OK, I now know several ways not to do this. Sounds simple - 4 holes,
evenly spaced, around a circle 0.600" in diameter.

The center of the circle, I can find easily (lathe & center drill). The
edges are concentric to the center, by definition, because I turned it
on that lathe.

I marked the 0.600" circle on the face of the disk by lightly touching
it with a cutting tool on the lathe & turning the work around, scribing
a circle at the right diameter.

Now, how do I get the 4 points layed out properly from there? I can use
a center finder to get two of 'em, but how do I get the other two evenly
spaced from those points? Or, worse yet, what if I wanted 3, or 5 holes
on that circle, rather than 4?

Dave Hinz

Get the two marked with a sharp punch, then use a compass to scribe the
other two.
- -
Rex Burkheimer


Dave Hinz wrote:
OK, I now know several ways not to do this. Sounds simple - 4 holes,
evenly spaced, around a circle 0.600" in diameter.

The center of the circle, I can find easily (lathe & center drill). The
edges are concentric to the center, by definition, because I turned it
on that lathe.

I marked the 0.600" circle on the face of the disk by lightly touching
it with a cutting tool on the lathe & turning the work around, scribing
a circle at the right diameter.

Now, how do I get the 4 points layed out properly from there? I can use
a center finder to get two of 'em, but how do I get the other two evenly
spaced from those points? Or, worse yet, what if I wanted 3, or 5 holes
on that circle, rather than 4?

Dave Hinz

Dave
Take a look he
http://www.metalwebnews.com/formulas...ordinates.html
Quickly found using "bolt circle" in Google.
hope this helps


"Dave Hinz" wrote in message
...
OK, I now know several ways not to do this. Sounds simple - 4 holes,
evenly spaced, around a circle 0.600" in diameter.

The center of the circle, I can find easily (lathe & center drill). The
edges are concentric to the center, by definition, because I turned it
on that lathe.

I marked the 0.600" circle on the face of the disk by lightly touching
it with a cutting tool on the lathe & turning the work around, scribing
a circle at the right diameter.

Now, how do I get the 4 points layed out properly from there? I can use
a center finder to get two of 'em, but how do I get the other two evenly
spaced from those points? Or, worse yet, what if I wanted 3, or 5 holes
on that circle, rather than 4?

Dave Hinz

Dave Hinz wrote:
OK, I now know several ways not to do this. Sounds simple - 4 holes,
evenly spaced, around a circle 0.600" in diameter.

The center of the circle, I can find easily (lathe & center drill). The
edges are concentric to the center, by definition, because I turned it
on that lathe.

I marked the 0.600" circle on the face of the disk by lightly touching
it with a cutting tool on the lathe & turning the work around, scribing
a circle at the right diameter.

Now, how do I get the 4 points layed out properly from there? I can use
a center finder to get two of 'em, but how do I get the other two evenly
spaced from those points? Or, worse yet, what if I wanted 3, or 5 holes
on that circle, rather than 4?

Dave Hinz


You can do it with a divider- make two arcs of nearly the diameter from
the center of each hole you've established (distance is unimportant, as
long as it's equal from both holes) and the interesections of these arcs
will be on the diameter perpendicular to the one you're starting from.

IIRC a chord of 1/2 the radius reaches one sixth of the circumference
from the starting point.

Dunno how to do five or seven, hope someone else does 'cause I've always
wondered how to do it.

For working with the torch/plasma cutter, a string and soapstone can do
pretty close work in dividing circles.

John

On Tue, 05 Jul 2005 13:16:04 -0500, Rex B wrote:
Get the two marked with a sharp punch, then use a compass to scribe the
other two.

I thought of that...right after I drilled & tapped the first two holes.
So, that would really work with any number of holes; once I have the
circle diameter known and marked, pick a point, determine the spacing,
and walk it around the circle. If I didn't screw something up, it'll
all line up to the original hole when I get all the way around - yes?

Wow, that metalwebnews.com site has some good info on it... time to
spend some quality reading time there.

Thanks,
Dave Hinz

"Dave Hinz" wrote in message
...
OK, I now know several ways not to do this. Sounds simple - 4 holes,
evenly spaced, around a circle 0.600" in diameter.

The center of the circle, I can find easily (lathe & center drill). The
edges are concentric to the center, by definition, because I turned it
on that lathe.

I marked the 0.600" circle on the face of the disk by lightly touching
it with a cutting tool on the lathe & turning the work around, scribing
a circle at the right diameter.

Now, how do I get the 4 points layed out properly from there? I can use
a center finder to get two of 'em, but how do I get the other two evenly
spaced from those points? Or, worse yet, what if I wanted 3, or 5 holes
on that circle, rather than 4?

Dave Hinz


Do you have a mill?

If so, trig the dimensions and do it by starting with the centerline of the
part, established by dialing it concentric with the spindle. That way you
can drill any conceivable hole pattern without any special tooling.
Needless to say, you must be able to hold your part vertically. If it's
too long to get under the spindle, this method may not work. Be sure to
keep backlash always in the right direction if you don't use a DRO.

Harold

On Tue, 5 Jul 2005 11:30:15 -0700, Harold and Susan Vordos wrote:

"Dave Hinz" wrote in message
...
OK, I now know several ways not to do this. Sounds simple - 4 holes,
evenly spaced, around a circle 0.600" in diameter.

Do you have a mill?

Couple of 'em.

If so, trig the dimensions and do it by starting with the centerline of the
part, established by dialing it concentric with the spindle. That way you
can drill any conceivable hole pattern without any special tooling.

Well, I thought of that too. I have a rotary table for the mill, and if
I could have figured out a way to hold the piece on it, I could just
find the center, go out 0.300", and poke a hole at each of 0, 90, 180,
and 270 degrees. But, what I have is more or less this:
http://www.sherline.com/3700inst.htm
....and I don't have anything to mount a chuck to it in the center.
Holding is the problem. For the lathe work, I drilled & tapped a hole
in the center for a bolt (which I needed on the finished product - I'm
making a sort of spanner wrench to be turned by an open-end wrench), and
located by using the 3-jaw chuck in the lathe on the head of the bolt.

Needless to say, you must be able to hold your part vertically. If it's
too long to get under the spindle, this method may not work. Be sure to
keep backlash always in the right direction if you don't use a DRO.

I don't have to worry about DRO on my mill

Thanks,
Dave Hinz

Dave Hinz wrote in
:

OK, I now know several ways not to do this. Sounds simple - 4 holes,
evenly spaced, around a circle 0.600" in diameter.

The center of the circle, I can find easily (lathe & center drill).
The edges are concentric to the center, by definition, because I
turned it on that lathe.

I marked the 0.600" circle on the face of the disk by lightly touching
it with a cutting tool on the lathe & turning the work around,
scribing a circle at the right diameter.

Now, how do I get the 4 points layed out properly from there? I can
use a center finder to get two of 'em, but how do I get the other two
evenly spaced from those points? Or, worse yet, what if I wanted 3,
or 5 holes on that circle, rather than 4?

You have to use trigonometry, or a protractor. Then there are a lot of
ways to skin this cat.

If you are laying this out by hand to drill in a drill press where you
don't have an X-Y table, then scribe a line across the face of the bar
using the center attachment on a combination square, or use a height
gage on a surface plate. Set your protractor to 90 degrees and scribe a
line 90 degrees off of the first line. Where those lines intersect the
..600" circle you inscribed is where you center punch and drill. Or use a
height gage, or surface gage set to .300" to scribe a line across the
face of the bar. Rotate the bar 90 degrees, by lining up the first line
to your machinist square, and scribe again.

To lay out more or fewer holes spaced equally, simply divide 360 degrees
by the number of holes, the resulting number is the number of degrees
each hole is spaced from the last.

If you have a mill with an X-Y table, find the center of the bar, set
your dials to zero, move X-.300" and drill, then move X+.300" and drill.
bring X back to 0.00" and move Y-.300" drill then Y to +.300 and drill.

To trig it out draw a quick sketch of the bolt hole pattern. Draw right
triangles from the center of the bar to the center of each bolt hole, by
drawing a line from the center of each hole to the center of the bar.
Now draw lines from the center of each bolt hole to the center of the
adjacent bolt hole. Bisect each of those lines by drawing a
perpendicular line to the center of the bar. The distance from center of
the bar to the center of the bolt hole will be the Hypoteneuse (side
"c")of the triangle, 360 degrees divided by (2x the number of holes)
will be Angle "A". Side a=Sin"A"* side"c". Side "b" will equal the
square root of (c^2-a^2). From this you can derive all of your table
positions, or the dimensions to scribe to using either a protractor or
surface gage.


--

Dan

On 5 Jul 2005 17:46:31 GMT, Dave Hinz wrote:

OK, I now know several ways not to do this. Sounds simple - 4 holes,
evenly spaced, around a circle 0.600" in diameter.

The center of the circle, I can find easily (lathe & center drill). The
edges are concentric to the center, by definition, because I turned it
on that lathe.

I marked the 0.600" circle on the face of the disk by lightly touching
it with a cutting tool on the lathe & turning the work around, scribing
a circle at the right diameter.

Now, how do I get the 4 points layed out properly from there? I can use
a center finder to get two of 'em, but how do I get the other two evenly
spaced from those points? Or, worse yet, what if I wanted 3, or 5 holes
on that circle, rather than 4?

Dave Hinz

Use this jig-boring table and your x/y coords on your mill
http://www.hp-h.us/p/littlemikey/hob...-ordinates.gif
Mike in BC

On Tue, 05 Jul 2005 19:32:26 GMT, wrote:

On 5 Jul 2005 17:46:31 GMT, Dave Hinz wrote:

OK, I now know several ways not to do this. Sounds simple - 4 holes,
evenly spaced, around a circle 0.600" in diameter.

The center of the circle, I can find easily (lathe & center drill). The
edges are concentric to the center, by definition, because I turned it
on that lathe.

I marked the 0.600" circle on the face of the disk by lightly touching
it with a cutting tool on the lathe & turning the work around, scribing
a circle at the right diameter.

Now, how do I get the 4 points layed out properly from there? I can use
a center finder to get two of 'em, but how do I get the other two evenly
spaced from those points? Or, worse yet, what if I wanted 3, or 5 holes
on that circle, rather than 4?

Dave Hinz

Use this jig-boring table and your x/y coords on your mill
http://www.hp-h.us/p/littlemikey/hob...-ordinates.gif
Mike in BC

Whoops! sorry, you wanted 4 holes didn't you?
Use trig for the distance between them.
Mike in BC

In article , Dave Hinz says...

Now, how do I get the 4 points layed out properly from there? I can use
a center finder to get two of 'em, but how do I get the other two evenly
spaced from those points? Or, worse yet, what if I wanted 3, or 5 holes
on that circle, rather than 4?

The drop-dead "works any time" approach to this is to turn the
polar coordinates into cartesian coordinates.

Basically you just center the part on the milling machine's
spindle axis, and then dial in X and Y to get points which are
all at the same radius from the center, but at different angles.

So for your example of a five hole BC, you need to put one hole
at X=0, and Y=R.

Then you just need two other paired coordinates, because the
thing is symmetric about the X=0 line.

One of pair, for example, will be X= +/- RSin 72, and Y = RCos 72 deg

Jim


--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

On 5 Jul 2005 12:38:09 -0700, jim rozen wrote:
In article , Dave Hinz says...

Now, how do I get the 4 points layed out properly from there? I can use
a center finder to get two of 'em, but how do I get the other two evenly
spaced from those points? Or, worse yet, what if I wanted 3, or 5 holes
on that circle, rather than 4?

(snip good description)

Then you just need two other paired coordinates, because the
thing is symmetric about the X=0 line.

So, just like so many other things, there are many, many correct ways to
do this. I wasn't thinking of it as an X/Y question, but as an angular
question. Looks like "offset from center" is the way to go, at least
for this particular project. Thanks! The second one should be
better...

Dave Hinz

Dave Hinz wrote:
On Tue, 05 Jul 2005 13:16:04 -0500, Rex B wrote:

Get the two marked with a sharp punch, then use a compass to scribe the
other two.


I thought of that...right after I drilled & tapped the first two holes.

That makes it a little harder. I suppose if your tapped holes were
tight, you could chuck a bolt into the lathe and center drill a small
hole, then screw one into each hole flush to locate the compass.

So, that would really work with any number of holes; once I have the
circle diameter known and marked, pick a point, determine the spacing,
and walk it around the circle. If I didn't screw something up, it'll
all line up to the original hole when I get all the way around - yes?

With just 4 holes it's actually easier than that. Quick trial & error
until both arcs intersect at the circle scribed earlier.

On Tue, 05 Jul 2005 15:55:20 -0500, Rex B wrote:
Dave Hinz wrote:
On Tue, 05 Jul 2005 13:16:04 -0500, Rex B wrote:

Get the two marked with a sharp punch, then use a compass to scribe the
other two.


I thought of that...right after I drilled & tapped the first two holes.

That makes it a little harder. I suppose if your tapped holes were
tight, you could chuck a bolt into the lathe and center drill a small
hole, then screw one into each hole flush to locate the compass.

Well, they're 10-32, and I have the grub screws to go into them, so
there is a good center to reference off of there... but that piece is
done but not perfect; the next one I'll lay out entirely before
starting.

So, that would really work with any number of holes; once I have the
circle diameter known and marked, pick a point, determine the spacing,
and walk it around the circle. If I didn't screw something up, it'll
all line up to the original hole when I get all the way around - yes?

With just 4 holes it's actually easier than that. Quick trial & error
until both arcs intersect at the circle scribed earlier.

So scribing the circle as I described seems to be the way to go if I'm
going to use the lathe to mark things - if I use it on the mill (if I
can figure out how to hold the darn thing) then it's a case of convert
it to X/Y coordinates and poke the holes where they belong. While I'm
not quite sure that I'm confident enough to do it that way without a
layout circle to double-check my work, maybe that'd be a good
experiment. Scribe the circle with the lathe, and then use the mill as
if that circle wasn't there, and make sure the holes are on the circle.

Oh darn, another evening in the shop. Maybe the next one will look
more presentable

Dave Hinz

"Dave Hinz" wrote in message
...
On Tue, 05 Jul 2005 13:16:04 -0500, Rex B wrote:
Get the two marked with a sharp punch, then use a compass to scribe the
other two.

I thought of that...right after I drilled & tapped the first two holes.

While I have no further insight into your hole circle problem, I have a
suggestion.

You should consider writting out work plans for your projects, before you
begin them. While this sounds like a waste of time and a lot of work, I
gaurentee you'll have to think about all the processes in the work plan
while you're at the machine (whether you've done a work plan or not).

The bolt-hole circle is a good example of why work plans are a good idea.
You've probably painted yourself into a corner from which you will not
easily emerge (at least with the original piece of material).

At work I see this a lot, although simple mistakes like yours could quickly
cost tens of thousands of dollars to repair as well as threatening the
safety of people on the floor.

Just my $0.02 worth...

Regards,

Robin

In , on 07/05/05
at 05:46 PM, Dave Hinz said:

OK, I now know several ways not to do this. Sounds simple - 4 holes,
evenly spaced, around a circle 0.600" in diameter.

The center of the circle, I can find easily (lathe & center drill). The
edges are concentric to the center, by definition, because I turned it on
that lathe.

I marked the 0.600" circle on the face of the disk by lightly touching it
with a cutting tool on the lathe & turning the work around, scribing a
circle at the right diameter.

Now, how do I get the 4 points layed out properly from there? I can use
a center finder to get two of 'em, but how do I get the other two evenly
spaced from those points? Or, worse yet, what if I wanted 3, or 5 holes
on that circle, rather than 4?

Dave Hinz

Use a 4 jaw chuck to hold the work, then when you've scribed the circle,
use a vertical prop ( piece of brass bar/rod is ideal) between the
underside of the 9 -o-clock jaw & the front shears of the lathe bed. Turn
the chuck anti clockwise( is that counter clockwise over there?) to trap
the prop. Now use the cross slide to move the tool ( at centre height) to
scribe a radial mark intersecting with your circle at 9 o-clock & 3
o-clock. Rotate the chuck to the next jaw & repeat using the same prop.
Result 4 marks evenly spaced on the PCD. Use a 3 jaw chuck for three
holes, marking once per jaw. 5 holes - use a 5 jaw chu.... now you are
back to trig GG
-----------------------------------------------------------

-----------------------------------------------------------

On Tue, 5 Jul 2005 17:08:53 -0400, Robin S. wrote:

"Dave Hinz" wrote in message
...

I thought of that...right after I drilled & tapped the first two holes.

While I have no further insight into your hole circle problem, I have a
suggestion.
You should consider writting out work plans for your projects, before you
begin them. While this sounds like a waste of time and a lot of work, I
gaurentee you'll have to think about all the processes in the work plan
while you're at the machine (whether you've done a work plan or not).

Well, I work in I.T., and when I'm doing something complicated with
dependancies like this, I do that. This was actually more of a "feature
creep" thing though - the tool I made is to turn a brake piston back
into the caliper - it has 4 holes in the face of it, and needs to be
turned in clockwise to retract it for the new pads. I made this out of
a disk of 1.45" diameter and 0.250" thick, drilled & tapped a bolt in
the center of it, and then these holes. Made it initially with just two
drive pins (grub screws in this case), but it "rocked" because it was
bottoming out in the holes. So, I figured adding 2 more pins in the
right place would give it a solid location without the rocking. I
probably would have thought about it more if the second pair of holes
hadn't been a later modification to the original design.

The bolt-hole circle is a good example of why work plans are a good idea.
You've probably painted yourself into a corner from which you will not
easily emerge (at least with the original piece of material).

That's OK, I don't mind time in the shop. And this tool meets a need
that a lot of folks with 70's and 80's Saabs (at least, and probably
more, as they're Girling brakes) share, so maybe I'll just run a batch
of 'em. Once it's set up, making extra ones isn't that much effort.
I could probably unload a dozen of 'em without trying, and if I can make
someone a gift for a buck worth of parts, that is a tool that they'll
use and appreciate, well, that solves several problems. Not looking to
go commercial with it by any means.

At work I see this a lot, although simple mistakes like yours could quickly
cost tens of thousands of dollars to repair as well as threatening the
safety of people on the floor.

Well, sense of perspective and all that...I see the first one as my
prototype, found that the plan didn't meet the needs, and revised the
design, trying to refit my changes to the prototype. Since the new
design needs skills I haven't yet mastered, I'm asking how to do it.

Just my $0.02 worth...

Thanks,
Dave Hinz

On Tue, 5 Jul 2005 21:28:19 +0000 (UTC), wrote:

Use a 4 jaw chuck to hold the work, then when you've scribed the circle,
use a vertical prop ( piece of brass bar/rod is ideal) between the
underside of the 9 -o-clock jaw & the front shears of the lathe bed. Turn
the chuck anti clockwise( is that counter clockwise over there?) to trap
the prop. Now use the cross slide to move the tool ( at centre height) to
scribe a radial mark intersecting with your circle at 9 o-clock & 3
o-clock.

OK, that's brilliant. I have the degrees of rotation inscribed on my
chuck, but wasn't sure how to locate with them, as there's no obvious
way to make a reference point. But, I could either do the prop thing as
you're suggesting, or since I have the degrees shown on the chuck, I
could use my magnetic base to hold a pointer just off of the inscribed
degree markings, and do whichever angles I want with that - without
trig. So, scribe the circle, let the chuck decide where on the round
piece we're going to call zero degrees, mark the part with the
cross-slide and tool, back off the tool, rotate to next target location,
um... lock the spindle, and repeat until I run out of points to mark.

Thanks, I wasn't thinking in that direction at all, but that might be
easiest - all done on the lathe, except for the drilling of the outer
circle of holes.

Rotate the chuck to the next jaw & repeat using the same prop.
Result 4 marks evenly spaced on the PCD. Use a 3 jaw chuck for three
holes, marking once per jaw. 5 holes - use a 5 jaw chu.... now you are
back to trig GG

Well, maybe having those degree markings on the chuck makes the trig
unnecessary... however, none of these methods involve making or buying
more tooling, so I'm not sure I've hit on just the right one yet

Robin S. wrote:
"Dave Hinz" wrote in message
...

On Tue, 05 Jul 2005 13:16:04 -0500, Rex B wrote:

Get the two marked with a sharp punch, then use a compass to scribe the
other two.

I thought of that...right after I drilled & tapped the first two holes.


While I have no further insight into your hole circle problem, I have a
suggestion.

You should consider writting out work plans for your projects, before you
begin them. While this sounds like a waste of time and a lot of work, I
gaurentee you'll have to think about all the processes in the work plan
while you're at the machine (whether you've done a work plan or not).

The bolt-hole circle is a good example of why work plans are a good idea.
You've probably painted yourself into a corner from which you will not
easily emerge (at least with the original piece of material).

At work I see this a lot, although simple mistakes like yours could quickly
cost tens of thousands of dollars to repair as well as threatening the
safety of people on the floor.

Just my $0.02 worth...

Regards,

Robin




YOu got a window to get out of the corner. Draw another larger
diameter ring with the same center, divide it off to the bolt circle you
want and then scribe a line to intersect the orginal circle.

John

On Tue, 05 Jul 2005 18:29:12 -0400, john
wrote:



Robin S. wrote:
"Dave Hinz" wrote in message
...

On Tue, 05 Jul 2005 13:16:04 -0500, Rex B wrote:

Get the two marked with a sharp punch, then use a compass to scribe the
other two.

I thought of that...right after I drilled & tapped the first two holes.


While I have no further insight into your hole circle problem, I have a
suggestion.

You should consider writting out work plans for your projects, before you
begin them. While this sounds like a waste of time and a lot of work, I
gaurentee you'll have to think about all the processes in the work plan
while you're at the machine (whether you've done a work plan or not).

The bolt-hole circle is a good example of why work plans are a good idea.
You've probably painted yourself into a corner from which you will not
easily emerge (at least with the original piece of material).

At work I see this a lot, although simple mistakes like yours could quickly
cost tens of thousands of dollars to repair as well as threatening the
safety of people on the floor.

Just my $0.02 worth...

Regards,

Robin




YOu got a window to get out of the corner. Draw another larger
diameter ring with the same center, divide it off to the bolt circle you
want and then scribe a line to intersect the orginal circle.

John

Draw the part (full size) on paper.
Locate paper on part to align with existing holes.
Pop center punch on needed holes.
Drill.

Ken.

Dave Hinz wrote:

On Tue, 05 Jul 2005 13:16:04 -0500, Rex B wrote:
Get the two marked with a sharp punch, then use a compass to scribe the
other two.

I thought of that...right after I drilled & tapped the first two holes.

Unfortunately, if you've tapped it, then you've lost the center. A
good approximation can be had this way:

Turn two buttons slightly smaller than 0.600 and with an ID that is a
close fit over your thread.

Turn two more buttons with a diameter of: 0.600*(SQRT(2))-D1

Where D1 is the diameter of the first two buttons.

Screw everybody down then remove all but the two smaller buttons.
Mount in a 4-jaw chuck. Indicate off each of the two smaller buttons
in turn and bore the two remaining holes.

George.

So, that would really work with any number of holes; once I have the
circle diameter known and marked, pick a point, determine the spacing,
and walk it around the circle. If I didn't screw something up, it'll
all line up to the original hole when I get all the way around - yes?

Yes. But. You do get a tolerance stack up that way.

Wow, that metalwebnews.com site has some good info on it... time to
spend some quality reading time there.

Thanks,
Dave Hinz

"jim rozen" wrote in message
...
In article , Dave Hinz says...

Now, how do I get the 4 points layed out properly from there? I can use
a center finder to get two of 'em, but how do I get the other two evenly
spaced from those points? Or, worse yet, what if I wanted 3, or 5 holes
on that circle, rather than 4?

The drop-dead "works any time" approach to this is to turn the
polar coordinates into cartesian coordinates.

Basically you just center the part on the milling machine's
spindle axis, and then dial in X and Y to get points which are
all at the same radius from the center, but at different angles.

So for your example of a five hole BC, you need to put one hole
at X=0, and Y=R.

Then you just need two other paired coordinates, because the
thing is symmetric about the X=0 line.

One of pair, for example, will be X= +/- RSin 72, and Y = RCos 72 deg

Jim
The Machinery handbook has table of jig bore coorinate, if you are going to
use a mill machine, page 78 of my 15th edition. Value are not given for
four holes since moving on the x and y axis the radius from center is all
that nessacery. 3,5,---12 are given in my book. Multiply the value showen by
the pitch circle.

--
www.billcotton.com

--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

Bill Cotton wrote:
"jim rozen" wrote in message
...
In article , Dave Hinz says...

Now, how do I get the 4 points layed out properly from there? I can use
a center finder to get two of 'em, but how do I get the other two evenly
spaced from those points? Or, worse yet, what if I wanted 3, or 5 holes
on that circle, rather than 4?

The drop-dead "works any time" approach to this is to turn the
polar coordinates into cartesian coordinates.

Basically you just center the part on the milling machine's
spindle axis, and then dial in X and Y to get points which are
all at the same radius from the center, but at different angles.

So for your example of a five hole BC, you need to put one hole
at X=0, and Y=R.

Then you just need two other paired coordinates, because the
thing is symmetric about the X=0 line.

One of pair, for example, will be X= +/- RSin 72, and Y = RCos 72 deg

Jim
The Machinery handbook has table of jig bore coorinate, if you are going to
use a mill machine, page 78 of my 15th edition. Value are not given for
four holes since moving on the x and y axis the radius from center is all
that nessacery. 3,5,---12 are given in my book. Multiply the value showen by
the pitch circle.

--
www.billcotton.com

--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================

Bill Cotton wrote:
"jim rozen" wrote in message
...
In article , Dave Hinz says...

Now, how do I get the 4 points layed out properly from there? I can use
a center finder to get two of 'em, but how do I get the other two evenly
spaced from those points? Or, worse yet, what if I wanted 3, or 5 holes
on that circle, rather than 4?

The drop-dead "works any time" approach to this is to turn the
polar coordinates into cartesian coordinates.

Basically you just center the part on the milling machine's
spindle axis, and then dial in X and Y to get points which are
all at the same radius from the center, but at different angles.

So for your example of a five hole BC, you need to put one hole
at X=0, and Y=R.

Then you just need two other paired coordinates, because the
thing is symmetric about the X=0 line.

One of pair, for example, will be X= +/- RSin 72, and Y = RCos 72 deg

Jim
The Machinery handbook has table of jig bore coorinate, if you are going to
use a mill machine, page 78 of my 15th edition. Value are not given for
four holes since moving on the x and y axis the radius from center is all
that nessacery. 3,5,---12 are given in my book. Multiply the value showen by
the pitch circle.

--
www.billcotton.com

--
==================================================
please reply to:
JRR(zero) at pkmfgvm4 (dot) vnet (dot) ibm (dot) com
==================================================


Give me your e-mail and i will send you a bolt hole and trig program.
Tim

On 5 Jul 2005 20:53:49 -0700, "tim" wrote:


Give me your e-mail and i will send you a bolt hole and trig program.
Tim

Me too please?
My posted address works.

Ken.

Ken your email address is spammotel?

On 5 Jul 2005 21:09:10 -0700, "tim" wrote:

Ken your email address is spammotel?
Yes. It is a forwarding service and the name spooks spammers.

Ken.

OK, I now know several ways not to do this. Sounds simple - 4 holes,
evenly spaced, around a circle 0.600" in diameter.

The center of the circle, I can find easily (lathe & center drill). The
edges are concentric to the center, by definition, because I turned it
on that lathe.

I marked the 0.600" circle on the face of the disk by lightly touching
it with a cutting tool on the lathe & turning the work around, scribing
a circle at the right diameter.

Now, how do I get the 4 points layed out properly from there? I can use
a center finder to get two of 'em, but how do I get the other two evenly
spaced from those points? Or, worse yet, what if I wanted 3, or 5 holes
on that circle, rather than 4?

Dave Hinz

Dave,
I have an "indexing ring" on the bullgear directly behind the chuck on
my lathe (Atlas 12") with 60 holes. Every 15 holes, scribe a line
across the 6" circle you have. You may not have the indexing ring on
your lathe, but I think in one of the posts you mentioned a degree
ring on the chuck - every 90 degrees... Maybe I'm not seeing the
entire picture.
Ken.

On 5 Jul 2005 20:53:49 -0700, the opaque "tim"
clearly wrote:

Give me your e-mail and i will send you a bolt hole and trig program.
Tim

That program sounds like a good candidate for the Dropbox, Tim.
www.metalworking.com/dropbox.html


-
Better Living Through Denial
------------
http://diversify.com Dynamic Websites, PHP Apps, MySQL databases

Lay it all out after it's chucked up in the lathe. Scribe the circle by
using the crossfeed micrometer to set the radius as you described, then
set the scribing tool as near as you can to vertical center. Use the
division pin stop in the lathe headstock to lock the chuck and cross
scribe with the crossfeed. Turn the chuck 180 degrees and lock again.
Repeat the scribe mark to confirm that it is centered.
Rotate 90 degrees and repeat for the other two holes.
This procedure works for any bolt circle that is divisible by the
number of stop pin holes in the headstock, usually 64.
Bugs

On Tue, 05 Jul 2005 21:37:52 -0700, Ken Davey wrote:
On 5 Jul 2005 21:09:10 -0700, "tim" wrote:

Ken your email address is spammotel?
Yes. It is a forwarding service and the name spooks spammers.

my spamcop.net address is also real, and I'd like to think has similar
effects if any of the spam harvesters are still manual. They block
98-99% of my incoming spam for me.

On Wed, 06 Jul 2005 10:48:34 GMT, Ken Sterling (Ken Sterling) Ken wrote:

I have an "indexing ring" on the bullgear directly behind the chuck on
my lathe (Atlas 12") with 60 holes. Every 15 holes, scribe a line
across the 6" circle you have. You may not have the indexing ring on
your lathe,

If I do, I haven't noticed it. It's a Rockwell 14", mostly like this:
http://www.lathes.co.uk/delta%20metal/page3.html
So, as long as I can use the degrees marked on the chuck, and lock the
spindle at the right points, I should get good accuracy in my marks.

Thanks,
Dave

On 5 Jul 2005 18:27:04 GMT, Dave Hinz wrote:

On Tue, 05 Jul 2005 13:16:04 -0500, Rex B wrote:
Get the two marked with a sharp punch, then use a compass to scribe the
other two.

I thought of that...right after I drilled & tapped the first two holes.
So, that would really work with any number of holes; once I have the
circle diameter known and marked, pick a point, determine the spacing,
and walk it around the circle. If I didn't screw something up, it'll
all line up to the original hole when I get all the way around - yes?

Wow, that metalwebnews.com site has some good info on it... time to
spend some quality reading time there.

Thanks,
Dave Hinz

You could thread some studs into the holes and then support the studs
on some 1-2-3 blocks on a surface plate with the disk vertical. If
you still have your center mark on the disk, you can use a square on
the surface plate to mark the other two holes.

Regards,
Ed

In , on 07/05/05
at 09:44 PM, Dave Hinz said:

Rotate the chuck to the next jaw & repeat using the same prop.
Result 4 marks evenly spaced on the PCD. Use a 3 jaw chuck for three
holes, marking once per jaw. 5 holes - use a 5 jaw chu.... now you are
back to trig GG

Well, maybe having those degree markings on the chuck makes the trig
unnecessary... however, none of these methods involve making or buying
more tooling, so I'm not sure I've hit on just the right one yet

OK then, once you've done the scribing, rotate the toolpost ( if a two or
four way ), or use another toolholder if you have a QCTP. In place of a
tool, insert a bit of 1" sq. bar through which you have previously (note
the catch?) drilled a hole using a 1/4" drillbit held in the lathe chuck,
thereby ensuring the hole is exactly at centre height. Once drilled, mark
the top of the bar ao it never goes in upside down. Now you can bring this
up to your marks with a 1/4" body centre drill inserted & use the cross
slide to position the centre drill on the PCD. Turn the centre drill with
a cordless drill to start each hole, then complete on the drill press. Or
you could make a Dremel mount to fit at centre height in the toolpost &
drill the holes directly with that Or
George Thomas' book the "ME Workshop Manual" has plans for a toolpost
mounted hand turned spotting drill.

Or, if you are brave enough, try " Sigh... what I really need to do this
easily love, is a jig borer. There's one on Ebay in Czechoslovakia for
only $1500. We could spend a week there, I hear the Skoda works is worth a
look"

-----------------------------------------------------------

-----------------------------------------------------------

In article .com,
Bugs wrote:
Lay it all out after it's chucked up in the lathe. Scribe the circle by
using the crossfeed micrometer to set the radius as you described, then
set the scribing tool as near as you can to vertical center. Use the
division pin stop in the lathe headstock to lock the chuck and cross
scribe with the crossfeed. Turn the chuck 180 degrees and lock again.
Repeat the scribe mark to confirm that it is centered.
Rotate 90 degrees and repeat for the other two holes.
This procedure works for any bolt circle that is divisible by the
number of stop pin holes in the headstock, usually 64.

A good approach. However -- not all lathes have stop pin hols
in the headstock. My 12x24" Clausing certainly does not.

Enjoy,
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 ---

Dave Hinz wrote:
On Tue, 5 Jul 2005 17:08:53 -0400, Robin S. wrote:

"Dave Hinz" wrote in message
...


I thought of that...right after I drilled & tapped the first two holes.


While I have no further insight into your hole circle problem, I have a
suggestion.
You should consider writting out work plans for your projects, before you
begin them. While this sounds like a waste of time and a lot of work, I
gaurentee you'll have to think about all the processes in the work plan
while you're at the machine (whether you've done a work plan or not).


Well, I work in I.T., and when I'm doing something complicated with
dependancies like this, I do that. This was actually more of a "feature
creep" thing though - the tool I made is to turn a brake piston back
into the caliper - it has 4 holes in the face of it, and needs to be
turned in clockwise to retract it for the new pads. I made this out of
a disk of 1.45" diameter and 0.250" thick, drilled & tapped a bolt in
the center of it, and then these holes. Made it initially with just two
drive pins (grub screws in this case), but it "rocked" because it was
bottoming out in the holes. So, I figured adding 2 more pins in the
right place would give it a solid location without the rocking. I
probably would have thought about it more if the second pair of holes
hadn't been a later modification to the original design.


The bolt-hole circle is a good example of why work plans are a good idea.
You've probably painted yourself into a corner from which you will not
easily emerge (at least with the original piece of material).


That's OK, I don't mind time in the shop. And this tool meets a need
that a lot of folks with 70's and 80's Saabs (at least, and probably
more, as they're Girling brakes) share, so maybe I'll just run a batch
of 'em. Once it's set up, making extra ones isn't that much effort.
I could probably unload a dozen of 'em without trying, and if I can make
someone a gift for a buck worth of parts, that is a tool that they'll
use and appreciate, well, that solves several problems. Not looking to
go commercial with it by any means.


At work I see this a lot, although simple mistakes like yours could quickly
cost tens of thousands of dollars to repair as well as threatening the
safety of people on the floor.


Well, sense of perspective and all that...I see the first one as my
prototype, found that the plan didn't meet the needs, and revised the
design, trying to refit my changes to the prototype. Since the new
design needs skills I haven't yet mastered, I'm asking how to do it.


Just my $0.02 worth...


Thanks,
Dave Hinz

If you work in IT, the quick and dirty way is to do a quick actual size CAD plot
and glue the paper to the workpiece as a template. "Good enough" in many cases.

On Wed, 6 Jul 2005 20:45:24 +0000 (UTC), wrote:

OK then, once you've done the scribing, rotate the toolpost ( if a two or
four way ),

Got a 4-way, yes.

or use another toolholder if you have a QCTP. In place of a
tool, insert a bit of 1" sq. bar through which you have previously (note
the catch?) drilled a hole using a 1/4" drillbit held in the lathe chuck,
thereby ensuring the hole is exactly at centre height. Once drilled, mark
the top of the bar ao it never goes in upside down. Now you can bring this
up to your marks with a 1/4" body centre drill inserted & use the cross
slide to position the centre drill on the PCD.

So, the height is constrained by the nature of the tool holder, and the
alignment is taken care of by making sure the bar is flush against the
work. Only trick is getting it aligned to drill the original hole,
which I should be able to reference against - what, the face of the
chuck?

So is this voice of experience here, or are you making this up on the
fly? Either way, it's impressive. The big problem with making this up
as I go along is that I haven't been exposed to creative techniques like
this, but of course once explained they make perfect sense.

Turn the centre drill with
a cordless drill to start each hole, then complete on the drill press. Or
you could make a Dremel mount to fit at centre height in the toolpost &
drill the holes directly with that Or
George Thomas' book the "ME Workshop Manual" has plans for a toolpost
mounted hand turned spotting drill.

So "spotting drill" is the critical term here?

Or, if you are brave enough, try " Sigh... what I really need to do this
easily love, is a jig borer. There's one on Ebay in Czechoslovakia for
only $1500. We could spend a week there, I hear the Skoda works is worth a
look"

I think I'll stay with the home-made stuff, at least for now.

Thanks,
Dave Hinz

On Thu, 07 Jul 2005 08:48:12 +1200, Roger_Nickel wrote:

If you work in IT, the quick and dirty way is to do a quick actual size CAD plot
and glue the paper to the workpiece as a template. "Good enough" in many cases.

3-M spray adhesive. I figured when I asked this, that I'd get a
half-dozen good responses. I underestimated by quite a bit.

In , on 07/06/05
at 08:53 PM, Dave Hinz said:

So is this voice of experience here, or are you making this up on the
fly? Either way, it's impressive. The big problem with making this up
as I go along is that I haven't been exposed to creative techniques like
this, but of course once explained they make perfect sense.

Well, I've not drilled directly like this, but I have used a 1/4" punch
made from silver steel ( drill rod in USA) through the hole in the bar. A
slight tap from a small hammer, when the punch is properly aligned with
the scribed marks is sufficient for the drill to pick up in a drill press.

Having said all that, I wouldn't have thought that the precision necessary
just for a caliper retracter would require more than scribing the marks in
the lathe & then centre punching & drilling in the usual way? My rear
calipers ( what a stupid bloody idea on a road car rear discs are by the
way!) are retracted using a nice simple 12mm Allen key, so no need to have
to make special tools. My wifes' old VW Golf GTI had a a pair of
triangular recesses in the pistons - I used to use a pin spanner made by
drilling the jaws of a cheapo Chinese adjustable spanner & pressing in a
dowel of silver steel to each jaw for those - worked for 157,000 miles!!!
-----------------------------------------------------------

-----------------------------------------------------------

On Fri, 8 Jul 2005 21:53:01 +0000 (UTC), wrote:

Having said all that, I wouldn't have thought that the precision necessary
just for a caliper retracter would require more than scribing the marks in
the lathe & then centre punching & drilling in the usual way?

Well, the problem came up in that I really needed all 4 pins, but only
made 2 marks initially thinking that would do, and by the time I knew I
needed 4 pins my initial 2 points were gone, so getting the angle
became...inconvenient...

My rear
calipers ( what a stupid bloody idea on a road car rear discs are by the
way!)

Why? Lots less complexity and unsprung weight than (shudder) drums...

are retracted using a nice simple 12mm Allen key, so no need to have
to make special tools.

The Saabs use a 5mm allen wrench to retract the rear pistons, or maybe a
7mm. Can never remember, but it's on the shelf of "special brake-job
tools" that I visit once a year or whatever.

My wifes' old VW Golf GTI had a a pair of
triangular recesses in the pistons - I used to use a pin spanner made by
drilling the jaws of a cheapo Chinese adjustable spanner & pressing in a
dowel of silver steel to each jaw for those - worked for 157,000 miles!!!

There ya go. I sure like being able to go downstairs into the shop, and
make something that looks reasonably professional, to take care of an
otherwise expensive or unsolvable obstacle to a project, from whatever I
happen to have on hand. Especially nice when it looks good.