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Mucking about Turning wheels


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Investigating what I can do on my Unimat with very rudimentary tools and parts available from the scrap bin. 

 

Fist up, thinning down some Romfords, from 100thou to 75 thou to fit better inside RTR wheel arches when used on EM axles. This was achieved easily but the Romford tyres are just shy of 6 scale inches thick and look utterly ridiculous to be honest. Fun exercise but I'll probably just buy a set of Ultrascales for the loco. 

 

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Second up, and much more involved, a proof of concept for making split frame locos. I'd read of using a 1/8" stainless steel tube outer, with an inner core of 1/16" silver steel with an insulating wrap around it and then splitting the outer tube to isolate the side. I thought I'd give it a go, and whilst at it see if my idea for a turning sequence for cast brass wheel centres would work. 

 

I don't have form tools yet, so I used a tyre from a knackered Exactoscale wagon wheel, and turned a billet of brass until it would press fit inside the rim. The brass billet extended both sides of the wheel, so I had something to grab in the lathe. This was then drilled (with an FC3 milling cutter standing in for a centre drill!) an reamed out to 1/8". The Rod was just over a thou oversize, and the hole came out slightly tapered due to runout in the 3 jaw chucks (collets will be used eventually) but luckily it was tight enough in the part that would become the wheel centre that it held tightly once pressed in. The excess wheel centre was turned off, leaving a little boss around the stub of axle. 

 

It was mostly successful, I used insulation tape wrapped round the inner silver steel rod which didn't form a solid enough centre to the axle, rather than cutting the silver steel core during facing the (by now blunt!) tool just pushed it through the axle tube. In future I might run a drill through the centre of the tube to give it some texture, and use a plastic tube soaked in cyano around the core. The finish on the stainless axle is marred because I didn't have a straight drill larger than 1/8" to open up the boss, so when I turned it down I had to turn it right down to the stainless outer face. 

 

The concept at least has been proved - next to order some cast centres and have a try with those. 

 

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You could follow prototype practice and turn down the Romford tyres until they are easier on the eye.

 

Sadly not, the actual separate tyre bit is quite thin, the majority of the thickness is in the insulation and the cast wheel centre rim. 

 

I'll be making my own Nickel Silver tyres eventually, although the cost of Nickel Silver bar stock is scary! (And the form tool still needs to be tackled)

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Teichmann produces a profile / form tool for HO-pur, which for practical purposes is somewhere between strict P87 and P4. Costs about 50 Euro.

 

Your other best bet is to ask Dave Doe at DD Wheelwrights if he could make a P4 tool or two for you. He already produces a small number of gauges for the Scalefour Society Stores. The only downside is that he won't be cheap.

 

I don't think anyone has produced P4 form tools commercially since Joe Brook-Smith died.

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Have you thought about using free turning mild steel for replacement tyres? There's a German firm that does a RP25 profile tool, I have one here, it cost about thirty quid, and bought direct.

 

Fohrmann? RP25-110 I think it is which is is 00 Train Set grade, I've drawn up a suitable tool, just waiting for payday so I can order a couple of them. Nickel Silver tyres are preferable, though I'd consider stainless if I can get away with it on my machine. 

 

Teichmann produces a profile / form tool for HO-pur, which for practical purposes is somewhere between strict P87 and P4. Costs about 50 Euro.

 

Your other best bet is to ask Dave Doe at DD Wheelwrights if he could make a P4 tool or two for you. He already produces a small number of gauges for the Scalefour Society Stores. The only downside is that he won't be cheap.

 

I don't think anyone has produced P4 form tools commercially since Joe Brook-Smith died.

 

I don't need P4, keeping things simple (!!) with EM. 

 

Today I received some samples from theplasticshop.co.uk for testing out making solid centres for the axles, I'm not convinced a 4mm loco will put enough force into an axle to need the steel core. I tried Glass filled nylon, polycarbonate and cast acrylic.

 

The glass filled nylon is pretty rigid even at 2mm dia (2.165 actually!) and has a nice matt finish which would glue inside the stainless nicely, the polycarbonate was too bendy, couldn't even turn it parallel it was just wobbling about all over the shop! Haven't done the acrylic yet, I'm still picking bits of plastic fuzz from my hair!

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If you have small enough lathe tooling, (or a grinder to make your own) you can make your own form tools in silver steel, and harden. You basically turn a disc, with a reversed profile of the shape you want, and drill, say, a 5mm hole in centre. Then cut a notch from the edge towards the centre of the disk, the bottom of the notch should be on a radial line. Use a 5mm cap screw to hold the disc on the end of a piece of drilled & tapped steel to go in your tool holder, and adjust the bottom of notch to be on centre height, or wherever it suits you depending if you want positive or negative rake ('centre height', in this case, will be on a line from the lathe centre to centre of the disc - i.e. the cutting face of the form tool need not be level). Hardening small bits of silver steel is easy. If you've no silver steel, then use free turning and case harden. It will pay you to make a few such discs at the same time, practice hardening, etc. Using the tool will need light cuts. You may find that the flange of the wheel you are finishing (the actual loco wheel, not the form tool) may tear, due to the tapered shape, wedging into the tool/whatever, so you may need to make two tools, one for the rim and face of the flange, another to do the back and round off the flange. (that would be easier than making a form tool with a narrow V for the flange). Go slow, and lubricate  if necessary. If you've not got any, get a few diamond slips, which used frequently will keep your tools sharp.

 

For the circular form tool that I've tried to describe, to keep it sharp, you only need to 'file' one of the flat cut edges, not mess with the actual profile. Probably a disc about 12mm diameter would be good enough.

 

Best wishes,

 

Ray

 

ps if you don't understand what I'm describing, I'll see if  can find one I made earlier.

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This may be of interest, or maybe not :)

 

I was playing around with my 3D printer to see what It could do, and I cooked this up as a test. The upper wheel is obviously the original Romford. Under it are 3D printed centers, one painted and the other straight off the printer. Not exactly perfect by any means, but they could be improved with a bit of clean-up work.

 

The material is PLA which is a fairly hard form of plastic. I never got around to turning a tire for it (I'll use "leaded steel" if I do - machines very nicely). Cyano glue seems to attach PLA to many things, so it would not be difficult to attach the tread to the center.

 

It's not very obvious from the photo, but the wheel center has a square aperture to accept a Romford axle.

 

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  • RMweb Gold

I gave up trying to make anything other than solid disc wheels sometime back.

 

I've always used free cutting mild steel.  But it is a crying shame to see more than 75% of the bar stock ending up as swarf when machining  just wheels rims from solid. (The axles were hub insulated using small nylon bushes.).

 

If you try using stainless steel for wheel rims you are a glutton for punishment.  In my experience it  is hard to machine and also is very slippery when in contact with the rail head, although the type of materiel used for the rail does have a significant impact on adhesion.

 

Persoinally, having investigated the cost of Ultrascale wheelsets, I now just buy in Gibson wheels, and use a GW models wheel press to mount the wheels onto the axles and quarter them at the same time.

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Oooh ordered! Very similar to my profile (Mine is 0.65x0.61 flange with a 0.3mm fillet into 3 degree tread and an overall width of 2.3mm) though I don't think it's quite right for RP25-88. 

 

RP25 is the profile now used on "Romford" wheels, I don't relate to any ref to "Train Set" wheels.

 

Look at them - then look at a Gibson or an Ultrascale and tell me which looks like a real wheel and which looks like a toy. Even Bachmann's standard wheels look better (old split framers excepted). Just because it doesn't have Pizza cutter flanges doesn't make it automatically good. 

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  • 2 weeks later...

The RP25 tools arrived from Deutschland, a bit on the blunt side but a bit of lapping will cure that, didn't realise they're actually double ended, so I have 4 cutting faces now, should last a while. Pretty hard going with them so far, however there was quite a lot of play in the saddle on the unimat, which I've spent the last few hours correcting as much as I can. Hopefully now it'll cut a bit easier. 

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I might ask them if they'll do another run of the Fremo HOpur/RP25 Code 55 TT tool that they show in some of the auction photos.

 

That would be nice for some narrow gauge wheels for me too.

 

It's the -110 that makes them train set really.

 

Yes, that and the chunky centres and weird looking crankpin boss. 

 

Anyway... it's only taken all afternoon to get this far, but here is my first Nickel Silver tyre! 

 

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The reason it took so long was 25mm bar is really awkward to work with in the Unimat, so I turned down an inch of it so it sits in the spindle bore, makes for a much better alignment when turning overhung. NS is surprisingly weighty so any runout makes for some nasty vibration. As it happens it worked out well, on those annoying occasions where the tool sticks instead of the bar spinning in the chuck it caused the belts to slip instead, ideal for me because my chuck is slightly de-centred, so if it slips in the jaws I lose all egocentricity. I've got a new 4 jaw on the way to bypass all that hassle! 

 

Anyway once that lot was sorted, there was yet more delay with the boring bar, all it did was squeal and shriek and not actually cut, I couldn't see the problem very well so I took a picture and zoomed in... the cause? too low in the toolholder, the cutting faces were nowhere near the work! Cue many, many shims and all was good! 

 

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Another 3 of this size (5'6") and a pair of 3' and I have the tyres sorted for a Cambrian 2-4-0. 

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25mm nickel-silver bar?  An investment of that nature must have scared your bank manager!

 

£25for a 6" length, Once I get a rotary table though It should be possible to use a 3mm slot drill to to cut out the centre bit leaving a core which can then be used for  3' bogie wheels, although for that to work I'll need to find myself a much slimmer boring bar! 

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£25for a 6" length, Once I get a rotary table though It should be possible to use a 3mm slot drill to to cut out the centre bit leaving a core which can then be used for  3' bogie wheels, although for that to work I'll need to find myself a much slimmer boring bar! 

 

You might be able to do that without a rotary table. If you grind a tool from HSS you should be able to cut a narrow slot in the face of the NS. I've done that with Mainline wheels to insulate the tread from the centers although those wheels are made from an alloy that is probably easier to machine than NS.

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