Thread: How square is a sheet of chipboard??

Darryn, judging from my experience, not very!
My wife paints in acrylics on 3 or 4mm mdf. I buy largeish sheets from various suppliers in Canberra ( not neccessarily Bunnings).
I have in the past assumed that I have at least one square corner and have set the sheet/s up on my Triton sliding table and cut to the required size with no further thought...
My wife has painted on the boards with the same assumptions of squareness, and my sins of omission have only come to light when I have tried to fit those painted boards into my own manufactured frames.
Hand on heart, those frames are square, but the damned boards are often out of square by up to 3mm.
I am now considerably more careful on setting up that first cut!
Don't trust what you get off the shelf!

Gooday,

The industry standard is 4 mm over 2.4 m.

It pays to never assume they are square. Use one edge as a straight and rip and cross cut from there.

Fank you - I dips me lid...

Originally posted by
Gooday,

The industry standard is 4 mm over 2.4 m.

It pays to never assume they are square. Use one edge as a straight and rip and cross cut from there.

Thanks for that and the 4mm over 2400 would come down to the 1.5-2mm or so error I am getting over 1200

I was always uder the impression the sheets were sized on a beam saw, which I was mistakenly taking for granted would be working to closer tolerances than that.

Darryn

Unfortunatly a machine that is capable of very low tolerances is still only as capable as the person feeding & operating it. Remembering manafactured board is mass produced so they have to have higher tolerances than if they only produced half dozen sheets at a time..

Cheers!
SHane.

Manufacture of chipboard and MDF is a continuous process, the boards are sawn as they come out of the press and the sawing takes place while the board is still moving. The Saw both cross-cuts and moves along the length of the board at the same time to get a straight (and hopefully square) cut. Although the movements are synchronised with the speed of the board, there must be a small amount of error.

Being cut in a continuous process I suppose the tolerance is not too bad. I thought it was sort of rip sized to width and then docked by the beam saw

Darryn

I've had sheet goods that were pretty spot on and some that best discribea as a romboid.

Any body with a serious rolling bed saw will tel you nothing is square till its been thru the saw.

Scary true story
I once cut a sheet of ply down its length with a reliable straight edge then pushed the cut back together to find a 5mm gap in the middle. The stresses in the sheet caused it to bow out from the middle.

For critical work I now break down then square & trimm each edge of the board to final dimensions on my squaring table.
I now find boxes go together much more easily an accurately than before.

Many forms of sheet goods will moove when cut due to internal stresses. Certain brands of ply are particularly bad.