Posting some build pictures of the H-Twin 4X scale

[Brian U]

Got organized here and decided to post some build pictures of Elmer's H-Twin engine 4X scale.

Glued CAD layout of side frames to aluminum stock for reference for rough band sawing contour and ball bearing bore for crank.
All operations will reference to the bearing bore and bottom machined edge where side meet base plate.

[Brian U]

Setting up the side frames to locate and bore for the crankshaft ball bearings and the bore for the bronze cylinder pivot bushing.
Working from the finished bottom edge for the bore "Y" distance and using the layout for "X" position. Plenty of material remains from band sawing so layout is accurate enough.

Also drilled the port holes for the inlet and exhaust.
Crankshaft bearings are 1/2" bore and bronze bushing is 3/8"

[Brian U]

Continued work on the side frames. Setup on sacrificial fixture plate on the Tormach to finish the outside contour. Also milled a 45 degree chamfer on the edges. Makes the side s right and left hand.

[Brian U]

Setting up the side frames to drill and tap the mounting holes, plus 1/8" slip fit dowel pin holes. Tapping 10/32 threads.

Machining the base plate square and drilling and c'bores for 10-32 SHCS. Also adding matching dowel pin holes foe side frames.

Add a 45 degree chamfer to the top edge.

Test assembly with the side frames.

[PaulR]

Very tidy! 

[Brian U]

The work continues with machining the manifold block. Finished size 1.500" thick x 2.000" deep and 2.750" wide.

Setting up in the mill with the manifold held between the side frames. Drilling thru the side frame and c'bore for 6-32 SHCS. Tap drill for the 6-32 threads in the manifold block and adding two slip fit 1/8" dowel pin holes. Finish drill the air passages in this setup. One air passage clear thru and the exhaust passage part way.

Same style setup to do the same operations on the opposite side frame.

Another trial assembly.

[Brian U]

Beginning work on the engine cylinders by squaring up stock to make two cylinder blanks. The overall size of each cylinder is 1 1/2" square x 3" long. After cutting the stock in half I set up to machine the overall length using my vise squaring jaw.

Machine a locating bore in one end for setting up in the lathe to do the bore. The bore is offset to the center of the 1 1/2" square blank.

Bored blind hole for the cylinder pivot shaft to have  press fit into the cylinder. Used a collet to hold the 3/8" pivot shaft to press into the cylinder. This insures perfect alignment to the cylinder face.
Any out of square to the cylinder face will cause problems with motion and air leaks.

[Brian U]

Setting up the cylinders at the lathe to bore. Indicating the bore done at the mill for location. Did the pivot pin press fit first so as not to distort the bore if done after boring.
The length of the pivot pin will be sized later in the build.

The cylinders being tapped for the heads.

[Brian U]

Setting up the piston/con rod after milling the required flat. Boring for ball bearings. Bearings are .500 O.D. x .250 I.D.

Next part are the crank throws, Set up after lathe work to drill and ream .250 diameter holes. Will Loctite the shafts in place.

[Brian U]

More work on the crank throws.

Made a fixture using a block of aluminum with matching center distance holes for the con rod pin and center bore. Using a gage pin to locate the center bore to the fixture. Edge find gage pin to find bore center and remove pin. Now the drilled and tapped hole to mount on the crankshaft rod will be exactly 180 degrees to the 1/4" pin.

Test fit assembly.

[Brian U]

All the parts finished and ready for assembly.


First trial run video.
https://www.youtube.com/shorts/FomPFO-srG0?feature=share

Thanks for the views and comments.

[Don1966]

Nice work and a very nice runner congrats!   

Don

[Kim]

Beautiful little engine! 
Kim