Back to basics - Elmer's #25 Wobbler

[arnoldb]

I mentioned in another post that I would "sleep on something to build next".  That was Saturday evening.  Sunday morning I woke feeling like something plain, quick and just pure fun.  I love Elmer's engines, and plan on building each and every one of them.  One that I have not built is his #25 Wobbler - exactly the kind of project to suit my mood.

I was in two minds about posting the build.  Well, I'll post it; there may be some points of interest, and, after all, everybody has a "Back" button in their browsers if they don't want to look 
Anybody that have questions or suggestions, please don't be shy; post up and join in the fun 

Sunday's shop time was limited; I only had a few hours in the afternoon to make a start.  I didn't get around to posting that, so here goes...

I printed out the single page of plans, and assembled most of the needed stock.  There's still a bit missing for the base from this photo. I (hopefully) would not use all this material; it's just the odds and ends I have as parent stock:


The frame was started by milling the block of aluminium plate to size.  The plan calls for 1/4" plate for the frame, but I only have 6mm or 8mm available; I went for the 6mm.  This is not a big issue; the frame can be made from just about any thickness of plate, as long as one is comfortable drilling the porting and have enough room for tapping the steam connection and so on.  I wouldn't go below 6mm though.  8mm will be a lot easier.  Just one thing when changing the thickness of the plate - and I got caught out with this  : The thinner section of the press-fit bearing's length must be changed to suit.  With thinner plate, the section must be made shorter.  I made the bearing to plan, but it ended up being 0.35mm too long (1/4" = 6.35mm).  If it's too long, the crank pushes the connecting rod off-center and things jam up tight.
Elmer added a little drilling jig and location pin to the plans for drilling the port holes.  This works very well, I used it on my "Fancy" which has the same running geometry as this engine.  I couldn't find the template I made way back, and with the luxury of the DRO on the mill, I just calculated the port hole locations (just some basic trigonometry) and set about drilling, reaming and milling.  The profiling cut was the last operation here:


In the photo above, I set the vise stop so that I could position the workpiece upright to finish the profile cut-out - as I didn't move the mill X handwheel, I could just raise the cutter and mill off the excess bit.  It was also easy to drill the holes to tap for the mounting bolts:


After that, the workpiece was stood upright to drill the steam  connector hole - 2.5mm to be tapped M3.  The plan calls for #5-40 - and M3 is a good metric substitute, but M4 would work here as well:


As a last machining step on the base, I milled off the "nose" bit.  Nothing fancy here; there is not even measurements on the plan for it, so rather than getting all accurate and engineery,  I just coloured in the section a bit with a permanent marker, and eyeball-scribed a line to set up and mill to:


Next, a bit of elbow grease.  And one of the most important bits of getting a wobbler to run well.  Flat lapping the port face against which the cylinder will run.  I started of on 320 emery lying flat on my glass "surface plate" and lapped away till I couldn't see any surface defects left.  Then I followed that on some 800 grit.  I left it at that; the slightly dull surface is great for retaining some oil, while having very little friction.  If one want's to polish an engine like this, that's OK, but DO NOT polish the area on which the cylinder will run.  Also, don't be tempted to de-burr the port holes; the lapping should remove any burrs and if one use a countersink or drill bit to de-burr the holes, the chamfer that's left can influence the engine's running.  A bit might be useful if the port holes are spaced too far apart, but it could also cause blow-by.  The frame after lapping - I did the other side as well to make it look more uniform:

(Clicky-piccy for more detail)

On to a bit of the 16mm square brass stock from the first photo - the cylinder.  I chose the best-looking side of the stock, and marked that as the port face.  Then I milled the adjacent sides down to leave it 12.7mm (1/2") thick.  I marked out the cylinder center on one end.  Off to the lathe and the 4-jaw chuck, and I centered up the workpiece on the cylinder center, and drilled just under size and bored the cylinder to about 9.8mm diameter.  My 10m reamer is a hand-reamer, and the taper on it makes it useless for a blind cylinder like this.  A drilled finish is by far not good enough for a cylinder.  This is where one of my favourite home-brew boring bars shine.  A simple one made from hardened silver steel (drill rod) - stoned to a nice smooth and very sharp cutting edge.  With a moderate machine speed, it bores a near-mirror finish.  I forgot to take a photo of the boring part - here I'd already finished turning the lip around the cylinder:


Next I mounted and centered the workpiece to drill the mounting pin hole and turn the necessary recesses to form the port face:


Back to the mill, and I drilled the port hole.  I centered the DRO on the pivot hole and cranked in the offset to drill the hole:


For the last machining operation on the cylinder, I used a good sharp  3-flute countersink bit to mill away some excess on it:


Soldering the pivot pin on wobblers can be a bit of a trial...  I made up a little aluminium jig to hold the pin square for soldering.  Soft solder; 60/40 lead based electronics for this one.  If you want to silver solder a joint like this, don't use aluminium for the jig - it _will_ melt. DAMHIKT 


I left off with this lot for Sunday's shop session:


I did get more done this afternoon after work and the engine runs  - but it's getting really late, so I'll post the rest tomorrow. 

In fact, it's now twenty to twelve on New Year's eve, so:

  Happy New Year everyone - I hope it's a good one for all 

Kind regards, Arnold   

[b.lindsey]

Looks great Arnold !!  At this rate you should have all of Elmer's engines done by Spring

Will look forward to seeing the rest of this one though for now.

Bill

[zeeprogrammer]

I was in two minds about posting the build.  Well, I'll post it;

Gasp! Be of one mind. Be of one mind. Post!
There's always good stuff in your threads and I for one want to see your work.

[Don1966]

Gee! When you decide to do a project, you don't waste any time Arnold. I will be tagging along on this one also. Should be an interesting built.

Don

[Bearcar1]

As will I. Always a pleasure to see you in action Arnold. And may your new year be even better to you than the last one.


Cheers 


BC1
Jim

[EmanMyford]

Thanks for posting this build Arnold. I love to see your work and appreciate you taking the time to include all the detail.
Happy New Year! 

[NickG]

Arnold,

I too keep looking at elmers engines and thinking, there's a nice looking engine I can just go out, hunt for some scraps of metal and start making, rather than messing on with CAD or changing things on the drawings etc. One of my new year's resolutions is to do more model engineering so maybe I need to take a leaf out of your book.

I'll be watching, great start.

Happy New Year! 

Nick

[steamer]

Absolutely Arnold!   POST!

Dave

[arnoldb]

Thanks Gents 

Bill, I'll aim for Spring - but I'm not saying which year though 

Nick, just do it.  Some of the most fun I've had building engines was with the ones where I would just wake up, choose a build and go for it.  It's about having fun, and while I do enjoy the detailed builds like the popcorn and so on, sometimes one must just do something that's quick and gratifying.  I mentioned in the first post that I already have the engine running - this is my twentieth engine, and the thrill of starting up an engine for it's first go has by no means dwindled 

I slept in a bit this morning, and it's very hot and humid here today; hopefully we'll get a bit of rain later to cool things down so I can get to the shop.  In the meantime, I'll just add yesterday afternoon's build antics.

First up was the crankshaft.  I turned a bit of bronze down to 17mm diameter, drilled and reamed the center hole, and then moved the chuck to the rotary table on the mill.  I centered it up under the spindle using a bit of 4mm rod in the mill chuck to locate in the hole, and then dialed in the crank throw offset and drilled the hole for the crank pin.  Next I milled out the cut-outs in the web.  There's no special need for using the rotary table for this job; it could have been done in the vise as well; it's just that it's very convenient for me to mount round work this way:


I parted off the web just over thickness and rounded over the throw end - nothing fancy; just by eye with a file.  I turned up the main shaft with a good tight press fit size for the web on the end and pressed the web onto it - taking care to fit the "nice" face toward the shaft side.  Then I just turned the front of the web to finished thickness taking several light passes; this cleaned up things nicely and as this also turned into the shaft, everything looks nice and flat.  Next I pressed in the crank pin - this was just made from some 2.5mm stainless steel.  Finished crankshaft:


The bearing bush followed - a quick and easy turning operation for a press fit in the frame.  I cheated just slightly though; instead of turning  the entire length on the "8mm" section for the press fit through the frame, I took an additional very light skim cut off about half way of the length to make that section a slide fit through the hole in the frame.  This means that it's easy to push the first section through the frame without getting it scratched up, and the press fit is in the frame section only.  All this boohah was purely for fun; I enjoy the challenge of turning to these kinds of tolerance levels.  There is nothing wrong with turning the bush for a slip fit through the frame and using retainer to lock it in place.  Finished bush:

Also a clicky piccy - on the full size photo one can barely make out the thinner section on the bush.  Also visible in the photo is a generous chamfer around the hole in the frame where the bush will be pressed in.  That is to allow the bush to be pressed in with the boss completely flush on the frame - I didn't bother to undercut the bush in the corner, so there's a slight radius from the turning tool in it.  The chamfer makes space to accommodate the radius.

On to the piston rod.  I decided to turn it up completely from solid rather than fabricating it.  In the past I just used some 3mm brazing rod and soldered a thicker bit on the end to make the pivot point from.  I used some 7mm brass stock, and turned a shortish section down to 3mm and took note of the reading on the cross slide dial.  The end was threaded with a tailstock die holder:


Next I extended the stock further out from the chuck, and turned the rest of the 3mm section down to size in one fell swoop by setting the cross slide back to the reading I noted earlier.  This makes light work of turning a longish section to a thin diameter without getting problems from the workpiece flexing.  There is a caveat to add to this however: The turning tool I'm using is my all-round general favourite, and gives great finishes in nearly any work I turn, but it's not ideal for brass work, as the side clearance is quite generous and combined with the angle on the top, it tends to want to auto-feed into brass or bronze. I used a very gentle carriage feed, just taking off small chips to prevent this auto-feed (grabbing) from happening.  In aluminium or steel this isn't as much of a problem and one can feed a bit more generously.  For stainless steel, a more generous feed is a must, otherwise it will work-harden.  As a final step, I turned the last section down to 6.3mm from the original 7mm:


At this point I nearly parted off the workpiece from the parent stock, but it would be much easier for the next steps to leave it on the parent stock. Zee knows all about this  . Off to the mill, and clamping down on the parent stock, I milled one of the flat faces:


Next I drilled the hole for the crank pin.  to mill the other side flat, I just rotated the workpiece and used the drill held in the chuck through the hole to get the orientation right.  Another caveat here - often times round stock will tend to want to roll a bit when one tightens the vise, so take a bit of care, otherwise you could end up bending the drill bit when you tighten the vise:


At this point I sawed the piston rod from the parent stock, and tidied it up with a fine file to remove the last of the machining toolmarks.  Finished piston rod:


On to the piston.  I've come to follow a certain process for making these pistons that provides me with great results.  I first drill and tap the the inside of the piston to plans.  Then I turn the outside diameter down to slightly (about 0.2mm / 10 thou) over size.  A partial parting cut is made at length.  Then I add a generous chamfer to either end; this chamfer should go down to below the final piston diameter.  I cheat a bit, and add the oil grooves with a sharp triangular needle file - also down to below final piston diameter - the more correct way would be to use a sharp tool to turn these grooves, but I prefer not to disturb my toolbit during the piston turning process, as I can use the cross slide dial readings through the entire process to turn the piston down to size.  This is the piston up to this point in machining following the steps - you might notice a slight file-lip mark on the middle groove, but that will be turned away when I turn the piston to final size:

All this "preparation" is to prevent issues later on.  In the past, I'd picked up problems if I turned the piston to size first and then added the chamfers - they tend to slightly raise edges around them, and the piston wouldn't fit after adding the oil grooves and end chamfers.  Once, on a thin-walled piston, it also "grew" in size from machining out the internal bore after first turning the outside to size.

This is also a good point to make a final check with the piston rod for overall dimensions.  If the overall length comes out a mm or so short on a single acting wobbler of this size, it's not a problem.  If it's a bit too long, it's easy to drill out some more metal in the counter bore to allow the piston rod to screw in a bit deeper.  This is easier than shortening the piston rod itself, as it can be awkward to hold it for shortening:


The piston turned down to final size:

This can be a bit tricky; I'm comfortable with getting a good turned finish on the piston - and with my nice sharp toolbit it's easy to turn away miniscule amounts at a time to get to size - at this point I do a fair amount of "reading between the lines" on the cross slide handwheel, judging down to 1/4 thou infeeds.  Like I mentioned earlier, I like this type of turning; there's nothing wrong with turning the piston close to size and lapping it down with some oil coated emery paper backed by a steel rule.

The finished piston and rod:


I did give it a test run after quickly turning up the steam connector and using a spare "dud" flywheel - sorry, no video yet:


   A nice rain shower passed through while I typed this lot up, and things have cooled down, so it's off to the shop for an hour or so now.

Kind regards, Arnold

PS - Here you go Dave - you posted while I was busy 

[zeeprogrammer]

All this "preparation" is to prevent issues later on.  In the past, I'd picked up problems if I turned the piston to size first and then added the chamfers - they tend to slightly raise edges around them, and the piston wouldn't fit after adding the oil grooves and end chamfers.  Once, on a thin-walled piston, it also "grew" in size from machining out the internal bore after first turning the outside to size.

Nice tips and reminders. I for one don't think enough about what's happening to the metal left behind.
I really appreciate posts that include the 'why'.

[b.lindsey]

Best not blink while watching this thread Arnold...you are making short work of this one!!  Great pictures and documentationwhich should be of great help to those just starting out.  Looks like just the base to go now so will look forward to a video soon

Bill

[Bearcar1]

How much ya wanna bet he stuffs up the base?  ......             


BC1
Jim

[Jo]

Maybe I need to make one of these simpler engines: They are so much quicker , and more satisfying to make than the little ones I seem all the time to choose to make.

Looking good Arnold .

Jo

[arnoldb]

Thanks Carl - I'll try to remember to add more "why's" in future 

Bill, thank you - flywheel and base; video to follow shortly - as soon as I can get it uploaded  - but more build photos first.

  That was a real possibility Jim - there's paint involved, so anything can happen.  I nearly did stuff up the flywheel though; I'll leave it as an exercise to find the booboo 

Thanks Jo  .  I'd like to start on one of your style "little" engines - so far I've just been getting used to my machines and learning the basics.  If things go well, I might get my hands on one of the smaller casting sets available this year - and I have a couple of projects in mind that will require quite a bit of time to build.  I think taking a break on a long build to do one of these "quick" small builds could potentially be a helpful diversion if one is busy  on a big project - or if you get to a  point like you did with the DTC.  Besides, these small engines can make great gifts to some people 

The flywheel in the last photo is a wonky dud I have lying around.  It's great for quick tests, but not fit to go on display.  And it's made of aluminium - I've found a heavier metal flywheel does wonders for running these engines.  The plans I have for the #25 don't feature the flywheel dimensions.  It's the same size as for many of Elmer's other small engines - 50mm / 2" in diameter and 10mm / 3/8" thick.  The dimensions are not too critical, but beware of making it much larger in diameter, as it will be too big to fit between the axle and the base.
I used a bit of 50mm brass round bar to make the flywheel from.  I mounted it using the outside  jaws in the three-jaw chuck - it's a bit thin, and the steps on the jaws provide a convenient backing against which to locate the workpiece while keeping enough machinable area available.  When using outside jaws, always make sure to check that you have enough clearance for all the lathe bits available before starting the lathe.  It's very easy to misjudge clearances, and run the toolbit, tool holder, cross slide or topslide into the jaws.  I dug around my selection of HSS toolbits, and found one I'd ground up a year or so ago with a 3mm radius and proper clearances for trepanning the recesses on the flywheel:

This was just done to eye and I jotted down the inside and outside readings from the crosslide so that I could turn the other side the same.

After reversing the workpiece and facing it down to about 12mm thickness (just using that same trepanning tool) and also trepanning and drilling and reaming the center hole, I moved it to the rotary table and drilled eight 4mm holes in the web to make it look slightly more interesting:


Next I drilled a 2.5mm hole in the hub to tap M3 for a grub screw (set screw for folks in the US).  Elmer's normal method for these flywheels is a through-hole from the rim to the center, tapped part way for a grub screw and a brass pin used to engage the axle.  I'm not too fond of this, purely because I don't like seeing a hole in the rim:


As you might have noticed by now, the rim is still unfinished.  I chucked up some 10mm brass round in the collet chuck, and turned a 5mm boss on it to fit the axle hole on the flywheel, but so that there was a gap between the flywheel and the collet chuck closer nut.  The flywheel is smaller in diameter than the nut, and I didn't want to machine into the nut      Then I mounted the flywheel on that, and turned the rim.  Fine cuts with a very sharp tool; otherwise it would chatter like mad and ruin the finish (the 5mm arbor can flex very easily while turning):


These wobblers can do a fair bit of walking around, and like fairly heavy bases.  The base in the plan is designed to be mounted on a wood base, but I really didn't feel like doing woodworking, so I settled on substituting a block of 60x10mm hot-rolled flat bar to form a big base.  The bit of hot-rolled needed some tidying up; that was done with the flycutter with a carbide tool - and doing the hot-chip dance ducking the chips  :


To get rid of the hard mill-scale on the flat sides, I used a sanding disk mounted on a rubber backing pad.  It was a bit coarse, as you'll see in the next photo.  Then I drilled the mounting holes for the frame:

The block was flipped upside-down, and a good deep countersink added to each hole, so that I could use M3 countersink screws to mount the frame.

Off to paint, and a good coat of primer from a rattle can added:


That dried enough by late evening yesterday that I could nip to the shop after dinner and add the colour coat - no photo of that though, as it was pouring down and I didn't want to run the camera through the rain.

Today's work to follow....

Regards, Arnold

[arnoldb]

The home stretch.

The paint job on the base looked quite good yesterday evening - I put it on thick hoping to hide some of the coarse marks still left on the base.  Well, after the overnight drying, some of the defects appeared as the paint solvent evaporated.

This is an unpretentious engine in design, and rather than bling it up to the n'th degree with polish and a better paint job on the base, I decided to leave it as-is: a simple honest quickly-built model that does not hide the flaws that crept in along the line.  It's not as pretty as some of my other models, but it was a LOT of fun with little effort, material and time involved.  A really good pick-me-upper and a good start to the new year.  Somehow I have a feeling that I'll be building more examples of this engine in future 

So, I assembled it up, and took a couple of photos:






And a video:
<a href="https://www.youtube.com/watch?v=sNlhquZCAWk" target="_blank">http://www.youtube.com/watch?v=sNlhquZCAWk</a>

  What next ? - I don't know...  Maybe I should sleep on it a bit 

Kind regards, Arnold