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Quarter-round router bit for half-round (bullnose) edge

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4 replies to this topic

#1 Bob Dylan

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Posted 27 October 2011 - 04:23 PM

I have used these bits for bullnosing an edge, but there is always a problem for me when cutting the second side. If you have cut one of these, you know what it is. The bearing tracks the flush square edge for the topside first cut just fine, but when flipping the piece to cut the second side of the edge, the bearing tracks the near-the-middle face of the quarter-round edge you just cut, and the resultant cut is a 32nd of an inch inboard, with a little lip remaining at the outer limit of the bullnose.

You say, echhhh! You sand it away, and are left with a less than bull bullnose, one with a little flat along its face. It takes real sculpting talent, which I have not, to sand it out to a true half-round again.

Maybe you have a solution for this, but I don't. The product design people at Amana Tool have one for you, but get out your checkbook. See the images, attached.

They sell a router bit that comes with two bearings, one of them conventional in shape, and cylindrical. You make your topside first cut with that bearing. Then you switch the flat-faced bearing with a second one, one that has a conical face, the angle just right for tracking the curve of the first cut, so that your second cut matches the first in its outer tangency.

Now, if you are doing this to, for me, the most common thickness of one inch, you'll want the 1/2"R bit, but save up a little before ordering, because it will run you close to $100. Why so much? Why, it must be for that second taper-faced bearing, with the outer ring and bearing surface being of delrin plastic.

Amana will sell you just the bearing for about $20, and you might say, aha, I can buy just the bearing and use it with the 1/2"R bit I already have. Right? You would be wrong.

Everybody out there selling 1/2"R quarter-round edge router bits with bearings, makes them with a total o.d. of 1-1/2", and the bearings are 1/4 x 1/2, meaning 1/4-inch i.d. by 1/2-inch o.d. But this Amana bit is an eighth inch bigger in diameter, both the o.d. and the bearing's o.d. A little hook built into the product by the designers, to make it tough on you, the buyer with limited money for new tools.

So, what does one do?

Do you have a quick and easy method, a trick of technique, for using a Freud, or MCLS, or Bosch, or Onsrud, or whatever make bit, with bearing, and doing a lip-free bullnose? Do you have a way to outsmart Amana? Or did you just scratch off the instant-win lotto ticket and win a couple hundred bucks, and decided to just buy the new Amana setup?

Inquiring minds want to know.

Attached Thumbnails

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#2 rmac


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Posted 27 October 2011 - 05:18 PM

Maybe forget the bearings and run the baseplate of the router against a jig something like the one shown.

-- Russ


#3 Torch02


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Posted 27 October 2011 - 05:43 PM

I've done this successfully on a router table.

I aligned the fence flush with the bearing, so I'm really supported against the fence. With this, I was able to just flip the piece over and route the bull nose. In this configuration, you just have to be careful that the horizontal edge (bottom in the table) is flush with or below the tabletop.

#4 Beechwood Chip

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Posted 27 October 2011 - 06:15 PM

OK, so let's assume that the piece is too big to maneuver on top of a router table, like a dining room table top. You could clamp a straightedge to the piece to guide the router baseplate like Russ suggested, and build a template guide for the corners.

Another way to do the straight parts would be to use a router base with an edge guide. Think of of your router as a tiny, hand held router table so it works like Torch suggested. You could attach a sacrificial spacer to the edge guide to go around the router bit.

I've never tried this - I just thought it up and it worked OK in my imagination.

[first edit] on straight edges, not curves.

[second edit] Although, I guess you could make a spacer that functioned like the expensive guide wheel. Bury the router bit in the spacer so there is bearing surface directly in line with the axis of the router bit, wax it so it's nice and slick, and use that to guide the bit against the piece. I think I just saved you $70!

#5 Bob Dylan

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Posted 27 October 2011 - 06:25 PM

Straight work can be bullnosed with a quarter-round bearing bit, if one does a really careful setup in a table with a fence. One can also use a full half-round bit without bearing, once again with a careful fence setup, to accomplish a straight nose.

My issue is with curved work, where the bearinged bit is used along with a guide post (or no guide post).

I'm really wondering if that Amana setup delivers a good and true bullnose. If it does not, all this discussion is academic.