Subject: drilled array

From: [email-masked] (Richard L Wagner)
Date: 23 Jan 1995 13:50:38 GMT

I need to drill some arrays of small holes, .021 in diameter, 1 mm apart.
I'm using a driller with an old vertical mill. Although the holes are 
going ok, the pattern of 4 x 14 holes looks bad since there are apparent 
errors in the table positioning. I'm always working from the same 
direction on the table screws so I imagine it's basic inaccuracies 
involved. What kind of positioner can I use to get accurate hole placements.?

Dick Wagner
Atlanta

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From: [email-masked] (James Kirkpatrick)
Date: 23 Jan 95 11:16:33 MST

In article <[email-masked]>, [email-masked] (Richard L Wagner) writes:
|>I need to drill some arrays of small holes, .021 in diameter, 1 mm apart.
|>I'm using a driller with an old vertical mill. Although the holes are 
|>going ok, the pattern of 4 x 14 holes looks bad since there are apparent 
|>errors in the table positioning. I'm always working from the same 
|>direction on the table screws so I imagine it's basic inaccuracies 
|>involved. What kind of positioner can I use to get accurate hole placements.?

One thought that comes to mind would be to magnetically mount a dial
indicator to the column, so that it bears against either the work or
a small piece mounted on the table.  This will then show how far the
table has actually moved, irrespective of what the handwheels claim.
Use a metric indicator for convenience.  However, you are limited in
your total travel to the range of the indicator, before you have to move
the indicator and re-zero it.

Jim

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From: [email-masked] (Mike Rehmus)
Date: 23 Jan 1995 22:39:39 GMT

In <[email-masked]> [email-masked] (murr rhame) 
writes: 

>I have a few suggestions that may help...
>
>You may get decent accuracy by laying out your pattern with bluing and 
a
>scribe then hand center punching the holes.  With a good eye you can 
lay 
>out a pattern within .005" or better true position this way.
>
You are right about being able to lay out patterns and get acceptable 
accuracy.  Actually, with a surface plate and height gage, you can get 
the marks into the 0.001" range and using a prick punch and magnifier, 
center the holes right on.  The eye is a marvelous instrument for this, 
as long as it can clearly see the marks/punch tip.  Should be able to 
hold 0.002" overall if sufficient care is taken.

Best,

Mike

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From: [email-masked] (Ron Ginger)
Date: Mon, 23 Jan 1995 19:56:44

I stronglysuspect drill wobble is the real culprit. 

As long as you are not getting backlash by aproaching from two directions, 
then even a grossly worn lead screw is still pretty damn accurate, over the 
range of only a few turns.  Now over its entire length it might be off by 
maybe 1/2 of the pitch, but in say a 30" mill table that is .050 in 15" 
travel, or less than  .003 per inch. So even a lead screw worn so bad that its 
center threads are one half their original width, you still have .003 per inch.

.021 is a very small drill. Unless started with a small sharp center drill, 
they could eailsy be off half a diameter or more.

Ron Ginger
my signature is http://www.ultranet.com/~ginger

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From: [email-masked] ([email-masked])
Date: 23 Jan 1995 18:06:58 GMT

Richard L Wagner ([email-masked]) wrote:
: I need to drill some arrays of small holes, .021 in diameter, 1 mm apart.
: I'm using a driller with an old vertical mill. Although the holes are 
: going ok, the pattern of 4 x 14 holes looks bad since there are apparent 
: errors in the table positioning. I'm always working from the same 
: direction on the table screws so I imagine it's basic inaccuracies 
: involved. What kind of positioner can I use to get accurate hole placements.?

: Dick Wagner
: Atlanta
	--This is a tough one, but a few basic questions need to be 
answered before you spend more time on the project, like: how many of 
these are you making and who's paying for it? If I had to do enough of 
these, I'd consider retooling with at the very least a new half-nut under 
the table on the X and Y axes; figure maybe $100.- and a day's work with 
a helper to remove the milling table and get it done. If the job is long and 
big enough, go for ball-screws; figure more than $1,000.- and the same 
amount of time, help, etc. 
	--If you are measuring position with the dial collars which, 
presumably are calibrated metric, and these seem to not give you the 
accuracy that you need, maybe the next thing to add is an indexer, i.e. a 
stepper motor on the X-axis, at least. Several of these are available 
commercially, or I suppose you could kludge something together, based on 
the CNC controlled do-dads that are being featured in HSM and ME these days.

--
"Steamboat Ed" Haas		:	Co-founder of the 
Voice: 805-968-7534		:	    SBSMEEBBQ
FAX:   805-JOB-TWAT		:	-Call about our Newsletter!
	--------Decks a-wash in a sea of words!!--------

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From: [email-masked] (Mike Rehmus)
Date: 23 Jan 1995 18:30:21 GMT

In <[email-masked]> [email-masked] (Richard L 

>involved. What kind of positioner can I use to get accurate hole 
placements.?

Sounds like the mill is really old!

The cheapest way is to mount a couple of inexpensive dial test 
indicators on the knee of the mill to measure X&Y position.  Then you 
don't care how worn the mill is, assuming it still moves "square".  The 
DTI's should cost you about $70 a pair from Enco, etc.  Mount them in 
any possible manner, just don't move the mounts once you start drilling. 

Best,

Mike

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From: [email-masked] (Mark Fraser)
Date: 23 Jan 1995 21:48:06 GMT

You could also do what I'm doing, and use digital calipers as
DRO to make sure the table moves by the amount you wish, to
the coordinates you wish....
/mark

Mike Rehmus ([email-masked]) wrote:
: In <[email-masked]> [email-masked] (Richard L 
: Wagner) writes: 

: >
: >I need to drill some arrays of small holes, .021 in diameter, 1 mm 
: apart.
: >I'm using a driller with an old vertical mill. Although the holes are 
: >going ok, the pattern of 4 x 14 holes looks bad since there are 
: apparent 
: >errors in the table positioning. I'm always working from the same 
: >direction on the table screws so I imagine it's basic inaccuracies 
: >involved. What kind of positioner can I use to get accurate hole 
: placements.?
: >
: >Dick Wagner
: >Atlanta
: >

: Sounds like the mill is really old!

: The cheapest way is to mount a couple of inexpensive dial test 
: indicators on the knee of the mill to measure X&Y position.  Then you 
: don't care how worn the mill is, assuming it still moves "square".  The 
: DTI's should cost you about $70 a pair from Enco, etc.  Mount them in 
: any possible manner, just don't move the mounts once you start drilling. 

: Best,

: Mike

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From: [email-masked] (murr rhame)
Date: 23 Jan 1995 16:28:46 -0500

You may get decent accuracy by laying out your pattern with bluing and a
scribe then hand center punching the holes.  With a good eye you can lay 
out a pattern within .005" or better true position this way.

If you are drilling strait into a flat piece of stock the drill bit may
"walk" a little before it bites into the metal.  If possible use a center
drill to prestart the holes.  If you can't run the patern twice once with
the center drill followed by the twist drill at least use as short and as
sharp a drill bit as you can get.

If you have doubts about the accuracy of your table, set up indicators to
directly measure the X and Y movement of the table.  Your pattern is only
14mm wide so a standard 1"  stroke dial indicators on magnetic bases
should work fine. 

-- 
        [email-masked]     /\/\ |_| |~ |~      Charlotte, NC

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From: [email-masked] (Ray Spinhirne)
Date: Tue, 24 Jan 1995 20:12:19 GMT

: Dick Wagner
: Atlanta
Before you do a lot of work with the mill find out:

	1.  Does the mill have "slack" in the jibs at 90 deg to the
	    movement.  If so fix this as always approching the work 
	    from the same direction will not help.

	2.  If not attach an indicator to see if positioning is
	    really off.

	3.  The problem could be in the drill itself.  If it is not 
	    running exactly on center, it may drill a little to one
	    side on each hole depending upon which way it is off when
	    it first touches the surface.

	4.  You don't say what material you are drilling holes in.
	    If it is not flat and uniform it will be almost impossible
	    to get accurately spaced holes, especially if the drill
	    itself is not rigid.

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From: [email-masked] (Dan Mauch)
Date: 26 Jan 1995 06:29:12 -0800

Do you have the phone number of the guy that  has the X-Y table attachment?

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From: [email-masked] (ChrisB1981)
Date: 24 Jan 1995 21:40:37 -0500

I recently bought a center drill from Campbell, has 1/8" shank and .020
tip.  Works well.  Also check your chuck.  If the chuck is running very
near concentric, (less than .002) you can sometimes dispense with the
center drill (at least in soft material like brass).  If it is not running
concentric, this may affect the placement of the holes.

An individual in my area makes a precision minature drill press with and x
y table attachment.  However they are expensive $300+ for the press and
$150 for the table.  Very good workmanship though + an Albrecht chuck.

Reg Barron

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From: [email-masked] (Alan Frisbie)
Date: 26 Jan 95 10:02:40 PST

> involved. What kind of positioner can I use to get accurate hole placements.?

I suspect that your problem is not positioning accuracy, but
your small drill bits "wandering" as they contact the work.
For accurate hole locating, you should first "spot" the holes
with a spotting (centering) drill.   This is similar in concept
to a center drill (typically used in lathes), but is designed
for use in mills and drilling machines.

Spotting drills are very short and rigid, and are made with
angles of 90, 118, and 120 degrees.   They have a very narrow
chisel edge and a very small web to ensure accurate starting.
90 degree spotting drills are recommended for use with drill
bits up to 118 degrees, but some people prefer 118 degrees.

In use, you will set up the machine's depth stop so that the
spotting drill will penetrate just enough to leave a hole of
the desired final diameter.   If you use a 90 degree spotting
drill, this is very easy to calculate (diameter is twice the
depth).   Also, if you go just a bit deeper, you can chamfer
or countersink the hole at the same time.

When you then follow this with the desired drill bit, the
outside (cutting) edges of the drill will contact the work
first instead of the web.   This will ensure that the drill
starts exactly in the desired position.   In a sense, this
is just an expansion on the use of a centerpunch.

MSC carries spotting drills from 1/8" to over 1".   A 1/8",
90 degree, "made in USA" drill is listed on page 152 of the
1994/95 catalog for $2.56 (Order number 71332048).

If you are going to be making a lot of these parts, you might
also want to consider making a drill jig.   Then you can avoid
the first pass with the spotting drill, because the jig will
keep the drill bits from wandering.

--  Alan E. Frisbie               [email-masked]
--  Flying Disk Systems, Inc.
--  4759 Round Top Drive          (213) 256-2575 (voice)
--  Los Angeles, CA 90065         (213) 258-3585 (FAX)

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From: [email-masked] (ChrisB1981)
Date: 26 Jan 1995 20:40:14 -0500

Yes, his name is Bill Brazelton Sr., and his phone is 703-476-6651.
Note, this is not an ADD!

                                             Reg Barron
                              (Posting from my Son's Computer -
ChrisB1981)