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post #1 of 8 (permalink) Old 11-19-2014, 03:14 PM Thread Starter
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Default Routing square

Hello this is my first post.
I need perfectly square pieces of 3/4" plywood for sculptures. Routing has been the answer. My problem is that when I do cut up 4'x8' plywood the router cut to the "waste" side is not square.
See attached drawing.
Thanks I appreciate any help I can get. This is probably going to be like the guy 20 yrs ago who called tech support concerning his first computer and asked, "I cant get this foot pedal to work", to which the tech person replied,"Its not a foot pedal its called a mouse and you use it on top of your desk"
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post #2 of 8 (permalink) Old 11-19-2014, 03:28 PM
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Welcome to the forum Steve. You obviously have a guide on the one side so that is the side that is good. In the meantime the router is bouncing around on the other side. It could be that you are feed in the wrong direction. Going one way, the force of the bit in the cut will push the router against the guide. Going the other direction it will pull it away from it. Sometimes it is also hard to control the bit when routing across the full face of the bit. My suggestion would be to cut the piece off with a saw and then take a small cut along the edge to clean it up. Otherwise I would use a guide on both sides of the router so that it can't dance around. Also, if you are starting the cut as a plunge make sure you are using a plunge cutting bit. Some aren't designed to plunge.

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #3 of 8 (permalink) Old 11-19-2014, 04:57 PM
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Steve, it appears to me that Charles "nailed it". Your first cut (the shallowest) has a lot of bounce-around. It appears you held a tighter tolerance with your subsequent cut and your final cut appears to be what you were hoping for throughout.

Otis Guillebeau from Auburn, Georgia


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post #4 of 8 (permalink) Old 11-20-2014, 11:02 AM
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Looks to me like Chuck has the answer. I too would make a table saw cut, then clean up with the router. If you had a pretty fine tooth blade in the saw and a zero clearance insert to eliminate tear out, you could possibly do the final cut on the saw. You can also put masking tape across the cut line as well. I use an 80 tooth Freud blade and get baby's behind smooth cuts even without the tape.
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post #5 of 8 (permalink) Old 11-20-2014, 12:00 PM
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I use my bosch cordless circular saw to cut the plywood with a straight edge. Then run it thru the table saw with a Freud glue joint rip blade. If you cut it with a saw first (a litttle wider than needed ) then clean it up with your router you will get a lot less waste than trying to cut it with a router, and a lot less effort too, 3 cuts with a pouter and a clean up cut on the off-cut is more work than one saw cut and two router cuts. And further, the glue in plywood raises heck with a router bit, so your bit life will be longer.

Charles pretty much figured out your problem, it is always better to cut with one side of a router bit than all way around when ever possible.
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post #6 of 8 (permalink) Old 03-04-2015, 12:18 PM
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Is there any necessity to cut the plywood in two pieces with the bit ? If so, my advice would be to clamp the plywood both sides of the cut, on a sturdy panel. If not, pre-sawing is the solution. It keeps the bit sharp longer, and produces less dust. The "waste" can be used to have the router resting both sides, just keep it away enough to avoid routing it.
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post #7 of 8 (permalink) Old 03-04-2015, 01:02 PM
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Not much to add--track saw would make that cut easily without the need to try to guide a full sheet of 3/4" plywood through a table saw. It's definitely not a cut that any router or bit was designed to do (though, it will do it--just not well!!)

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post #8 of 8 (permalink) Old 03-04-2015, 02:12 PM
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A) You are not keeping the same face of the router base to the straightedge. Router bases, unless made to be centered are not round, and you are probably moving the router slightly and on the last pass are cleaning up the straightedge side. B) The plunge action is not perpendicular, one side is looser than the other, so you are not going down straight and again you cleaning up on the last pass.

What I have done in the past to cut up ply up to 3/4" is to use a 1/4" downward cutting spiral bit in one pass all the way through. Your DeWalt with a solid carbide (Solid Carbide Spiral Router Bits | Carbide Router Bits) bit can handle this no problem. You will have to go a bit slower, but it will be only one past. Use a downward spiral so your waste ends up on the floor and not in you router. I made a follower that was attached to the router and ran in the kerf with a dollar store funnel cut and duct taped to the end of my shop vacuum. it gathered almost all of the chips and dust.

A 1/4" bit is desirable as there is less mass and cutting surface for the router to spin and less waste in the kerf. The supplier above is for reference and not a recommendation (I liked their illustration). For these kind of bits you will be able to find an industrial supplier and get a better price.

Very important: A very sharp bit is absolutely necessary, run your router at top speed and mark the base so you don't move it around as you run it across your straight edge.

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