Engine Timing Case

Progress this past month ceased due to computer and hardware problems .I now have the system running on Windows  7 via a Smooth Stepper, which is availiable from Peter Homann Designs. This hardware allows the system to run from the USB .The new  computer has a parallel port which runs the Rutex drivers but would not drive the Gecko 540 .Modern PC computers  can be fitted with a parallel port .A plug in board is availiable for about $14 but is not suitable to run CNC drivers. The smooth stepper is powered from the USB but can easily be powered from a 5volt regulated supply. This should make it possible to run CNC machines from a laptop. The smooth stepper's output is two parallel ports. The stepper motors run very much quieter with this system.
  The intermittent problems with the y axis on both my CNC mills have been located and rectified.The plug on the servo driver board had a loose connection and one of the wires to the stepper motor had been sheared by the grub screw.In both cases these caused catastrophic destruction of the job and tool breakage
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This image shows the tool path for the back plate of the engines timing case.These apertures are the position of the crankshaft at the bottom , the fan drive directly above,the camshaft to the left and above and the magneto drive on top.The prototype has 38 teeth on the crank 76 on the camshaft,38 on the magneto drive and 18 on the fan which is driven off the camshaft gear. The design of the model engine had to be based  on the crakshaft being in line with the input shaft of the gearbox and the fan to be in the center of the radiator.To achieve these position I have chosen 1 module gearing ,30 , 60 , 30 and 14 teeth.
Now that these shaft positions have been set the engine can  be designed.The timing case has now been fabricated as in image below.The cylindrical housing is the cover for the governor, the other protrusion is the fan shaft bearing. The tube at the top is the breather for the engine which is also where the engine is filled with oil.The cover was brazed using manganese bronze filler wire which simulates the fillets of a casting.Shot blasting will further make the cover look as if it were a cast.
                                                                              
                                                                                 

Main Clutch

This is the clutch complete with the throw out fork with its linkage to the clutch lever. This clutch follows the prototype designs toggle action but I have made the clutch plate with four lug to fit into four keyways in the flywheel . In full size the plate is driven by reinforced rubber straps. The full size flywheel is relatively narrow and light weight.The flywheel in the model will be 130 mm in diameter and 40 mm thick to maximise its inertia for the engine to run at 650 r.p.m.The wide flywheel is not visible under the sheet metal cover.
The assembled clutch.The internal drive spline is a commercial part shrunk into the body









The components of the clutch.
The main frame was machined from 100 mm en25 bar with a cermet tip tool . A very tedious job on a small lathe.This frame is threaded for the spider which allows for adjustment for wear of the clutch plate .Note the bronze bush which is the bearing for the clutch plate. The clutch plate was profiled from 3.2 mm gauge plate. The plate is faced with leather.To assemble the clutch the plate is fitted first, next the splined nut which is pinned to the frame ,then the drive plate( which has a matching spline) is placed
over the nut. The spider assembly is scewed on top, adjusted to give appropriate pressure and clamped.
This image shows the spider which was first threaded in the lathe so that it could be mounted on the frame for machining. It has four slots for the cams .In one of the slots there is slit to the thread. A bolt across this slit clamps the spider



This is one half of the actuating trunion.

Radiator

The core attached to the top and bottom tanks. These tanks have been fabricated from brass and copper using silver solder. The caterpillar emblem has been engraved from a drawing traced from a photograph by David Micklethwaite who supplied me with a DXF file. Dave has a program for converting bitmap files to vector files. These tanks are joined by square headed bolts yet to be made.







The core under construction. The tube plates where jig drilled by CNC. The tubes are 3/16 thin wall copper salvaged from a Caterpillar tractors oil cooler. There are 100 tubes 5 rows of 20 soft soldered to the tube plates.






The radiator side frames where made from brass angle and flats silver soldered








This image shows the sixty logo being engraved. On this model these engraved signs are soft soldered in the frames .








This photo shows trial machining of the logo using a 1mm four flute end mill running at 12,000 rpm at a feed rate of 100mm per minute. The method was to pocket the sign and later profile each letter with different offsets to adjust their thickness. The final logo was inserted into a pocket machined in the top tank. This machine is an old BCA mill I converted to CNC using a Gecko 540 stepper driver. The Z axis is new with high precision NTN angular contact bearings. The original head with plain bearings was scrapped.

Brake and Steering Controls.

These are the components for the brake and steering linkages. The clevises are machined flat, then bent to shape red hot. The prototype clevises appear to be made by drop forging. Once formed they are brazed to the rod using silver solder flux and manganese bronze filler wire.





This picture shows the components of the steering stand, the steering arms, linkage parts and levers. The base of the stand and the web were cut out by CNC. The rest of the stand and the steering arms were made on the lathe and using hand tools.
Note the steering arms are very close to the design of the prototype.




The steering stand assembled (brazed).









This image shows the brake pedals on the shaft that operates the right hand turning brake, the left hand brake pedal hinges on this shaft and has the actuating lever attached.







The brake pedals were CNC machined from 6.5 mm steel plate, the treads were fluted using a D bit and then brazed on. The pockets on the sides of pedals were machined to 1mm deep using a 1mm diam 4 flute carbide end mill at 8000 RPM at a feed rate of 100 mm per minute cutting 0.25mm per pass with 40% cut over. This cutter has performed remarkably well considering the slow RPM




The right hand bell crank was also pocketed with the 1mm cutter.









The left hand side of the brake shaft is the axle for the main clutch lever.








The rear of the tractor showing the brake linkages coupled.

Preliminary Painting

The model has been painted grey in a satin finish. Prototypes were painted this colour to facilitate photography. The parts were etch-primed before using an airbrush to paint them.







The tracks will be immersed in a mixture of colloidal graphite and white spirit. This will help with lubrication. They will then be painted.

Gear Selector

The gear lever installed. There are three forward gears and reverse in an H pattern. The gears are locked in neutral with spring loaded pins. Moving the gear lever left or right acts on these pins which releases the interlocks - as in the prototype.






Here is the underside of the gear selectors. The forks are CNC machined from gauge plate. They are attached to steel blocks which slide on 4mm steel bars. The detents which hold the gears in mesh are machined in these blocks.

Transmission Manhole Cover

This is the left manhole cover for the transmission. There is another matching plate on the right. They give access to the steering clutches.







The hand wheel was initially threaded on the lathe and the spokes cut on the mill in a vertical chuck. The spokes were drawn in AutoCAD.







This was the jig used to braze the ball bearing onto the spokes. The jig is made from a graphite block and was jig-drilled to hold the balls in the correct position.







The finished cover before painting. The covers were machined out of 4mm steel. The ribs were machined before the outer profile was cut. The taper was hand filed.