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| machine an eccentric |
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| John Rudd:
Guys, I need the wisdom of the collective... I need to machine a cam as per the crap-o-cad sketch... Basically, I want to machine an 8mm dia stub on a piece of bar that is 12mm in diameter...I've checked in my TC handbook on how to machine an eccentrc but it is as clear as mud... So I bow to the knowledge of the collective to tell me how to do this please... |
| Chuck in E. TN:
I have made eccentrics with a 3 jaw chuck by putting a shim under one of the jaws . Kinda trial and error way of doing it until you figure out how thick a shim you need. I have also done it in a 4 jaw independent chuck. Much easier. Chuck |
| John Rudd:
--- Quote from: Chuck in E. TN on December 29, 2012, 11:05:33 AM ---I have made eccentrics with a 3 jaw chuck by putting a shim under one of the jaws . Kinda trial and error way of doing it until you figure out how thick a shim you need. I have also done it in a 4 jaw independent chuck. Much easier. Chuck --- End quote --- Chuck, I've tried the spacer trick in the 3 jaw just as a trial...Seemed to work but I ended up with a spigot about 6mm in diameter.. :dremel: There must be an empirical way of doing this rather than trial and error....... :coffee: |
| mklotz:
If you must use shims, there's a program on my page (ECCENT) that will help you calculate the required shim size. Also included in that distribution is another program that uses a far safer technique than the redneck shim approach. For a 4jaw, spot the center of the tenon you wish to turn on the end of the stock, then use a pump center to get that spot running true, then cut away. |
| Lew_Merrick_PE:
John, Your sketch leaves a lot to be desired. You have an ø8 mm spud sticking eccentrically from the end of a ø12 mm round, right? The edge of the ø8 mm spud should be tangent to the ø12 mm round, right? The centerline of the ø12 mm round is 6 mm from the edges (duh). The centerline of the ø8 mm spud will be 4 mm "inside" the OD of the round (right?). Therefore, you need to offset the ø12 mm round by (6 - 4 =) 2 mm to make everything line up. An independent 4-jaw chuck is the way to go if you have such a beast. Otherwise, you stick a 2 mm shim inside one jaw of your 3-jaw chuck, tighten everything down, and walk through all the alignments to make sure that nothing is tipping. If my assumptions (stated above) are correct, this should work for you... |
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