Vickers Inverted Engine

[JasonBModerator @jasonb]

Onwards and downwards to the bearing pedestals.

I started by milling some 6082 Aluminium into rectangular blocks, tapped the bottom halves M4 and drilled the tops 4.0mm. These were then screwed to a scrap block on the CNC to cut the oval shape.

The pedestals have an arched shape on the side, I replicated this by JB Welding on some rectangles of 1mm aluminium to the bottom halves and some arched shaped pieces cut on the CNC to the tops. Once the JBW had set the pedestals were screwed together and drilled & reamed

The bronze bearings were basic turning and boring

The crankshaft has an offset on one side so I made the webs for the built up construction two different thicknesses which were drilled & reamed on the manual mill. I then used the holes with some top hat bushes to secure them to a scrap piece and let the CNC cut the dog bone profile.

The web with the offset had the waste cut away with a hacksaw and was then held on a mandrel to round the remaining metal to match the CNC’d shape

The pin and rod were 10mm PGMS and it was all stuck together with Loctite 648 and left overnight.

The unwanted piece of shaft was sawn out and the faces filed flush.

All seems to go round and round as it should.

I then decided to do the big end. Two pieces of bronze were milled to size along with a steel bottom keep plate and drilled for the fitted bolts. capheads and nuts were used to hold the bronzes together for drilling and reaming.

Then onto the same 10mm mandrel used for the cranks to turn down each side to leave the round bosses.

Lastly the keep plate was added and a 3mm rounding over bit used to profile the sides

[DiogenesParticipant @diogenes]

..the rounding-over bits are okay for ‘short-chip’ material? – I notice you use a router cutter for the ali. bits…?

[JasonBModerator @jasonb]

Either type of cutter will work on most metals, I was just that I needed a larger radius for the aluminium base than I had in HSS or Carbide milling cutters.

[JasonBModerator @jasonb]

While down at the bottom end of the engine I decided to do the eccentric and strap next. For the strap two pieces of brass were milled leaving a bit of extra material on the one for the lower half. I then milled the flats before drilling and tapping for bolts. A non ferrous cutter with 3 flutes was used cutting a full 20mm height, may as well use all of the cutting surfaces you have paid for!

The two halves were then held together with some temporary cap heads to bore the hole for the eccentric and cut the 1mm x 1mm slot to accommodate the retaining rib of the eccentric The extra bit of material on the bottom half helps stop things being distorted by the 4-jaw but I did not overtighten to be sure.

A previously used arbor was altered to be a close fit in the strap which was then clamped in place with a couple of penny washers and a screw so that the outer profile could be completed on the rotary table. A bit of file work finished it off where I could not do the full arcs due to the screw heads being in the way

A narrow parting insert was used to turn the eccentric first getting the outer spigot a nice fit in the strap and then using the same handwheel setting to do the area behind the central rib. No measuring once I got close just using the starp as my gauge.

With the material held in a square collet block it was easy to offset and ream the hole for the crankshaft and then reposition the block to drill and tap for a grub screw directly inline with the highest part of the eccentric throw which helps when setting the initial timing as you can see the angle by where the allen key is pointing

The block also ensured the balancing hole was correctly orientated on the curre cutting machine which made quick work of it using a 3mm dia cutter

Last thing was to hold it on a piece of 10mm stock and turn the boss on each side using a tip with 0.8mm radius to leave a nice looking fillet.

In hindsight I would probably leave a bit more thickness between the counterbalance hole and the outer edge as it looks a bit thin in the flesh.

[JasonBModerator @jasonb]

Thanks.

With the eccentric and its strap done the next logical part was the valve. Nothing too exciting just the usual rectangular block with a slot for the nut and another at 90degrees for the valve rod and a bit of eight reduction around the sides.

Flip it up the other way and cut the cavity with a 2mm dia cutter

A scrap of 3mm thick brass was found and three sides of the nut machined and the central hole tapped before sawing it off and milling the final edge. I find it easier to do it that way than fiddle with a small piece of material.

The clevis for the valve eccentric rod had the end turned before drilling and tapping M2.5 then over to the spin indexer to square it up and drill the hole. After sawing off and rounding the end a 2.5mm cutter formed the slot.

No photos of the valve rod but it was just a piece of stainless steel threaded M2.5 at one end for the nut and a small 1.5mm dia x 1mm long spigot turned on the other. This spigot located in a hole drilled in the edge of the “eye” to hold it in place while the two were silver soldered together. A small guide bush in the entablature stops the rod being pushed sideways by the action of the eccentric rod.

I had designed and scaled the engine to suit the generic Stuart 7″ casting but decided to make my own as it keeps me out of mischief for a bit longer than just machining another cast flywheel would. As with several other engines, I started with some 203mm OD x 25mm thick wall steel tube leaving the diameter and width a bit oversize. The profile of the inner edge was done with a series of co-ordinate cuts using a 0.8mm tip radius insert in a boring bar – 22 cuts from each side. You can see the contours of these cuts best just below the boring bar.

With a piece of round bar in the toolpost to act as a tool rest a woodworking HSS scraper was used to take the tops off the contours and blend them into a smooth profile.

The 10mm bar for the spokes had a suitable concave curve cut on the end to sit closely against the profile of the rim.

Then after ctr drilling both ends the boring head was used to offset a small rotating ctr and the spokes were tapered.

The two halves of the hub were profiled in a similar way to the rim, a spigot on one locates the other and a 6mm hole allows them to be bolted together.

I then drilled 6 holes with a 6mm drill followed by plunging with a 10mm 3-flute cutter to form pockets for the other end of the spokes to locate into.

Quite a nice push fit into the holes and no spokes falling out which will mean no jigs needed for the next steps

The spokes were then machined to final length and a couple of chamfers were added as the bottoms of the pockets actually meet. I then redid the chamfers in the correct positions which should have been at the sides not top and bottom.

The rim joints were fluxed and silver soldered

Then when cooled the hub joints were done.

After a clean up it was back onto the 4-jaw to bring the slightly distorted rim to final size, skim the face of the hub and bore to fit the 10mm crankshaft

Lastly keyways were cut and a gib head key filed up from gauge plate.

Then it was time to play.

[Andrew CrowParticipant @andrewcrow91475]

I have been following this build since the start and I have to congratulate you on a first class design and build. Some ingenious manufacturing, e g the fly wheel.

Once again very well done.

Andy

[DiogenesParticipant @diogenes]

👍..looks great – won’t be long ’til we see it with it’s clothes on..

..found a piece of brass lying on the doormat yesterday..

 

[JasonBModerator @jasonb]

Thanks both.

There are a couple of changes from the drawings you have so wait a week or two until it is running and I’ll send you the part files, mainly eccentric and valve related.

[JasonBModerator @jasonb]

With the round and round bits done it was time to get on with the bits that go up and down.

Starting with the piston this was faced and tapped M4 with a 3mm deep x 4mm dia counterbore and after turning to 0.5mm over diameter I cut the piston ring slot to the final inner diameter and width.

After cutting it off from the stock on the bandsaw I held it in my soft jaws to face to width and bore a counterbore for a lock nut.

It was then screwed onto the piston rod and the nut fitted – no need for scale looking nuts here, off the shelf plated or stainless will do. A few light cuts had it down to final size, I don’t know what that is but it just “fits” the lapped cylinder bore with the right feel but probably less than 0.025mm smaller diameter.

The conrod started out as an offcut of 8mm structural Hot Rolled steel flat, milled and drilled/reamed as required with a bit of extra length on the little end for chucking.

The turning was then done in the lathe, the end thirds being tapered 1.5degrees and then all blended with files and Emery. The chucking material was then cut off, the end rounded over and a bronze bearing Loctited into place.

The cross head had all the important holes reamed while it was an easy to hold rectangle and I also milled out the pocket for the conrod at the same time.

With some packing to prevent the pocket from getting deformed it was held in the 4-jaw to turn the top spigot where the piston rod fits.

Then a couple of scalloped cuts to make it look nice.

There is still some external profiling to do on the cross head but it was far enough along for me to see if the engine would run. Just knocked up the wrist pin and retaining nut then fixed the piston rod to the crosshead with a taper pin and gave it a whiff of air at 5psi. One quick adjustment of the eyeballed eccentric position and it was off

Just needs the piston gland, oilers and a bunch of studs making then it will be ready for paint and a wooden base.

[DiogenesParticipant @diogenes]

That’s a very clean milled finish on your conrod blank..

[JasonBModerator @jasonb]

That’s what a 63mm facemill with 5 inserts for nonferrious can do for you.

[DiogenesParticipant @diogenes]

Aha – 👍

[JasonBModerator @jasonb]

With the engine proven to be a runner the last remaining items could be done.

The ends of the cross head were reduced down in height and a couple of top hat bushes machined so I could screw it down to a bit of aluminium and shape the outsidewhich was done on the CNC. An adaptive pass to remove the majority of the waste leaving 0.3mm to be taken off with three contour cuts, all done at the full 12mm height.

The 1mm spigots around the guide bar holes were then completed on the rotary table and a couple of buttons knocked up to shape the area around the underside of the wrist pin by file.

I’ll probably bead blast this and the eccentric strap for a nice even satin finish.

Some 8mm brass was used for the oil pots, turning a spigot and threading to start with, then into the spin indexer to machine the hex. Back into the lathe to cut the waist with a rounded tool and blend into the diameter of the cup with a file. Once sawn off they were screwed into a threaded arbor and a 5mm ball nosed cutter use dto hollow out the inside.

I also made just over thirty assorted studs but not worth taking a photo of them or the couple of stubby lengths of pipe for inlet and exhaust. Time to strip and paint it now.

 

[Nigel Graham 2Participant @nigelgraham2]

Beautiful work!

 

Valve-Chest Covers – Recesses.  Certainly more elegant than a plain slab, but are such recesses mainly for stiffening the plate? Some engine manufacturers used ribs instead.

 

Gib-head keys – yes, recently I used basically the same technique. Cutting the key from the end of a fairly long stock bar, I scribed two lines 300mm apart, and used a 3mm drill shank. My text-books give 1:100 taper as British Standard apparently irrespective if inch or metric, averaged from usual practice that varied from 1:96 (1/8″ : 1 foot) to 1:108.

 

Eccentrics – my project’s are as your engine, with a single central retaining rib, but differ in using separate retainers, like circlips without lugs, or piston-rings, with grooves in both sheave and strap. Thereby being able to turn right across at one diameter, rather than two matching diameters in opposite directions… mine likely wouldn’t match!  I might indeed investigate using circlips with the lugs removed.

 

Router bits. Neat way, successful at least on softer metals. A long time passing I made a replacement arbor for a Pallas horizontal mill, cutting the long keyway with a straight-flute, single-flute cutter. I vaguely recollect the material was stainless-steel, but do remember that sitting on a high stool at the end of the table rather than in front of it, helped me give a nice steady manual feed, and I succeeded in producing a straight, good-quality channel. It was only much later, when trying to find such milling-cutters,  I discovered I had used a woodworking router-bit!

 

 

 

 

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