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

On 02/07/2020 13:41, Thomas Prufer wrote:
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?

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

On 02/07/2020 13:41, Thomas Prufer wrote:
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

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."
"Don't what?"
"Think about Gay Marriage."

Martin Brown Wrote in message:
On 02/07/2020 13:41, Thomas Prufer wrote:
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?

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.


He said cm.
--
Jimk


----Android NewsGroup Reader----
http://usenet.sinaapp.com/

The Natural Philosopher Wrote in message:
On 02/07/2020 13:41, Thomas Prufer wrote:
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

If it is not in line with the blade any wiggle will change the radius.

Personally I would cut undersize and use a rasp...


Oversize unless your rasp magically adds material...
--
Jimk


----Android NewsGroup Reader----
http://usenet.sinaapp.com/

On 02/07/2020 13:41, Thomas Prufer wrote:
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?


A holesaw will leave you a circular bit of ply:
https://www.screwfix.com/c/tools/holesaws/cat5920018
TW

In article ,
Thomas Prufer wrote:
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?


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 London SW
To e-mail, change noise into sound.

On 02/07/2020 15:23, TimW wrote:
On 02/07/2020 13:41, Thomas Prufer wrote:
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?


A holesaw will leave you a circular bit of ply:
https://www.screwfix.com/c/tools/holesaws/cat5920018
TW


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?

On Thursday, 2 July 2020 13:41:41 UTC+1, Thomas Prufer wrote:
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

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

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 accepts longer blades up to 150mm, you can cut any lumbers as thick as 100mm without any issues.

The table is also equipped with a T slot for circular cutsΦ80~Φ450��) and a foot pedal for maximum efficiency and control.

On Thursday, 2 July 2020 13:41:41 UTC+1, Thomas Prufer wrote:
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

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 outside 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

"Thomas Prufer" wrote in message
...
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

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

....

Wrote in message:
On Thursday, 2 July 2020 13:41:41 UTC+1, Thomas Prufer wrote:
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

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 outside 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


Via A&E?
A 2ft + diameter piece of plywood "mounted in a drill" spinning
whilst you hold sandpaper against the rough edge....

Riigghhtt....
--
Jimk


----Android NewsGroup Reader----
http://usenet.sinaapp.com/

On 02/07/2020 16:12, GB wrote:
On 02/07/2020 15:23, TimW wrote:
On 02/07/2020 13:41, Thomas Prufer wrote:
Given: plywood, jigsaw
wanted: circular bit of plywood, diameters 60-80 cm, small hole in
the middle is
OK.

[...]


A holesaw will leave you a circular bit of ply:
https://www.screwfix.com/c/tools/holesaws/cat5920018
TW


He wants 600-800 mm.

[...]

Oh, yeah, ta. I thought mm.

TW

On 2/7/20 10:41 pm, Thomas Prufer wrote:
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

Router will make a neater job and most routers are easy to make an arm
using one of the guide clamps hole.

On 02/07/2020 20:21, wrote:
On Thursday, 2 July 2020 13:41:41 UTC+1, Thomas Prufer wrote:
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

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 outside 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

+1. Drill "by eye" outside the line, and finish up with belt sander,
disk sander, or sanding disk in angle grinder.

In article ,
newshound wrote:
On 02/07/2020 20:21, wrote:
On Thursday, 2 July 2020 13:41:41 UTC+1, Thomas Prufer wrote:
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

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 outside 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

+1. Drill "by eye" outside the line, and finish up with belt sander,
disk sander, or sanding disk in angle grinder.

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 London SW
To e-mail, change noise into sound.

On 02/07/2020 13:41, Thomas Prufer wrote:
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?

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?v=6dTzIHCPBuk

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



--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

On 03/07/2020 14:29, John Rumm wrote:

then pin and glue
blocking to the ply to trap the base plate of the saw

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.





A quick search turns up this which looks about right:

https://www.youtube.com/watch?v=6dTzIHCPBuk

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

Yes ever tried cutting holes for speakers in cabinets, I mean takes ages.
Brian

--
----- --
This newsgroup posting comes to you directly from...
The Sofa of Brian Gaff...

Blind user, so no pictures please
Note this Signature is meaningless.!
"Martin Brown" wrote in message
...
On 02/07/2020 13:41, Thomas Prufer wrote:
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?

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

On Fri, 3 Jul 2020 14:29:23 +0100, John Rumm
wrote:

You want the blade on the radius.

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.

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.

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.

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

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

On 03/07/2020 21:00, Thomas Prufer wrote:
On Fri, 3 Jul 2020 14:29:23 +0100, John Rumm
wrote:

You want the blade on the radius.

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.

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.

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.

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

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?)

I thought the thumbnail for the video told you all you needed!


--
Cheers,

John.

/================================================== ===============\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/

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\)"
wrote:

Yes ever tried cutting holes for speakers in cabinets, I mean takes ages.
Brian


--
Cheers, Rob

In article ,
Brian Gaff \(Sofa\) wrote:
Yes ever tried cutting holes for speakers in cabinets, I mean takes ages.
Brian

See my earlier post.

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

Dave Plowman London SW
To e-mail, change noise into sound.

On Fri, 3 Jul 2020 22:31:07 +0100, John Rumm
wrote:

On 03/07/2020 21:00, Thomas Prufer wrote:
(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?)

I thought the thumbnail for the video told you all you needed!

Fast-forwarded through it, just in case:-)

I wonder why the older-but-nice Metabo pendulum-action jigsaw doesn't seem to
have the mounting holes for the circle cutter... maybe I missed them.



Thomas Prufer

On 06/07/2020 08:05, Thomas Prufer wrote:
On Fri, 3 Jul 2020 22:31:07 +0100, John Rumm
wrote:

On 03/07/2020 21:00, Thomas Prufer wrote:
(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?)

I thought the thumbnail for the video told you all you needed!

Fast-forwarded through it, just in case:-)

I wonder why the older-but-nice Metabo pendulum-action jigsaw doesn't seem to
have the mounting holes for the circle cutter... maybe I missed them.

Not all do - although some have a mount for a side fence that you can use.

On those with a pressed steel baseplate, once could drill through it and
then screw to something, but I would be less keen to do that on a
quality cast baseplate :-)


--
Cheers,

John.

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| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/