Cutting MDF --- HELP!!!

[bfrikken]

I know I've seen this discussion before. I'm actually in process right now. I have some 3/4 inch sheets of MDF. I've never had problems cutting it before. They are actually 48" x 68" as I pulled them out of a closet.

I have 2 work bench type saw horses setup. The sheet is laying on that. When I attempt to make a cut with my straightedge and circular saw, its lke the saw doesn't want to run against the fence and I can't make any sort of straight cut. It also sounds like the blade is getting ready to bind. The little bit of a cut I made is all wavy looking.

SO, I'm sitting and having lunch now thinking right now the best thing is to move the sheet to the ground? Is it binding cause there is some sag up in the air?

CONFUSED!! HELP!! oh, and thanks.

[LCHIEN]

Basics first:
is your circular saw blade in backwards? Sharp?

Then:
Support it at four places, rather than with two saw horses. It may be sagging in the middle when partially cut and hence binding.

[milanuk]

MDF is fairly heavy, but not very stiff - no grain structure to speak of to resist sagging, hence it can bind the blade fairly easily when only supported at the ends. If you have some sacrificial 2x4's you can put under the MDF on the saw horses you should be fine. Otherwise get a sheet of ridgid foam insulation siding, put it on the floor, set your saws cut depth to about 1/8" more than the thickness of the MDF, and do your cutting on the ground.

[cabinetman]

Have a spacer large enough or able to support both subsequent pieces that will result from the cut. The support (s) can be strips of wood. They should raise the sheet enough for the blade to clear. You can do this on the floor, or on a folding table.

The straightedge should be high enough so the shoe of the CS doesn't ride up on the edge.

The straightedge should be wide enough or designed so if clamped the clamps won't interfere with the saw passing by.

If you're going to paint, a straightedge out of plywood or wood could even be screwed down.

When starting your cut, the guard may be hanging up on the lead in edge of the sheet. You may have to rotate it up enough to get started, and once its over the sheet let it return.

And just a safety word. Make sure your cord is out of the way, and free enough to allow the whole cut to be made.
.

[steve-norrell]

As noted by others, use at least four supports to prevent sagging. Two of them should be close to the cut. Although probably not necessary with MDF, sometimes its helps prevent binding by dropping a couple of wedges (those cedar thingees you can buy) into the kerf as you cut across the sheet.

Regards, Steve

[Uncle Cracker]

And don't breathe that sawdust!!

[drumpriest]

My solution to this problem is to simply throw two 2x4s under the MDF, do the same for plywood, and set the blade so that it'll only cut a bit deeper than the MDF. Then you don't have to worry about cutting through your saw horses, and 2x4s are cheap.

[docrowan]

Based on the fact you say that it binds with only a little bit of cut made, and that it is already wavy, I highly recommend you check your saw base for square and true to the blade.

I had a Ryobi circular saw that I had dropped a few times so that the saw base sprang. It took me a long time to figure out why it would drag and jump when I was cross cutting using a straight edge guide. I measured the distance from the edge to the saw blade at the front of the blade and at the rear of the blade and found almost a 1/4" difference. I had to get rid of the saw, no way to adjust. I am much, much more careful with my new saw.

[bfrikken]

I did some test cuts on some panelling that I have. Cut like butter, and the cuts look straight to the eye. Real easy cut too.

When I get back to the MDF, I"m going to try them supported on the ground with my sacrificial board setup.

[Ed62]

You might alsao want to check to be sure the blade has been tightened properly. That's probably not it, but a possibility.

Ed

[bfrikken]

You might alsao want to check to be sure the blade has been tightened properly. That's probably not it, but a possibility.

Ed

That was my first thought. It was a new blade put on for the MDF. I double checked tried the cut again and it was a no go. This was before I had posted. I'm not sure when I'm going ot get to the MDF again as I spent the rest of the day working on some trim and panelling. However, the circ saw worked well with the panels. It's a Makita that I've never had any problem with, so I'm sure its the setup I had.

[pierhogunn]

grab your self about 8 1 X 4 X 10's and build a sacrificial culling grid that you can strap on top of your saw horses.

next time I'm cutting mdf I'm gonna build one of these, and either put it on my saw horses, or even better since I often work alone, on the floor...

[docrowan]

I made a grid from 3/4 plywood. I cut five, 5 inch wide strips, cut two of these in half to wind up with three 8' chords and four 4' chords. I cut 2.5 inch notches in the appropriate spots so it fits together like a light bulb carton. Works beautifully, sets up in a couple of minutes on a pair of plastic sawhorses. The only problem I have is if I work alone I have trouble getting a whole sheet of 3/4 MDF up on top. Fortunately LOML is usually close by. Lifting and cutting up 1/4" plywood and pegboard is a snap with no snag and at waist height.