1/32 A Loco for the Garden

Discussion in 'G1/32' started by JimG, 28 August 2015.

  1. JimG

    JimG Western Thunderer

    With all the work proceeding on the base for the garden layout, I thought it best to start thinking about a locomotive to run on it. the choice was a MacIntosh Class 782 tank - the Caledonian workhorse 0-6-0 tank as shown here in LMS days


    Some may recognise it as the prototype for the Wills 4mm whitemetal kit of many years ago.

    As is my habit, I never start a locomotive until I've got the wheels in hand - a habit with modellers in S scale. :) The 782 tank needs 4' 6" drivers and I could find no suitable 1:32 scale ones ready made, so it was back to wheel making on the mill. :) The first thing was to purchase a sheet or 1/4" clock brass from Ian Cobb - I use clock brass because it is flat and is of CZ120 brass which machines very well.


    The first job was to machine the basic front profile of the wheel. The brass plate was screwed to a sheet of MDF which was in turn bolted to the mill table and the profile milled with a 5mm cutter to get rid of a lot of brass quite quickly. The Caledonian had quite deep bosses on its inside cylinder locomotives - hence the depth of the boss.


    The next job was to cut the basic spoke shapes, drill an undersize axle hole, and drill a pilot for the crankpin.


    The next process was to finish the shape of the boss and machine the front profile of the spokes. This was done with a 4mm diameter ball-nose mill, and the first c**k up happened - as can be seen by the half round groove through the boss. :) I worked out the reason fairly quickly. I had hand written the CNC program for the ball nose milling for S scale wheels and the last operation on my CNC program is to raise the tool to safe height and reset to (0,0). I had changed the values throughout the program for the 1:32 scale wheels but had forgotten to change the rise to safe height. It was still set to 5mm for S wheels and the 1:32 wheels are 6.35mm high, so a nice furrow of 1.35mm was ploughed across the boss when the tool was en route to (0,0). :) The joys of CNC. :)

    The first question was what to do. I could just scrap the wheel as it stood and start again. But the brass sheet had been purchased of a size to do ten driving wheel centres and four bogie wheels (there's a Class 104 0-4-4T in mind after the 0-6-0T) and this would torpedo that idea. So I opted to try a repair.


    I first cut across the area of the groove to remove the problem.


    ...then soldered a piece of brass of just more than the required thickness in the machined area. I managed to do the soldering with my 100 watt Weller - I wasn't too happy at the thought of using a small torch for the job with the MDF base under the brass.


    Next I machined the brass to shape - oversize to allow for the shaping with the ball nose cutter.


    Then I milled the brass to get it level with the existing surface of the boss


    ...then finished off with the ball nose cutter, and the top of the spokes are further machined with a smaller diameter mill to get the proper shape.

    The repair is pretty well invisible and the only noticeable area is the joint area in the axle hole. I attempted to re-bore the hole but the cutter picked up the edges of the existing bore. However the hole diameter is 6mm at the moment and it will be opened out to 6.35mm for the 1/4" axle, so that might minimise the problem, or I will have to use some filler if the problem still shows. The bosses will be painted, so there would be no obvious problem using a small amount of filler. However, it's the first time I have tried doing a repair using CNC and was quite pleased at the end result.


    I then started off on the next wheel and that is now finished. It takes about three hours to do all the machining and I'm now working on one or two things to speed the process up a bit.

    Once all six wheels are cut, they will be released from the plate - each one is held in place by four 0.2mm tabs after machining. After that, the final shaping of the spokes will be carried out by hand with scrapers and needle files.

    By the way, the bit of Plastikard held upright by the toolmaker's clamp to the right of the spindle is a quick and dirty chip fence to keep the chips out of the rest of the workshop. CZ120 brass machines beautifully, but the chips go everywhere. :)

  2. jamiepage

    jamiepage Western Thunderer

    Superb, Jim.
  3. JohnFla

    JohnFla Western Thunderer

    There is no end to your talents Jim, Again the like button is not enough. Cracking workmanship. Look forward to seeing the finished article.
  4. Jon Nazareth

    Jon Nazareth Western Thunderer

    There are some very clever people about, Jim

  5. JimG

    JimG Western Thunderer

    I got the wheel centres finished over the weekend. It was taking about 2 1/2 hours per centre and I had to stay with the milling as it carried on to clear the mountain of brass chips accumulating during the machining. But all got finished yesterday afternoon.

    Here they are still held in the sheet by their tabs...


    ...and separated out on the workbench with a bit of basic cleaning up to get rid of some rags. The next job will be to shape the spokes by hand - the Caledonian had oval spokes on these locomotive wheels.

    The next job was to make some steel tyres to go on the centres. I hate making tyres out of solid bar since so much finishes up as a pile of swarf on the lathe tray. I remembered using some steel nuts some years ago as a source for tyres so I got some 1 1/4" Whitworth nuts off Ebay which would let me get the 4' 6" tyres out of them.


    However, the nuts turned up on Saturday and they turned out to be black hot forged steel - not mentioned in the Ebay listing. I had never worked with hot forged steel before but a bit of research showed that it was supposedly readily machinable. So I took about a third of the nut down to circular before reversing it in the chuck jaws to turn down the remainder - as shown above.

    ... and here's the remained of the hex being cut down. I was using a carbide insert and it seemed to cut fairly well on the lowest direct speed on the ML10. Then it came to parting off into 6mm wide rings.


    Parting off was a bit of a trial - using the Eclipse HSS blade in the rear toolpost. I had to drop down onto the highest backgear speed to get any success. Funnily enough, the metal cut well at the start of the cut and then I started getting a lot of dig-ins as I got close to the thread in the nut. I got there in the end once I had worked out the feed which avoided the dig-ins. I had intended getting four rings from the nut but I opted not to try for the next cut since it would have meant having very little material in the chuck jaws and a dig-in could pull the metal out and possibly damage the chuck as well. So I opted to turn down the remaining piece of metal to about 8mm wide and get three rings from a nut.

    The three rings placed on the lathe bed with the thicker, third ring on the left.

    I'm not sure about proceeding with the steel from the nuts. It machines quite well but I would like to have finished the wheels off in my smaller Cowells in the inside workshop and I'm not sure how well I can deal with it on that lathe. I'll maybe have a few experiments on the wider ring on the Cowells and see how it deals with the metal with HSS tools. In the meantime, the weather looks like it is improving, so I might be able to get back out into the garden to continue the baseboards.

  6. mickoo

    mickoo Western Thunderer


    Interesting stuff, one question, why are you running in reverse and using a tool post to the rear of the work? I've not seen that approach before, there must be a logical reason I presume. Did you use a rear tool post method when taking the flats off the nut as well?

    All the best

    Mick D
  7. JimG

    JimG Western Thunderer


    The parting tool in the rear toolpost is upside down so it cuts with the lathe running in the normal direction. This method is recommended for people with smaller, modellers' lathes when using tools taking heavy cuts - like a parting tool - and I would agree. It can also be quite handy for simple repetition work if you set up the tools in your front toolpost and rear toolpost so that you can part off a piece after turning with the front tool without having to measure up for the parting off.

    The tool with the carbide insert in the front, four-way toolpost did the turning work on the nut.

    I also might have found a local source of more amenable steel for tyres through a member of my club - I'll find out on Friday. :)

    mickoo and Len Cattley like this.
  8. jamiepage

    jamiepage Western Thunderer

    If it's not too late to be of interest, I have a scrag end of (probably) EN1A, partly drilled through the centre at c. 1/2 inch, and partly turned down to 1 5/8 in. (from 1 3/4)
    Overall about 1 7/8 in. long.
    Very happy to stick it in the post. No charge, happy to see it used- if it's any help that is.
  9. unklian

    unklian Western Thunderer

    Great work there Jim, I am following this closely .
    I was very interested to see this way of making wheels, as I have been attempting something similar for a G3 loco. I was able to draw the wheel centres I wanted, but I had to get a friend to machine them for me, we elected to use aluminium for ease of machining and as the loco is relatively light and electrically powered they should be strong enough. You may notice that the lefthand centre has a small machining mistake on it . I have had fun with my tyres too, as I decided on stainless steel, and also bored them out to leave enough material on the centre of the slug to turn the smaller tyres from. The larger tyres are 77mm diameter on the tread and I had to borrow a big lathe to turn them, I am hoping I can turn the smaller ones on my ML10 !
  10. JimG

    JimG Western Thunderer


    Many thanks for your generous offer. 1 5/8" is just a wee bit tight for my needs - a 4' 6" wheel in 1:32 is 1 9/16" over the tread plus 0.072" for the flange, so I would have to turn to a "worn size". :) Can I wait until tomorrow since I have just got an opportunity from a fellow club member to visit an engineering workshop about three miles away from my home who might be able to supply me with bits and pieces? If they have got a waste bin next to a capstan lathe with loads of short ends of bar stock, then that might be a happy hunting ground. :)

    Another source of material for wheel tyres is thick walled steel hydraulic tube if you can source a size which suits your wheels but my problem is finding a supplier who would supply in lengths shorter than four metres. :)

  11. jamiepage

    jamiepage Western Thunderer

    Of course. It's here if you want it. Just miked it up at 41mm, so a bit bigger than I thought.
  12. JimG

    JimG Western Thunderer

    These wheels look excellent - congratulations. :) It is good to get wheels exactly to your needs and not have to put up with something "nearly but not quite". :)

    I would think the that the alloy will be fine for the wheel centres and stainless steel for the drivers. Are the tyres a push fit on the centres or will you have to use adhesive (cyanoacrylate or Araldite?)? I still prefer using brass and mild steel since I can always fall back on using solder to stick things together - witness my rescue job on the wheel boss above. :)

    I note you appear to finish turn your tyres before fitting to the centres. I prefer to work the other way and fit the unfinished tyre to the centre mounted on a mandrel on the lathe, then finish turn to the tyre profile. This is why I am worried about doing that with the hot forged steel tyres since my preference is to use my Cowells lathe in my inside workshop for the job and I have doubts about the small lathe handling the material. I am also looking at making my own tyre form tool using the CNC mill and I will have to use silver steel and harden it after cutting. I suspect that the hot forged steel might be a bit tough if I want reasonable tool life from the silver steel.

  13. unklian

    unklian Western Thunderer

    Thank you Jim,
    I am hoping to Araldite the tyres to their centres. I turned the tyres in one go to keep them as concentric as possible, and I anticipated turning the centres on a mandrel to keep them as concentric as possible too. However the turning of the tyres was quite a struggle, I actually broke one of the first boring tools I used. The machine I used whilst big and powerful enough was quite worn and not as accurate as I would have liked . So I have one tyre a very tight fit and the other a sliding fit !! The amount of torque needed to turn the stainless steel would have been far too much for the ally centres if I had turned the tyres attached to them like you do. Your method is of course quite sound. I would try your form tool turning some plain disc wheels first if I were you to get a feel for how much force is involved.
    Best of luck
    PS to avoid dig ins when parting off, have you tried setting the parting tool to below centre height, or a bit above with your upside down back post ?
  14. JimG

    JimG Western Thunderer


    What I usually do is actually turn most of the tyre profile wiat a standard tool with the topslide set over by three degrees and leave an embryo square profile flange, then use the form tool to, effectively, form the flange only. So the load on the form tool is comparatively low with it not cutting the wheel tread. I usually have one or two pegs in the mandrel to drive the spokes dso that I get a direct drive but I do have the same worry as yourself about the spokes being deformed with a dig in. It actually happened to me some years ago when turning the tyre on a Gibson 7mm scale brass centred wheel and I finished up with a badly kinked spoke where the driving pin had acted on it. :)

    I wasn't sure what was happening with the steel in the nut. The parting tool worked very well for about three to four millimetres into the cut, then you could hear it starting to work very hard on part of the revolution as it got close to the internal threads of the nut, and that's when it started digging in. It could have been the method of forming the thread in the nut was causing local hardness.

  15. JimG

    JimG Western Thunderer

    Today's visit to the local engineering works was very successful.


    ...manna from heaven. :) The two pieces closest to the camera will do the 4' 6" drivers - EN1 steel which is free cutting. They originally were solid but a very helpful gentleman with a very big lathe put a 1 1/4" drill through them to cut down on my machining time. :) The part behind was given to me for a set of wheels for a Caley Jumbo which is the next loco intended after the 0-6-0T and the 0-4-4T. This bit could have a good maturing time on the shelf. :)

    If the weather is good this weekend, then the baseboards might take precedence, but I hope to start cutting the wheel tyres anytime soon.

  16. Steph Dale

    Steph Dale Western Thunderer

    Hmm, I wonder if the nuts you were using had rolled threads? That would account for local hardening and internal rolled threads aren't completely unknown.

    simond likes this.
  17. JimG

    JimG Western Thunderer


    It could be. The nut itself wasn't very square/concentric when chucked up in the lathe so it didn't look as though it had been near a capstan lathe in its existence. I wonder if the thread is formed after the hex forging process while the metal is still red hot.

    I remember seeing round bar being hot rolled in the steel making area near Motherwell in Scotland many years ago. Red hot bar was being passed from one side to the other of graduated rollers with men on each side catching the ends and feeding them back through the next set of rollers. It was an amazing site with red hot bars snaking all over the place and the operators in amongst it all. I suspect that Health and Safety hadn't paid a visit. :)

  18. JimG

    JimG Western Thunderer

    While waiting on some glue to dry on the track making front, I ventured out to the outside workshop and started cutting some metal again.

    This is one of the bits of mild steel I got a couple of months ago to turn into tyres for the wheels for the Class 782 tank loco. There was enough metal there to provide six tyres cut to 5mm wide which would be finished to 4.5mm wide on final turning.

    This certainly wasn't a job for the Cowells in the indoor workshop - more like second backgear on the Myford in the garage. But the steel cut beautifully which bodes well for further turning exercises. I have a problem, living on my own, that when I go out to the workshop in the garage, I could be at the other end of the world. So I only tend to venture out there when grandson has come round looking for a lunch and can keep watch in the house. :)

    The finished result with the six tyres cut and enough metal left in the stub in the chuck to provide another two smaller diameter tyres - a nice job done while grandson's bolognese was cooking. :) I'll see if the Cowells has enough grunt to finish turn the tyres indoors this coming week.

    3 LINK, BrushType4, JohnFla and 4 others like this.
  19. richard carr

    richard carr Western Thunderer

    What a great thread, I almost missed it given the title, maybe you could add a note about making wheels.
    Which CNC mill are you using and what software do you use to drive it ?
    For parting off I bought a carbide tipped tool about 15 years ago, I have to say its one of the best tools I have ever bought, it just slices through anything, including stainless steel. I have it mounted in a rear tool post on my Myford super 7.


    Dog Star likes this.
  20. JimG

    JimG Western Thunderer


    I will as I go along.

    The Seig KX1

    Sieg KX1 CNC Hobby Mill - Arc Euro Trade

    I got it over five years ago and it has been a great purchase for me. The control software is Mach3 and I use Vectric Cut2D to do the majority of my CAM work using AutoCAD LT for the CAD work. But I've just updated to the latest Cut2D Desktop and it has quite a reasonable set of CAD facilities included so I might start using it for CAD as well.

    My parting tool is an Eclipse one which I got too many years ago to remember now - maybe about forty. :) It is HSS and the blade is thin - 0.51" - so not much wastage when slicing things. :)

    Dog Star likes this.