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Radial engine build


ptwizz
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I'm milling because I don't fancy swinging 15kg of steel 20mm off centre on my Drummond round bed. It wouldn't swing over the cross slide anyway.

I'll cut the billet to a rough approximation on the mill, then finish turn on the lathe with a fixture to set the throw and provide dummy centres.

Picking swarf out of my beard!

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  • 1 month later...

Some of the operations involved in machining the drive half of the crankshaft:

The billet had to be roughed out on the mill so that I could get it onto the lathe.

The first operation in the lathe had to be a series of facing cuts, reducing the main shaft to a diameter that would clear the lathe's cross slide.

With the mainshaft turned, the billet was mounted on a faceplate with the crankpin centre running true. Note the counterbalance bar bolted to the faceplate.

This job was just possible on my ageing lathe. All the turning was done at low speed (~300RPM) to keep distortion of the eccentric mass down to a tolerable level.

To bore the taper in the crankpin, I had to rig up a fixed steady. This uses one of the connecting rod side plates and it's bearing.

For some reason, the pictures have appeared in reverse order.

57336424c5855_2014-02-0215.45.49sml.jpg.

57336424cb974_2014-02-0818.38.15sml.jpg.

57336424d6b96_2014-02-2318.15.45sml.jpg.

57336424daf96_2014-03-0118.53.27sml.jpg.

57336424deb40_2014-03-1613.07.35sml.jpg.

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  • 2 weeks later...

I have to keep this in perspective:

I am building what is essentially a copy of a 100 year old design. I have a motorised lathe and a milling machine with digital readouts. 100 years ago, the first of this type of engine were built by men in sheds with considerably less resource than I have available. Those guys were the real heros.

The only skill I would claim credit for is patience. Everything else can be easily learned.

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  • 4 weeks later...

6kg of crankshaft assembly. Convincingly chunky.

Next - pistons. I've only made one piston for an internal combustion engine before - and that was a copy of an existing part.

For this engine, I have rejected the original four ring pistons which go with the Dnepr heads - mainly because the valve pockets are in the wrong orientation.

I have designed a slipper piston with oil control more suited to a radial, in which the pistons have to work in all orientations.

57336425395e3_2014-04-2222.09.08sml.jpg.

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  • 3 months later...

Progress has been inhibited by other stuff recently, but not halted completely.

After some investigation I've found the right material for billet machined pistons (it's Aluminium 2618A-T6511 if anyone's interested).

The first piston is turned to slightly oversize, cross bored for the gudgeon pin and then the inside machined.

The first is a test piston. To verify my design, I will make this one with an O ring groove in place of the top compression ring. This will be fitted to a simple test rig (a dummy cylinder with one end capped) and hydraulically pressurised to the predicted peak cylinder pressure (50 Bar) while the piston is prevented from moving by a support at the centre of the gudgeon pin.

I will then measure elastic distortion of the skirt areas and the pin to establish whether I need to alter the design.

573364286702e_2014-07-2614.15.39sml.jpg.

573364288bbbf_2014-07-2614.16.07sml.jpg.

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More piston machining.

The sides of the slipper skirt are milled, leaving 2.0mm wall thickness at the webs, 3.0mm around the gudgeon pin bosses.

The piston is then supported between a centre and a fixture which ensures true running, for the crown and grooves to be machined.

5733642948433_2014-08-0318.24.23sml.jpg.

573364295596c_2014-08-0321.43.09sml.jpg.

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  • 2 weeks later...

Yesterday I scrapped piston #1. :x:oops:

It's my own design and my own manufacture, so entirely my own fault. I hadn't allowed sufficient crown thickness at the location of the exhaust valve clearance pocket, so there's a hole in it now.

It's not even any good as an ashtray!

Today I will saw off another 80mm of aluminium bar and start again. :roll:

:explode:

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  • 4 weeks later...
  • 3 weeks later...

Some progress, at last.

Before starting (again) on a set of pistons, I worked out how to set up the Drummond lathe to turn the pistons (too big Ø to pass over the cross slide) without a long overhanging tool.

The new, stiffer setup allowed me to make short work of seven blanks. The finish is also considerably better than that achieved on no.1.

Provided my life doesn't get in the way too much, I should have a set of pistons before too long. Then I can get onto the really interesting bits. :D

Edit: Why do the pictures show in reverse order? I attached the lathe setup photo first.

5733642a202b4_2014-08-3020.35.26sml.jpg.

5733642a2c144_2014-09-1919.28.09sml.jpg.

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  • 2 weeks later...

Once the pistons are done, I will indeed get onto the main crankcase.

The crankcase will not be from castings, but a bolted structure consisting of a front plate, a back plate and seven 'sides'. All will be machined from 1" thick Aluminium 5083, which I have just ordered.

I had investigated the possibility of a two piece cast casing, but the design would have made for awkward assembly of the engine and I couldn't find a foundry interested in the job.

Yesterday, I machined the pockets in the undersides of two pistons. This operation takes about 3 hours per piston (and since the cockup on the first piston is quite stressful :| ).

Everything I touch is contaminated with tiny flecks of aluminium :roll:

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  • 1 month later...

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