Drilling accurate router sub-base mounting holes

Your radius for the PC router base is off. It is 2.3225. This taken directly
from PC's factory drawings. This puts the center to center distance between
holes at 4.0227.

"Rick Nelson" <[email protected]> wrote in message
news:[email protected]...
> Hi all,
>
> I got Spielman's "Router Jigs and Techniques" and a sheet of 1/2"
> acrylic then sat down to make a few of the custom sub-bases he shows in
> his book.
>
> For acrylic I figured I needed to get the mounting holes pretty close to
> exact in relation to each other and waste as little acrylic as I could
> in the process. The problem is that the mounting holes on the Porter
> Cable 690 series (and possibly other makes and models - I don't know)
> are arranged in an equilateral triangle with the centers 4" apart from
> each other. That's great and all, but I needed to know how far those
> screws are from the center so I could lay it all out.
>
> I broke open the absolutely most useful book on the planet (Pocket Ref -
> Thomas J. Glover) and fired up MS Excel then sprained a few brain cells
> going through some trigonometry to get the answer.
>
> That answer is 2.309".
>
> If you have a router with a 4" triangular mounting hole configuration
> and want to make a new sub-base, here are the steps I used to lay out
> the sub-base:
>
> Mark off a square slightly larger than the radius of your router base on
> the corner of your base material.
> Draw an X to find the center.
> Set your compass to a radius of 2.309".
> Draw a circle with the pivot point at the center of your square.
> Move the pivot point to some point on the circle and use the compass as
> a divider to walk off and mark 6 points on the perimeter of the circle.
> The seventh mark should fall exactly on the first mark. If it
> doesn't, make a small adjustment and start over.
> Three of those marks will intersect the circle exactly where you need to
> drill for the mounting screws.
> Drill and tap (if necessary), then mount the router to the sub-base
> material.
> Now would be a good time to trace the outline of your base and cut it out.
> Insert a center cutting bit (V bit), fire up your router, then lower the
> bit until it just scores the material. This mark is exactly where to
> cut/drill to make the center hole.
> If you wanted to be real spiffy, you could drill a small hole at the
> center mark and put it on a pivot pin the rotate it against a sander.
> This will give you a perfectly round base with a perfectly centered bit
> and eliminate the concentricity offsets that may be encountered by using
> the factory base.
>
> The same general technique would work for making a base for a router
table.
>
> For different router bases, here are the magic numbers based on the
> distance between mounting holes:
>
> 2" 1.155"
> 2.5" 1.443"
> 3" 1.732"
> 3.5" 2.021"
> 4" 2.309" (PC 690 series)
> 4.5" 2.598"
> 5" 2.887"
> 5.5" 3.175"
> 6" 3.464"
>
> Here are the radiuses you would use for locating the mounting holes on
> routers that use four mounting screws arranged in a square. The column
> on the left is the distance between two adjacent mounting holes:
>
> 2" 1.414"
> 2.5" 1.768"
> 3" 2.121"
> 3.5" 2.475"
> 4" 2.828"
> 4.5" 3.182"
> 5" 3.536"
> 5.5" 3.889"
> 6" 4.243" (PC 7518)
>
>
> I thought I'd post this info on for the archives. Hopefully it will
> come in handy to someone someday.
>
> Good luck!
> -Rick
>

In article <[email protected]>, Rick Nelson <[email protected]> wrote:
>Doug Miller wrote:
>
>> This is a joke, right? I mean, really -- how do you propose to set a
>> compass to a _thousandth_ of an inch?
>
>How do you propose to set a compass to the 4.000" you suggested in your
>method? It's no different. Welll...I take that back - your method has
>half the margin of error.

I didn't say "4.000 inches". I said 4 inches. There's a difference.

>The way I do it is to swipe the pencil lead against a piece of sandpaper
>a couple times to make a chisel edge. Set a dial caliper to the desired
>width then lay the caliper and compass facing each other on a flat
>surface and align the points. You can see down to a couple thousandths
>of an inch with the naked eye.

And as soon as you start drawing arcs, the pencil point wears down, and the
accuracy of your setting disappears.
>
>> Holy Smokes, what a load of unnecessary work!
>
> >Set your compass at 4". Make a mark _at_random_ on the base. This is
> >Point One. Set the point of the compass on that mark, and draw an arc.
> >Mark _at_random_ any point on the arc. This is Point Two. Set the point
> >of the compass there, and draw a second arc intersecting the first.
> >Where the arcs intersect is Point Three. Points One, Two, and Three
> >define an equilateral triangle with side 4". Drill holes at those >points.
>
>My verbosity probably makes it seem like a lot more work than it is.

Maybe so, but it's still a lot more trouble than it needs to be.

>The whole process takes about two minutes. Both of our methods involve
>only one compass setting. Mine has the addition of drawing a circle and
>three more points. Not what I'd consider a "load" of unnecessary work.

And the addition of some totally unnecessary calculations. The method I
described will lay out an equilateral triangle in less than ten seconds,
without any calculations whatever. The center can be located, if necessary,
with a few seconds further effort using only a compass and straightedge.


--
Regards,
Doug Miller (alphageek-at-milmac-dot-com)

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On Fri, 25 Jun 2004 15:53:27 -0700, Rick Nelson
<[email protected]> wrote:

>Hi all,
>
>Router.... sub-base..... mounting holes...... arranged in an equilateral triangle......
>Good luck!
>-Rick



get some screws threaded to match the mounting holes. cut off the
heads, sharpen the ends and screw them part way into the base. set the
base on top of the subbase material, pointy screw shafts down, and
smack the top of it once lightly with your open palm. lift it off and
drill at the resulting punch marks. countersink to match your mounting
screws and mount the result on your router base. install a plunge
cutting bit in the router collet and use it to cut the hole in the
middle.

Leon wrote:

> Umm take the base off your router, EYE ball it over the new base" or measure
> center the base over the new base and use a marker or punch through the
> router base attachment holes to mark the location on the new base holes
> .

Use the original base and a "Vix" bit for the mounting holes. Chuck a "V" bit
in the router, mount the base and use the "V" bit to locate the center hole.

--
Jack Novak
Buffalo, NY - USA
(Remove "SPAM" from email address to reply)

Dang! That was the one thing I wasn't sure of. I just made the
assumption that they were at exactly 4". Can you provide a link where
you found those factory drawings?

Thanks,
-Rick

CW wrote:
> Your radius for the PC router base is off. It is 2.3225. This taken directly
> from PC's factory drawings. This puts the center to center distance between
> holes at 4.0227.
>

Doug Miller wrote:

> This is a joke, right? I mean, really -- how do you propose to set a
> compass to a _thousandth_ of an inch?

How do you propose to set a compass to the 4.000" you suggested in your
method? It's no different. Welll...I take that back - your method has
half the margin of error.

The way I do it is to swipe the pencil lead against a piece of sandpaper
a couple times to make a chisel edge. Set a dial caliper to the desired
width then lay the caliper and compass facing each other on a flat
surface and align the points. You can see down to a couple thousandths
of an inch with the naked eye.

> Holy Smokes, what a load of unnecessary work!

>Set your compass at 4". Make a mark _at_random_ on the base. This is
>Point One. Set the point of the compass on that mark, and draw an arc.
>Mark _at_random_ any point on the arc. This is Point Two. Set the point
>of the compass there, and draw a second arc intersecting the first.
>Where the arcs intersect is Point Three. Points One, Two, and Three
>define an equilateral triangle with side 4". Drill holes at those >points.

My verbosity probably makes it seem like a lot more work than it is.
The whole process takes about two minutes. Both of our methods involve
only one compass setting. Mine has the addition of drawing a circle and
three more points. Not what I'd consider a "load" of unnecessary work.
How about we agree to call it a "smidgen" or a "dash" of unnecessary work?

Either way works perfectly and I'm glad you took the time to reply and
provide your own method.

Thanks,
-Rick

Jack wrote:
> Um, maybe this is just a dumb question.
> Why not drill a hole.
> Drill another 4" away.
> Drill a third 4" from both
> Bisect the lines which connect them
> Draw 3 (you could even use two) lines which connect the holes with the
> centers of the line opposite them.
> Bore the center hole using the intersection of those lines as the center.
> Trim rest of base as required. (using any of your methods below - trace,
> rotate about center ...)
>
> Fewer measurements (less error)
> No math required.
>
> -Jack

Even if your layout is perfect, you are still assuming that the collet
is exactly centered to the mounting holes of the router base. Until
Mitutoyo or Starret starts making router bases, I'll stick with the
point-plunge method to determine where the center of the bit falls.

No measurements (no error)
No math required.

-Rick

[email protected] wrote:
>
> get some screws threaded to match the mounting holes. cut off the
> heads, sharpen the ends and screw them part way into the base. set the
> base on top of the subbase material, pointy screw shafts down, and
> smack the top of it once lightly with your open palm. lift it off and
> drill at the resulting punch marks. countersink to match your mounting
> screws and mount the result on your router base. install a plunge
> cutting bit in the router collet and use it to cut the hole in the
> middle.

I think that this is the most accurate and foolproof way to do it. I
never said my method was the best way to do it, it is just *another* way
to do it. I figured maybe not everybody has a way to quickly cut down
screws to centered points, but everybody should at least have a compass.

Thanks for taking the time to post your method!

-Rick

Doug Miller wrote:

> I didn't say "4.000 inches". I said 4 inches. There's a difference.

How do you figure?

> And as soon as you start drawing arcs, the pencil point wears down, and the
> accuracy of your setting disappears.

That's true. The same thing would happen with your method.
Realisticly, either way would work perfectly fine. A couple thousandths
here or there isn't going to make any difference. If it did, you could
easily swap out the pencil lead for a scribe point. To really split
hairs, you'd also have to consider inaccuracies in punching the divots,
the shift that occurs when the piece is clamped to the drill press
table, squareness of the DP table to the drill, etc..

> Maybe so, but it's still a lot more trouble than it needs to be.

I don't work at such a furious pace in my shop that a minute or two is
going to kill me. If it was a production environment where those
minutes start to add up, then neither of our methods are worth a damn.

-Rick

Earl Creel wrote:
> Well IMHO you are on the right track but you should also consider the
> following: When the base is removed and then reinstalled will it return to
> the exact position it was in when the center hole was drilled? If you mark
> the base so the base lines up with the same holes in the router casting you
> will probably be fairly close but not necessarily dead on. Even the
> sequence of tightening the screws may cause the base to shift. If you are
> using a plunge router, is its axis of rotation absolutely perpendicular to
> the base? If not, the center of the base can only lie on the axis of
> rotation at one plunge depth?
> Earl Creel
>

You bring up some excellent points. Unfortunatly, there doesn't seem to
be a whole lot we can do about any of these things. For the things I
can control, I try to be as accurate as I can. For everything else, I
use a belt sander <G>.

-Rick

Want to say that there are pointed pins that you can use with a
centering pin to accurately mark the screw locations. You center onto
the acrylic/plastic plate, then clamp and tap the pointed pins with a
hammer to mark the screw hole location centers

John

On Sat, 26 Jun 2004 16:57:09 -0500, "Earl Creel" <[email protected]>
wrote:

>
>> You bring up some excellent points. Unfortunatly, there doesn't seem to
>> be a whole lot we can do about any of these things. For the things I
>> can control, I try to be as accurate as I can. For everything else, I
>> use a belt sander <G>.
>>
>> -Rick
>Some inaccuracies in router bases can be fixed but most just are not worth
>the trouble. Perhaps the most important thing is to realize that some
>router castings and/or bases are off by quite a bit and take that into
>account if you are trying to make a cut where accuracy is important. Pat
>Warner strongly recommends pattern type bits for cuts requiring accuracy
>because with pattern bits the base only controls depth and does not control
>where the cut is made.
>Earl Creel
>

What's the problem?

"Edwin Pawlowski" <[email protected]> wrote in message
news:[email protected]...
>
> "Rick Nelson" <[email protected]> wrote in message
> > That answer is 2.309".
> >
>
> > Set your compass to a radius of 2.309".
>
> You're kidding, right?
> .
>
>
>
>
>

In article <[email protected]>, Rick Nelson <[email protected]> wrote:
>Doug Miller wrote:
>
>> I didn't say "4.000 inches". I said 4 inches. There's a difference.
>
>How do you figure?

It indicates the degree of precision of the measurement. Google on
"significant figures" for more information. One example:
http://www.swt.edu/slac/math/SigFigur.html
>
>> And as soon as you start drawing arcs, the pencil point wears down, and the
>> accuracy of your setting disappears.
>
>That's true. The same thing would happen with your method.

Which is precisely why I did not specify precision to a thousandth of an inch.

>Realisticly, either way would work perfectly fine. A couple thousandths
>here or there isn't going to make any difference. If it did, you could
>easily swap out the pencil lead for a scribe point. To really split
>hairs, you'd also have to consider inaccuracies in punching the divots,
>the shift that occurs when the piece is clamped to the drill press
>table, squareness of the DP table to the drill, etc..
>
>> Maybe so, but it's still a lot more trouble than it needs to be.
>
>I don't work at such a furious pace in my shop that a minute or two is
>going to kill me. If it was a production environment where those
>minutes start to add up, then neither of our methods are worth a damn.
>
Still more trouble than it's worth. The unnecessary calculations and the extra
steps are additional sources of potential error, and thus should be avoided.

--
Regards,
Doug Miller (alphageek-at-milmac-dot-com)

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Fri, Jun 25, 2004, 3:53pm (EDT-3) [email protected]
(Rick=A0Nelson) amazes us all with his superior knowledge:
<snip of a lot of stuff> sprained a few brain cells <snip of a load of
more stuff>

I'm not that smart, I did it wrong. I used my base to mark where I
needed to drill, and drilled. I didn't have to think about it at all.
I'm so ashamed.


JOAT
Use your brain - it's the small things that count.
- Bazooka Joe

Well IMHO you are on the right track but you should also consider the
following: When the base is removed and then reinstalled will it return to
the exact position it was in when the center hole was drilled? If you mark
the base so the base lines up with the same holes in the router casting you
will probably be fairly close but not necessarily dead on. Even the
sequence of tightening the screws may cause the base to shift. If you are
using a plunge router, is its axis of rotation absolutely perpendicular to
the base? If not, the center of the base can only lie on the axis of
rotation at one plunge depth?
Earl Creel

> Even if your layout is perfect, you are still assuming that the collet
> is exactly centered to the mounting holes of the router base. Until
> Mitutoyo or Starret starts making router bases, I'll stick with the
> point-plunge method to determine where the center of the bit falls.
>
> No measurements (no error)
> No math required.
>
> -Rick
>

"Nova" <[email protected]> wrote in message
news:[email protected]...
> Leon wrote:
>
> > Umm take the base off your router, EYE ball it over the new base" or
measure
> > center the base over the new base and use a marker or punch through the
> > router base attachment holes to mark the location on the new base holes
> > .
>
> Use the original base and a "Vix" bit for the mounting holes. Chuck a "V"
bit
> in the router, mount the base and use the "V" bit to locate the center
hole.
>
> --
> Jack Novak
> Buffalo, NY - USA
> (Remove "SPAM" from email address to reply)
>
yep VIX bit my method also plus I use carpet tape to "clamp" the pieces
together as well. I only recently discovered carpet tepe for WW its a
miracle

In article <[email protected]>,
[email protected] says...
> Hi all,
>
> I got Spielman's "Router Jigs and Techniques" and a sheet of 1/2"
> acrylic then sat down to make a few of the custom sub-bases he shows in
> his book.
>
[snip]
>
> If you have a router with a 4" triangular mounting hole configuration
> and want to make a new sub-base, here are the steps I used to lay out
> the sub-base:
>
> Mark off a square slightly larger than the radius of your router base on
> the corner of your base material.
> Draw an X to find the center.
> Set your compass to a radius of 2.309".

This is a joke, right? I mean, really -- how do you propose to set a
compass to a _thousandth_ of an inch?

[snip remainder]

Holy Smokes, what a load of unnecessary work!

Set your compass at 4". Make a mark _at_random_ on the base. This is
Point One. Set the point of the compass on that mark, and draw an arc.
Mark _at_random_ any point on the arc. This is Point Two. Set the point
of the compass there, and draw a second arc intersecting the first. Where
the arcs intersect is Point Three. Points One, Two, and Three define an
equilateral triangle with side 4". Drill holes at those points.

Once you have the triangle laid out, locating the center (if you actually
need it) is trivial: bisect any two of the three angles, any two of the
three sides, or any one side and any one angle. Where the two bisectors
intersect is the center of the circle containing the vertices of the
triangle.

Any high school geometry text will show how to bisect angles and lines.

"Leon" <[email protected]> wrote in message
news:[email protected]...
> Umm take the base off your router, EYE ball it over the new base" or
measure
> center the base over the new base and use a marker or punch through the
> router base attachment holes to mark the location on the new base holes

...or uuuhh take the base off your router and make a photocopy. Glue, tape
or affix the photocopy to your plastic. Drill, cut or punch as req'd.

J T wrote:
> I'm not that smart, I did it wrong. I used my base to mark where I
> needed to drill, and drilled. I didn't have to think about it at all.
> I'm so ashamed.


You should be.



--
Mortimer Schnerd, RN

[email protected]
http://www.mortimerschnerd.com

"Rick Nelson" <[email protected]> wrote in message
news:[email protected]...
> Doug Miller wrote:
>
> > I didn't say "4.000 inches". I said 4 inches. There's a difference.
>
> How do you figure?
>
He apparently is referring to the old method (seldom used anymore) of
specifying tolerance based on the number of decimal places. Four places
would be +- .0002 if I remember correctly.

"Rick Nelson" <[email protected]> wrote in message
news:[email protected]...

> The way I do it is to swipe the pencil lead against a piece of sandpaper
> a couple times to make a chisel edge. Set a dial caliper to the desired
> width then lay the caliper and compass facing each other on a flat
> surface and align the points. You can see down to a couple thousandths
> of an inch with the naked eye.

Maybe YOU can see well enough to set the compas to 2.309" using YOUR eye,
but I seriousely doubt that will do you any good as you are not going to
get the pencil lead point sharp enough to indicat that measurement.

Man, and to think that I stupidly just used the original base as a
template!

--

Larry Wasserman Baltimore, Maryland
[email protected]

A couple of years ago, someone on here posted them or had them on a website.
Not sure which. I have no idea how ti get there now. If you would like a
copy, send me an email. They are in DWG format so you will need a cad
program to open it. I could put it in PDF if you don't have cad.
[email protected]

"Rick Nelson" <[email protected]> wrote in message
news:[email protected]...
> Dang! That was the one thing I wasn't sure of. I just made the
> assumption that they were at exactly 4". Can you provide a link where
> you found those factory drawings?
>
> Thanks,
> -Rick
>
> CW wrote:
> > Your radius for the PC router base is off. It is 2.3225. This taken
directly
> > from PC's factory drawings. This puts the center to center distance
between
> > holes at 4.0227.
> >
>

"CW" <no adddress@spam free.com> wrote in message
news:[email protected]...
> Your radius for the PC router base is off. It is 2.3225. This taken
directly
> from PC's factory drawings. This puts the center to center distance
between
> holes at 4.0227.
>

Oh man... my head is hurting already. I gets me a piece of string, I
stretches it out to exactly 2.3225" and firmly hold it at that point, I
anchors the end of the string and scribe a circle and presto, I 've got an
exact PC router base. Oh shit - I've got a DeWalt router... Sca-rew it,
maybe there's something I can do with my jig saw today.
--

-Mike-
[email protected]

> You bring up some excellent points. Unfortunatly, there doesn't seem to
> be a whole lot we can do about any of these things. For the things I
> can control, I try to be as accurate as I can. For everything else, I
> use a belt sander <G>.
>
> -Rick
Some inaccuracies in router bases can be fixed but most just are not worth
the trouble. Perhaps the most important thing is to realize that some
router castings and/or bases are off by quite a bit and take that into
account if you are trying to make a cut where accuracy is important. Pat
Warner strongly recommends pattern type bits for cuts requiring accuracy
because with pattern bits the base only controls depth and does not control
where the cut is made.
Earl Creel

Um, maybe this is just a dumb question.
Why not drill a hole.
Drill another 4" away.
Drill a third 4" from both
Bisect the lines which connect them
Draw 3 (you could even use two) lines which connect the holes with the
centers of the line opposite them.
Bore the center hole using the intersection of those lines as the center.
Trim rest of base as required. (using any of your methods below - trace,
rotate about center ...)

Fewer measurements (less error)
No math required.

-Jack

"Rick Nelson" <[email protected]> wrote in message
news:[email protected]...
> Hi all,
>
> I got Spielman's "Router Jigs and Techniques" and a sheet of 1/2"
> acrylic then sat down to make a few of the custom sub-bases he shows in
> his book.
>
> For acrylic I figured I needed to get the mounting holes pretty close to
> exact in relation to each other and waste as little acrylic as I could
> in the process. The problem is that the mounting holes on the Porter
> Cable 690 series (and possibly other makes and models - I don't know)
> are arranged in an equilateral triangle with the centers 4" apart from
> each other. That's great and all, but I needed to know how far those
> screws are from the center so I could lay it all out.
>
> I broke open the absolutely most useful book on the planet (Pocket Ref -
> Thomas J. Glover) and fired up MS Excel then sprained a few brain cells
> going through some trigonometry to get the answer.
>
> That answer is 2.309".
>
> If you have a router with a 4" triangular mounting hole configuration
> and want to make a new sub-base, here are the steps I used to lay out
> the sub-base:
>
> Mark off a square slightly larger than the radius of your router base on
> the corner of your base material.
> Draw an X to find the center.
> Set your compass to a radius of 2.309".
> Draw a circle with the pivot point at the center of your square.
> Move the pivot point to some point on the circle and use the compass as
> a divider to walk off and mark 6 points on the perimeter of the circle.
> The seventh mark should fall exactly on the first mark. If it
> doesn't, make a small adjustment and start over.
> Three of those marks will intersect the circle exactly where you need to
> drill for the mounting screws.
> Drill and tap (if necessary), then mount the router to the sub-base
> material.
> Now would be a good time to trace the outline of your base and cut it out.
> Insert a center cutting bit (V bit), fire up your router, then lower the
> bit until it just scores the material. This mark is exactly where to
> cut/drill to make the center hole.
> If you wanted to be real spiffy, you could drill a small hole at the
> center mark and put it on a pivot pin the rotate it against a sander.
> This will give you a perfectly round base with a perfectly centered bit
> and eliminate the concentricity offsets that may be encountered by using
> the factory base.
>
> The same general technique would work for making a base for a router
table.
>
> For different router bases, here are the magic numbers based on the
> distance between mounting holes:
>
> 2" 1.155"
> 2.5" 1.443"
> 3" 1.732"
> 3.5" 2.021"
> 4" 2.309" (PC 690 series)
> 4.5" 2.598"
> 5" 2.887"
> 5.5" 3.175"
> 6" 3.464"
>
> Here are the radiuses you would use for locating the mounting holes on
> routers that use four mounting screws arranged in a square. The column
> on the left is the distance between two adjacent mounting holes:
>
> 2" 1.414"
> 2.5" 1.768"
> 3" 2.121"
> 3.5" 2.475"
> 4" 2.828"
> 4.5" 3.182"
> 5" 3.536"
> 5.5" 3.889"
> 6" 4.243" (PC 7518)
>
>
> I thought I'd post this info on for the archives. Hopefully it will
> come in handy to someone someday.
>
> Good luck!
> -Rick
>

Rick Nelson wrote:

> Hi all,
>
> I got Spielman's "Router Jigs and Techniques" and a sheet of 1/2"
> acrylic then sat down to make a few of the custom sub-bases he shows in
> his book.
>
> For acrylic I figured I needed to get the mounting holes pretty close to
> exact in relation to each other and waste as little acrylic as I could
> in the process. The problem is that the mounting holes on the Porter
> Cable 690 series (and possibly other makes and models - I don't know)
> are arranged in an equilateral triangle with the centers 4" apart from
> each other. That's great and all, but I needed to know how far those
> screws are from the center so I could lay it all out.
>
> I broke open the absolutely most useful book on the planet (Pocket Ref -
> Thomas J. Glover) and fired up MS Excel then sprained a few brain cells
> going through some trigonometry to get the answer.
>
> That answer is 2.309".
>
> If you have a router with a 4" triangular mounting hole configuration
> and want to make a new sub-base, here are the steps I used to lay out
> the sub-base:
>
> Mark off a square slightly larger than the radius of your router base on
> the corner of your base material.
> Draw an X to find the center.
> Set your compass to a radius of 2.309".
> Draw a circle with the pivot point at the center of your square.
> Move the pivot point to some point on the circle and use the compass as
> a divider to walk off and mark 6 points on the perimeter of the circle.
> The seventh mark should fall exactly on the first mark. If it
> doesn't, make a small adjustment and start over.
> Three of those marks will intersect the circle exactly where you need to
> drill for the mounting screws.
> Drill and tap (if necessary), then mount the router to the sub-base
> material.
> Now would be a good time to trace the outline of your base and cut it out.
> Insert a center cutting bit (V bit), fire up your router, then lower the
> bit until it just scores the material. This mark is exactly where to
> cut/drill to make the center hole.
> If you wanted to be real spiffy, you could drill a small hole at the
> center mark and put it on a pivot pin the rotate it against a sander.
> This will give you a perfectly round base with a perfectly centered bit
> and eliminate the concentricity offsets that may be encountered by using
> the factory base.
>
> The same general technique would work for making a base for a router
> table.
>
> For different router bases, here are the magic numbers based on the
> distance between mounting holes:
>
> 2" 1.155"
> 2.5" 1.443"
> 3" 1.732"
> 3.5" 2.021"
> 4" 2.309" (PC 690 series)
> 4.5" 2.598"
> 5" 2.887"
> 5.5" 3.175"
> 6" 3.464"
>
> Here are the radiuses you would use for locating the mounting holes on
> routers that use four mounting screws arranged in a square. The column
> on the left is the distance between two adjacent mounting holes:
>
> 2" 1.414"
> 2.5" 1.768"
> 3" 2.121"
> 3.5" 2.475"
> 4" 2.828"
> 4.5" 3.182"
> 5" 3.536"
> 5.5" 3.889"
> 6" 4.243" (PC 7518)
>
>
> I thought I'd post this info on for the archives. Hopefully it will
> come in handy to someone someday.

You're going to an awful lot of unnecessary work.

1. Go to Staples and get some double stick tape or ask your kid for a stick
of gum.

2. Remove the base from your router.

3. Find a drill bit the same size as the holes in the base.

4. Using double-stick tape, gum, or a reasonable facsimile thereof, stick
the router base onto your acrylic (or polycarbonate or phenolic or armor
plate or transparent aluminum or whatever)

5. Stick the drill bit into your drill, put the end of it into each hole in
the base, in turn, and drill through your acrylic (or whatever).

6. Countersink each hole.

7. Put a bit in your router that is the same diameter as the bit in your
circle-cutter, hole-saw or whatever, mount the acrylic on your router, turn
on your router, plunge it.

8. Remove the acrylic from the router, and using the hole you just routed
to find the center, cut the appropriately sized center hole.

>
> Good luck!
> -Rick

--
--John
Reply to jclarke at ae tee tee global dot net
(was jclarke at eye bee em dot net)

"Rick Nelson" <[email protected]> wrote in message
> That answer is 2.309".
>

> Set your compass to a radius of 2.309".

You're kidding, right?
.

Buy a router razier, it comes with all the patterns already, just tape
one on and drill away.

Alan

Opus, Jack, I just now read this hint about 1 minute after I posted this
suggestion also. I give you all the credit. ;~)


"Nova" <[email protected]> wrote in message
news:[email protected]...
> Leon wrote:
>
> > Umm take the base off your router, EYE ball it over the new base" or
measure
> > center the base over the new base and use a marker or punch through the
> > router base attachment holes to mark the location on the new base holes
> > .
>
> Use the original base and a "Vix" bit for the mounting holes. Chuck a "V"
bit
> in the router, mount the base and use the "V" bit to locate the center
hole.
>
> --
> Jack Novak
> Buffalo, NY - USA
> (Remove "SPAM" from email address to reply)
>
>

"J. Clarke" <[email protected]> wrote in message
news:[email protected]...
> Rick Nelson wrote:
>
> You're going to an awful lot of unnecessary work.
>
> 1. Go to Staples and get some double stick tape or ask your kid for a
stick
> of gum.

OK, that is already too much trouble.. LOL.

"Doug Miller" <[email protected]> wrote in message
news:[email protected]...
> In article <[email protected]>,
> [email protected] says...
>> > Draw an X to find the center.
> > Set your compass to a radius of 2.309".
>
> This is a joke, right? I mean, really -- how do you propose to set a
> compass to a _thousandth_ of an inch?

If you use deviders rather than a compass, within .002 or .003 is not to
hard.
>
> [snip remainder]
>
> Holy Smokes, what a load of unnecessary work!

Agreed but there are many ways to get there. His method works though it is
not the one that I (or you) would take.

>
> Set your compass at 4". Make a mark _at_random_ on the base. This is
> Point One. Set the point of the compass on that mark, and draw an arc.
> Mark _at_random_ any point on the arc. This is Point Two. Set the point
> of the compass there, and draw a second arc intersecting the first. Where
> the arcs intersect is Point Three. Points One, Two, and Three define an
> equilateral triangle with side 4". Drill holes at those points.
>
> Once you have the triangle laid out, locating the center (if you actually
> need it) is trivial: bisect any two of the three angles, any two of the
> three sides, or any one side and any one angle. Where the two bisectors
> intersect is the center of the circle containing the vertices of the
> triangle.
>
> Any high school geometry text will show how to bisect angles and lines.

Wrong method. To easy. You will have to throw it away and start again. Use a
more complex method this time. :) :)

"Lawrence Wasserman" <[email protected]> wrote in message
news:[email protected]...
> Man, and to think that I stupidly just used the original base as a
> template!
>
> --
>
> Larry Wasserman Baltimore, Maryland
> [email protected]
>

Too damn easy, Jack. Where's the fun in that????

:)

"Jack" <[email protected]> wrote in message
news:[email protected]...
> Um, maybe this is just a dumb question.
> Why not drill a hole.
> Drill another 4" away.
> Drill a third 4" from both
> Bisect the lines which connect them
> Draw 3 (you could even use two) lines which connect the holes with the
> centers of the line opposite them.
> Bore the center hole using the intersection of those lines as the center.
> Trim rest of base as required. (using any of your methods below - trace,
> rotate about center ...)
>
> Fewer measurements (less error)
> No math required.
>
> -Jack
>
> "Rick Nelson" <[email protected]> wrote in message
> news:[email protected]...
> > Hi all,
> >
> > I got Spielman's "Router Jigs and Techniques" and a sheet of 1/2"
> > acrylic then sat down to make a few of the custom sub-bases he shows in
> > his book.
> >
> > For acrylic I figured I needed to get the mounting holes pretty close to
> > exact in relation to each other and waste as little acrylic as I could
> > in the process. The problem is that the mounting holes on the Porter
> > Cable 690 series (and possibly other makes and models - I don't know)
> > are arranged in an equilateral triangle with the centers 4" apart from
> > each other. That's great and all, but I needed to know how far those
> > screws are from the center so I could lay it all out.
> >
> > I broke open the absolutely most useful book on the planet (Pocket Ref -
> > Thomas J. Glover) and fired up MS Excel then sprained a few brain cells
> > going through some trigonometry to get the answer.
> >
> > That answer is 2.309".
> >
> > If you have a router with a 4" triangular mounting hole configuration
> > and want to make a new sub-base, here are the steps I used to lay out
> > the sub-base:
> >
> > Mark off a square slightly larger than the radius of your router base on
> > the corner of your base material.
> > Draw an X to find the center.
> > Set your compass to a radius of 2.309".
> > Draw a circle with the pivot point at the center of your square.
> > Move the pivot point to some point on the circle and use the compass as
> > a divider to walk off and mark 6 points on the perimeter of the circle.
> > The seventh mark should fall exactly on the first mark. If it
> > doesn't, make a small adjustment and start over.
> > Three of those marks will intersect the circle exactly where you need to
> > drill for the mounting screws.
> > Drill and tap (if necessary), then mount the router to the sub-base
> > material.
> > Now would be a good time to trace the outline of your base and cut it
out.
> > Insert a center cutting bit (V bit), fire up your router, then lower the
> > bit until it just scores the material. This mark is exactly where to
> > cut/drill to make the center hole.
> > If you wanted to be real spiffy, you could drill a small hole at the
> > center mark and put it on a pivot pin the rotate it against a sander.
> > This will give you a perfectly round base with a perfectly centered bit
> > and eliminate the concentricity offsets that may be encountered by using
> > the factory base.
> >
> > The same general technique would work for making a base for a router
> table.
> >
> > For different router bases, here are the magic numbers based on the
> > distance between mounting holes:
> >
> > 2" 1.155"
> > 2.5" 1.443"
> > 3" 1.732"
> > 3.5" 2.021"
> > 4" 2.309" (PC 690 series)
> > 4.5" 2.598"
> > 5" 2.887"
> > 5.5" 3.175"
> > 6" 3.464"
> >
> > Here are the radiuses you would use for locating the mounting holes on
> > routers that use four mounting screws arranged in a square. The column
> > on the left is the distance between two adjacent mounting holes:
> >
> > 2" 1.414"
> > 2.5" 1.768"
> > 3" 2.121"
> > 3.5" 2.475"
> > 4" 2.828"
> > 4.5" 3.182"
> > 5" 3.536"
> > 5.5" 3.889"
> > 6" 4.243" (PC 7518)
> >
> >
> > I thought I'd post this info on for the archives. Hopefully it will
> > come in handy to someone someday.
> >
> > Good luck!
> > -Rick
> >
>
>

You hit it Leon. That's my method. I use a transfer punch.

"Leon" <[email protected]> wrote in message
news:[email protected]...
> Umm take the base off your router, EYE ball it over the new base" or
measure
> center the base over the new base and use a marker or punch through the
> router base attachment holes to mark the location on the new base holes
> .
>
>
>

"Lawrence L'Hote" <[email protected]> wrote in message
news:O11Dc.117113$0y.59017@attbi_s03...
>
> "Leon" <[email protected]> wrote in message
> news:[email protected]...
> > Umm take the base off your router, EYE ball it over the new base" or
> measure
> > center the base over the new base and use a marker or punch through the
> > router base attachment holes to mark the location on the new base holes
>
> ...or uuuhh take the base off your router and make a photocopy. Glue,
tape
> or affix the photocopy to your plastic. Drill, cut or punch as req'd.


Actually I bet a Vix bit would work great to drill the holes through the
router base.

Umm take the base off your router, EYE ball it over the new base" or measure
center the base over the new base and use a marker or punch through the
router base attachment holes to mark the location on the new base holes
.