How much material is removed with 3/4" radius roundover bit? - Router Forums
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post #1 of 14 (permalink) Old 03-10-2018, 11:50 AM Thread Starter
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Default How much material is removed with 3/4" radius roundover bit?

I'm building a speaker cabinet out of 5/8", 13 ply baltic birch plywood, with 5/8" box joints, would rounding the corners with a 3/4" radius roundover bit remove too much material?
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post #2 of 14 (permalink) Old 03-10-2018, 11:58 AM
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post #3 of 14 (permalink) Old 03-10-2018, 12:07 PM
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Hi and welcome. I’m curious why you would want to round it off that much? I would probably only use a 1/4r at the most.
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post #4 of 14 (permalink) Old 03-10-2018, 12:15 PM
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Guitar; Hey, welcome!
No, but there is a an issue. If you draw a 2" square, find the exact center, and scribe a 2" circle inside the square, the circumference will be perfectly mated to the perimeter. Visually, each of the four sides will flow smoothly into the arc.
That doesn't happen if your circle is larger than the square. When you slide the arc back so that it's within the square, the arc creates an edge, or angle if you like, where it intersects with only two of the adjacent sides where it's still tangent.
Try the 3/4 bit on a piece of 5/8" scrap; nothing bad will happen. Obviously, the same thing doesn't happen when you use a smaller radius bit.
This discussion has happened here in the past; a lot of us use small radius bits (1/8" R.) for rounding over on a regular basis.
If you're worried about the appearance, maybe buy some/a smaller rad. bit?
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post #5 of 14 (permalink) Old 03-10-2018, 12:16 PM
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First off, there won’t be any material to run your bearing against. If you try just using a portion of the bit you won’t get a true radius.


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post #6 of 14 (permalink) Old 03-10-2018, 12:23 PM
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After re-reading your original comment it occurred to me that what you're asking is if if the 3/4" rad. will remove too much of the joint!
Will it damage the fingers? Yeh, I'd be worried too! Perhaps try Charles's suggestion of a 1/4" rad. first; you can always re-cut it with the larger bit if you don't like the look...or you really want to risk it.
By the way, you didn't mention whether this is handheld or being done on a router table?
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post #7 of 14 (permalink) Old 03-10-2018, 12:24 PM Thread Starter
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I'm matching the radius of a marshall cabinet so the marshall corners will work. I'm also adding 3/4" material to inside so baffle can be mounted, which also allows me to radius corner with router
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post #8 of 14 (permalink) Old 03-10-2018, 12:25 PM Thread Starter
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I'm using a hand-held
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post #9 of 14 (permalink) Old 03-10-2018, 01:32 PM
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Quote:
Originally Posted by guitar413 View Post
I'm using a hand-held
Makes sense now...I'd still personally do the 1/4" or 1/2" RO first. It'll remove some of the waste and give you a feeling for easily the material is peeling away. Can you back up the corners so the first and last fingers aren't damaged as the bit starts/leaves the cut? I think that'd be my major worry.

Guitar; this is why the members like to see a bit of info in the profile about what tools and experience the poster has. I get the feeling you're way above the newbie level!
It really helps members when they're replying to the comment. We love helping out folks just getting into woodworking, but there are several members here with years (decades) of commercial/production experience who are excellent resources for more
technical issues.
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post #10 of 14 (permalink) Old 03-10-2018, 02:07 PM
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The backing, glued in and fitted tight, will let you use a larger rountover bit without losing strength. When I look at PA and loarge studio speaker cabinets, I notice that they have large roundovers, however, most are made of MDF. It is very hard to get a grip on such an edge, given how heavy speakers and ply are. So I hope you're working on some sort of grip, possibly a recessed grip. I do AV for our senior group and hate wrestling with large, gripless speakers. Not sure there's much advangage to using box joints if you're going to do roundovers, and even less advantage if you're going to cover the outside of the box with some sort of fabric.
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