Woodworkers – teach me how to cut a straight line

A line that doesn’t touch the edges of the piece, that is.

I can do it when cutting right across, but this one is giving me trouble:

(artist’s impression)

It’s a large bit of 18mm ply, approx 2300*900mm.
The middle cut is about 1800 long.

I want to keep the 3 cut out pieces (it’ll turn into a window sill/seat to fill a bay window, the cutouts will lift up on hinges to store stuff inside).

How do I cut those lines neatly & accurately?

Tools available: table saw, circular saw, jigsaw. Also have an attachment thingy to turn the circular into a track saw. And a hand saw, I guess.

Any circular saw will leave a slope at the end of the cut. I can’t cut a long perfectly straight line with a jigsaw to save my life.
Stumped, and don’t particulary want to try something and ruin the wood, which is pretty expensive.

i would use the track saw and then a hand saw to get rid of the last bit of ‘slope’

Any circular saw will leave a slope at the end of the cut

Stop short of the corners – just before the top of the cut reaches the corner – then finish the last bit with a hand saw – the handsaw will have a thinner kerf than the circluar saw so you can tidy ip the corners with a file / chisel or whatever.

The cut through the middle of the board is tricker – with a proper plunge saw you can plunge to start a cut in the middle of a board – if you’ve got a track attachment for a regular track saw thats not possible because the saw will have a reiving knife that will prevent that

your overall dimnensions ware less than a full sheet so you could effectively shift the three smaller peices in your drawing downwards so that top edge of those peices and the inside cut of the larger piece don’t have to be the same cut

I would do it with my tracksaw. But mine’s a plunge saw, so you can start off with the blade above the surface and lower it into the board. I would start with the awkward long cut, a little ahead of the corner, plunge, then pull back gently to the line. Just use your eyes to see where the blade has got to. finish off with the jigsaw to cut out the circular slope.

If doing it to precise measurements, make sure you cut the right side of your line or take into account the blade width (kerf). My blade is 2.2mm wide and I have a couple of handy 2.2mm spacers if I’m lining up on the “waste” side.

What they said ^

Just don’t try doing it with a jigsaw. You could drill a hole the same diameter as the blade width at each junction to help finish the cut with a hand saw, and I would score any cross grain cut on both sides with a sharp knife to reduce splintering on the plywood- just take care so the knife doesn’t slip and mark where you don’t want it to

Ok thanks all, will give it a try.

My track saw is this: https://www.amazon.co.uk/Kreg-KMA2700-KREG%C2%AE-Accu-CutTM/dp/B073PGP96S

Might be able to plunge cut with it, never tried though. Don’t have a riving knife.

Also have an attachment thingy to turn the circular into a track saw.

Is that just a clamp on straight edge, or does the saw base have a ridge or such that means it runs on top of it ?

If you’ve no tracksaw/plunge saw then you could clamp a long piece across your board to act as a guide that the edge of the circular saw base to run against, only you would have to make sure you push the saw tight against it or it might want to wander off.. Then as above, finish the last bit with a handsaw. As above the saw kerf on the handsaw is less so you’ll need to finish that with a hand or block plane which will give better results than a file or chisel.

Only issue I see if using a circular saw you’ll need to plunge cut it, which is a dangerous operation that required 100% concentration as you can only hold the tool with one hand.

.

If you are neat and accurate, you can just use a hand saw and make the start of the cut in the middle of the board

EDIT: Ok seen the link with the kreg thing.

Is the saw clamped to it ?. in which case lift the saw using its depth of cut right up and use that action of letting it back down as the method of making the plunge. Easier if theres no riving knife.

One thing about making a plunge cut without a riving knife is it is easier, but the danger factor increases, plus cutting board material using a circular saw without a riving knife also increases the risk of a kickback, unless its on a track or running against a straight edge, but again care and attention must be 100%

When I say hand saw I mean a regular bog standard saw, not a keyhole/coping saw or anything. It’s not going through any small holes! (which is what I usually do with the jigsaw)

Plus I can’t cut holes as I need all the pieces square for the seats.

@maccruiskeen good idea but I’ve already cut out this size board less than the full sheet.

Is the saw clamped to it ?. in which case lift the saw using its depth of cut right up and use that action of letting it back down as the method of making the plunge. Easier if theres no riving knife.

The saw clamps to the sled, this then runs along ridges on the track.  It’s loose and I can lift it up at any point. The track has rubbery strips underneath to stop it sliding around.

I could probably plunge either with your suggestion or simply by lifting the whole saw/sled onto the front lip of the sled and lowering it onto the track.

Rough cut it out (undersize) with a jigsaw, then using a router and a flush trim bit (as well as a straight edge/guide) cut to size. Tidy the little corner radii with a chisel if needed.

Routers are brilliant.

> Routers are brilliant

But not in the OP’s Tools available list… currently 🙂

I would cut right across the board then cut your 5 pieces. Domino biscuit or whatever the two end bits back on as you assemble it in place.

Whole thing will be easier handle.

The saw clamps to the sled, this then runs along ridges on the track. It’s loose and I can lift it up at any point.

If the saw has got a Riving Knife behind the blade you can’t plunge it.

Is there any reason why you can’t just cut straight across the board, then cut your two sides and your three middle bits then join your two sides back on when you assemble your seat?

Might be able to plunge cut with it, never tried though. Don’t have a riving knife.

I would practice that part on an old bit of hardboard first.  That’s the bit that is most likely to go wrong

“If the saw has got a Riving Knife behind the blade you can’t plunge it.”

You can. The riving knife will plunge with the saw, with the saw more exposed to the board when raised. To plunge you will need to move the saw forward slightly as you plunge.

I used to plunge a Makita saw that wasn’t a plunge saw, just an ordinary circular saw. You could bodge it to (temporarily) hold up the riving knife. The purpose of the riving knife isn’t to prevent kick back, it’s to stop the cut closing up because of the stresses in the wood and grabbing the blade.

> Routers are brilliant

But not in the OP’s Tools available list… currently 🙂

1. No man ever had enough tools 🙂

2. a circular saw is not the tool for this job.

3. See no.1.

I’m actually intrigued to hear from the proper wood-bothers here on the ‘right’ way of doing this.

Is there a tool library in your area where you could hire a track saw or router to get the job done properly?

s there any reason why you can’t just cut straight across the board, then cut your two sides and your three middle bits then join your two sides back on when you assemble your seat?

Get your own sensible suggestion!

Rough cut it out (undersize) with a jigsaw, then using a router and a flush trim bit (as well as a straight edge/guide) cut to size

doesn’t help when the OP wants to keep the 3 cutouts as hinged lids

Instead of pissing about with a circular saw you need something similar to one of these:  Shokunin Japanese Atsuba Crosscut Saw – 180mm | Axminster Tools, allowing you to start your cuts in the middle of the sheet

A bit of elbow grease and it’ll be done in the time it takes you to find a plug socket.

@simian.

…a circular saw is not the tool for this job.

[…]

I’m actually intrigued to hear from the proper wood-bothers here on the ‘right’ way of doing this.

How do you know that the answers aren’t from proper wood botherers?

Plunging a circular saw for the bulk of the cut, with the ends finished up using a hand saw is a perfectly valid way of making this sort of cut. A plunging track saw is even better, but they’re a relatively recent invention (1980s??).

You could use a floorboard saw to manually make that first cut through; or a multi-tool cutter or something. But I’d probably try and use your circular saw as a plunge cutter, just take it real slow and be careful* 😀

* – I am not an expert.

Edit – floorboard saw: https://www.toolstation.com/irwin-floorboard-saw/p53087

Yeah as Dyna-ti and BigJohn say up there, you can use a regular circular saw to plunge. You just need to be mindful of the risks. Tracksaws are literally designed for the job and circular saws are not.

If you slacken the depth adjustment knob, bring the saw up and clear, start up, and slowly and carefully plunge to full depth, and then perform your cut all in one smooth action start to end.
You don’t need to take a hand off and tighten the depth knob necessarily. Just leave it but be aware that it’s not tightened and keep the saw down and steady with both hands.
You can make your plunge, move forward a little then stop, nip the knob up, then carry on, but move the saw back a few mm so you’re not starting in the cut.

Being at full depth will reduce the length of material you need to hand cut into the corners.

Kickback is a possibility, especially if you don’t come down straight or you skew the tool as you come down.
You can reduce the chances of kickback by getting the saw where you want it, and then clamping a block behind the saw against the sole plate to prevent any backwards movement.

Ok, I’m going to try this in a few minutes. Will post back the results if I still have enough fingers.

I would love a router. And a whole array of fancy Japanese saws. But I’m skint 🙁

This is my saw: https://www.diy.com/departments/erbauer-1400w-220-240v-165mm-corded-circular-saw-ecs1400/3663602795773_BQ.prd

No riving knife.

Is there any reason why you can’t just cut straight across the board, then cut your two sides and your three middle bits then join your two sides back on when you assemble your seat?

This was considered… but then I’d have a seam where they join, which would make me sad.

1. No man ever had enough tools 🙂

Amen.

If you buy the wood in B&Q, they’ll cut it for you FOC. Our local store has a very funky computer controlled cutter, I’d be surprised if they can’t do it.

Well that worked just fine 🙂  Thanks all.

If you buy the wood in B&Q, they’ll cut it for you FOC. Our local store has a very funky computer controlled cutter, I’d be surprised if they can’t do it.

The one here just has a big wall mounted circular saw thing, they’ll only do straight across cuts.

Congratulations OP… but I can’t help but think this thread is poorer for the lack of @worldclassaccident 

I heard my name…

Japanese / floorboard saw as I already have one and that one that is linked is less than £30. i was given a cheap Axminster Japanese saw and was sceptical but am now a big fan of them. So much easier to cut accurate and straight that the traditional saws.

Failing that I am sure I could rig up some kind of laser/plasma cutter powered from the street lights supply…