Frame Spacing

Wyorin
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Frame Spacing

Postby Wyorin » Tue Nov 03, 2020 6:58 pm

I have been asked the following question and I have been trawling the site to find an answer without luck:

"Are you able to go onto the S4 members web site and pull off the specifications for building locomotive frames? The specific measurement I’m after is the width across the outside of S4 frames. I can then double check the width of the spacers needed for S4 frames."

Can some knowledgeable person provide an answer please?

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grovenor-2685
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Re: Frame Spacing

Postby grovenor-2685 » Tue Nov 03, 2020 8:58 pm

In the beginning, which you will find in the P4 Manual and issues of Prototype See history section of this website) there were two recommended widths depending on side play wanted and I think the spacers were 15 mm and 15.5 mm with 0.5 mm thick frames. Since then kit designers have done their thing with quite variable results.
Best is to start with the wheelset needed for the model which will give you the space available between wheelbosses, then work out from the minimum radius requirement how much sideplay you need. Then look at your preferred axlebox design and see if any space is needed outside the frame, eg if using Comet or Brassmasters boxes. Yhis should allow you to arrive at a suitable width over frames.
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Keith
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Will L
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Re: Frame Spacing

Postby Will L » Tue Nov 03, 2020 9:11 pm

Wyorin wrote:I have been asked the following question and I have been trawling the site to find an answer without luck:

"Are you able to go onto the S4 members web site and pull off the specifications for building locomotive frames? The specific measurement I’m after is the width across the outside of S4 frames. I can then double check the width of the spacers needed for S4 frames."

Can some knowledgeable person provide an answer please?


Try Scalefour Digest 41.9 in there somewhere it does give a maximum dimension (16.5mm). Click to follow the link. This gives very little side play so most of us use a lesser dimension. Real S4 modellers as opposed to us ordinary P4 people, may go as far as scaling the actual frame dimension, which varies from loco to loco. So perhaps a fixed dimension isn't really appropriate. I tend to go with 15.5mm as this allows for 1mm side to side on one axle at least which gets me round 3'6" corners.

martin goodall
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Re: Frame Spacing

Postby martin goodall » Tue Nov 03, 2020 10:54 pm

Keith's reference to the wheel boss is important. Ultrascale driving wheels (unlike some others) have a substantial boss at the back of the wheel.

On one occasion, when retro-fitting Ultrascale wheels to existing frames which had previously been fitted with different wheels, I had to pare off the bosses of the Ultrascale wheels, in order to avoid having to rebuild the frames. It did not affect their trueness on the axles or their running qualities.
Last edited by martin goodall on Wed Nov 04, 2020 7:21 pm, edited 1 time in total.

davebradwell
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Re: Frame Spacing

Postby davebradwell » Wed Nov 04, 2020 8:03 am

I believe a large gap between wheel and frame looks ugly and toy-like so have always considered the boss on the back of a wheel to be adjustable and irrelevent to frame width. It's easily filed. Have been using 16.2 over for years with axlebox flanges outside this. Most wheels need washers and everything goes round 1 metre curves - you need very little sideplay even at this radius because there is already clearance in the track, more so when the gauge is widened.

DaveB

Julian Roberts
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Re: Frame Spacing

Postby Julian Roberts » Thu Nov 05, 2020 9:19 am

Just to add my two pennyworth - I'm sure DaveB that we can all take your word for that, except my first P4 loco was an 0-4-4, where the bogie did not have any sideplay, but was pivoted. So this effectively gave a much longer wheelbase than any likely loco fixed wheelbase. I'd used the spacers supplied, and there was not enough sideplay on the inner driving wheel except by moving the pivot of the bogie.

Since then I always work out the sideplay required, but Dave's post makes me think I'm being too far on the safe side, as I don't make an allowance for the slop in P4, nor gauge widening. I'd rather have slightly narrow frames than have to rebuild it from scratch though!

Filing down the inside wheelboss is mentioned several times here. If the length of boss as manufactured is unnecessary in order for the wheel to run true, without wobble, I wonder why they are made like that?
Last edited by Julian Roberts on Thu Nov 05, 2020 11:32 am, edited 1 time in total.

Philip Hall
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Re: Frame Spacing

Postby Philip Hall » Thu Nov 05, 2020 9:33 am

Julian Roberts wrote:Filing down the wheelboss is mentioned several times here. If it is unnecessary for the wheel to run true, without wobble, I wonder why they are made like that?


I don’t understand this comment. A wheel MUST run true without wobble, or as near to that ideal as can be achieved. The boss on a wheel does help this, because the longer the hole in the wheel is, and if it’s a rigid wheel, it will help to prevent wobble. The point I think Martin was making is that on an Ultrascale wheel, which is very rigid, carefully reducing the boss a small amount should not affect its truth.

Whilst I agree generally that big gaps behind wheels don’t look too good, I take the approach that the model has to work and if that means the gap has to be a bit bigger, then so be it.

Philip

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Re: Frame Spacing

Postby Julian Roberts » Thu Nov 05, 2020 11:33 am

HI Philip, I've edited my previous post wording as I think it must have been ambiguous?

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David Thorpe
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Re: Frame Spacing

Postby David Thorpe » Thu Nov 05, 2020 12:20 pm

Julian Roberts wrote:Just to add my two pennyworth - I'm sure DaveB that we can all take your word for that, except my first P4 loco was an 0-4-4, where the bogie did not have any sideplay, but was pivoted. So this effectively gave a much longer wheelbase than any likely loco fixed wheelbase. I'd used the spacers supplied, and there was not enough sideplay on the inner driving wheel except by moving the pivot of the bogie.


I'm finding exactly the same with the 0-4-4T I'm currently working on.

DT

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Re: Frame Spacing

Postby Julian Roberts » Thu Nov 05, 2020 2:55 pm

Hi David - My kit was the DJH Class 439. I used Gibson frames with (in my innocence) his P4 spacers. Fortunately the chassis screwed to the body between the inner driving wheel and the bogie, so it was easy to design an arm for the bogie to pivot around that screw, with a roller where the body rests on the bogie, so the bogie has kind-of prototypical sideplay. No more problem on the curve. Here is the view from below. You can see it swings rather than pivots now. Also here is Russ' versine calculation in case it's useful for anyone.

VERSINE.gif
VERSINE.gif (1.63 KiB) Viewed 1476 times
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IMG_0293.JPG
Can't find an in focus pic!

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David Thorpe
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Re: Frame Spacing

Postby David Thorpe » Thu Nov 05, 2020 3:32 pm

Thanks, Julian - mine too is a DJH 439 with Gibson frames, and spacers that seem to be somewhere between P4 and EM in width - I don't know where they came from. Initially I made a pivot for the bogie where I assume the prototype had it, ie directly above the centre of the bogie. As you indicated, that arrangement wouldn't go round even fairly gentle curves, so now I'm following a procedure very similar to yours and that is popular in RTR (I can understand why). This kit has not been one that's given me any great deal of pleasure as I've had considerable difficulty carving and grinding away enough white metal to accommodate the chassis and wheels, I've had an intermittent short that I think I've now cured, and the bogie fiasco was almost (but not quite) the last straw. Unfortunately I'm now fixated on getting it to run properly!

David

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Re: Frame Spacing

Postby Julian Roberts » Thu Nov 05, 2020 3:51 pm

Aha David! Now I remember why sideplay was not very desirable! Actually I'm quite happy with the arrangement for the bogie - I think unlike the RTR style the back of the loco rests firmly on the bogie. It runs very well and I recently improved it with the motor to gearbox shaft changed from single UJ to double. High Level 1 to 108 gearing of course for quality slow controllable running on DC analogue....now I dive for cover from DaveB's critical brickbat!
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Last edited by Julian Roberts on Thu Nov 05, 2020 4:05 pm, edited 1 time in total.

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Will L
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Re: Frame Spacing

Postby Will L » Thu Nov 05, 2020 4:02 pm

Julian Roberts wrote:Since then I always work out the sideplay required, but Dave's post makes me think I'm being too far on the safe side, as I don't make an allowance for the slop in P4, nor gauge widening. I'd rather have slightly narrow frames than have to rebuild it from scratch though!


While I'm sure Dave is right that the allowances you suggested and which often quoted by people like me are probably a bit more generous than necessary. When Dave aims at a 0.8mm clearance I suspect he hits the target more reliably than I would. After all he is a real engineer, while what I did for a living may be credited with the word engineering in the title these days (systems engineering) and is even taught on the same degree course as my son discovered, the skill sets are rather different.

Understanding the interrelationship between, P4 clearance, gauge widening and axle slop and the impact it had on our ability to get round corners was (should have been) the upshot of the conversation we had on gauge widening (viewtopic.php?f=96&t=5030&start=75 - if any body who's interested and doesn't rememberer back to 2017. This thread contains a spread sheet that does most of the maths. After the first page and a bit the thread wonders off into more esoteric concerns)

I have 4-4-0s with both a fixed bogie pivot and side play on the leading driving axle, and a side play on the pivot and nothing on the leading axle. Both work. My current thinking would be to go for the fixed pivot if I can get sufficient side play on the diving axle. This isn't prototypical but then quite a lot of what we do to make our chassis work isn't.

davebradwell
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Re: Frame Spacing

Postby davebradwell » Thu Nov 05, 2020 4:06 pm

My current project has Gibson 6ft - 2in wheels. Front and rear needed a 0.3 washer each side and centre did without to give some sideplay, although this is rather excessive and I hope won't give trouble shorting on the rather complicated brakes. No wheels were harmed in the making of this model which has my standard 16.2 frame width plus a 0.25 axlebox flange each side. I think this was first calculated for Ultrascale wheels which I've also used without modification. It's even possible to put overlays outside such frames as long as they avoid the axlebox flanges. I suspect Gibson rear bosses vary across the range as I know I've reduced some of them.

I'm fortunate that the prototypes I've copied have all had a nice arch for carrying wheels to pass through. N2 is an exception but here I copied the dished frame that gave clearance on the real thing. For a while I've been looking at a Thompson O1 which doesn't have a nice frame cut-out so that will require a proper solution. Don't see why one wheelset should dictate the width of the whole frame but you have to work these issues out before you start. Shouldn't bogies just have a central pivot with slide? This makes it easier to limit travel when there's no frame cut-outs as seems to be the case with the 439.

DaveB

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Re: Frame Spacing

Postby Julian Roberts » Thu Nov 05, 2020 4:29 pm

With a whitemetal kit basically designed for 00, fixed outer wheels are very useful for avoiding splashers!

Yes Will actually my unfortunate first Forum foray into controversy started nearly 5 years ago! viewtopic.php?t=4732
Now I'm building a layout of Kyle of Lochalsh shed to prove the ideas I learned there and in the threads you linked (or disprove.. ..!)

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Re: Frame Spacing

Postby davebradwell » Thu Nov 05, 2020 5:02 pm

A thought, WillL. With 4-4-0 or 0-4-4 and fixed pivot on bogie might it be better to have a little sideplay on both coupled axles so they traverse in opposite directions on a curve so sharing the required offset between them? Certainly allowing play on the axle furthest from the bogie will reduce the side movement of the bogie wheels as it shorten the effective rigid wheelbase. I suspect, however, that it will be difficult to get away with no side movement on the bogie slide. It depends on what you define as a "little sideplay" - say 0.2mm per side. It all has to be ground out of the body, too.

DaveB

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Re: Frame Spacing

Postby davebradwell » Thu Nov 05, 2020 5:11 pm

Sorry, Julian, I missed your motor photo. Indeed the drive shaft is a very sound arrangement and it could never work with a single u/j although there are ways it can be done with the right kind of coupling. Can't see the gearbox restraint so will always be suspicious. Is it on a rubber pad to reduce noise, especially with your mega reduction?

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Re: Frame Spacing

Postby Julian Roberts » Fri Nov 06, 2020 3:12 pm

Well it was 2007 I made this Dave, but looking at it I can see bits of rubber including in the smokebox, I recall all sorts of travails - I hadn't realised then that the articulation of this gearbox needs to be soldered into its orientation so as not to fold up on itself. Anyway here is a scruffy video to prove that it goes, maybe rather too noisily for general taste, but it needs re-running in still.


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Re: Frame Spacing

Postby davebradwell » Fri Nov 06, 2020 4:02 pm

It's possible, Julian, that some of the noise may be related to how you contain the endthrust of the worm which isn't visible in the gearbox photo. The bearings supporting the worm shaft should have their flanges towards the worm to give the greatest area and then pack between worm and bearing face with washers/spacers leaving just a few thou' endfloat. Spacers should clear worm wheel but give good contact area to bearing face. Bearings can be moved in frame to suit spacers.

It's also possible that the troubling growl is down to over-restraint of the gearbox, unless your controller is a 100Hz pulsed type.

You should shout very loudly about soldering the trailing arm on the gearbox as there's still some doubters around.

DaveB

Julian Roberts
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Re: Frame Spacing

Postby Julian Roberts » Sat Nov 07, 2020 9:31 am

HI Dave - sorry, been struggling with stretcher bars.

20201107_082234.jpg

20201107_082208.jpg




Here is a photo of the gearbox which I made following the High Level instructions. There is about 1mm end float with a washer each side of the worm. The loco body restrains the gearbox but I came up with this after a lot of experiment. The main point is that I'm happy with the way the loco goes, see below slow speed, and don't think it's worth spending more time on it. I certainly don't want to disassemble the gearbox. Another point is that it goes better now with double UJ, faster top speed which I take to mean the mechanism is more free - though I changed the motor at the same time as the previous one didn't work any more, which in itself indicates the previous arrangement was unsatisfactory. However the metal UJ is noisier than the previous plastic.

Also a video of what happens to the gearbox in each direction, unrestrained by the smokebox.

However I'm really grateful for your advice to bear in mind next time, and the very high standards you're taking us toward.

:idea: Yes the swing arm is fixed rigidly to the bogie. (To my mind this means the bogie steers the loco, just as it would when set up as you suggest. If the arm wasn't fixed, the bogie would just flop around)

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David Thorpe
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Re: Frame Spacing

Postby David Thorpe » Sat Nov 07, 2020 11:00 am

Julian Roberts wrote:The main point is that I'm happy with the way the loco goes, see below slow speed, and don't think it's worth spending more time on it. I certainly don't want to disassemble the gearbox.


:) Quite. My mantra is that once something's running well, leave it alone! Efforts in the past to "improve" something that's already fine have all too often led to things becoming worse rather than better.

DT

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Will L
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Re: Frame Spacing

Postby Will L » Sat Nov 07, 2020 11:51 am

Julian Roberts wrote:Here is a photo of the gearbox which I made following the High Level instructions. There is about 1mm end float with a washer each side of the worm. The loco body restrains the gearbox but I came up with this after a lot of experiment. The main point is that I'm happy with the way the loco goes, see below slow speed, and don't think it's worth spending more time on it. I certainly don't want to disassemble the gearbox. Another point is that it goes better now with double UJ, faster top speed which I take to mean the mechanism is more free - though I changed the motor at the same time as the previous one didn't work any more, which in itself indicates the previous arrangement was unsatisfactory. However the metal UJ is noisier than the previous plastic.

Also a video of what happens to the gearbox in each direction, unrestrained by the smokebox.


David Thorpe wrote:
Julian Roberts wrote:The main point is that I'm happy with the way the loco goes, see below slow speed, and don't think it's worth spending more time on it. I certainly don't want to disassemble the gearbox.


:) Quite. My mantra is that once something's running well, leave it alone! Efforts in the past to "improve" something that's already fine have all too often led to things becoming worse rather than better.

While a keen supporter of the "if it aint broke..." philosophy and yes the loco does seem to run well enough, I would still be worried about the way the UJs are being forced out of line. That must be causing additional internal resistance and long term wear? Also it may be the source of much of the noise.

I presume there must be suspension on that front axle, otherwise why the UJs at all? If so a DaveB style torque ration link looped over the top of the lead UJ/gearbox would solve the problem and looks easy enough to add without doing anything significant to the gearbox.

Julian Roberts
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Re: Frame Spacing

Postby Julian Roberts » Sat Nov 07, 2020 4:48 pm

Hi Will - I put that gearbox video there to show how the gearbox isn't soldered up as I would now, but the point is that the loco body gives all the restraint needed so it doesn't move like that when the body is fixed on. Of course I can't then see what is going on, but it's done 13 years of good service at exhibitions so I've got worse problems to deal with! Fairly sure the gearbox has minimal but adequate movement once body is on. It has a UJ because the motor has to be remote from the gearbox to fit. The front wheel is fixed. Now I would put the motor in the bunker, maybe drive the inner wheel, and fill the boiler with lead to increase haulage power, but still might retain fixed front wheel in this DJH kit for clearance reasons as mentioned above.

Happy to receive pointers to improvement. This model seems to have hijacked the thread, apologies to OP author!

davebradwell
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Re: Frame Spacing

Postby davebradwell » Sun Nov 08, 2020 9:06 am

You might slot out the hole in a couple of 2mm washers so they can be clipped onto the worm shaft to reduce the end-float without any risk to the running, Julian. Top tab is my favourite method of restraint but that will probably interfere with your ballast weight. As you say, if axle can rise, fall and rock and gearbox can't flop too much then it's probably not too bad. Check axle can rock - that's the usual trap and can lead to derailments.

DaveB

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johndarch
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Re: Frame Spacing

Postby johndarch » Mon Nov 09, 2020 6:47 pm

Back to the original topic. Malcolm Mitchell used 14mm spacers while Martin Finney used 15mm which give a more prototypical appearance. I am about to start building a Mitchell 4575 tank loco and am seriously considering adding 0.5mm styrene overlays between the frames and the etched overlays.


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