the sordid details.

Well he didn't resort to EM flanges, let's put it that way...

[martin goodall]

The wheels originally fitted to my 45XX conversion were P4.

The new wheels when fitted to the second attempt at this conversion will be Ultrascale EMF, set to the P4 back-to-back.

[Tim V]

Russ has got it spot on. All I have done is to modify the rods to suit the existing chassis block, which is untouched. As I said the rivet joint was in good condition, with no sign of being bent, loose, sloppy or at an angle.

For those, like Martin, who have the Ultrascale conversion set, that is all that needs to be done.

Note that the excursion into looking at the crankpin jig was only because I was using Gibson wheels. I have another Bachman conversion using the Ultrascale wheels, and modifying the coupling rods was all I did on that one.

To modify the chassis block would not be easy. And it isn't needed.

I don't think the rods are etched, they could be stamped.

The fiddling around the cylinders merely involved thinner crankpins. No bending of cylinders, nor fiddling of slidebars was needed. I merely checked they were straight.

Additionally I had to do a bit of grinding of the body to fit the motion bracket. This could be because I have a mixed pair. The chassis came from a 55XX complete model, the body of which I put on the Comet chassis detailed on my workbench. The body I'm using now I bought from a stand on its own, and is possibly much older. If someone else was doing this with a complete engine, I doubt this grinding would have to be done.

I could bring the engine to Scaleforum for perusal if anyone wanted to see it.