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Tim V's workbench - broad gauge tomfoolery

Posted: Fri Jun 18, 2010 7:26 pm
by Tim V
Here is my latest project. It's the new replacement chassis for the Bachmann 45XX from Comet.

Quite neatly etched in nickel silver, a typical Comet kit, no frills.

I am building this as a split frame and sprung, so the frame spacers will be discarded. The coupling rods can also easily be modified to incorporate the correct joint. All in all an excellent basis for a P4 conversion.
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I intend using some simple jigs, and as is customary for me, the wheels will be removable.

Re: Tim V builds a chassis

Posted: Fri Jun 18, 2010 11:38 pm
by Philip Hall
Tim,

Looks to be a nice way to start an engine. However, from looking at Comet's own photo of the result in the magazines, it seems they've used their standard crosshead. This to me is too small, making the slidebars too close together. I first noticed this in Tim Shackleton's book when he built a 'County' using Comet bits for the valve gear. Maybe you could investigate whether the crossheads and cylinders can be re - used from the Bachmann chassis, with slidebars replaced and beefed up. I have one of these to go into shops one fine day - I find myself unable to resist just a few GW engines for the new layout.

Philip

Re: Tim V builds a chassis

Posted: Sat Jun 19, 2010 1:02 pm
by Mike Garwood
Hi Tim
How is the loco to be sprung...CSB's or another CUBAn method? If you are going to use CSB's is it possible to show the marking out process. If that's not asking too much.

cheers

Mike

BTW, you were right about the use of the 'sprog', brilliant bit of kit!

Re: Tim V builds a chassis

Posted: Sat Jun 19, 2010 6:49 pm
by Tim V
Thanks for the comments guys.

I was extremely suspicious of the crosshead, which in my kit looks nothing like a GW one, or anything like the drawing or the one on Comet's website. http://www.cometmodels.co.uk/
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I am tempted to ask Comet about this, in case it's been incorrectly packed.

Other than that the rest of the cylinder arrangements seem OK, though we'll see what happens when I get in closer.

Mike, I will be using Brassmasters blocks and springs which I have successfully used on several locos.

Re: Tim V builds a chassis

Posted: Sat Jun 19, 2010 10:48 pm
by grovenor-2685
Those look like LNER style crossheads, definitely no use for the GW slide bars, must be a packing problem.
Regards

Re: Tim V builds a chassis

Posted: Sun Jun 20, 2010 6:09 am
by Tim Hale
I find the GW crossheads from Markits are above average and well worth the outlay for a quality product.

Re: Tim V builds a chassis

Posted: Sun Jun 20, 2010 9:47 am
by grovenor-2685
I find the GW crossheads from Markits are above average and well worth the outlay for a quality product.

Refer to http://www.scalefour.org/forum/viewtopic.php?f=30&t=18 for picture, the bottom one of course.
Keith

Re: Tim V builds a chassis

Posted: Sun Jun 20, 2010 4:03 pm
by Tim V
Tim Hale wrote:I find the GW crossheads from Markits are above average and well worth the outlay for a quality product.


However, I'm trying to use the chassis "as is", once I get the correct item, I'll report on whether it's any good, and what needs to be done to correct it.

Re: Tim V builds a chassis

Posted: Mon Jun 21, 2010 3:56 pm
by Tim V
Now for a word about assembly jigs. I use these excellent jigs from the EM society, the ends unscrew, poke the jig into your slot (ready etched as you can see), tighten up the knurled nuts and one chassis ready for soldering. The frames are then spaced at 14.8mm.

The health warning is that the diameter over the jig is ever so slightly less than the etched slot. However we know this so we can make allowances.
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Re: Tim V builds a chassis

Posted: Mon Jun 21, 2010 6:21 pm
by Tim V
It takes a couple of moments to chop the frames out, and clean up the tabs that join the frames to the rest of the etch. I use a large flat file for this.

First job is a trial run before going any further to check that the frames fit the chosen body. Any alterations necessary are easier when the frames are flat, rather than when assembled. That's a straight Bachman body, bought as a spare.
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Yes they do!
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Note that the jigs have only been temporarily placed in position, for the purposes of this test. While this is being done, an assessment can be made of likely frame spacer and motor positions.

Re: Tim V builds a chassis

Posted: Mon Jun 21, 2010 8:09 pm
by Tim V
A couple of strokes with the file, and the block slides nicely in its slot. Very little tweaking.
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A picture of the file, 6" long with a handle. Better control with a handle.
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I must tidy up my work bench!

Re: Tim V builds a chassis

Posted: Tue Jun 22, 2010 1:15 pm
by Stephen F
I must tidy up my work bench!


Looks a lot like mine, Tim!
Good luck with the job, I'm thinking of using some of the Brassmasters hornblocks so am interested to see how it goes, eg especially setting the ride height. Lots of photos please!

Steve

Re: Tim V builds a chassis

Posted: Tue Jun 22, 2010 3:11 pm
by Mark Tatlow
I found that the springs on the Brassmasters hornblocks were prone to dissapearing into the ether, sometime after it was assembled.

Eventually I tacked the base of the spring onto the top of the hornblock with solder. They are fine now and eventually those springs will come down from orbiting the modelling room!

Re: Tim V builds a chassis

Posted: Tue Jun 22, 2010 4:46 pm
by Tim V
Mark Tatlow wrote:I found that the springs on the Brassmasters hornblocks were prone to dissapearing into the ether, sometime after it was assembled.

Eventually I tacked the base of the spring onto the top of the hornblock with solder. They are fine now and eventually those springs will come down from orbiting the modelling room!


I've not had that problem, and I've built four locos with this system.

Re: Tim V builds a chassis

Posted: Tue Jun 22, 2010 6:20 pm
by grovenor-2685
IIRC John Brighton was recommending a dab of vaseline to hold them in during assembly.
Rgds

Re: Tim V builds a chassis

Posted: Tue Jun 22, 2010 6:27 pm
by Tim V
Progress.

All the tabs in the horn slides have been broken out, the lower holes for the spring fixings have been drilled 0.6mm, the upper holes for the brakes have been drilled 0.75mm. Now comes the difficult bit, setting out the frames so they are parallel and the axle slots are aligned. I use two squares as here with bits of wire through the holes and a piece of 1/4" rod.
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Some work to do on this, as the frames are slightly out, though the picture doesn't show it :!:

Re: Tim V builds a chassis

Posted: Wed Jun 23, 2010 2:26 pm
by Captain Kernow
Tim V wrote:the lower holes for the spring fixings have been drilled 0.6mm, the upper holes for the brakes have been drilled 0.75mm

Wouldn't mind a photo or two of that particular part of the process, please Tim, if possible? Thanks.

Re: Tim V builds a chassis

Posted: Wed Jun 23, 2010 3:46 pm
by Tim V
Bit difficult Tim, as I've already drilled them!

The frames are marked with centre pops, so I just drilled through.

Re: Tim V builds a chassis

Posted: Wed Jun 23, 2010 6:22 pm
by Tim V
If you are still with me, now for the first specialised tool, a 1/8" parallel reamer. Note that not all reamers are created equal, there is some rubbish out there.

A parallel reamer is what you're after, this one is in High Speed Steel (HSS). It was put through the bearing by hand and just enough metal was removed to give a close fit over the piece of 1/8" ground steel (from Eileen's). At this stage I want a very close fit as the plan is to put two bearings on the steel, and try them in the slots. If the bearings slide up and down, we can be reasonably certain that the frames are correctly aligned. The running fit in the bearings will come later.
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At this point we have spent nearly half an hour on the chassis. I've taken longer as I keep taking photos :!:

Re: Tim V builds a chassis

Posted: Wed Jun 23, 2010 7:04 pm
by Tim V
So with the steel through, it looks like this.
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Everything is OK, so it's time to think about the frame spacers.
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Note that the Comet drawing shows spacers very close to the lower holes which we will need later, so the spacers will have to be higher up. Next stage is to make the spacers from double sided copper coated fibreglass, Maplin etc are the usual suppliers.

Re: Tim V builds a chassis

Posted: Wed Jun 23, 2010 7:07 pm
by Will L
Mark Tatlow wrote:I found that the springs on the Brassmasters hornblocks were prone to dissapearing into the ether, sometime after it was assembled.

Eventually I tacked the base of the spring onto the top of the hornblock with solder. They are fine now and eventually those springs will come down from orbiting the modelling room!


No they never come back, I always thought that such small springs were the preferred sacrificial offering to the great Carpet God, or that less entity who inhabits the gaps between the tiles on the kitchen floor.

Will

Re: Tim V builds a chassis

Posted: Wed Jun 23, 2010 7:12 pm
by Andy W
Maybe this question will be answered as this excellent thread evolves, but when Brassmaster hornblocks are used directly in the frames - rather than using guides - how do you set them at the correct distance using the coupling rods? There, presumably, isn't any side-play to allow adjustment?

Andy

Re: Tim V builds a chassis

Posted: Wed Jun 23, 2010 7:41 pm
by Dave Holt
You don't adjust the axle-box spacing - that's fixed by the frame etching.
The two possibilities are:
1) With modern CAD generated artwork, the accuracy of the frame cut-outs and rod centres is such that no adjustment is necessary at all. I've built two Brassmasters chassis and a Comet Crab chassis on this basis and had no trouble with getting smooth running with reasonable crank-pin bush clearances; or
2) You use the John Brighton method of making the rods fit the frames using the usual extended axles. To do this, you cut off one crank-pin boss off each rod so each layer only has one boss, fit the two laminations over the extended axles, hold together with hair-grips or sprung tweezers and solder the layers together, then re-attach the removed boss(es) - this can be arranged to be the back layer to avoid unsightly gaps on the front face. (Hope John doesn't mind me giving away his secrets!) I've also tried this method and found it very successful and it works even if the etched centres don't match.

Dave.

Re: Tim V builds a chassis

Posted: Wed Jun 23, 2010 8:02 pm
by Tim V
Got it in one Dave, but it's no secret as John has explained his methods. I will be going on to show how it's done.

The beauty of the system shown here is the paucity of components - leading to less room for errors to creep in!

Re: Tim V builds a chassis

Posted: Wed Jun 23, 2010 8:03 pm
by Captain Kernow
Tim V wrote:Bit difficult Tim, as I've already drilled them!

The frames are marked with centre pops, so I just drilled through.

Thanks, I wasn't after a YouTube video of you drilling metal, just a photo of where the respective holes were! But if you've drilled pre-dimpled holes, then it can't be that hard when I come to do something similar!