What size rounding bit for 3/4" stock?

[jtpr]

If I want to create a rounded edge on a piece of 3/4" wood, what size router bit would I use? I want it to be smooth round, not have that little jag at the top.

-jim

[SeeAll]

Hi,

I'd use a Staff Bead cutter.

In your case a 9.5mm - Trend.

SeeAll

[Jim]

Up to 3/4" radius (to suit your taste). As for the jag, you control whether there is one or not by setting the height of the bit. Jim

[DJ Delorie]

If you mean a half round (3/4" diameter), use a 3/8" radius bit. Duh.

The trick is the technique, not the math. If you can attach an auxiliary board to the routed board for the second side, that's the easy solution. In my case, I used a steel straightedge to align my incra fence with the bearing on the bit to within a thou (yay for the micro adjust!) and just routed both sides - the board rubs along the fence at JUST the tangent point, and you end up with an essentially perfect 3/4" half round.

[fredfighter]

Uh huh. Anyting less than 3/8" and you will have to leave a flat spot somewhere on the edge, or that 'jag'. You can use larger radiused bits, then the curved edge may be tangent to either face, with a sharp edge at the other, or tangent to both with a sharp edge in between.

A roundover with a 'jag' is called a bead.

Draqing the profile on graph paper can help a lot.

[Edwin Pawlowski]

I like the look of a 3/8" myself. Any size properly adjusted won't leave any marks at the top. You can use a 3/4" also, but that tends to make it look more like a full rounded edge rather than just a nice break of the edge. Depends on what you want as a final result.

[CW]

Change that "thou" to "a little bit and I'll believe you.

[BillyBob]

Please explain. The only factors I know which will cause a jag are bit height or fence setting relative to the bit. The radius has nothing to do with it. The radius choice is not related to the thickness of the wood, other than cosmetic preference.

Bob

[pat]

Example at the

link. The cutter has a 1/2" radius; the work is 3/4" thick, the fence is offset for a full thickness cut.

[jtpr]

Thanks. But what I want is half that. So the bottom is flat and the edge curves up to the the top. It will be the top of a tongue drum. I believe the first post was correct with 3/8" (I won't comment on the "duh"...;+}) I guess it is obvious when you think about it.

So I went and looked at bits... wow. $30!

-jtpr

[fredfighter]

I think you missed the word 'or'. Suppose you roundovah 3/4" stock with a 1/4" bit. Will you not get a flat spot on the arris _OR_ a jag or one or both edges? (Or all three.)

[DJ Delorie]

The dial is marked in 1/1024 inch units, and yes, "off by one" makes the difference between "straightedge rocks" and "straightedge doesn't rock". You do realize that your fingers can feel a 0.001" offset, right? A thou really isn't as small as you think.

Besides, that was kinda the whole point of spending over a thousand dollars building an ultra-precise router table.

[bridger]

it only takes 16 or so of them to make 1/64"

I thought that the reason to do that is because you can...

[DJ Delorie]

Actually, I justified it as "practice for the dining room cabinets" and "I need this to *build* them too" :-)

I was using it this weekend to make tenons for the face frames, and it turned out that a few thou made the difference between "too tight" and "just right". Eventually I figured out that the tenon had to dial in at 0.238" to 0.243" to get that "sweet" fit in the mortises. The mortises were all made in a batch first, so they're all essentially the same, but the wood for the face frame is not consistent thickness, as the store had S3S at the time, and it doesn't matter as long as the

*front* lines up, so I used the router table to cut the front cheek of each tenon FIRST[1], in a batch, without adjusting the router height at all, then used the dial calipers and PRL's thou indicator to custom cut the back cheeks individually.

Cut. Measure: 0.256". Raise bit 0.016". Recut. Measure. Perfect. Next piece.

Of course, this was after the usual shoulder cuts on the table saw and rough slabbing of the cheeks on the bandsaw. A few extra steps, but each step was fast and easy and it went pretty smoothly.

[1] The mortises were started at the router table, with the front face against the fence every time, and finished with a hollow mortiser, again with the fronts against the fence[2]. The tenons were cut fronts first, so the front faces all line up. This way, I don't care how thick the boards are. [2] The router table couldn't go deep enough, but my drill press is a cheap store brand with lots of quill wiggle. So, I route first, deep enough to guide the hollow mortising chisels. That way I use the strengths of each tool to avoid the weaknesses of the other.

FYI I learned the "reference face" technique at last year's GNHW Joinery Symposium.

- the "machine mortise and tenon" session. DVD number 05-JS5 if anyone wants to buy a copy

[CW]

I've been a machinist and toolmaker for 19 years. I have a pretty good idea of how big .001" is. Your setup is not ridgid enough to hold it. Nothing on that fence is strait enough to reference. Your adjustment screw probably is accurate (precision screws are pretty easy) but that alone won't get you that kind of precision.

[DJ Delorie]

Have you seen one in person?

Besides, I can only speak for my own experience. A thou on the dial is a useful increment for that kind of setup. A thou on the lift is a useful increment there. On my setup, a thou sometimes makes a difference.

[Edwin Pawlowski]

If you want a 1/4" shank, much cheaper right now

a good price here brands are top quality bits. The 3/8" roundover is one of the most used bits in my shop so I don't mind paying for one that will last a long time.

[CW]

Nope, don't need to. I know what it is made of, I know how it is made, I know what the target customer is and I know the price.

Might make a difference but just because you lable it .001 doesn't make it so. Your dealing in "little bits".