Straight cuts on a 2.4m x 1.2m 18mm MDF

[Jupiter01]

I own a Makita Circular Saw and have recently replaced the blade with one that has 48 teeth for smoother cuts. I have used the straight edge clamp on method in the past to run the saw down to achieve straight cuts.

Q. When cutting along the 2.4m length, is it advisable to place 4x2s width wise (how many do you suggest?) and adjusting the cut depth so it only just pierces through the 18mm MDF?
I will have the display face of the MDF facing down and am hoping that this method avoids kickback and provides a neat cut.

Can you please advise.

Thanks in advance.

 

[big-all]

4x2 = industrial crude cutting
assuming you have a bench then sacrificial 12mm sheet cut down a few mm if end on strait side edge clamps
your blade should be 2/3 tooth 2/3mm greater depth than cut material thickness[ 21 for 18mm]

 

[^woody^]

Just set yourself up so that you both sides of the cut are supported and the board is raised on something or you use my favourite of the gap between the jaws of a workmate and a patio table under the other end and a couple of bricks.

The cut face will need some work to smooth and flatten it

 

[Deleted member 174758]

Q. When cutting along the 2.4m length, is it advisable to place 4x2s width wise (how many do you suggest?) and adjusting the cut depth so it only just pierces through the 18mm MDF?-

Setting the teeth to project by the minimum amount is good practice and to be recommended. When ripping down sheet material on site I make myself a couple of trestles (if I don't have any with me) and support the sheet on 3 or 4 pieces of CLS 4 x 2 or whatever is to hand placed lengthways. This is sacrificial - you will end up scoring it. To get a truly straight cut your sheet material needs to be adequately supported and flat

In view of the volume you'll be cutting for your shelf project, to make straight cuts easier you may be as well off making up a cutting guide. This is basically a full length (8ft/2440mm long) piece of thin plywood or MDF (4 to 8mm thick) about 3 inches (75mm) wider than the baseplate of your saw. On the top surface of that you screw a piece of 2 x 1in PAR softwood (or even stop lath) checking with a straight edge that it is dead straight all the way down (6ft level). The saw runs on top of this guide against the lath (which acts as a guide) and the first cut with that trims the excess off the edge of the plywood. After that the edge of the guide can be lined up to your cut marks and the saw cuts should be reasonably repeatable.