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3.5 inch wheel form tool..?

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Ron Laden27/01/2022 10:13:06
2297 forum posts
452 photos

I have 12 off 3.5 inch gauge wheels to make in steel.

Width is 3/8" and tyre diameter 2.7" I was wondering if a form tool would work or would it be asking too much. I have made and used smaller form tools and they worked fine on alu but I have never tried a 10mm tool on steel. If not I can machine in stages but a form tool would be quicker and easier to produce the same on all 12 wheels..?





Edited By Ron Laden on 27/01/2022 10:29:58

ega27/01/2022 12:39:10
2487 forum posts
199 photos

If a Quorn builder can produce a 3/4" dia steel ball with a carbon steel form tool then I think it entirely possible.

MikeK27/01/2022 20:29:34
226 forum posts
17 photos

The size of the lathe being used matters. I would think a Chinese mini-lathe would not be up to the task.

HOWARDT27/01/2022 20:45:21
900 forum posts
39 photos

I produced ten steel wheels of 3 3/4 inch on my mini lathe by not using a form tool. Unless you really want to produce the form there is little to be gained by being too picky in my opinion. But if you do want to use a form tool only use it to do the final finishing.

duncan webster27/01/2022 21:45:05
3919 forum posts
61 photos

I use a semi-form tool, it has the radius B and the 20 degree angle, but is fed up the 3 degree slope. I happened to have a brazed carbide tool that was about the right shape to start with, but HSS would have been OK unless the casting has hard spots

Perko729/01/2022 11:48:00
422 forum posts
33 photos

+1 to Duncan's reply. I used a round-nose tool of the correct radius fed up the 3 degree angle until the diameter at the root of the flange was correct, then fed down the 20 degree angle until a smooth transition was obtained. The radius C was achieved using files and a template to check progress. It was slow and somewhat tedious but enjoyable at the same time. I only had 8 to do, each one took maybe an hour after the castings had already been turned roughly to size. Was my first attempt so someone more experienced could no doubt do it faster.

Ron Laden30/01/2022 05:40:31
2297 forum posts
452 photos

Thanks guys, I think I will go with a semi form tool as Duncan suggests and see how I get on. I dont have castings though the wheels will be from steel blanks so a bit tougher to machine than castings.


Hopper30/01/2022 09:32:34
6188 forum posts
319 photos

You haven't said what kind of lathe you have got. If it's a 16" swing Monarch or DSG, Colchester etc etc the full-width form tool would be the quickest way. But a Chinese mini lathe will most likely chatter like a garrulous matron at a christening. I wouldn't try it on my Myford either, for the same reason.

Ron Laden02/02/2022 10:55:06
2297 forum posts
452 photos

Hopper, my lathe is a Warco 918 (9 x 20 type) 3/4HP VFD drive and all the niggles have been well engineered out by the previous owner so a pretty capable lathe but how it would cope with a full width tool I dont know, I have steel blanks on the way so I guess there is only one way to find out.smiley


ega02/02/2022 11:05:27
2487 forum posts
199 photos

Perhaps worth mentioning that Professor Chaddock (see my earlier post) mounted his tool upside down in the rear tool post. His lathe was "light" and "elderly", a Drummond i think.

Ron Laden02/02/2022 11:40:23
2297 forum posts
452 photos

Thanks Ega

I never gave the rear tool post a thought, I have one on the 918 which is pretty rigid. Although the 918 is more than a mini lathe it would be considered "light" and for a Chinese machine I would think it it could certainly claim to be "elderly" (24 years) yes its had the VFD drive added and some well engineered mods but the original bed and other parts are still in very good condition. I will give the rear tool post approach some thought.



Edited By Ron Laden on 02/02/2022 11:41:14

ega02/02/2022 12:01:58
2487 forum posts
199 photos


I will just add that Professor Chaddock found that his three jaw chuck slipped under the load imposed on the work by the form tool but I imagine that your wheels will be secured to the faceplate and trust you won't have this problem.

Good luck!

Ron Laden03/02/2022 07:56:13
2297 forum posts
452 photos

The steel blanks arrived which the supplier says are S275 which is a new one on me. I did a couple of test cuts on one of the spares and it cuts really well with inserts even a GT, havnt tried a HSS tool yet but optimistic it should be ok. It feels somewhere between EN1A and EN3 if I had to guess, any idea what grade its closest to..?

SillyOldDuffer03/02/2022 10:23:23
8469 forum posts
1885 photos
Posted by Ron Laden on 03/02/2022 07:56:13:

The steel blanks arrived which the supplier says are S275 which is a new one on me. I did a couple of test cuts on one of the spares and it cuts really well with inserts even a GT, havnt tried a HSS tool yet but optimistic it should be ok. It feels somewhere between EN1A and EN3 if I had to guess, any idea what grade its closest to..?

There doesn't seem to be an 'Emergency Number' grade equivalent to S275.

EN steels have an interesting history. During WW2 the UK government found it necessary to discipline British Steel producers, each of whom wanted to do their own thing. Government set specifications for all the common steels in a 'War Emergency British Standard Specification' (BS970), and mandated it. So rather than having six or seven mild-steels similar to EN3, there was only one. This useful simplification caught on after WW2 and people still order some steels by Emergency Number today, even though the system was phased out fifty years ago. Although it may not matter, there's some uncertainty today about what an 'EN' steel actually is. Whilst 'EN3' bought today might meet the 1941 specification, it could be a modern equivalent.

The most obvious difference between the EN system and modern steel specifications is EN doesn't demand very high accuracy of the mix. Sensible given production methods in 1940, but modern steel specifications are tighter.

S275 is a low-carbon steel improved with a dash of Manganese. It's one of the mild-steels outstandingly useful for structural and basic metal-work: cheap, reasonably strong, and easily sawn, drilled, machined and welded. For ordinary general purpose structural and mechanical engineering - 'Parts that will not be subject to high-stress.'

Judging by it's constituents, S275 is similar to EN3 except it's more tightly specified (less variation.) It contains slightly more Carbon and noticeably more Manganese: it should be stronger. Some variants also contain Copper to improve corrosion resistance. In a home workshop I doubt there's much difference between EN3 and S275.


duncan webster03/02/2022 17:22:59
3919 forum posts
61 photos

Are the blanks cut from plate? The purists would say that plate is rolled in one direction, so it has a grain. I wouldn't use such blanks for full size wheels, but they will be fine on a small wheel. I did once spend a weekend churning out a pair of wheels for a 2ft g loco from rashers sawn off the end of some big round bar. Helps to have contacts in the oil field equipment industry. As far as I know those wheels are still in service, probably been reprofiled in the ensuing 50 years.

Tyres for full size wheels were ring rolled, so the grain went round. I think modern rolling stock uses forged wheels

Ron Laden04/02/2022 06:01:13
2297 forum posts
452 photos

Thanks Dave for the explanation on EN materials, I didnt know the history of EN.

Duncan, yes the blanks are 10mm x 75mm dia discs laser cut from S275 plate and they are very reasonably priced and been quite close to finished size I thought they would save some work. Like you suggest I would have thought they would be fine on a 3.5 inch Co-Co loco. I am having a go at scratch building a Kestrel, dont worry guys I wont be boring you with a build thread I appreciate there is little interest here in electric diesels which is fine. I may pop up now and then though for advice if I have an engineering/machining query.


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