Jigsaw failings

Jigsaws always seem to wonder a bit. Good excuse to buy a track saw 😁

It'll never be great and a circular saw (or track saw) is the better tool. IME trying to use a guide makes things worse. Best is to go steady and not push it, let the saw cut at its own pace, which will be pretty slow cross cutting oak

Or should I just switch over to my circular saw

Yes. Circular saws cut straight, jigsaws don't. Jigsaws are extremely useful tools but not for cutting straight.

Different blades behave differently but you seem aware of that when you say that you used the appropriate blade.

Edit: When I saw the thread title for some reason I genuinely assumed that it was going to be a jigsaw puzzle. I was going to suggest using a hammer to make the pieces fit. Which would have been a tad more amusing than my above comment.

Let the blade do the work, don't force it forwards.

Don't cut anything too thick.

Sounds standard for jigsaws. Better saws suffer less, but not suffer none.

IME, the only jigsaw that will cut true even through thicker stuff is the Festool.

Only ever use a jigsaw for rough work or when prepping a piece that is going to be routered.

Wrong tool for the job really.
50mm of oak probably needs a router (and probably a rough cut first and more than one pass...)

A good jigsaw will cut 50mm oak tops just not very well good blades will help. But it's definitely not the best tool for that job.
Jigsaws are for rough work pre template and router.
A heavy jigsaw like my old DeWalt is better at taking the vibration out of the cut and your hands and in turn leaving you with a more accurate cut.

Even using a horizontal guide

They problem if the blade is not giving your a square edge to the cut is the edge of the footplate and the blade being out of alignment with each other. If you make the foot plate follow a straight edge the blade is trying to go left or right and can't because is fighting against the guide so you're effectively putting a side loading on the blade when you try to cut straight and thats why the blade curves and gives you a sloped cut

You can see of theres any adjustment in the foot plate - .. or given you already have the right tool for the job you could used the right tool for the job 🙂

Very reassuring.
For big cuts I used my circular saw. But I was enlarging a cutout for a hob. The jigsaw did OK, but that vertical wandering 😩

What you can do to get straighter / squarer cuts with a jigsaw is free hand a cut close to your line then use a guide rail  to  sort of shave your way to you final line. When the blade is just grazing off some material it doesn’t get pulled away from the line and should stay squarer

Yep mine will sort of go straight if I go slow and crab the footplate diagonally to offset the wandering. I can see how using a straight edge would exacerbate any tendency to wander and start cutting diagonally.

I use a circular saw now and only use the Jigsaw to trim into internal corners.

Stumpy nubs on YouTube did a video recently on jigsaws and how to improve your use of them. I think 🤔

Stumpy nubs is very good, great tutorials.
Time for a router though if you want a good finish on a curve

Wrong tool for the job really.
50mm of oak probably needs a router (and probably a rough cut first and more than one pass…)

As would be a router, unless clouds of dust are your thing. Routers are for making edge profiles, or dados or rebates, but not for cutting up timber.

Handheld circular saw, or plunge saw if you can afford it.

You cant really rip using a jigsaw, even if the blade is large tooth, because it has a tendency to follow the grain, which is why the cut goes all out of shape, raggedy or squint. Best used for cutting curves, or for use in plywood or mdf.

Using a guide rail/board will make little to no difference, as its usually the bottom part of the blade that does the wandering. The blades are thin with a tendency to bend in use. They just aren't strong enough to force the cut to remain straight.

I was just using my flash new festool plunge saw to take 8mm off the bottom of a door to accommodate a new carpet/underlay. Took the door off and the bottom edge i could see had already been trimmed by someone using a jigsaw by how horrifically chewed up the cut was. stops,starts due to them trying to stop the wander, pretty horrendous overall.

Owning a small cheap table saw is a good proposition. Its probably safer than a hand held saw, and is a good bit more versatile. You dont have to spend hundreds, and something cheap out of aldi/lidl/B&Q or along the lines of that ilk would be ideal.

Jigsaw - there's a clue in the name 😂

Yeah, jigsaws and thick oak worktops are not happy bedfellows.

Mind you, using a circular saw without a plunge to cut internal cuts such as worktop holes is potentially very dangerous. You see circular saws used for that type of cut but you've got to really know your tool, material and what the steps are, and it's still pretty dodge and not something you generally advertise as something you do these days. It can go wrong very quickly.

Doing that cut on a tablesaw is also iffy as you have to either lower the worktop against a fence onto a moving blade or drop the blade and wind it up into the cut, all by feel only (and without a riving knife usually) Very iffy with a large, heavy worktop and a tiny little site saw from the middle aisle.

Even using a track saw can be pretty gnarly if you're used to gently plunging into mdf or something.
Thick oak can cause a serious bite and the saw can jump out of the cut. You need a model with anti kickback or at the very least a considered method of preventing it, most of which is experience frankly.

To be honest a worktop hole hasn't got to be that pretty so using a jigsaw freehand is the way I'd go if that's what you've got (I realise this thread is old) As long as any mild undercut is on the underside that is.

Get a pack of brand new blades, the wider the better for straight cuts and plenty of length and I would cut from the top so that any blade undercut isn't so much the end of the world.

Jigsaws are never the best for thick material but if the blade is deflecting really badly then it's likely a combination of blade condition, blade type, settings and technique.

Use a dedicated brand new blade. Max out the pendulum and really take your time.
Shaving off material from the edge isn't generally something jigsaws are best suited to as the blade is very prone to deflecting at the furthest from the holder.

I use a circular saw now and only use the Jigsaw to trim into internal corners.

Oscillating multitool is great for finishing into internal corners.

Jigsaws with pendulum adjustability need to have lots of pendulum action for hard, thick materials. Pendulum is the motion where the blade rocks against the face as it makes the cut rather than just straight up and down. It helps clear the kerf and keeps the blade temperature more sensible. The leading face of the cut will not be a straight vertical but because you force it less, the blade finds a straighter path. Still not the right tool but better than a non-pendulum cut. For the final sliver into the corner you can wind down the pendulum to make a neater finish into the crosscut (not that it matters for this job).

jigsaws are for a rough cut, Routers for tidying.

Once you get into the habit the world is a better place.

How about trying a rough cut 3-5mm inside the line, then lots of cuts perpendicular up to the line, before finishing. Does that help or is it just for tight turns?

How about trying a rough cut 3-5mm inside the line, then lots of cuts perpendicular up to the line, before finishing. Does that help or is it just for tight turns?

That technique is more about releasing the blade in a curve, usually when your blade is a bit too deep for the radius you're cutting.
Not helpful for straight cuts really. Would cause a bit of jarring as you cut.