Trimmng between opposing Dados - Router Forums
 
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post #1 of 10 (permalink) Old 11-06-2013, 06:16 AM Thread Starter
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Default Trimmng between opposing Dados

I need some help with the best technique to use to remove the material between opposing dados in a bookcase upright. As much as I tried, Iím sure the dados are not matched perfectly and I donít want to destroy either face of the upright. Currently I plan on removing the rough stock with a jig saw and cleaning up (to match the dado cuts) with a router.
1. If I use a flush trim bit against the bottom dado edge, I run the risk of run out on the top side.
2. Conversely, if I use a rabbeting bit with the bearing on the top, I run the risk of the same problem on the bottom although I may be able to adjust this bit (shorter) to not cut all the way through.
3. I suppose I could attempt to remount the exact size dado jig on one side and trying the same but the bit is too large to clean out the end of the cut. Iím anticipating a lot of manual work with this.
I'm not confident I could get a safety edge guide for the router, mounted precise enough on top for use with technique #1. Anyone have any idiot proof techniques for the idiot? Or recommendations?
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post #2 of 10 (permalink) Old 11-06-2013, 08:13 AM
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I hope I understand your problem. If not, try to explain what you are doing better with more pictures.

I have good luck using this jig. It provides a fence on each side of your dado that can easily be adjusted to the thickness of your shelf by using the edge of the shelf to set the space between the jig fences. Then, using a mortise bit with a top bearing that is a smaller diameter than the width of the desired dado you can cut the dado by following the fences. If you do this carefully your shelf will fit perfectly every time.

https://www.google.com/search?q=rout...m=122&ie=UTF-8

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post #3 of 10 (permalink) Old 11-06-2013, 09:20 AM
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You might want to try a flush trim bit with a shear angle cut.
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post #4 of 10 (permalink) Old 11-06-2013, 09:58 AM
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Mark; from the picture, you've already cut the opposing dadoes on opposite faces of the gable so that can't be the material you want to work on? You want to remove other wood? Perhaps a sketch would clarify, maybe just showing the completed cuts?
Foe what it's worth, I'd probably have done what you've done; a fancier solution might be a stopped dado. In this case, I'm not sure there'd be any advantage.
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post #5 of 10 (permalink) Old 11-06-2013, 10:25 AM
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I too am trying to understand what you are trying to do.

A. Cutting an upright into two separate piece along the existing dado, using the dado's as a guide...

--OR--

B. Making the existing dados deeper.

The way you were describing: "Doing a rough cut with a jigsaw..." he using a flush trim bit... It sounded like "A". ... And you were asking for something somewhat idiot proof.

Without outside support, using the existing dado as a guide, there is the risk of rounding the beginning and end of the cut... As you try to move the router to the dado with the bearing and as you exit the existing dado and lose that support. As we say, you ease it in and are careful as you exit. For most of us, that is good enough.

*** BUT-
You asked for something "idiot proof." Some may say this following method as overkill, but you asked...

I would use a straight edged guide, just a bit longer than each edge, clamped even with the edge of the dado. Use it as the guide instead of using the existing dado.

With a guide, there is support for a confidently getting straight edge, including where the cut will start (before the material starts) and end, where the absence of existing material would not be able to support that (after the material ends)...

"Don't worry, I saw this work in a cartoon once."
"Usually learning skills and tooling involves a progression of logical steps."

Last edited by MAFoElffen; 11-06-2013 at 10:30 AM.
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post #6 of 10 (permalink) Old 11-06-2013, 03:08 PM Thread Starter
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Guys, Thanks for the quick responses. My apologies for the lack of clarity. My proficiency with Sketch-Up leaves something to be desired (go figure, I spend my days on computers). The existing dados on both sides go for the width of the bookcase upright (shown on edge). I need to ďconnectĒ the dados on each side for about a third the length of the dado from one edge to allow the shelf to slide in and interlock. (Mike, itís your option A).

I did use the dado jig on the dados allowing for about .02 extra for the slide fit of the shelf (the information I was working from suggested 1/32) but my concern was/is the variability (thickness/straightness) of the Birdís Eye Maple used for the shelves, and of course more so due to any misalignment of the opposing dados. So Iím assuming some manual fitting on the 14 locations / 28 dadosĖ hopefully material removal only and not needing to fix something too loose but I have some ideas for that type of fix anyway.

I wasnít thinking of the potential start/end runout problem so thanks for catching that, Mike, and I may use some sort of external longer guide. I was mostly concerned with misalignment of the dados and cutting out on the side of the upright where the bit wasnít guided (top or bottom) Ö best case I want a 3/8 x 1Ē bit with bearings on both ends 
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post #7 of 10 (permalink) Old 11-07-2013, 05:51 AM Thread Starter
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POST NOTE: I trimmed the cutout between the dados by trapping a top bearing bit between some lexan guides aligned to the existing dado - I couldn't reuse the dado jig, the bit was about 1/8" too short for that. I guess I'll chalk this up to lessons learned - I should have ignored the project plans, thought for myself and not cut the matching second dado until the front cutout was in place to align the second dado to - a pencil line was just not close enough. I did have 2 sets of the 14 that were misaligned (not much but visible). (I guess I should have suspected something when the plans indicated to cut the dados on a table saw which would require hanging 6' of lumber off the one side)
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post #8 of 10 (permalink) Old 11-07-2013, 08:05 AM
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Quote:
Originally Posted by FreeTime View Post
I need some help with the best technique to use to remove the material between opposing dados in a bookcase upright. As much as I tried, Iím sure the dados are not matched perfectly and I donít want to destroy either face of the upright. Currently I plan on removing the rough stock with a jig saw and cleaning up (to match the dado cuts) with a router.
1. If I use a flush trim bit against the bottom dado edge, I run the risk of run out on the top side.
2. Conversely, if I use a rabbeting bit with the bearing on the top, I run the risk of the same problem on the bottom although I may be able to adjust this bit (shorter) to not cut all the way through.
3. I suppose I could attempt to remount the exact size dado jig on one side and trying the same but the bit is too large to clean out the end of the cut. Iím anticipating a lot of manual work with this.
I'm not confident I could get a safety edge guide for the router, mounted precise enough on top for use with technique #1. Anyone have any idiot proof techniques for the idiot? Or recommendations?
For my last bookcase I decided to use biscuits instead of rebates and made this simple jig to ensure that the slots were inline on both sides. I see no reason why this couldn't be used as a fence for the router to run against. In use the jig is of course clamped.
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post #9 of 10 (permalink) Old 11-07-2013, 08:50 AM Thread Starter
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Harry,

Thanks, great idea - I did use a similar two sided jig for getting the angle of the rebate correct (with respect to the front) on each side (the risers were not square ... front angles back 10deg, back 5deg). But I didn't think it through - I didn't use it for synchronizing the location of the opposing rebates, just orientation. I located the rebates using a square from one side to the other. I agree that I should have used whatever (once clamped) to cut both sides and skip the "lost in translation" by remounting the dado jig on each face.
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post #10 of 10 (permalink) Old 11-07-2013, 09:17 AM
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I was actually thinking crosscut saw 16th inside the line, then a chisel to cut it in nice and smooth. Of course not a "router' answer to your problem.

If you use a marking knife to mark the lines rather than a pencil you won't have that nasty tear out problem... That is with the saw/chisel option anyway.
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