Bullnose an edge on a circular table top - Router Forums
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post #1 of 13 (permalink) Old 10-04-2016, 12:04 AM Thread Starter
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Default Bullnose an edge on a circular table top

I'm new to this forum and could use a little advice/encouragement regarding the use of a 3/4" bullnose bit to rout a curved edge on a circular oak table top (43" diameter). I made the top by laminating several oak boards and cut the circle with a spiral cutting bit in my router attached to a trammel that I had built a few years ago to make an oval table top. My first thought was simply to rout a 1/2" or slightly larger round-over on the top edge. However, since I have a 3/4" bullnose bit (never used up to now), and the table was made with 3/4" stock, I thought maybe I could do the bullnose feature by using the trammel, lining the bit up accurately on center edge and walking it back with small cuts with each rotation of the router. I practiced tonight cutting bullnoses on straight stock with my router table and learned the necessity of accurately aligning the bit to the edge to get a smooth circle. Am I on the right track here? It should go without saying that I don't want to have to start over on this project because I had used the router bit improperly. Am I missing anything here?

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post #2 of 13 (permalink) Old 10-04-2016, 02:46 AM
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Hi Lynn and welcome. Bullnose bits can be a little tricky because sometimes the stock thickness varies very slightly as you move along a board and because it can be very hard to stay flat without an offset base. With that bullnose bit in the router you may have 40% of the base on top of the table, or even less. Uneven thickness or wobble will leave small fillets in places which usually can be sanded out but may still be slightly visible as a slightly unsmooth curve. Some prefer to use a round over from each side instead as it eliminates the the risk of fillets but in order to use a round over you have to leave a small flat in the center or use an edge guide so that you don't need the guide bearing. Either way can be a trade off of minor issues.

I've never tried a bullnose on a round table but if I did I would use an offset base on my router for better stability. Leaving a router attached to a router table insert plate works well for that. You already see the need for using the edge guide. The only option to that I would suggest is that if you don't feel that it is tracking well around the circle you might want to add a piece to it that has the same curve as the table and that would make it a bit more stable when trying to follow the table edge.

On a curve like that the only method I know of to set the bit exposure properly is trial and error. If you were putting a bullnose on a straight edge then it is easy to set the guide using a round dowel slightly smaller in radius than the bullnose.
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post #3 of 13 (permalink) Old 10-04-2016, 04:09 AM
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First Welcome to theRouterForums Lynn.

I agree with everything @Cherryville Chuck wrote, in fact I was beginning to compose a reply when his reply appeared.

A bullnose bit with a 3/4 inch cutting diameter is a large bit; the one I own is 1-5/8 inch diameter with a carbide height of 1-3/16. This bit would cut a (bead, fillet) of up to 7/32 inch on each side of the diameter. In order to avoid any (bead, fillet) the bit will have to be very carefully aligned with the table top, and the oak table top must in no place exceed 3/4 inch thickness. A bit his large is really intended for table use.

I am uncertain as to what your mean by a "trammel". Unfortunately with only 2 posts you cannot yet post a photo. By any chance is your "trammel" a template? And if so did you cut on the inside or on the outside of the trammel?

In your other post you saw a round table with roundover edges. 43 inches is very large for use in a router table. Thus I suggest that you use a roundover bit of perhaps 1/4 inch radius on each surface. Such cuts would leave a central 1/4 inch flat surface but there would be no (bead/fillet) and any variation in the thickness of the table top would show up in the flat surface area and would be undetectable.

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post #4 of 13 (permalink) Old 10-04-2016, 06:25 AM
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Quote:
Originally Posted by mftha View Post
I am uncertain as to what your mean by a "trammel". Unfortunately with only 2 posts you cannot yet post a photo. By any chance is your "trammel" a template? And if so did you cut on the inside or on the outside of the trammel?
Tom, a trammel would be the kind of circle cutting jig that pivots around the centre of the workpiece... perhaps you would know it as a compass jig?

On the original question, I think Chuck has it covered. Using a round-over bit to do a quarter-round from both sides would be my suggestion too. The first side you could do easily with a bearing guide, then some other sort of guide when working on the second side. A matched-radius fence as Chuck described is probably the ideal. But if the table is perfectly circular then a guide that contacts the edge at two points would be enough.
You could also do it using the trammel. Should be easier than using the trammel with bullnose bit, since you can set the trammel radius once and plunge to start.

Last edited by AndyL; 10-04-2016 at 06:35 AM.
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post #5 of 13 (permalink) Old 10-04-2016, 08:21 AM
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Here is a design for an offset base with an edge guide. In your application I would make this larger and make the edge guide arc instead of strait, to match the radius of your table.
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post #6 of 13 (permalink) Old 10-04-2016, 09:11 AM Thread Starter
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Thanks for the prompt responses. Based on what you all provided, it looks like the better part of valor for me will be to use a round-over bit for the top and bottom of the table top. It never occurred to me that the thickness of the table top may not be uniformly 3/4" all the way around, and the consequences of that being the case had I used the bullnose bit. I'm thinking that I should be able to get the full-round effect by routing the top round-over via the bit's bearing, and the bottom round-over using the same bit, but using my trammel (circle jig), which should avoid the need for a flat surface for the bearing. The router is attached to the base for my router table, so there's lots of support for routing the upper round-over. The circle jig likewise provides firm support for the router.

Thanks again for the great analysis and advice.
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post #7 of 13 (permalink) Old 10-04-2016, 09:57 AM
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Beating a dead horse here.
But, as a rule, bullnose bits are unpiloted.
And it they are (bearing guided) then they do not produce a full radius on the work. (They produce a beaded profile.) But I agree with IRwindy, that profile is a nice one.

If there is a threat of the work thickness varying, I'd get a 7/8" (7/16" rad.) tool.
And if the work was produced from an ellipse maker, a bullnose instead of the straight bit would have made and shaped the top from the get go.

But for a safer, lower risk approach, I would have made a templet from the device rather than the work itself. Now with a templet, and several different diameter collars, the edge could have been profiled and sized with only the bullnose cutter and in stages.
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post #8 of 13 (permalink) Old 10-04-2016, 11:19 AM
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Quote:
Originally Posted by mftha View Post
First Welcome to theRouterForums Lynn.

I agree with everything @Cherryville Chuck wrote, in fact I was beginning to compose a reply when his reply appeared.

A bullnose bit with a 3/4 inch cutting diameter is a large bit; the one I own is 1-5/8 inch diameter with a carbide height of 1-3/16. This bit would cut a (bead, fillet) of up to 7/32 inch on each side of the diameter. In order to avoid any (bead, fillet) the bit will have to be very carefully aligned with the table top, and the oak table top must in no place exceed 3/4 inch thickness. A bit his large is really intended for table use.

I am uncertain as to what your mean by a "trammel". Unfortunately with only 2 posts you cannot yet post a photo. By any chance is your "trammel" a template? And if so did you cut on the inside or on the outside of the trammel?

In your other post you saw a round table with roundover edges. 43 inches is very large for use in a router table. Thus I suggest that you use a roundover bit of perhaps 1/4 inch radius on each surface. Such cuts would leave a central 1/4 inch flat surface but there would be no (bead/fillet) and any variation in the thickness of the table top would show up in the flat surface area and would be undetectable.
Tom, it was late when I replied and trammel didn't automatically register when I read it either even though I have a set of compass tools that attach to a common yardstick to turn it into a marking trammel. I got them from LV and they enable marking up to a 6' circle.

I hadn't thought of using a trammel guided router and it would help greatly with wobble issues provided that the trammel rod was stiff enough for that. Another issue with using the trammel is that a bullnose bit cannot be plunged into position so to use the trammel means that you have to slide the router inward on the rod(s) to the final cutting position while the router is turning and then lock the router into position on the trammel to start cutting. That can be very tricky, even if you have extra hands available and it quite often shows where you started as that part is hard to keep smooth when working that way.

Otherwise I would use the edge guide on the router, preferably with a piece added on with the radius equal to the table as I mentioned earlier. This depends on the gap between the two sides of the edge guide. If the gap is fairly wide on the stock edge guide then it should track fairly well without a piece added to it as long as it slides smoothly.
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post #9 of 13 (permalink) Old 10-04-2016, 07:21 PM
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Quote:
Originally Posted by Cherryville Chuck View Post
I hadn't thought of using a trammel guided router and it would help greatly with wobble issues provided that the trammel rod was stiff enough for that. Another issue with using the trammel is that a bullnose bit cannot be plunged into position so to use the trammel means that you have to slide the router inward on the rod(s) to the final cutting position while the router is turning and then lock the router into position on the trammel to start cutting. That can be very tricky, even if you have extra hands available and it quite often shows where you started as that part is hard to keep smooth when working that way.
I agree with Chuck... There's no good way to start your cut with a trammel and bull-nose bit. The trammel would be hard to center if you were thinking of doing each side separately with a round-over. An edge guide would probably be best. I think that I would round over one edge
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post #10 of 13 (permalink) Old 10-04-2016, 09:00 PM
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Welcome to the forum Lynn.

Ross,
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Enjoy the knowledge of others that can be found within.

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