Cutting circles with a jigsaw

Given: plywood, jigsaw wanted: circular bit of plywood, diameters 60-80 cm, small hole in the middle is OK.
Yeah: "make a jig", i.e. an arm with the wanted radius, attached to the jigsaw
base, screw middle down and cut around.
But: I seem to recall there's a catch there somewhere, or a best way of doing this, in positioning the radius arm with respect to the blade. Should the radius arm attach to the jigsaw a) ahead of the blade, b) exactly off to the side of the blade, or c) further back from the jigsaw blade?
Thomas Prufer
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 02/07/2020 13:41, Thomas Prufer wrote:

You can buy a jig that has a drill down the centre and three jigsaw blades that adjust out on a spiral to about 90mm diamtere. It works quite well and stays balanced in use.
You definitely want it balanced and on three point cutting support or it will snatch the moment the blade tips touch the surface.
--
Regards,
Martin Brown
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Yes ever tried cutting holes for speakers in cabinets, I mean takes ages. Brian
--
----- --
This newsgroup posting comes to you directly from...
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Wouldn't fancy using a jigsaw for smaller holes, at least with the blades I've got. I've just done some (14cm and 5cm diameters) using a router, by hand for the cutout, and using a plank of wood/nail for the rebate.
Didn't take that long, although in my pre-power tool days not such fond memories of fret saws etc . . .
On 3 Jul 2020 at 18:35:23 BST, ""Brian Gaff \" <Sofa\)"

--
Cheers, Rob



Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

See my earlier post.
--
*According to my calculations, the problem doesn't exist.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 02/07/2020 13:41, Thomas Prufer wrote:

If it is not in line with the blade any wiggle will change the radius.
Personally I would cut undersize and use a rasp...
--
"What do you think about Gay Marriage?"
"I don't."
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 02/07/2020 13:41, Thomas Prufer wrote:

A holesaw will leave you a circular bit of ply: https://www.screwfix.com/c/tools/holesaws/cat5920018 TW
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 02/07/2020 15:23, TimW wrote:

He wants 600-800 mm.
In answer to the OP, the blade needs to be at 90 degrees to the radius. As others have said, you might want two radius arms, to hold the jigsaw steady. But it's easier just to use a rectangular piece of ply with a hole at one end for the pivot?
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 02/07/2020 16:12, GB wrote:

[...]

[...]
Oh, yeah, ta. I thought mm.
TW
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Don't suppose you have a router, hence asking?
My feeling is a jigsaw isn't going to make an accurate job of this - so perhaps easier for a one off to simply cut as near as possible and plane or file down round?
--
*Since light travels faster than sound, some people appear bright until you hear them speak.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thursday, 2 July 2020 13:41:41 UTC+1, Thomas Prufer wrote:

ddle is

igsaw

oing

radius

e of

How about this approach? A jigsaw table with a blade stabiliser mechanism. Could be worth it if you are going to do this repeatedly.

https://youtu.be/wFnbcOLF4qU

https://youtu.be/wFnbcOLF4qU

JSK-koubou 565K subscribers Hey guys, I made a jigsaw table this time.
[Download the plan here] https://jisaku-koubou.com/downloads/j ... 【Plan List】 https://jsk-koubou.stores.jp/
2-way locking arm system allows you to control your jigsaw easier than ever . Even with a large project, the arm will not get in your way. The arm accept s longer blades up to 150mm, you can cut any lumbers as thick as 100mm with out any issues.
The table is also equipped with a T slot for circular cutsΦ80~Φ45 0mm) and a foot pedal for maximum efficiency and control.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On Thursday, 2 July 2020 13:41:41 UTC+1, Thomas Prufer wrote:

ddle is

igsaw

oing

radius

e of

A jigsaw is not what I'd recommend, they often wander all over the place & require endless steering to get back on track. There are various other ways depending on exactly what you have. One possible is to saw it a little out side the line, mount the disc in a drill & hold coarse sandpaper upto it to sand it as it spins. Not too fast :)
A more suitable power tool would be better, but this approach would get you ther.e
NT
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 02/07/2020 20:21, snipped-for-privacy@gmail.com wrote:

+1. Drill "by eye" outside the line, and finish up with belt sander, disk sander, or sanding disk in angle grinder.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Yup.
Ages ago, I got a Lidl mini router kit with jigs for cutting either holes or disks. Has proved invaluable for making speaker baffles. A normal router often won't cut small enough holes - and a holesaw maybe not available in exactly the right size. It is odd in that it uses US spec (imperial) Dremel cutters, which aren't so easy to find in the UK.
--
*Speak softly and carry a cellular phone *

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Use a spare piece if ply as a base. The saw end needs to be as long as the saw base for stability. The hole end can be narrower. Start of by cutting a big hole with a spade bit in the base accommodate the saw blade. As has already been said the blade should be at a dead 90 degree angle to the hole.
To start the cut in the wood, before mounting the saw and base drill a hole on the outside of the intended radius using a spur point (for positioning) wood drill to accommodate the blade.
Use a thick blade for maximum rigidity. At that radius the size of the blade relative to the curve isn't a big issue IMO.
It goes without saying that the work will need to be firmly clamped ideally with a minimum of two clamps Maybe most important of all don't hesitate to stop the operation and reposition and re-clamp the work as many times as is necessary; making sure at all times that you won't be cutting into the support, bench or whatever.
michael adams
...
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 2/7/20 10:41 pm, Thomas Prufer wrote:

Router will make a neater job and most routers are easy to make an arm using one of the guide clamps hole.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 02/07/2020 13:41, Thomas Prufer wrote:

You want the blade on the radius. I would make a ply guide say 5" wide and as long as needed. Stick a hole through the jigsaw end with a spade bit to allow some clearance round the blade, and then pin and glue blocking to the ply to trap the base plate of the saw, with the blade poking through. Then add a screw etc for the centre pin.
A quick search turns up this which looks about right:

https://www.youtube.com/watch?vmTzIHCPBuk

Although I would not drill the start hole such that it leaves a divot out of the circle!
--
Cheers,

John.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 03/07/2020 14:29, John Rumm wrote:

That's a faff, although just a small one.
I've had to do similar with my router recently. Fortunately there were some holes already in the base plate, so I just screwed it to the supports.
As my jigsaw is an ancient B&D, I'd have no qualms about drilling a couple of holes in the baseplate if needed.
Then add a screw etc for the centre pin.

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
wrote:

Got it. And I have both hollow-ground sawblades and blades with a set, plus pendulum action, so I can adjust the kerf to suit.

Yup, though I may be using sheet metal -- depends on what's kicking around in the odds & ends corner. And there's two holes in the base, so It'll probably be just two screws to connect tot he base.

Aaaargh, and a big one, too. Though in my case, I can make a big divot, 'cause I'm notching the edge of most circles 22x44mm wide, and can put the divot in the waste:-)
(Why ever do people show a ten-minute video to show something that would be self-evident in a drawing that can be grasped in seconds?)
Thomas Prufer
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
On 03/07/2020 21:00, Thomas Prufer wrote:

I thought the thumbnail for the video told you all you needed!
--
Cheers,

John.
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.