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2019 in the workshop
 

Making an integrated spinner backplate

24 June, 2020 - Spinner backplate &nbsp; I always thought it would be fun to make a spinner backplate that fits directly over the split cone on the engine's crankshaft. In a practical sense, this fixes the occasional problem where the engine backfires when starting and spins the propeller loose. <div style="Font-size:5.0pt" 24 June, 2020 - Spinner backplate &nbsp; Before starting, I sketch the dimensions of the finished product. I add ¼" to the length. <div style="Font-size:5.0pt" 21 June, 2020 - Spinner backplate &nbsp; I buy a chunk of 60 mm alloy and centre it in the 4 jaw chuck. Because of its length, I also "indicate" the work piece at its end to get rid of any wobble. This takes some time. <div style="Font-size:5.0pt" 21 June, 2020 - Spinner backplate &nbsp; My parting tool is not large enough to part through 60mm so I cut through the rest with a hacksaw. I refit the 3-jaw chuck but it has about .0015" run out. Not good enough, so I fit the four-jaw again. <div style="Font-size:5.0pt"
21 June, 2020 - Spinner backplate &nbsp; "Indicating" before starting operations in the 4-jaw chuck. I'm using US measurements because I'm more comfortable using them for fine measurements than metric. <div style="Font-size:5.0pt" 24 June, 2020 - Spinner backplate &nbsp; I machine the front (spinner) end first. The first few steps involve machining the end square, using a centring bit to provide a centre for the drills, machining the O.D. for a 2" spinner and bringing the hub down to its final diameter of roughly 1". The hub is eventually machined off; it is only there to hold the work piece when it is reversed to machine the back (motor) end. <div style="Font-size:5.0pt" 24 June, 2020 - Spinner backplate &nbsp; The crankshaft of the RO-Jett 67 is 10mm (.394"). I get a 10 mm drill and fit the split cone to it and check the angle, 18°. The previous time I did this, I adjusted the tool post and checked the angle with engineer's blue until I had a perfect setting. This turned out to be 18°. <div style="Font-size:5.0pt" 24 June, 2020 - Spinner backplate &nbsp;I drill the work piece out with a drill slightly smaller than 1/4", the size of the prop shaft. <div style="Font-size:5.0pt"
24 June, 2020 - Spinner backplate &nbsp;Then I use a 1/4" end mill to machine the hole to its finished size <div style="Font-size:5.0pt" 24 June, 2020 - Spinner backplate &nbsp;I now machine the cutout for the spinner <div style="Font-size:5.0pt" 24 June, 2020 - Spinner backplate &nbsp;After creeping up on it a few thou. at a time, the spinner is a push fit <div style="Font-size:5.0pt" 24 June, 2020 - Spinner backplate &nbsp;I then reverse the work piece and machine the motor end. This takes a few attempts to align it but the runout is nearly perfect <div style="Font-size:5.0pt"
24 June, 2020 - Spinner backplate &nbsp;There is a huge amount of waste to machine away. All of that metal up to the backplate itself has to be removed until it's about 1" in diameter, the same measurement as the engine-casting's diameter. I've added a shaft extension of ¼" to its length. It's at this point that I machine the width of the backplate to 4mm. <div style="Font-size:5.0pt" 24 June, 2020 - Spinner backplate &nbsp;I machine the hole out part way to fit the 10mm portion of the crankshaft ( On a RO-Jett 67, the crankshaft is 10mm and a separate 1/4" x 28 stud is screwed in) The crankshaft is 10mm because the engine uses metric sized bearings front and rear. <div style="Font-size:5.0pt" 24 June, 2020 - Spinner backplate &nbsp;I set the tool post to 18° to suit the taper. <div style="Font-size:5.0pt" 24 June, 2020 - Spinner backplate &nbsp;This cutting tool and holder cost me quite a bit but it was worth it for the job it does. I machine out the 18° taper stopping many times to check its size against the split collet. <div style="Font-size:5.0pt"
24 June, 2020 - Spinner backplate &nbsp;I forgot to photograph the shaping of the rest of the engine side. When that is complete, I turn the job around again and machine away the hub which is now no longer required. I push the work up against the jaws of the four jaw chuck and "indicate" it to make sure the work piece is running true. <div style="Font-size:5.0pt" 24 June, 2020 - Spinner backplate &nbsp;Everything fits nicely but is a bit heavier than I want at 28 grams (1 ounce) <div style="Font-size:5.0pt" 24 June, 2020 - Spinner backplate &nbsp;This is the finished product from the rear. I can see a few places here that are over engineered and where weight can be saved. Next time, better. End of this project &nbsp; Click to go to home page <div style="Font-size:5.0pt"  
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