Wednesday, December 21, 2011

Splice Clamp Support Block

 When I grind with the belt sander I am careful to set the table and miter fence as square as I can get them.  Then to minimize uneven grinding I make a couple passes and then rotate the part 180 degrees and make a couple passes.  If you use light pressure you can do a very good job of it.  The center for the pivot hole was then located on one end of the blocks.
 Before drilling the hole down the split between the blocks I used the bandsaw to create a guide hole to help the drill go straight down the center.  The saw cut was made about 1/32" deep.
 The centers for the screw holes were laid out 1/4" from the ends and 3/16" from the sides.  The blocks were then clamped together and the screw holes drilled with a #26 drill (tap drill size for 10-24 UNC threads).  To control the drill better I like to mark the hole with a spring loaded prick punch and then improve the mark with a center punch (fits the drill better), and start the hole with a center drill.  In this case I used a #2 (3/16) center drill.  Once the holes were drilled through I drilled a clearance hole from the screw head side 9/16" into the block, a little past the center split.
 The holes were tapped for 10-24 threads.  By working in the same direction that the screws go, the clearance hole helps keep the tap going straight in.  With the holes tapped the blocks were separated and the screw holes countersunk for the flat head set screws.  I used stainless Allen head screws so I could torque them easier than Phillips or slotted screws.  The screws are arranged so 2 install in opposite corners on each side.

 With the blocks screwed together, the pivot hole was drilled.  The hole was started with a #3 center drill ( 1/4") until it the hole edge was about 1/32" deep.  It was then drilled through with a 1/4" drill following the saw cuts.  Unless you own a drill vise or finger wrestle regularly with Superman, the wrench lets you get a good grip on the part being drilled.
 The hole was then increased at the start with a #4 1/2 center drill (3/8") about 1/16" deep at the hole edge.  The shape and short length of center drills minimize how much they can wander. The hole was then finished with a 25/64" drill to give clearance for the 3/8" bolt.  The steel bushing from Lowe's is 3/8" ID x 1/2" OD x 1-1/2" long.I need 9/16" sticking out the end for the 1/2" support piece and washer between the parts.
 The 1/2" hole for the bushing was drilled 15/16" deep after opening the start of the hole a little more with a #5 center drill (7/16").
 To get this block to clamp the bushing the mating faces of the blocks were ground down until there was about .002" gap with the bushing installed in clean parts.
 The screw holes and the busing interfere so a notch was filed in each side of the bushing the allow the screws to clear it.
The parts were then cleaned in MEK to get rid of cutting oil, etc. A little Krazy Glue was used on the bushing to secure it to the blocks.  The screws were secured with Threadlocker and tightened to squeeze out the gap between the blocks.  The edges of the block were then ground to remove the little bit of the screw heads sticking out past the edges.

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