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
You're kidding, right? .
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 .
Too damn easy, Jack. Where's the fun in that????
:)
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.
...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.
Fri, Jun 25, 2004, 3:53pm (EDT-3) snipped-for-privacy@n0spaam.charter.net (Rick=A0Nelson) amazes us all with his superior knowledge: sprained a few brain cells
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
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're going to an awful lot of unnecessary work.
You should be.
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.
What's the problem?
You hit it Leon. That's my method. I use a transfer punch.
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)
Lawrence L'Hote responds:
You guys stole BOTH my secret methods! :)
Charlie Self "It is even harder for the average ape to believe that he has descended from man." H. L. Mencken
[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.
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
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.
Buy a router razier, it comes with all the patterns already, just tape one on and drill away.
Alan
Actually I bet a Vix bit would work great to drill the holes through the router base.
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