The Burrell eccentric pushrods are rather small, the inside diameter of the strap is just 10mm. This is a 1/20th scale traction engine and so they will be quite small. Two off to give forward and reverse.
I made the 2 eccentric straps up from 1.8mm thick brass. I had to mill to this thickness from a thicker sheet as I just didn’t have anything the right size.
Here I’m using a ceramic breadboard and pins to arrange the eccentric straps so that I could then silver solder the clamp. Amazon – CooksonGold Ceramic Breadboards
The two pieces have easy flow silver solder paste applied to the interface prior to heating them up. Amazon – CooksonGold Easy Flo Paste
Machining the outer ring on the rotary table. I made an MT2 stub that has a 10mm hole through the centre. This then allows me to drop in different mandrels.
For this job I used a piece of 1/2″ diameter brass, drilled it 6mm through for the clamp down bolt and gave it two shoulders of 10mm diameter. A longer section that drops into my MT2 adaptor and a shorter upper section that the eccentric locates onto.
I then used a brass washer and a nut to lock this all down prior to end milling.
The arm for the eccentric was silver soldered to the strap. Again the ceramic breadboards are great here as they are flat and you can stop parts moving around with the pins.
A lid with the eccentrics, conrod, crankshaft, eccentric and one of the main crank bearing blocks.
The clamp was a piece of 3mm diameter brass that had been pre-drilled and tapped 10BA prior to it being silver soldered to the eccentric strap.
The strap was then sawn through using a thin model makers saw. Shown here clamped in the vice between two pieces of aluminium.
I then drilled the upper section of the fixing out to a clearance fit for 10BA.
That gave a simple way of clamping the eccentric pushrod strap around the eccentric itself.
Still quite a bit of fettling to do, but here you can see the eccentric being powered by an electric drill.
I might have to reduce the small end of the strap down in size. Will wait to finish this before finally tidying these up.