How to CNC a finger-jointed box?

Signals
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Re: How to CNC a finger-jointed box?

Post by Signals » Wed Apr 30, 2014 2:53 pm

I have been building them by hand with miter joints. It gets pretty tedious, and it requires me to put a lot of time in for something that should be fairly "passive" income.

Also my Shapeoko has a 4 foot by 6 foot bed, so it could mill a few sets in one "go".

Also I'm going to get the CNC to carve acoustic diffusion patterns in the interior walls of the speakers, which can not quickly be done by hand.

cvoinescu
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Re: How to CNC a finger-jointed box?

Post by cvoinescu » Wed Apr 30, 2014 3:04 pm

You can still do them in one go, because the joints I suggested must be milled from the face that will become the inside of the box. If you can use one tool for everything, it gets even easier. A palm router should make short work of this, especially with a good quality 1/4" or 3/8" endmill.
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WillAdams
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Re: How to CNC a finger-jointed box?

Post by WillAdams » Wed Apr 30, 2014 3:44 pm

If you just want miter joints, then why not use a 90 degree V-bit to cut them out?

Then all you'd need to do would be:

- mount the parts
- mill the acoustic diffusion patterns
- switch bits to the 90 degree V-bit
- cut things out (using the table as your reference surface)
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets

Woodworker
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Re: How to CNC a finger-jointed box?

Post by Woodworker » Wed Apr 30, 2014 4:36 pm

Miter joints in wood, with standard glues, are not very sturdy. The glue wicks into the end grain and starves the joint of strength. You can add splines to the joint, but that just complicates it again.

Will these speakers be painted, stained or naked?
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crazeegeek
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Re: How to CNC a finger-jointed box?

Post by crazeegeek » Wed Apr 30, 2014 7:33 pm

WillAdams wrote:If you just want miter joints, then why not use a 90 degree V-bit to cut them out?

Then all you'd need to do would be:

- mount the parts
- mill the acoustic diffusion patterns
- switch bits to the 90 degree V-bit
- cut things out (using the table as your reference surface)
I agree, this seems to be a standard practice and seems to work well. It's something I have been wanting to test out myself and seems like it would work well here since the OP stated "the joints don't have to be particularly strong".

crazeegeek
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Re: How to CNC a finger-jointed box?

Post by crazeegeek » Wed Apr 30, 2014 7:47 pm

Sorry if I am hijacking this thread, but...
Woodworker wrote:Miter joints in wood, with standard glues, are not very sturdy. The glue wicks into the end grain and starves the joint of strength. You can add splines to the joint, but that just complicates it again.
I have never heard this before, but I also have not done a lot of woodwork that required gluing.

I assumed it would make the bond stronger by penetrating into the grain?
Is it only caused if too much glue is wicked into the grain?
Is this more prevalent in certain woods?
Any recommended references or tips for issues like this?

Thanks

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Re: How to CNC a finger-jointed box?

Post by WillAdams » Wed Apr 30, 2014 8:39 pm

End grain doesn't take gluing well --- wood glues work best length-wise or cross-grain.

For a mitered box I'd suggest pinning the joints --- but for speakers you should be able to do all long-grain glue-up by orienting the wood grain front-to-back for the top, bottom and sides, then you just rabbet panels for the front and back.

I believe this has information on glues: http://www.fpl.fs.fed.us/documnts/fplgtr/fpl_gtr190.pdf
Shapeoko 3XL #0006 w/ Carbide Compact Router w/0.125″ and ¼″ Carbide 3D precision collets

crazeegeek
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Re: How to CNC a finger-jointed box?

Post by crazeegeek » Wed Apr 30, 2014 9:17 pm

Thanks Will.

Woodworker
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Re: How to CNC a finger-jointed box?

Post by Woodworker » Wed Apr 30, 2014 9:36 pm

You can go to most any woodworking forum or magazine site and find that info. The most often used method is splines, ether external like this: https://woodgears.ca/frame/glue_miter.html

Or internal like this: http://www.woodworkersjournal.com/resou ... BoxJoints/

I've had a woodworking shop for more than 15 years. Make everything from beds to earrings. :-)
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additv
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Re: How to CNC a finger-jointed box?

Post by additv » Wed Apr 30, 2014 10:01 pm

I have had good success doing blind joints like this:
ImageImage

You just extend the hole by your cutter radius to make it deep enough when you cut it.

I've found them to give reasonably attractive results and be quite strong even without glue (on the scale I'm doing them anyhow).

Here's what they end up looking like:
Image

You could easily sand the corners round to give a better finish as well.

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