I've never checked the precision of my drill press (Delta 14", model
14-070). So I picked up a piece of drill rod at McMaster-Carr (convenient
having a distribution center on the north end of the town I live). I
chucked it and could tell visually that there was substantial runout. I
pulled the chuck off and measured runout of the taper and got 0.002" TIR,
which I think is pretty good. So, now I'm considering replacing the chuck.
Trouble is, the instruction manual doesn't specify the size. I started off
assuming this was a Morse taper, but I think I'm finding out it's a Jacobs
taper. I measured the part on the drill press to have a minor diameter of
0.767" and a major diameter of 0.814". From what I can tell, this should
line up with a Jacobs taper #3. Does that sound right? Grizzly sells a
precision 5/8" x JT3 chuck for $40. Anywhere else to check for a
The taper that is in the chuck is a Jacobs taper. The taper that is in
the drill press spindle (if it has one; on some presses a male jacobs
taper is machined on the end of the spindle) is a morse taper.
I don't have access to the dimensions right now, but you are on the
right track. You can look them up in a Machinery's Handbook or easily
find them on the web. Look for the min dia, max dia, and lenght. There
is generally enough of a difference bewtween the different sizes that
it is easy enough to tell which you have. Also, the jacobs taper is
often marked on the chuck itself.
If you don't mind some watching and waiting, I recommend trying for a
genuine Jacobs chuck on ebay, or perhaps a Rohm or Albrecht or other
quality unit. Not trying to disparage the Grizzly, they may be fine,
but I've bought some very nice Jacobs chucks at very good prices
on ebay. Just takes some patience and restraint to find one at a good
Runout of even .002" on a jacobs isn't too good. How bad it is depends
on the type of runout.
If the runout is the same at the top and bottom of the taper, and on
the same side of the taper, then the taper is at least parallel to the
axis of the spindle and the runout of the chuck or a cutter won't be
If it's not the same at the top and bottom of the taper, or if it
changes direction, then the taper is not parallel to the spindle axis
and the runout will get worse at the chuck and cutter.
If the Delta manuals don't specify the taper - which they should - see
if it is marked on the chuck. It is not as likely to be a J3 as it is
a J33 or one of the other tapers. The Jacobs #3 was typically used
only for some of the heavier chucks.
What chuck you use is up to you. If the spindle taper is off, using a
precision chuck may be overkill. I like the Albrecht keyless chucks,
but they are pretty expensive. MSC carries a variety of decent
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