Finger Joints With Rounded Fingers/Sockets

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4DThinker
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Re: Finger Joints With Rounded Fingers/Sockets

Post by 4DThinker »

Tim... I learned drafting 35+ years ago while in high school, and how to draw orthographic views (top/front/back/left side/right side) and so on. The vectors needed were an end view (front view) of the finger tops plus a line to connect them. Knowing I was going to use a 1/4" diameter end mill to cut the 5/16" wide fingers, and a 1/4" ball end bit to cut the swept profile:

I started with a 1/8" vertical segment,
Then a 1/8" radius (1/4 of a 1/4" circle)
joined to a 1/16" horizontal straight line,
another 1/8" radius,
then a 1/8" vertical drop (to account for the 1/4" ball end but that will be cutting the swept profile toolpath),
then a horizontal 5/16" line (fingers were 5/16" wide).

Join all those segment together, then use the linear array tool to extend copies right as far as I wanted fingers. Join all the copies together. Use that joined vector as the profile you want extruded down the guide rail.

For the guide rail I used a single straight vector, at the beginning edge of the finger row, that started at the board end and went in the finger length - 1/2 the ball end bit diameter.

This took more time to type out than it took to just draw it up. Hope it helps.

4D

cac67
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Re: Finger Joints With Rounded Fingers/Sockets

Post by cac67 »

4DThinker wrote:The smaller a ball nose you use the less of a fillet there is to worry about. If you don't mind what the inside of the corner looks like you can just run the moulding toolpath right up to the inner edge and let the ball nose go past to its tangent/center point. I've played a bit with using a v-bit and the VCarve toolpath but so far haven't been able to completely clean it up. If you don't care that wood touches wood everywhere inside the joint you could run a v-groove just inside the inside corner at 1/2 the ballnose bit diameter depth. That should get rid of any interfering wood.
V-Grove trimmed inner line..jpg
4D
You could also run a rabbet along the edge of each board before cutting. That would give you slightly smaller pins but hide the joint on the inside of the box.

sseale
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Re: Finger Joints With Rounded Fingers/Sockets

Post by sseale »

4D thanks for posting the details. I'm using your .crv3d file to try and work out fillet removal with various cnc methods like you mentioned. Just noticed the tops of the fingers are level with the material in the posted file, but in the pic showing end view after you chiseled away the fillets, the fingers seem a bit lower than the top surface?
Thanks,
Scott

4DThinker
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Posts: 1701
Joined: Sun Sep 23, 2012 12:14 pm
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Re: Finger Joints With Rounded Fingers/Sockets

Post by 4DThinker »

sseale wrote:, but in the pic showing end view after you chiseled away the fillets, the fingers seem a bit lower than the top surface?
Thanks,
Scott
The board I used was a scrap left over from a previous project, and had been resawn using my bandsaw. It was a bit thicker on that end than I'd told Aspire thus the small lip. Since the other side of the joint was as thick as I'd told Aspire and the fingers were sized to fit it still went together fine despite that lip (after I got rid of the fillets).

I'm generally more careful about checking thickness on both ends of any board I use if I'm working on anything other than a sample to show on a web site. ;)

4D

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