PMR 7 Twin Cylinder Steam Engine

[AOG]

Zee, I have a suggestion. Try trueing up the inside face of the rim. Then flip the part and expand the chuck to grip the face you trued up. You get a much better grip. After you have rough cut the rim, go back to gripping on the shaft and do some light cuts to make it run true to the shaft.

Tony

[crueby]

Tony's suggestion is a good one. Another way to go, especially if the shaft hole is large enough, is to make an arbor with a step to fit the hole, and a center screw and thick washer to squeeze it onto the hub, like a circular saw arbor.

[zeeprogrammer]

Thanks Tony and Chris.

In preparation for my next question  ...

One concern was having the flywheel too close to the chuck in order to face the rim.
Another concern was the shaft hole is 1/4" and the rod would be sticking fairly far from the chuck. (Hence the live center.)

The rim is 'domed'.

I have two approaches. Both involve cutting with the compound set at 5 degrees.

1) Cut from the nearest edge to just past the center line of the rim. Flip the flywheel. Cut from the nearest edge to the center.
2) Cut from the furthest edge to just past the center line of the rim. Set compound to -5 degrees. Cut from nearest edge to the center.

For the 1st approach, I suppose I could cut from the furthest edge each time.
For the 2nd approach, it shouldn't matter which edge I start with.

Does it matter?

[Jasonb]

I've never machined a flywheel with it on a bit of rod.

If it were me I would get the 4 jaw out then by the looks of it* you should just be able to hold by the inside of the rim with the jaws reversed, set it so that the inside of the rim runs as true as possible. In this position you can face one side, turn the diameter and add any tapers cutting towards the chuck, then face the hub followed by drilling and then boring use the crank material as your plug gauge once you get close to size.

Now flip it around and face the other side of the rim and hub.

* if you can't get the jaws inside then hold by the outside with minimal jaw engagement so you can still turn most of the diameter. Also if the part is cast fairly true you could use the 3-jaw to hold by the inside.

[Gas_mantle]

Carl

I was having similar trouble machining flywheels a couple of years ago when I bought my first lathe.

The method I use seems to work well for wheels up to about 6", I'm not saying it is the best way but it may be worth considering.

1) Hold the casting in the chuck by the inside rim if you can and try to leave the rim clear of the jaws to allow machining of the full width. If you can't hold by the inside then the outside will do but leave as much of the width clear for machining as you can.

2)Do all the machining necessary to the side (face the rim, turn the hub etc)

3)Start turning the outside of the rim (If the cut is intermittent and the hold you have in the chuck isn't great go gently), Depending how you mounted it in the chuck you may be able to turn the full width but if not turn as much as you can. Don't worry too much about the finish yet but turn till you are slightly above the finished diameter you want and past the intermittent cut stage.

4) Once you are happy the outer rim is running true to the hub etc (nothing has shifted in the chuck) then drill and ream the centre hole to the finished size. Check everything is still running true before removing from the chuck.

5) With a piece of round stock in the chuck turn a very close fitting mandrel to locate in the wheel centre hole. Don't be tempted to use a bar of the right size and centre it - it needs to be turned so it is accurate to the lathe centre line.

6) Don't remove the mandrel from the lathe. Once you are happy the wheel fits closely with no wobble you can Loctite it in place with the unmachined side outermost. I use 638 and find it gives a solid bond easily strong enough for the job in hand

7) Leave the Loctite to cure for a few hours, using a dial indicator you should find the rim runs true. Now turn your side details, the hub etc (use a tailstock centre if you can). Although the Loctite is strong take it easy, the last thing you need is for it to break away now.

8 The final job now is just to lightly skim the outside of the rim - if you took care a stage 3 you should only have a few fine cuts to take to true it up an get a good finish.

9) Once satisfied with the result remove from the chuck then use a heat source to break the bond (on a small piece you may find something like a spirit burner flame with a gentle heat will do it )


Peter

[kvom]

I attended a small machine/product show a couple of weeks ago and talked to a Loctite guy.  I generally have been using 620 (green) and was interested in the difference with 638 that a lot on here use.  It seems they're pretty similar except for the cure time.

[Jo]

I attended a small machine/product show a couple of weeks ago and talked to a Loctite guy.  I generally have been using 620 (green) and was interested in the difference with 638 that a lot on here use.  It seems they're pretty similar except for the cure time.

620 is four times as viscose as 638 = it is thicker

620 takes 20 times as long to do its initial "stick" on steel (80mins vs 4 mins)

620 is not contaminant/oil tolerant and only comes in 250ml bottles... 638 also works on passive metals like Stainless.


I also have 601 which is even runnier.

Jo

[zeeprogrammer]

Jason and Peter...thanks for the very detailed posts. Very helpful. I probably should have considered this before I had drilled/reamed for the crankshaft. I think the 3-jaw is probably out of the question. It would result in the rim not running true to the shaft. The 4-jaw would be better, particularly for keeping the rim true to the shaft, but I think my skill level would still result in an unsatisfactory result. I also wonder what the consequences are if I can't keep the shaft perfectly straight to the lathe.

I was following the process Dean had used. I'm not sure why he did it this way rather than what you all described. Perhaps some limitation in his equipment?

At this point I'll continue with what I was attempting. All I have left is the rim (and Jason's picture answered one of my questions). However, I may chuck the flywheel up and rough cut the rim. This would reduce the interrupted cut due to the bit of sprue sticking out. I should have done this before doing the crankshaft hole.

Thanks kvom and Jo for the additional information on the Loctite.

[Jasonb]

620 is not contaminant/oil tolerant and only comes in 250ml bottles.. 

And 50mls and 36mls 


Zee, as you have the hole you could try making the arbor as Peter suggests, it will be more solid than a length of rod.
642 is the one I usually reach for.

[zeeprogrammer]

Well I went ahead and roughed out the rim. I held the flywheel by its hub, machined one half, flipped the flywheel onto the other hub, and machined the other half.
(Outer faces were already done and not touched.)
I just eyeballed the center of the rim. (I have a bad eyeball.)

Overall I'm surprised and pleased. When I spin the flywheel by hand there is very little wobble. Unsurprisingly, there's quite a bit of wobble in the center line of the rim. That would be due to flipping the flywheel and not being quite true.

The next step is to either make the mandrel or continue with my method and finish the outer rim so I have the centerline truly centered and even.
Or, the next step is to leave as is. This isn't a show model.

Attached is family pic of what I have so far.

[Jo]

And 50mls and 36mls 

Those are not in their UK catalogue... which lists 5 sizes of 638 and only one of the 620.

[Jasonb]

Zee is not in the UK either

[Jo]

The fact that 638 comes in multiple sizes is an indication that there is more demand for it and 620 is more specialised

Jo

[b.lindsey]

Very impressive Zee. That's a nice collelction of parts you have there, and the flywheel looks good as well.

Bill

[crueby]

Nice progress! 


Been waiting to say this back to you for a while,  how do you get so much done? Do you ever sleep?!