1 1/8" Groove Cut Jig- Need advice

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Forum topic by GerardW posted 09-23-2013 04:05 PM 1194 views 0 times favorited 10 replies Add to Favorites Watch
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44 posts in 1995 days

09-23-2013 04:05 PM

I am working on a new router table top made out of 3/4 phenolic faced ply, which is going to be so much nicer than my current plywood tabletop. I’m also adding in t-track and, pertinent to this post, a mitre channel. For the mitre channel I need a 1 1/8” wide groove.

Lucky for me I just purchased a new dado set (my first!) and figured I could use some fancy shop math and diagrams to figure out a smart way to do this. My dado set maxes out at 7/8” cut, so it is going to be a minimum of two cuts to make this work.

My idea was to use a piece of 1/2” plywood as a secondary fence along my rip fence, and stack the dado up to 5/8”. After the first cut, I would remove the secondary fence, run it through again with the 5/8 set, , and end up with a perfect 1 1/8” groove.

Many of you are already aware of how this story ended. What with 1/2” plywood actually being 15/32”, in the end my groove was off by 1/32”. Searching through my shop with a caliper, I quickly determined that I had no true 1/2” stock in house (I also don’t have a planer to make any). Further, my dado set doesn’t have the flexibility to handle n/32”.

So- suggestions for how to get this groove right on the first try? I of course will practice with scrap wood first to make sure its working, but is there any better solution than running it through once, then jimmying the fence just a tad, running it again… and repeating until its done (or you’ve gone over too far?)

-- Gerard in Bowie MD

10 replies so far

View bpalmer60's profile


11 posts in 2817 days

#1 posted 09-23-2013 04:28 PM

You get get some 1/2 in MDF and create a fence. MDF is actual thickness and very flat and conistant,

-- Bill, Missouri,

View Woodendeavor's profile


276 posts in 2779 days

#2 posted 09-23-2013 04:49 PM

use a router with a template guide. Take your 1 1/8” mitre channel and put a scrap piece of plywood on each side. screw another scrap to the end keeping the width set by the mitre channel. Use a bottom bearing router bit and cut the grove. This gives you the exact size of the mitre channel and will fit like a glove

View Nicky's profile


695 posts in 4265 days

#3 posted 09-23-2013 05:00 PM

With your dado installed, and at the correct height….

Take a straight edge, and hold it against your dado blade. Draw a line on your insert plate to determine the line of cut for the dado blade. You can make your first cut, then use the line you drew as your reference to move your fence. You may want to use masking tape on your insert, and draw a line on the tape for clarity, and accuracy. A good straight edge, and a sharp pencil will be required. Be sure your straight edge touches a tooth in front and back. I’m assuming here that you will have a 5/8 dado installed.

You can practice on your scraps

-- Nicky

View firefighterontheside's profile


19236 posts in 2029 days

#4 posted 09-23-2013 05:22 PM

I may be oversimplifying this, but I would mark on the edge of the top the location of the dado, set the table on the saw and move the fence so that the dado set matches up with one side of the intended dado, of course set the height of the dado to the depth of your dado. Make this first cut with your full set. Then move your fence so that the dado set lines up with the opposite side of the the intended dado and run it through again. That’s what I would do.

-- Bill M. "People change, walnut doesn't" by Gene.

View C_PLUS_Woodworker's profile


601 posts in 3080 days

#5 posted 09-23-2013 06:03 PM

What “firefighter” said

View pintodeluxe's profile


5783 posts in 2986 days

#6 posted 09-23-2013 06:27 PM

Just sneak up on the cut by moving the fence. When the track fits in the groove, you are done.
Aim for an easy friction fit, otherwise you can chip the edge of the phenolic when installing t-track.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View GerardW's profile


44 posts in 1995 days

#7 posted 09-23-2013 06:44 PM

Wow! All of these are great ideas, from the simple and effective to the more elegant and creative. I will probably be using the dado set as I just got it and need some practice. I’ll report back on what I did and how it goes.

-- Gerard in Bowie MD

View gfadvm's profile


14940 posts in 2863 days

#8 posted 09-24-2013 01:37 AM

I would use a hand held router and jig similar to woodendeaver’s comment above.

-- " I'll try to be nicer, if you'll try to be smarter" gfadvm

View Jim Jakosh's profile

Jim Jakosh

21514 posts in 3278 days

#9 posted 10-01-2013 02:59 AM

Set up a straight edge on the board for a guide for the base of your router and rout it in with a 3/4” bit- 2 cuts. It is easier than setting up dados. Check it out on a piece of scrap first because some of the router bases are not right on center with the bit so get to know what the router cuts and adjust for it after measuring the cut in the scrap piece…..........JIm

-- Jim Jakosh.....Practical Wood Products...........Learn something new every day!! Variety is the Spice of Life!!

View GOOD LUCK TO ALL's profile


418 posts in 1900 days

#10 posted 10-01-2013 03:15 AM

Make your first pass in your top and then also on a couple pcs of scrap.
Set your fence for the second pass, test it first on one of the pcs of scrap.
Re adjust if necessary, test again with second pc of scrap. After making sure the fit is correct, run the second pass on your top and it should be perfect.

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