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Router bit for finger joints

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Forum topic by NoSpace posted 07-16-2016 10:00 PM 626 views 1 time favorited 15 replies Add to Favorites Watch
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NoSpace

73 posts in 704 days


07-16-2016 10:00 PM

So I built this router table, fence, and finger joint jig, and I think I can see my way out getting it dialed in for accuracy for finger joints, but I’m have a problem with tear-out. So far just practicing on pine and plywood but it’s taken some chunks. I don’t know the name of it, but I’m using the widest bit I have, maybe 3/4” and it’s the key bit I use for removing material with the plunge base for inlays.

For those who have done finger joints on a router table, what kind of bit do you use? I know you can buy bits specifically for finger joints, but I guess what I thought was weird is in the youtube videos I’ve watched on the subject I don’t remember bit selection mentioned.

Any other factors besides bit selection?

Also, I know using a dado set would be the superior method so thanks in advance for not mentioning it..:)


15 replies so far

View Bob Kassmeyer's profile

Bob Kassmeyer

184 posts in 2388 days


#1 posted 07-16-2016 10:23 PM

I’m sure there are many people here who have more knowledge on this. I’m don’t believe it makes much difference what bit you use you will get some tearout if you do not use a backer board. Maybe try cutting a small dato on the back side of the boards then you would not see any tear out. Good luck I always do mine on the table saw.

-- Bob Kassmeyer, Nebraska

View distrbd's profile

distrbd

2227 posts in 1910 days


#2 posted 07-16-2016 11:26 PM

I have 2 Oak Park box joint jigs ,I’m not sure if they are still in production but I liked my box joint jigs very much and used them often until I decided to build my own jig for table saw.

The best bits for that jig in my opinion is Spiral bits, I used to use 1/4” MLCS bits and did not have much tear-out-but I would put all 4 sides together.hardwood like Maple,Cherry etc. have less tear-out than pine.

Use a brass setup bar for finding the exact distances:

The pictures below are from Router forums .com Harry sinclair is the source:
http://www.routerforums.com/jigs-fixtures/4602-oak-park-box-joint-jig-update.html
http://www.routerforums.com/jigs-fixtures/65202-box-joint-jig.html

-- Ken from Ontario, Canada

View Charles Holland's profile

Charles Holland

63 posts in 159 days


#3 posted 07-16-2016 11:29 PM

Spiral bit. I’d think an uncut bit would work. For year out use a backer board

View Kirk650's profile

Kirk650

291 posts in 212 days


#4 posted 07-16-2016 11:59 PM

Just me, but I quit using a router for finger/box joints, and now use the table saw and a good dado stack. And, of course, I built a nice jig. Took me a while to get it dialed in just right.

View Redoak49's profile

Redoak49

1950 posts in 1452 days


#5 posted 07-17-2016 01:42 AM

I use spiral bits but never anything that large. Trying to cut a 3/4” finger in one cut will be a challenge.

View NoSpace's profile

NoSpace

73 posts in 704 days


#6 posted 07-17-2016 04:12 AM

So the back board support did help a lot for the plywood but not perfect. I then went on to .2” padauk scrap and major tear out. Maybe it’s too thin. I went to HD and got a 1/4” spiral bit (1/4” collet, another problem) in the name of science and if I go really slow and even it does ok on the padauk, but I did get tear out there too. I’m wondering if my jig doesn’t feed as cleanly as it should. anyway, that’s enough for today.

Also, I get it would be better on table saw—not an option for me right now.

thanks for the comments.

View Charles Holland's profile

Charles Holland

63 posts in 159 days


#7 posted 07-17-2016 10:38 AM

odd. I don’t do many finger joints but I never get tearout with my spiral bit. I don’t even use a backer board. all I’ve ever tried lumber wise is oak and cherry though.

View splintergroup's profile

splintergroup

828 posts in 686 days


#8 posted 07-17-2016 02:57 PM

Spiral bits get $$$ above 3/8”

My router table has an Incra system and it does finger (box) joints very well (I use a backer board), but over 1/2” is tricky. I’ve since grown to adore my Freud box joint blade set and a simple TS jig, It only does 1/4” and 3/8”, but the fit is perfect. The blade also is handy for any grooves I need to cut, perfectly flat and crisp.

View johnstoneb's profile

johnstoneb

2143 posts in 1636 days


#9 posted 07-17-2016 04:09 PM

When making my jig I use the same bit i will use for the joint the jig serves as a backer board. I have very little if any tear out.

-- Bruce, Boise, ID

View HorizontalMike's profile

HorizontalMike

7146 posts in 2377 days


#10 posted 07-17-2016 05:46 PM



Spiral bits get $$$ above 3/8”
My router table has an Incra system and it does finger (box) joints very well (I use a backer board), but over 1/2” is tricky. I ve since grown to adore my Freud box joint blade set and a simple TS jig, It only does 1/4” and 3/8”, but the fit is perfect. The blade also is handy for any grooves I need to cut, perfectly flat and crisp.
- splintergroup

BINGO that! I originally built my own DIY Jig but found:
  • The DIY Jig moves, out of adjustment, over time since it is made almost entirely out of wood.
  • DIY Jig is hard to adjust, since you pretty much have to tap-N-go until you get it “right” (and pretty much for THAT session only).
  • The Incra System makes adjustment so much easier that it is addicting to use!
  • The Incra System can be used on either the BS or the TS.

-- HorizontalMike -- "Woodpeckers understand..."

View NoSpace's profile

NoSpace

73 posts in 704 days


#11 posted 07-23-2016 05:39 AM

Been super busy with other things, but converging on a solution. The poor results I had with the new 1/4” spiral bit I think proved something else was majorly wrong, namely the piece wasn’t properly secured and feeding evenly. My homemade router table doesn’t have a miter slot, nor does my jig, it just rides the table width like a track and is a little clunky; no way to make it precise. For some reason, looking at the incra thing gave me the idea of installing a quality aluminum drawer slide to extend the jig/work piece into the bit. So the whole thing feels super controlled and precise now. No tearout on the thin padauk with the 1/4 spiral now, even when leaving a tiny space between cuts. I put the 3/4” mortising bit back on and tried it on plywood and pretty clean. Doesn’t feel like I can do much better. I have yet to complete an actual joint yet so let’s see how it goes.

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NoSpace

73 posts in 704 days


#12 posted 07-25-2016 12:28 AM

Ok, I thought I was on the right track and then i went from practice cuts to a real future drawer piece and the tear-out came back in spades. The setup is so tight at this point i can’t imagine how I could make it more stable. I moved on to the walnut—the most forgiving wood made—and where my test cuts were great on a walnut test piece, immediate tear-out – bad tear-out, ruined the piece.

One obvious difference: the clean test cuts just happened to be with the router bit parallel to the grain and going for the real thing, the cuts were were perpendicular to the grain. Well, it seems obvious with the grain would produce better result and I feel like an idiot for having to ask this but I will anyway: are finger joints supposed to always be with the grain? Just an image search on Google seems to confirm, but I’m not finding articles on finger joints that call it out directly, and that to do otherwise results in problems.

The testing and drawers I’m making are just out of scraps, never even thought about this. When I turned the piece of walnut tearing out on its end, I completed the row of cuts with flawless results, not even being that careful.

so now i’ve revealed I’d been sometimes cutting perpendicular to the grain, would y’all say that with a professional jig, Dado blade set, the incra system, or whatever, that I should have trouble with that, or would you say—well you can’t cut in the grain with any system.

View splintergroup's profile

splintergroup

828 posts in 686 days


#13 posted 07-25-2016 05:19 PM

Having the fingers run parallel to the grain is far stronger that running perpendicular.

You can route a finger with either grain orientation. With the fingers running parallel to the grain, the bit is only severing the fibers at the tip of the bit, tear out is minimal, but still can show up.
Cutting perpendicular to the grain causes the bit to lift fibers off the surface of the board as the bit exits the wood. This can only be prevented with a backer board on both sides of the material being cut.

View NoSpace's profile

NoSpace

73 posts in 704 days


#14 posted 07-25-2016 11:48 PM



Having the fingers run parallel to the grain is far stronger that running perpendicular.

You can route a finger with either grain orientation. With the fingers running parallel to the grain, the bit is only severing the fibers at the tip of the bit, tear out is minimal, but still can show up.
Cutting perpendicular to the grain causes the bit to lift fibers off the surface of the board as the bit exits the wood. This can only be prevented with a backer board on both sides of the material being cut.

- splintergroup

Nice. thanks.

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NoSpace

73 posts in 704 days


#15 posted 07-26-2016 03:33 AM

Ok, after getting calibrated and doing some test pieces the ultimate test was the oak plywood that was nearly disintegrating before. Going parallel with the grain, but for this plywood pretty sure that’s not enough so I tried the trick of sandwiching it (clamped) with a scrap of 3/4” generic white wood leading the charge. Flawless results, and the whole operation was extremely smooth. I’ll probably use that front board for everything for a while. thanks!

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