Metalworking (rec.crafts.metalworking) Discuss various aspects of working with metal, such as machining, welding, metal joining, screwing, casting, hardening/tempering, blacksmithing/forging, spinning and hammer work, sheet metal work.

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Default centering a hole with a drill press

I have a drill press, and I need to center a hole in the face of a
cylinder. I would be perfectly happy to one hundredth of an inch
accuracy. An X-Y table attached to the drill press stage would do the
job, but I suspect that for the level of accuracy that I need, there is
a simpler solution--and I just don't know it.

I've tried scribing diameters across the face, and picking where they
intersect--but the results have been less than impressive. Does
someone have a trick for this?

Clayton E. Cramer


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DoN. Nichols
 
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In article .com,
wrote:
I have a drill press, and I need to center a hole in the face of a
cylinder. I would be perfectly happy to one hundredth of an inch
accuracy. An X-Y table attached to the drill press stage would do the
job, but I suspect that for the level of accuracy that I need, there is
a simpler solution--and I just don't know it.

I've tried scribing diameters across the face, and picking where they
intersect--but the results have been less than impressive. Does
someone have a trick for this?


What did you use for positioning the diameters? A V centering
head on a combination square should do a pretty good job, as long as
your scribe has a very skinny point, and you angle it so the point is
right along the edge of the scale.

Then, you need a spotting drill and good magnification to get
the hole started as close to the intersection of the lines as possible.
Once that is done, you can move up to a larger bit. But 0.010" may be
pushing it if you don't have experience in doing this.

Better, of course, would be a lathe of sufficient size with a
4-jaw chuck, and a good indicator, and a center drill in the tailstock
chuck once you get the end running true.

Good Luck,
DoN.
--
Email: | Voice (all times): (703) 938-4564
(too) near Washington D.C. | http://www.d-and-d.com/dnichols/DoN.html
--- Black Holes are where God is dividing by zero ---
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Wooding
 
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DoN. Nichols wrote:
In article .com,
wrote:

I have a drill press, and I need to center a hole in the face of a
cylinder. I would be perfectly happy to one hundredth of an inch
accuracy. An X-Y table attached to the drill press stage would do the
job, but I suspect that for the level of accuracy that I need, there is
a simpler solution--and I just don't know it.

I've tried scribing diameters across the face, and picking where they
intersect--but the results have been less than impressive. Does
someone have a trick for this?



What did you use for positioning the diameters? A V centering
head on a combination square should do a pretty good job, as long as
your scribe has a very skinny point, and you angle it so the point is
right along the edge of the scale.

Then, you need a spotting drill and good magnification to get
the hole started as close to the intersection of the lines as possible.
Once that is done, you can move up to a larger bit. But 0.010" may be
pushing it if you don't have experience in doing this.

Better, of course, would be a lathe of sufficient size with a
4-jaw chuck, and a good indicator, and a center drill in the tailstock
chuck once you get the end running true.

Good Luck,
DoN.


Here's a very simple, but surprisingly accurate method.
Place a small pointed rod in the drill chuck, a countersink bit will do
at a pinch as long as it comes to a point. Place the bar in position as
close as you can by eye and lay a flat metal strip horizontally across
it - a 12" steel rule will do nicely. Lower the drill chuck so that the
pointed end of the rod gently pinches the rule between it and the bar.
The chances are that this pushes the rule off the horizontal because the
point is not on the highest part of the bar. Move the bar so as to get
the rule as horizontal as you can get it. Replace the pointed rod with a
slocome and start the hole.

If you do the maths you will find that the rule being off-horizontal by
1/2 degree translates into an accuracy of approx. 0.004 x the diameter
of the bar. Half a degree from horizontal is very easy to spot when you
compare it to other horizontal things around, so this method can easily
give an accuracy better than 2 thou on an inch diam. bar.
I hope this helps.

--

Regards, Gary Wooding
(To reply by email, change feet to foot in my address)
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Stan-O
 
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Just use a dial indicator in the chuck and indicate around the
periphery of the shaft, once it's all dialed in you will be bang on the
center.

Any type of dial indicator will work, just detach the post form the mag
base and put it in the drill chuck, if you have a scrap one, chop it
down if there is a height restriction.

-S

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Jeff Wisnia
 
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Wooding wrote:
DoN. Nichols wrote:

In article .com,
wrote:

I have a drill press, and I need to center a hole in the face of a
cylinder. I would be perfectly happy to one hundredth of an inch
accuracy. An X-Y table attached to the drill press stage would do the
job, but I suspect that for the level of accuracy that I need, there is
a simpler solution--and I just don't know it.

I've tried scribing diameters across the face, and picking where they
intersect--but the results have been less than impressive. Does
someone have a trick for this?




What did you use for positioning the diameters? A V centering
head on a combination square should do a pretty good job, as long as
your scribe has a very skinny point, and you angle it so the point is
right along the edge of the scale.

Then, you need a spotting drill and good magnification to get
the hole started as close to the intersection of the lines as possible.
Once that is done, you can move up to a larger bit. But 0.010" may be
pushing it if you don't have experience in doing this.

Better, of course, would be a lathe of sufficient size with a
4-jaw chuck, and a good indicator, and a center drill in the tailstock
chuck once you get the end running true.

Good Luck,
DoN.



Here's a very simple, but surprisingly accurate method.
Place a small pointed rod in the drill chuck, a countersink bit will do
at a pinch as long as it comes to a point. Place the bar in position as
close as you can by eye and lay a flat metal strip horizontally across
it - a 12" steel rule will do nicely. Lower the drill chuck so that the
pointed end of the rod gently pinches the rule between it and the bar.
The chances are that this pushes the rule off the horizontal because the
point is not on the highest part of the bar. Move the bar so as to get
the rule as horizontal as you can get it. Replace the pointed rod with a
slocome and start the hole.

If you do the maths you will find that the rule being off-horizontal by
1/2 degree translates into an accuracy of approx. 0.004 x the diameter
of the bar. Half a degree from horizontal is very easy to spot when you
compare it to other horizontal things around, so this method can easily
give an accuracy better than 2 thou on an inch diam. bar.
I hope this helps.


To avoid confusing the poor OP, I gotta stick my .02 in and point out
that you've just given him a good way of drilling a hole through the
SIDE of a round bar so that it comes out close to being exactly on a
diameter of the bar.

But the OP said he wanted to drill the hole in the center of a "face" on
the bar, which most machinists would read as being the "round" end of
the bar.

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"As long as there are final exams, there will be prayer in public
schools"


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Wooding
 
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Jeff Wisnia wrote:
Wooding wrote:



Here's a very simple, but surprisingly accurate method.
Place a small pointed rod in the drill chuck, a countersink bit will
do at a pinch as long as it comes to a point. Place the bar in
position as close as you can by eye and lay a flat metal strip
horizontally across it - a 12" steel rule will do nicely. Lower the
drill chuck so that the pointed end of the rod gently pinches the rule
between it and the bar. The chances are that this pushes the rule off
the horizontal because the point is not on the highest part of the
bar. Move the bar so as to get the rule as horizontal as you can get
it. Replace the pointed rod with a slocome and start the hole.

If you do the maths you will find that the rule being off-horizontal
by 1/2 degree translates into an accuracy of approx. 0.004 x the
diameter of the bar. Half a degree from horizontal is very easy to
spot when you compare it to other horizontal things around, so this
method can easily give an accuracy better than 2 thou on an inch diam.
bar.
I hope this helps.


To avoid confusing the poor OP, I gotta stick my .02 in and point out
that you've just given him a good way of drilling a hole through the
SIDE of a round bar so that it comes out close to being exactly on a
diameter of the bar.

But the OP said he wanted to drill the hole in the center of a "face" on
the bar, which most machinists would read as being the "round" end of
the bar.

Jeff


Whoops, mea culpa - I must learn to read posts properly.
I must learn to read posts properly.
I must learn to read posts properly.
I must learn to read posts properly.
--

Regards, Gary Wooding
(To reply by email, change feet to foot in my address)
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Stan-O
 
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I was a little confused by his post, to me the "face" of a cylinder is
the end of the bar, and the cylinder itself would be to put a hole
through the periphery of the cylinder. Perhaps i have been machining
too long for laymans terms.

-S

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Depends on what tools you have available. Assuming you don't have
things as surface tables and height gages, or even a good
caliper..........
I would use a divider or compass. Just set it at your best guess at
half the diameter, and scribe arcs from the outside. If the arcs from
opposite sides don't intersect, increase the size of the arc. If three
or four arcs define an area that is too big, decrease the size of the
arc. Should be able to get to your 1/100th of an inch, but not much
closer.

Dan

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