On 2010-06-08, Spehro Pefhany wrote:
When spindle bore is specified as (say) 1", does that mean I can pass
a typical piece of 1" stock through it?
The tolerance on standard stock is, say +/-0.002" so the actual
hole would have to be a few thou bigger than nominal. Is it that
way or is the bore size usually just the nominal size?
That depends on the machine. Usually it is slightly oversized
with US made (or European made) machines -- except that the nominal
diameter on the European machines will likely be a metric dimension, not
inch.
If the dimension is too close, you could hit problems with
runout in a 3-jaw chuck causing interference.
I'm talking bout Griz import lathes if it makes any difference.
It probably does. Those were probably actually made to metric
dimensions (Chinese and Taiwanese machines). The closest integer
dimension to an inch is 25mm (lacking 0.4mm of full inch size), so it
depends on just how oversized the spindle bore really is.
I have heard stories of spindles which were the nominal
dimension at the ends, but which necked down in the middle. This would
call for a gun drill driven by the carriage to open it up full length,
letting the to-size part at the chuck end act as a pilot for the drill.
If the spindle won't quite clear your workpiece diameter and the
workpiece is the nominal size of the spindle bore, I would just make a
gun drill and take off those extra few thousandths. (Ask here if you
don't know what a gun drill is.) However, I would *not* consider taking
it up to the next size up. :-)
And, of course, this would almost certainly void your warranty.
And, BTW, what would be nicer is a bore of 1-3/8" 34.9mm, which
means that 35mm would be the nearest integer size). The reason for this
being a particularly desirable bore is that this will pass the drawbar
for 5C collets, the most common (and thus the most affordable) size of
collets.
So -- you have my thoughts on the matter.
Good Luck,
DoN.
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