Large Flywheels

[Jo]

I centred partly on the inner rim of the flywheel but also on the two other ridges and found a happy medium between the two.

Another 2mm off the flywheels and I still have bits of casting showing and that around that area it is a little harder than the machined surface:



The other side is still showing the casting mark and this is a bit deeper:




Finally having removed the casting marks from the outside area you can see it is still slightly hard:




The other side is looking better:



Finally after taking 6mm off the outside of the rim I am going to stop with only this slight mark showing:




Ignoring the temptation to smooth off the first of the inside curves it is time to bore for the crankshaft. Start by finding a suitable piece of bar to use as a plug gauge:

 

As you can see this piece of 3/4" bar is not 19.05mm diameter, clearly someone was sold 19mm bar when they asked for some more mature material 

Back to boring the hole: I started by drilling a small hole through from the tailstock. When the lathe is doing 85rpm it takes a long time to drill a small hole 



But drilling becomes much quicker as the sizes go up:



Now I need to bore the hole  so that it is a nice snug fit on the plug gauge. What this needs is a long thin boring bar which is small enough to go through the hole (17.5mm). I have a 16mm diameter bar but the two tee bolts are sticking too far out to be able to use my boring bar held directly in a tool holder on the tool post, without some dreadful flexing  .

So time to support the bar by finding one of my DA tool holders to hold the boring bar in, then hold the DA tool holder in the toolpost holder:



Having checked that the tool can go all the way through without anything hitting  We come to the boring part   



At this point I decided best not finish it today and risk rushing it but leave it until tomorrow when there is less chance of making mistakes 

Jo

[Jasonb]

Graham, is this flywheel much larger in diameter than the 11" one shown on the retlas drawings?

Jo what was the reason you had to drill at such a slow speed? that may have been what you chose for the rim but would have thought you could wind up the wick for drilling and boring as clamping looks reasonably well balanced.

[Roger B]

Discretion is the better part of valour. I think I would have done the same with an unknown casting 

[Jasonb]

I thought all castings were a bit of an unknown as you can't really tell what's going on inside until you cut into them

Then again I do tend to turn my flywheels quite fast, usually around 250m/min but make sure they are held securely

[Alyn Foundry]

Graham, is this flywheel much larger in diameter than the 11" one shown on the retlas drawings?

Jo what was the reason you had to drill at such a slow speed? that may have been what you chose for the rim but would have thought you could wind up the wick for drilling and boring as clamping looks reasonably well balanced.

Hi Jason.
Just a smidgen, 1/4" to be exact. but one heck of a lot heavier, weighing in at just under 8Kg.

Judging by Jo's photos I'm hoping there weren't any " hidden extras "  supplied.   

I too run at much greater speed when at the hub. If nothings moved whilst doing the rim then I assume we're tight enough to go.

Cheers Graham.

[Jo]

Then again I do tend to turn my flywheels quite fast, usually around 250m/min but make sure they are held securely

I would like to see you try mounting that flywheel on your lathe and spin it at that speed. I reckon when you turned it on it would take a large lump out of its bed   

Jo

[Roger B]

I did some calculations a while ago on maximum speeds for cast iron flywheels they are actually quite low I will have to look them up.

[Jasonb]

Then again I do tend to turn my flywheels quite fast, usually around 250m/min but make sure they are held securely

I would like to see you try mounting that flywheel on your lathe and spin it at that speed. I reckon when you turned it on it would take a large lump out of its bed   

Jo

Well I've happily turned 10.75" ones at 250rpm (215m/min) that's cutting speed at the rim, faster for the hole , Though they were a bit lighter I was limited by the fact they had cast in balance weights. However as I did it with the 4-jaw griping inside the rim all up weight probably not far off.

The Allman is just under 7kg and 10.5" dia that was done at 300rpm again with the 4 jaw weight and that's almost spot on 250m/min cutting speed

I'd actually need to cut a hole in the bed BEFORE turning it on as 11" is my max diameter

Roger, tip maker's data gives 140-380m/min for CI so I'm about mid range. https://www.shop-apt.co.uk/carbide-inserts-for-turning-carbon-alloy-steel-general-use/ccmt-09t304-mpn-pc15-carbide-inserts-for-turning-cvd-coated-for-steel.html

[jadge]

For a 4ft flywheel with a tangential rim speed of 6600ft/min the rotation speed is 525rpm. So I don't think speed is likely to be a problem for the smaller flywheels being discussed.

I initially turned the OD of my flywheel at 85rpm, but that proved a bit sporty for the boring bar, so I dropped to 40rpm with a feed of 8 thou per rev and depth of cut of 40 thou. The hub was drilled and bored at 180rpm, again 8 thou per rev, for the boring and turning.

Andrew

[kvom]

That's about the same size as on my Greene engine. Casting was bigger to start.

[Jo]

I'd actually need to cut a hole in the bed BEFORE turning it on as 11" is my max diameter

Exactly: if you mounted it on your faceplate it would hit the bed on the first rotation. As they say: size matters  It is in industry where speed matters at home we can take our time and do things less stressful.

Graham expressed concern over potential casting problems so I took account of his concerns in choosing to turn at 85 RPM. In fact the casting has proven to be very nice and of good quality

Jo

[Jasonb]

It is in industry where speed matters at home we can take our time and do things less stressful.

I've long been an advocate of faster can be better in some situations and said it many times, if you missed it this is my reasoning.

Those with variable speed hobby lathes will know that the torque drops off as speed is reduced and this becomes even worse as the diameter of the part increases. It is for this reason that using carbide and running the lathe faster than the "lowest backgear" favored by the old Myford stalwerts method is a far better option as it allows the motor to run at a better speed not only increasing torque but also increasing airflow from the inbuilt fan which saves the motor getting too hot which it would running dead slow under a lot of load and maybe even getting stalled.

The feed and DOC also need to be somewhat lighter (compared to Andrew's figures) due to the reduced torque and general lighter build of machine, I would be looking at a max DIOC of 0.25" (0.6mm) and a feed of 0.0025" ( 0.06mm) /rev. on a 9-10" flywheel.

Hopefully from this you can see that the job will not actually be done any faster as although my work may be moving faster it will need more passes. But the tool will be cutting within it's parameters and motor not getting stressed.

Just had a count up and having now done 34 cast iron flywheels of various sizes I'm happy that my methods work on the type of machines many hobby users have and would suggest they give it a try and also run faster when drilling the hole.

[Jo]

Those with variable speed hobby lathes will know that the torque drops off as speed is reduced and this becomes even worse as the diameter of the part increases.  It is for this reason that using carbide and running the lathe faster than the "lowest backgear" favored by the old Myford stalwerts method is a far better option as it allows the motor to run at a better speed not only increasing torque but also increasing airflow from the inbuilt fan which saves the motor getting too hot which it would running dead slow under a lot of load and maybe even getting stalled.

Big C is a British made quality industrial lathe with a geared head so lower speed = more torque, same motor speed.

Jo

[Jasonb]

I know that and did not query your turning speed but that is the reason why the same methods of machining don't work well on the imported hobby machines

J

PS Missed three flywheels of the count should have been 37

[jadge]

Those with variable speed hobby lathes will know that the torque drops off as speed is reduced and this becomes even worse as the diameter of the part increases.

And they'd be wrong. In general as the speed is decreased the torque stays constant. However, since the speed is decreasing the power also decreases in proportion. Torque does not vary with work diameter, although the tangential force available, and hence cutting force, does. With an old school belt or geared head as the speed decreases the torque increases, keeping the power constant.

Andrew