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Posted on October 12, 2012:
Hello Folks!!! I am back at working on the magneto build where I am just about to finish up the magneto body. The next step is to drill out the holes for the points assembly but before I can do that I need to substitute the M3 points spring screw (below left) with a suitable SAE alternative. For that I will be using a 4-40 x 5/8” screw (same as the ones used on the laminations) that is cut down to .400” (below right) to hold the points spring in place on the magneto body.
Now that I know what size screw I will be using for the points spring I can drill and tap the hole needed for the screw.
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Next I lined up the spindle with the wiggler tool on the points spring anchor point which was laid out in the last episode.
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I now drilled the hole with a #43 drill to a depth of .350”.
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I tapped the hole with a 4-40 two-flute hand tap using my “custom” 3/8” drill chuck handle ;0)
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The next hole to drill is for the follower bushing of which I “spotted” with a #2 center drill.
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I Now followed the CD with a #14 drill bit as seen below...
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Next I used a 3/16” chucking reamer to clean up the hole.
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The next hole is more of a pocket and it is used for the tungsten tipped points contact. I drilled an 1/8” hole to a depth of .150” which will help the contact be seated into the larger pocket hole later on.
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The next step is to drill a 7/32” wide pocket for the contact point to be driven into. Normally I would use a end mill to make a pocket (or a counterbore bit) however I do not have a 7/32” end mill on hand so I will be using a flat ground 7/32” twist drill as seen below.
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I drilled the points pocket to a depth of .100” with the flat bit which worked OK however the bit wobbled around a bit due to the flex of the bit’s flutes. I could of fixed that by grinding the bit shorter so that there was less flute exposed past the chuck :0/
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The next step is to drive the contact into the pocket hole. This particular contact has a malleable steel base that is brazed (?) to the tungsten top. As the contact is driven into the hole it will “flower” out and lock itself into the hole. I believe the 1/8” hole in the center of the pocket helps this process out.
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Next I made an aluminum driver tool to set the points contact in place. I punched down the contact with a few smart blows from a hammer making sure I did not hit the contact at an angle. The tungsten top of the contact can shatter so do not use something sharp to drive the contact in.
Note: It is a good idea to make sure that the points contact is slightly above the magneto body so you can clean the contacts with fine sandpaper later on. This will be much harder to do if the points are recessed into the body of the magneto...
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The next thing I wanted to work on is the rotor dust cover. The dust cover will keep stray metal shavings from sticking to the rotor which would inevitably accumulate over time.
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The dust cover is made from a 1.250” x 1.250” x .125” piece of brass bar which is included in the kit. It needs to be trimmed down to 1.15” x 1.2” so I trimmed down the sides to get it to spec.
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The next step is to lay out the cover screw holes per the prints...
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Once again I will be substituting the M2 metric hardware (below left) with some stainless 2-56 x .250” fillister machine screws (below right) that I got from McMaster-Carr (Cat# 91794A077).
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I centered up the first hole with the wiggler tool and spotted it with a #1 center drill (not shown).
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Next I drilled out the hole with a #50 drill bit.
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I now drilled out the other three holes which are currently undersized as they will be used as a drill jig on the magneto body later on...
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The next step is to mount the cover in a four-jaw chuck so that the rotor pocket can be bored into the inside face of the cover. I centered the cover in the chuck using a set of center lines and the wiggler tool which was trued in the mill before placing it into the tail stock chuck. I also used a parallel bar to align the cover flat with the chuck’s face of which I removed before spinning up the chuck.
Note: I used aluminum shims on the sides of the cover to protect it from the jaws.
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Next I used a 5/8” end mill to plunge cut a .063” deep hole in the center of the cover.
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I now used a boring bar to widen out the pocket to an ID of 1.010”
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The next step is to use the cover as a drill jig to drill out the cover screw holes in the body. I clamped the cover in place on the milling table and drilled out the four #50 holes in the body with a cordless drill to a depth of about .250”...
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Next I widened out the cover screws with a #44 drill to allow the 2-56 screws to fit.
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Lastly I tapped the #50 holes in the body with a 2-56 tap...
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I cleaned up the brass dust cover with a green Scotch-Brite pad and then tested the fit with the 2-56 screws. Looks good so far...
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The next step is to make the points cam which is made from a piece of 3/4” steel bar that is provided in the kit (seen below). The cam is what opens and closes the points every rotation of the rotor shaft and must be rotationally positioned correctly with the magnetic poles of the rotor for a proper spark. Because of this the cam will ride on a sleeve that will allow the cam to be adjusted rotationally when inside the magneto for future adjustment.
The plans call for a .472” ID on the cam which is slightly larger than the inner race of the bearings. This means that the cam could come into contact with the bearing’s dust shield if adjusted incorrectly. I have decided to bore the cam with an ID of .438” so this cannot happen which will change the plans for the cam and the inner spacer.
I have also decided to substitute the 3/4” mild steel supplied with the kit with some W1 water-hardened tool steel which can be heat treated to a super hard state once machined. This will allow the cam to survive countless cycles of the points follower without it rounding over the cam’s profile.
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The first step is to square off one end of the tool steel as seen below.
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Next I bored a 13/64” hole in the end of the rod to a depth of .800”.
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I now used a 7/16” chucking reamer to bore out the rod to it’s final ID.
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Next I turned down the OD to .632” at a width of .700”.
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The next step is to part off the cam to a length of .660”. Note: I turned the rod around so that the big end was facing out of the chuck.
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I now trimmed the parted side so that the cam blank was at a length of .640” which is about .010” shorter than the inside spacing of the bearings at .649”.
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Before cutting the profile of the cam I decided to polish the blank with some 320 grit sandpaper. This is done to ensure the least amount of friction on the follower and must be done before the cam’s profile is cut.
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The next step is to lay out how wide the cam’s flat will be (.236”). During this time I also scribed a vertical line across the one side of the cam so that it can be rotationally aligned in the milling vise for machining (not shown).
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I now positioned the cam in the milling vise using the vertical line on the end of the cam (barely seen) and then mounted up an end mill to cut the flat of the cam. I then used the depth indicator to find out where the end mill begins to contact the surface of the cam (while spinning). The depth indicator was then zeroed out and I dropped the quill to a depth of .040” to make the flat on the cam as seen below.
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The next step is to drill and tap the adjustment screw for the cam of which the kit provides a M3 grub screw (below left). Once again I will substitute the metric set screw with a 4-40 x .125” stainless screw (below right) which I got from McMaster-Carr (Cat# 92311A103).
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I flipped over the cam in the milling vise using the vertical alignment line and laid out the set screw hole in the center of the cam.
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I spotted the hole with a #1 center drill and then drilled a #43 hole for the set screw.
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And now for the 4-40 tap...
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I now removed the cam from the vise and slightly rounded over the edges of the flat so the follower would not be damaged by the sharp edges.
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The next step is to heat up the cam to a cherry red with a propane torch.
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Next I quenched the cam in water as seen below. This makes the water-hardened tool steel really hard. I also lightly tempered the cam by heating it again to 400° F for a few minutes so that the metal would not be too brittle (not shown).
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A quick polish with some Scotch-Brite and the cam was finished!!!
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Please join me again on the next episode of the Red Wing Project where I will be finishing up the magneto build and hopefully making some sparks ;0)
Till then be well my friends!!!
Don R. Giandomenico
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