Another newcomer's question re wagon suspension

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davebradwell
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Re: Another newcomer's question re wagon suspension

Postby davebradwell » Fri Jan 31, 2020 11:49 am

If we're going to have drawings, can I suggest that they should meet reasonable professional standards as none of those I've seen do so and I would certainly not have passed them for prototype manufacture, let alone signed them off. We've kept them secret, too. Tolerances, dimensioning of cones, treatment of non-functional features, plain errors, lack of change procedure, they're all there. 2mm and EM society drgs don't define the flange shape at all.

I've never seen the 24mm axleguard spacing as a standard before this thread although accept it is v close to scale - I can't find it in the Digest Sheets, although admit that doesn't mean it isn't there. I've tended to use 23.5 as this suits plain brgs like Exactoscale made to the society drg........and I'm not going to argue about a few thous' tolerance on something 0.3 thick that waves about in the breeze. It seems our leading manufacturers have, in the main, produced better parts than we have drgs, although we are still living with the ambiguities and secrecy - they were never in the Digest Sheets. At least 2mm have gone public although the EM people are being rather slow.

Your Protofour Maanual is interesting, Keith, but without a reference from our Digest Sheets must remain a curiosity. In any case it gives the CSU dimension as 24 over outside faces - another dimension to a non-functional face but similar to the dimension I arrived at. It's difficult to say as material thickness isn't given. Disastrously the document doesn't carry a date or issue.

This thread also shows, I suspect, that using a vernier calliper to achieve a degree of accuracy takes some practice.

DaveB

jasp
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Re: Another newcomer's question re wagon suspension

Postby jasp » Fri Jan 31, 2020 4:26 pm

I do agree with Dave B that the use of a vernier calliper requires some practice but I imagine a large number of people use digital callipers, many of which are inherently inaccurate, often with non-reproducible measurements - could this, perhaps help explain the discrepancies
I have relegated my digital set to woodworking and returned to my Mitutoyo non-digital one for model making. It doesn’t require battery replacement either.
Jim P

DaveHarris
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Re: Another newcomer's question re wagon suspension

Postby DaveHarris » Fri Jan 31, 2020 8:52 pm

Thanks for the replies and explanations guys.
I have had my local engineering workshop check my electronic calipers, and they were reading wrongly at times!
I took a selection of axles and wirons with me and most axles were reading 25.7 to 25.97, but a very small number read under 25mm.
My stock was bought years ago and from different sources. I know not which came from where.
The vast majority of the Scalefour wirons internal b2b come out at 23.65 to24.03
The BB wirons come out at 24.15 to 24.27mm internal dim.

Having read and reread the above comments/explanations and armed myself with various thickness washers I will try and get close to Tim's original specs

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Tim V
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Re: Another newcomer's question re wagon suspension

Postby Tim V » Fri Jan 31, 2020 9:25 pm

I'm with Jim on this, get a non digital calliper, I've had mine 30 years and no batteries need replacing!
Tim V
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Daddyman
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Re: Another newcomer's question re wagon suspension

Postby Daddyman » Mon Feb 03, 2020 4:38 pm

Any advice on a good non-digital Vernier? Mitutoyo, presumably, but there doesn't seem to be much to choose between the models between £30 and £50. Perhaps the £100 model with the fine adjust is a good bet?
Thanks,
David.

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grovenor-2685
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Re: Another newcomer's question re wagon suspension

Postby grovenor-2685 » Mon Feb 03, 2020 5:16 pm

For 99% of what we do the cheap plastic ones are fine, very rare that I get out my micrometer and my Mitutoyo languishes in the cupboard. The the digital caliper I got was a mistake long consigned to the rubbish.
Regards
Keith
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John Palmer
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Re: Another newcomer's question re wagon suspension

Postby John Palmer » Mon Feb 03, 2020 5:21 pm

I've been entirely satisfied with my 'High Accuracy Vernier Caliper 0-150mm / 0-6", Thumb grip (Sku 531-128)' which I bought direct from Mitutoyo in 2016 for just under £50. Although I find myself using a micrometer for most measurement of workpieces on my Unimat, the Mitutoyo caliper has seen plenty of recent use measuring existing models and etch frets in connection with the preparation of CAD drawings, and I had little difficulty acclimatising myself to reading it. Determining which division on the vernier scale best aligns with a division the main rule is straightforward, and frequently the most difficult part of the measuring operation is getting the caliper arms accurately located on the piece to be measured - particularly if it's still attached to a fret.

Daddyman
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Re: Another newcomer's question re wagon suspension

Postby Daddyman » Mon Feb 03, 2020 6:50 pm

grovenor-2685 wrote:For 99% of what we do the cheap plastic ones are fine, very rare that I get out my micrometer and my Mitutoyo languishes in the cupboard. The the digital caliper I got was a mistake long consigned to the rubbish.

Thanks. What does a cheap plastic one mean? I've only ever seen cheap plastic digital ones, but from your last line that's clearly not what you're referring to.

John Palmer wrote:I've been entirely satisfied with my 'High Accuracy Vernier Caliper 0-150mm / 0-6", Thumb grip (Sku 531-128)' which I bought direct from Mitutoyo in 2016 for just under £50. Although I find myself using a micrometer for most measurement of workpieces on my Unimat, the Mitutoyo caliper has seen plenty of recent use measuring existing models and etch frets in connection with the preparation of CAD drawings, and I had little difficulty acclimatising myself to reading it. Determining which division on the vernier scale best aligns with a division the main rule is straightforward, and frequently the most difficult part of the measuring operation is getting the caliper arms accurately located on the piece to be measured - particularly if it's still attached to a fret.


Helpful, thank you. They're up to about £80 now (or £145 on Amazon!).

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grovenor-2685
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Re: Another newcomer's question re wagon suspension

Postby grovenor-2685 » Mon Feb 03, 2020 7:04 pm

Looks like this, scanner does not focus well as its not flat to the bed. Given me good service for years.
Caliper-Scan.jpg


Closest I can see on ebay currently
Mule caliper
Or you could try second hand
use mitutoyo
Regards
Keith
Grovenor Sidings

Daddyman
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Re: Another newcomer's question re wagon suspension

Postby Daddyman » Mon Feb 03, 2020 8:04 pm

grovenor-2685 wrote:Looks like this, scanner does not focus well as its not flat to the bed. Given me good service for years.
Caliper-Scan.jpg

Closest I can see on ebay currently
Mule caliper
Or you could try second hand
use mitutoyo

Brilliant, thanks!

jasp
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Re: Another newcomer's question re wagon suspension

Postby jasp » Mon Feb 03, 2020 8:09 pm

David
I have a second (mechanical) calliper which I bought from Screwfix - Magnusson @ £12.99 - a reasonable piece of kit for the price.
Jim P

Daddyman
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Re: Another newcomer's question re wagon suspension

Postby Daddyman » Tue Feb 04, 2020 6:38 am

Thank, Jim P. At that price I can go for one of those and add to the Mitutoyo I've just bought on ebay (thanks Keith). I'm afraid I went against the consensus on here and got a digital one, but I'm hoping that a unit with a retail price of £136 (£25 on ebay) will be better than the £15 cheapo digital ones; if it isn't, it doesn't matter too much as £25 is not a massive investment. Having said that, I'm curious what the objections are to the digital ones - just the batteries or something more? Do you all object even to quality digital ones?
Thanks, David.

davebradwell
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Re: Another newcomer's question re wagon suspension

Postby davebradwell » Tue Feb 04, 2020 9:49 am

Surely measuring equipment should give a meaningful result. There would seem to be 2 types of engineering equipment - those that specify accuracy and those that use loose words like "precision", etc. I note from the Mitutoyo website that they now make a lower grade of vernier, only accurate to +/- 0.05mm and presumably aimed at cabinet and assorted model makers. At this accuracy you could well be a drill size out if making a hole for that piece of wire you just picked up. It might be 0.45 or possibly 0.5 so I would suggest a better grade is called for, even in routine work. It can only be assumed that the undefined verniers are less accurate than this - I'm sure they are useful but wouldn't let them near my track, wheels or chassis. Don't be fooled by the impressive string of numbers on the digital types - this doesn't indicate accuracy. A good vernier should be accurate to +/- thou' (0.025mm) and the spec. should say so. It is the ideal piece of measuring equipment for our applications. An investment.

DaveB

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Guy Rixon
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Re: Another newcomer's question re wagon suspension

Postby Guy Rixon » Tue Feb 04, 2020 10:04 am

Tim V wrote:I don't "recommend" these dimensions, they are the dimensions that items should accord with. Unfortunately, I have checked the S4 Digest (and the EMGS manual!) but these fundamental dimensions are not specified. No wonder more than one manufacturer got it wrong.

Of interest, the 2mm Scale Association actually do set out the specifications (attached). It occurs to me that this kind of information is sorely lacking in 4mm, perhaps someone needs to sit down and draw it out.
2mm standards.jpg


The distance between axleguards in 2FS is critical as the bearing cones are very shallow, much less than half the 4mm-scale equivalent.

Yes, this part of the design should certainly become an explicit part of the P4 standard ... but do we know what tolerances to put on the parts? What's the acceptable range for end-float in a pin-point bearing?

Regarding the axleguards "waving in the breeze" as per Dave Bradwell's post above, the original Studiolith axleguards were pressed from steel. I expect they were a bit stiffer.

billbedford
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Re: Another newcomer's question re wagon suspension

Postby billbedford » Tue Feb 04, 2020 11:26 am

Guy Rixon wrote:Yes, this part of the design should certainly become an explicit part of the P4 standard ... but do we know what tolerances to put on the parts? What's the acceptable range for end-float in a pin-point bearing?


Yes maybe, but it's a bit of an indeterminate quantity as it depends on a/ the w-iron being perfectly square and b/ the model is no weighted so much that the w-irons splay out.
Bill Bedford
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davebradwell
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Re: Another newcomer's question re wagon suspension

Postby davebradwell » Tue Feb 04, 2020 11:41 am

The true reason for my breeze reference was that on a previous occasion I had been shot down for losing the odd thou' in tolerances so was noting the difficulty of making an accurate measurement to something bendy in order not to have my main point lost.

Yes, axleguards would have been stiffer in steel but you'd better check thickness as stiffness goes with its cube.

We seem to have discovered, however, that we started at around 23.5 between with the plain, flanged pin-point brg. Somebody then thought they would "improve" matters by widening the axleguards to 24 between and drawing the waisted brg with a shallower cone. The result has been disastrous for new starters - is anyone going to own up? I still use 23.5 as it results in the width over solebars coming out nearer to scale with steel underframes. If 24 is declared correct then we're going to need washers and get distorted wagons, especially hoppers and Parkside conversions using the plastic axleguard.

I still maintain that the critical dimension on the brg drgs (including the 2mm) should be between the back of the flange (the side that touches the axleguard) and the bottom of the cone. This would comply with the standard on engineering drgs - BS308 in my day, when such documents could be purchased for just a few £s. There's also the issue of dimensioning cones, but that has no place here.

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Tim V
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Re: Another newcomer's question re wagon suspension

Postby Tim V » Tue Feb 04, 2020 3:44 pm

For information, the RCH diagram for a metal underframe shows the same dimension as the wooden underframe.
RCH metal.jpg
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Daddyman
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Re: Another newcomer's question re wagon suspension

Postby Daddyman » Tue Feb 04, 2020 5:36 pm

davebradwell wrote:Surely measuring equipment should give a meaningful result. There would seem to be 2 types of engineering equipment - those that specify accuracy and those that use loose words like "precision", etc. I note from the Mitutoyo website that they now make a lower grade of vernier, only accurate to +/- 0.05mm and presumably aimed at cabinet and assorted model makers. At this accuracy you could well be a drill size out if making a hole for that piece of wire you just picked up. It might be 0.45 or possibly 0.5 so I would suggest a better grade is called for, even in routine work. It can only be assumed that the undefined verniers are less accurate than this - I'm sure they are useful but wouldn't let them near my track, wheels or chassis. Don't be fooled by the impressive string of numbers on the digital types - this doesn't indicate accuracy. A good vernier should be accurate to +/- thou' (0.025mm) and the spec. should say so. It is the ideal piece of measuring equipment for our applications. An investment.

DaveB

Thanks, Dave. The Mitutoyo I have bought is accurate to 20um, whatever that means (it's not "um", but I'm sure you know the symbol!).

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Noel
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Re: Another newcomer's question re wagon suspension

Postby Noel » Tue Feb 04, 2020 5:39 pm

Except that the distance between the inside faces of the solebars is slightly greater and the axleguards are joggled to bring them inwards. Not likely to be a practical issue though.
Regards
Noel

davebradwell
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Re: Another newcomer's question re wagon suspension

Postby davebradwell » Tue Feb 04, 2020 8:04 pm

I don't question the scale dimension for axleguards, just the possibility of keeping to it when the back of a solebar channel or plastic axleguard is thicker than scale. I'm not going to defend it to the last man as I sometimes end up with 24 axleguard spacing on a brass wagon, in which case I design a modified spring carrier to avoid the need for a loose washer. I just work from the outside in as the most visible bits are out there. We have to make little adjustments here and there - splashers on locos and frame width so moving an axleguard 10 thou' doesn't seem a big deal. It's just odd that there was a standard and now we're trying to have a different one.

Anyway, what about coach bogies - I just happen to have an LMS bogie drawing in front of me and it shows 5ft 9in between axleguards. I think the LNER 8w tender is less, despite the 6w coming in at 6ft 1 1/2in. It's easier to pack out from a narrow starting point than go narrower.

.....and Mr Daddyman, your vernier sounds just the thing, a tool you can rely on - I hope its batteries will live long and prosper.

DaveB

billbedford
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Re: Another newcomer's question re wagon suspension

Postby billbedford » Wed Feb 05, 2020 12:44 am

And the elephant in the room is:

A 26mm axle can't be fitted into blind holes in a 24mm wide shallow channel without distorting the legs of the channel*.

Note that in all other applications of pinpoint bearings at least one of the bearings is adjustable, usually on a screw thread.

* the limit for thin metal, eg brass, is about 3 degrees if it is bent more than that the metal takes on a permanent set.
Bill Bedford
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Guy Rixon
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Re: Another newcomer's question re wagon suspension

Postby Guy Rixon » Wed Feb 05, 2020 9:05 am

billbedford wrote:And the elephant in the room is:

A 26mm axle can't be fitted into blind holes in a 24mm wide shallow channel without distorting the legs of the channel*.

Note that in all other applications of pinpoint bearings at least one of the bearings is adjustable, usually on a screw thread.

* the limit for thin metal, eg brass, is about 3 degrees if it is bent more than that the metal takes on a permanent set.


Hence the much shallower cones in the 2FS bearings and their axle length of 12.25mm. 24.5mm or 25mm would have been better choices for 4mm scale.

This is a particular problem for bogies, where the axleguards are not so tall. I've taken to separating the sides of my bogie etches and fixing them to a brass slab with machine screws so that the axleguards can be tilted to admit the wheels.

davebradwell
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Re: Another newcomer's question re wagon suspension

Postby davebradwell » Thu Feb 06, 2020 9:29 am

Trouble is the steeper cone angle would give a greater outward force on the axleguards and our 60 deg cone only just works here. The 2mm scale axleguard works out stiffer than ours. Of course the extra space with a shorter axle would be welcome but the cone is already about to disappear into the wheel which is, in any case, thicker than a scale wagon or coach wheel. I take your point Bill that we are wrecking any pretences at precision just getting the wheels in.

The careful modeller might slot his axleguards or bogies out at the bottom so that wheels can be dropped in to be retained correctly by the keep hinged at the side. No, I don't do it either.

DaveB

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Guy Rixon
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Re: Another newcomer's question re wagon suspension

Postby Guy Rixon » Thu Feb 06, 2020 12:41 pm

Consider an 2mm-diameter axle with the ends turned down to 1mm-diameter stubs, starting just clear of the wheel seat. Now cut those stubs into 55-degree pinpoints. This should allow shorter axles in shallower cones of 60-degree opening.

davebradwell
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Re: Another newcomer's question re wagon suspension

Postby davebradwell » Thu Feb 06, 2020 7:51 pm

That would be a fine thing - a sort of shortened Exactoscale axle. The shallower cones would maintain whatever we think is the standard axleguard width and it tackles Bill's point and reduces distortion of the model just to get the wheels in. There would have to be a trendy name for the bits to avoid even more confusion but it leaves me wondering if a parallel brg wouldn't be easier in the long run with the difficulties in defining, manufacturing and inspecting cones with blunt ends.

DaveB


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