How to cut old flywheel into gear blanks

Some time ago I posted about making new gears for a friends 1920s SB. While dumping my trash, I spotted an old flywheel at the dump, which is now in my garage. The flywheel that is, not the dump. I think. No idea what it's from, but it's about 16-18" diameter and relieved on one side. It was cast and says GM2 on it. There's easily enough material to get some gear blanks out of it, but I'm not sure how to cut it up- for me "big" parts are an inch or two in diameter. My options are my O/A torch, though I have little experience cutting anything, the big Grob bandsaw at work, but there's aren't any blades there for steel, just aluminum, my little woodworking bandsaw (probably hopeless for this), or maybe set it up on the mill and crank my way through it. I don't think I have any kind of circle cutter strong enough for this. I need 3.7" diameter by 1/2" blanks- the thin part of the flywheel is 3/4" thick, so it's close. Also, what are flywheels made out of? Though cast, this seems more like steel than cast iron. How to tell? Yes, I could buy metal, but I'm way too cheap. Ideas?

It is probably cast iron, so a cutting torch will not work well. A steel-cutting band saw is best. Second best is a 4" bi-metal hole saw run very slow in a big drill press. But watch out for hard spots.

I dragged home a nice shiny (no rust yet) truck flywheel from a recycling business (junk yard) years ago. It was big enough to carve into some nice lathe parts. It was beautiful cast iron with a ground face for the clutch facing to engage. I began to saw into it and it was easy going until I hit one of many blue spots, caused by localized heating from the clutch. Those spots were glass hard and wrecked my blade. So that thing went to the land fill.

Larry

Larry

Conrad Hoffman said:

Yes, I could buy metal, but I'm way too cheap. Ideas?

Click to expand...

Ha, well, there's a good chance you'll be money out trying to carve discs out of this thing. Certainly it's a fun project and all, but gosh, you can't beat pre-cut money-wise. FWIW, I have a hunk of 4" 1144SP that I can cut some gear blanks off of for you. Not much fun doing it that way I understand, but easy and most likely cheaper.

Regards.

Finegrain

Oh, if you can get some time on a decent-sized mill, you can cut them out with a trepanning tool on a boring head, that would probably be the quickest, and you're only out a few bucks for a HSS lathe cutter.

Regards.

Finegrain

The cheapest way to get what you want is to buy the gear blanks. But if you insist, here is my approach, given I have little knowledge of the flywheel material. It is probably mild steel. I suspect that because I have balanced and lightened many a flywheel and never had trouble removing metal. A shrunk on ring gear would reinforce this guess. With an integral ring gear, there is going to be some carbon in the steel, but ring gear teeth are usually induction hardened which localizes the hardening to the tooth area.

After layout, the fastest way to cut out the blanks is by torch or plasma cutter. This seems to raise discomfort with your skill with a torch, so you might get a quote on cuts by a journeyman.

Next, I would get an appropriate blade for the band saw at work.

Next, you could machine on the OD of the blanks with an end mill and rotary table, rotabroach, hole saw, or flycutter. If you have a robust mill and tooling this would have already occurred to you.

Next, I would drill holes around each blank layout and use one of several methods to break the metal left between the holes. The closer the holes are together, of course, the less work you have left after the drilling. A chisel or file or combination could get the job done. A saber saw would probably be faster. Maybe unskillful use of a cutting torch would be your best way to free the blanks. Or, by using your woodcutting band saw and turning the blade around backward, you could friction saw out the blanks. This latter method may not be feasible if you can't re-weld your blades once they are fed for an inside cut.

Since all of these ways are wasteful anyway, it may help to remember that you do not have to cut out round blanks. All the shaping of the blanks could be done once they are free from the flywheel, although I don't particularly like turning square stock into rounds on a lathe.

Save the flywheel for a grinder base, drill press table, lathe faceplate, etc.. Lots of good uses for a big disc of iron. Pick up gear blanks or scavenge some large round material and cut them off in slices.

I can only think of a couple scenarios where it makes sense to salvage a flywheel in this manner. One, if the gear you want to make is about 12" diameter and two, if you really don't have any other choice for whatever reason. It's likely you'll damage tooling in the process.

Hey, everything's a learning experience! This afternoon I learned about O/A cutting of cast iron- melted some metal and made lots of sparks, but just couldn't get all the way through it. If it had been steel it would have succumbed like a stick of butter. You guys (like always) have given wise advice to just buy some blanks, but I'm going to torture the band saw for a bit before I give up. Just think, if the government tried to stretch a dollar like I do, your taxes would be $.50/year. Better yet, they'd be so busy doing it, they wouldn't have time to cause trouble.

Conrad Hoffman said:

Hey, everything's a learning experience! This afternoon I learned about O/A cutting of cast iron- melted some metal and made lots of sparks, but just couldn't get all the way through it. If it had been steel it would have succumbed like a stick of butter. You guys (like always) have given wise advice to just buy some blanks, but I'm going to torture the band saw for a bit before I give up. Just think, if the government tried to stretch a dollar like I do, your taxes would be $.50/year. Better yet, they'd be so busy doing it, they wouldn't have time to cause trouble.

Click to expand...

I think you should have gone with Finegrain's advice. NOW, you have used up O/A gas, and now you are gonna have a go at it with a bandsaw. You will waste the blade and have a hunk crap to show for it.

You would already be ahead of the game if you had just bought the correct dimension stock from the get-go. Now your "cheap" endeaver will cost more than had you just done it right (Finegrain's advice) in the first place.

Try to understand, I am not trying to be rude. I do dumb things all the time because I am hard-headed. The guys on this forum give advice that is sound (for the most part). Sometimes it is best to just heed their advice.

The flywheel would be a good base for a grinder pedestal though!

Hey, the flywheel was free and can just go back to the same scrap pile where it came from if I don't get anything out of it. Gas is of no concern- I actually need to use it up faster because I change out my tanks so infrequently they sometimes go past their test date. It's a rainy Saturday and the project provides both entertainment and the opportunity to learn something about materials. Obviously if I were doing this for profit I'd take a different path, but that's not the goal here.

Since you now know it's cast iron, chain drill the blanks out. A sharp 3/8" drill will make the job go very quickly. Centre punch along the line you want to cut at 3/8" intervals and just go for it. Once you get to the end, knock the blank out with a club hammer.

Where can I buy gear blanks?

Cuchullain said:

Where can I buy gear blanks?

Click to expand...

There's really no such thing as a "gear blank," no more than there is a "pulley blank" or "axle blank." Get a slice of bar stock a bit over what you need the gear OD to be, face x 2 to get the desired thichness, turn OD to the correct size, bore a hole and broach a keyslot to suit, and that's your gear blank.

Regards.

Finegrain

Gear blank to me is a Boston or similar gear of the proper pitch and tooth count with an unbored hub, which you make to the spec you need.

conrad i know its a little bit of a drive but if you would like to bring it up to my garage we could cut your blanks. i buy new stock only when i have to. scrounging is half the fun.

Well, sometimes the fun of the journey is in the travel. And it is a learning experience.

That said, I'd be concerned that once you got the darn blanks cut, you'd blow up your gear cutters or hobs on a chill. So I'd say screw three foot pads on the thing and use it as an excellent grinder base.

Learning is learning, but a gear cutter will run from $50-300, and a hob more than that. Plus the endmills to cut it, or the inserts or tool bits to turn it.

Jim

That's definitely a concern. I'd hope that when I turn the blanks it will be obvious if they have any hard spots, at which point I'll backpedal to commercial material quite quickly.

bosleyjr said:

I'd be concerned that once you got the darn blanks cut, you'd blow up your gear cutters or hobs on a chill.

Click to expand...

Me being a frugal sort...I've chain drilled some discs from a flywheel m'self. There were a few blue spots on the face so I ground them away first with an angle grinder. The material itself machined very nicely; a fine grained cast iron. The 'wheel was off a British car and had a replaceable ring gear.

I 'spec even the cheapest of vehicle manufacturers wouldn't use crappy iron full of junk in an engine flywheel. Too much liability at stake to chance an explosion. (Unlike barbell weights.)

ps: Solid brake discs (usually on the rear) make a good source of 1/2" to 5/8" thick cast iron. Again, a nice fine grained material that machines like a dream.