3.5" Northumbrian Loco

[Baner]

Almost done!
I don't need the chucking piece on the pump anymore so that gets parted off and cleaned up:

I need a lock nut to clamp the pump to the stay. I didn't have the right sized Hex bar so a stub of 3/4 round goes to the rotary table and get milled into shape. Then to the lathe and finished off:

All that's left is to form the ball seats, (the balls have yet to arrive) clean up a bit and I'll probably paint the leftover raw cast areas. Here it is installed in the chassis:

Dave.

 

[Baner]

Up next are the eccentric straps.
I'm not overly impressed with the castings I'd received, but they can be made to work. They're not going to match the drawing but the critical dimensions should be achievable. First a clean face:

Northumbrian by DAVID BANER, on Flickr

Now that there's something flat to clamp against I started to chase flat surfaces around the straps:

Northumbrian by DAVID BANER, on Flickr

Eventually they all came in at matching, usable dimensions. Then the straps are marked for the next operations:

Northumbrian by DAVID BANER, on Flickr

Dave.

 

[Baner]

Now I drill through at 2.3mm and then drill 3mm clearance to 6mm deep, which is about half the depth of the side boss. Then the bottom half is tapped 6BA:

Northumbrian by DAVID BANER, on Flickr

Then it's over to the mill to split the piece in two. I'm using a 0.5mm saw here so I take it easy and make several passes to get through:

Northumbrian by DAVID BANER, on Flickr

Then 6BA studding is screwed in with a bit of loctite 243 for good measure:

Northumbrian by DAVID BANER, on Flickr

 

[Baner]

I haven't had a lot of time for the loco lately so just a little bit more on the straps:
The rough cored hole leaves no reference for centering in the four jaw so a piece of flat bar is clamped in the tool post and the top edge brought to center height. Then we can eyeball the split line and the vertical center marked out on the surface plate back at post#22:

Northumbrian by DAVID BANER, on Flickr

Unfortunately the boring bar is going to hit the outside jaws, so the set up is changed and the straps are bored to size:

Northumbrian by DAVID BANER, on Flickr

The easiest way to machine the straps to width is to make a mandrel to clamp them to. The diameter is turned to just slightly larger the the strap's bore so they will clamp on without spinning. This also ensures the sides of the strap will be machined parallel to the bore:

Northumbrian by DAVID BANER, on Flickr

All three are done in the same way:

Northumbrian by DAVID BANER, on Flickr

Though these castings will be functional, as can be seen in the photo, they are not the nicest looking things. They'll be hidden from view inside the chassis, but I might need to do something about their appearance.
If I can figure out what to do.

Dave.

 

[Baner]

There's not much to add I'm afraid. I've been busy, just not with loco parts. There's been a bit of shop re-organizing, work on another project, house and garden work, and preparing for a new baby due on Sept 4th...
All that's been done is slotting the eccentric straps for the rods:

Northumbrian by DAVID BANER, on Flickr

And cutting out some blanks for the rods themselves:

Northumbrian by DAVID BANER, on Flickr

I need to print out a drawing of the rod profile to glue onto the blanks to use as a shaping guide. Trouble is I don't have a printer at the moment, so I need to get to the local library and print there.
When I find the time...

Dave.

 

[Cymro77]

Very interesting, good photos. Understanding of how process is determined really helps. I will be better able to tackle my own castings in the future.
Thanks for sharing.
Best wishes for the soon to arrive family member!

 

[Baner]

Thanks Cymro77.

 

[Baner]

Alright, some progress!
I'd needed to profile the eccentric rods and my normal practice would be to print out a drawing to scale, glue it to a blank and have at with a file. Unfortunately my printer had long since died and I'd not been motivated to replace it. Turns out eccentric rods are the right sort of motivation:

Northumbrian by DAVID BANER, on Flickr

And after some drilling and filing:

Northumbrian by DAVID BANER, on Flickr

These fit in the slot previously machined in the eccentric strap. Whilst the cutter used was 2mm, and material used was 2mm, the fit was quite loose. This is an easy fix with shim stock. I keep a selection of sizes on hand for just this occasion. A small piece was cut and super glued to the rod (for convenience of handling):

Northumbrian by DAVID BANER, on Flickr

The pump eccentric strap was drilled:

Northumbrian by DAVID BANER, on Flickr

And finished by riveting the rod to the strap. The other eccentric straps will stay loose for now until more of the valve gear is made, in case any adjustments need to be made for fitting. I also managed to put some dings in the strap with the rivet snaps. I'll need to come up with some new snaps that give a little more clearance.

Northumbrian by DAVID BANER, on Flickr

Dave.