First chassis in P4

Help and advice for those starting in, or converting to P4 standards. A place to share modelling as a beginner in P4.
Daddyman
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First chassis in P4

Postby Daddyman » Wed Feb 26, 2020 6:44 pm

Hello,
I'd like some advice on my first P4 chassis please.
I'm building an old kit for an LNER J79. The kit was shot down from 0 gauge, with all the associated problems. One of these is that the chassis has no half etch lines for cutting out hornways. Now, that's not a big problem as for my first P4 chassis I don't particularly want to be a hostage to hornblocks. Instead, I'm using a method that I know from Mike Edge's kits, which consists in having conventional round 1/8 bearings soldered into compensation beams. The axle is free to move up and down because the hole in the main frames is broached slightly larger than 1/8 - to allow, say 1/2 mm up and down travel. However, so far I have only made the beams for the leading two drivers. I could leave the rear drivers uncompensated (many beautiful models in old MRJs are built this way after all). But my priority is not to have any body rock, and one set of uncompensated drivers would make that almost inevitable.

Instead, I'd like to go a bit further in two directions. First, I'd like to rig up some kind of springing on the leading beam. In my imperfect understanding of these things, I could solder some guitar wire to, say, the leading bearing and then locate the other end of this in a piece of tube/a handrail knob/a CSB pivot somewhere at the front end of the main frames. Have any of you ever tried such a system - sort of "sprung compensation"? How critical would the distance between each end of the spring wire be?

The other thing I'd like to work on is somehow compensating the rear axle too. Some of Mike's kits (the Kiston long boiler, for example) have this system - a beam connecting the first two drivers and a separate beam pinned to a point in the chassis and allowed to swing around a knife edge compensating the rear ones. This beam would have to be very short as (as the photo below shows) there is not much spare main frame. Alternatively, there was an article in an old MRJ detailing the build of some MW locos and the builder suspended the beam for the rear axle on the middle axle (that is, there were two beams on the middle axle). Do any of you have any thoughts? I wonder if there is also a way of springing whatever system I adopt on the rear driver too.

Thanks in advance for your help!
David Addyman.

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PeteT
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Re: First chassis in P4

Postby PeteT » Wed Feb 26, 2020 8:59 pm

I can't really help answer the question - but would like to comment on the very clean soldering, it looks brilliantly assembled!

My 2 penneth on chassis is that I prefer the hornblock option for all wheelsets, to allow them to drop out not only for maintenance/fettling if necessary but also to help paint it all in the first place.

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Will L
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Re: First chassis in P4

Postby Will L » Wed Feb 26, 2020 9:06 pm

The simple solution, surely, is to have a central fixed pivot/bearing point over the rear axle. The axle hole in the chassis frame would need to be narrowed so the axle can move vertically but not horizontally. Net result 3 point compensation with no fixed axle.

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grovenor-2685
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Re: First chassis in P4

Postby grovenor-2685 » Wed Feb 26, 2020 10:46 pm

Will L wrote:The simple solution, surely, is to have a central fixed pivot/bearing point over the rear axle. The axle hole in the chassis frame would need to be narrowed so the axle can move vertically but not horizontally. Net result 3 point compensation with no fixed axle.

Another pair of your beams from middle axle to rear, but not pivotted anywhere will locate the rear axle longitudinally and ensure the centres match the rod centres, you will still need Will's centre bearing over the rear axle.
Regards
Keith
Grovenor Sidings

Daddyman
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Re: First chassis in P4

Postby Daddyman » Thu Feb 27, 2020 6:45 am

Many thanks to all of you!

Pete - the loco is in the late stages of cleaning up; there's nowt particularly clean about my soldering. That nice Mr Rathbone said that my Aerolite was the dirtiest loco he'd ever been given to paint. I'm not sure if he meant it in a good way, but I bought an ultrasonic cleaner soon afterwards. The J79 has been admonished with fibre-glass brushes, dowsed in Shiny Sinks and then plunged in the U/C bath, which may explain the sparkliness.

You're right too, Pete, of course about hornblocks, but I don't fancy my chances of cutting out hornways to the required precision using only hand tools.

Will, thanks. It's your recent comments on a video on the site that makes me want to eliminate body rock at all costs. Is compensation with no fixed axle something that's often practised? - that is, before compensation went out of fashion.

Keith, thanks - you've given me the courage to press on with double beams, with the rear one pivoted off the centre axle, and the rear axle balanced on a knife edge.



No thoughts on springing compensation beams? Just a daft idea?

Terry Bendall
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Re: First chassis in P4

Postby Terry Bendall » Thu Feb 27, 2020 8:33 am

The alternative of course would be to beg, buy borrow or steal a copy of Mike Sharman's book on chassis construction and use the methods Mike recommended. All fairly simple to do. It is old technology but it works.

Terry Bendall

Julian Roberts
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Re: First chassis in P4

Postby Julian Roberts » Thu Feb 27, 2020 9:56 am




Hi David

That's my High Level Barclay at Model Rail Scotland a few years ago, compensated with twin longitudinal beams between the rear and middle drivers, and a central beam on the front axle. I think it's probably as smooth as you are looking for - bearing in mind that the smaller the wheel the more any small bump in the track, such as the gap at a crossing, will show up, and these wheels are 3 foot something. Having no axle fixed is the big step forward I've found. All Sharman ideas as Terry says. Though I read the concepts in Iain Rice's book on chassis construction where it is explained in greater length.

Springs are a whole different problem and I would suggest either a Dave Bradwell kit with its spring system, or a kit with CSBs built in at least as an option as the latest High Level ones. I doubt you'd be able to make a springy compensation beam work any better than one of these three options, but that's my thought based on just 10 years of loco making with a lot to learn still.

Anyway good luck and have fun!

Daddyman
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Re: First chassis in P4

Postby Daddyman » Thu Feb 27, 2020 3:52 pm

Thanks to both. So the message I'm getting is "sprung compensation" is a daft idea, and no one has ever been silly enough to try it? Or are you saying, Terry, that I should read Sharman's book as it answers my two specific questions - viz how to do all-wheel compensation, and whether springing compensation beams is desirable/advisable/possible? You're right Julian, of course, that Rice's book answers the first of these questions.

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Will L
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Re: First chassis in P4

Postby Will L » Thu Feb 27, 2020 6:21 pm

Daddyman wrote:... Is compensation with no fixed axle something that's often practised? - that is, before compensation went out of fashion...

Perfectly legit and some modellers have made very good use of them, see the Sharman book for the various options. Being that bit harder to do, less confident models tended not to attempt them, although all axle compensation well executed can produce very acceptable running. Given the proliferating beams and pivot points, I think CSB solutions end up being simpler to build.

Daddyman wrote:...So the message I'm getting is "sprung compensation" is a daft idea, and no one has ever been silly enough to try it?..

Actually, quite hard to get right is nearer the mark.

Daddyman
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Re: First chassis in P4

Postby Daddyman » Thu Feb 27, 2020 7:01 pm

Thanks, Will. Would you personally set up a chassis for CSBs which has no etched hornway marks, using only hand tools? I'd like to do it on the next loco - a Y7 (0-4-0) - but don't fancy my chances.

Armchair Modeller

Re: First chassis in P4

Postby Armchair Modeller » Thu Feb 27, 2020 7:26 pm

If you use High Level hornblocks and their hornblock jig, your slots don't have to be 100% accurate.

davebradwell
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Re: First chassis in P4

Postby davebradwell » Thu Feb 27, 2020 8:11 pm

Here's a thought, David - you already have a hole, presumably in the correct position in the frames but need a slot to allow an axlebox to slide up and down. Why not use the holes to locate the axleboxes and hornguides? I expect the holes need bushing temporarily to locate the axle, thread the 'boxes onto the axle and hold against frames. Solder hornguides made from short pieces of angle inside the frames pushing them up against the axlebox whilst holding them upright with a square. Bit of a fiddle but no worse than the usual coupling rod jig. Finally cut out bits of frames between hornguides.

You'd need to mark the axleboxes so they go back in the same orientation and position. Standard axlebox is 5mm square but if you can get hold of some Exactoscale ones they're 4mm and will fit better. They have a flange on the outside of the frame and I'm assuming you'd do the same if using the larger size.

Will you be making your usual trip to Wakefield?

DaveB

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ArthurK
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Re: First chassis in P4

Postby ArthurK » Thu Feb 27, 2020 10:49 pm

Daddyman wrote:Hello,
I'd like some advice on my first P4 chassis please.
I'm building an old kit for an LNER J79. The kit was shot down from 0 gauge, with all the associated problems. One of these is that the chassis has no half etch lines for cutting out hornways. Now, that's not a big problem as for my first P4 chassis I don't particularly want to be a hostage to hornblocks. Instead, I'm using a method that I know from Mike Edge's kits, which consists in having conventional round 1/8 bearings soldered into compensation beams. The axle is free to move up and down because the hole in the main frames is broached slightly larger than 1/8 - to allow, say 1/2 mm up and down travel. However, so far I have only made the beams for the leading two drivers. I could leave the rear drivers uncompensated (many beautiful models in old MRJs are built this way after all). But my priority is not to have any body rock, and one set of uncompensated drivers would make that almost inevitable.

Instead, I'd like to go a bit further in two directions. First, I'd like to rig up some kind of springing on the leading beam. In my imperfect understanding of these things, I could solder some guitar wire to, say, the leading bearing and then locate the other end of this in a piece of tube/a handrail knob/a CSB pivot somewhere at the front end of the main frames. Have any of you ever tried such a system - sort of "sprung compensation"? How critical would the distance between each end of the spring wire be?

The other thing I'd like to work on is somehow compensating the rear axle too. Some of Mike's kits (the Kiston long boiler, for example) have this system - a beam connecting the first two drivers and a separate beam pinned to a point in the chassis and allowed to swing around a knife edge compensating the rear ones. This beam would have to be very short as (as the photo below shows) there is not much spare main frame. Alternatively, there was an article in an old MRJ detailing the build of some MW locos and the builder suspended the beam for the rear axle on the middle axle (that is, there were two beams on the middle axle). Do any of you have any thoughts? I wonder if there is also a way of springing whatever system I adopt on the rear driver too.

Thanks in advance for your help!
David Addyman.


David,
I note that this kit carries on with the assumption that the the round windows of NER cabs had a bezel on the outside. They didn't. The only brass to be seen was the hinged opening widow itself behind the cab sheet. Yes I did put a bezel on my J24, but not anymore.
ArthurK

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Will L
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Re: First chassis in P4

Postby Will L » Fri Feb 28, 2020 12:09 am

Daddyman wrote:... Would you personally set up a chassis for CSBs which has no etched hornway marks, using only hand tools? I'd like to do it on the next loco - a Y7 (0-4-0) - but don't fancy my chances.

Yes I would and I'd use the Highlevel hornblocks to do it. Highlevel do this CSB Jig to help mark up the fixed fulcrum positions from the axle holes, it also lets you insert a pin in to the frames to ensure the first horn guide etch goes in the right place relative to the axle centres. As a bonus you can also use it to mark out the corners of the frame cutouts if you haven't already got them. The accuracy of these cut-outs isn't critical in getting the hornblocks in the right place and so they are well within the capability of hand tools.

Daddyman
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Re: First chassis in P4

Postby Daddyman » Fri Feb 28, 2020 6:41 am


David,
I note that this kit carries on with the assumption that the the round windows of NER cabs had a bezel on the outside. They didn't. The only brass to be seen was the hinged opening widow itself behind the cab sheet. Yes I did put a bezel on my J24, but not anymore.
ArthurK


Arthur - no, not at all. What I have represented here is the window frame, which on a North Eastern loco sits proud of the cab front when the window is closed. If you are suggesting that there should be no visible sign of the window frame, that it should be perfectly flush with the spectacle plate, then that is simply not the case. Plenty of photos, especially of dirty locos, show the frame proud when the window is closed - a picture of this loco (1787) on page 116 of Record 3 shows just exactly how proud. To represent round windows with no visible frame - as, say, your J72 appears to do here - https://www.rmweb.co.uk/community/index ... ts/page/8/ - is not correct (unless the windows are to be represented open). Your kit of the Q5 here has the frames proud, but perhaps the builder added them:
https://www.rmweb.co.uk/community/index ... s/page/10/


Dave - that's crystal clear, thanks. I could perhaps use a 1/8 bolt and a nut in place of the axle while setting up, to keep the block in place while soldering the guides?

Will and Armchair Modeller - thanks for these ideas. I have the HL jig in question but didn't realise I could use it to help cutting out hornways. I'll investigate more for the Y7 at Wakefield. For now, all four compensation beams are cut so there's no going back with the J79. I still have a mad desire to spring these beams...

davebradwell
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Re: First chassis in P4

Postby davebradwell » Fri Feb 28, 2020 8:29 am

No David, to get an accurate location for the hornguides as I suggested, you'd need an axle and close fits everywhere. It's using the frames instead of the coupling rods to set the horns. I'm assuming the axle hole is reasonably precise so why chuck it away and create false datums which won't be as accurate?

DaveB

Armchair Modeller

Re: First chassis in P4

Postby Armchair Modeller » Fri Feb 28, 2020 8:41 am

The High Level jig uses the axle hole as a guide. You only cut out the slots for the hornblocks after using the jig.

Daddyman
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Re: First chassis in P4

Postby Daddyman » Fri Feb 28, 2020 5:17 pm

davebradwell wrote:No David, to get an accurate location for the hornguides as I suggested, you'd need an axle and close fits everywhere. It's using the frames instead of the coupling rods to set the horns. I'm assuming the axle hole is reasonably precise so why chuck it away and create false datums which won't be as accurate?

DaveB

Then I don't understand Dave, sorry! In your original post you said "Why not use the holes to locate the axleboxes and hornguides? I expect the holes need bushing temporarily to locate the axle, thread the 'boxes onto the axle and hold against frames. Solder hornguides made from short pieces of angle inside the frames pushing them up against the axlebox whilst holding them upright with a square." My suggestion of using a nut and bolt in place of the axle was to help with the process I've put in bold in my quote from you. But that's not a good idea? Thanks for your patience!

Armchair Modeller wrote:The High Level jig uses the axle hole as a guide. You only cut out the slots for the hornblocks after using the jig.

I think I get this now! Thanks.

Armchair Modeller

Re: First chassis in P4

Postby Armchair Modeller » Fri Feb 28, 2020 6:24 pm

There is a tutorial for the High Level CSB Jig here

http://www.highlevelkits.co.uk/jigtutorial1.html

Daddyman
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Re: First chassis in P4

Postby Daddyman » Fri Feb 28, 2020 7:00 pm

Armchair Modeller wrote:There is a tutorial for the High Level CSB Jig here

http://www.highlevelkits.co.uk/jigtutorial1.html

Thanks!

davebradwell
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Re: First chassis in P4

Postby davebradwell » Fri Feb 28, 2020 9:43 pm

Just to be sure it's clear - the purpose of the axle is to align the hole in the axlebox accurately with the hole in the frames. This is only useful, of course, if the frame hole is in the correct place to start with.

If you use the High Level csb jig to cut a slot in the frames then you still have to use another jig to set the hornguides in the correct position from the coupling rods. You haven't mentioned matching frame and rod centres but you've built enough chassis to have this in hand.

It occurred to me that if this was a modern kit drawn on CAD with accurate photoplotted tooling then setting the hornguides from etched holes as I described would mean no setting of centres - the rods would match the axlebox centres very well and better than when coupling rod jigs are used. I suspect, however, that such recent kits have slots in the frames ready for hornguides so this short cut wouldn't apply.

DaveB

Armchair Modeller

Re: First chassis in P4

Postby Armchair Modeller » Fri Feb 28, 2020 11:03 pm

I get the impression that you don't quite understand how the High Level system works Dave ;)

Look at the tutorial mentioned above and all should become clear.

Daddyman
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Re: First chassis in P4

Postby Daddyman » Sat Feb 29, 2020 9:02 am

davebradwell wrote:Just to be sure it's clear - the purpose of the axle is to align the hole in the axlebox accurately with the hole in the frames. This is only useful, of course, if the frame hole is in the correct place to start with.

If you use the High Level csb jig to cut a slot in the frames then you still have to use another jig to set the hornguides in the correct position from the coupling rods. You haven't mentioned matching frame and rod centres but you've built enough chassis to have this in hand.

It occurred to me that if this was a modern kit drawn on CAD with accurate photoplotted tooling then setting the hornguides from etched holes as I described would mean no setting of centres - the rods would match the axlebox centres very well and better than when coupling rod jigs are used. I suspect, however, that such recent kits have slots in the frames ready for hornguides so this short cut wouldn't apply.

DaveB


Thanks again, Dave.
My next P4 chassis, the Y7, on which I'll use hornblocks instead of compensation beams, is from the same stable as the J79 chassis pictured at the top of the thread - Connoisseur. The kit is young enough to have been photo-etched, as evinced by the fact that it has been shot down from 0 gauge, but for some reason doesn't have half-etched lines for hornways (nor does the J79, as can be seen from the photo). The kits are pretty basic (the body of my J79 comprises 214 pieces, fewer than 35 of which came from the original kit!), and this may be why there is no provision for springing or compensation in either the 4mm kits or the 7mm.

So the problem is not setting centres: my Y7 has previously run perfectly well in 00.

Rather, my problem is in converting round axle holes into square hornblock holes. I'm absolutely clear that in your method the purpose of the axle is to hold the hornblock accurately with the hole in the frame. However, to me it seems like I will need three hands - one to hold the axlebox in place, one to position the angle iron which you use as the hornguide, and a third to solder; replacing the axle temporarily with a 1/8 bolt with a nut on it was my idea for obviating the need for one of these three hands (the hand holding the hornblock): as with the axle, the bolt would got through the frame hole (with bearing temporarily attached) and through the hornblock, aligning both. But the fact that I can see why it's better to use an axle and not a bolt which is an equally tight fit is possibly a result of me not quite been able to visualise what's involved.

One thing we haven't spoken about is whether I should perform the squaring of the round hole with the frames erected, or with them still in the flat.

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Will L
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Re: First chassis in P4

Postby Will L » Sat Feb 29, 2020 1:00 pm

Daddyman wrote:...One thing we haven't spoken about is whether I should perform the squaring of the round hole with the frames erected, or with them still in the flat.

If your going for the Highlevel style hornblocks, once you have prepared the frames by drilled out the CSB fulcrums (if that's what your doing), drilled out the corners of the frame opening and inserted the pin to ensure one hornblock is centred on the axle hole, then cut out the frame opening. Whether you fit the hornblock before you assemble the frames will depend in how you plan to jig the axles. If you use a full chassis jig then you do it before, if you use single axle jigs, after. In both cases your aligning the hornblock using the rod centres as disused by DaveB above.

Daddyman
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Re: First chassis in P4

Postby Daddyman » Sun Mar 01, 2020 7:31 am

Thanks, Will. That's clear.


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