Setting the compound at 0* or 30*

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RSG
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Setting the compound at 0* or 30*

Post by RSG » Sat Jan 05, 2019 6:58 pm

I was working on the lathe today and got to thinking about how I set the compound on the lathe at 0* while performing regular machining operations but every video and other persons lathe I see its set to 30*.

What's the difference/advantage of setting the compound at 30* as opposed to just leaving it at 0* when performing standard machining operations. I've always set my to 0* unless I was threading.

Thanks in advance.
Vision is not seeing things as they are, but as they will be.

curtis cutter
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Re: Setting the compound at 0* or 30*

Post by curtis cutter » Sat Jan 05, 2019 7:02 pm

I am by no means an expert but my QCTP can rotate 360 degrees to any angle and I leave the compound at just under 30 degrees for threading.
Gregg
Just let go of it, it will eventually unplug itself.

John Hasler
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Re: Setting the compound at 0* or 30*

Post by John Hasler » Sat Jan 05, 2019 7:18 pm

I set it at whatever angle keeps it out of the way. If it isn't in the way it stays where I last used it which is quite likely to be 29.5. Don't leave it set at almost but not quite 0 or almost but not quite 90, though.

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wlw-19958
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Re: Setting the compound at 0* or 30*

Post by wlw-19958 » Sat Jan 05, 2019 9:04 pm

Hi There,

Like others have said, most people just leave the compound at
whatever angle they last used. Setting the compound at 30° (or
29.5°) is convenient for threading.

Another compound setting I use is 84°. This gives a reasonably
close 10 to 1 ratio in that a .001" movement of the compound
will move the cutter .0001" towards (or away from) the centerline
of the lathe. (actually, 84.26° will yield a true 10 to 1 ratio but
this would be difficult to set on most compounds and 84° has only
a 4.5% error).

Good Luck!
-Blue Chips-
Webb
Last edited by wlw-19958 on Sat Jan 05, 2019 9:11 pm, edited 1 time in total.

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GlennW
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Re: Setting the compound at 0* or 30*

Post by GlennW » Sat Jan 05, 2019 9:11 pm

I seldom set my compound slide to zero as it blocks my view of the cross slide dial...
Glenn

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Harold_V
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Re: Setting the compound at 0* or 30*

Post by Harold_V » Sun Jan 06, 2019 2:42 am

What Glenn said.
I keep my compound @ 29° at all times unless I am generating a desired angle. Once done, it is returned to 29°.
I choose 29° because there's no guarantee that the marks on a lathe are properly applied. The extra half degree does no harm when chasing a thread, and guarantees the tool is fed at less than half the angle, which is mandatory if one hopes to keep steps out of the trailing flank of the thread. I am far more likely to need the 29° setting than any other, and it's completely out of the way in regards to lathe operation.

I also keep my compound locked down (compound has no lock--but I keep the gib snug). I rely on dial settings, so keeping the compound locked assures I don't lose registration between not only the spindle centerline, but the carriage as well. To leave it loose is an invitation to problems one doesn't need, and it's all too easy to bump, especially if it is located where it's in the way. I'd also make mention that the ability to pick a tenth by setting @ 84° tends to create its own problems, as once you move the compound, your cross slide and carriage settings are no longer valid.

H
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ctwo
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Re: Setting the compound at 0* or 30*

Post by ctwo » Sun Jan 06, 2019 8:29 am

why is the cross slide used as a reference and not the spindle axis? I thought "American" style was to leave it at 90.
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RSG
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Re: Setting the compound at 0* or 30*

Post by RSG » Sun Jan 06, 2019 8:55 am

GlennW wrote:
Sat Jan 05, 2019 9:11 pm
I seldom set my compound slide to zero as it blocks my view of the cross slide dial...
Perhaps 0* on my machine and yours are different then Glenn? Setting mine at zero aligns it perpendicular to the top slide which is completely out of the way of the cross feed dial, unless I am miss understanding you.


Image
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spro
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Re: Setting the compound at 0* or 30*

Post by spro » Sun Jan 06, 2019 9:00 am

When I look at a "fish tail" setup gage, all those numbers are there for a reason. They denote the actual infeed at 29 1/2 degrees.

spro
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Re: Setting the compound at 0* or 30*

Post by spro » Sun Jan 06, 2019 9:18 am

RSG, Yes the markings are different but there is value to a set of 30*. Your pic displays a situation where the thrust is entirely against the compound lead screw, exploiting all play. I know you don't do that but the opposite 90* isn't perfect either. The balance is 30* relating to the cross feed. This allows continuous pressure by the slides and adjustment.

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SteveHGraham
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Re: Setting the compound at 0* or 30*

Post by SteveHGraham » Sun Jan 06, 2019 12:30 pm

John Hasler wrote:
Sat Jan 05, 2019 7:18 pm
I set it at whatever angle keeps it out of the way.
Sums up my policy.
Every hard-fried egg began life sunny-side up.

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tornitore45
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Re: Setting the compound at 0* or 30*

Post by tornitore45 » Sun Jan 06, 2019 1:10 pm

My compound is set at the last position it was set for a purpose
UNLESS
Is 90* (parallel to the spindle) Because it keeps the tail stock to move closer to the carriage
Is too close to 0* because it interferes with the cross slide crank
Is set to 6 degree (rarely) when need to advance a fraction of a 1/1000
It may be set to 45* to cut a large chamfer that would otherwise chatter if cut with a wide tool.
Mauro Gaetano
in Austin TX

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