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View Full Version : PM Research #1 - Flywheel Casting - Machining Advice Needed



RoyG
12-27-2016, 10:07 PM
Greetings,

I've recently started machining a set of castings for PM Research's #1 Steam Engine. The Flywheel on this engine is 6.75 inches in diameter (and roughly 0.5 inch wide at the rim), and it is posing a challenge for me to work out how best to safely hold the flywheel casting for machining. The two flywheel castings that I've machined in the past have been small enough to be able to be held safely using expanding jaws in my 100mm (4 inch) 4 Jaw Chuck. But, this flywheel, at 6.75 inches, if far too big for my 4 jaw chuck. Even if I did have a larger four jaw chuck (say a 6 inch one), I think that I'd still have problems holding the casting due to the casting having five spokes. My lathe can swing up to 8.5 inches diameter, so if I can devise a suitable work holding method, my lathe will be able to do the job.

http://i724.photobucket.com/albums/ww247/Bocean/PM%20Research%201B1%20-%20Flywheel%20Casting%20-%20Ruler_zpsv8rdaddh.jpg (http://s724.photobucket.com/user/Bocean/media/PM%20Research%201B1%20-%20Flywheel%20Casting%20-%20Ruler_zpsv8rdaddh.jpg.html)

So, I'm looking for advice regarding how best to go about holding and machining this casting - safely. So far I've come up with two possible ways of machining this casting, but both of my ideas so far don't look like they would allow me to successfully complete the machining.

Option 1: I've considered mounting the casting on a lathe faceplate (yet to be made) for machining, but as a lot of shim material would be required between the casting and the faceplate to get the casting running true, I'm worried that when the lathe is running, the shim stock could come loose.... Plus, this method poses challenges maintaining concentricity when the casting is turned over to machine the second side. So, this option is possibly not the best available.

Option 2: Mount the casting on an arbour, and machine it between centres in the lathe. This is my preferred method at the moment, BUT I have some reservations. This option would involve drilling and reaming the centre hole (0.375 inch") and facing the two faces of the flywheel's hub, on the milling machine. My concern with this option is whether an arbour that is cut down to 0.375 inch diameter to fit in the casting, will be stiff enough when held between centres to allow successful machining of the casting.

So, any suggestions regarding how to go about machining this flywheel casting - safely ?

Many thanks,

RoyG

Manufacturer of finest quality swarf.

wierdscience
12-27-2016, 10:17 PM
I could explain it,but Myfordboy has done a video that includes the process-

https://www.youtube.com/watch?v=wRohxIEDYeY

He is using a faceplate with a chunk of MDF board screwed on and faced off IIRC. It's a fairly straight forward process and if you want to stabilize the mounting,get the flywheel mounted and running true,then stop the lathe and add some hot melt glue between the inside of the rim and the faceplate.

Your flywheel being cast iron,the biggest hurdle you may have is getting your lathe to turn slow enough to make a cut on the rim without burning up tools.

jtrain
12-28-2016, 12:12 AM
I mounted mine on a faceplate and clamped it on the inside rim.

J Tiers
12-28-2016, 12:58 AM
There is no law that says the arbor must be LONG.

All it has to do is be sized right for the bore, so there is no looseness and wobble. It can be just a couple inches long, which should be fine There is more trouble however, in holdimg the wheel for torque, it has 5 spokes, so a 3 jaw chuck may not fit through to drive it via a jaw against a spoke.

The great part about a faceplate is

1) You hold it with alignment by a large diameter, so the error off perfectly perpendicular to the spindle is small for initial setup, even with the rough finish.

2) You can machine the rim, hub face, and bore at one setting, so you guarantee concentricity as well as any method.

3) There is normally no problem with torque, the clamping should hold it fine. Clamp against the inside rim, away from machined surfaces.

Tricky part is getting it concentric to start with, but that is not too bad. I'd watch the hub and especially the inside of the rim, that won't get machined and needs to run visibly true.

BCRider
12-28-2016, 02:54 AM
Using a disc of plywood or MDF as shown in the Myfordboy video is a really nice way to hold the raw casting. And if you're worried about shims flying loose you can run some screws through the plywood to act as jacking pads. But really you shouldn't need that.

The beauty of the plywood or MDF or other wood sheet is that you can even shape the wood easily to provide whatever level of support you wish on which ever parts.

ammcoman2
12-28-2016, 08:37 AM
When I built the same model I used this method of fixing the flywheel to a faceplate - my independent 3 jaw chuck.
http://i56.photobucket.com/albums/g189/ammcoman2/PA060001_zpsa40275xw.jpg (http://s56.photobucket.com/user/ammcoman2/media/PA060001_zpsa40275xw.jpg.html)

I made up a bunch of these holders and washers are used if more standoff is needed.

Gepff

J Tiers
12-28-2016, 09:10 AM
Your flywheel seems FAR more nicely cast. Has PMR gone that far downhill? Or did you fettle it up with a file etc first?

Mcgyver
12-28-2016, 11:26 AM
like Geoff did. its about impossible on an arbor - too flimsy a set up imo. Chatter city.

I'd roughly block it on wood, machine one edge, flip and and machine everything else metal to metal blocking - bore and turn the rim so things are nicely concentric. be careful with than first blocking....clamping can bend it then you forever have wobble - after removing the clamping it springs back. An alternative is bondo - seat when soft with a release agent (grease, Vaseline)

I agree, that casting does look very rough.

ammcoman2
12-28-2016, 06:50 PM
I can' remember how rough mine was when received - it's been a few years now.

Lots of filing, sanding and filler went into it before paint was applied but the payoff is the way it elegantly spins on the completed model.

http://i56.photobucket.com/albums/g189/ammcoman2/IMG_0453_zpsrnf6ro7v.jpg (http://s56.photobucket.com/user/ammcoman2/media/IMG_0453_zpsrnf6ro7v.jpg.html)

I purposely left the bed castings fairly rough as these engines were normally used unpainted in the oil fields - a coat of crude was the only finish they received.

Geoff

wierdscience
12-28-2016, 07:01 PM
Very Nice!

J Tiers
12-28-2016, 07:59 PM
like Geoff did. its about impossible on an arbor - too flimsy a set up imo. Chatter city.

...

While I would think it far better to use the faceplate, for many reasons, I suspect the issue of chatter with an arbor is more a matter of what sort of cut you want to take, and what the arbor is like.

If you use an arbor 200mm long and 10mm diameter, well, sure... You will get what you deserve.

But if you were to use a stub arbor of 30mm diameter, turned down at the end to accept the 10mm bore, I expect your problems with chatter would be close to non-existent.

RB211
12-28-2016, 08:10 PM
I agree, hardest part might be getting the lathe slow enough

RoyG
12-28-2016, 08:41 PM
Well, thanks very much to everyone for all the suggestions. I particularly like the "3 jaw independant chuck" idea. I've got a suitable faceplate from a previous lathe, and I've worked out how to adapt it to the current lathe, so all should be well with the machining.

As far as the finish on the raw castings - what you see in the photo is what all the castings look like before they've been touched up with files etc. I was rather disappointed with the casting finish when I first received the castings, as the quality is lower than the two previous casting sets that I've had from other suppliers in the UK and Australia. I guess there will be a pile of car body filler and elbow grease involved in preparing these castings for painting.

Regards,

RoyG