Re: [CAD_CAM_EDM_DRO] loose fit

On Tue, 22 Apr 2003 16:27:52 -0000, you wrote:

>Hi,
>
>Sorry for this lathe newbie question. This the the first time I'm
>trying to turn something on a CNC'ed Sherline lathe.
>
>I need to drill a just a mite over 2 mm hole into the face of the
>part. So I attact a drill chuck onto something which I think is
>called a "taper" which then fit into the tailstock. Turning the
>handwheel on the tailstock feeds a 2mm twist drill bit into the face
>of the part, producing the 2 mm hole. I have 2+ concerns:

OK, I can give you 2- answers.

>
>
>1. There is nothing to secure firmly the "taper" into the tailstock,
>and while the "taper" do not rotate when the twist drill is fed in,
>withdrawing it frequently result in the "taper" coming loose.

The taper is "self holding" It's probably an MT-2 (Morse Taper #2) or
perhaps an MT-1 taper. Under pressure (such as drilling) it will not
come loose. However, the taper is longer than the hole in the
tailstock for it, so withdrawing it all the way causes it to "bottom
out", and the taper is forced out of the socket. Cure: simply don't
withdraw it that far.... sorry, but that's really the answer.

>There
>is a thumbscrew on the tailstock with somekind of "rubberseal", but
>turning it in fulling don't seem to result in anything. It appears to
>me to be more of a decoration piece?

Probably not a decoration piece. It might lock the tailstock in
place, so you cannot change the setting. It's used to help lock the
work in place when you use the tailstock with a center to support a
long piece of work (long is defined as about 2 or more times the
diameter... )

>
>2. I need to get the hole just a mite over 2 mm (for a "loose fit?")
>but the next bigger twist drill is way too large. How do I enlarge
>the 2mm hole for a "loose fit"?

One very good way is to ream it, but that requires an oversize reamer
(I think you would want about 2-3 thousandths over for loose).

One way is to make a D-Bit and use it for the final cut. If the hole
were larger, you'd be boring it, and be using a boring bar. Have you
considered a set of number drills? They have far more sizes available
than the standard fractional sets... typically, you'd get a set of
drills #1 to #60 (smallest)....

>
>3. I need to turn the outer diameter down, with CNC control. How do I
>zero the Z-axis?

that one I can't help you with,

>
>I find using the radius as the z-axis to be logical, but I understand
>that for lathe, the diameter is taken to be z-axis? Not very sure how
>to handle that from a programming point of view.

ditto.

>
>Thanks in advance to all those who respond.
>
>Peter
>
>

Harvey