3/4" Scale Tender

JBodenmann · Post by **JBodenmann** » Sat Nov 07, 2009 4:33 pm

The process of cut and rotate 60 degrees has been repeated six times. This will produce a 7/16" hex that will make removing the caps to service the valves a snap.

JBodenmann · Post by **JBodenmann** » Sat Nov 07, 2009 4:37 pm

Now back to the lathe. Using the same cutter that was used to cut the threads there will be some cosmetic cuts. Totally unnecessary from a practical standpoint, but will give the parts a finished appearance.

JBodenmann · Post by **JBodenmann** » Sat Nov 07, 2009 4:38 pm

Cutting a chamfer on the top side of the lip.

JBodenmann · Post by **JBodenmann** » Sat Nov 07, 2009 4:49 pm

Using the parting tool and only cutting in about 1/8". These little parting tool are very handy. They are only .040" thick and are an important part of the model builders tool arsenal. You will have to make a holder for them. As they are making a narrow cut they are not creating a heavy tool load and will work in a light duty machine. I get them from MSC part #02643088. I'm sure Rutland and other tool suppliers have them also.

JBodenmann · Post by **JBodenmann** » Sat Nov 07, 2009 4:53 pm

Here is why the parting tool was only plunged in a bit. Now we are using the same cutter that we cut the threads with to chamfer the top of the cap. Like I said earlier, this is only a cosmetic cut, but it will give the little cap a more finished appearance.

JBodenmann · Post by **JBodenmann** » Sat Nov 07, 2009 4:55 pm

Now that the cap is basically done it can be parted off completely. As is often the case holding a part is the challenge. So the very last thing we want to do is to make the part into a little piece that is hard to hold.

JBodenmann · Post by **JBodenmann** » Sat Nov 07, 2009 5:01 pm

And here we have the four little caps and a highly detailed precision blueprint, drawn with an actual pencil! Have you ever thought about how many great and wonderful things started out with some pencil scribbles?

JBodenmann · Post by **JBodenmann** » Sat Nov 07, 2009 5:10 pm

Here is one important facet of the design. You will remember that one of the design criteria was that the valves must be serviceable without removing the pump from the tender. Once the caps have been removed the poppet valves may be lifted out of their cavities with tweezers. The original plan was to make the threads for the caps 7/16"-40 but that didn't quite allow enough room for the tweezers to fetch the little valves out. So the size of the threads was bumped up to 1/2"-40. This is how we learn!

JBodenmann · Post by **JBodenmann** » Sat Nov 07, 2009 5:22 pm

And here is the pump stuffed into the water leg of the tender tank. As you can see the caps are easily accessible once the water leg top sheet is removed. There will be a slot on the water leg top sheet for the pump operating handle to zoom back and forth in. I have been thinking about some sort of boot or sliding cover to keep cinders and dirt out of the water tank. What a delightful little puzzle the tender is, still a bit more to go and then time to start on the beautiful set of cylinder castings that John K at Friends Models- Yankee Workshops has sent me. I have never made a piston valve cylinder, or a Baker Valve gear. More fun little puzzles!
See you in the funny pages.
Jack

JBodenmann · Post by **JBodenmann** » Mon Nov 16, 2009 10:40 pm

Hello My Friends
Managed to get some time in on the little engine this Sunday. Back to the hand pump. First order was to make the little yoke that holds the operating lever and moves the piston back and forth. Started out with a piece of 1/2" x 1-1/4" brass. Just a scrap that was laying on the shelf.

JBodenmann · Post by **JBodenmann** » Mon Nov 16, 2009 10:49 pm

Here is our piece of brass after a bit of whittling and some scribbling with the Sharpie. The workpiece was first squared up, and then cross drilled 5/16" for the bushing that has been inserted here. Then the inside radius was simply cut with a 7/8" end mill. Then it was cut down using the milling machine and the large outside radius was zoomed on the disc sander.

JBodenmann · Post by **JBodenmann** » Mon Nov 16, 2009 10:50 pm

And here we are a bit later in the day. Pretty much assembled.