PDA

View Full Version : what compound angle .0001

Hal
03-28-2013, 03:55 PM
What angle do you set the compound at to for the .001 marks to equal .0001 ?

Thanks
Hal

Mcgyver
03-28-2013, 04:10 PM
What angle do you set the compound at to for the .001 marks to equal .0001 ?

Thanks
Hal

5.74 degrees, eyeballed as best you can to 5 3/4's will advance the tool bit in .0001" for every 1 thou on the compound.

This can work, but with the compound almost parallel to the lathe, the slightest inaccuracies, clearance and slop in the dovetail mess you up. tighten up the gib

Hal
03-28-2013, 04:14 PM
Mcgyver

Thanks for the info. I have it written down someplace.

Hal

John Garner
03-28-2013, 04:35 PM
Hal --

That angle is not some "magic number", but is very easy to derive. The derivation is basic trigonometry, the angle is calculated as the ArcSine of (0.0001 inch / 0.001 inch), which is exactly equal to the ArcSine of 0.1.

The only other thing you need to know is that at the zero angle, the compound travel is parallel to the spindle's axis of rotation.

John

KiddZimaHater
03-28-2013, 08:00 PM
If I need to remove .0001, I just grab the 60 grit sandpaper. :)

Scottike
03-28-2013, 09:17 PM
Enquiring minds what to know how this works out for you.

Hal
03-28-2013, 10:43 PM
John

I didn't really need .0001 exactly. I was just wanting a finer feed and remembered reading on this forum about about setting the compound just off of 90° would allow a .0001 feed. I just couldn't remember the correct angle.

Thanks
Hal

Hopper
03-28-2013, 10:55 PM
If you want to go one step more sensitive/accurate you can set the compound slide so that .001" on the dial moves the tool .00001", ie a hundredth of a thou. So this way to take a tenth of a thou cut you move the compound dial .010".

To do it, you need to set up a parallel bar between centres in the lathe, or turn one up if you dont have one. Then put a piece of flat plate in the tool holder that is about one one inch wide and four inches (100mm) long. Set the compound rest parallel to the lathe axis and clamp up the flat plate so it is firm against the parallel bar all along its 4" edge.

Then take a 1mm (.040" or so) drill bit or piece of wire or shim and reset the compound so that the lefthand end of the flat plate is firm against the parallel bar and the 1mm drill or shim just fits between the parallel bar and the flat plate at the right hand end.

This gives the compound an angle of about 0.6 degrees, or 1 in 100.
By using a larger movement of the compound slide to achieve an inward tool movement of .0001", this method may be a little more forgiving on older worn machines and is fun to play with on the newer ones.

Of course a very sharp tool finished on an oilstone is needed to take such fine cuts.

Euph0ny
03-29-2013, 02:05 PM
Here's Mr Peterson doing something along the line of angling the compound to get fine changes in diameter. He calls it 'splitting hairs':

http://youtu.be/n_dZe3K0a5M

Paul Alciatore
03-29-2013, 02:46 PM
If I need to remove .0001, I just grab the 60 grit sandpaper. :)

If you only want to remove 0.0001", you better go REAL EASY with 60 grit paper. You will take that much off with one or two revolutions of the work.

I usually start with 100 or 150 grit and even that will take off 0.0005" on a diameter very fast. The cutting tool usually leaves a slightly rough finish and the peaks of that finish will be removed quickly with sand paper. The process slows down after the first 0.0005" or so, depending on material and sharpness of the tool. Then it takes progressively longer to remove more. 50 or 60 grit paper may be more useful if one or more thousandths need to be removed.