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Thread: How to set an angle on lathe compound?

  1. #1
    Join Date
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    Default How to set an angle on lathe compound?

    I'm lacking in imagination, I need to set my lathe compound to 10 deg for the 5c adapter that I'm making. Lathe compound scale is set to 10 deg but the angle is still off a fraction of a degree. Tools that I have available include parallels, 123 blocks, mag base with indicator. Once I have the surface roughed in, I'll need to set up the same angle on the tool post grinder. Two images of the spindle, spindle rotated 180 deg.

    Sent from my 5049W using Tapatalk

  2. #2
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    One way is to chuck a known good collet in the spindle and using an indicator attached to the compound, sweep the length of the angle until it reads zero all along it. It's critical that your indicator tip is on center or error will result. Then remove the collet and chuck-up your workpiece.

    Here's a good video showing another way using measurements to set the angle:
    https://www.youtube.com/watch?v=YCllVu4K738

  3. #3
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    Quote Originally Posted by Galaxie View Post
    One way is to chuck a known good collet in the spindle and using an indicator attached to the compound, sweep the length of the angle until it reads zero all along it. It's critical that your indicator tip is on center or error will result. Then remove the collet and chuck-up your workpiece.
    Often it is a problem how to mount the "good collet" in the lathe.
    3-jaw has easily too much runout and angular error. And mounting existing good collet between centers is not necessarily easy.

    edit: there might be some trick to to spin the "good collet" to some "neutral" position even if there is runout but I have had one too much at the moment to think it trough.
    Last edited by MattiJ; 08-17-2019 at 01:30 PM.

  4. #4
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    Its called trial and error. You know it isn't quite right, you know which way the topslide (oh alright, compound if you must) needs to swing, so tap it with a copper hammer, then take another couple of thou out, try the collet again etc till its right.
    Simples.
    'It may not always be the best policy to do what is best technically, but those responsible for policy can never form a right judgement without knowledge of what is right technically' - 'Dutch' Kindelberger

  5. #5
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    Quote Originally Posted by MattiJ View Post
    Often it is a problem how to mount the "good collet" in the lathe.
    3-jaw has easily too much runout and angular error. And mounting existing good collet between centers is not necessarily easy.
    Yes, the only way I can think of is to use a 4-jaw. So if one were to use a 1/2" collet, one would have to place a 1/2" dowel pin in the collet and use the chuck to collapse it as best one can while watching the runout. Richard's answer is probably the best way in the end.

  6. #6
    Join Date
    Jun 2011
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    Why not put a chunk of oversize in the 3 jaw, and turn it down? Then you can fit the collet over that to measure. Using finishing tricks like a shear tool with the topslide set over at 5.75 degrees (that makes .001" feed on the topslide = 0.0001" infeed, since sin(5.75) = 0.100) and fine sandpaper, it's not *too* hard to hit within tenths of diameter. Once the spud is on size, it will also be on center for your spindle axis (assuming the truth of the spindle). Mount your collet, and measure away.

    Truth told, I never measure 5.75 degrees for my topslide. I just set at a light 6 by the scale and cut, cool, measure, repeat.

  7. #7
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    Thanks all. This is one of the few times where I am tring to really get the angle right.
    I've always used Richard's suggestion of trial and error (and up to now that's how I got it to about 1/2 deg of correct).

  8. #8
    Join Date
    Sep 2013
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    Use the travel indicator and trig out the angles. A piece of paper and a pencil is the correct tool for this prep work. After the first trial cut, make an evaluation as to which way the compound needs to go. Use the DTI to verify the changes you want to make. .001 over an inch is a lot of angle change, and you don't want to be chasing your tail bumping the compound back and forth.

  9. #9
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    My Chinese lathe has machined sides on the topslide/compound and I find useful to set to an angle by measuring (protractor) between the topslide and a bar in the lathe.

  10. #10
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    It will require a lot of patience and trial and error, I have the luxury of a taper turning attachment which is ten times better than a top slide and it still takes time to teach the required accuracy of a couple of minutes of arc.

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