Cutting sheets of wood safely

Question

I have ordered a jig-saw. I need to cut the following things to size:

1. Cut shelves to size, they are too long to mount.
2. Cut panel of MDF to smaller rectangular size.

I know that jig-saw has a small saw that moves vertically and cuts the wood. However, the problem is, where do I place the wood? I can't place it on ground. I can't place it parallel to wall. I do not have a special bench for wood cutting like all the wood working folks on youtube have. I do have a small computer desk sandwitched between a wall and a chimney breast.

This now leaves these issues:

1. Where to put large shelves and wooden panels to cut them, that can't fit on any desk or surface in my own home.
2. How to make sure that I don't damage the surface on which I am keeping the wood when cutting.
3. Make sure that I cleanly cut in straight line using jig-saw.

Answer 1

One should determine how deeply beyond the undersurface of the wood the blade of the saw will extend. One should place supports of any kind to keep the wood at least that distance above the surface on which the assembly is placed.

The floor is a reliable, non-moving surface. Books, blocks, anesthetized tortoises, anything solid enough to support the weight of the board being cut can be used.

For minimal possibility of destruction, one should support the board in four places: one at each end of the entire length of the board and one on each side of the cut, leaving enough room to avoid cutting through the tortoise.

To provide for a straight cut, secure a board at ninety degrees to the primary target, displaced from the cut line by the same distance as the blade edge to the saw's shoe. Ensure that the guide board is thin enough to pass under any components of the saw, or place it on the side of the shoe opposite to the conflicting components.

Many videos exist, using the search terms "cut straight with jigsaw," although the very first one that appeared in my search used a hand-guided method!

https://www.youtube.com/watch?v=EFCGYVH1frc

The above video uses a bench top (with a somewhat unsecured board) and a carpenter's square as the shoe guide, but is a good representation.

Answer 2

The basics of jigsaws and their blades:

• Jigsaws cut as you push them. Normally you will be starting the cut close to you, and pushing it away from you as the blade makes the cut; be aware if you're making a cut that is longer than your reach that you may have to stop and change position mid-cut, or adopt a different posture and walk the saw along the cut.

• Make sure the saw is at full speed before you begin cutting.

• Most blades intended for cutting wood cut on the upstroke (the teeth point upwards), and this can lead to splintering on the upper surface. The simplest way to reduce this is probably to apply masking tape along the cut line, burnish it down well and saw right through it; when you're done, peel off the tape carefully to avoid lifting flakes.

• Coarse blades cut faster, but leave a ragged surface. Finer blades with more teeth cut more slowly but leave a much better surface and there is less splintering. 10tpi blades may be the sweet spot.

• Regardless of the number of teeth let the saw do the work. In other words, cut slowly. Forcing cuts using a jigsaw is probably the number one source of frustration for inexperienced or impatient users. Pushing the saw into the cut with force leads to rougher sawn surfaces, worse splintering and additionally the blade is likely to flex in use leading to the cuts not being square to the face.

• Jigsaws can be quite loud, it would be best to plug your ears or wear earmuffs.

For lots more guidance see these:
Jigsaw BASICS for Beginners. from DIYForKnuckleheads.
How I made my jig saw cut a LOT better from Stumpy Nubs.

Shortening the shelves
The simplest way for someone with no workbench to cut boards to length is just to rest each one across the seats of two matching chairs¹, kneel on the wood and saw off the projecting part.

If you're a right-hander the projecting end should be to your right. If you're a leftie it should be the other way around.

Practice makes perfect. If you feel it is necessary you can make multiple practice cuts on the material you know will be cut off before sawing your shelves to finished length.

Cutting the MDF to size
It's perhaps more difficult to arrange to cut the MDF, but it is generally possible in an apartment setting using the furniture available and some ingenuity.

The best way is probably to cut with the MDF on a table or desk, obviously with the portion to be cut well off the edge of the supporting surface so there's no chance your cut can wander into the tabletop. You can do this quite conveniently on a low coffee table, but you can successfully make your cuts on a table of any height.

If your table isn't low enough to kneel on, clamping the MDF in place would be ideal (and the clamps would have many future DIY uses). If you don't want to invest in a couple of clamps, heavily weight the part of the sheet that rests on the table, for example with numerous heavy books, so it can't easily move².

Because your rectangle of MDF will be out of sight once mounted at the back of your desk your cuts don't have to be perfect by any means. So instead of trying to saw along a straightedge to guide the jigsaw I suggest you just guide it freehand to the best of your ability, following a pencil or ballpoint pen line, and don't sweat it if your cuts are irregular.

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¹ You can do it on a single chair, but you have to be more careful as there's a greater tendency for the wood to shift as you're cutting it.

² If you have any non-slip drawer lining material definitely put some under the MDF as well.

Answer 3

The other answers provide good solutions for supporting your work. However I want to directly answer this part:

Make sure that I cleanly cut in straight line using jig-saw.

My first reaction is that for cutting a straight line, a jig-saw is the wrong tool; use a circular saw instead. (A circular saw will make supporting the work easier too, because you can adjust the depth of cut so the blade only projects a short way under the workpiece.)

You can get a cheap circular saw from Screwfix for £30 and it will probably be good enough for this job.

With a circular saw, clamping a straight edge to the workpiece and pushing the saw along this will produce a very straight cut. With a jigsaw it won't; once the blade has veered sideways for some reason, it is almost impossible to get back on the line unless you can twist the jigsaw and a straightedge will stop you doing this.

For a jigsaw you are better clearly marking the line and following it - you can then twist the saw to get back to the line whenever you need to.

Answer 4

However, the problem is, where do I place the wood?

Invest in a pair of sawhorses. You can buy folding sawhorses made of metal or plastic at any home center, starting around $40 for a pair, or you can build a pair that stack instead of folding for about $20. A small folding workbench like a Black & Decker Workmate can be a good alternative, but will cost more.

Where to put large shelves and wooden panels to cut them, that can't fit on any desk or surface in my own home.

A nice thing about sawhorses is that you can set the any distance apart, so they easily adjust to fit workpieces of different sizes. Also, you can set a couple pieces of lumber across the top to support your workpiece along its entire length. Many commercial sawhorses will include notches meant for 2x4's for just this reason.

How to make sure that I don't damage the surface on which I am keeping the wood when cutting.

Another nice thing about sawhorses is that they're not the dining room table -- if you start to cut into them by accident, it's not a big deal. Some people even design their sawhorses so that the top bar can be replaced, and they just don't worry at all about cutting into it with a circular saw. That said, it's not hard to have some basic awareness of where the work supports are and avoid them by moving the workpiece as needed.

Make sure that I cleanly cut in straight line using jig-saw.

Using a straight edge to guide the saw will help you cut along a straight line. Just measure the distance between the side of the saw's foot and the blade, and clamp a piece of straight lumber at that offset from your cut line. Select an appropriate blade for the material you're cutting to get a relatively clean cut, but know that a jigsaw won't give you a perfectly clean cut -- you'll probably want to do some sanding with a flat sanding block afterward.

Answer 5

Frame challenge — hand saw

Since we know the cuts you need to do here, a power saw is actually not explicitly needed, both to make the cuts in the first place but also to get good straight cuts, and quickly enough to be reasonably classed as acceptable.

I'd guess it's fewer, but if you have as many as six shelves to shorten you're still only doing eight cuts here, with half a dozen of them being quite short crosscuts. That does not exactly scream "power saw"!

With some guidance from the Internet and only a little practice you should be able to complete all your cuts by hand to an acceptable standard in under 10 minutes (not factoring in setup time which can be nearly the same either way; note that cleanup time would not be equal).

I'll list the advantages and disadvantages as I see them relating specifically to what you're doing now. [A pro/con list like this would be much longer if taking into account the full potential uses of each tool, such as a jigsaw's ability to cut metal, or a hand saw's ability to saw through sizeable logs.]

Advantages

• Quieter. Much, much quieter. Jigsaws can run at upwards of 100dB, which is loud enough to strongly point to the need for hearing protection. There's also an argument to be made in an apartment setting of the nuisance value to neighbours, but here you're doing so few cuts that shouldn't be an issue.
• Cheaper. Depending on the jigsaw possibly substantially cheaper — suitable handsaws vary from around a tenner to maybe 20 quid, while the average price of jigsaws is around £60-70 (prices for name-brand saws vary from roughly £35 to over £220, without even including premium brands).
• Much less fine dust. To be fair, jigsaws aren't bad offenders for creating airborne dust (compare to a circular saw!!) but still, sawing by hand will generate virtually none, which is a factor when working indoors in a domestic setting.
• Slower. You ask explicitly about safety and any process that's slower is inherently safer; it's far harder to make a very bad mistake slowly.

Disadvantages

• Slower. Yes I know this is in the other list as well but while being an advantage for safety it is seen as a disadvantage by many people because it takes much longer to complete cuts. I mention this only for completeness however, because for your current needs I think the speed difference is too small to really be a convincing argument in favour of a power saw.
• Possibly takes more practice to get good cuts? This is debatable since all tools have a learning curve, and in the context of what you need to do only the shelf cuts actually need to be neat and tidy — once in place the MDF panel will be permanently hidden from view so how clean/straight its edges are doesn't matter except in an OCD way :-)