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Mill Engine from Bar Stock By Thor Hansen After making a few slide valve engine with a trunk guide I decided to try and make a milltype engine with bar crosshead slides and a cylinder fabricated from gunmetal. With the stockI had available I could make a cylinder with approximately 19mm bore and 28mm stroke, thatmight be a bit short for a mill engine. Many thanks to Graham Meek for his advice and encouragement.

Materials The mild steel used I found in my scrapbox or in a skip nearby, some mild steelrods, the free-cutting stainless steel, M3threaded rod and nuts and the brass andgunmetal were purchased.Flywheel I started with the flywheel since I founda short piece of 3 in. steel tube in a skipnearby and another thick-walled piecewith an outer diameter of 90mm. Theinner diameter of the thick-walled piecewas less than 3 in. so I could turn thetwo pieces so one fitted inside the other.

I started by drilling six6.1mm holes 60 deg. apart inthe 3 in. steel tube using myhome made indexer – rightphoto. The holes were first spottedusing a centre drill before anordinary twist drill was usedto drill the holes. The hub was made from apiece of 20mm black mildsteel turned down to around

19mm and a 7.9mm hole drilled through and thenreamed to 8mm. The work was then transferred to my indexer and six5mm holes drilled 60 deg. apart almost into the 8mmhole and then tapped M6. I used a length of 6mm bright mild steel rod for thespokes, the rod was cut into 35mm long pieces andone end threaded M6 for a short distance. The leftphoto shows the wheel after silver soldering and alsothe jig used to make sure the hub ended up in the

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centre. The wheel was thenmounted on a betweencentres mandrel in the latheand the wheel turned to runtrue – right photo. I used a long bolt as a lathedog to drive the wheel, thisworked fairly well as longas I took light cuts.

The "tyre" was mounted inthe 4-jaw and centred andthe inside diameter turnedto a light push fit on thewheel. I didn’t take the lastcuts entirely through, butleft a small (about 1mm)ridge at the end closest tothe chuck, this will preventthe wheel from fallingtrough when gluing theparts together. I drilled three 2.5mm holes120 deg. apart in the wheeland used a short piece froma broken 2.5mm drill tospot these holes on theinside of the "tyre" so Icould use the same brokendrill in my Dremel tool and drill ashallow depression. The 2.5mmholes were tapped M3 for somegrub screws, I used a scriber tomake some witness marks that linedup the tapped holes with the marksin the tyre.

I applied epoxy to the two matingparts and pushed the two partstogether and let the epoxy cure ontop of my hot water tank. After the glue had cured theflywheel was mounted on the samemandrel between centres and finishturned. The right photo shows thefinished wheel (the inside got a coatof black paint).

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Crankshaft The Crankshaft was built up from a pieceof 8mm diameter bright mild steel rod andI found a couple of pieces of mild steel Icould use to make the webs. The two webs were glued together andthe centres for the Crankshaft andCrankpins marked. I drilled the two holesand reamed them to 8mm.The webs were milled to size and usingthe hole in the centre I could mount a webin the lathe chuck and turn the outside. The pieces were cleaned and I usedanaerobic glue to glue the pieces together– right photo. The Crankshaft is resting ontwo V-blocks while the glue cures.

I decided to pin the webs to the Crankshaft andCrankpin. The two V-blocks were used to clampthe work and 4 holes drilled for the 2mm pins –left photo. When I inserted the pins I first put adrop of anaerobic glue in the hole. The finished Crankshaft is shown below.

Bearing Blocks I found a couple of pieces of mildsteel in my box of scrap that I coulduse for the Bearing Blocks. First Imilled the underside and markedout the position of the M3 tappedholes that will be used to clamp theBearing Blocks to the Base. Theholes are 18mm apart so I used thedials on the milling machine handleto get the correct distance. I made a small jig to mount theBearing Blocks on, the jig couldthen be mounted on an angle-plate

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mounted on the lathe faceplate. On the frontBearing Block I had marked out the centreof the hole for the Bearing Bush and thehole for the bush could then be drilled andreamed. I don’t run my small engines for longperiods of time so I just used two pieces ofbrass tube for the two bushes that are a lightpress fit in the Bearing Blocks – rightphoto.

The left photo shows how I milled thecorners of the Bearing Blocks at 45 deg.

Base The Base was made from a piece ofaluminium 3mm thick. The work wasclamped to the milling machine table withsome scrap steel pieces as spacers to liftthe work well clear of the table. I the usedan end mill to mill one short side todimension – right photo. I could thenmove one clamp and mill that side todimension, so the move the clamp againand mill until all sides were milled. The sides were chamfered the same way.

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The next job was to mill a hole in thebase for the webs of the Crankshaft –right photo.

The position of the Bearing Blocks weremarked out and four 3mm holes drilled,the holes were countersunk on theunderside of the Base. I also drilled a 2.5mm hole in eachcorner and tapped M3, these tappedholes are used to clamp the Base to awooden box. The right photo shows the Base with theBearing Blocks (and Crankshaft andFlywheel) mounted.

Cylinder Cover I decided to combine the CylinderCover (with gland for the Piston Rod)and standard. I didn’t have a largeenough brass block, so I made thelargest part from mild steel and silversoldered (brazed) a few brass parts to thesteel part. I started with the steel part and milled itto dimensions – right photo.

I wanted the Piston Rod Gland recessed in thestandard so I used a 30mm face mill to mill therecess – left photo. I then drilled a 10mm hole in the centre of themilled recess.

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I cut off a suitable piece of 1.5mm brasssheet and a piece of brass rod and silversoldered (brazed) the parts together. The right photo shows the part after silversoldering and pickling in citric acid.

I used the dials on mymilling machine to drillfour 2.5mm holes on theunder side of the coverand mounted it on a sub-plate that I clamped to anangle plate on the lathefaceplate – right photo.

I could now face the endthat will face the cylinderand turn a 19mm spigotand drill a 3.8mm holethrough the brass rod andream it to 4mm.

The work was then mounted on my homemade rotary table with the 4mm reamedhole at the centre of the rotary table. Thework is a couple of millimetres above thetable surface. Then 6 holes spaced 60 deg. apart werecentre drilled on a 26mm PCD using a longcentre drill – left photo. I just marked theposition of the 6 holes, then used a 3mmdrill and drill through.

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The Cover was mounted on a piece ofangle iron on my rotary table and the tophalf milled round – right photo.

I also milled the "side walls" of the cover –left photo.

Cylinder The Cylinder was fabricated from a pieceof 32mm dia. leaded gunmetal and Isilver soldered (brazed) another piece ofgunmetal to the turned cylinder. The gunmetal rod was first centred in the4-jaw and the end faced, then the piecewas turned around and the other endfaced and centre drilled. The cylinder wasslightly over length as this stage. Thework could then be moved further out andsupported by a tailstock centre – rightphoto. Part of the cylinder was turneddown to a diameter of 25mm – as seen inthe right photo.

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The portface was made from anotherpiece of leaded gunmetal, first thepiece was squared up in the millingmachine. I then used a milling viseclamped on its side to hold the workwhile using a 20mm slot drill to mill acurve on the side that will face thecylinder – right photo that also showsthe cylinder.

I then used my boring head to bring the curve tofit the cylinder – left photo.

The two parts were then fluxed and silversoldered (brazed together) – right photo.

The work was then mounted in myindexer on the milling machine tableand the portface finish milled – rightphoto.

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The work was then mounted in the4-jaw and I could use the previouslydrilled centre hole to centre the workon the cylinder part. I drilled throughthe cylinder and finished with aboring bar – right photo.

The work was then mountedon an expanding mandrel sinceI had a sleeve that fit thecylinder bore. This way Icould finish turn each end ofthe cylinder – right photo.

A friend sandblasted the cylinder for me – leftphoto. I used the Cylinder Cover to spot and then drilland tap (M3) six holes in the Cylinder flange.

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The cylinder was then mounted with theportface up in the vise on the millingmachine, and I used the hand dials tomark out the position of the three ports –right photo. I then drilled a hole in each

port to make it easier for the tiny slot drills Iused to mill the ports – left photo. I also turned the work 90 deg. and drilled a holefrom the outside and into the exhaust port.

I used my tilting vise to drill the 2mmsteam passages from the end of theCylinder and into the steam ports – rightphoto. Before drilling I used a small slot drillto mill a flat to make it easier to start thedrill. I had marked out the bottom of the porton the side of the portblock so I couldmeasure how deep to drill (you don’twant to drill through the steam port andinto the exhaust port).

I also made a Cylinder Cover for theother cylinder end.

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Steam Chest I fabricated the steam chest frompieces of brass. To try and prevent thepieces from moving during the brazingprocess I drilled a few small blindholes and put short pieces of brass rodinto the holes – right photo.

The left photo shows the parts fluxed and readyto be silver soldered (brazed) together. In spite ofthe pins used some parts did move slightly.

The right photo shows the Steam Chestand cover after pickling and use ofemery cloth.

The Steam Chest was transferred to the millingmachine and the position of the various holesmarked. The left photo shows the drilling of four3mm holes – one in each corner.

I used a long centre drill to mark the position at the2.5mm dia. blind hole at the rear of the Steam Chest –right photo. This will give the Valve Rod some extrasupport

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The Steam Chest could then be usedto mark out the position of the four2.5mm holes in the Portface of theCylinder, the 2.5mm holes were thentapped M3 – right photo. The same procedure was used for thecover except I used a 3mm drill.

Slide Valve The Slide Valve was made fromfree-cutting stainless steel (303). Thestainless steel rod was clamped in asquare ER-32 Stevenson block so Icould mill the protruding partrectangular – right photo. I alsodrilled two 3mm holes at rightangles, these will make the bottom ofthe slots for the Valve Rod and nutrounded.

The work was then transferred to mylathe and a light facing cut taken. Ithen used a slot drill to mill the recessin the valve, the corners were dealtwith later.

Then the rectangular piece was parted offand transferred to the milling machine tofinish the recess – left photo.

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The work was then turned around inthe vise and the slots for the Valve Rodand Valve nut milled – right photo.

The left photo shows the Valve and nut.

Conrod and Big End Bearing The Conrod was fabricated from apiece of 5mm dia. mild steel rod and apiece of mild steel. The two parts weresilver soldered (brazed) together. Afterpickling in citric acid the Conrod wasdipped in a Sodium Bicarbonatesolution to neutralise the acid. The endof the rod with the mild steel piecebrazed on will be the Big End, theother end of the rod was heated andhammered flat. After the work hadcooled I milled the sides flat – rightphoto. I just measured the length fromthe Crosshead to the Crankpin andadded about 5mm when cutting the5mm rod,. This end of the Conrod was now a bitover length so I drilled a small centrehole and mounted it in my lathe. Imounted my Boring Head in the lathetailstock and placed a small revolvingcentre just off centre so I could turnthe main part of the Conrod with aslight taper (largest diameter at the bigend) – right photo. The part with thecentre hole was removed whenshortening the rod to correct lengthand threading M4.

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The Big End bearing was made fromtwo pieces of gunmetal left over fromthe portblock. I milled the two flatsthat will be joined and drilled two 3mm holes through and clamped themtogether – right photo.

The centre was marked and drilled and reamed to8mm – left photo.

The bearing was then mounted on amandrel with a diameter slightly over8mm so when the two screws weretightened the bearing was firmlyclamped on the mandrel and I couldturn the sides so the bearing would fiton the Crankpin – right photo.

Valve Rod The Valve Rod was made from 3mmfree-cutting stainless steel (303). Oneend was turned down to 2.5mm to fitin the blind hole in the Steam Chestand I used a tailstock dieholder whenthreading the M3 thread – rightphoto. The other end was threaded M3 thesame way for about 4mm.

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Piston The piston was turned from a piece offree-cutting stainless steel (303). I useda narrow parting tool to cut twopacking grooves – right photo.

The Piston rod was also made from4mm dia. free-cutting stainless steel(303) and threaded M4 at each end.

Crosshead and guides The Crosshead guides weremade from pieces of Cast Ironfrom old car disc brakes. Thematerial was fine grained andeasy to machine. The guide supports were partedoff from a 6mm mild steel rod,before parting off I drilled a3mm hole in the rod.

The Crosshead was made froma piece of mild steel milled todimensions and a 3.3mm holedrilled in the end facing theCylinder, the hole was tappedM4 to connect with the PistonRod. At the other end of theCrosshead a slot was milled forthe Conrod end, and a 2.5mmcross-hole drilled. The hole wasopened up to 3mm for most ofits length, the last part wastapped M3. A 3mm brass rodwas threaded at the end andused to connect the Conrod to the Crosshead.Since the guide supports were slightly short I hadto shim the bottom guides with some pieces ofstiff paper.Eccentric I used some Cast Iron for the Eccentric Sheaveand fabricated the Eccentric Strap from a shortpiece of mild steel tube and a piece of mild steelsilver soldered (brazed) together right photo. The hole for the Crankshaft was drilled 2.6mm

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off centre and reamed to 8mm. A 3.3mm hole was drilled radially and tapped M4 for a grubscrew. The Eccentric Strap’s protruding end was drilled 2.5mm and tapped M3 and a 3mm mildsteel rod was used for the Eccentric Rod.

Here’s a photo of the finished engine.

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