Right Jack,
I am winging this, at 3.45am, hope the timing on the post doesn't give up before I've finished.
Recycle what you have already done, we will start from scratch, it will be a lot simpler. What you need to do is turn down your MS bar to 0.002" larger than it says, this is to allow for filing and polishing. This will allow you to make a cam that works.
1 start off with a bar 2" long. Turn down for a length of 1" to 0.714". Using a small centre drill put a small 'dimple' on the end to allow you to use spring dividers for layout, and to allow for pickup for the centre after finishing laying out.
2 Blue up, and mark a pair of lines thru the centre at 90 deg to each other.
3 Scribe a circle of about 0.564 dia. (this is only for use as a guide for cutting the lift faces).
4 Set one of the lines horizontal, and using your height gauge scribe a line parallel to the horizontal one 0.128" above it, rotate thru 180 deg and repeat.
5 Scribe a line at a tangent from the circle to where the parallel lines hit the edge of the outside OD. You should end up with what is shown in rough sketch.
6 Put it back in the lathe and finish the centre bore (being careful not to remove your layout).
7 Put blank into RT (put a bit of screwed up paper down into the chuck to stop you 'losing' the piece downwards) with your turned to diameter bit about 1/16" above the jaws and centre the job under the cutter chuck. Set RT to zero, set x & y handles to zero.
8 Put a fine point in your milling chuck and slacken off the RT chuck jaws and hand rotate your piece until you can move the y axis of the table back and forth and the point follows the centre line of the cam.
9 Recentre the the job under your cutter chuck, recheck your x & y are still at zero.
10 All your cutting will be 'conventional', NO CLIMB MILLING. So cut, rewind, put on another cut, and so on. NO CUTTING BOTH WAYS.
11 You are going to offset the RT to your right using the x axis handles by half of the cutter diameter plus half of the cam diameter. I would suggest something like a 1/4" cutter. So 0.125" (half cutter) plus 0.282" (half cam) = 0.407" (remember the clean up oversize of 0.002"). You are NOT going to be moving the x axis at all during the subsequent operations, so this can be fully locked up.
You should be looking at something like this.
12 Lock your miller table up and put a downwards cut on of about 0.010", and rotate the RT clockwise until it reaches 180 DEG, rewind to zero, put another cut on and repeat until you get a rythm going of depth of cut and and rotation speed, until you get to about 1" deep (or less if your cutter is shorter).
13 Lift up the cutter, slacken off your y table lock and wind the table towards you about 1/2". Turn the RT counter clockwise by a couple of degrees, wind forwards on the y until the cutter is over the blank and gently come down and just touch on and see where you are at. What you are looking to do is bring the line you marked to the edge parallel to the y cut of the miller by rotating the RT, it is a bit finicky. Eventually by rotating the RT you will get the cutter following the side lift line. See sketch. In fact it is the point where the line hits the outer edge that you need to aim for, the scribed line is just a marker.
14 Once you have it spot on the outer intersection mark, note the setting on the RT and lock up the RT. By using downwards cuts on the y axis you can now form the first lift face. Take it down to the same depth as the other cut.
15 Take off the cut, wind the y axis towards you by about 1/2".
16 Now these are guesstimate figures, don't use them, but use the figure for the RT that you noted down. Say you moved the RT counter clockwise to 350 deg. That means to get onto the line required an extra 10 deg 'off centre'.
17 Rotate the RT clockwise to 180 deg plus about 8 deg. This will give you a fiddle factor to get to the line. Cut the second lift side like the first. See sketch
18 You should now have the basic cam profile cut. You might need to blend the small diameter with the side lift faces at this point with a file, suck it and see.
19 Put the bit back into your lathe and using fairly fine emery, polish the outside of the cam, do not take off too much, this should also round off slightly the intersections of the flat lift sides and the roundy bits of the cam profile.
20 Part off the correct width, you should be able to get about 3 cams out of 1" depending on the width of your parting tool.
This has taken over 2.5 hours to compose, I would expect to make the cams in about half that time.
If I have made any obvious mistakes, let me know.
Cams for these small engines are not super critical, a few thou here or there makes really no difference, so what you are making should be perfectly OK.
John
