This is a re-post of my build of Elmer's Tiny; the third engine I completed. Nearly three years on, it's a really good little runner; easily running on breath power. This engine was built using only a lathe and drill press; no milling machine.
Warning: There is a redrawn CAD drawing available of Tiny's plans. Use either Elmer's original plans, or the CAD drawing, don't mix them as there are some dimensional differences relating to the port locations, especially if one choose to use the "locating jig" that Elmer drew up.
18 September 2009 I collected a couple of off-cuts together - some pieces of printer shaft, a bit of 6mm brass from a cistern ball-valve and so on:
Started with the column. Piece of printer shaft chucked up, faced at the end, and the length marked as per Elmer's instructions:
Then turned down to the top of the column's diameter:
And did the turning on the bottom part of the column and some cleaning up with emery paper. It's obvious I still need some practice at free-hand ornamental turning...:
After this, I parted off the column - this printer shaft is very nice to machine, and parting was a breeze:
Next up was the bearing; I nearly made it too small on outer diameter; that's why it's pretty rough on the surface... I'll just polish up the parts that will be visible later on:
The crank followed; I chucked up a bit of 10mm silver steel, and just marked the center with my smallest center drill. Coloured up a part of the surface with a permanent marker, and used a compass to mark the crank-pin distance and center-punched:
Having done the marking-out, I turned the crank web to size, and drilled and reamed the center for the main shaft.
Then transferred the lot to the 4-jaw chuck, and set it up off-center to drill for the crank pin. At this point some perverse whim took a hold of me, and I ended up actually turning the crank pin as part of the web (apologies for the blurry photo):
Before having to set up the lathe for milling, I also made the pivot pin from some 2mm brazing rod. Deviating from Elmer's specifications here, I threaded both sides; one end short for screwing into the cylinder, and the other for taking a nut rather than the cross-drilled retaining pin called for in the plans.
Then I made a d-bit to be used for finishing the cylinder and found a spring from a car tire-valve that should work as pivot spring. One thing I forgot to make is the "measuring pin" for locating the port holes; that I'll do tomorrow before setting up for milling. The crank web and shaft were also loctited together to cure overnight
Last photo for the day with a selection of Namibian coins...
19 September 2009
First off, I turned the locating pin to be used with the drilling jig. Then marked out the jig. Note how I jotted down the drill sizes for the three holes - this came back to bite me later on in the day. I find it easier to use a scriber to push a little hole into the work where the mark-out lines cross, and then center-punch - it is easier to get on the correct spot with the scriber. Jig marked out:
Turning done (for now), I set the vertical slide & vice up nice and square; my vice appears to be slightly out of square, so I clamp an accurate piece of square HSS blank to the vice bottom and use that to tram in using a dial indicator.
A side-hint from my own meagre experiences: If you don't have a dial indicator or DTI, a useful way of setting the vertical slide square to the spindle is to use a piece of round bar of consistent diameter; mount it in the vertical slide & bottomed in the vice - as square as you think you can get it. Then take a light milling cut across it. If the flat face you milled appears to taper, rotate the vertical slide slightly to the side where the milled flat is narrowest. Repeat a milling cut. Once the milling cut is of equal width along the entire length, you have the vice squared up to the spindle.
Once set up, I started to mill the cylinder block to size (I use a small fine file to deburr after each rotation of the block, and a tooth brush to brush away swarf in the vice before the next setup):
Cylinder block nicely squared off to size on all sides:
Once again, I deviated from Elmer's instructions; instead of using the 4-jaw chuck to make the cylinder bore and pivot hole, did it in milling-mode; and started with the drilled and threaded(in my case) pivot hole - to about half of the depth of the cylinder block:
While still centered after tapping, I counter-bored the recess using a 6mm slot mill; not ideal, but by doing infeed using the tailstock, and backwards pressure on the apron wheel it went well, without grabbing:
After this, I rotated the cylinder to drill & ream the bore; I made sure it was set to a nice square angle by clamping a bit of straight 6mm steel in the chuck and locating the side of the cylinder block against that. Drilled it out to just under size as far as I could and then used the d-bit reamer I made yesterday to finish it to size and depth.
The bevel marks on the bottom of the bore is where the reamer shoulder hit; I made the reamer tip to exact depth, and this was the easy way to see I got there:
Next up was the flats on the column:
I got a bit busy at this point and forgot to take photos... Just milled both flats, marked out and drilled & reamed for the bearing and pivot shaft and spring-clearance
On to drilling the ports...
First up I had to drill the jig - remember what I said earlier about the size markings ? - Well, if you do that, put them DIRECTLY next to the holes you need to drill... I got it wrong and drilled the hole for the steam port locator in the jig at 2mm - I think because the "2" was directly opposite it
.
Being the lazy rotter that I am, I just decided to use the hole and the 2mm drill through it to spot the hole centers in some mark-out dye (a.k.a. permanent marker scratching) on the column for the steam ports and drill them. Marked out (you can just see the 2 spots for the ports):
Right there I had one of those "gut-feel" moments that something was still wrong. Put the cylinder on it, and realised the cylinder's steam port would have to be way too close to the top of the cylinder... - Thats when I looked at both sets of plans and realised there were differences.
I used the other side of the drill-jig to mark out and make a new one, with the hole for the ports 1mm closer to the pivot pin - that should leave enough room at the cylinder top for the steam port... This makes the inlet and exhaust ports come a bit closer toward each other on the column; I just used a smaller drill than intended to compensate, and drilled the ports, as well as drilled and tapped the side hole M3 for the steam connection. I might have to make the piston a bit shorter as well.
Loctited the bearing into place after this, and stopped for the day; piston, flywheel, pivot nut, and steam connector left to do tomorrow:
20 September 2009On to the finale:
The treading for the pivot pin backfired slightly; if I turn it in fully, it ends up off-square, so soldering was the easy way out. From building Fancy, I know that keeping the pivot pin is a bit of a pain to keep square while soldering, so I first made up a little jig.
Cross-drilled a scrap piece of 12mm aluminium round bar with a 6.5mm drill, so that the drill broke through the end of the bar, leaving a "slot":
Then I shoved it in the collet chuck, and trimmed the end flat and removed some of the OD, then turned it around in the chuck and drilled a 2mm hole for the pivot pin right through. Screwed the pivot pin loosely into the cylinder (about 1/4 turn from full depth) and pushed the jig over it to square the pivot pin:
The cross-drilled hole makes it easy to see where you are trying to solder - here it is soldered already:
Next up was the piston & con rod - turned down to con rod end diameter with piston-side towards the headstock:
And then very carefully turned the con rod shaft down to 1.6mm diameter with a sharp round-nose tool:
After that, finished the piston off to size (less the 1mm that I needed to compensate for the shifting of the ports), with oil grooves - here it is ready to part off:
Next up, the steam connector - just needing parting-off:
And the little 2mm nut to retain the spring on the pivot shaft (not in the plans; my improvisation):
Set the vertical slide up for milling again, and milled the flat on the big-end. This was a bit tricky; I used a small flat bar to align the connecting rod shaft parallel to the vice, and clamped on the big-end, with a scrap bit of the same diameter on the other side of the vice to help it clamp flat. Then very fine cuts (2-3 thou each) followed with the 6mm slot mill to bring the big-end to size:
I had already turned and parted the flywheel from some stock earlier, so while the lathe was set for milling, I just clamped the flywheel, and center drilled and drilled and tapped 3mm thread for the grub screw:
My last 3mm grub screw in the bin was too long, so I ground it down on the bench grinder to a suitable length.
Then assembled Tiny and took a couple of photos. Couldn't test it immediately, as it was "Sunday Afternoon Nap Time" for my elderly neighbors, and my compressor's a bit noisy.
When siesta time was over, gave it a test run; was a bit stiff and needed high pressure, so I clipped a few coils off the spring, and it ran a lot better.
Apologies for the poor video quality & the shakes; done using my digital camera, and having to reach away to adjust pressure on the compressor...
All-in-all, building Tiny was a LOT of fun
Regards, Arnold
