Re: [CAD_CAM_EDM_DRO] Dumb question on the drilling of holes

Guys,
I'm following this subject with great interest. One of the reasons I
subscribe to this group, is to learn enough to convert my mill to CNC. I
have been fabricating some parts on a mill, using the DRO, and have run into
problems drilling holes. Using certain drill bits, many of the holes have
come out oversize, and some completely out-of-round. Changing bits has
helped, especially if I use a shorter length bit, but I'm going to
investigate using the 135 degree, or other similar drills. I'm looking
forward to a CNC conversion, when I intend to center drill the holes before
using the correct drill bit.

Marv Frankel
Los Angeles

----- Original Message -----
From: "Alan Marconett KM6VV" <KM6VV@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Tuesday, October 22, 2002 12:05 PM
Subject: Re: [CAD_CAM_EDM_DRO] Dumb question on the drilling of holes


> Hi Alan,
>
> I've read that you DON'T want to center punch the holes for CNC,
> although you might want to make light "witness" crosshairs to mark their
> location. Best would be to always start with a center drill, then
> follow with the appropriate drill. The trouble with a punch mark if not
> EXACTLY where you want it, is that it will pull a drill bit off. If the
> CNC has moved to the proper location, then you just want to drill where
> you are!
>
> To position the mill to a hole's location, set up a "wiggler" in the
> spindle, and, using a magnifying glass if necessary, move it tho the
> crosshairs. Or, you might prefer to locate everything relative to a
> pair of edges (LL corner is often good), and let the CNC work from
> that. I like using the edges if it's a new part, and then let the CNC
> find the other points.
>
> I'm using Vector CAD/CAM, and if I put a point at each hole location,
> down at the depth I need for the center drill, Vector will do a move to
> a location ABOVE Z=0, and then a slow Z down to the required depth,
> center drilling it for me. It will also generate a following G81 with
> the coordinates, which I modify to G83 to actually drill the hole (I
> like the "peck" and "dwell"). I "comment out" the G83's with a '/' in
> the part program, and turn on "block deletes" on the controller program
> (DON'T FORGET!). With the center bit "touched off" in Z, I run the
> program with block deletes on. This way, the center drill drills all
> the holes I want. Then I replace the center drill with a drill bit of
> the required size (you may want to repeat the process with two or more
> drill bits), disable block deletes, and run the part program again.
> With block deletes disabled, the G83's will be run, and the holes
> drilled. OK, this may not work for a "PRO" shop with tool changers and
> the like, but it works fine for my Sherline's, and I assume it will work
> as well on my RF-31 mill (when I finally get it converted) and possible
> a lathe in the future.
>
> HTH
>
> Alan KM6VV
> P.S. You can set the Z depth to just "kiss" the stock with the center
> drill, and thus run a "verify pass" first, to check your program! Also,
> a "pen holder" in the spindle, and a piece of paper can give you
> re-assurances that you've programmed the Gcode correctly. I've taken to
> printing a 1:1 of the part and the cuts on paper (HP laser is not far
> off), and this also helps to verify setup, CLAMPS, etc.
>
> alan@... wrote:
> >
> > Forgive me this seemingly dumb question, but how does a person "drill"
> > accurately placed holes under CNC control without first center-punching
> > them.
> >
> > I currently use a center drill to start the hole ( for deep holes ) or
> > just mill the hole via G02/03 command for shallow ones.
> >
> > But it occurs to me that there's got to be a better way. Are "spotting
> > drills" that better way ?
> >
> > Thanks in advance for any thoughts.
> >
> > Alan
> >
> > --
> >
> > Alan Rothenbush | The Spartans do not ask the number of
the
> > Academic Computing Services | enemy, only where they are.
> > Simon Fraser University |
> > Burnaby, B.C., Canada | Agix of Sparta
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> OFF Topic POSTS: General Machining
> If you wish to post on unlimited OT subjects goto:
aol://5863:126/rec.crafts.metalworking or go thru Google.com to reach it if
you have trouble.
> http://www.metalworking.com/news_servers.html
>
> http://groups.yahoo.com/group/jobshophomeshop I consider this to be a
sister site to the CCED group, as many of the same members are there, for OT
subjects, that are not allowed on the CCED list.
>
> NOTICE: ALL POSTINGS TO THIS GROUP BECOME PUBLIC DOMAIN BY POSTING THEM.
DON'T POST IF YOU CAN NOT ACCEPT THIS.....NO EXCEPTIONS........
> bill
> List Mom
> List Owner
>
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
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