Laser Cut Flywheels

[Sub MandrelParticipant @submandrel]

First try

[Sub MandrelParticipant @submandrel]

Today I received two laser cut flywheel, courtesy of John Stevenson. They are rather nice and very accurate. The only blemishes are a tiny groove where the laser started on the internal cut-outs and a blip on the outside where the laser ran in and out. 8mm and 10mm thick they have a dish of about 5 thou, which is not an issue – the cast flywheel one replaces was useless with over 1/4" of dish

I haven't started machining them yet and I'm aware there may be local hardening so I might need to use a carbide tool. One will simply be thinned down to 1/4" rim, ~3/16" spokes as it's to match an old plate. The other is for Lady Stephanie, and rather than copying the original I will use my imagination a bit.

I will make a photographic records of how I get on, but my impression is that this is a viable alternative to castings, as long as the shape is appropriate in my case the original has square section spokes and rim).

Neil

[JasonBModerator @jasonb]

I'll be interested to see how you get on with them. I've been drawing up a 10" one for my E&A and was thinking of doing it as a spoked "cog" to get the baring holes and then two additional flat rings to make up the rim.

[Ian PParticipant @ianp]

Neil

What material are the parts you have had cut?

Ian

[Russell EberhardtParticipant @russelleberhardt48058]

How does the cost compare to casting?

Russell

[Sub MandrelParticipant @submandrel]

Not sure the exact material spec – looks like standard blue-grey mild steel plate. Cost was comparable to casting, but without the having to make a pattern.

Neil

[Ian PParticipant @ianp]

I have had numerous parts laser cut in stainless and MS. The MS was '43A' grade.

Not particularly by choice its just their standard material, I think I have heard that it made specifically for laser cutting, it bends and welds well, machines on the lathe to a beautiful finish, it looks like Chrome plated!

Probably not high tensile though.

Ian

 

Edited By Ian Phillips on 17/11/2012 20:21:54

Edited By Ian Phillips on 17/11/2012 20:22:35

[Sub MandrelParticipant @submandrel]

I have already discovered an interesting difference from cast iron – the steel sings like a bell no more like a tuning fork! Even with the hub gripped in the 3 jaw (it's a big hub) a light tap on the rim and it will ring for ten seconds or more!

The obvious thing following from this is chatter giving a fine surface pattern (like the old embossed silver paper ciggies used to come in, but finer) when I tried to thin down the rim. I think I will have to do everything on the faceplate, to damp the vibrations. The heat discoloured parts of the metal don't seem to be hardened, at least not enough to blunt HSS.

Unfortunately feeling a bit under the weather today (and it's my birthday!) so Maybe tomorrow to have another try.

Neil

[Sub MandrelParticipant @submandrel]

I've just finished machining the thinner flywheel. It did blunt my HSS tangential tool very fast

I used TCT tipped tools, but they have a small tip radius, so ths finish is not perfect (better than a casting though!) except the outer rim which came out perfect straight away on self-act.

Procedure:

Mount inside outside jaws and skim outside of rim.

Reduce width of rim by 50% of overall reduction.

Avoiding jaws remove some metal on spokes inside rim and around boss.

Drill and bore boss to tight push fit on crankshaft.

Turn around in chuck and finish thining rim.

Again remove some metal from spokes to mark inside of rim and outside of boss.

Mount on an expanding stub mandrel.

With top slide set to about 89 degrees taper spokes (required a two stage cut as the topslide handle interfered with the cross-slide index)

Reverse and repeat

Deburr using deburring tool, except around outside of rim (use emery cloth).

Neil

As received:

Pip where laser ran in and out:

Mock up of engine:

Close up of machined flywheel:

[David ColwillParticipant @davidcolwill19261]

Happy Birthday for yesterday!

Edited By David Colwill on 19/11/2012 08:10:58

[Jeff DaymanParticipant @jeffdayman43397]

Happy Birthday Neil, and nice job on the flywheel, looks great.

JD

[Sub MandrelParticipant @submandrel]

Thanks guys,

I just went over the spokes and the inside of the rim (i.e. what would have been the 'cast' surfaces) with a rotary tool and a 10mm sanding drum. Gave an excellent finish for these areas, but the sparks were big and bushy (most like the mangnese steel drawing in Tubal Cain's book), so i think it must be a fairly high-carbon steel. No wonder it took a bit of machining!

Neil

[Stewart HartParticipant @stewarthart90345]

Hi Neil

Just read this through very intersting I was pondering the posibilities of making a fly wheel this way. Just about to start making the fly wheel for the Dake engine, this is going to be fabricated from tube and plate quite a bit of maching required to generate the forks.

Just an obeservation about the bell ringing when boring out, an old time trick was to stick a lump of plastersine to the boring bar this changes its natural frequency and stops the ringing.

Stew

[colin hawesParticipant @colinhawes85982]

Perhaps annealing/stress relieving would reduce/eliminate the vibration problem? Colin

[Sub MandrelParticipant @submandrel]

Hi Colin,

Annealing might also make it easier to machine, but I fear causing distortion.

Neil

[Sub MandrelParticipant @submandrel]

Hi Colin,

Thinking that I wanted to do rather more fancy work on the 'Lady Stephanie' flywheel, including reducing the boss, I've changed my mind! Drilling six holes for where the spokes will meet the smaller boss made me realise just how tough the steel was, and sawing one of the remaining triangle out and filling flush convinced me this must be semi-hardened steel.

I heated the wheel up to a dull red using a propane torch. To concentrate the heat and make it more even I put it on a skamolex block. I preheated it evenly until a few bits started to get red, but I didn't want to distort it by having big temperature differences. I made a 'roof' of skamolex bits. This worked almost like a muffle furnace (although I pointed the flame inside) and I got a nice even dull red, and was able to hold this for 5-10 minutes. I then tapped the roof so it collapsed and put a stainless stell dog dish over the top as a lid.

I left it to cool for an hour – it still rang, but an octave lower. I was able to machine it all over using HSS, even using a 3/32" wide parting tool to make a recessed 3/16" wide groove 1/32 deep in each side of the rim. I was amazed to see a continuous ribbon of swarf from the parting tool at nearly 6" diameter.

The one hard spot, as you might expect was dead in the middle of the boss – probably it didn't get hot enough – it was hard going drilling through and the final reaming didn't give quite as perfect a finish as I wanted. At 1/4" it's too small to bore, but this could be blessing in disguise as it looks like it's reamed undersize, a force fit on 1/4 silver steel which will help ensure I don't suffer wobbly wheel syndrome.

So you were right, and there wasn't any noticeable distortion – I think the steel plate must have been heat treated to harden and temper it and so free from locked up stress. I wonder what stype of steel it was?

Neil

[Ian PParticipant @ianp]

Neil

Why dont you ask the supplier what steel it was laser cut from?

I am surprised that the steel is so tough, but thats going on my experience of laser cutting. I have sometimes found that where the cuts starts of finishes there is a slightly hard spot and it pays to take a proper cut rather than letting the cutter rub.

The steel the people I use is A43 grade, (I am not sure of the full number but it includes '43'

Ian

[Sub MandrelParticipant @submandrel]

Hi ian,

My job piggybacked on another job, so I didn't get a chioice of material -it was by way of an experiment.

Neil

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