Drilling accurate router sub-base mounting holes

[Leon]

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

[Leon]

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

[Rick Nelson]

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:

[Rick Nelson]

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.

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

[Rick Nelson]

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

[Rick Nelson]

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]

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)

Get a copy of my NEW AND IMPROVED TrollFilter for NewsProxy/Nfilter by sending email to autoresponder at filterinfo-at-milmac-dot-com You must use your REAL email address to get a response.

[Leon]

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.

[Mike Marlow]

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.

[Ron Magen]

I was going to explain how I used a 'kit' that had 'pointed' headless screws sized for the base-plate {and a 'center point' to fit the chuck}. Put them in, put on plastic, push down - screw holes are marked. Later, chuck up the 'center point' and mark for either a 'guide' cut-out, Zero Clearance, or just a big hole.

However, a photo copy sounds even easier. One caveat . . . I'd include a 6 inch steel ruler when making the copy. Some of the machines don't make exact

1:1 copies. Even a 1/10 off may give a headache with screwheads winding up at an angle.

Regards & Good Luck, Ron Magen Backyard Boatshop

use a marker or punch through the router base attachment holes to mark the location on the new base holes

[Earl Creel]

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

[CW]

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. [e-mail]

[bridger]

to be sure, use two reference measurements, at right angles to each other....

[CW]

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]

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

[Doug Miller]

It indicates the degree of precision of the measurement. Google on "significant figures" for more information. One example:

>> And as soon as you start drawing arcs, the pencil point wears down, and the

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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[Rick Nelson]

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 .

-Rick

[Earl Creel]

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

[John]

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

[Lawrence Wasserman]

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