Repeatable cross cuts long boards

[Zundy]

How can I make accurate and repeatable cross cuts on long boards? 

In my current project i've had to cross cut multiple 9.5" wide 3/4 ply boards to 83.25" long. I do not have a sliding miter saw but just a chop saw. Unfortunately my chop saw fence isn't long enough to accommodate a 83" cut - which eliminates the "set the fence, cut half, flip over" method. Instead I've tried using my circular or jig saw with a jig clamped the board to ensure a straight cut.  However I always have little errors setting up the second cut. I can never get the jig set to precisely duplicate the first cut without a small error. I could clamp the boards together and cut both at once but what about subsequent boards?

What do you do?

[Cooler]

A jig for your circular saw.  It will give clean cuts if you use the actual blade to trim the base.  It mimics a track saw.  If you work carefully you can get excellent results.  For your application it can be a fairly short fence.  Measure carefully.  The "straight edge" portion will prevent tearout if you use the  same blade to trim it to size as you use to cut the boards.

Or buy a track saw.  They are very handy.

[Zundy]

A jig for your circular saw.  It will give clean cuts if you use the actual blade to trim the base.

Cooler, I do use one of those. Produces a straight cut but not a repeatable cut. I can't seem to move the jig to following boards without introducing a small error.

[brianwelch]

A jig for your circular saw.  It will give clean cuts if you use the actual blade to trim the base.  It mimics a track saw.  If you work carefully you can get excellent results.  For your application it can be a fairly short fence.  Measure carefully.  The "straight edge" portion will prevent tearout if you use the  same blade to trim it to size as you use to cut the boards.

Or buy a track saw.  They are very handy.

What has worked for me is a pair of saw horses (actually a Jawhorse and a sawhorse) and a piece of plywood or longer 2x material. I set them up so the table top of the mitersaw is level with the other surface. I fasten a stop to the ply or 2x at the proper distance and cut away. Make sure the supports are secured so the proper distance doesn't change. I also set up a short fence at the stop to keep the wood I am cutting parallel to the saw fence and provide an intermediate support if the distance is long enough that the substrate or pieces I am cutting deflect.
Can also be done on the floor of your shop if you don't mind bending down...

[srv52761]

A jig for your circular saw.

This is what I used, but don't stop there.

If you have a bench or saw horses with 2x
Put a piece of 3/4" foam insulation board down
Clamp a straight 1x along the bottom edge as a spacer.
Clamp another 1x more about a foot  away from the bottom 1x, no need to worry about parallelism, but eyeball kinda close.  This will be your spacer/fence.
Use a framing square or similar, screw your circular saw jig to the top fence perpendicular, then screw the other side of your jig to the other spacer.

You now have a poor man's radial arm saw. 
Measure your length, clamp a stop.
Place your work on the table, slide it under your jig to the stop.

Did this on a lot of jobs with a door and insulation board as my table.

[Cooler]

Make the straight edge from 1/4" thick x 96" long piece of plywood, 24" wide.  

Mount the fence across the 24" dimension near one end and trim with the saw.  

Mount a stop block under the straight edge to the exact length required.

Slide the jig over the stock and pull it snug to the stop block. 

Use clamps to lock the jig to the stock.

Make your cut.


You will probably want to dismantle the jig after you are done as it will be big and bulky and lack versatility.  But it should give you repeatable lengths.

A second fence underneath the straight edge running the length of the 96" will assure squareness.

Or use the first board to mark all the remaining boards and cut on the line each time.


I have a Festool track saw.   But I probably would use my radial arm saw for this.  There is not reasonable way to do this on a table saw.


I used this Freud blade to cut butcher block counters to size (before I got the Festool).  It makes nice, clean cross cuts.

https://www.amazon.com/gp/product/B001CZ...UTF8&psc=1

[jteneyck]

Make a jig with a piece of 3/4" plywood, about 16" wide by 8' long.  Screw another 3 or 4" wide x 8' long piece along one edge, and then a stop on one end.  Then screw a 20" or so long piece of plywood that's 6 to 8" wide on top of the 4" wide edge piece so that your circular saw will cut off your workpiece to exactly 83.25" long when butted against the stop.  

You could adapt the same idea to a chop saw by screwing or clamping the jig, minus the 20" long piece of plywood, to the table.  

John

[mike4244]

How can I make accurate and repeatable cross cuts on long boards? 

In my current project i've had to cross cut multiple 9.5" wide 3/4 ply boards to 83.25" long. I do not have a sliding miter saw but just a chop saw. Unfortunately my chop saw fence isn't long enough to accommodate a 83" cut - which eliminates the "set the fence, cut half, flip over" method. Instead I've tried using my circular or jig saw with a jig clamped the board to ensure a straight cut.  However I always have little errors setting up the second cut. I can never get the jig set to precisely duplicate the first cut without a small error. I could clamp the boards together and cut both at once but what about subsequent boards?

What do you do?

Mark each piece for length minus the set back for your circular saw fence.  Hold or clamp a speed square on the line and make your cut. Might your errors begin with out of square cut from the end you measure from? Not sure what kind of jig you used, check your jig for square first. 
mike

[Cooler]

What are y0u making?  What kind of tolerances do you require?

You could always make one piece of a  perfect length and all the rest 1/8" over.  Then use a router with a trim bit to make them all the same.  Extra work, and I'm not sure about tear out.

Alternatively, stack the 4 x 8 plywood sheets and cut them all to the right length at one time.  That will assure that all the boards are the same length.  

Then rip the plywood to width. 

Depending upon your saw and feed rate you should be able to cut 2 or 3 sheet thicknesses of 3/4" ply.  (But make a test cut first)

[Admiral]

Alternatively, stack the 4 x 8 plywood sheets and cut them all to the right length at one time.  That will assure that all the boards are the same length.  

Then rip the plywood to width. 

This ^^^^^^^^^