Machining of trigo wheels - Machine Shop recommendations?

[Paul Blore]

You're right about it needing to be parallel Kev, but that should be really easy to do by just mounting the wheel on its outside rim on the milling machine bed and taking the required depth off the inside mounting face.

However, thinking on it further, you're almost certainly going to need to re-cut the inside taper as well, which will need a lathe.

As you were...

[Roger King]

...which is much more of an issue. I don't know this type of wheel but if it has an inside taper, like a wire wheel, that is the area that the wheel is located by. The flat inner face is irrelevant. That taper must be milled to the correct taper and it must be uniform. It would have to be done on a lathe, and hopefully you're not talking about removing enough to affect the fit of the splines inside the hub. If the wheel is going further onto the hub than it was designed to, you will need to be sure that the spinner has enough clearance to turn further on the thread of the hub to locate the wheel firmly. If the spinner has a cap, you may need to turn the end of the hub to avoid the spinner bottoming out on the thread.

[Paul Blore]

If they're pin-drive as I believe they are, there isn't a spline Roger. Pins on the hub locate into holes in the back of the wheel. If the back of the wheel is trimmed back, then the taper will just need re-cutting by the same amount.
The 3-eared spinners don't have a cap, so they will just spin on until they meet the wheel, provided the thread doesn't run out first, but I don't think we're talking enough here for that to be an issue.

[KevinW]

Thanks for the replies.
Yes they are pin drive wheels.

The new hub (see link in OP) is the key - this brings everything inboard by the required amount, and so avoids a taper-clash. There is plenty of 'meat' on the back face of a trigo wheel that can be machined off, and that should be all that is needed; the taper isnt used in driving the wheel forward, no splines present - when i measured this up i seem to recall about a cm difference in the original geometry between the internal wheel and the external hub tapers (I assume you are referring to the 'shoulder bevel' on the hub?).

The proposed mod has been done on I believe ~200 cars now, so i am assuming that if there was something complicated needed, or poorly engineered, I hope it would already be public knowledge.

[Roger King]

As I said, I don't know this system - however, I would caution that the taper may still be the bearing surface for the inside of the wheel. If there is a spinner locating the outer end of the hub, it works axially and usually holds the wheel against an inner taper for inside location. I've never seen a combination of a flat back (like a modern wheel) and an outer spinner. There has to be a radial location where the inside of the wheel mounts to the hub - I guess the drive pins might do that, but they'd have to be a very tight fit. Drive pins or splines, makes no difference.
If you have these components now and they can be assembled pre-machining, I would strongly advise assembling them with some engineer's blue or other marking medium on what you think are the contact surfaces to ensure they are indeed that. If the taper is not the seating surface, why is it there? You will need to ensure the angle of taper is correct when re-machining.

edit - just had a look at the pic posted above of 'before and after' hubs, sorry, should have looked earlier. I am sure that taper is the seating surface, not the flat face of the hub with the pins protruding. If you effectively reduce the hub width of the wheel, I reckon you will have to remachine the taper in the back of the wheel very carefully.

[Paul Blore]

I'm with Roger on this one Kev. Make sure you know which surfaces are important. I'm pretty sure the taper on the rear of the wheel is the mating surface with the hub.

Paul

[KevinW]

Thanks Paul.
I got out the trigo adaptor and the rear wheel last night from its original box.
Hub/wheel tapered surfaces definitely do not touch.

[Paul Blore]

You're right Kevin, I checked and I meant to come back and say. The wheel is held tight against the flat of the back-plate on the hub and centred by the taper on the spinner. Which makes it all much easier of course.