So I cut a length off a full sheet of 3/4" MDF. Being too large to feed
through my table saw I used my long sawboard[1]. Normally I am just
breaking down a big sheet so I can machine it further, but this time was
actually cutting to finished size.

When I checked the cut part in the middle, I thought "that's odd, its
2-3mm too wide". Then I checked both ends, and they were spot on. So a
bit of further investigation showed that the trusty sawboard had a very
slight bend along its length! Not sure if its always been there, or for
some reason it had warped.

Anyway, to fix it I clamped it to the factory edge of the MDF sheet, and
used a router with a fence to trim the face part of the board parallel
to the edge of the MDF sheet - vutting just deep enough to take the face
edge flush to the top of the board. Then I re-cut the board edge with
the circular saw to make it match the now slightly shifted (and
straight!) fence on the board. So it works ok again now...


[1] http://wiki.diyfaq.org.uk/index.php/Sawboard


--
Cheers,

John.

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

On 2/5/2017 10:48 PM, John Rumm wrote:
So I cut a length off a full sheet of 3/4" MDF. Being too large to feed
through my table saw I used my long sawboard[1]. Normally I am just
breaking down a big sheet so I can machine it further, but this time was
actually cutting to finished size.

When I checked the cut part in the middle, I thought "that's odd, its
2-3mm too wide". Then I checked both ends, and they were spot on. So a
bit of further investigation showed that the trusty sawboard had a very
slight bend along its length! Not sure if its always been there, or for
some reason it had warped.

Anyway, to fix it I clamped it to the factory edge of the MDF sheet, and
used a router with a fence to trim the face part of the board parallel
to the edge of the MDF sheet - vutting just deep enough to take the face
edge flush to the top of the board. Then I re-cut the board edge with
the circular saw to make it match the now slightly shifted (and
straight!) fence on the board. So it works ok again now...


[1] http://wiki.diyfaq.org.uk/index.php/Sawboard


Weird! Mine (4 foot and 8 foot) are both two bits of 9 mm ply, I would
be surprised if they distorted that way. A very elegant fix though, I
will try to file that away mentally. Will check my boards when they come
back from loan too.

On 05/02/2017 23:34, newshound wrote:
On 2/5/2017 10:48 PM, John Rumm wrote:
So I cut a length off a full sheet of 3/4" MDF. Being too large to feed
through my table saw I used my long sawboard[1]. Normally I am just
breaking down a big sheet so I can machine it further, but this time was
actually cutting to finished size.

When I checked the cut part in the middle, I thought "that's odd, its
2-3mm too wide". Then I checked both ends, and they were spot on. So a
bit of further investigation showed that the trusty sawboard had a very
slight bend along its length! Not sure if its always been there, or for
some reason it had warped.

Anyway, to fix it I clamped it to the factory edge of the MDF sheet, and
used a router with a fence to trim the face part of the board parallel
to the edge of the MDF sheet - vutting just deep enough to take the face
edge flush to the top of the board. Then I re-cut the board edge with
the circular saw to make it match the now slightly shifted (and
straight!) fence on the board. So it works ok again now...


[1] http://wiki.diyfaq.org.uk/index.php/Sawboard


Weird! Mine (4 foot and 8 foot) are both two bits of 9 mm ply, I would
be surprised if they distorted that way. A very elegant fix though, I
will try to file that away mentally. Will check my boards when they come
back from loan too.

This was one made from 6mm ply, so perhaps that's part of it. Come to
think of it, I did wax it the other day...

--
Cheers,

John.

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

On 06/02/2017 00:19, John Rumm wrote:
On 05/02/2017 23:34, newshound wrote:
On 2/5/2017 10:48 PM, John Rumm wrote:
So I cut a length off a full sheet of 3/4" MDF. Being too large to feed
through my table saw I used my long sawboard[1]. Normally I am just
breaking down a big sheet so I can machine it further, but this time was
actually cutting to finished size.

When I checked the cut part in the middle, I thought "that's odd, its
2-3mm too wide". Then I checked both ends, and they were spot on. So a
bit of further investigation showed that the trusty sawboard had a very
slight bend along its length! Not sure if its always been there, or for
some reason it had warped.

Anyway, to fix it I clamped it to the factory edge of the MDF sheet, and
used a router with a fence to trim the face part of the board parallel
to the edge of the MDF sheet - vutting just deep enough to take the face
edge flush to the top of the board. Then I re-cut the board edge with
the circular saw to make it match the now slightly shifted (and
straight!) fence on the board. So it works ok again now...


[1] http://wiki.diyfaq.org.uk/index.php/Sawboard


Weird! Mine (4 foot and 8 foot) are both two bits of 9 mm ply, I would
be surprised if they distorted that way. A very elegant fix though, I
will try to file that away mentally. Will check my boards when they come
back from loan too.

This was one made from 6mm ply, so perhaps that's part of it. Come to
think of it, I did wax it the other day...

I suppose one should invest in plastic but it's so damned expensive. I
suppose narrow strips might get chucked by fabricators.

On 05/02/17 22:48, John Rumm wrote:
So I cut a length off a full sheet of 3/4" MDF. Being too large to feed
through my table saw I used my long sawboard[1]. Normally I am just
breaking down a big sheet so I can machine it further, but this time was
actually cutting to finished size.

When I checked the cut part in the middle, I thought "that's odd, its
2-3mm too wide". Then I checked both ends, and they were spot on. So a
bit of further investigation showed that the trusty sawboard had a very
slight bend along its length! Not sure if its always been there, or for
some reason it had warped.

For some reason my circular saw has has a bit of an occasional startout
wobble and taken some material out of the start and end of my aging thin
MDF sawboard.

It's a mm or so, so me using either end to match measured points on the
workpiece doesn't work out that well for accuracy. I now prefer to align
further down the sawboard against straight drawn pencil lines, where
this sawboard damage hasn't happened.

--
Adrian C

John Rumm writes:

So I cut a length off a full sheet of 3/4" MDF. Being too
large to feed through my table saw I used my long
sawboard[1]. Normally I am just breaking down a big sheet so
I can machine it further, but this time was actually cutting
to finished size.

When I checked the cut part in the middle, I thought "that's
odd, its 2-3mm too wide". Then I checked both ends, and they
were spot on. So a bit of further investigation showed that
the trusty sawboard had a very slight bend along its length!
Not sure if its always been there, or for some reason it had
warped.

This has happened with my MDF one. I noticed when I cut some
strips of ply off the long edge of a full sheet. I suspect that
when used on a full sheet, because it can only be clamped at the
ends, pushing the saw against the guide bends it a little. After
a few goes this bend sets in. I had hoped that switching to ply
for the sawboard would solve this, but your experience suggests
not.

--
Jón Fairbairn
http://www.chaos.org.uk/~jf/Stuff-I-dont-want.html (updated 2014-04-05)

On 07/02/2017 10:46, Jon Fairbairn wrote:
John Rumm writes:

So I cut a length off a full sheet of 3/4" MDF. Being too
large to feed through my table saw I used my long
sawboard[1]. Normally I am just breaking down a big sheet so
I can machine it further, but this time was actually cutting
to finished size.

When I checked the cut part in the middle, I thought "that's
odd, its 2-3mm too wide". Then I checked both ends, and they
were spot on. So a bit of further investigation showed that
the trusty sawboard had a very slight bend along its length!
Not sure if its always been there, or for some reason it had
warped.

This has happened with my MDF one. I noticed when I cut some
strips of ply off the long edge of a full sheet. I suspect that
when used on a full sheet, because it can only be clamped at the
ends, pushing the saw against the guide bends it a little. After
a few goes this bend sets in. I had hoped that switching to ply
for the sawboard would solve this, but your experience suggests
not.

Well mine was bent in the other direction - bowed against the direction
of push...

I think 6mm base board, and 9 or 12mm ply fence is probably a better
combination.


--
Cheers,

John.

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

On 2/7/2017 11:53 AM, John Rumm wrote:
On 07/02/2017 10:46, Jon Fairbairn wrote:
John Rumm writes:

So I cut a length off a full sheet of 3/4" MDF. Being too
large to feed through my table saw I used my long
sawboard[1]. Normally I am just breaking down a big sheet so
I can machine it further, but this time was actually cutting
to finished size.

When I checked the cut part in the middle, I thought "that's
odd, its 2-3mm too wide". Then I checked both ends, and they
were spot on. So a bit of further investigation showed that
the trusty sawboard had a very slight bend along its length!
Not sure if its always been there, or for some reason it had
warped.

This has happened with my MDF one. I noticed when I cut some
strips of ply off the long edge of a full sheet. I suspect that
when used on a full sheet, because it can only be clamped at the
ends, pushing the saw against the guide bends it a little. After
a few goes this bend sets in. I had hoped that switching to ply
for the sawboard would solve this, but your experience suggests
not.

Well mine was bent in the other direction - bowed against the direction
of push...

I think 6mm base board, and 9 or 12mm ply fence is probably a better
combination.


Certainly a bit easier to use with a thicker fence. I had spare 9 mm
when I made mine. You lose a bit of cut depth with a 9 mm base board,
but not a problem if you are mainly cutting sheet up to 18 mm. With 9
and 9 or 9 and 12 it is easier to screw and glue to make a very robust
board.