What back to back setting do you use?

Model and prototype rolling stock, locos, multiple units etc.
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Jol Wilkinson
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Re: What back to back setting do you use?

Postby Jol Wilkinson » Sun Jan 07, 2018 11:19 am

Julian,

I don't know the answer to your problem.

What I do know is this, which may not be of much help. I have built my models and trackwork using the gauges I referred to previously. It almost always worked first time and I never found the need to measure the results I was getting. If it didn't work, then something had gone wrong during the assembly process and rechecking the B2B usually showed an error which was corrected. The only time that was not possible was with Loctite secured wheels, usually Exactoscale C&W but increasingly with plastic centered steam loco wheels following Tom Mallard'd approach when he used Sharman wheels in two LSWR Black Motors (MRJ 165 and 167). The Exactoscale wheels are assembled using the Exactoscale B2B gauge/jig with light pressure to hold them in place until the Loctite sets. The loco wheels are assembled off the frames where possible, using a GW wheel press, set to provide a fit on my BSB gauges.

On London Road we run stock from several builders regularly plus the occasional visitor. They have all been built using the "standard" B2B gauges available from the usual culprits over the years. The usual (and thankfully fairly uncommon) problem we get tends to centre around C&W wheels where the B2B has altered. This usually affects plastic centre push on wheels. The L&WMRC team that operate Clarendon wrote some time ago that they found it necessary before a show to check the B2B of the stock and adjust as required to ensure satisfactory running.

"So I push the wheels a little more while twisting them. Now there' s no sideplay at all but they can still revolve freely - perfect. The maximum BB is down to around 17.75, the minimum is about 17.55. Yuk. Is that the best I can do? But with a cup of tea things seem to improve - is it me or is the wheel itself settling? Am I measuring it more accurately now or has it really changed? Who knows?"

That sounds as though the plastic centre is distorting slightly and then returning to its normal position. In twisting them the centre may have temporarily become distorted. When Mike Sharman was still producing and selling Sharman wheels he would demonstrate how it was possibly to "tweak" loco wheels to remove any eccentricity,- something I haven't been able to emulate with the more recently produced versions, but that may be due to a different plastic used.

So our experiences differ. I and many of my friends and acquaintances have built P4 models using commercially supplied tools and products and without going into metrology to assess their results, have managed to produce models that work.

To end on an interesting note, a distant (geographically) friend who had always modelled in OO but recently built several locos that run on "London Road", has just announced he has built a loco with Markits wheels and Markits P4 axles, that runs perfectly on a S4 (not P4) layout at another friends home nearby. I have seen neither the loco or the layout, but I do wonder if his news means that we can all look forward to a more relaxed future.

Jol

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Will L
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Re: What back to back setting do you use?

Postby Will L » Sun Jan 07, 2018 1:14 pm

Julian

Reading your most recent post a few thoughts pass through the mind.
1. A vernier caliper really, really isn't a good way to routinely measure back to back, because the sources of potential error are so great.
2. The right tool for routinely measuring a fixed dimension is a fixed gauge designed for the job. In this case a B2B gauge.
3. The round varieties, the GW adjustable and the Exactoscale block are very good for assembly but to check your stock the L shaped tool is the one for the job, mostly because getting the other ones in can be impossible.
4. On the L shaped gauge, the depth and length of the arms minimises your chances of not getting the wheels against it square. Yes the actual B2B will be slightly above the gauge value by a variable amount, but that's what tolerances are all about and experience with the tool should insure you don't stray beyond the allowable maximum.
5. Wherever possible wheels should not be assembled in the chassis as it is next best thing to impossible to do it accurately and square. This of course means a chassis design that allows the wheels to be dropped out. Working out how that is achieved will IMHO improve the running of our models far more than obsessing about the exact B2B.
6. Jol talks a lot of sense.

One thought, for those not inclined to trust their judgment of how much free play around the gauge is allowable, how about an L shaped B2B with an one extended arm ground at the end to the max B2B value, giving a go-nogo gauge which would help find the occasional over gauge wheel.

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Le Corbusier
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Re: What back to back setting do you use?

Postby Le Corbusier » Sun Jan 07, 2018 1:34 pm

Will L wrote:5. Wherever possible wheels should not be assembled in the chassis as it is next best thing to impossible to do it accurately and square. This of course means a chassis design that allows the wheels to be dropped out. Working out how that is achieved will IMHO improve the running of our models far more than obsessing about the exact B2B.


Presumably this means that compensation with a rigid wheel such as on the original Perseverance Flexichas system is a non starter? Also, presumably the 'L' shaped gauge is necessary for the gear wheel?
Tim Lee

Philip Hall
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Re: What back to back setting do you use?

Postby Philip Hall » Sun Jan 07, 2018 1:36 pm

Julian,

I think it could be fairly said that you have, over the period of this thread, opened quite a can of worms! In a good way, as I think that you have aired ‘problems’ that have existed but not addressed, perhaps not needed to be addressed in some ways, but interesting nonetheless.

Can I firstly make an observation on measuring equipment. Lindsay has said quite rightly that the quality (essentially price) of a vernier may have some bearing on its accuracy. I can vouch for this, because I have two, and the cheaper of the two has begun to give a markedly different reading to the ‘better’ one. So much so that the cheap one has just thrown in the sponge and has to be replaced. I have one vernier on one bench and another alongside the lathe. For obvious reasons they both have to give the same readings but until recently I was not aware they were different. Which gave me all sorts of problems with basic things like axle lengths; I set these as close as I can to ‘bang on’, so that when assembling wheelsets with the GW gauge the back to back was correct. I was measuring axle lengths with one vernier and the axle lengths with another. So you will see where this is leading...

I was always told that the most accurate of measuring devices is a micrometer. Mine is an old Moore and Wright one and I have no doubt at all that is as close to perfect as we are ever likely to need. It is my benchmark when measuring. So the first thing I found many years ago was that nominal drill sizes are anything but! So I now measure all gauges only with the micrometer, unless I am sure that that the vernier and the mic are near as dammit the same.

Sharman wheels of old did move, and Mike did say that the wheels settled down on the axles a bit, which made them a tighter fit eventually. They were also tweakable, to get them to run more truly. I have found this to be so, to a degree, with AG wheels. Not so with Ultrascale, which are made of a much harder plastic, and anyway generally run dead true to start with. Your comment about the difficulties of measuring accurately the back to back with a vernier is well founded; it is all too easy to put a little too much pressure in the gauge and find an inaccurate reading.

As Jol says, there is really not a definitive answer to all this. We are in the hands, to a degree, of the manufacturers of the measuring tools we use and the gauges we buy. And our skill in using them. We can check these things and use only the tools which are the most accurate and suited to our needs. We have a set of standards, which, by and large, make it possible for any vehicle built to those standards to run on any railway similarly built. But to achieve absolute perfection (which we all would love!) I think there is only really one way, and that is to have one set of gauges to which all rolling stock is set. And to have a set of trackwork gauges to match. For a home layout, that is fairly practical, and the way I am intending to go. But I have no qualms that all of my stock, and the stuff I build for others, will also run reliably on any other P4 railway. At least I hope so. No one so far has told me that my engines fall off from time to time so I guess it must be working.

Lest anyone might thing that I am trying to downplay these discussions, I really am not. I think it is very useful that such things can be aired so that reliability of running can be improved. It’s a good way to go, but not perhaps for anyone contemplating moving to P4 for the first time! And I do find it interesting, but tempered with the realisation that it is a technically difficult path that not everyone will want to follow...

Philip

Crepello
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Re: What back to back setting do you use?

Postby Crepello » Sun Jan 07, 2018 3:24 pm

Jol Wilkinson wrote:To end on an interesting note, a distant (geographically) friend who had always modelled in OO but recently built several locos that run on "London Road", has just announced he has built a loco with Markits wheels and Markits P4 axles, that runs perfectly on a S4 (not P4) layout at another friends home nearby.

I wonder why Mr Markits would go to the trouble of manufacturing a P4 axle, and not make sure we all knew about it?

Enigma
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Re: What back to back setting do you use?

Postby Enigma » Sun Jan 07, 2018 3:47 pm

Regarding vernier calipers, I wouldn't trust a digital one that is obviously dependant on electronices and batteries. To much to potentially go wrong. I do however still trust my eyeballs (especially with 3x modelling specs!) and with my trusty Mitutoyo with its fine adustment facility can distinguish a variation from 0.1mm - 0.15mm - 0.2mm. That's close enough for me. However, I would very rarely use it to check a B-2-B.

As I've said above, I will continue to use my existing B-2-B gauge which has proved over the past 35+ years to be quite acceptable and will not find the need to stick a bit of Sellotape along one edge.

Reading this thread I honestly get the feeling that to much emphasis is being given to minutiae (ie fractions of thous and millimetres) in the same way that people once discussed the number of angels on a pinhead. Just use the gauges and be very careful and precise when doing so. In the same way ensure that driving wheels are sitting flat and square in the GW Wheelpress before using it (I have found on some AG wheels that the outside centre boss is deeper than the 'padding' so wheels are can end up skewed), that the axle holes are prepared, lightly countersunk and clean (de-swarfed from the c/sink and degreased) and the axle ends are free of burrs and the edges lightly rounded.

If I do have problems with stock (and who doesn't!) then it is very rarely due to dodgy B-2-B's and more to do with sticky compensation, dirty crud-bound wheels or something coming loose on a point (eg checkrail unsoldered).

Enigma
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Re: What back to back setting do you use?

Postby Enigma » Sun Jan 07, 2018 3:49 pm

Crepello wrote:
Jol Wilkinson wrote:To end on an interesting note, a distant (geographically) friend who had always modelled in OO but recently built several locos that run on "London Road", has just announced he has built a loco with Markits wheels and Markits P4 axles, that runs perfectly on a S4 (not P4) layout at another friends home nearby.

I wonder why Mr Markits would go to the trouble of manufacturing a P4 axle, and not make sure we all knew about it?


They appear on their website and I seem to remember that 247 Developments were selling them at S4UM?.

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Flymo748
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Re: What back to back setting do you use?

Postby Flymo748 » Sun Jan 07, 2018 3:56 pm

Enigma wrote:
Crepello wrote:
Jol Wilkinson wrote:To end on an interesting note, a distant (geographically) friend who had always modelled in OO but recently built several locos that run on "London Road", has just announced he has built a loco with Markits wheels and Markits P4 axles, that runs perfectly on a S4 (not P4) layout at another friends home nearby.

I wonder why Mr Markits would go to the trouble of manufacturing a P4 axle, and not make sure we all knew about it?


They appear on their website and I seem to remember that 247 Developments were selling them at S4UM?.


I think that it was Mr Tatlow that first commented on here about them...

Because they are repeatedly dismantleable, and the Markits wheels should be quartering square because of their design, then they can be used as "sacrificial" wheels (but of the reusable type, IYSWIM) for the assembly and testing of chassis.

A clever idea, and one that I may adopt in future.
Cheers
Flymo
Beware of Trains - occasional modelling in progress!
www.5522models.co.uk

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Will L
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Re: What back to back setting do you use?

Postby Will L » Sun Jan 07, 2018 4:15 pm

Le Corbusier wrote:
Will L wrote:5. Wherever possible wheels should not be assembled in the chassis as it is next best thing to impossible to do it accurately and square. This of course means a chassis design that allows the wheels to be dropped out. Working out how that is achieved will IMHO improve the running of our models far more than obsessing about the exact B2B.


Presumably this means that compensation with a rigid wheel such as on the original Perseverance Flexichas system is a non starter?

Not necessarily, in the past I've used a keyhole shaped slot wide enough for an axle at the bottom, but opening out to take a standard top hat bearing. There are other ways. But rememberer I woudn't do a basic fixed axle compensation any more either.
Also, presumably the 'L' shaped gauge is necessary for the gear wheel?
The Exactoscale block has a hole down thw middle which allows for a gearwheel on the axle,
buck chass 11.jpg
buck chass 11.jpg (290.6 KiB) Viewed 4603 times
but yes an L can be necessary to assemble a busy axle.
csb W&M 4.jpg
csb W&M 4.jpg (248.09 KiB) Viewed 4603 times

Enigma
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Re: What back to back setting do you use?

Postby Enigma » Sun Jan 07, 2018 4:38 pm

For a fixed - but removable - driving axle I open the fixed axle hole to accept the top-hat bearings I'm using then cut down to the bottom of the frame so that the top-hat will slide in. With an axle fitted and the top-hats pushed to the top of the slot/hole I then solder a length of fine bore brass tube across the bottom of the top-hat and the edges of the frames. The tube is then cut either side of the top-hat and an L-shape piece of wire that is a good fit in the tube is used to hold it all in place. The wheels/axle/gearbox assembly can then be dropped out of the frames as required for painting, fettling etc.

Barclay Frames with Compensation Pivot.2.A.jpg


The large brass 'wheels' are parts of my home-brewed frame assembly 'jigs'.

Mind you, I do not have any locos more than 6 coupled and find that a fixed drive axle with compensation on the others is quite adequate for my skills and expectations. I tend to follow the Iain Rice 'pragmatic' approach.

Terry Bendall
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Re: What back to back setting do you use?

Postby Terry Bendall » Sun Jan 07, 2018 5:04 pm

Enigma wrote:Regarding vernier calipers, I wouldn't trust a digital one that is obviously dependant on electronices and batteries
Philip Hall wrote:I was always told that the most accurate of measuring devices is a micrometer.


Paul and Philip are quite right. Because digital vernier calipers and micrometers are easily available there is a tendency to use them without a lot of thought and of course they avoid leaning how to read a manual device. Such things are useful but the battery can fail and give an inaccurate reading. It is a bit like using a calculator and assuming that the answer is always going to be correct when a low battery, or hitting the wrong key will give an error.

A micrometer will generally be more accurate than a vernier caliper, provided that it is used with care and both require the correct degree of "feel" as is the case with using a back to back gauge. Such things only come from experience so patience is needed. A good source of quality precision measuring tools are second hand tool stands at model engineering exhibitions. Such stands will often be selling off tools from people who are now working in the great workshop in the sky and can usually be relied on to have been well looked after.

The way to check both devices is to measure something that is known to be a set distance. A piece of silver steel is normally fairly accurate and it is possible to buy checking gauges for micrometers.

Terry Bendall

Philip Hall
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Re: What back to back setting do you use?

Postby Philip Hall » Sun Jan 07, 2018 8:30 pm

One other use for the Markits axles would be to make it possible to turn down Markits Wheels to P4 profile. So long as you have a suitable lathe and a form tool. I don’t!

Beware though that when I recently used some Markits wheels for an EM conversion I found that the back to back was 16.45 mm, which of course is not right. I ended up turning the backs of the wheels down (which I can do, which also reduces the flange thickness) which gave me a useable back to back of 16.65mm for a finer EM wheel. So what the P4 back to back might be...?

Philip

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Le Corbusier
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Re: What back to back setting do you use?

Postby Le Corbusier » Sun Jan 07, 2018 8:35 pm

Enigma wrote:For a fixed - but removable - driving axle I open the fixed axle hole to accept the top-hat bearings I'm using then cut down to the bottom of the frame so that the top-hat will slide in. With an axle fitted and the top-hats pushed to the top of the slot/hole I then solder a length of fine bore brass tube across the bottom of the top-hat and the edges of the frames. The tube is then cut either side of the top-hat and an L-shape piece of wire that is a good fit in the tube is used to hold it all in place. The wheels/axle/gearbox assembly can then be dropped out of the frames as required for painting, fettling etc.

Barclay Frames with Compensation Pivot.2.A.jpg

The large brass 'wheels' are parts of my home-brewed frame assembly 'jigs'.

Mind you, I do not have any locos more than 6 coupled and find that a fixed drive axle with compensation on the others is quite adequate for my skills and expectations. I tend to follow the Iain Rice 'pragmatic' approach.

Paul,

Just to make sure I have understood this correctly, when you say you cut the tube either side of the top hat, am I right that this then gives you three sections .... the two outer ones soldered to the frames and the inner attached to the bearing and so to the axle and wheels?

To make these cuts what do you use? Are the axles insitu when you do it or removed again.

Thanks

Tim
Tim Lee

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Le Corbusier
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Re: What back to back setting do you use?

Postby Le Corbusier » Sun Jan 07, 2018 8:39 pm

Will L wrote:The Exactoscale block has a hole down thw middle which allows for a gearwheel on the axle,buck chass 11.jpg


This makes me wonder if I could machine a similar hole out of the middle of my 'Mallet" back to back. Presumably I would need to find someone with a Milling machine to do this. hmmm!
Tim Lee

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Jol Wilkinson
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Re: What back to back setting do you use?

Postby Jol Wilkinson » Sun Jan 07, 2018 8:52 pm

Le Corbusier wrote:
Will L wrote:The Exactoscale block has a hole down thw middle which allows for a gearwheel on the axle,buck chass 11.jpg


This makes me wonder if I could machine a similar hole out of the middle of my 'Mallet" back to back. Presumably I would need to find someone with a Milling machine to do this. hmmm!


As they are brass, a big file should do tbe job. However, I don't think they are "deep" enough to have a big sufficient rebate. .

Tony Wilkins
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Re: What back to back setting do you use?

Postby Tony Wilkins » Sun Jan 07, 2018 9:07 pm

Terry Bendall wrote:
A micrometer will generally be more accurate than a vernier calliper, provided that it is used with care and both require the correct degree of "feel" as is the case with using a back to back gauge. Such things only come from experience so patience is needed. A good source of quality precision measuring tools are second hand tool stands at model engineering exhibitions. Such stands will often be selling off tools from people who are now working in the great workshop in the sky and can usually be relied on to have been well looked after.

Terry Bendall


Better quality micrometers incorporate a slipping clutch arrangement between the finger knob and the anvils to give a consistent force on the measured object and hence repeatable readings. These should therefore only be turned by the finger knob and not by the main barrel for obvious reasons. They are though not as versatile as a vernier as they can generally only make external measurements.

My local area group held its first meeting of the year and several B2B gauges were measured using several devices. The vernier readings were predictably the most variable. We had three micrometers at our disposal one of which was imperial only. The two metric ones were consistently within 0.01mm overall.
The gauges gave measurements between 17.65mm to 17.87mm (excluding an EM and a OO example submitted)
Several factors were noted.
Most of the L shaped gauges gave varying readings the worst being 17.65, 17.69, 17.67mm reading from end to corner to end.
Most of the samples came in at the 17.67 end of the spectrum with one L gauge at 17.73/4mm
A couple of the L gauges had burrs on the end corners producing wider readings at the very ends and the burrs could be felt. Gently abrading with VERY fine emery paper removed them but the suspicion has to be that these gauges had been dropped at some stage and the edges suffered as a consequence. These are precision items and should be treated as such.
The Exactoscale block gauges were the most consistently accurate.
I draw no conclusions from this other than those already mentioned.

Below is a picture of my collection of B2B gauges.
DSCF2211.JPG

From left to right.
Exactoscale 17.67mm.
P4 17.70,17.74,17.73
S4 17.84,17.85,17.84
Home made S4 17.84
Exactoscale S4 17.87mm.
The roller type gauge is useful for checking wheels where the plastic centre is proud of the back of the tyre. The intended dimension was 0.703", so I don't think I did too bad with a Unimat lathe.
Regards
Tony.

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Le Corbusier
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Re: What back to back setting do you use?

Postby Le Corbusier » Sun Jan 07, 2018 9:31 pm

Jol Wilkinson wrote:
Le Corbusier wrote:
Will L wrote:The Exactoscale block has a hole down thw middle which allows for a gearwheel on the axle,buck chass 11.jpg


This makes me wonder if I could machine a similar hole out of the middle of my 'Mallet" back to back. Presumably I would need to find someone with a Milling machine to do this. hmmm!


As they are brass, a big file should do tbe job. However, I don't think they are "deep" enough to have a big sufficient rebate. .


I see what you mean .... presumably you could file out two and then they would meet in the middle ?
Tim Lee

Enigma
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Re: What back to back setting do you use?

Postby Enigma » Sun Jan 07, 2018 10:39 pm

To make these cuts what do you use? Are the axles insitu when you do it or removed again.

Thanks

Tim[/quote]

i have used both a razor saw and a piercing saw. The cut doesn't have to be to precise as the tubes will line up no matter how wide the saw cut. The axles are removed as it is easier to saw without them. The top-hats complete with tubes are fitted onto the axles - along with any necessary spacing washers - whilst fitting the wheels.

Terry Bendall
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Re: What back to back setting do you use?

Postby Terry Bendall » Mon Jan 08, 2018 9:11 am

Tony Wilkins wrote:Better quality micrometers incorporate a slipping clutch arrangement between the finger knob and the anvils to give a consistent force on the measured object


Yes they do and Tony is quite correct that the clutch or ratchet mechanism can help with consistency in measuring. On micrometers that I have used I have always felt that the point at which the "slip" occurs is too loose. I have an imperial micrometer which probably dates from the 1930s and a metric one which is probably from around the early 1970s, both inherited The ratchets on both are broken but they still give accurate measurements

Tony Wilkins wrote:They are though not as versatile as a vernier as they can generally only make external measurements.
ments.

Yes quite correct. It is possible to get internal micrometers but only for internal measurements above 50mm. A telescopic hole gauge will cope with smaller holes but you then need to use a micrometer to measure the distance. I tend to use the vernier for measuring where accuracy to greater than (less than?) [0.1mm is not required - things like buildings from styrene, wagon bodies and the parts for scratch building of locos bodies and frames.

Tony Wilkins wrote:My local area group held its first meeting of the year and several B2B gauges were measured using several devices


Sounds like a very good idea and perhaps a good thing for other groups to do. . In days gone by large engineering works would have a testing and inspection department where measuring equipment used on the shop floor would be checked against precision references sources held in a clean environment.

Terry Bendall

Tony Wilkins
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Re: What back to back setting do you use?

Postby Tony Wilkins » Wed Jan 24, 2018 10:36 pm

Hi Terry.
Toy Mic.jpg

Best 2 shillings and 6 pence I ever spent.
1/2 inch capacity but accurate to a thou.
Regards
Tony.

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Le Corbusier
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Re: What back to back setting do you use?

Postby Le Corbusier » Wed Jan 24, 2018 10:39 pm

Karl ... or Groucho ? :D
Tim Lee


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