Author Topic: Ohrndorf 5 Cylinder Radial  (Read 7344 times)

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #105 on: November 01, 2021, 02:09:39 AM »
I will discuss the cylinders next. Spoiler alert – in my case it wasn’t quite a straightforward path making 5 cylinders, liners & heads as per drawings in batch mode. I first make some tester parts as per design to get an idea of what was in front of me. This highlighted a few issues where I thought some modifications might be a better way to go. But these 3 components in particular closely integrate with one another, so a design change to one part for whatever reason very likely has a direct knock-on effect to the other parts they mate. I guess we will ultimately see if my decisions were right, wrong or somewhere in between. Overall, I tried to stick to the critical dimensions.

So why the departure from the plans?  The cylinder head (to be discussed later) is really the most critical part to have nailed down first because it encompasses many features (read lots of invested machining time). The inlet & exhaust ports are comprised of a smaller diameter gas passage drilled through into the valve cage. And a larger ID counterbore segment, threaded for a steel screw-in fitting which retains the tubing into the head against the counterbore ledge. This threaded style is used in other model engines, including commercial RC engines. Because the port axis is orientated to the head at an oddball angle in top view, the threads of the retention fitting are not initially fully engaged the way they would be like a bolt enters a nut. They must first hook up to a portion of the head thread for a few turns before becoming fully engaged around the port ID. At that point, it’s only a few more turns before the fitting bottoms out, sandwiching the tubing flared end to the counterbore step. No mention was made in the plans of a seal washer at the end of the pipe which I wanted to use particularly for induction pipe, but this would further reducing the engaged thread length. In other words, the design counterbore length is kind of short IMHO. To complicate matters, the heads also have a series of radial cooling fins cut through the port area which further reduces thread contact area. I figured with heat cycles & fuel mung & vibration, it might be asking a lot of these threads. I could select a finer pitch bottoming tap, but I was trying to avoid turning oddball metric threads in my imperial lathe for the matching fittings if possible. As it turns out, some imperial threads might be better candidates. This is a very longwinded way of saying that I really wanted the head to be slightly larger diameter to get more threaded meat in port area.

I modelled the new head in CAD. Everything looked good except aesthetically the head diameter was now extending over the original cylinder top diameter, not as pretty as when they were the same diameter. I’ve seen full size radial examples of both, but I preferred the original look & it solved other issues. So, I changed the cylinder crown diameter, which then meant a different taper angle to end up the same base skirt area dimensions. I also changed the cooling fin thickness & pattern to match my grooving inserts & a more nominal inch spacing pattern. The net change helped provide a bit of cylinder meat for what were shaping up to be slightly thicker liners. More on that later.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #106 on: November 01, 2021, 02:12:51 AM »
So, with a new plan in place, on with actual cylinder making. They start out as drops of 6061-T6. I rough drilled them 7/8" in a batch mode. Then each is chucked & machined with most all features to preserve the setup. A boring bar was used to open ID to ~0.005" undersize. Then a 1.0625" reamer passed through so the ID would all be consistent diameter & finish in preparation for the liners.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #107 on: November 01, 2021, 02:15:37 AM »
Next was the bring the crown and skirt flange to finish OD & turn the taper portion

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #108 on: November 01, 2021, 02:17:19 AM »
Next was cutting the cooling fin grooves. I used a 0.043" wide Nikcole insert. They cut like a dream, just keep a bit of cutting fluid on it. Some groove depths are different. The top 3 are a bit shallower to stay clear of the threaded head bolt holes. The next 3 are limited by maximum DOC of the insert ~0.220". Then the remainder grooves are one constant base diameter which then & matches the diameter occurring above the skirt flange. All the edges were lightly chamfered using one of those HSS triangular scraper tools & cleaned up with fine 3M pad. Then parted off.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #109 on: November 01, 2021, 02:18:48 AM »
I had one of those machinable expansion arbor blanks handy, so turned the main portion to match the cylinder ID with the bolt lightly engaged & also a raised step datum surface for the cylinder top to rest against. With the cylinder lightly gripped I could face the bottom flange & bring the cylinder to final length.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #110 on: November 01, 2021, 02:20:50 AM »
Next, I turned a spacer collar so the chuck jaws could grip the head portion, because at this point the skirt flange is a larger diameter. Using a rotary table, drill & tap the 5 x M3 holes for the head bolts. These holes were then utilized to attach a rectangular fixture plate. The assembly was held in a vise so the flange could be drilled for clearance bolt holes & milled to the rectangular profile. I have a choice to use SHCS, or threaded studs in the crankcase with topside nuts on the flange.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #111 on: November 01, 2021, 02:22:13 AM »
Partial assembly pics. BTW, the liners will extend through the cylinders bottoms and that portion is what mates the matching hole in the crankcase 

Offline Don1966

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Re: Ohrndorf 5 Cylinder Radial
« Reply #112 on: November 01, 2021, 04:34:49 AM »
Oh wow! A whole lot of things going on in this thread. That’s a very interesting build……. :Love:



Don

Offline Admiral_dk

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Re: Ohrndorf 5 Cylinder Radial
« Reply #113 on: November 01, 2021, 11:09:32 AM »
So now we can see a 'Round Engine' appearing  :praise2:

Offline Zephyrin

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Re: Ohrndorf 5 Cylinder Radial
« Reply #114 on: November 01, 2021, 11:17:30 AM »
this is a great build, very informative, thanks to share this...

on the new design of the cylinder head, I wonder how the threaded fitting will be inserted, as the extremity of the pipe is enlarged in the head and bent in the other extremity, which may hinder the insertion of the threaded ring ?

Offline Craig DeShong

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Re: Ohrndorf 5 Cylinder Radial
« Reply #115 on: November 01, 2021, 01:20:17 PM »
Great work.  :ThumbsUp:

Love the machinable expansion arbor blank, had never seen one used before.
Craig
The destination motivates us toward excellence, the journey entertains us, and along the way we meet so many interesting people.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #116 on: November 01, 2021, 06:37:00 PM »
on the new design of the cylinder head, I wonder how the threaded fitting will be inserted, as the extremity of the pipe is enlarged in the head and bent in the other extremity, which may hinder the insertion of the threaded ring ?

You will see some actual parts pretty soon as I continue to post pictures. But yes, it is a rather delicate balance of accommodating the flared or trumpet shaped tubing end inside the threaded port. Then the threaded fitting must be able to slide over the tubing bend radius. Therefore the fitting length + ID + chamfer must all be sized accordingly. Threaded ports seem straightforward just looking at them, but actually there are a few things going on behind the scenes. Personally I don't care for them much. Next engine I will do what it takes to have bolted flanged tubes. I spent quite bit of time in CAD to see if I could modify the existing design for this, but it got to be a deeper & deeper rabbit hole. Next engine I will mill the outer head profile in rotary table (as opposed to turn it round in the lathe) so that an extending boss for the port can be integrated. Then the fins would also have to be milled on a rotary table.

Offline petertha

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Re: Ohrndorf 5 Cylinder Radial
« Reply #117 on: November 01, 2021, 06:59:45 PM »
Great work.  :ThumbsUp:
Love the machinable expansion arbor blank, had never seen one used before.

Thanks. I was lusting over some expanding ID collets but they are spendy. At least in 5C which i would prefer because I have a set-tru chuck. Other systems you are relying on runout or need to chuck in 4J to dial in. (I'm talking hardened non-machinable collets here of course). The nice thing about the pre-slit blanks is they are turned in-situ prior to mounting work so should be very close to concentric. I have since made a few blanks with a single slit just to see if they can be replicated in the home shop less expensively. They work 'ok'. Ideally they should be turned quite close to ID because a single slit requires more screw torque to open the beak. Maybe a better plan is drill a larger hole traversing the end of the slit. The commercial one is steel with more slits. Theoretically you can keep turning it down for successively smaller jobs.

Online crueby

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Re: Ohrndorf 5 Cylinder Radial
« Reply #118 on: November 01, 2021, 07:03:41 PM »
I've made several expanding arbors, drilled/tapped for the screw, counterbored and tapered slightly the end of the hole for the screw head (which was also tapered). Sawed in two slots 90 from each other so it expands out better. Works quite well, used that setup for eccentric followers and such. As you say, you want the OD turned to a close fit on the bore of the part you are holding.
 :popcorn: :popcorn: :popcorn:

Offline bent

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Re: Ohrndorf 5 Cylinder Radial
« Reply #119 on: November 02, 2021, 08:01:08 PM »
Neat work. :popcorn: