Cross-Twin Engine

[Cobra]

Started the Cross Head guides the other day by starting on the spacers required under and between the guides.
Soon ran into problems keeping all of the spacers the same length using my long spindle stop.
Took a deviation from the Cross Head to make up a 5C Collet stop shown in one of the other posts.
Much better results with the stop in the collet.



With the eight spacers completed, I could move on to the actual guides.

Started with 0.25" Aluminium flat brought to dimension and then just skimmed to flatten the faces. Unfortunately that then meant go back and do the spacers again as the guides were now no longer 0.25" thick.
Made new spacers to accommodate the very slightly thinner plate.




Started with the centre cutout. Every time I do this kind of cutout in the middle of a piece, I thank Tom Griffin for the hints on plunge milling instead of using the side of the cutter to do the bulk of the metal removal.



Cut the 1/2" wide tracks with a 7/16" mill. Ran down the centre line first and the stepped over to each side and climb milled the finished edge and the last 3 thou of the depth.
Slots came out nice.
Drilled the four corner holes to finish each guide.



Start on the crankshaft next.

 

[Cobra]

Started on the crankshaft.
You can tell that hobbyists (at least me) have a low value of time! I needed a piece of 5/8" flat to make the web of the crank shaft.
All I had was a piece of 1" flat, 6" wide. So cut it roughly with the 4X6 and then start milling!


Eventually got it to size. NEXT TIME GO BUY A NEW PIECE OF MATERIAL!!!



Done and ready to start drilling the three shaft holes.
Decided the best way to ensure alignment of the three pieces of the web was to drill in one piece and then cut it apart for the three pieces.



Drilling and reaming for the 3/8" shafts.



Nice slip fit on the 3/8 drill rod used for the shafts.
Didn't try to do a shrink fit as they will be Loctite glued and pinned with spring pins at each joint.



Cut the first side piece off the main block. Notice that to preserve registration among the holes, they were marked to maintain the same orientations.
As a result of the saw cut, I now have one machined face on the TL side and a saw cut face. Before cutting the second side off, the saw cut face on the main block had to be machined to allow me to keep the square orientation of the holes in the main block. After milling the cut face it was returned to the saw to remove the other side piece.



Re-milling the centre block to keep the face square to the holes.



Cutting the second end piece off the main block. Had to set up blocking to clamp the short piece in the saw!



Milled both end pieces to keep the same thickness. (and save some time!)



Three blocks completed and ready for trial fitting. Note that I did manage to hold the orientation the same. (Major win!)



Trial fit with the three shafts.
The centre block will now have to be cut down to the angled connector.



Angle cuts laid out on the centre block. The block was set in the vise using a 1/8 parallel laying flat on the jaw to align with the scribed line.
The second cut is done with the initial cut face on a parallel.



Ready to start the assembly. All parts will be washed in acetone and then the two small shafts will be glued to the end webs using Red Loctite. They were left over night to harden before using the adhesive on the centre web.



Crankshaft all glued together. It will sit overnight before trying the drilling and reaming for spring pins at each of the seven joints.

 

[Cobra]

Getting back to posting some photos.



Drilling and reaming each joint for 3/32" spring pins. Amazed at how much personal stress is removed by moving to a spotting drill instead of the centre drills!




Pressing in the spring pins. need to make a smaller nose for the press so I can actually see that the pin is going in straight.




Back into the mill to remove the unneeded ends of the two outer arms.




Crankshaft completed.




Installed to the bearing blocks with Teflon spacers to centre the shaft.

 

[T Bredehoft]

Those pinned shafts look scary. I can't imagine they would last very long running. I've only turned cranks from solid. It's really a great exercise, however.

 

[Cobra]

Those pinned shafts look scary. I can't imagine they would last very long running. I've only turned cranks from solid. It's really a great exercise, however.

I am sure I wouldn't use that method for the Cobra, but I have never had a problem with steam engine models.

 

[Cobra]

In preparation of the piston work, I needed to finish off the cylinders. The outer surfaces were completed and the ports for the steam valve were added.






Finished the sides and the top surface.




Used a 5" Sine vise to cut the 45 degree edges.



With the cylinders finished, on to the four pistons.

 

[Cobra]

There are four pistons, two per cylinder. The outer pistons are connected to the crossheads by 1/8 rods and the inner pistons will be connected via stuffing boxes and cross links to the crossheads.



Turning the two pairs of pistons from 1-1/8 aluminium bar.



Completed piston sets.



Pistons installed and waiting for the crossheads.

 

[Terrywerm]

Nice work so far Jim. Thanks for sharing it with us. Is your engine per chance inspired by Elmer Verberg's engine of similar design?

 

[Cobra]

Nice work so far Jim. Thanks for sharing it with us. Is your engine per chance inspired by Elmer Verberg's engine of similar design?

Exactly Terry. I have built a number of his designs.
Lately I have started using his design as a start and redrawing, modifying and figuring out how to make.
Gives something for an activity while hiding from Canada's winter down south.

 

[Cobra]

Cross heads for the two cylinders.
Made as a single piece and the cut in half and trimmed to size.



Cross heads attached to the outboard pistons.



Cross heads fitted between the upper and lower guides.