TS55 Cuts Wider in the Middle

[ElectricFeet]

I was attempting to rip down a 10" x 5' piece ... but the middle of the rip is something like 1/32" wider than either end.

I initially made my cut using the edge that was the cut [in] the store ... [then] I made another 10" rip using the factory edge.  This time it looks to be almost 1/8" wider in the middle...

My gut tells me that the material was bowed (in storage) or is bowing (while cutting), but more data is needed:

First, let me get this straight (no pun intended). You have tried to cut 2 x 10" pieces from either side of a single piece and they are both wider than the desired 10" in the middle.

Question: How wide is the remaining centre piece -- at the ends and centre? That is, the centre piece you left behind when you cut off 10" from either side.

If EITHER (1) the edges of that centre piece are parallel (it is of equal width all the way along) OR (2) the width increases uniformly from end to end, then you're cutting straight and the factory or the shop (or both) are messed up.

If on the other hand, they too are bowed, then something's happening in the cutting or the material itself is bowed.

 

[sancho57]

Ok coming in this thread late, my suggestions are

1) remove factory edge first.
2) verify you cutting technique, using 2 hands on the saw even pressure through the cut.
3) make sure you ply is supported completely under the ply. Some people use foam insulation
4) Clamp the ply make sure it isn't moving on you (prolly isn't but thought id throw it out there)

Hope tis helps

 

[GoingMyWay]

I finally got around to test the straightness of the guide rail. I may have done the testing incorrectly or what I have measured may be totally irrelevant, but nonetheless here is what I did:

The splinterguard appears to match up with the cut edge of the plywood.  It also appears to match up if I flip the guide rail upside down and place it against the cut edge.

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When I tested the back of the guide rail against the cut edge there was quite a large gap.  The back of the guide rail appeared to be flush with the factory edge of the plywood.

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I also placed a 30" Stabila level against the middle of the cut edge and there was a .009" gap.

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P.S. the plywood is bowed - I have been storing it at an angle against the wall.  I'm not sure if it was bowed when I bought it or my cut piece developed the bow from leaning against the wall for the last 2 weeks.

My gut tells me that the material was bowed (in storage) or is bowing (while cutting), but more data is needed:

First, let me get this straight (no pun intended). You have tried to cut 2 x 10" pieces from either side of a single piece and they are both wider than the desired 10" in the middle.

Question: How wide is the remaining centre piece -- at the ends and centre? That is, the centre piece you left behind when you cut off 10" from either side.

If EITHER (1) the edges of that centre piece are parallel (it is of equal width all the way along) OR (2) the width increases uniformly from end to end, then you're cutting straight and the factory or the shop (or both) are messed up.

If on the other hand, they too are bowed, then something's happening in the cutting or the material itself is bowed.

The 5'x5' piece of plywood was cut into approximately 3'x5' and 2'x5' pieces.  I actually made 1 cut from each different piece of plywood. 

The remaining large piece that I have measures approximately 25 15/16" at the top, 25 15/16" in the middle, and 25 7/8" at the top (the width did seem to be tapering as I went up).    That makes it sound like the guide rail might have been askew when I made the cut.

Would it make more sense to "start from scratch?"  I have a GRS-16 guide rail square if that might help me.

 

[lwoirhaye]

Well, plywood is not an inert material.  When cut sometimes internal stresses change and an edge can go a little banana-shaped.  For some work this is not an impediment and can generally be ignored.

I have an edgebanding press that requires quite straight cuts to do a good job, so I'm obliged to pay attention.  On long pieces of ply I want to band, I rip them a little oversized, let them move overnight if they want to and recut any edges that have gone wonky.

 

[GoingMyWay]

I'm thinking this is more operator error (incompetence) rather than any internal or external plywood movement.

 

[ElectricFeet]

If you’re clamping a long rail at both ends to a bowed piece of plywood, then things will inevitably shift during the cut.

The board looked to be bowing “up” at the edges in the photo of your first cuts. If the straight rail is sitting on top of a concave board like this, then there will some space between the rail and the board as you reach the middle of the cut. The weight of the saw (and the not inconsiderable forces it’s exerting on the board) will force either the wood to conform, or the rail to conform, or the “far” clamp may shift slightly.

I don’t think the GRS-16 will help over these distances. Measuring a large 3-4-5 Pythagorean triangle will get you squarer. But “being square” won’t solve the “being straight” problem.

A flat floor with a well-supported board would be my first choice if it’s available. Or you could try clamping the rail to the ply AND something else that’s straight undeneath — effectively sandwiching the ply flat for the cut.

Or wait another couple of week for it to bow back again  [wink]

 

[Michael Kellough]

Well, plywood is not an inert material.  When cut sometimes internal stresses change and an edge can go a little banana-shaped.  For some work this is not an impediment and can generally be ignored.

I have an edgebanding press that requires quite straight cuts to do a good job, so I'm obliged to pay attention.  On long pieces of ply I want to band, I rip them a little oversized, let them move overnight if they want to and recut any edges that have gone wonky.

Unfortunately this is necessary more often than one would expect.

 

[DynaGlide]

Bowed plywood from Hardwoods in the Rough?  : Same thing happened to me but it wasn't as nice as your 5x5 BB. The stuff I bought from Colonial Hardwoods has some leftover sitting against a wall on end and to my eye is still straight.

 

[semenza]

I have had plywood bow in the horizontal direction, not much but  a little. It has always occurred with plywood from a big box.  And also with 5 x 5 baltic birch.

Seth

 

[Michael Kellough]

Well, plywood is not an inert material.  When cut sometimes internal stresses change and an edge can go a little banana-shaped.  For some work this is not an impediment and can generally be ignored.

I have an edgebanding press that requires quite straight cuts to do a good job, so I'm obliged to pay attention.  On long pieces of ply I want to band, I rip them a little oversized, let them move overnight if they want to and recut any edges that have gone wonky.

Unfortunately this is necessary more often than one would expect.

No plywood is really flat (if that’s what you guys are talking about) compared to MDF or particle board. What bugs me and Iwoirhaye is when the core plys are stressed differently than the surface plys and when the sheet is cut the cut line is not straight. Sometimes it’s an immediate reaction sometimes it takes a while. Once made a bunch of cabinets from pre-finished maple ply (Columbian, not made in Col.) and every part had to be rough cut oversized then cut again later to get a straight edge.

 

[GoingMyWay]

If you’re clamping a long rail at both ends to a bowed piece of plywood, then things will inevitably shift during the cut.

The board looked to be bowing “up” at the edges in the photo of your first cuts. If the straight rail is sitting on top of a concave board like this, then there will some space between the rail and the board as you reach the middle of the cut. The weight of the saw (and the not inconsiderable forces it’s exerting on the board) will force either the wood to conform, or the rail to conform, or the “far” clamp may shift slightly.

I don’t think the GRS-16 will help over these distances. Measuring a large 3-4-5 Pythagorean triangle will get you squarer. But “being square” won’t solve the “being straight” problem.

A flat floor with a well-supported board would be my first choice if it’s available. Or you could try clamping the rail to the ply AND something else that’s straight undeneath — effectively sandwiching the ply flat for the cut.

Or wait another couple of week for it to bow back again  [wink]

I don't recall that the plywood was bowed when I initially got it and made my cuts a day or 2 later.

Ah yes - being square and being straight are 2 different things.  I mentioned in another post that I too frequently mixup the keep side from the offcut side.  I thought having a tracksaw would help that, but me being the "genius" that I am I still manage to mix them up occasionally.  That just shows what a terrible woodworker I am.

Bowed plywood from Hardwoods in the Rough?  : Same thing happened to me but it wasn't as nice as your 5x5 BB. The stuff I bought from Colonial Hardwoods has some leftover sitting against a wall on end and to my eye is still straight.

In fairness, I don't recall if it was bowed when I first brought it home.  I think it was pretty flat and the bow developed in the last 2 weeks when it was leaning against the wall.

I have had plywood bow in the horizontal direction, not much but  a little. It has always occurred with plywood from a big box.  And also with 5 x 5 baltic birch.

Seth

Wow.  I thought baltic birch was supposed to be the best stuff ever.  I guess even baltic birch can have problems too.  Would 4x8 baltic birch be less susceptible to movement than the 5x5?  4x8 baltic birch does seem to be harder to find.

Well, plywood is not an inert material.  When cut sometimes internal stresses change and an edge can go a little banana-shaped.  For some work this is not an impediment and can generally be ignored.

I have an edgebanding press that requires quite straight cuts to do a good job, so I'm obliged to pay attention.  On long pieces of ply I want to band, I rip them a little oversized, let them move overnight if they want to and recut any edges that have gone wonky.

Unfortunately this is necessary more often than one would expect.

No plywood is really flat (if that’s what you guys are talking about) compared to MDF or particle board. What bugs me and Iwoirhaye is when the core plys are stressed differently than the surface plys and when the sheet is cut the cut line is not straight. Sometimes it’s an immediate reaction sometimes it takes a while. Once made a bunch of cabinets from pre-finished maple ply (Columbian, not made in Col.) and every part had to be rough cut oversized then cut again later to get a straight edge.

I had no idea so much thought and planning had to be put into cutting even basic sheet goods.  Luckily I was just cutting the baltic birch for a parallel clamp rack so it really doesn't matter if the cuts were even, square, or straight.

 

[peter halle]

Hopefully you get it all worked out.

I want to compliment you on your quoting / posting talents.  I haven't even attempted that.

Peter

 

[GoingMyWay]

Thanks.

LOL.

What I severely lack in woodworking ability, I make up for in posting ability  [big grin].

It makes a little bit of sense since I do work in IT.

 

[semenza]

Wow.  I thought baltic birch was supposed to be the best stuff ever.  I guess even baltic birch can have problems too.  Would 4x8 baltic birch be less susceptible to movement than the 5x5?  4x8 baltic birch does seem to be harder to find.

No idea on the 4x8 BB.  I have never had any. I mostly put the 5x5 in to make sure people knew I really meant baltic birch no just birch veneer.  I am pretty sure there are differences even within the baltic birch "family".

Just to be clear I am talking about bending in the same plane as the plies. Not the sheet curving like a slide due to leaning against a wall. Not flatness.

Seth

 

[GoingMyWay]

Ah I see.  Thanks for clarifying that.

 

[Sparktrician]

Wow.  I thought baltic birch was supposed to be the best stuff ever.  I guess even baltic birch can have problems too.  Would 4x8 baltic birch be less susceptible to movement than the 5x5?  4x8 baltic birch does seem to be harder to find.

I've never gotten a piece of plywood of any variant that didn't need to have one long edge straightened to be used as a reference edge before being cut for use. 

And Baltic birch does seem to be harder to find.  Garnica is a very good alternative, as is ApplePly, if you can find a local vendor.