Building A Billabong Engine

Home Model Engine Machinist Forum

Help Support Home Model Engine Machinist Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.


Active Member
Apr 29, 2010
Reaction score
G’day All,
Going back a few years a mate of mine (Len) decided to design and build a scale model stationary engine loosely based on one of the full size engines in his collection. He made all of his own patterns and even had a crack at doing the casting himself before deciding to get this done at a foundry. The story of how he designed and built The Billabong Engine (as it’s named) can be found on his website and is worth a read if you get a chance:

In January 2014 he was getting some castings done for a steam engine and asked me if I would like to get a set Billabong engine castings done at the same time and of course I jumped at the chance. After picking the castings up from the foundry they sat in a box for a few months and it was not until April 2014 that I started to do some work on them. This will be my first model engine build and is going to be a long term project. Given that I started on this a year ago now these first few posts will cover the work done since then and may give the false appearance of rapid progress. Unfortunately this is an illusion and progress has been slow however I endeavour to keep working away on it and will post updates as things progress.

First job was to machine the bottom of the crankcase casting which will become the reference surface. The crankcase doesn’t have another surface parallel to its base so Len had made a fixture (which I borrowed) to support it so as to avoid messing around with jacks and packers. Just enough material was machined from the bottom of the casting to make an even surface which only required a couple of .020” passes to complete.


Base casting and support fixture.


Machining the base.


Job done.

Main Bearing Caps
The main bearing caps needed to be finished to final dimensions so the seats in the base casting could be machined to a matching snug fit.

The first cap was clamped on its side in the vice and indicated in as even as possible before making a couple of clean up passes. The cap was then flipped over and positioned on a parallel so the other side could be machined flat and the width bought to a size that would fit neatly on the crank case. This process was then repeated for the second bearing cap.

I should probably mention at this point that there are no detailed plans or drawings for this engine, Len gave me a copy of his notes which includes hand sketches of the major components with indicative dimensions but nearly all of the machining needs to be done by the seat of your pants. This offers a lot of freedom but also means that careful thought needs to be given as to how work done on one component will affect its fit to another that may not yet have been machined. I have heaps of photos of a finished engine to refer to and will be able to discuss things with Len on the phone if necessary but the rest is pretty much up to my imagination

With the sides of both bearing caps now parallel they were clamped together in the vice so they could be machined to their final length of 2.625”. Both caps were then mounted together with the bottom facing up and the shoulders bridged across a couple of parallels and the bases machined to bring them to a height such that they would sit aesthetically on the crankcase while leaving enough meat to bore later on for the crank bearings.

Finally they were flipped over and positioned on a parallel so the tops of the oiler bosses could be machined flat. The positions of the bolt and oiler holes were then marked out, spotted with a centre drilland pilot drilled to 4mm. The bearing cap castings don’t have bosses for the retaining bolts so each mounting hole was counter-bored with a 16mm slot drill just enough to allow the mounting bolts to sit flat.

Unfortunately I didn’t take any photos of this process and apologise if this is a bit wordy.


Finished bearing caps.
Back to work on the crankcase casting where the next job was to machine the front which will mate with the cylinder. I think the cast surface looks better so rather than machining the entire front perpendicular to the base I used a facing head to remove only the circular area required to mate with the cylinder. Because of the pattern draft, this machining will create a small shoulder which will act as a seat for the cylinder.

The base was clamped directly to the table so the front was square to the Y axis then centred to the horizontal spindle of the mill in the X plane. To determine the distance from the top of the crankcase to the centre of the cylinder I simply came down half the width which should position the cylinder rim symmetrically to the crankcase.

I am lucky enough to have a Wohlhaupter UPA-4 boring and facing head which will be used a fair bit during this build as a number of the parts are just a bit too big for my lathe. Using the UPA-4 in facing mode the front of the crank case was machined back just enough to create a ring of clean material which will be the mating surface. The boring head didn’t have enough travel to work all the way to the centre without changing the tool position but as the centre will be removed in the next operation this was not necessary anyway.

The clearance hole for the cylinder liner was first spotted with a centre drill before progressively drilling it out to 27mm (my largest drill bit) before moving on to boring. I soon realised it was going to take a long time to get to 2.250” taking 0.030” cuts and decided to try using a 2” hole saw to remove a large chunk of the material. I was not sure how well this would work but the cast iron cut like butter with a spindle speed of 60 rpm and I had a 2” hole cut in about five minutes as opposed to what was probably going to take an hour or more of boring. With most of the material removed the hole was soon finished bored to the required diameter.

6YDQjhq.jpg Engine/Base 04_zpspvfihkji.jpg.html

First cut on the cylinder mounting face.

WRZKtV1.jpg Engine/Base 05_zps43ylibn1.jpg.html
Cutting cylinder liner clearance hole the quick way.

In order to maintain alignment with the cylinder mounting face the main bearing seats were machined next without disturbing the base. It was at this point I realised that by the time enough material was removed to create a suitable surface (about 0.125”) the centre of the crank would end up sitting about 0.125” below the centre of the cylinder. I don’t know if Len intentionally designed this engine to have a Désaxé layout or not but that is going to be the case for this one. The main bearing caps were then positioned on their corresponding mounts and the holes for the retaining studs spotted through the 4mm pilot holes.

8tk5nTJ.jpg Engine/Base 06_zpsi9fk5uzt.jpg.html

Base showing main bearing seats.

9ZrlVnl.jpg Engine/Base 07_zpsr6nrnq4r.jpg.html

Base with bearing caps in position.
That was about all I could do on the crankcase casting at this time so it was time to move on to the cylinder. This required a little bit of thought as to what would be the best way to proceed. Ideally most of the work on the cylinder would have been done in the lathe but I was not comfortable with the idea of hanging the 3kg+ casting unsupported from the four jaw of my little Hercus. So the mill was again pressed into service and the boring and facing head utilised.

The facing head was mounted in the horizontal spindle and the cylinder casting supported on a pair of matched v-blocks then clamped so the base mating surface (crank end) could be machined as the primary reference. It was indicated in as close as possible and about .100” removed to get a clean mating surface.

CYU0jtK.jpg Engine/Cylinder 01_zpsxbisfc9d.jpg.html

Facing the crank end of the cylinder action shot.

I0zDr4v.jpg Engine/Cylinder 02_zpsyfesx9th.jpg.html

The final facing cut on the crank end of the cylinder (the reference face)

tjefoZL.jpg Engine/Cylinder 03_zpsxsxnverj.jpg.html

A shot showing how the cylinder casting was clamped down.

The cylinder was then flipped to a vertical position so the reference surface could be clamped directly to the table and with the facing head in the vertical spindle the head mating surface was machined down until clean, sorry no photos of this part.

The cylinder now needed to be bored to bring the crank end to 2.25” and the head end 0.100” smaller to facilitate the cylinder liner installation. My original plan was to support the cylinder reference surface on a pair of parallels which would allow clearance from the table then bore the cylinder for the liner. As soon as I started to clamp things down though I realised that this setup wasn’t going to work as it left me no means of measuring the crank end bore. I know I could have bored them both to the smaller dimension then flipped the cylinder and finished the larger one but I wanted to machine both in the same setup to guarantee concentricity.

Another small problem was that the mould core must have shifted slightly during the casting process as the void for the water jacket was about 0.180” off centre but a bit of measuring confirmed that there was enough meat in the casting to allow this to be corrected.

With the cylinder again supported on the v-blocks the tilting table on my mill proved its worth here. The cast surface of the cylinder made repeatability virtually impossible so the cylinder was first indicated in to the X plane then clamped down. The table tilt locks were then slightly loosened and a few judicious taps allowed the Z plane to be quickly aligned and the table locked down. The whole thing was then roughly aligned to the spindle by using the boring head to swing a tool over the circumference of the cylinder flange while adjusting in the X and Z until it made even contact.

F4euAD0.jpg Engine/Cylinder 04_zpspfckzsgc.jpg.html
Clamped on its side again after facing the head end. The non-concentricity of the void is now quite visible.

aofv2Uq.jpg Engine/Cylinder 05_zpsqforlzmv.jpg.html

Marked out to verify there is enough meat to bring the bore back on centre.

The crank end was bored to the required 2.25” diameter using the shortest boring bar for the head, unfortunately the longest boring bar was a bit short to reach through to bore the head end so I ended up using an 8” long 16mm insert boring bar. I was a bit concerned about chatter but it worked better than I expected.
I started off taking 0.015” cuts which were only partial contact due to the non-concentricity and they cut fine with little chatter. I continued the 15 thou cuts once the tool was cutting for the entire circumference until the bore was close to size then took a few spring cuts to allow the bar to equalise and the chatter marginally increased but was still acceptable.
The final cuts were made by in 0.004” increments taking a primary cut advancing the tool, a spring cut withdrawing the tool, then a final spring cut advancing the tool. This seemed to work well and although a bit tedious it allowed me to sneak up on the final size and finish up spot on. The small amount of chatter left a slight pattern on the surface but a bit of a rub with fine emery cleaned this up and I’m pretty happy with the final finish.

aofv2Uq.jpg Engine/Cylinder 07_zpsgpuhxhyl.jpg.html

The crank end bored on size.
Next operation was to clean up the water jacket which was also off centre due to the shifted core. This was a fairly straight forward operation using the longest boring bar for the head. First boring roughly to size with the HSS cutter in the 90° end then clean up the end faces with the tool in the 45° end and finally a couple of light finishing passes across the length to bring to size.
Last job was to trim the cylinder flange and a bushing I'd made previously which allowed me to use 10mm shank lathe insert tools in the boring head came in handy for this. The operation was a straight forward enough but there was only about 1/8" clearance between the boring head and the mill table which looked pretty scary. Here's a short video showing some of the cylinder machining operations:
With the flange down to the correct size the cylinder was mounted on the rotary table and the six cylinder mounting stud holes drilled.


Cylinder on the rotary table ready to drill stud holes.


Finished stud pattern.
The casting I have for the cylinder liner is one that my mate Len cast himself. He was not sure of it's quality or if it might have some inclusions or porosity but we figured it was worth giving it a crack. Once again the core must have shifted a little during the pour and the void was a bit off centre. More measurements and head scratching to determine the best approach then the casting was mounted vertically on the mill table using vee blocks on an angle plate to get vertical in the X plane then a square to get it close enough in the Y plane, this with about 1/8" clearance from the table.

First off the top end was machined flat then the top 1.5" of the bore was machined out using a short boring bar until a complete circumference was cut. This was repeated on the outside surface of the liner so I would have something to indicate off if needed. Next the bottom 1.5" of the bore was machined using the 16mm insert bar, again until a full circumference was cut. Finally flip the liner upside down then mount on the angle plate with the machined end flat on the table, I couldn't get a 0.002" feeler gauge between the liner and the table so I was happy with that. A couple of quick clean up passes and that was about it for the mill work. These surfaces will be used as references for machining the outside of the liner to final dimensions in the lathe. Unfortunately I didn't get any photos of this work, my brain was hurting just getting things set up and cut.

To hold the casting in the lathe I made an expanding mandrel for the spindle end and a simple tight fit plug mandrel for the tail stock end to let me swing the casting between centres.

oTzfUIs.jpg Liner 01_zps3o5yli3x.jpg.html

Cylinder liner after machining reference surfaces on the mill.

AfPoNqu.jpg Liner 02_zpsi1cbrdji.jpg.html
Here you can see how the core had shifted.

e454p5d.jpg Liner Mandrel_zpsqyvslwmz.jpg.html
Mandrels to hold cylinder liner in the lathe.

E55W2xb.jpg Liner 03_zpswpocwsig.jpg.html

Mandrels installed in the liner.

lhbr8H8.jpg Liner 04_zpsqxqicbn4.jpg.html

Liner casting mounted between centres and ready to go.
Working on the liner involved machining to different classes of fit on different sections. There were two LN1 interference locational fits and two LC2 clearance locational fits (see refer to photo below).
Len's casting turned out to be very good with no porosity inclusions or voids, it machined well and I'm very happy with the final result.
The mandrels worked perfectly and didn't budge either during the initial heavy interrupted cuts or when the casting was removed to check the final fit. It would have been nice if the driven end mandrel had been about half an inch longer to allow a bit more access between the drive dog and the end of the liner but as I made it using a bit of scrap I had to hand, it was what it was.
In the end the final cuts were so light I could machine the driven end without the drive dog anyway so all was good. The final bore is still to be machined but this will be done later when the cylinder has been mounted on the crank case.

The LN1 sections are 0.0005" oversize on a 2.150" and 2.250" nominal diameter and the LC2 sections are 0.001" undersize on a 2.400" and 2.250" nominal diameter.


Work in progress, all the heavy cuts are done and working on rough machining to size.


Finished liner indicating fits.

That nearly brings the build up to date, I have done a bit of work on the head casting but the photos are still on the camera. As soon as I get them off I'll post another update.
Thanks for your interest.
Looks like a great project, I'll be following along with your progress.

I read the story of the development of the engine and it was a very interesting read. I've had to count my fingers to make sure they were all still there a couple of times and his accident made me cringe, but I can also relate to checking the part for damage before seeking help. Thanks for the link.
Thanks for your interest Al, knowing how Len squashed his hand is the main reason I'm doing a lot of the machining on the mill rather than the lathe. My lathe is smaller than his and given the size of some of these castings there's no way I'd take the chances of trying to swing them in it.

It was time to work out which side of the cylinder would be the top so the oiler and water ports could be drilled. I had already decided to have the parting lines of the cylinder casting positioned at the top and bottom when finally mounted on the base but I needed to decide which way around. I spent an hour or so fettling the cylinder casting so I could see which side would clean up and present the best and make this the top. I found that a hand scraper worked well when blending file marks and small casting imperfections and was pretty happy with the finished result. Having determined the top of the cylinder I needed to work out a way to mount it. The method I came up with was to place 0.250” rods in a couple of the cylinder mounting holes which were then rested against the top edge of an angle plate, thus ensuring the oiler and water ports would be vertical and perpendicular to the bore. This is kind of hard to explain so hopefully the picture below will make it a bit clearer.


Photo: The cylinder mounted on an angle block to drill, tap and counter-bore bottom water port.

The water port was drilled and tapped ¼”BSPF while a pilot hole was drilled for the oil port which will be finished off when the cylinder liner is installed. Both were slightly counter bored to provide flat surfaces to tighten fittings against.


Photo: Water and oiler ports all done.
I need to get the head fitted to the cylinder in order to work out where to cut the water jacket flow through points so the next job was to start the basic machining of the head. The cylinder mating surface, which will be the primary reference needed to be cleaned up first and again as this is a fairly large casting I’ll be doing this work in the mill. The casting includes a protrusion for mounting in a lathe so I clamped this in the mill vice using a v-block with the four head stud bosses resting on a couple of parallels. Shims were placed under a couple of the bosses to position the head as level as possible and minimise the amount of material to be removed.

Rm2UXmE.jpg Engine/Head 01_zpsuv3sohxx.jpg.html

Ready to cut the first pass.

A few quick passes with a face mill and the base was clean, an hour of fettling and shaping the casting and it came up looking very presentable. I have been quite impressed with the quality of the castings so far.

FbefepF.jpg Engine/Head 02_zpsoosdvwhz.jpg.html
After a couple of 0.050" passes.

The head stud bosses will be used as a reference surface when machining the combustion chamber so with the head clamped directly to the table each of the four bosses were milled to the same level. I also machined a couple of flats on the lathe mounting protrusion so it could be clamped in the vice without using a v-block. Engine/Head 03_zpsk3w8g2ke.jpg.html

All fettled and mounted ready to machine head stud bosses.

The locations of the four head stud holes were marked out and the head clamped to the table resting on a couple of parallels so they could be drilled.

mooE6DA.jpg Engine/Head 04_zpsthgks3uq.jpg.html
Drilling the last head stud hole.
There is a surface on the head where the side shaft bearing will mount. This was machined next so it could used as a reference to orient the head on the cylinder. With the head sitting directly on the mill table this surface was indicated in as close as possible and clamped down so a few clean up passes could be made. The cylinder was then placed upright on the mill table with two 0.250” rods in a couple of the cylinder mounting holes resting against a T slot. The head was positioned on the cylinder for the best fit and indicated in using the flat for the side shaft bearing. The whole lot was then clamped down so the cylinder could spotted for the head stud holes. Engine/Cylinder 12_zpsm1m2iygf.jpg.html

Setup for indicating the head orientation on the cylinder in preparation for spotting stud holes.

With the four holes marked the head was removed and the cylinder clamped down so they could be drilled and tapped 5/16 BSF. I prefer to drill and tap each hole before moving the table, doing it this way means a few extra tool changes but I know everything will be nicely aligned when finished.

6dZUbAG.jpg Engine/Cylinder 13_zpsm7xlkney.jpg.html
Tapping the last stud hole in cylinder.

The bosses in the head casting are not perfectly aligned (like corners of a square) and I scratched my head for a while over this before drilling them and decided to position the holes in the centre of each boss rather than trying to align them. This resulted in a slightly misaligned stud pattern that will require a bit of jiggery pokery when making gaskets but I figured this is far less noticeable than having the head nuts off centre to their respective bosses. The combination of the misaligned holes in the head and the positioning of the head on the cylinder that looked best resulted in the stud holes being a bit off centre in relation to the bore. However there was enough meat for the threads and when the cylinder liner is installed there will be enough surface area for a gasket to seal against so I’m not too concerned.

Next job was to make the head studs for which I used stainless steel as they might be exposed to coolant depending on how I cut the water galleries in the head. I only had 10mm stainless rod on hand which was machined down to make the 5/16” blanks before cutting the threads. The studs for the main bearing caps are a shorter version of the head studs so while the lathe was set up I made these too using 1045 rather than stainless. I’m pleased with how they came out and most importantly the head fits nicely on the cylinder with no movement whatsoever so I’m very happy with the result.

NHMfzLk.jpg Engine/Cylinder 14_zpsepuxrmeq.jpg.html
Main bearing cap and head studs.

66Drmi2.jpg Engine/Cylinder 15_zpsjl5h9guv.jpg.html

Cylinder with head studs installed. Here you can see that the right hand studs are closer to the bore than those on the left.

MZMCxq1.jpg Engine/Cylinder 16_zpslnxilfeo.jpg.html

Head and cylinder assembled.
I still haven’t made up my mind how the water galleries between the cylinder will be laid out (yes I’m too chicken to commit just yet) so in order to try and keep things moving along I decided to finish mounting the main bearing caps. These had already been pilot drilled so it was really just a matter of drilling the final 5/16 holes in the caps and drilling and tapping the 5/16 BSF stud holes in the crank case casting. The base was clamped directly to the mill table and with the first bearing cap in position one hole was drilled out to 6.8mm (required tap drill for 5/16 BSF) in both the cap and crank case. The cap was then removed and this hole drilled out to 5/16” in the drill press and the crank case tapped 5/16 BSF. One of the studs was installed and the cap replaced then clamped down with a nut and the process repeated. I did it this way as the caps fit very neatly into the recesses in the base so there is no wiggle room to compensate for any misalignment in the studs. This whole process was then repeated for the second bearing cap. The caps and crank case were also witness marked to facilitate correct installation.

MGgRDvB.jpg Bearing Caps 02_zpsfihzxqpn.jpg.html

Drilling the last main bearing cap stud hole.
Dqi6k9o.jpg Bearing Caps 03_zpsshripvjm.jpg.html

Tapping the last bearing cap stud hole 5/16 BSF.

As mentioned in an earlier post, the bearing cap castings did not include bosses for the studs so I made some inserts to simulate the look. Unfortunately as they’re only machined from BMS they don’t look quite right so eventually I will either make some from cast or machine up nuts that sort of have the boss built in but that is something that I’ll deal with a bit later on.

jTPx7c8.jpg Bearing Caps 04_zpsgwmtfjfr.jpg.html

Main bearing cap studs installed.

EgFa9I9.jpg Bearing Caps 05_zpsadrnzxxx.jpg.html

Main bearing caps assembled. The studs will be shortened later on.
Looking great so far. Love the tapping arrangement.
Thanks Herb and Gus for your kind comments.
I have certainly watched and learned a lot on this forum so anything I can contribute in return will only ever be a small repayment.
A "pro" is certainly not me, just someone bumbling my way along trying not to make too many mistakes.
I got some shed time on the weekend and used it to cut the water galleries in the cylinder. The casting was mounted upright on the rotary table and a 6mm carbide end-mill used to cut each of the four galleries. I had done a few mark-ups on paper to try different layouts but in the end just went with cutting them to within 1/4” of each stud hole.


Setup ready to cut first water gallery.


All Done.

The misaligned head stud pattern resulted in the galleries being slightly different sizes and as can be seen in the photo below, the bottom and top galleries are slightly off centre to the water inlet and outlet ports but I don’t think this will be an issue.


The finished water galleries.
Apologies for the overdue update but there has been incremental progress on the Billabong engine. The next job to tackle was some of the head machining, particularly establishing the location of the combustion chamber and water galleries. Unfortunately I didn’t take any progress photos of this work so I apologise for this post being a bit wordy.

When mounting the head for machining I use the bosses on the head as reference surfaces. The problem was that the length of the actual head studs would prevent the cylinder from mating fully with the head when it was mounted in the mill vice. In order to get around this I used the shorter studs I made for the main bearing caps which allowed the cylinder to sit flat on the head while remaining correctly oriented to it. The cylinder was temporarily installed to the head and the bore swept with an indicator to centre it to the spindle. The cylinder was then removed and the head centre drilled before using a 0.75” slot drill to cut a 0.125” deep hole which was them bored out to 1.0” diameter to mark the location of the combustion chamber.

The actual head studs were reinstalled on the cylinder and the head re-fitted so the location of the water galleries could be scribed. The head was then mounted in a vice on a rotary table and the combustion chamber used to centre everything so the water gallery pockets could be cut. The two side pockets were cut to their final depth of 1.5” while the top and bottom pockets were only cut to 0.25” so as to not interfere with the future valve chambers.


Photo of the head showing water galleries and combustion chamber machining.
Note the side water galleries are actually top and bottom in this photo.


Photo of the head installed on cylinder showing alignment of water galleries.

I have not yet decided how I will go about making the valve chambers. One option is to machine them directly into the head casting itself which is how Len does his but I am thinking of boring right through the head and using an insert for each valve which will allow them to be water cooled. My plan is to make a wooden mock-up of the head and try the insert method to see if it practical.

With the water galleries and combustion chamber now located on the head I could finally install the cylinder liner. I am very happy with the final fit of the liner which slid in nicely and after a few judicious hits with a rubber mallet was snugly fitted in the cylinder.


Cylinder liner installed into cylinder.


Cylinder viewed from head end.


Cylinder viewed from crank end.
It’s been a while between drinks but I’ve been getting a bit of work done on the engine when time has permitted.
The holes for the cylinder to crank case studs were drilled and tapped so the cylinder could finally be mounted, although I have yet to make the final studs.
To drill the holes, the crankcase was clamped to the mill and indicated in using the cylinder mounting surface. The cylinder and head were then positioned on the crank case so the side shaft mounting surface of the head could be used as a reference to indicate the position of the cylinder to the correct orientation. An extra long 0.250” drill was used to spot the location of the first hole and the cylinder was then removed and the hole drilled and tapped ¼” BSF. The cylinder was replaced and a temporary screw inserted in the first hole to set its position so the remaining five holes could be spot drilled. The cylinder was again removed and the holes drilled and tapped.

cJVg4SV.jpg Engine/Crank Case 08_zpsvztxh3jx.jpg.html

Engine mounted on the mill ready to spot the first cylinder to crank case stud location.

The angled surface of the cylinder flange from the pattern draft means the nuts that will hold the cylinder in place do not sit flat. I will need to make an extended counter-bore of some sort to machine a flat section for each nut but this is a job for another day.
Next job was to start work on the crank shaft components. Two pieces of 3” x 1” BMS were cut to the appropriate length for the webs and welded together at each end so the two webs could be machined at the same time.


Stock for the crank webs welded together and ready to machine to required thickness.

Each side was first machined flat and parallel then the two outer faces were machined down so each piece was the required 0.750” thick. Most of the stock was removed with an 80mm carbide face mill then the boring head was used as a fly cutter to remove the last couple of thou.


The nice pile of pretty blue chips produced by the carbide face mill.

With stock now the required thickness the web was marked out and the holes for the main shaft and crank pin were drilled and bored to size. The plan was to use a rotary table to facilitate cutting the angled sides of the webs so a hole was centre drilled at each of the two points of rotation allowing clearance for a 6mm end-mill. These would then be used to indicate the work in for the machining of each side.


Holes bored for main shaft, crank pin and reference holes for cutting webs to shape.

The rotary table was centred to the mill spindle and the X and Y axis zeroed. The work was loosely mounted on the rotary table then positioned and indicated in such that the first of the angle reference holes was centred to the table rotational axis. Finally the rotary table was roughly zeroed then slightly altered back and forth until the side of the crank web ran parallel. At this point the rotary table was zeroed and the mill table repositioned ready to take the first cut.


Indicating the initial position ready to cut the first side of the crank webs.

Starting from the smaller end where the web is parallel, the mill was fed in towards the rotational point taking a 0.020” cut. When the cutter reached the point of rotation the rotary table was set to 14⁰ and the cut continued on until the work piece was clear. The mill table was then moved back to the rotation point, the rotary table reset to 0⁰ and the mill table returned to the starting point. This was repeated for a few passes and worked ok but it became apparent as the slot got deeper that this was not going to work well because the cutter could not clear the chips properly from the narrow slot. At this point it occurred to me that a far better process would be to drill a series of 6mm holes 0.250” apart along the line of the cut then simply use a hacksaw to remove the excess and finish off to size using a larger end-mill.
The holes were centre drilled then through drilled for the first side, the work repositioned and the process repeated for the second side before removing it and cutting along the line of the holes with a hacksaw which worked a treat.


Holes drilled along the first side.


Cut ready to rough machine.

With the work now roughly to shape it was mounted back on the rotary table using the main shaft bore as the axis of rotation as the additional reference holes were no longer useable. This meant the cutter had to be repositioned after each cut rather than simply rotating the work under it. Using a 0.750” roughing end-mill the first side was cleaned up and bought close to size before finishing off with a 1” end-mill. The X axis position of the mill table in relation to zero was noted at the point where the angled section of the web began so it could be replicated on the other side. The rotary table was rotated 180⁰ and the procedure repeated. Measurements were then taken at several points to verify symmetry of the webs.


One side of web cleaned up with roughing cutter.


Side of web finish machined.


Both sides finish machined to size.

The last job was to round the ends of the webs which would also remove the welds and separate them. Again using the rotary table the work was clamped down with the bore of the main shaft as the axis of rotation and a roughing end-mill used to remove most of the material before taking a couple of passes with a finishing end-mill. Arranging the clamps to hold the work securely while not interfering with the cutter path was a bit tricky and I had to change things a bit after the work moved a slightly during one of the early roughing passes but the second arrangement held better and things proceeded smoothly from then on.


Setup for machining rounded ends.

The operation was repeated on the other end followed by a little bit of filing to clean things up and in all I’m pretty happy with how they turned out.


The completed crank webs.
hi there, just wondering if this thread has ended or maybe you finished the engine without a commentary.
Sorry I have only just found your build thread, as I was researching the billabong engine as an engine worth getting the castings for and I am very impressed with your description of your build.
I would love to see more of the engine, a video would be nice if possible.

Latest posts