Hi Guys,
Made the pins for the small end of the return crank this afternoon. Had my first covid jab this morning so got outside this afternoon.
For a decent pin that should wear well I decided to use some stainless I have acquired. It is chrome plated so needs some work to get through that but once through the stainless is very nice and machines well. These are the offcuts from some materials used for the R&D job of a friend of mine who is currently designing parts for the ejector seats on fighter jets. Obviously it is of excellent quality. I have several pieces set aside for various parts on this loco and the next.
On the prototype Sweet Pea the vibrating lever is held onto this pin with a washer and a spring pin. I have decided to thread the end and use a stainless washer and an M5 stainless locknut.
The first 12mm is reduced to 5mm then tapped M5. The next part is turned down to 1/4" to suit the return crank for a distance of 7/16". It is turned so it is a good press fit. I cut it off with 3mm spare and turned another one. They were then reversed in a 1/4" collet to turn the head, This is left at 5/16" and is 1/16" wide. Both were polished up and labeled for their corresponding crank.
Both had a washer and a nut put with them and were bagged ready for later use. They cannot be pressed in until the cranks are set and glued in.
Next job was to find the correct setting on the rear wheels for the cranks. They have to be exactly 180 degrees opposite the crank pins in the wheels. Both wheels need to both be set the same. In the build book a simple jig is made but the sizes used do not suit my axles. I have deviated slightly from the design sizes.
As I could not be bothered to work out the new sizes for a jig I chose a different route. In the lathe I turned two odds of mild steel to just fit the axle and drive pin holes. They were cut to length to fit within the thickness of the wheels. The ends to be used for this job were turned with the tool set exactly to centre height. This left a very nice centre mark.
Once in a wheel a steel rule was lined up exactly along these two centre points and a scribe used to mark the wheel.
This left a very accurate mark on the wheel at exactly 180 degrees.
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This mark will be used for crank setting in the next few days.
With nothing more to do to the wheels today I have taken this opportunity to paint them as cleaning the edges will be easier without the crankpins in the way. I used smooth black hammerite.
Once dry the excess will be removed from the faces to give a sharp edge to the paint. I painted the back aswell to keep the dreaded rust at bay.
I decided to start on the eccentric strap for the water pump as I need the eccentric to fit to the axle before I fit the wheels onto the axles. The strap is a bronze casting which was mounted in the four jaw on the lathe and faced both sides until it was down to a thickness of 1/4"
The white ring behind it was a plastic holder for plumbers pfte tape which I used as a spacer.
Next three lines were scribed on. One at the eventual centre and one at 1/32" on each side.
The strap was set in the mill vice with the centre line exactly aligned with the vice jaws.
All the faces were machined to size. The two outer faces where the clamp bolts will go were both machines to the same height to give a level to work to. The strap was then turned over in the vice.
The strap was set in the wice on two lengths of 1/8" tool steel. This means when the opposing faces are machined to size they are dead on parallel.
You will notice a bit of damage inflicted by the mill. As it is prone to do the bronze grabbed the mill cutter and tried to re-machine itself!
Luckily or hopefully it should be just out the way of the eccentric but we will see.
Next will be the drilling of the clamping bolt holes, cutting the strap in half and its boring out. I decided this could wait until tomorrow to save more damage.
I apologise again for mixing measurement units I prefer metric but use imperial when the design requires them. From the book or the plans there is no point in converting for use.
Cheers
Julian