Split Eccentrics- Advice on manufacture

[arch1947]

G'Day Everyone, I need to make 2 split eccentrics to drive oil pumps on the J Class. My thoughts were to completely finish the eccentric and then, using a .032" slitting saw, cut the finished part in 2 and that's that. I figure the small gap in the eccentric would not present a problem to the sheave and the eccentric should pull up tightly on the axle.
OR
The other option is to split the blank at the start, solder the 2 pieces together and then finish machine the whole part. Having done that I can separate the 2 parts and, using a file or emery on a surface plate, finally fit the pieces to give a good grip on the shaft and minimum the gap.

Not having done this before I will be grateful for any suggestions.

Cheers,
Arch

[Doug]

I personally would opt for option 2 you will get a much better fit for the eccentric strap, option 1 could cause wear by being too tight one side making the eccentric not completely round.

[uuu]

Another vote for option two.

Wilf

[albert]

Hello,
I would go for 2 but machine to width, clean up outside edges, drill for bolts then split the eccentric clean up the split add bolts then machine away internally.
Albert

[GWR 101]

Hi Arch, as always there are lots of ways of doing this, I have recently just made one of these for my Juliet build because I changed the location of the oil pump. I used a variation on the second method for ease of manufacture I adopted the "part on a stick" (thanks roger) approach. Firstly I chucked a short length of bar slightly larger OD. than the finished eccentric (s) and faced and centre drilled it. I then milled a flat down to where I wanted the axle hole.

 

I then cut a short length of rectangular bar and bolted it on to the flat with socket headed cap screws, I placed a very thin piece of silver paper in between the mating faces (not sure if this is absolutely necessary).  Then put it back in the lathe and machined the outer profile, parted off to correct width, centre dotted axle hole on join line. Back in lathe four jaw for boring etc.

Awaiting final tidy up. Hope this helps, Regards Paul

[eightpot]

Hi Arch, I had to make a split eccentric for my 'Enterprise' (Martin Evans LNER V1 2-6-2 tank loco) not long ago as I wished to have an axle pump of the 'Simplex' design fitted. I also opted for a two-part steel bar soft soldered together construction with counterbored Allen 1/4" cap-head screws to hold the two parts together. The only thing to bear in mind is that for this construction the eccentric will need to be a bit larger in diameter to accommodate the screws. In my case for a 1/2" stroke and a 3/4" diameter axle it ended up at 2-1/4" o/d for the flanges and 2-1/8" for the running surface. No boss to one side as space did not permit that. Also for the eccentric strap I needed a 7-1/4" gauge 'Holmside' casting.

[arch1947]

Hi Everyone, Thanks for your help. I finished up using a method similar to Paul's and the eccentrics came out OK. I couldn't attach any photo's for reasons I don't understand.
Thanks again,
Arch