# MiniRad - Elmers #23 as a 6-Cylinder Radial



## crueby (Dec 7, 2015)

Back in the metal shop after a number of woodworking projects (RC tug and submarine, carvings), and decided to make something a little different but fairly straightforward. I've always liked the #23 'Tiny' wobbler engine from Elmer Verburg, built one a number of years ago, and figured a fun variation on that theme would be a radial engine version of it. I did a little sketching, and it looks like a 6 cylinder version of it will just work at the original parts size - as long as I bevel the bottom of the cylinders a bit so there is clearance between them.

It seems like someone must have done this at some point, but so far I have not found one, other than the slightly larger 3-cylinder plan that Elmer did. I am going to stick with the original plans for the cylinder, crank, and piston designs, but rather than the original pedestal base it will mount to a disk base with the 6 engines all off of one crank pin. 

After looking at some larger radials I did in the past, it became obvious that having the piston rods attach to a disk on the crank pin as in most radials would not work at this size, for two reasons: it would need to have the cylinders slightly farther out, plus as the master pin rotates the disk, it would change the angles on the other pistons too much which would effect the valve timing (on a fixed-cylinder engine the piston shaft is pivoting in the piston end, but on a wobbler it moves the whole cylinder). So, back to using a single crank pin and will have the piston rods end in flat plates that are offset from each other along the length of the crank pin. Will show that later, as the parts come together...

So, off to the shop...
First up is to make a set of six cylinders. These are to the original Tiny plans, made out of a length of 5/16" brass square bar. Each piece was long enough to get two parts out of - that left enough length to hold in the chuck till final parting off to length. The pieces were chucked up in the 4-jaw, centered with a dial indicator, then offset to one side since the cylinder bore is offset to leave room for the pivot rod on the back of the cylinder.
The holes were center drilled,



drilled slightly undersized, 


then reamed to final dimension,


and cut off to length.



Next step was to mount the cylinder sideways in the 4-jaw, with the back side facing out, and offset so that the centerline was where the pivot rod will go. The piece was given a light surfacing pass to ensure it was nice and flat (bar had some dings in it), then a shallow recess was cut around the pivot rod location,


then the hole for the pivot rod was drilled.





At this point, the cylinders are all shaped for the functional surfaces, just need to bevel off the front/side corners.



For the bevelling step, the 4-jaw was moved over to the tilt table on the mill and the table set to about 55 degrees to do the ends of the cylinders. With the parts set in the 4-jaw using a 1/4" square bar as a guide to how far out the end projected (that way all the parts could be milled with one setup without having to readjust the cutter every time), the front and side corners were milled off the top, and just the side corners milled off the bottom (since the cylinder bore is so close to the front side). Between cuts the rotary table was cranked around to bring the next face up for cutting. With this setup it all went pretty quick.




Next, the table was lowered to a 45 degree angle, and the front sides were milled in the same manner.


At this point, the cylinders are done, ready to have the pivot posts installed. Those will be made later, once I have the back plate done and know the length they need to be (fun part about building an engine as you go!).


With that done, I turned (pun, yes) to the pistons. They were made from some 303 stainless rod. Since the shape of the end where they will attach to the crank pin is different on each one, I am going to make up the pistons and rods as one piece, and add the connecting part later - this is the first place where I am deviating from Elmer's plans. With the rod chucked up in the lathe, the piston rod end was turned down to size, and the sides of the pistons themselves got a light cut to get a good fit in the cylinders, plus some oil grooves.


Last two photos show the parts so far....




Next up will be to cut the disk for the backplate - will be using a big chunk of 303 stainless left over from some train wheels made for an previous model (got a 3' length cheap from Yarde Metals Drop Zone as a drop cut - handy site to pick up stock).


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## xpylonracer (Dec 7, 2015)

Hi crueby

Those jpg files don't open with my system, do I have a fault or is it the files ?

Emgee


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## deverett (Dec 7, 2015)

They open OK on my system: Windows 7 + Opera 12.16

Dave
The Emerald Isle


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## crueby (Dec 7, 2015)

Pics show fine on my win7 pc in firefox and on chrome/android tablet. I uploaded them to the forum site itself, do you have images blocked for this site maybe?


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## xpylonracer (Dec 8, 2015)

Just logged in from the link and all pictures are visible, strange !!

Emgee


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## crueby (Dec 8, 2015)

With the cylinder blocks all made, time to make the backplate. This will take the place of the pedestal base on the original Tiny, and hold all 6 cylinders rather than just the one. First photo shows the sketch I made to figure out the dimensions of it. The back side has a shallow groove around it towards the middle - this will get a plate over it, and form the pressure manifold to take the air or steam supply around to each cylinder. This will eliminate needing a bunch of piping later.


So, to start, I cut a disc of 303 stainless off and trued it up. Then drilled the center hole to take the bushing for the crankshaft.


One side got bored out larger, to make room for the bearing lip and also to recess the crank disc. The crank disc is recessed to make room for stacking up the tabs that will be on the ends of the piston rods (more on that in a couple days when they get made).


With the front side done, the back side was turned down to shape.


Then, the crank disc was made by drilling the center of a rod to take the crankshaft (press fit, with some loctite red for good measure) and parting it off.


With the 3-jaw moved over to the mill, holding the crankshaft and disc vertically, the table was centered on the shaft then offset the distance for the crank pin, and the disc was drilled for the pin, which was also loctited in place.


Last up for the day was the main bearing, out of brass.


Last photos show all the parts so far arranged as they will go.




Next job will be to drill the backplate for the pivot pins and get the cylinders mounted on the plate....


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## crueby (Dec 8, 2015)

Got the pivot rods made for it now - they are very simple, just some 1/16th steel rod with a 0-80 thread at one end. The original plans from Elmer showed the end of the rod drilled for a cross pin rather than threaded, but this was much simpler (was harder to get the camera to auto-focus on such a small subject!).


With the rods threaded and cut to length, they were red-loctited into the cylinder bodies and fitted with some 0-80 steel nuts (have a bag of those so did not have to make them).




Next, put the backplate in the 3-jaw chuck on the rotary table on the mill (sounds like a nursery rhyme - The Machine That Jack Built!) to drill the pivot holes. Went round once with the center drill to spot the locations, 


then again with the drill.


Next couple photos show the assembly this far. 




Last step for this session was to wind up some spring wire - smallest ones I had on hand were ball-point pen ones, which were too big. So, just wound the wire around the length of 1/16th rod, not as even as doing it on the lathe but quick and works fine.


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## purpleknif (Dec 8, 2015)

Look very similar to the Liney 5 I finished recently.


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## crueby (Dec 8, 2015)

purpleknif said:


> Look very similar to the Liney 5 I finished recently.



This one is half the size but much much simpler than the liney 5. I built one of them several years ago, it is a nice engine, I had trouble getting the valves all working right for a while. As a wobbler this one has a tenth the parts.


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## crueby (Dec 10, 2015)

Well, it took a couple of false starts to figure out a good way to make the connectors from the piston rods to the crank pin, but got it done. Since all the conectors have to stack on the crank pin, they need to be offset from one another. To show where I am going with these parts, first I'll show a photo of 4 of the 6 done and in place, then go back to how they were made. The last two will stack above the ones in place in the photo.


Second photo is the sketch of the part dimensions.


So, to make them, a length of 1/8" x 1/4" bar stock was clamped in the mill vise with a little protruding, resting on the bottom of the vise to level the bar. Then the end was squared with the mill, that position became the zero point for measuring in for the main cut. With the mill hieght set to leave a 0.060 tounge on the piece, a cut was made 0.175" in from the end.


The mill was switched for the drill chuck, and the hole was drilled in the tounge - this hole will fit over the crank pin.


At this point, the piece was sawn off to length and the end cleaned up with a file. Once all 6 parts were made to that stage, it was time to drill the holes for the piston rods in the ends. To get them to offset properly they need to be drilled in three pairs, with first pair drilled 0.060 from the long edge, next pair 0.125 in, and the last pair 0.190 in from the long edge. The first pair will be the center two in the stack, the second pair the ones outside them, and the last pair will make the outside ones in the stack. So, with the mill vise set to 0.060 from the front jaw face, the first two were drilled.


Then the table was moved out another 0.065, and the second set drilled.


And so on - another 0.065 out to drill the last set.


With all of them drilled, they were press fit/loctite-red'ed onto the piston rods. Once dry, it was time to round the leading edges so they would clear each other at the tightest angles as the crank goes around - you can see the rounding in the first photo.

Last photo shows everything assembled and tested - spins freely. There is a lot packed into that little space! 


Next up will be to disassemble it again, and drill the cylinders and backplate for all the air passages....


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## crueby (Dec 10, 2015)

On to some easy parts, and starting on the air passages. First up was the cover plate for the air manifold. This is just a simple ring of brass, with a recess in the face to match up with the one in the backplate to carry the air around to all the cylinders. First three photos show making that part. I will go back and drill/tap for mounting screws after all the air passages are done, just to make sure I dont put a screw where a passage needs to be.






After that I made up a small brass flywheel. It is a tight push fit on the crankshaft, will only loctite it if need be so I can pull the engine apart as needed.




Next photo shows all the parts so far - getting to be quite a little pile.


Last two photos show drilling the air passages into the backplate face. The inlet holes go halfway through the plate, the exhaust ones go all the way through. I used a drilling jig like what Elmer shows in the original plans. 




On the very last exhaust hole I must not have been using enough oil, or moved the vise a little, and snapped off the tip of the drill in the hole. :wall:
A number of choice words later, I carefully drilled through from the back side till I could just hear it ticking on the broken bit, then enlarged the hole a little with a diamond tip bur in the high speed air tool (it is a very small football (american football that is!) shaped dental bur) till I could punch the remnants of the bit back out. This left a slightly larger hole on the back side, but that does not matter, only the size/position on the front matters.

The remaining steps will be to drill the air hole into the top of the cylinders using the same jig, drilling the passages to link the intake holes up to the manifold, then I can make a base and a hose connection and see if it runs! It will probably be Monday before I get back to it, the next three days have other events filling them up (dont you just hate cliffhangers?!)


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## crueby (Dec 14, 2015)

Back from the local train show over the weekend and back in the shop: I got the air passages drilled from the rim down through the intake and to the manifold ring,




and then marked out the position of the final passage from those holes to the manifold using a ruler and a drill in the hole to have something to eyeball against.


Then drilled the connecting hole. After that, plugged up the outer end of the passage at the rim.


With the passages all done, I could be sure of where to drill/tap for the mounting screws for the manifold cap.


The manifold was installed with two o-rings, one at the inner hub and one outside the air passage. The mounting screws compressed them and made a good seal.


Last step before assembly was to drill the air passage into the top of the cylinders using the same jig that was used to drill the holes in the backplate.


With it all assembled, it was time for a test run. The base is not made yet, but who can wait?! Ran pretty well right off, needs a little lapping compound between the cylinders and the backplate to polish up that joint and get rid of some slight air leaks, but sounds like an angry beehive, not much vibration at all. 
Here is the video:
https://www.youtube.com/watch?v=FzeX3qdQUUA&feature=youtu.be


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## crueby (Dec 20, 2015)

All right - finally done! Finishing off this engine turned into one of those 1-week-and-30-minute jobs....

Got the base for it made, a simple cone section of brass with a post screwed into it, and got some pictures/videos taken. It runs great, down to a slow speed (hard to adjust the pressure with the knob on the compressor). Here are some pics of it done, and some video too....

Chris










Here is the video:
[ame="https://www.youtube.com/watch?v=wpYzBDk-1pY&feature=youtu.be"]https://www.youtube.com/watch?v=wpYzBDk-1pY&feature=youtu.be[/ame]


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## Cogsy (Dec 20, 2015)

First up, an excellent little engine. Congrats.



crueby said:


> For some reason I am not seeing it in the post other than as a link - seems like it used to convert to video in the post....?


 
Your link is a little off - it works but is not the right type to show the video in the post. The correct link (with a slight mod to the spacing so it doesn't auto display the video) is https ://www.youtube.com/watch?v=wpYzBDk-1pY&feature=youtu.be . I got it by clicking your link and copying the address that it lead to.

And here it is with the space removed :

[ame]https://www.youtube.com/watch?v=wpYzBDk-1pY&feature=youtu.be[/ame]


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## crueby (Dec 21, 2015)

Thanks cogsy!


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## Cymro77 (Dec 21, 2015)

Very nice little engine.  Darned cool actually!  Thanks for sharing.
DW


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