And Now for the Twin

[Mike Rometer]

Oh my aching head!

Following my desire to make this as smooth a running engine as possible, I have been trying to work out the balance weights for the crank webs. It is actually quite straight forward if you are a mathematician, some thing that I will never be, while I sit down to poo!

There were many things against me from the start, perhaps I should have worn out a pencil, or three, ages ago. Probably the worst was an early miscalculation of the crank throw. causing me, in my haste to get on, to drill a crank pin in the wrong place. The correction was what caused a lot of hassle, if I hadn't turned it so far from the wrong position, I would have been able to use the angle shown on the early calcs. Of course I could have thrown it away and started again but I didn't come by the material easily, so was determined to use it.

The pic shows the final (?) thoughts, a throw width of 35mm with an angle of 67 degrees. IF I could have increased that to 80 degrees I could have lost the roundy bit in the middle with a throw width of 45mm, but I had to save weight somewhere, and that errant hole was in the way.

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I have to say I've learned a thing or six (no bad thing). In some places small things have big effects, and sometimes big things have almost no effect. Will I sleep tonight? Probably, til 03.00, then I will awake with some hair-brained idea and change it all again!

[Mike Rometer]

Beautiful work as always. Really exciting seeing the whole thing come together.

Very satisfying too Tom. Not a short term project for me, but then there are a lot of distractions. I would love to build a steel, or wood, hull for it, but that is unlikely due to space limitations. I have the technolgy, just not the 6,000,000 square inches ($ - very old TV program)!

[Mike Rometer]

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Too late now to change my mind. The bulk has been removed with the band-saw and the set up and method tried by giving a dry run-through using the laser centre/edge finder for the tool. It works! (or seems to!)

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Set up ready to go when some new cutters arrive.

[dampfspieler]

Hello Mike,

nice to see, but why you didn't span the four parts together in a vice and finish the surfaces in one step? So all parts would be equal i think.
You can use a flycutter or a milling head to get a fine surface.

---
Dietrich

[Mike Rometer]

Hello Mike,

nice to see, but why you didn't span the four parts together in a vice and finish the surfaces in one step? So all parts would be equal i think.
You can use a flycutter or a milling head to get a fine surface.

---
Dietrich

Nice thought Dietrich. Four together would be over 100mm thick. I'm not sure the mill or the set-up would be stiff enough. Plus they need to be turned over for side 2 because of lack of table travel.

[Mike Rometer]

One is now done!

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Further to Dietrich's idea, I think in the vice, the curve for the boss would be difficult with a fly-cutter, meaning they would probably need to go on the Rotary table anyway for finishing off. The raised bosses would also make them difficult to grip well. I cut this one (very carefully) in just short of half an hour, so not too bad. The slowest part was picking up the end of the boss curve to cut the weight edge (and remembering which way to wind the R/table! ).

[Mike Rometer]

Sorry Guys, no I hadn't abandoned the project, just took a few days off. Though I do have to say progress has slowed, as I'm taking greatest care not to need a re-make, and it nearly happened!

I made a drive flange and a thrust spacer and measured the shaft length and forgot to add in one web thickness. Fortunately there was enough material to just re-cut the keyway and cut off to the correct length. Small beer in the scheme of things.

Great thought has gone into the M. O. for the Crankshaft assembly, as I don't want to get into the territory of having to un-press anything "because I forgot!"

To that end the first section has been pressed together, drive end and first web.

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I fitted my best 3-jaw to the lathe and with and small addition (see pic) to the D.T.I. to clear the throw and weight, checked out this first piece.

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The next stage will be to press in the crank-pin and then drill, tap and screw in 16mm long grub-screws to lock the parts together, any other order would leave me unable to access one of the faces for drilling and tapping. Before then I checked out the run of the shaft. No chuck is perfectly true so it is important when truing a crank to know where you stand at the start. See next post.

[Mike Rometer]

Set the D.T.I to zero at Jaw No 1

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Rotate by hand and check the run-out as you turn. Mine is worst on N0 2 jaw, note 0.0015". This will be checked again at each intermediate stage as the chuck may not settle at exactly the same reading next time. The run-out here will need to be equal (as near as possible) on the centre section and the tail. I will also always re-set with the 'throw' on Jaw 1.The run-out on the face of the web is just 0.001". I'll live!

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All the parts awaiting final fettle before assembly.

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[RNoe]

Good looking progress!
RussN

[Mike Rometer]

Thanks Russ, I'd like to say it's all plain sailing (pun), but I had a hiccough this afternoon. I was drilling and tapping some of the screw-keys. I think it might have been Fred, on here, who called them "Po' boy keys". Very apt!

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and suddenly found that the shaft wouldn't pass in the hole through the centre of the drill table. I think they call that an "O. S." moment. I could get it in the mill but couldn't support it accurately, so had to remove the drill table and make a collar for the support arm. Caused a little head scratching for a few minutes.

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When I fit these I try not to use lube on the taps and never use a bottom (plug) tap, only seconds. My theory is that they grip better as the last bit of thread gets tighter which really grips the grub-screw. I also fill the hole with Loctite and hope the screw forces it into places it didn't know it had.