3/4" Scale J1e

[JBodenmann]

Hello My Friends
Here is a bit more on the throttle lever assembly. The master for the main casting is finished up. It will hold the sliding throttle shaft and the pivot for the throttle lever. It also holds the quadrant which is held in place here with a small clamp. This all bolts to another casting that fits to the back head. That is what the four raised bosses are for.

[JBodenmann]

Here is the casting that bolts to the back head. This is what the other part of the throttle will bolt to. This part has a hole in it with a round bead trimming it out. This bead was made from 1/16" brass round stock. It was first draw filed to make half round. I only needed a couple inches of half round so it was just draw filed. Then it was annealed and formed to shape around some pins. A stop was used to hold the half round and it was bent around the pins with a small piece of wood. One pin was 5/32" and the other was 1/8". After forming it was silver soldered to the work piece and the center was cut out with the mill using 5/32", and 1/8" end mills. Some small files were then used to finesse things. Two more masters to make, the handle that releases the latch, and the lever that will move the throttle rod down to the lever on the smoke box. Then some molds and off to the foundry. The bottom photo shows the two masters held together with a small clamp. Quite a fiddly little puzzle. The parts will all be cast in some sturdy bronze. More to come.
Jack

[Asteamhead]

Hello Jack,
What an achievement first to make that precise master (patern) to get a couple of perfect bronze castings
Asteamhead

[JBodenmann]

Hello My Friends
Thank you very much Asteamhead. I have made masters for molds and castings for a number of reasons. One is that I have made parts in the past, and later wished I had pulled a mold off them to reproduce more parts. Now when I make a cool little trinket, I will quite often make a mold, even if I may not need more in the future. Another reason is that it's often easier to make a master than an actual part. The master can be soft soldered and glued together. It can also have body filler and primer to help in finishing it out. The quadrants were cut using an EDM machine and it can cut ten just as easily as one. So I will probably get ten casing sets for the throttle lever and have them for sale for my 3/4" scale friends. I will probably never sell all ten, but they will be available anyway.
Jack

[JBodenmann]

Hello My Friends
The sand dome got some attention today. First the dome pattern was finessed to its final shape. Some rough cutting was done using the disc sander and some #80 grit. This removes material really fast so you have to be careful. Then a coarse aluminum file was used, checking frequently with a card stock pattern. Final shaping was with a fine single cut file, once again checking frequently with the pattern. Then a piece of .030 cold rolled was cut out and clamped to the form tool. The top of the form has an arch to it. The sheetmetal was heated with the oxy acetylene torch and massaged down onto the die with a hickory mallet. Get the sheetmetal dull red and gently worry it down with the mallet. Move around a lot and gradually work the metal down. Using a die and hot forming is a great way to make things out of steel sheetmetal. Steel is a wonderful metal to work with. You can stretch it. You can shrink it, which is what we are doing here. Gathering metal as the edge is worked down over the curved die. And you can weld steel. Great for joining formed parts. Welding steel is also handy as it allows you to correct mistakes. Cut too much off...weld some more back on.
More to come.
Jack

[NP317]

Impressive, as always!
Thanks for sharing.
russN

[JBodenmann]

Hello My Friends
Thanks Russ, this is something that may be useful. Now that the top portion is made it's time to start the sides. First a card stock pattern was made, using an old file folder. It was taped around the form tool and plunked down on the boiler. Then it was marked up using a Sharpie. Don't worry aboutt getting it too close on the fist try. Mark it and then trim it. Then put it back on the form and mark and trim it again. It may take a few tries to get a good fit. Then use the pattern to mark out some sheet metal. For this sand dome .030" cold rolled was used. It was trimmed using the band saw. The next step is to fit it tightly around the form tool. It was clamped around one corner and then heated to dull red with the torch. This will relax it nicely around the form. Then proceed to the next corner, making sure it is clamped closely. Work around the form tool until all four corners are formed. It should now be a nice snug fit all the way around. It was then given a good soak and scrub with Ospho metal prep, this will remove all the oxides and get it ready for welding the seam.

[JBodenmann]

Now it's time to weld the seam. This is done with it snugly clamped around the form tool. First make sure the edges are carefully aligned tack it and then check the alignment again. It may need a couple taps with a hammer. Then fully weld the seam. A TIG welder was used here, but in the bad old days this was done with the oxygen acetylene torch. This works fine but requires a bit more clean up. Go with what you got! Now it's clamped to the form tool again and the upper edge is curved in. Use a rawhide or wooden mallet. This can be formed without heat as we are just gathering a small amount of metal. Now the top and sides can be fitted together. This is done on the form tool, careful fitting pays off here. The disc sander and drum sander in the drill press was used. Trim a little, check the fit, trim a little more.... Once it is fitted up nicely the top part is clamped in place. Check that the two edges are lined up well. A few taps with the rawhide mallet may be needed. Then tack it where it's lined up. Tack your way around, checking and tapping to get things lined up as you go. It's easier to join pieces midway around a curve than where the curve meets the flat part. Curves are very forgiving and can be adjusted easily. Flat surfaces are not, there is only one flat, and it isn't very forgiving. Metal finishing on a curve is also easier than on the flat. After all is tacked and things are looking good the final weld can be made. The little hole on the top of the dome was for indexing, making sure it went on the form tool the same way every time. It is where one of the sand filler hatches will go later on. To me this is a really the fun part, hammering and fitting sheet metal to a pattern. The drudgery is making the form tool. But your finished part will only be as good as the form. Next up the base plate and fitting the dome to it.
See you in the funny pages...
Jack

[FKreider]

Wow! Nice Work as always!

[JBodenmann]

Hello My Friends
Why thank you FKreider, I appreciate your kind compliment. Well now that the side is joined to the top it's time to do a bit of metal finishing and trimming. The dome is a bit tall at this point, that was intentional, as it's easier to make it smaller than bigger. Its height was adjusted by removing metal around the bottom edge with a drum sander in the drill press. At this point it's roughly fitted to the boiler. It won't get too much refining at this point in case I mess it up and have to start over. Now it's time to make the base plate. On the prototype, the dome was made of three parts. The top was a steel stamping. The rest of the dome was formed plate, made to size to fit the curvature of the boiler, and to determine the overall height of the dome. This was welded to the top stamping. Then the whole mess was then welded to the base plate. Here an old file folder is being used for a pattern. It was sandwiched between the dome and the boiler, and the dome was traced around with a Sharpie. Then over to the work bench and some more scribbling with a Sharpie, a straight edge and a draftsman's 45. The pattern, also a bit oversize, was then transferred to another piece of .030" cold rolled and cut out with the kick shear. As you can see after a few careful zooms through the slip roll it was taped down to the boiler for a good look.

[JBodenmann]

Now its time for careful fitting. The dome had a centerline marked on it with the Sharpie, also the base plate and boiler jacket. The dome was also lebeled front and back. That way after each trim session with the drum sander, it would go back on the base plate the same way. A flat spot was intentionally left on the top of the dome so a small level could be placed on it. As it was trimmed for height and level, it was checked both side to side, and front to back with the level. It's a bit hard to see but in the second photo the dome still has a flat area on top. The dome was trimmed and fitted until it was the same height as the stack. It now fits the base plate very precisely. Now it's time for metal finishing. This consists of finessing and refining the arc across the top of the dome, and smoothing the surface. When making things like this you will have high and low spots. First thing is to raise the low spots. The third photo down shows the dome after sliding a flat file over it. The file only hits the high spots. That shows us what needs to be raised or "bumped up". This is done with a round faced body hammer, on two different surfaces. If very localized bumping is needed, it's set on some hardwood end grain. The hardwood is soft enough to allow very localized metal movement. Find the spot to be raised, flip it over and tap very lightly on the back side. If a larger area must be raised it is bumped once again with the round faced body hammer, but on a hard smooth surface. Here a 1-2-3 block is being used. Now you are stretching the metal. This will raise a general area. Once again, tap very lightly. After every few taps have a good look. This is a very controllable process, but it requires careful observation as you tap, continually checking the profile. Also keep using the file to find the low spots.

[NP317]

Jack:
I really like your techniques. Very basic hand metal forming that most anyone can learn to do well.
The resulting dome is forming really well.

And I learned to use a file for defining high spots. Obvious in retrospect!
Thanks.
RussN