Drilling accurate router sub-base mounting holes

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On Fri, 25 Jun 2004 15:53:27 -0700, Rick Nelson

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.
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snipped-for-privacy@thanks.com wrote:

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
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Fri, Jun 25, 2004, 3:53pm (EDT-3) snipped-for-privacy@n0spaam.charter.net (Rick Nelson) 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
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J T wrote:

You should be.
--
Mortimer Schnerd, RN

snipped-for-privacy@XXXXcarolina.rr.com
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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.
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.

--
--John
Reply to jclarke at ae tee tee global dot net
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stick
OK, that is already too much trouble.. LOL.
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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.

table.
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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:

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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. snipped-for-privacy@earthlink.net

directly
between
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directly
between
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-
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snipped-for-privacy@n0spaam.charter.net says...

[snip]
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.
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says...

If you use deviders rather than a compass, within .002 or .003 is not to hard.

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

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Doug Miller wrote:

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.

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

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

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

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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Doug Miller wrote:

How do you figure?

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..

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
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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.
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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

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

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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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.
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Buy a router razier, it comes with all the patterns already, just tape one on and drill away.
Alan
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Man, and to think that I stupidly just used the original base as a template!
--

Larry Wasserman Baltimore, Maryland
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