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What's the secret to making square cuts on 4x8 plywood?

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Forum topic by Silverline posted 02-17-2019 04:25 AM 1683 views 1 time favorited 21 replies Add to Favorites Watch
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Silverline

11 posts in 37 days


02-17-2019 04:25 AM

Full disclosure, I am a complete novice, but getting better. My biggest issue right now is I just cant seem to make square cuts when making cuts on a 4×8 sheet of plywood. For example, cutting pieces for side panels, tops and bottoms to make cabinets.
I am limited in equipment, so I use a circular saw and a straight edge. My circular saw is square. I’ve checked the blade angle to make sure its 90 and also checked to make sure it runs parallel to the saw base. My straight edge is a level so that is true as well.
The only thing I can think is I just don’t measure accurately when setting up for my cuts? What else could it be?

Thanks!


21 replies so far

View William_D's profile

William_D

20 posts in 772 days


#1 posted 02-17-2019 04:37 AM

Get a track saw. It reduces the possible wobble. Also, what do you use to measure? a story stick ro a tape. If a tape, the attachement point is moveable. i.e. you have the lasp at the ed of wood and pull it it extends, push it against a straitght edge and it retracts. it is variable by about a 16th. Width of a blade.

View waho6o9's profile

waho6o9

8598 posts in 2880 days


#2 posted 02-17-2019 04:48 AM

For example on a 4×8 sheet I crosscut a half an inch for a reference edge.

Left turn and rip a half inch for the length and that corner must check out square before proceeding.

After which I can rip parallel panels or crosscut the other end of the sheet good.

Check your diagonal measurements and when they’re the same you’re good to go.

You can do this.

A drywall square helps with the layout as well.

And welcome to LumberJocks!

View Aj2's profile

Aj2

2063 posts in 2101 days


#3 posted 02-17-2019 05:03 AM

You probably need to get a accurate square to set your rip fence. Waho6o9 suggestion is very good
If I didn’t already have a accurate framing square I would get one of those fancy blue drywall thingy.

-- Aj

View Rayne's profile (online now)

Rayne

1162 posts in 1843 days


#4 posted 02-17-2019 05:43 AM

How many cuts are you making to try to get something square? I’ve found that 4×8 sheets doesn’t necessarily have a square corner nor the length of the sides being straight. You may need to make 4 cuts to get a square cut.

#5 posted 02-17-2019 06:40 AM

ha ha ha, especially from a big department stores.


How many cuts are you making to try to get something square? I ve found that 4×8 sheets doesn t necessarily have a square corner nor the length of the sides being straight. You may need to make 4 cuts to get a square cut.

- Rayne


View Sylvain's profile

Sylvain

806 posts in 2802 days


#6 posted 02-17-2019 11:21 AM

If you don’t have a big square use Pythagoras theorem:
trace a triangle with the three side being in the proportion 3, 4 and 5, it will be square.
(3²+4²=5²)
The bigger the triangle, the better the accuracy.

You can make yourself a big square with this.

-- Sylvain, Brussels, Belgium, Europe - The more I learn, the more there is to learn

View ChefHDAN's profile

ChefHDAN

1336 posts in 3153 days


#7 posted 02-17-2019 12:22 PM

You say straight edge, are you using just a level or 2×4 or have you made a saw guide like this Track saws are nice but very expensive. Before I got my table saw I cut loads of sheet stock with one of these, I have an 8 foot and a 4 foot one. The custom cut to get the wide and narrow side of your saw plate makes layout simple since it goes right on your line and you can’t mistake the offset.

You can use a combination square for cutting strips up to 11”, If you’ve got some scrap around the shop, you can make a gauge stick, to set your saw guide a specific, exact distance from the edge.

Overall the best path is practice, the old adage rings true, a poor carpenter blames his tools, gain proficiency with your layout and marking, there is rarely “good enough” unless your doing rough carpentry. Welcome to LJ’s!

-- I've decided 1 mistake is really 2 opportunities to learn.. learn how to fix it... and learn how to not repeat it

View Silverline's profile

Silverline

11 posts in 37 days


#8 posted 02-17-2019 12:47 PM

Thank you! I do have a drywall square like you are referencing here. It’s only 48” long. So should I start by setting it on one of the 96” edges to create a reference edge crosscut 1/2”from one of the ends. Then make all my crosscuts on the panel measuring up from that reference edge. Then once I have smaller pieces from my crosscuts I can use the drywall square to square a length side edge on those pieces before measuring for my rips to get to finish width?


For example on a 4×8 sheet I crosscut a half an inch for a reference edge.

Left turn and rip a half inch for the length and that corner must check out square before proceeding.

After which I can rip parallel panels or crosscut the other end of the sheet good.

Check your diagonal measurements and when they re the same you re good to go.

You can do this.

A drywall square helps with the layout as well.

And welcome to LumberJocks!

- waho6o9


View ChefHDAN's profile

ChefHDAN

1336 posts in 3153 days


#9 posted 02-17-2019 01:01 PM

Silverline, here’s a pretty decent video walk through of using a saw guide for cutting ply

-- I've decided 1 mistake is really 2 opportunities to learn.. learn how to fix it... and learn how to not repeat it

View CaptainKlutz's profile

CaptainKlutz

956 posts in 1797 days


#10 posted 02-17-2019 01:21 PM

+1 use a Drywall square to set up your cuts.
Always use the SAME side as the reference for cross cutting to keep cuts parallel to each other.
Can double check square from both sides to see if errors are being introduced due bad edge. There is no guarantee that edge of sheet from the BORG is smooth and perfectly parallel. The longer leg on drywall square helps avoid errors from bad edge when using smaller combination square.

Track saws are nice, but expensive. There are many different circular saw guides available if you don’t want to make them. I picked up a 4pc set of AIO guides years ago for ~$100, including a 100” long guide. Aio Sets used to go on sale for 1/2 price? Kreg, Bora, and others sell something similar. With drywall square and guide, plywood is easy to cut square.

Best Luck.

-- I'm an engineer not a woodworker, but I can randomly find useful tools and furniture inside a pile of lumber!

View bondogaposis's profile

bondogaposis

5266 posts in 2654 days


#11 posted 02-17-2019 01:59 PM

Rough cuts with circular saw and finish cuts on table saw.

-- Bondo Gaposis

View jdh122's profile

jdh122

1065 posts in 3121 days


#12 posted 02-17-2019 02:05 PM

A track saw is nice, but with a guide you can do fine with a circular saw. But not with a cheap circular saw. Generally the ones that have a base made from stamped steel will flex considerably through the cut and give results that are less than satisfactory.

-- Jeremy, in the Acadian forests

View Redoak49's profile

Redoak49

3844 posts in 2292 days


#13 posted 02-17-2019 02:20 PM

Sounds like you have a measuring problem..

Is your blade sharp? Is your guide moving when you are cutting or aligning it?

View Silverline's profile

Silverline

11 posts in 37 days


#14 posted 02-17-2019 03:12 PM

Not an option for me unfortunately. I have a smaller table saw. Max rip width is 13”.


Rough cuts with circular saw and finish cuts on table saw.

- bondogaposis


View GaryCN's profile

GaryCN

397 posts in 4238 days


#15 posted 02-17-2019 03:30 PM

I’ve used this one for years, it has a great sale price now.
https://www.eurekazone.com/Track-Saw-Systems-s/2070.htm

-- Quando Omni Flunkus Moritati

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