How do you get a straight edge in plywood?

[Mark Borowsky]

Hi,
This seems so basic I hate to ask. I've cut up some plywood sheets into rough sized parts for a desk for my kid. Now I want to get a straight reference on each piece so I can cut everything square and parallel and join it up. Some of the edges are definitely not straight.

My first thought was to joint them up. But Tage Fride says edge jointing plywood is a no-no. Besides, some of the pieces are quite large to run over a jointer on edge.

I'd love to hear how you all do it.
Thanks,
Mark

[John Michaels]

Try attaching one of the crooked sheets of plywood to one with a straight edge with a hot glue gun. Run through the table saw, then detach, flip it over and run it again.

[glenn bradley]

I use this (http://www.sawmillcreek.org/attachment.php?attachmentid=71201&d=1188928235) and his longer brother.

[Stuart Johnson]

I hope I remember this right:

I took a cabinet class at Woodcraft and the instructor called it the ABC method after you rough cut the pieces.

A: Run the piece through the table saw cutting cut a little over 1/8" off.
B: Run the piece through again with the fresh cut side against the fence cutting off just a bit.
C: Run it through the third time with the last cut edge against the fence, cutting to size.

[John Michaels]

I use this (http://www.sawmillcreek.org/attachment.php?attachmentid=71201&d=1188928235) and his longer brother.

Glen,

How do you draw the straight line on the plywood if all of the edges on the plywood are crooked?

[Mike Marcade]

I clamp a straight edge onto the piece and run the router along it to get my first true edge. Then I use that edge I just cut and run that along my table saw fence to get a parallel straight edge. Then I use my miter gauge or a miter sled (depending on the size of the piece) on the table saw to get two edges that are square to the parallel ones I already talked about.

[Jon Bonham]

Glen,

How do you draw the straight line on the plywood if all of the edges on the plywood are crooked?
The guide IS the straight edge. Cut it where you want, then you have a straight edge.

[Dale Lesak]

I do the same as Glenn, except I bought the aluminum straight edge and fixed it to a 1/4 plywood base. also made a follower that fit over the guide so the saw can't stray off. I have a 8' and a 4' use them all the time for sheet goods. :)

[glenn bradley]

Glen,

How do you draw the straight line on the plywood if all of the edges on the plywood are crooked?

The large piece of the jig should be wide enough to leave room on the non-saw side to clamp to your work without the saw motor hitting the clamps. This side does not have to be straight but I prefer that it is. The saw-side of the base should be large enough to be cut off by your saw on your first run down the jig. Since it is cut off to create the 'zero' edge it does not have to be initially straight, just wide enough to be cut off. This cut creates a straight edge that is exactly where your blade will cut when you use the jig.

To create the guide strip in the first place I use the table saw to rip it to width. If I have no scrap with at least one reasonably straight edge I would use a builder's level as a guide and use a router to create the first straight edge. Place this straight edge against your TS fence and rip to width.

Another method I have used is to place the concave edge of my crooked board against a builder's level and place the level against the fence. I can now guide the board and fence through the cut as a unit to create a straight edge. Flip the board and rip to width.

Once you have one straight edge, creating a 90* cut to it is just a matter of measuring. If the boards to be cut are not too large, a sled will handle the 90* issue. If the panels are large, you can build a sled on steroids like I did here (http://www.sawmillcreek.org/showthread.php?t=50581) or a smaller one like this (http://www.sawmillcreek.org/showthread.php?t=53569). They don't take that long and are one of my most used jigs.

[Rob Blaustein]

Glen,

How do you draw the straight line on the plywood if all of the edges on the plywood are crooked?

John, I could be mistaken but I get the sense that terminology is part of the issue here. I wonder if you might be confusing straight, as in an edge, with square, as in making a cut that's perpendicular to your straight edge. As others said, a straightedge combined with a circular saw or jointer can generate a clean edge on your piece of ply that can be used against the table saw to generate a parallel cut. Then you need to be able to make cuts perpendicular to those parallel edges and that means you need something that you are confident will form a 90 degree angle. People often use a miter gauge that is set at 90, or a table saw sled, or you can clamp your straightedge at 90 degrees and use a circular saw at the desired point. To check for 90 degrees you can use a machinist or combination square, a drafting triangle, a speed square, or a piece of wood that you have constructed to be square, etc, thought these can differ in their accuracy. --Rob

[glenn bradley]

I hope I remember this right:

I took a cabinet class at Woodcraft and the instructor called it the ABC method after you rough cut the pieces.

A: Run the piece through the table saw cutting cut a little over 1/8" off.
B: Run the piece through again with the fresh cut side against the fence cutting off just a bit.
C: Run it through the third time with the last cut edge against the fence, cutting to size.

Stuart's method is viable as well as long as the errant edge is not long enough to move out of position as it passes the outfeed end of the fence. ;-)

[Colin Giersberg]

There is always the Festool way:D.
Use their saw and saw guide, and you should get a nice, straight edge.
While expensive, you will be able to cut plywood to the size you need, without needing to use a tablesaw to make the cut. Muscling a sheet of plywood up onto a tablesaw, then guiding it accurately, will more than likely result in a less than straight cut. With festool's saw and guide, the only thing that you have to move is the saw, not the plywood.

Regards, Colin

[glenn bradley]

There is always the Festool way:D.
Use their saw and saw guide, and you should get a nice, straight edge.
While expensive, you will be able to cut plywood to the size you need, without needing to use a tablesaw to make the cut. Muscling a sheet of plywood up onto a tablesaw, then guiding it accurately, will more than likely result in a less than straight cut. With festool's saw and guide, the only thing that you have to move is the saw, not the plywood.

Regards, Colin

Colin is correct, you could always buy a couple Festool 55" guides for about $80 each and of course the other stuff to go with it. A formal guided system is quite impressive. I drop a couple pieces of 2' x 4' x 2" thick foam insulation board (about $5 each) on the ground to allow me to through-cut and use my shop made jig. This will get me an acceptable straight edge so I can go on about my business. If you visit Festool or EZ Smart's site you will see that the formal setup has a boatload of options.

[Joe Chritz]

Not to hijack but it is only partly on topic.

Plywood is normally straight enough to run a factory edge against the fence then flip and cut to size. For really bad ones or if I want to do rough sawn on the tablesaw, I use a shop made jig of plywood with an L glued and pinned on the bottom.


On the guided rail systems, how do you measure to get each piece, exactly 23 1/4 and parallel? Currently I am cutting down with a TS55 and then running it on the tablesaw.

Joe

[Rob Blaustein]

On the guided rail systems, how do you measure to get each piece, exactly 23 1/4 and parallel? Currently I am cutting down with a TS55 and then running it on the tablesaw.

Joe

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Joe, I mark that width in several spots, lay the rail down at the mark, clamp it down, and cut. The parallel cuts of that width are dependent on your ability to mark accurately. But also important for square cuts is the ability to set the fence square to the rail. There are discussion about this in the Festool Users Group site--it's worth going through the archives. Of course, your way of making an initial cut with the TS55 then going to the TS works well too. --Rob

[Steven Wilson]

I use a sliding tablesaw to get straight and square cuts in plywood (or anything else). Every other way I've used is error prone.

[Jim Broestler]

Maybe this is the cheating amateur's method, but I almost always have the guys at the home centers I buy it from cut it to rough size on their $5000 panel saw. Granted, the edge is ugly, but that's why I have them cut it oversize. The important thing is it's straight, and brought down to a size that's much more manageable on a table saw or straightedge with a router and 1/2" compound spiral bit.

I'm betting if you brought the pieces back to the store, explaining that the edges aren't true, they'd be willing to cut them straight on their panel saw, and probably not even charge you. I mean, if they're selling material that's supposed to be straight and it isn't, it really isn't too much to ask that they correct it if within reason. And since you're only talking a few sheets, I see no reason why they can't accomodate you on that.

[Art Mann]

If squareness is the issue, it is not safe to assume plywood factory edges are square, although they are usually straight. That is my biggest challenge. If the ultimate dimensions of the piece I am cutting are larger than I can square on a tablesaw, I resort to using a framing square of known accuracy and then checking the pencil marks on the diagonals with a tape measure before cutting. Even an expensive saw guide requires you to mark things square unless it is used in some sort of elaborate panel saw configuration.

[Burt Waddell]

I find that the EZ stuff works great. When I am building cabinets, I normally put a sheet on a large bridge and rip it down the center. Since most parts are either just under a foot wide or just under two feet wide. I then put the square edge to the fence and start ripping parts.

A lot of people just put the sheet of plywood on a table, use their guide rail and trim off a half inch or so from the edge.

Burt

[Dan Barr]

i do the same thing. the good thing about the skilsaw jig is that it is Zero Clearance and will prevent a lot of tearout. I used 3/16" hardboard and i get VERY LITTLE tearout at all.

its a very simple and effective method. you dont need to spend festool money to get good results.

cheers,

dan

[Craig D Peltier]

Use a sheetrock square from the Borg.

[Kevin Godshall]

All things being equal.......it's simple geometry. A straight line is defined as a vector that passes between two points. So..... a simple chalk line from a taut string lays out a "straight" line, without the expense of any other guides, tools, etc. The problem left is how exactly to cut the line laid out, but the ABC method works if you get close enough on the rough cut.

[Jim Mims]

I use this (http://www.sawmillcreek.org/attachment.php?attachmentid=71201&d=1188928235) and his longer brother.

There's some more of Glenn's left over pegboard!
Or is that part of some sort of downdraft table? :rolleyes:

By the way, I'm running about a year or two behind you.
Got my Align-A-Rip installed and am getting ready to order a grr-ripper and mj splitter.
A question, did you ever put a higher auxiliary fence on Craftsman table saw fence?

- Jim

[Rod Sheridan]

Hi,
This seems so basic I hate to ask. I've cut up some plywood sheets into rough sized parts for a desk for my kid. Now I want to get a straight reference on each piece so I can cut everything square and parallel and join it up. Some of the edges are definitely not straight.

My first thought was to joint them up. But Tage Fride says edge jointing plywood is a no-no. Besides, some of the pieces are quite large to run over a jointer on edge.

I'd love to hear how you all do it.
Thanks,
Mark

Hi Mark, I find that the factory edges on the plywood are straight, so I use them for ripping the piece a little wider than needed, then rip the factory edge off to obtain two straight parallel edges.

To square the next cut to one of the edges, I use a sled on the tablesaw, same for the remaining cut.

Hope that helps..........Rod.

Of course if I purchased a Felder Format saw........