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Discussion Starter · #1 ·
I'll be routing a 3/4x3/8 groove to install some "T" track. I asked the guy at Rockler checking me out if a 3/4" bit would do the width of the groove in one pass. He advised against it, saying there would be a chance of straying from the cut line. Instead, he suggested multiple passes with a 1/2" bit to get to the 3/4" groove width.

On the way home I was thinking. Wouldn't there be a greater chance of a bad cut if I used a 1/2" bit, set a guide strip, routed a pass, moved the guide strip over and routed a final pass vs. one shot with a 3/4" bit?

Or, is there a better way to do it than using a guide strip?
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With this jig I use a 1/2" bit and make multiple passes as needed, but I would be a little concerned trying multiple passes without it. That said, before I built the jig, I did cut dados with a 3/4" bit and edge guide or a clamped straight edge. Every now and then, the cut was not perfect; hence the jig!

 

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When I did my router table and put T-tracks in it, I used my table saw and stacked dado blade set. That way it was a more perfect cut.

If you can remove the table top, that is the way I would suggest.

If you use a metal or wood guide to move the router against and take shallow passes, I think the 3/4 router bit will do a good job, and don't try to go the full 3/8 depth in one pass.
 
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I did mine with a 3/4" bit in multiple passes, increasing the depth a little till i reached the final depth.
 

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John
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Bladeburners jig... only way to fly as it adjusts to the exact width of what is being mated. Believe me, it won't be a one-time use jig.
 

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where's my table saw?
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this would require a test pass or two

Use the 1/2" bit against a straight edge. Then place a 1/4" strip against the straight edge and make another pass, being careful NOT to vary away from the straight edge or you will have a "divot" in your groove. You may have to make several 1/4" strips to get one that's exactly the correct thickness + or - 1/128" or so....

The bladeburner jig is the best method, the above is a quick and dirty solution and does not require reclamping the straight edge in a new location.

How to make the jig:


Look in at 1:40 secs
 
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"Bad advice"?......maybe,but it should be looked at as sort of a "lite bulb moment"IOWs,theres more than one way to skin this problem.

Generally in machineshop world it's,use the smaller cutting diam. and then sneak up on width.When every bit of accuracy is desired.But back in the wood millshop.......I see it yet another way.That would be in the direction of cutting forces.

As an example,in your slot.....which is the more critical dimension?Is the width more critical than the depth?..........Don't really need an answer to this,just using it as an example.When you look at the cutting forces generated during "the cut"....which direction are they being applied?how or what is this doing to your more critical dimension?

A router "bit",or endmill sees its cutting forces effecting the width of slot moreso than depth.Hence,using a more narrow "bit" and then sneaking up on dimension.An alternative is to use a horizontal milling machine(which is how TS slots are cut).......back in woodshop,this means a Dado head.

This should be looked at in a positive sense......its not really an indictment against one tool vs another.Its looking at cutting forces and how they effect accuracy.Carry on.
 

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I used a good straight edge with my skill saw (circular saw) to make the outer cuts and hogged out the the bulk with the router. A circular saw is rigid and wants to cut in a straight line on its' own design. Worked for me. Those router jigs are fine and work well, but that's the way I did mine.
 

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Discussion Starter · #10 ·
Thanks, guys. Lot of good ideas. That jig looks like it would do the job. Lets see now, I need a router table to build the jig to help me build my router table .....

Actually, the idea of using the piece that will go into the groove to set the groove width looks like a winner. I think I can make a quick and dirty version of the jig that will get me through the three grooves I need to cut.

I'll post the results.
 

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where's my table saw?
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hold on there ....

Actually, the idea of using the piece that will go into the groove to set the groove width looks like a winner. I think I can make a quick and dirty version of the jig that will get me through the three grooves I need to cut.

I'll post the results.
That's not what I had in mind, if you are using the concept I proposed above. :no: Here's what I intended:
Rout your first pass using the 1/2" bit against a straight edge. That gives you a 1/2" wide dado.
Next, you want to move the router over exactly 1/4" to get a 3/4" wide dado. :yes: To do that, place a 1/4" strip against the straightedge and make another pass which is now moved over 1/4" from the original.
This is assuming you will use the base of your router held firmly against the straight edge at all times and not change the position of the router as you move it along.... the base may not be centered exactly on the router motor.
Using the "add a strip" method avoids having to change the location of the straight edge, and trying to get it exactly parallel and accurately moved over the 1/4" you need. The strip needs to be accurately made in the width necessary for your application of course. :yes:
 
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Keeping It Simple

I found that procedures that keep settings and adjustments to a minimum are less likely to cause problems. Routing from one side of a proposed groove to another just doesn't do it for me. I like a single set-up and go with it. The jig in post #8 sets the left edge of the dado. No measuring, just set it to a mark. Once clamped down it's good to go.

I usually just orient the handles on the router to where they were in making the first pass on the jig. A round base may not be concentric to the bit. So, If the router I use has "ears" for handles, they may be in line with the jig. I think that explains it.

I can't remember having a ¾" bit that was larger than ¾". If the bit is right on for the size of the track, the pass is a simple one. If the bit is smaller than the size of the track, a shim of a thin nature can be used to space the base over whatever the negligible amount is.





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Discussion Starter · #13 ·
"Bad advice"?......maybe,but it should be looked at as sort of a "lite bulb moment"IOWs,theres more than one way to skin this problem.

Generally in machineshop world it's,use the smaller cutting diam. and then sneak up on width.When every bit of accuracy is desired.But back in the wood millshop.......I see it yet another way.That would be in the direction of cutting forces.

As an example,in your slot.....which is the more critical dimension?Is the width more critical than the depth?..........Don't really need an answer to this,just using it as an example.When you look at the cutting forces generated during "the cut"....which direction are they being applied?how or what is this doing to your more critical dimension?

A router "bit",or endmill sees its cutting forces effecting the width of slot moreso than depth.Hence,using a more narrow "bit" and then sneaking up on dimension.An alternative is to use a horizontal milling machine(which is how TS slots are cut).......back in woodshop,this means a Dado head.

This should be looked at in a positive sense......its not really an indictment against one tool vs another.Its looking at cutting forces and how they effect accuracy.Carry on.
Good questions. Had to think about what I'm doing and take a look at some "T" track installations. The ones in Rockler seem to be just below flush with the table top to about 1/16" below the table top. So, it appears depth is important, but not necessarily critical (as long is the track is below the table top.

For width, seems like I want the track to fit easily into the groove, but not too sloppy. Seems like a little over-width would mainly result in a dust trap along the edge of the "T" track. So, again, appears width is important, but not critical.

In looking at my "T" track, it doesn't seem to want to bend to a curve. So, I'm thinking the most important characteristic of my grooves is that they be straight.
 

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Discussion Starter · #14 ·
That's not what I had in mind, if you are using the concept I proposed above. :no: Here's what I intended:
Rout your first pass using the 1/2" bit against a straight edge. That gives you a 1/2" wide dado.
Next, you want to move the router over exactly 1/4" to get a 3/4" wide dado. :yes: To do that, place a 1/4" strip against the straightedge and make another pass which is now moved over 1/4" from the original.
This is assuming you will use the base of your router held firmly against the straight edge at all times and not change the position of the router as you move it along.... the base may not be centered exactly on the router motor.
Using the "add a strip" method avoids having to change the location of the straight edge, and trying to get it exactly parallel and accurately moved over the 1/4" you need. The strip needs to be accurately made in the width necessary for your application of course. :yes:
Actually, I was looking at the jig in Post #2. Seems like with a simplified version of that, I could set one guide on one side of the groove, then use the "T" track as a spacer to set the other guide (gives the option of fitting the groove anywhere from tight to sloppy) and rout between the guides using a 1/2" straight bit with a template guide (both of which I already have).
 

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Actually, I was looking at the jig in Post #2. Seems like with a simplified version of that, I could set one guide on one side of the groove, then use the "T" track as a spacer to set the other guide (gives the option of fitting the groove anywhere from tight to sloppy) and rout between the guides using a 1/2" straight bit with a template guide (both of which I already have).
A template guide is not incorporated in this jig design, to allow maximum dust extraction. It's setup for a specific router base, and I used a Milescraft base so I can use every router I have. The router base rides against two outside fences, whereas the spacer gates are initially oversized and matched to the router base, bit and spacer gates with the very first cut.
 

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John
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Actually, I was looking at the jig in Post #2. Seems like with a simplified version of that, I could set one guide on one side of the groove, then use the "T" track as a spacer to set the other guide (gives the option of fitting the groove anywhere from tight to sloppy) and rout between the guides using a 1/2" straight bit with a template guide (both of which I already have).
Like bladeburner said, that jig guides off the router base. However, you can modify the plans and make a version of that jig to use template guides. You just need to make it so the router rides on top of the guide strips and the bushing guides off of them. Construction is exactly the same. That's the way I made mine, using a 1/8" offset. This way it will make perfect dado's from 1/8" up to whatever the jig capacity is. You are also not locked into a specific router, bit or bushing. All you need to do to make it work is make sure the bit/bushing offset is 1/8", or whatever it is you want to make it.:smile:
 

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I used a good straight edge with my skill saw (circular saw) to make the outer cuts and hogged out the the bulk with the router. A circular saw is rigid and wants to cut in a straight line on its' own design. Worked for me. Those router jigs are fine and work well, but that's the way I did mine.
bought one of these for just this type of work, man it works great for me...and only $10. I also clamp it against my table saw fence to make sure it doesn't move.

http://www.harborfreight.com/24-inch-clamp-and-cut-edge-guide-66126.html
 

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Actually, I was looking at the jig in Post #2. Seems like with a simplified version of that, I could set one guide on one side of the groove, then use the "T" track as a spacer to set the other guide (gives the option of fitting the groove anywhere from tight to sloppy) and rout between the guides using a 1/2" straight bit with a template guide (both of which I already have).
I use a jig like post 2 as well. One word of caution, be careful not to exert too much sideways force against the jig as you slid the router along. I pushed too hard trying to keep my router firmly against the edge and bowed my guides out. This caused a wide spot in the center of my dados that took me awhile to understand. And this happened while using a jig built from 1/2" plywood that had 6" wide guides.
I thought the 6" width would not deflect but i failed to realize that my dados were too long (4 feet) for even a 6" guide to stay rigid. Now I'm more careful with the pressure and use wider guides for my longer cuts to eliminate the deflection issues.
 

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Use the 1/2" bit against a straight edge. Then place a 1/4" strip against the straight edge and make another pass, being careful NOT to vary away from the straight edge or you will have a "divot" in your groove. You may have to make several 1/4" strips to get one that's exactly the correct thickness + or - 1/128" or so....
I believe an important word of caution should accompany this method. check cutter rotation and te material being removed. I believe this method may need cut with the router traveling the opposite direction, or he may be in for a wild ride.
 
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