How do I locate screw holes for a shop-made router base?

[Jim Broestler]

I always have trouble locating and drilling the screw holes on shop-made router bases so that the base is still perfectly centered. No matter how careful I am I still end up being at least 1/32 off. Any tips?

[Jim Dwight]

I would clamp the new base to a "good" one with holes where you want them to be and drill carefully. If they are still a little off, I would open up a hole or two so I could get it centered.

[Jim Broestler]

Sorry, I should have clarified. I have a PC router that uses a 5 3/4" base and a Craftsman that has a 6" base. I'm wondering how to make a 6" base for the PC so both will have the same sized base, so I don't have to move my edge guide to use both (I'm routing sliding dovetails).

[glenn bradley]

Are the screws counter sunk as opposed to counter bored? Most quality routers have counter bored holes to allow the base to be centered after mounting. A difference of 1/32" is not problem to align-out with (at worst) a cone type centering tool or (at best) a machine set like so

317763

or like so (http://patwarner.com/precision_subbase_kit.html). I have also seen a tip to photocopy the existing plate and use that as a template. I just use the existing base as a template at the drill press to do the through holes and then counter bore after.

[John Lanciani]

Make the base with just a small pilot hole for the bit and use the router itself with an appropriate bit to cut the hole after you install the base.

[Mike Cutler]

Jim

There are two methods that I use.
One is too simply mark the holes with a magic marker through the plexiglas.

The second is to get threaded rod the same pitch as the screws that hold the base plate on. I then make 3 threaded sections that are sharpen to a tip. Put them in the holes, put the router on the plexiglas and push down. If done properly you should have "pin pricks" indicating the exact center of the mounting holes.
The bigger concern is getting the round piece of plexiglas perfectly centered so that any point on it's outside edge is the same radius distance form the cenertline of the router bit, should you ever need to use it as the edge for routing. If you don't need to do that, just center as best you can. If you need to center that baseplate you need to find the exact center first. Drill a 1/4" hole and use it as a pilot with some 1/4" round stock chucked up in the router collet.
Combine the two methods and you should be dead on.

[john bateman]

There are something called "threaded transfer pins" that look look these from Woodcraft. You would need to find the correct ones to fit your router.
http://www.woodcraft.com/Images/products/600/142169.jpg

http://www.woodcraft.com/Images/products/600/142169.jpg

[Curt Harms]

"Vix" (self centering) bit. Clamp the factory sub base to the new plate. Mark the centers with the vix bit then counter bore/drill the correct sized hole. I screw the plate to the plunge base and install a V bit and plunge just enough to make a mark then drill the desired hole. Two forstner bits (1 3/16" and 1 3/8" if I recall correctly) will form the correct sized holes for a P-C style bushing.

http://www.leevalley.com/us/images/item/Woodworking/Drilling/66j0824s1.jpg

[Max Neu]

You might be able to lay it out with a compass,set it up using the center of 2 screws, then pivot around from there.

[Nicholas Carey]

You use a router centering pin and cone like this one:

http://www.highlandwoodworking.com/bosch-ra1151-centering-pin-and-cone.aspx

to center the router(s) on the baseplate. Then, being the good machinist you are, you use transfer punches like these

http://littlemachineshop.com/products/product_view.php?ProductID=4884

http://littlemachineshop.com/products/product_view.php?ProductID=2031

To punch the baseplate for the screws. Take it to the drill press, drill the appropriately sized pilot holes and tap them for your screws.

[Jerome Stanek]

I would make it over sized and use the old base with a 1/8 offset guide

[Larry Edgerton]

I use Vix bits.........

[Tom M King]

As many special purpose router sub bases that I've built, and it's more than a few, I don't think I've ever hit all the holes exactly without having to "improve" one of the locations. They have all done their jobs fine regardless. If it's one that the bit needs to be perfectly centered in, I plunge a bit up through it after mounting the sub base-includes with a screw adjustable "fixed" base.

[Larry Edgerton]

As many special purpose router sub bases that I've built, and it's more than a few, I don't think I've ever hit all the holes exactly without having to "improve" one of the locations. They have all done their jobs fine regardless. If it's one that the bit needs to be perfectly centered in, I plunge a bit up through it after mounting the sub base-includes with a screw adjustable "fixed" base.

Tom, I make a lot of my bases out of plastic I buy as scrap. I have the same issue, but with the plastics all you have to do is heat up the final screw with a torch and then screw it in. It melts a perfect pocket.

Larry

[Bruce Wrenn]

I drill center hole (1/4") first. Then using pointed set screws. slide base onto router which has a piece of 1/4" drill rod chucked into it. Points of set screws locate holes, which I drill with brad point bit. After this is done, I then remove base, and using 1/4" hole as a pivot point for trammel' cut base round. If base needs to be square, or rectangular, I have a custom jig for that. Bill Hylton's book "Router Magic," has a section on making custom bases. Well worth the purchase price.