Issue machining driving wheels

Hi. Need some guidance please. I am machining the driving wheels for a 5” gauge DonYoung Aspinal and encountered an issue for which I am not sure of the cause. I mounted each wheel in the independent 4 jaw with the back face outwards gripped on the tread. The 4 jaw was adjusted to give the best concentricity on the inner edge of the wheel tyre. I then turned the outer diameter to + 0.5 mm and then machined the back face to give the best axial position of the spokes. Then the centre axle hole was drilled, bored within 0.3 mm of size, then reamed. I was very careful only taking 0.25 mm cuts with a 6mm diameter insert tool. Having read lots of threads on machining wheels I decided to mount the first wheel back in the 4 jaw (my 3 jaw is not quite big enough) gripping on the turned outer diameter and with the back face against the chuck. The wheel was tapped into place against the chuck and clocked into the centre axle hole for good measure. Again taking small cuts I took off enough to clean up the front face of the tyre, I still have 2 mm to take off the front face. This is where I found a problem. I check the tyre width all round and found it is running out by .155 mm or 6 thou. So what is causing this I would have expected it to be a lot closer. I stopped at this point although the wheel is still in the chuck.

Questions:

1. Is it just bad set up by myself. If so what can I do to reduce the error?

2. Is it the chuck?

3. Is it something else?

I am seriously considering the following route. Put the face plate up. Take a skim cut across it just to ensure it is square, then mount the wheel on that and face the front features. Is that a reasonable approach?

For the tread I will use an arbour to rough nearly to size and then finish turn after the wheels have been assembled to the axles.

I machined the joy valve gear slide shaft last week. It seemed easy compared to this!

Dave

With the wheel still in the chuck as you machined it, can you get a feeler gauge to slip between the back of the wheel and the face of any of the chuck jaws? It might just be that you haven’t seated it properly or perhaps there is a burr or piece of swarf trapped.

Dave,

Try mounting your face plate and clock it up. It might not need the skim. I would seriously consider boring the wheels also at the same setting.

This is my recent experience;

I have just machined a set of driving wheels (about 4 1/2" diameter) for a locomotive called Betty. I have previously learned not to rely on my 4 jaw chuck - not completely anyway.

You could also try this - clock the jaws up - mine were 0.002" out front to back!!!! And the chuck is a high quality version. The chuck body is fine but the jaws are slightly out.

The other error I had made with previous wheels is to bore the holes similar to your method. For whatever reason, the bores can wander (hard spots maybe?).

For Betty, I drilled the holes undersize then clocked the wheels up on my face plate (having checked the faceplate runout of course) and bored them to size with a stout boring tool. I never ever liked reamers - I now hate them.

I ended up machining the Betty wheels using methods that don't appear to be anywhere near the so called words and music.

Phil H

If you get any lift of a jaw when they are tightened it could cause this. Inwards pressure at the base of the jaw and outward pressure where the jaw is in contact with the workpiece. Not being in line these two forces try to rotate the jaw. Any wear will allow this rotation. If they rotate different amounts then the back will not run true. I can't remember who it is but someone on YouTube has mounted removable pillars on the front face of his chuck between the jaws. The faces are skimmed to ensure they are running true as required then the part is mounted and tapped down onto the pillars.

You can also make a spacer that goes between the chuck face and the workpiece that is slotted for the jaws to fit in to do something similar. It was in a recent "what is it thread, I'll let the maker put a link in here for it.

Martin C

Found the YouTube video.

Edited By Martin Connelly on 26/05/2020 21:23:12

Pretty much par for the course. Doing similar I'm pleased if I have a variation in thickness of less than 3 thou. If you want to get down to a thou or so then everything needs to be scrupulously clean. Even the tiniest bit of swarf can throw things off. Also tap the work back when the jaws are reasonably tight. If you tap too early the work just hits the back of the jaw and bounces back slightly. The same effect happens when tapping down in a machine vice which isn't tight enough.

Andew

Gents

Food for thought to consider tomorrow. The chuck mod is very interesting and I may do that anyway.

Dave

If you remove the jaws from the chuck you can skim the face true. Then you can use parallels against the face of the chuck and the back of the wheel. This means you don't have to rely on the jaws being spot on. You should be able to remove te parallels before turning, failing that wire them in place.

regards Martin

Ah I see that was mentioned already. I got called away and then just posted when I got back.

Edited By Martin Kyte on 26/05/2020 22:25:57

There was also this tool in an thread that I mentioned earlier.

Chuck spacer tool

Martin C

Edited By Martin Connelly on 28/05/2020 15:29:30

Been busy. I ended up with a big block of ally on my face plate. Turned it all square and made up a removable arbour (so It becomes universal) which was final machined in place. Wheel bolted to block and roughed down to +0.5mm on final size which will be done on the assembled axles. Took a bit of time to set up, but it will also be used for machining the crank pin holes.

Thanks

Dave