This page gives some tips and hints that I learned while machining my first backplate from a rough casting.  A full description of machining such a backplate (by Mike Rehmus) can be found on the Metal Web News Site (click to go to that write up).

    I used a carbide insert threading bar for cutting the internal threads.  This greatly simplified the task (as opposed to trying to grind my own bit).  The tool I used is avialable from Wholesale Tool <http://www.wttool.com/wtool/frames.asp>.  It costs ~$30 (quite cheap) and is either "Right Hand Bar" order no. 2230-0005 or "Left Hand Bar" order no. 2230-0006. (Sorry I forget which, the salesman should be able to tell you).  The tool bar is shown in Figure 1

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Figure 1

    The backplate (6" size) comes with much more material than is needed for the finished part.  I cut part of the smaller end off for future use before I started the machining of the plate.  The backplate was too large to cut while clamped in my small bandsaw, so I mounted it on an angle plate bolted to the saw bed, in place of the regular vise.  A more detailed explanation can be found in the Locomotive Construction section.

    The first thing I discovered was that not all the spindles from the same manufacturer are identical!  I have a spare spindle (the one that came with the original babbit bearing headstock), and used that as a gauge.  When the back plate was "finished" I removed it from the chuck, and tried to install it on the spindle.  It was too tight and stopped about 1/32" from fully seating on the headstock spindle!!  Lesson 1 - Try the backplate on the spindle it will actually be installed on before removing it from the chuck!!!  Recentering the part and picking back up the thread is an "interesting" activity!  At lest I know that I have progressed to the point that I was able to do so, though the rest of the mistakes I made cast some doubt on how far I've come :-)

    I had originally planed to place the larger end by the headstock and use the smaller end as the locating stub, and machined the plate accordingly, to move the chuck as close to the headstock as possible.  However, once I tried to mount the plate I discovered a problem!  The plate now hit both the backgear lever and the indexing pin!  Figure 2 shows the two parts in relation to the corrected backplate.  So the plate went back on the chuck and I turned off 1/2" of the large end (of its' 1" thickness) to form a new shoulder.  Lesson 2.  This was not an over all "Bad Thing", the plate really did not need to be that thick and this took off some unneeded weight.  At least I did not have to pickup the thread again :->

Figure 2

    The chuck was supposed to come complete with the mounting bolts, but they were missing when the box arrived.  Rather than contacting the company, I decided to buy some cap screws to use for mounting.  It was several weeks until I got around to machining the backplate.  When I went to buy such large and long (7/16 X 4") cap screws I could not find any!!  Lesson 3 - Get all the parts you paid for!!  I bought equivalent sized hex bolts (Grade 8 was my only choice, I would have preferred Grade 5 (a little more ductile)), and modified the head as shown in Figure 3.  First I ground the head round, then I cut a screwdriver slot in the head.  To cut this slot I used a Dremel tool with two cutoff disks mounted on the arbor (Figure 2).  Dip the head into a cup of water as you go to keep it cool, during both operations.  This gave me the correct width slot, with a thin web left in the center (where the two disks had a slight gap between them).  I removed the web with a small file.

Figure 3

    When taping the mounting holes I used the Mark 1 eyeball method.  Wrong!  Lesson 4 - Always use the drill press, mill, etc. to guide the tap whenever any sort of accuracy is needed!!

    Lesson 5 - A rough cast backplate has a LOT of material to be removed!  Be prepared to spent some time at the lathe before you are finished.

    While it was a lot of work to machine this backplate, I learned how to do (and how not to do) many machining operations I had never done before.  Lesson 6 - New challenges can lead to a feeling of accomplishment when they are surmounted!!

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