Cutting large holes in ply with jigsaw

[Mark Rogers]

I want to cut a circular hole of approx 200mm in a sheet of 6mm birch ply.

As my old barely used battery powered jigsaw had died a death, I used the e xcuse to buy a cheap (£20) B&Q jigsaw which has a straight edge guide, an d tried a couple of test cuts with the edge guide which were pretty good (n o reason why they wouldn't be).

So I then drilled a hole into the end of the edge guide, inserted it upside

-down into the jigsaw and put a screw through that hole into the ply, the i dea being that this would guide the jigsaw in a nice circle. (Having first drilled a hole in the ply for the blade, of-course!)

However, I've tried this several times now and every time the blade gets pu lled towards the centre of the circle, bending the blade (pulling it away f rom the guide wheel) and jamming. I have tried different blades, different speeds, even adjusting the footplate to different angles. I tried clamping the wood and moving the jigsaw, and I tried holding the jigsaw stationary a nd moving the wood. The result is always the same.

I could (sort-of) understand it if the blade was bending outwards (as if tr ying to continue in a straight line) but bending inwards makes no sense to me at all.

Suggestions as to why this is happening, and what I can do to stop it (or b etter ways to do the job) welcomed!

[Mark Rogers]

It's been puzzling me for days, but no sooner do I post here than I (think I) work it out for myself.

The problem is that the guide does not line the blade up with the centre of the circle. I'm going to need a more elaborate jig to do that - I've found some on ebay for about £25 but first I need to see if I can make one for myself! Suggestions (and corrections!) still welcome!

[Dave Liquorice]

Use compass and pencil to mark circle on ply, cut freehand.

Take it slowly and let the saw do the work. Only gently guide the saw in the direction you wish the cut to proceed, most of the force applied to

the saw should be along the line of the blade in both axis (front/back,

left/right).

[John Rumm]

Sounds like you have answered your own question... if the attachment point on the sole plate is fore or aft of the blade (which since it needs to pass right through the plate it needs to be!) it will in effect be dragging the blade very slightly to one side or the other as you cut.

I would expect a thin ply template that you can fix the jigsaw to at one end, with the blade on the radius, and a screw through the other end ought to do it.

(you have not said if its the hole or the cutout circle which is the bit you need, if its the latter, you may not want a screw hole in the centre of it, so use double sided carpet tape to fix a scrap block to it first and screw into that)

[Mark Rogers]

My skills in this area are, er, pretty pathetic.

I can't cut a straight line with a normal saw, never mind a decent circle with a jigsaw!

I do have plenty of scrap to play with so I may give it a go though.

The tips are appreciated, thanks!

Mark

[The Natural Philosopher]

better still, buy a router and a circle cutting jig.

Or make a circle template out if thin ply or hardboard..carefully sanded to an accurate shape, and use that with the router.

[Steve Firth]

Mark Rogers wrote: [snip]

Probably not what you want to hear, but the way to do this properly is to use a router, not a jigsaw.

[Mark Rogers]

I had to draw it out to prove it to myself but once I had done that it's pr etty obvious really.

That's pretty much what I'm thinking at the moment, the only question in my mind is how best to fix the jigsaw to the ply?

It's the hole I'm interested in. It's actually just an access hole for a ma ins socket behind a shelving unit I'm building, and it won't be visible, so this is really just an opportunity to learn how to do something where it d oesn't matter if I screw it up. A rectangular hole would be quite quick and simple to do instead but doesn't give me the satisfaction!

The tip for keeping the cutout is appreciated though, might come in handy o ne day. Thanks!

Mark

[Mark Rogers]

I looked into this before I bought the new jigsaw (and given I only spent £20 on it you can see one of the reasons I didn't go for the router).

I'm still tempted to get and learn to use a router, but it's quite a lot of outlay for a tool for a single job like this that may just gather dust aft erwards. I get enough grief from 'er indoors already about the ever growing collection of tools!

Given the problems I'm having here, my next question would be how do I make a good circle to use as a template!

Mark

[Mark Rogers]

I knew this before I started, but replacing a broken tool is more wife-frie ndly than buying a new tool, and it turns out that you can get a fairly rea sonable jigsaw for £20 (and blades are cheap too). For cutting one hole t hen putting the tool on the shelf it's a lot easier to justify!

(So far this project has gained me a biscuit jointer and a nail gun, so I'm not doing too badly! But both of those have been used extensively already so they're easy to justify.)

Mark

[fred]

excuse to buy a cheap (£20) B&Q jigsaw which has a straight edge guide, and tried a couple of test cuts with the edge guide which were pretty good (no reason why they wouldn't be).

de-down into the jigsaw and put a screw through that hole into the ply, the idea being that this would guide the jigsaw in a nice circle. (Having firs t drilled a hole in the ply for the blade, of-course!)

pulled towards the centre of the circle, bending the blade (pulling it away from the guide wheel) and jamming. I have tried different blades, differen t speeds, even adjusting the footplate to different angles. I tried clampin g the wood and moving the jigsaw, and I tried holding the jigsaw stationary and moving the wood. The result is always the same.

trying to continue in a straight line) but bending inwards makes no sense t o me at all.

better ways to do the job) welcomed!

I never found this method of cutting a circle worth a rats ass and I've tri ed with Bosch's pukka circle attachment.

Same goes for circle cutting jigs on a band saw.

I prefer to do it by hand and eye. Its not difficult. Make sure you have a good quality SHARP blade and go very slowly. You can neaten it after with a sanding block

[Steve Firth]

Hmm my experience of £20 jigsaws is that they don't cut straight and they don't cut curved. They are very good at jagged.

For circles a blade that can turn easily and cut cleanly is a real help. Bosch have the "Extra Clean" blades that are ideal for this. They cut on up and down strokes and produce a fine finish on both sides of the cut. For Black and Decker I think the closest blade to the Bosch ones are 104-1 "Clean Fine Cutting". £3 for three unless you buy at a robbing shed.

As others have said cutting by eye to a scribed circle is probably going to be easier.

[Dave Liquorice]

You turn it, so there's an excuse to go and buy a lath to make the template to use with the new router to mak the hole that could be rectangular. But where is the satisfaction in that? B-)

Give it a go freehand as you have the scrap. Make sure the 6mm ply is well supported maybe place it on top of something thicker (but not too thick 1/2" would be ample) and cut both. If not cutting something thick don't be afraid of stopping repositioning the support and starting again. Back the blade a tad away from the cut before stopping start a little away and move back in.

[The Natural Philosopher]

on it you can see one of the reasons I didn't go for the router).

outlay for a tool for a single job like this that may just gather dust afterwards. I get enough grief from 'er indoors already about the ever growing collection of tools!

good circle to use as a template!

the problem with a jigsaw is controlling it. anyone can draw a circle. he problem is achieving the accurate cut, but its a lot easier on thin material with a jigsaw.

jigsaws do not like doing deep cuts.

You cut away from the finished line and finish with a bit of sandpaper wrapped round a dowel to get a good inside edge, or a sanding block like permagrit if you are making an outside disk edge.

Then its down to using that to guide the router.

For small templates you can use a lathe..to spin them up.

If its just a rough access hole use a hole cutter..

[Martin Brown]

a jigsaw!

Depending on how big it is and how critical that you get it right you might want to try marking two circles on the job. An outer one that you must never exceed and an inner one that you aim to follow. Then tidy up the result with a half round file to get the exact to the line shape.

If you drift out too far stop and start again from a new drilled hole.

You should be able to follow the line fairly well with a bit of practice but there is definitely a knack to it. Blowing the sawdust away so you can see a line to follow is half the battle. YMMV

[Mark Rogers]

Based on the comments here I'm definitely going to try freehand and see where I end up. Like I said elsewhere it doesn't have to be pretty!

Mark

[polygonum]

excuse to buy a cheap (£20) B&Q jigsaw which has a straight edge guide, and tried a couple of test cuts with the edge guide which were pretty good (no reason why they wouldn't be).

upside-down into the jigsaw and put a screw through that hole into the ply, the idea being that this would guide the jigsaw in a nice circle. (Having first drilled a hole in the ply for the blade, of-course!)

pulled towards the centre of the circle, bending the blade (pulling it away from the guide wheel) and jamming. I have tried different blades, different speeds, even adjusting the footplate to different angles. I tried clamping the wood and moving the jigsaw, and I tried holding the jigsaw stationary and moving the wood. The result is always the same.

trying to continue in a straight line) but bending inwards makes no sense to me at all.

better ways to do the job) welcomed!

A number of years ago I used a router to cut the tops of some fences to a nice semi-circle. Then the router fell apart. So I finished off the remaining ones with a jigsaw and a piece of string. Worked remarkably well.

[Mark Rogers]

The trial (straight) cuts I made using the cheap jigsaw and the edge guide were actually pretty impressive, and that was with a blade from a pack of a dozen or so from Aldi that I had lying around.

Compared with the cheap jigsaw it replaced there's a huge difference.

£3.50 for 6 delivered on eBay: - I 'll give them a go, thanks. (Found the Bosch ones at 5 for £4.50 if anyon e is interested:

Mark

[Fredxx]

wife-friendly than buying a new tool, and it turns out that you can get a fairly reasonable jigsaw for £20 (and blades are cheap too). For cutting one hole then putting the tool on the shelf it's a lot easier to justify!

not doing too badly! But both of those have been used extensively already so they're easy to justify.)

The costs of tools is cheap when compared to getting a man in. It's easy to justify any cost on that basis alone.

Even if the tool does collect a little dust, the resale value of a pristine tool isn't bad.

[Mark Rogers]

I know, that's how I got the router and nail gun :-)

The cost isn't really the issue to be honest, it's more that I don't have space to keep all the tools and I can't make arguments about her shoes if I have a garage full of tools I really wanted but have never worn^H^H^H^Hused...

Mark