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Elmer’s ‘Tiny’ #23

Jim Greethead from New South Wales enjoying a pint of amber nectar at the recent Bristol Model Engineering Exhibition during a recent visit to the UK.

Jim Greethead from New South Wales enjoying a pint of amber nectar at the Bristol Model Eng Exhibition during a recent visit to the UK.

Jim's trio of beautifully built 'Tinys' each fed with air from a neat three way manifold. I think Elmer Verburg would have been well pleased.

As soon as I heard that ‘Aussie Jim’ was building Elmer Verburg’s #23 ‘Tiny’ I asked Jim if he would consider taking some step by step photographs and prepare write up notes on his build procedure. The following is the result.

Jim was recently over here from his home in Bywong, NSW, Australia and made a point of visiting the 2009 Model Engineering Exhibition in Bristol.

Thanks Jim, this is a first class article and introduces a number of innovative solutions to problem solving from which we can all learn - so over to you Jim for the full story……….

Building Elmer’s ‘Tiny’ Engine

When I saw the Elmer’s Tiny that John Somers built, I knew that I just had to have one. This story is not a tutorial or an instructional article, it is just a few photos and a couple of things I learnt on the way.

The first task was to convert Elmer’s drawings to metric to suit my workshop. This involved DesignCAD and quite a bit of learning. It would have been faster on the back of an envelope but I need to learn DesignCAD anyway. You can see a couple of pencil changes to the drawing as it appears in the photos but it was good enough to work with.

The next decision was whether to make it in aluminium (my favourite material - easy to work and it is clean), or brass (looks good but is expensive and the finished engine needs polishing ) or stainless (hard to work and the only available piece of unknown origin). It seemed easier to make three then to decide between them and, as everyone knows, it is just as quick because the setup time is shared. Mind you, I think “everyone” knows this from theory not from experience.

: Not having a form tool or ball turning tool....

: ...I used a chainsaw file to form the grooves.

: Elmer's drawing shows the bit where the crankshaft goes as being spherical so on the aluminium engine, I rounded it off with a flat file.

: But on the others, I just left it cylindrical and I am happy with the result.

: Then I buffed them so the buffing would not round off the edges of the subsequent machining. Buffing can hide a multitude of sins (and tool marks).

: So now I had three bodies ready for the next step.I actually left them on the stick until they were finished and running. They are easier to handle like that.

: For machining convenience, I dimensioned the body from the top end , set an x axis stop and then established both x and y zeros.

: A handy bar of 38mm brass was sufficiently accurate for finding the y axis zero.

: The 19mm bar fitted nicely in the slots, needing only a couple of clamps to hold it.

: After that, the flat was machined and the holes spotted and drilled (and deburred) for the cylinder pivot and the crankshaft bearing.

: Then came the ports. Elmer's drawing shows the ports being #57 drill which equates to about 1mm. After a couple of calculations, I increased this to 1.2mm and then to 1.5 when my last 1.2mm drill broke (in the hole).

: The 1.5 gives some overlap but that doesn't matter-it just wastes a bit of air (and that's free until they find a way to charge for it).

: I also calculated the position of the ports instead of using Elmer's gizmo.

: The next bit was interesting! Leaving the x axis lined up with the ports, I rotated the body left and right and drilled the inlet and exhaust connections (I made them symmetrical).

: I found that I needed to set a stop where the drill just breaks through into the port hole because the drill tends to grab and wind itself right through to the other side and then it is back to square one and start all over again.

: One more rotation to relieve the pivot hole for the spring. I used a drill in the pivot hole to line it up.Once the crankshaft bearing hole is deburred, the body of the engine is finished.

click for part two >>>

Elmer’s ‘Tiny’ #23 part two

The crankshaft bearing was completed before moving on to the cylinders.

Having completed the three engine bodies Jim’s build moves on to making the crankshaft bearing before tackling the cylinders

Machining the body was a bit traumatic; three broken drills and three restarts from scratch so for a bit of light relief I made the crankshaft bearing next.

Almost nothing can go wrong with this job, and nothing did. The bearing hole doesn’t need to be reamed, I just drilled it , 2.5mm and then 3mm. I then turned the outside to size, checked that it fitted in the hole in the body and parted it off. After it had been reversed in the chuck and cleaned up, the job was done.

And now the cylinders

: All this messing around with the angle plate was a pain so when I did the replacements, I cut the cylinders off first and used a couple of parallels to set them up in the vice. With a depth stop set so the bore went just down to the port, the whole job was completed in a fraction of the time and without constantly swapping from Jacobs chuck to slitting saw. This is called experience.

: Cutting points were spotted between each of the cylinders. In a later attempt, I just dropped the centre drill onto the work without it rotating. This gave a point mark that improved the accuracy of the subsequent cutting. The y axis stops were just pushed up against a piece of silver steel in the chuck to align the work parallel to the y axis.

: I needed to make 3 cylinders, each 8mm x 8.5mm from 3/8 inch square brass bar so the first steps were to machine the bar to size, spot and drill holes for the port and the cylinder pivot. Once again, the dimensions were taken from one end .

: I used this Heath-Robinson arrangement to drill each cylinder in turn and then cut it off the stick. I think I was influenced by some articles on workholding in Model Engineers Workshop. If you look carefully, you can see that the hole in the cylinder has been drilled off-centre. And if I had looked carefully, I would not have had to make another set of cylinders.

The pistons and crank disc came next

: This was my only piece of stainless steel , so everything had to be made from it. I turned each one down to match a cylinder. The small diameter was carefully chewed out with the parting tool and then filleted in with a round file. Blessed be the buffing wheel.

: Looking at the photos, I have no idea why I chose this method of holding the work to mill the flats and drill the hole instead of putting it in one of the slots. And using an end stop would have been a good idea. Hindsight!

: These are the first lot of cylinders (before I noticed that the holes were off-centre). You can see the remains of the spots with which I marked the cuts between cylinders. That is why I just dropped the centre drill onto the work for the next lot.

: Had I studied the plans more carefully I would have seen that the holes were off-centre.

: The crank disk was turned with a bit of relief to minimise friction, and then attached to the crankshaft with Loctite before being rechucked for truing and cleaning up.

: Set up in the milling machine for drilling. It is easier to measure in from the circumference than to find a centre from which to offset the hole. Once setup, each of the cranks were drilled in turn.

: This time, I checked with a dti that the work did not move under pressure from the drill but still, the points were not square

: It has been my practice to Loctite the crank pins in the holes. But no matter how carefully I drill, the pins never end up square.

Incidentally I noticed that in one of his other designs Elmer uses a press fit for the pin. Despite the difficulties of getting the tolerances right at this size, I might try that next time. This time, I cheated and increased the size of the hole in the piston.

click for part three >>>

Elmer’s ‘Tiny’ - part three

The flywheels

Three flywheels to make: brass, aluminium and stainless. It’s a simple task so I didn’t take too many photos.

And lastly, a note on the springs

You can forget all the fancy stuff, I ended up manually rotating the chuck and advancing the slide. The springs were actually quite tricky.
I made the first ones to minimise the pressure (and thus friction) between cylinder and body. But I found that the cylinder lifted off at angle, jamming the pivot pin. They were alright at 5psi but not at 20psi. So I had to experiment to get a spring that worked at 20 psi and still allowed the engine to run at 5 psi. Anyone got a use for a small box of springs?

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