Start Model Engineering

Elmer's 'Wobbler' #25

The perfect choice for your first engine

The choice of your first engine build project is critical and should follow the ‘KISS’ principle.

Keep It Simple and Straightforward!

Get it right and you will get a huge buzz and a big smile on your face when your creation leaps into life!

* Go for a simple oscillator design.
* There are fewer moving parts.
* It will not require sophisticated tooling.
* It can be built in a matter of days.
* The forgiving design improves your chance of success.

Free Plans !

In my view you can not make a better choice than one of Elmer Verburg’s classic designs. His ‘Wobbler’ #25, for example is well worth a look at and the plans are free - available for you to download complete with build notes from

http://www.john-tom.com/html/ElmersEngines.html

This was the choice of Tim Evans of Northern Ireland - a professional photographer (which becomes apparent when you view the superb quality photographs of his build sequence which Tim has kindly agreed to share with us). Click on each thumbnail for a larger image.

Tim had the benefit of owning a milling machine but this is not strictly essential. Providing you have a lathe for all the round bits you can get by with hacksaw and files for the flat bits. Similarly for holding smaller parts in the lathe a collet system is useful for achieving a higher level of accuracy (reduced run out). This could result in improved running of the finished engine but Elmers #25 is a very forgiving design and tolerances are fairly accommodating - anyway over to Tim………..

Well after being advised to try a simple wobbler engine as my 1st project I’ve decided on Elmers #25. The fun part has been converting the imperial to metric measurements.

So I dug up a little slab of 6mm ali plate and hacked off a piece approx the size I needed. Then came the 1st issue to overcome, as the biggest milling cutter I have at present is 6mm I felt it was unwise to size the frame piece in one pass. So I took off my milling vice and decided to clamp the frame to the top of a 3-2-1 block that was squared up to the table, and use the side of my 4 flute mill to size.

Once sized up I then marked up for drilling,

After boring all the holes I tapped the intake M4, I meant to tap it M3 but messed up the drilling :doh: so I had to enlarge to M4 as I dont have a M3.5 tap.

So after drilling and tapping all the relevent holes the frame was done, or at least it was machined, I have to clean it up and polish it up a bit.

I then moved on to the cylinder. I had a piece of 19mm square brass bar. This presented a new challenge, I dont have a fly cutter or a milling cutter over 6mm. So how can I machine this 19mm square bar to 17mm x 15mm, and get a reasonable finish?

Up steps the 4 jaw chuck.

I remember reading somewhere about how to turn a cube using a lathe, and I just borrowed the idea, and what do you know, it worked!!

So I now have the cylinder blank sized and ready to bore, and that’s as far as I got.

However, in the process of sizing on the lathe I found out that getting a nice finish relies on smooth advancement of the cross-slide. ( yea, I know that you all know this, but it was new to me ) I found a bit of a cheats way of taking the monotony out of winding it back and forth, and getting a better finish. I just attached my cordless drill to the capscrew holding the handle on the cross-slide and just ran it on a low speed. Got a far better finish than I could’ve got otherwise. You just have to be careful to keep the drill in line as best as poss.

Here’s a pic of the completed (but desperately needing cleaning up) frame and the prepared cylinder blank.

I spent a total of 3 hours to mark out and bore just 1 hole The marking out went easy enough, and I even managed to center punch on the “x” :headbang: I even got it mounted in the 4 jaw and centered up within a gnats whisker.

The center drilling went well, and even the drilling with progressively larger drills until the bore was 3/8″ ( this time I had an imperial drill set, so no metric convertion needed ) It was at this point I realised that the 9.5mm and 10mm reamers I thought I had as a part of a set were not there, the set only went up to 8mm and all are hand reamers, not machine reamers, and so even if the set went up to the needed size they would be useless as the bore is blind and only just over 1″ deep.

So this is where the newbie-ness gets a little more obvious, instead of thinking that I could get a correctly sized and type (machine) reamer in a few days time, this numpty decided to spend 2.5 hrs trying to make one.

Sense has finally prevailed after making the bore look rather rougher than when I had just drilled it, and so I called it a day before I totally wrecked the cylinder blank.

So a total of 3hrs to bore one hole, and even that’s gonna need reaming out.

This is what it looks like,

You wouldn’t believe how much of a numpty I feel. When I read your post Bogs it hit me like a ton of bricks, “I have a boring bar set for my mill” :bang: (looks around for the hole in the ground to appear ) But I will file your C-o-C for future reference thankyou very much

Anyway, when I finally got over my numptyness this is what I got done today. I mounted the cylinder blank into the 4jaw, centered it and then took a couple of light skimming cuts and then about 4 repeated cuts to eliminate any springing of the boring bar.

I then remounted the cylinder the other way and bored out the pivot pin socket being careful not to break through into the piston bore.

Onto making the pivot pin. I didn’t have any small diameter brass bar and I didnt fancy wasting some 3/4″ square bar. I thought I’d try and be clever and use a little piece of 19mm x 3.5mm flat stock and turn it down. So I cut some off and chucked it in the 4 jaw.

Then to turn down the other end I wanted to chuck it in a ER32 collet to not leave markings on the pin, but I dont yet have a ER32 chuck for my lathe, but I do have a MT3 ER32 chuck for the mill, and the headstock on the lathe is also MT3. Not having a long enough drawbar I brought up the tailstock to ensure that I wasn’t chased around the workshop.

continued in part two

Once the pivot pin was turned down to the right size to be tapped M3, I then cut the M3 thread. You probably noticed that the tailstock is removed for this, I ran the lathe at the lowest speed ( I thread at the lowest speed so I dont run into the chuck ) and as I found out when trying to remove the ER32 chuck it was well stuck in there.

Once that was done, I removed the pin and then loctited it into the cylinder. (it was a pretty good press fit)

And that’s as far as I got today. Thanks to Bog’s for reminding me of what I actually had sitting in the corner of the workshop.

I managed to sneak a couple more hours in the workshop this afternoon. I started off by hacking off a little lump of brass for the piston and chucking in the 4jaw, turned down half to diameter.

I then chucked it the other way round in the ER32 collet but made the error of not tightening it enough and it came loose just as I was parting it off to length so I added to my collection of spare “smaller than I wanted” pieces and hacked off another lump of brass, chucked it and turned it down as before. This time I also drilled and tapped M3

I find this to be a good method of tapping on the lathe, to explain; The drill chuck is not jammed in the MT of the tailstock, it has some grip but is free to turn with light pressure. Also the tailstock is also free to move on the ways, and the tap in the chuck is also loose enough to turn if the tap jams in the work. I then run the lathe at a very low speed.

So that’s all I got done today, just 2 pistons made, 1 junked and one that fits ok. If I put a M3 screw in the piston and slide it into the cylinder and turn it upside down the piston gently slides down and stops at the entrance of the cylinder, with out the screw it just falls out. I dont know if it’s too loose, if I pull the piston out rapidly I get a satisfying “pop”.

Things I’ve learnt today;

I learnt that my ER32 chuck has a runout of 0.02mm,
Always start off with a piece of metal that is longer than you need as it makes life easier.
I also tried making a con-rod out of 303 stainless, it didnt go quite as planned but I learnt that it really helps to use sharp carbide tooling and that it doesn’t like my Hss threading tool.(prob was a bit dull, I must resharpen it) I’ll try again the next time with some brass as per the plans.
Also learnt to think a few steps ahead to see what I can do while workpiece is still chucked and true before taking the piece out and then spending 15mins truing it up with the trusty dial indicator.
And finally, always remember to check that whatever chucking device is used it is properly tightened up.

Today’s update.

I started out by sharpening my threading tool and spending 15-20 mins trying to single point 3mm 303 stainless for the con-rod. Deciding that beating my head against that particular spike was not fruitful :bang:, I moved on to machining a new con-rod out of brass. This was much easier.

Then I extended a bit more out of the chuck and turned that down.

Once turned to size it was over onto the mill, I mounted it into the spin indexer thingy, supported the free end with a 3-2-1 block and a little stepped thingy and drilled out the hole for the crank, 2.4mm if I recall correctly.

After a little cleaning up and filing the edges round I have a piston with con-rod

After that I had a little time so I made a start on the crankshaft assembly, specifically on the crank disc which I made out of some unidentified steel, turned some down to 17.5mm, hacksawed it off and remounted it in the ER32 chuck, faced it off and then drilled it 4mm.

Ok, managed to get a couple of hours in the workshop today. Started off by setting up and drilling the offset hole for the crank pin.

The more observant of you will have noticed that the Crank-disc is not properly seated on the 3-2-1 block and so did not drill square. I didnt notice that until I’d finished today and as I’ll explain in a bit I may have to re-bore the pin-hole square. Anyway, after that I found a use for the screwed-up piston, I turned it down to make the crankshaft bush shown below in the middle of the other hacked out bits.

I then chucked up a length of 6mm 303 stainless to turn down for the crankshaft, I turned down to 5mm for the main shaft and a short section 4mm to fit the crank-disc.

Then I did something similar for the Crank-pin, except I started with some 4mm stainless, turned it down to 2.4mm for the press fit into the crankdisc and 2.3mm for the easyfit into the conrod. I also pressed the crankshaft bush into the frame, after I cleaned up the frame,

then did a little assembly just for fun.

Once I did the assembly and tried to turn over the crank I found that it was sticking at TDC and BDC. After a little wondering I checked the squareness of the crank-pin ( it’s amazing how hard it is to use a 4″ engineers square on a part that’s only 17mm wide and the pin’s only 3.5mm high !!) I then realised that the crank-pin is not square and is what is binding up twice per revolution. I’ve not totally decided what to do about this. I could pull the pin out and re-bore the hole wider and square and then make a new pin to fit. Or to just try and bend the pin to square. I’m leaning towards just bending the pin back to square, and that’s what I did.

I managed to make a start on the flywheel, and got one side shaped, to a fashion, and today I bored and reamed the 5mm hole for the crankshaft, then remounted to machine the other side, centred it using the 5mm hole as a reference and then shaped the 2nd side. ( I was so excited about getting so close to completion I forgot to take any pics of these parts )

I then turned a some 6mm brass rod to a close fit for the flywheel, and threaded the end M5, and mounted the flywheel to it to clean up the rim and make sure (hopefully) that I dont have a wobbly flywheel.

After that I drilled and tapped the flywheel for the setscrew I then turned to the air-intake-to-aquarium-type-tubing-adaptor-thingy. I used the same 6mm brass rod and turned some down to 4mm and then threaded it M4 and then bored it through with a 2.2mm bit

Then after some jiggery-pokey with a parting tool,

It was over to the spin-indexer to make a nut-shaped bit.

continued in part three

At this point I did a quick mock-up of all the parts and positioned the crank for transferring the hole position from the exhaust of the frame to the cylinder. Then after removing the indexer from the mill and clamping down the vice, I drilled the cylinder with a 1.6mm bit.

I then found a spring that was about the right size and assembled all the bits together, and here’s the result.

( notice the immaculate chatter on the flywheel )

The other side

Imagine my joy, now to get it running. But how? I have a little air compressor, but no way to attach the length of 3mm (id) tubing to it :bang:

So I decided to build an adaptor. I just copied the connector off one of my air-nailer, and bored a 4mm hole up the centre.

I then made another air-intake-to-aquarium-type-tubing-adaptor-thingy as above, except I haven’t milled the nut-shaped-bit on it yet as I had to come in to make me grub, and that’s all I got done.

I started today with the air-hose adaptor that I started last post, I drilled the other end and tapped it M6, and then I milled a flat and then drilled and tapped M4 for the air-hose-barb-thingy.

Then back onto the lathe, I chucked a 6mm brass rod, and turned a 5mm to 3.5mm taper on the end. This is gonna be the inner tapered pin that will block or let a controlled amount of air through to the air outlet.

Then I threaded the rod M6, and then knurled the end

(notice the slight mess-up on the threading, I hadnt got enough of the rod sticking out and didnt match the thread up well enough during the 1st pass on the 2nd section :doh:)

But when put together it fits and works ok. There is a little leak of air from around the knurled/threaded area when the home-brew valve is open, but not so much that would bother me at the moment.

I then made up a round base out of some ali bar I had, drilled it and counterbored for the mounting screws, and also drilled and tapped a center hole M6. The center tapped hole is for mounting the Ali base onto a wider turned wooden base that I plan to make. (if folk are interested I’ll do a project log on that too)
Here’s the little wobbler on its little base.

And then, (drumroll please)

It runs

I finally got round to finishing off this project by turning a wooden base for it. Now this is more familliar territory for me, and while I did this on my woodworking lathe, the techniques are the same on an engineering lathe equipped with a toolrest. 1st of all I got a chunk of oak that happened to be around my dad’s workshop (that’s where my woodturning lathe is residing), and that chunk of oak just happened to be quartersawn ( nice looking grain ).

I then marked it out with lines on the diagonals. This was because I was going to mount it on the faceplate, but then I realised that I had my external jaws on my 4jaw self-centering so I just gripped it with that.

I then turned a dovetail recess on what will become the underneath of the base. ( this was to match the dovetail jaws that I then mounted on the 4jaw ) then I removed the oak from the external jaws and bandsawed it into a rough circle. (the only type of circle I can cut on a bandsaw )

Then I mounted the dovetail jaws onto the 4jaw, and mounted the oak base onto them. Then I turned a recess to fit the ali base of my elmers#25.

I then turned a concave section, 2 flat bits and 2 tiny grooves.

Then I sanded it 120,220,230 and then 420grit, burnished it with 0000 wire wool (sourced locally from steel sheep ) Then I finished it with quick-drying friction polish, then I polished it up with some canuba ( I think that’s how it’s spelt :scratch: ) wax.

These are the tools I used,

I find woodturning a very tactile experience, when I started to turn the base I didnt fully know what shape I was going to make, the wood sometimes just lends itself to a certain shape. The shape just flowed on this one.

The key to getting a good finish off the tool is to let the bevel of the tool rub against the wood as the tip cuts, this gives a clean cut and also burnishes the wood, this is especially true when turning woods that are not close-grained (such as Oak, Pine, Balsa … )

Anyway, I spent some time today doing some final photos of this project, I’ll post up a bit about how I did it in my post about photography.

But here are 2 pics