Edwards Radial 5 build thread --- PHOTOS!

[JRaut]

Welp, I expected to have a new post ready by now with my pistons and rings finished. But instead I added another chunk of stock to my 'learning opportunities' pile.

The pistons are finish (teaser photo below) but I intend to write a more detailed post on making those only after I finish the rings.


The cast iron rings is where I got hung up this time. The drawings have a nice detailed instruction inset on exactly how to make the rings. Basically goes like this:
(1) rough turn and bore a cast iron tube about 3" or so long;
(2) slot it full length;
(3) clamp the slot closed on the lathe;
(4) finish turn and bore;
(5) slip a 'parting cap' onto the end;
(6) part off one of the rings to the correct length; and
(7) repeat steps 5 and 6 until you've got enough rings.


Well, when I made my parting cap, I made it a couple thousandths undersized on accident so it wouldn't fit over the finished OD of the cast iron tube. I thought: **what the heck, what could go wrong?** and tried to part off the first ring anyway, without using the parting cap.

I found out exactly what could go wrong. See, I reckoned the main purpose of the parting cap was to catch the ring as the parting operation was finishing up. I failed to recognize the importance of keeping the ring gap closed each time the slit comes around and snags on the parting tool. Combine that with brittle cast iron, and the results oughtn't be all that surprising.


Anyway, I'm currently in the process of re-making the rings. If all goes well, I should be posting again in the next couple days describing the piston and ring construction.

 

[ErichKeane]

That is a really cool way to make rings! I only had a single ring to make, but my plans had me cut the slot after parting the ring (I used side cutters), then 'expand' the ring by applying heat. I thought it was a hinky way of making a ring at the time, and even more so now that I see that! Thats really clever.

 

[JRaut]

That is a really cool way to make rings! I only had a single ring to make, but my plans had me cut the slot after parting the ring (I used side cutters), then 'expand' the ring by applying heat. I thought it was a hinky way of making a ring at the time, and even more so now that I see that! Thats really clever.

Your way is the way I've seen/done it in the past, too.

I'd never seen this method of doing it either and was similarly struck by how clever it is; I think I'll use this method from here on out, assuming it works... I think I'll find out tonight after work. I've re-made the CI tube and parting cap, just need to let'er rip and start slabbing off rings.

 

[Flyinfool]

Those oil rings look like a PITA to make.

Are you going to make some extra rings while you are set up, just in case you snap a few getting them on the pistons?

 

[JRaut]

I plan on doing the heavy lifting for machining the oil rings using a rotary table on my mill. It may look ugly on the print, but I think it'll be quite manageable. We'll see.

And I absolutely do plan to make extra rings. I've got enough material on hand for a couple screw ups, plus at least 4 extra compression rings and at least 2 extra oil rings. I'll make as many extra as I can. Making a single ring if I snap one too many would be a pain.

 

[JRaut]

Success! The compression rings came out perfect once I learned how to follow directions...


(Cast iron makes for some dirty hands.)

Next up will be the oil rings. Similar to the compression rings, but a fair bit more complex.

And again, I'll write up the next 'official' detailed post describing how I made the pistons and rings once I get the oil rings done. So hang tight.

 

[rogerl]

My dad built a 4 cylinder opposed engine years ago. The instructions for his motor called for machining the tube for the ring and then parting it off. Then you took the ring in your fingers and cracked one side of the ring to make the gap. Then you opened up the ring put a small block of a specified size in the gap and then put them in the oven to heat treat them. My dad make extras because he broke a few cracking the and putting them on the pistons.

Roger L

 

[petertha]

RogerL what you've described is often referred to as the Trimble method. It was described in a magazine called Strictly IC. One can still get back issues. Many successful model engines have used this method. I wrote a spreadsheet that mimics the calculations. There has been subsequent writings since it was popularized but I believe the only challenge was the 'set' temperature. Some feel Trimble's assumption was not quite correct.

Just to clarify. Once the annular ring is turned meaning finished ID, OD and thickness, it is 'cleaved or broken clean if you will (as opposed to gapped which is taken to mean remove extra material). The ring is then placed on a jig with the open end straddling a specifically sized dowel pin & heat set. This isn't the only way to make rings but from what I've gathered, a very good way. Also of note, I measured as many RC 4S engine rings as I could get my hands on & they are very close to this open dimension.

 

[JRaut]

Thanks for sharing, @petertha.

I've made a few rings using the Trimble method in the past.

But now that I know about the method described in the drawings for the Edwards 5, I'm not sure I'll ever make a ring any other way.

This method takes no guess/check. No estimation. No calibration. No calculation. Fewer worries about snapping it during manufacture. And perhaps best of all, no heat treating.

And the results are (I think) the same: a well-sprung piston ring which is perfectly round when fully compressed. The 'gap' is essentially zero for both methods, and in both methods that gap can be increased with a few strokes of a file.

(Also, I successfully made a few of the oil rings last night. Easy as pie. Well, almost.)

 

[macardoso]

Very impressive work - keep it up!