Bench work problem, again

 Could the floor being unlevel cause that much difference in measurements? ---- Yes. Think about it like a triangle. You can use the Pythagorean Theorem to understand the effect. 

George

George S posted:

 Could the floor being unlevel cause that much difference in measurements? ---- Yes. Think about it like a triangle. You can use the Pythagorean Theorem to understand the effect. 

George

I'm not that good at math what is the Pythagorean Theorem? Should I go ahead and screw this thing together as long as the corners are square?

Here is my opinion....

As long as you are doubly sure you have every piece of lumber cut to the correct length...

I would just screw all the corners together making sure the top of all the boards are level and smooth across the joint.

I would then add my legs and get the layout off that uneven floor. I would install "T" nuts with full thread carriage bolts in the bottom of the legs to level out each corner at the correct elevation.

Now you have a frame that is level based on the posts and it looks like a box. There should be enough flexibility in your framing that you can "push / pull" the "box" until you get perfect corner to corner measurements. At that point, take a few pieces of scrap lumber and screw them across the corners on a diagonal to keep everything square.

I guarantee this will work as long as the first statement is true....everything is cut correctly to length.

Have fun and do not stress out over a few fractions of an inch.

Hope that helps.

Donald

Adjust the legs to satisfy a horizontal datum level.  If all edges are level with top edges on a flat plane and the "X" dimension is not equal there is a variance in either the actual perfect corner fit  or component lengths.

Was the plywood Pine or Maple/Birch?  Pine is cheap and  popular with many RR D.I.Y. ers until it warps horribly on them.   What was the moisture % when you purchased the wood?  If you used Pine plywood at 4" wide frame sizing, expect acclimation movement.

Are the cuts perfect/straight with corners at a right angle.

If carpentry is not your bag consider  taping the  two 8 X 8 deck sheets together and place / assemble the frame upside down on top of the edges.  Make sure all mating edges are as you want them.  Fasten 30" diagonal braces on all four corners in order to hold the 90 degrees.

Never worry about an inclined floor.  The issue is not incline but rather FLAT.  Flat and level are different considerations.  If you assemble a  squared frame on a flat inclined floor which is truly flat, any subsequent  repositioning of  the frame will not affect the geometry once leveled.  

Also, check the  4 x 8's,  In todays world they are frequently oversized just a tad.  I would go as far as saying your boards are not string straight and / or true.

I build my benchwork on a of pair 5' X 10'  X 1 1/4" surface plate and clamp the corners and two sides.

Opinion.

Tom Tee posted:

Adjust the legs to satisfy a horizontal datum level.  If all edges are level with top edges on a flat plane and the "X" dimension is not equal there is a variance in either the actual perfect corner fit  or component lengths.

Was the plywood Pine or Maple/Birch?  Pine is cheap and  popular with many RR D.I.Y. ers until it warps horribly on them.   What was the moisture % when you purchased the wood?  If you used Pine plywood at 4" wide frame sizing, expect acclimation movement.

Are the cuts perfect/straight with corners at a right angle.

If carpentry is not your bag consider  taping the  two 8 X 8 deck sheets together and place / assemble the frame upside down on top of the edges.  Make sure all mating edges are as you want them.  Fasten 30" diagonal braces on all four corners in order to hold the 90 degrees.

Never worry about an inclined floor.  The issue is not incline but rather FLAT.  Flat and level are different considerations.  If you assemble a  squared frame on a flat inclined floor which is truly flat, any subsequent  repositioning of  the frame will not affect the geometry once leveled.  

Also, check the  4 x 8's,  In todays world they are frequently oversized just a tad.  I would go as far as saying your boards are not string straight and / or true.

I build my benchwork on a of pair 5' X 10'  X 1 1/4" surface plate and clamp the corners and two sides.

Opinion.

I don't think the plywood is pine but don't know .  Moisture content unknown but I left it set for a few days before cutting it. I assume it might be high as it was in a unheated building when I bought it. It is 4x8. The plywood I bought was $46.00 a sheet and a product of Chile. It is AC grade if that tells you any thing.  Cuts are straight and true. I have a miter saw and a Kreg ripping gig for my circular saw.  They are not string true but I can fix that and did so before I measured the frame. Thanks.

feet posted:

George S posted:

 Could the floor being unlevel cause that much difference in measurements? ---- Yes. Think about it like a triangle. You can use the Pythagorean Theorem to understand the effect. 

George

I'm not that good at math what is the Pythagorean Theorem? Should I go ahead and screw this thing together as long as the corners are square?

The other guys are giving good advice. You don’t need to do the math. The gap in squareness is being caused by not having a level frame. As you note, it is corrected when you block up the leg.

George

That Kreg jig is kinda OK but no match for a panel saw.  When I just need one sheet cut I would have them cut at the shop on their panel saw.  I pre plan the sizes I want and have them cut to double size +.  

Panel saws provide excellent straight edges but do not cut consistent repeat narrow widths.  Then I do a final cut against a good fence.  All widths dead nut, 

Our local wood shop has this ginornmous $24,000 table saw which can do repeat cuts with super precision.

When I would go to build up a stack of stock I just  would let them  rip all my sheets.

Lumber yard wood moisture content is frequently in the mid to high teen percentages.  It should be acclimated down to high single digits. 

Plywood should be stocked on flat beds.  Not on three steel fingers or lumpy pallets.  New pallets of plywood sheets should be covered with water resistant protection. Uncovered stacks should be out of the weather.

I would never buy any wood hitting a moisture content of 20% or more.

If the pallet is tightly banded I will start pulling stock from about 6 to 10 sheets down.  NEVER BUY THE TOP OR BOTTOM SHEETS.

Always look at the side edges of plywood.  There should never be a void nor any overlapped layers.  It's your money.  The store owner can give you a hard time concerning cherry picking but the hourly service staff usually has no skin n the game.   The is always someone who will buy anything.

This discussion is for framing plywood.  I recommend Advantech for decking material.