#37 Hi all. Today I decided to make the 'lever pivots'. Making two on opposite ends of a block seemed like a good way to eliminate too many repeated steps if they were made individually.
Below is a picture of the block with four 1/16" saw cuts. It turned out well with all four blocks measuring up within .001". I was thrilled! When I walked over to the bench to look at the plans something didn't look quite right. After re-examining the plans under magnification, I became painfully aware that the read 3/8" width of the block was actually 5/8" on the plan! My poor eye sight got me again! Turns out that I just spent nearly two hours practicing 'block sizing' and 'slot cutting'! With my adrenalin pumped up, and my experience level enhanced, the replacement block took less than one hour.
#38 The block needed to hang out one side of the mills vise for slotting. This type of clamping can offset the movable jaw and cause uneven pressure on the work piece that could lead to it shifting. To even out the pressure, the opposite end of the vise needed support. To accomplish this I made up two sets of space blocks to match the dimensions on the work piece. This is the first time I used these blocks, and they turned out to be a real secure time saving way to do this set up.
#39 To cut the out side profile on the sides of the 'lever pivots' I set up a vise stop block to do all the machining on four sides with one set up. After setting the end mill height, and moving the table over the width of the cut, it was simple to crank through each cut by flipping and rotating the work.
#40 Using the same flip and rotate stop block method I center drilled and drilled all twelve pivot pin holes. I shut off the mill only once to change out the center drill for the drill.
#41 To part off the pieces using the same slitting saw I used the same flip and rotate method.
However, this time the edge of the vise became my set up stop.
#42 Earlier on I decided the two mounting holes would be drilled as a last step. After zeroing out the spindle I randomly set up two pieces in the mill vise on top of two parallels. After each piece was individually zeroed out on the left side, the mill table was moved .0942" and then .5317" to drill the two mounting holes on the work pieces.
#43 After a little careful filing and sanding the 'lever pivots' are finished. Only three are needed for build #1 and build #2. It would have been more work to avoid making the fourth one, and it gave me a spare just in case one decides to jump off my bench, and commit suicide. The block at the bottom of the picture was my "practice" block. :
#44 It was still early in the day, so I decided to make a few more pieces. I couldn't find the diameter of the crank disc on my copy of the plans and decided that 1" would be about right based on the given 3/4" throw of the crank. Since build #1 is a single piston engine the plans specify a counter balanced crank disc.
To make the discs I machined up an over size round brass bar to 1" in diameter. After drilling and reaming the 'shaft' hole deep enough for two discs, they were individually faced smooth and cut off at 3/16" + .005" for a latter clean up of the less than acceptable surface finish created by the cut off tool.
I drilled a mounting hole in a scrap block mounted in the mill, and then zeroed out both hand wheels. I used a tight fitting bolt and mounted one of the discs faced side down separated by a piece of paper to prevent marring it. After off setting the table .375" the crank pin hole was drilled and reamed through the disc and part way into the scrap block. The second discs crank pin hole was drilled and reamed without breaking the set up by simply bolting it down. After reaming, a pin was pressed through it and into the scrap block to become an indexing pin for milling the counter balance profile needed on build #1. The cuts were made as calibrated moves based on the center of the disc being zeroed out. One cut strait in towards the center and out the right side completed the profile on one side. After returning the cutter to the starting point, the work piece was then flipped and the identical cut repeated on the other side. I found this method to be a simple solution to the problems I encountered in the past with reading hand wheels in reverse or dealing with lead screw back lash. Another example of the simple flip and repeat method I used earlier today.
#45 To complete the crank two pieces of 'shaft' were cut to length and ends were given a ground finish. I pressed them into the 'crank discs' from the faced side .005 short of bottoming out along with Loctite. The crank shafts were returned to the lathe for facing off the additional .005 left on the discs to clean up the sides cut with the parting tool. In the picture below you will notice that one crank disc was not profiled for counter balance. Build #2 is an opposed two cylinder and does not require a counter balanced crank.
I learned quite a bit today, and documented it as best I could in hopes that a beginner like me might find the methods I used today of some use.
-MB
