#38 In today's post I'll show how I made the 'crosshead guide' assembly. I started by cutting two rectangles from a flat 1/16" brass plate. I drilled the 1/16" hole through both plates. Then I milled out the 3/16" 'crosshead' slot, and milled the stepped profile seen in the photo below.
#39 I made a two piece filing button to guide my filing while I produce the 7/32" radius shown in the drawing.
#40 The small radius on top was milled by rotating the work piece against a small end mill.
#41 After the radius's were finished a little bit of sand papering was used to finish up the pieces
#42 In the lathe I machined up the face of a 1" piece of brass and machined the outer diameter down to 15/16". This will be the lower part of the 'crosshead guide' assembly. I drilled and reamed a 1/4" hole in the center before removing the collet and work piece from the lathe.
#43 The next machining steps require the use of a 'hex' collet block. Since it will be used in a vertical position, I checked it for squareness in that position. The squareness check showed that the bottom face of the collet was perpendicular to the sides of the block. If needed I would have chucked the block and collet in the lathe for a light truing cut on the bottom of the collet.
#44 Two slots that position the upright parts of the 'guide' will be milled into the disc. Their center lines will be located with calibrated table moves, and their length will be achieved by milling between scribed stop lines. The only accurate way I could think of doing this scribed layout of the stop lines was to use my surface plate and height gauge. This was the very first time I used my height gauge for this type of layout. Its a nice accurate tool, and I liked working with it, once I figured out how to use it.
#45 To center the spindle on the center line of the work piece I used the conical end of my edge finder. I have developed a good feel for this method by using the tip of my finger nail to 'feel' for a step that indicates an improper line up between the two surfaces on the edge finder.
#46 I milled out the two 1/16" slots with a four flute center cutting end mill. I started the first cut in the middle by lowering the quill .020" and traversing slowly to one end and then to the other. The following passes were from end to end with the quill lowered .025" at each stop till a depth of .120" was reached. To keep my view unobstructed, and the cutter free of chips, I used 2 lbs of air pressure delivered by aquarium air line tubing. The key to success is low air pressure for safety, and very, very, slow speed of cutter advance. I usually pull up a chair and try to relax with hand cranking this size of end mill.
#47 With the quill already zeroed out on the work piece, and a work stop in place the next logical stop was drilling out the six 'bolt clearance holes for the screws that will bolt the 'crosshead guide' to the top of the 'cylinder'.
I used a center drill to spot all six locations by indexing the collet block, and then I switched to a #43 drill to finish up by drilling all six 'bolt clearance holes'.
#48 The work piece and collet were returned to the lathe to drill out the center hole to the specified size, and to part off the disc.
#49 I machined up a 'space block' type of fixture with a drilled 1/16" through hole. This enabled me to accurately line up and space the parts for soldering.
#50 I used a very small amount of flux to control its flow distance, and the flow distance of the following molten solder. This minimized and controlled the visible size of the solder joint. I worked exactly as planed, and the result can be seen in the picture below.
#51 To finish up the 'crosshead guide' assembly I added a 1/8" round brass spacer that was drilled all the way through for the specified 1/16' line up pin. It seemed to me that the pin alone could be easily bent.
That concludes today's progress report.
-MB
