Re: Wheel Profiling

[MikeWilliams]

A question for the techies amongst us.  If I take a "commercial" steel wheel or tyre, cut it in half, making two semi-circles, case-harden it, and use it as a lathe tool to make a matching female part in steel, can I then cut that new part also in half to form a cutting face, case harden it and hey presto - I have a form tool?

Or is it not that easy?

Mike

[cabbage]

Mike -I don't think that it is this simple(!) Over the last weekend I was simply facing the front of my bogie wheels prior to painting them and although at the centre I was turning the slide with three fingers -by the time I had reached the tyre I was having to use both hands to feed the slide. The drag on the cutter was simply enormous and it was T/C one too!!!

The only thing I could see that would work would be a sort of inverted Forstner bit -or a heavily modified type of "tank cutter" that could take an indexable tip(?)

What would be useful is some form of "blind mandrel" that would repeatably hold wheels for turning. I have decided to standardize on 1cm holes for my wheels -but my supply of M10 nuts and bolts has taken a hammering while I learn...

regards

ralph

[John Candy]

Mike,
Even if it were possible to make the tool, I think you would find that the large contact area between tool and work piece would set up vibrations which would result in 'chatter' (the cutting edge jumping on and off the wheel leaving a 'ripple' pattern).
Good turning practice (as I understand it) relies upon a small area of contact between work piece and cutting edge.

Regards,
John.

[Andy B]

There's an article here along the lines that Mike proposed. In 4mm scale I'm sure it would work fine. For 7mm, I think you'd need a reasonably big / solid lathe to avoid chatter (a Myford should be OK).
But by the time we get to G3, our wheels are 6-7mm wide, so with the flange as well our total cutting edge is 10-12 mm. So even for a scale 5' driving wheel, a very solid slide / toolpost would be needed - probably get away with it on a Colchester Bantam, Viceroy 280, etc. The wheel would need holding very securely though to resist the cutting force - a simple expanding mandrel probably wouldn't do the job.

One's time would probably be better spent making some saddle / slide stops (which are useful for other batch-turning jobs anyway) and a couple of gauges to speed up setting the top-slide angles consistently for the tread and flange.

Andy

[Kalinowski]

Folks, wheel turning in 2.5"/G3 is no different from G1 only you need at least an ML10. The 2.5" Wheel castings are heavier than G1 and sometimes have hard spots around the rim. I have turned circa 36 drivers on my ML10 and use a standard tool to cut away the waste on the rim and tyre until the final finish, when I use a home made profile cutting tool as sharp as possible for the last operation at low speed to get a smooth finish. However, I still get chatter sometimes and smooth most of this away with fine emery paper.

The worst problem by far is when a wheel gets stuck on the mandrel, this can take a very long time to free up and the air in the workshops turns blue!!

regs PK 

[cabbage]

I am not an engineer and my choice of lathe and milling machine might strike you as odd... I have a Cobra Mill and Lathe AKA Seig C-1 and X-1, (I spent £410 on the pair of them). However despite the low power and small chuck size I have been able to do quite a lot of wheel turning with it. I do however have a feeling that most of this is down to luck, (and the fact that I didn't know that I really needed a bigger lathe to do it!!!)

It is possible to use "toy lathes", (to quote some of my friends), to make G3 wheels.

Whether it is an act of "sheer madness" to make a wheel that looks like this as a first attempt on a lathe is debatable...



As this is quite probably the only lathe that I will ever have, (I did research it) -and I have a nice lathe that I can pick up and carry with me and move around my shed as required. While I would love a Myford -I just don't have the space to fit one. My shed has enough room for a vertical mill, a lathe, and a pillar drill, anyone of which has to "live on the floor" -if I need the workspace...

regards

ralph

[MikeWilliams]

Well, that all seems to have demolished by ideas for a form tool!  I didn't mean it to perform all the cutting, just to act as a gauge/template and take off the smallest of final cuts, but I do see your point and it is true that even my 7mm scale wheels made my little Pultra lathe chatter a bit.

The worst job on the lathe was making a curved guide for Joy valvegear - a flat steel plate about 3in diameter, cutting a slot in the face.  Slices were then cut and soldered to a bar to make the weighshaft.  That was done in the Unimat before I had the Pultra and really made it chatter and get hot!

Thanks for the feedback.

Mike

[IanT]

Well I don't use form tools as such, simply a round-nosed finishing tool that is really sharp. I'm not sure the size (swing) of lathe is that important if the wheel will fit and you are taking very fine cuts (which is pretty hard to do with a form tool). I use the top-slide set over to get the general profile and then use a file to just round over the top of the flange.

The only time I really get problems is when I don't get far enough under the skin on castings and create my own 'hard' spots. But if I was using a very small lathe (I have several) I would use an old file to get through the crust first. But these days being idle - this is when I use a carbide-tipped tool and just dig in to rough it out.

But generally I use HS Steel tools, sharpen them often, try to get the speed right and take fine cuts with the saddle locked. A file (with handle) carefully applied does the rest. OK - I am talking here about my old and somewhat worn 'Super Seven' but I think my even older little (2.5") Rollo Elf would do most of my G3 turning work IF the tool was sharp and the speed right. It would just be slower because I'd have to take smaller cuts (OK - shavings!)   

So my view is that if the lathe can "swing" it - then you can turn it - just needs lot's of patience.