Well I think Geoff and Ron can take the blame for this one as their versions got me thinking about making my own.

I took the basic design out of Muncaster's book and redrew it in metric at a slightly larger 12mm bore (7/16" original) x 20mm stroke. to keep a constant theme I also drew and CNC cut a curved spoke flywheel from a slice of cast iron.

Having recently repaired a Mamod traction engine for some one I thought adding a reverser that works on the same principal would make things a bit more interesting both in the design, build and eventual running stages.

Quite a quick build even for me, looking at the dates on the photos I started it on a Friday evening and it was running 8 days later on the Saturday morning. The video starts off with direction and speed being controlled by the reverser then after about 60 seconds I'm just using the flow valve to alter speed, compressor regulator set to about 10PSI throughout. It will run by blowing down the airline but I did not think you would want to see film of me going blue in the face.

After taking the video I refilled the small 12lts tank on my compressor and then switched it off at the mains before setting the engine running at approx 100rpm. It ran for 38minutes which is rather good as my compressor is a bit on the loud side

Edited By JasonB on 07/03/2020 19:21:49

Edited By JasonB on 30/03/2020 13:56:59

So with us all on lock down I thought it would be a good time to get a set of drawings together and write up the build if anyone wants a small project to pass the hours. This time rather than separate drawings I have put all 10 sheets into one pdf which should make it easier when looking over them on the computer as you can scroll up and down rather than having to open multiple files. I have also done a Bill of materials for those that like to have one, note that sizes are generally of the finished part so make your own allowances for holding, parting etc.

In most cases materials can be substituted as well as methods, anyone with queries please ask. Also if you find anything wrong or missing on the drawings please let me know and I will update as needed.

Column

Start by facing the end of your 15 or 16mm stock and then form the spigot on the end followed by a small ctr drilled hole. The material can then be pulled further out of the chuck and tailstock support used while the tapered section and decorative beads are turned.

Transfer the part to the mill and hold by the remaining bar in a collet block or indexer to mill the two flats at the top followed by drilling and reaming for the bearing.

With the work back in the lathe form the small boss for the oil hole before parting off. The oil hole can be drilled while lightly holding the top of the column in a collet or in the 4-jaw, you could even leave it until later and just use the bench drill.

Bearing

This is a straight forward turning job, the column can be used to gauge the outside diameter and the 5mm hole is best reamed. The bearing is Loctited into place with 1mm protruding on the cylinder side and then the oil hole drilled through but don't do either of these things yet.

Crankshaft

A very easy part to make from either Precision Ground Mild Steel or Silver Steel (Drill Rod) but leave it say 1.0mm over length for now.

Crankpin

Another simple part from Silver steel

Crank Web

Start by forming the 8mm dia boss on the end of a piece of 25mm dia steel then drill and ream 5mm. Part or saw off leaving the web 1mm over thickness.

Transfer to the mill, locate the ctr and then move 10mm to one side to drill for the crankpin.

To mill the tapered sides slip the crankshaft material into the 5mm hole letting it rest on the vice jaws and the 2.5mm drill into the pin's hole but raise this up 2.75, you can see the black 2.8mm drill shank I used for this and then mill one side before repeating for the other though there is not so much to hold this time around so light cuts after sawing off most of the waste.

After rounding the corners to the final profile with a file the web can be Loctited to the crankshaft with 638 or 648 and set aside to dry. Then holding the shaft preferably in a collet a couple of cuts can be taken across the end of the web & shaft to bring them both to final size. deburr and then Loctite the pin into place.

Drawings to download

Bill of materials to Download

Thanks Rod, just don't expect a full write up and drawings at the same rate!

Actually I've probably spent more time with the Bonsai over the last couple of weeks than in the workshop as it's the time of year for repotting etc. have not really got myself motivated for a new build yet though there are a few casting sets sitting about and scratch builds that are 3D modelled, I did dig out my Hoglet that has been sitting around almost done for too long and have progressed that, just waiting for a couple of magnets to trip the ignition. How is your Farm Boy?

Before going on with the build I'll explain a bit about the reverser as the parts for that are the next to be made.

As I mentioned I recently repaired a Mamod traction engine for someone and got the idea from the reverse lever fitted to them which is simply a pressed steel lever that rotates and has an eccentric hole for the cylinder pivot.

There are three ports on the base, a central one that is the inlet with the ones either side acting as exhausts. As the cylinders pivot point is moved from one side to the other it will use two of the three holes depending on what side of ctr it is.

So with the lever down the pivot moves towards the right when viewed from the back.

Looking at the front you can see that the cylinder will oscillate between the left exhaust and central inlet.

If the lever is now moved upwards so that the pivot is now on the opposite side

Which means that the cylinder is now oscillating between the right hand exhaust and central inlet, this has the effect of making the upward power stroke take place when the crank is on the other side of centre thus reversing the direction in which the flywheel rotates. An added bonus of this arrangement is that with the lever placed somewhere between these two extreams the amount of time that the ports are open for is altered so the reverser can also be used to control speed and or save air/steam.

After turning the pivot bush it can be held in a collet block to firstly drill an dream the 3mm hole.

The collet block can then be repositioned so that the 1.5mm hole can be drilled at right angles to the first.

The size and shape of the adjusting nut is not critical and a diamond knurl will do if you don't have straight wheels. The pivot shaft is just a simple rod threaded at either end and hopefully you can find a spring of approx the right proportions to that shown.

The reversing lever is bent from 1.5mm rod and Loctited into the pivot bush.

The column can also be joined to the base at this stage with Loctite if you have a good fir or JBWeld if there is any movement. To endure the part face is at right angles to the bearing hole lay the two parts onto a flat surface when bonding and if you have a vice that opens far enough that can be used to holed them together while the adhesive dries. Once it has the cankshaft bearing can be loctited into place with 1mm protruding on the port face side and then the oil hole drilled through.

You should have something that looks like this if all has gone to plan.

Top Cover

The cylinder top cover helps guide the piston rod so turn the 1mm deep spigot and ream the hole at the same setting. Then transfer the work to the mill so that the three holes can be drilled while you have plenty to hold.

Then saw off from the bar and turn the external profile, if you like this can be a simple straight spigot 7mm dia but the curve looks a bit nicer and more like a casting when painted and the ring around the edge left bare.

Bottom Flange

The bottom flange can be made in much the same way but with threaded holes and is fitted to the end of the cylinder with Loctite, 648 if you intend to run on steam.

Bottom Cover

The bottom cover is just a dummy and made like the two items above. You could omit this part if you wanted in which case don't bother to drill and tap the bottom flange.

Big End

I started with some 3/8" round stock and turned the end down to 4.5 mm and tapped M3 before using the spin indexer to mill the 5mm square and drill & ream the cross hole. After sawing off from the bar filing buttons can be used to round over the end.

Piston Rod

Simply a piece of 3mm stainless steel threaded M3 at one end, use a tailstock die holder if you have one to make sure the big end screws on squarely.

Piston

Rough this out a little over diameter and cut the oil grooves before attaching to the piston rod with Loctite, 648 again if running on steam. Once this has cured hold by the rod in a collet, split bush or 4-jaw and skim the piston so it is a sliding fit in the cylinder.

'twas easy to place one in the middle and then one in each half doing it by eye though the large photo shows I was a bit off

Actually I have put two on the drawing and doubt 2 or 3 would make much difference.