How to make plunge cut in MDF sheet?

[Richard Perkin]

[John Rumm]

Plunge cut with what?

Doing it with a circular saw is discussed here:

[Richard Perkin]

I have a requirement to cut a rectangle from a larger piece of 18mm MDF sheet. The dimensions of the 'hole' are approx 800mm x 400mm

I need the cut edges to be true, ie with no 'wavy cuts'. I would also like to reuse the 'cut out' material to form a sort of 'door'.

Before doing it in anger, I have experimented using both a jigsaw (with the expected result of a 'wavy cut') and the Bosch 'MultiMaster clone' tool (with slightly better, if fairly slow, results). Neither of these is satisfactory.

Any suggestions for cutting an accurate rectangle, please?

I don't really want to fork out many £££ x 100 for new power tools, but am willing to consider it if it's something I will use again. I do have a handheld circular saw, but no table saw - and while I've looked at saws with a slide I haven't seen any that slide to the dimensions I'm looking for - but I could easily have overlooked something obvious.

I've thought of plunging a cut with the Bosch tool, then completing the job with a hand saw - but I'm sure there must be a way with the 'right' power tool...

Many thanks in advance

[dom]

Whichever method you use, you'll loose the thickness of the saw kerf at least in the cut (and on each side of the cutout board). You could batten the edges after making the cut, in which case you would have the opportunity to clean up any irregularities.

As John says, plunge cut with a circular saw (riving knife, if there is one, removed). Practice on a bit of scrap board first, and use a guide for the cut (especially when starting plunge cuts). It isn't really that skill demanding, more about having the nerve to do it. Ensure the start and stop points allow the visible upper curve of the blade to stop just short of your corners, leaving about an inch on the underside.

To get tight, square corners with no overcut, you'll then have to handsaw/jigsaw/multimaster the first and last inch (again with a guide, unless your skill level is up to it).

It's possible to plunge cut with a jigsaw (very gently tipping back from the front edge, whilst very slightly moving forward), but that is somewhat skill demanding.

[Cicero]

================================== A pull saw will do this job if you're careful and take your time. This type of saw is used at a low cutting angle and can be used to cut into a solid board by carefully working on one line until a through cut is achieved. A pull saw also has the advantage of probably the smallest possible kerf.

[TheOldFellow]

Circular saw with guide batten would be my way. You need to take off any riving knife, but the cut in MDF will not close up, so it's safe.

If you ARE going to buy a new tool, my advice is to buy a SMALL circular saw. Although a large one has more oomph and can make bigger cuts, accuracy with a circular saw is enhanced by lightness (unless you are a weightlifter) - especially if you are reaching over a big board. I have three saws, but only ever use the smallest one (It's a American Porter-Cable used with a 110Volt transformer).

R.

[Matty F]

A biscuit joiner would be the safest and easiest way. The blade is quite thick however. Biscuit joiners are quite cheap these days, and you'll find all sorts of uses for it.

[Andy Hall]

Not with either of those for that kind of size.

I've normally done this on a saw table by accurately positioning the material and then raising the blade, stopping before the corners.

The nearest simulation for that would be to make sure that you can fully support the material over more than just the cutting area first and to use a circular saw. Bear in mind that once the centre panel is removed, the surrounding sheet will have lost some rigidity so must be well supported and flat. One way to do that is to lay a row of battens of 50x25 spaced apart on a bench. The battens can be part sacrificed so that the saw blade depth can be made a few mm more than the material thickness.

Carefully measure the distance between the edge of the plate of the saw and the edge of the blade and position a straight batten on the top surface that distance from the line. You can safely remove the riving knife from the saw in this application because the material can't close the gap, provided that the sheet is properly supported.

The saw can now be carefully plunged. Keep in mind the shape of the blade and stop before the ends. You can finish the last few mm with a pull saw.

Using a dust mask with MDF cutting, especially with a circular saw is important.

[The Medway Handyman]

Oh good, its not just me who has that opinion then!

I searched high & low for a new 165mm circ saw - everyone wanted to sell me a 190mm +. Settled on the Makita 5604. Still has a 54mm depth of cut which is enough for me.

Completely agree, much better accuracy (and I was a weightlifter) :-)

[Andy Hall]

It is a shame. there are several makes of small saw in the U.S., although the PC one is the popular one.

There are also circular saws with worm drives for more torque, I suppose. When you build houses all with wood, you need that.

So why aren't you using your table saw up trees?

[TheOldFellow]

Damn good point. MDF dust is carcinogenic. And even the smallest amount can bring on asthma in those susceptible (like me - I have to use a full-head filtered-air thingy with MDF, and for a few days afterwards, in my workshop).

R.

[Pete C]

Hi,

What blade exactly did you try in the jigsaw?

cheers, Pete.

[The Medway Handyman]

Because I'm an ex weightlifter who isn't as daft as he looks :-)

[Andy Hall]

Have you thought about one of those box type powered dust filters? I installed one of those and found it made a difference with materials like teak; or do you think you are affected by vapour?