Author Topic: TS55 Cuts Wider in the Middle  (Read 3545 times)

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Offline GoingMyWay

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Re: TS55 Cuts Wider in the Middle
« Reply #30 on: September 27, 2018, 05:56 PM »
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.
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Offline Peter Halle

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Re: TS55 Cuts Wider in the Middle
« Reply #31 on: September 27, 2018, 07:08 PM »
Hopefully you get it all worked out.

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

Peter

Offline GoingMyWay

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Re: TS55 Cuts Wider in the Middle
« Reply #32 on: September 27, 2018, 07:14 PM »
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.
Inquiring Minds Want to Know

TS55, CT26, RO150, CXS, ETS 150/3, ETS EC 150/5, MFT/3, TS75, DF500, DTS400, OF1400, CT SYS

Offline SRSemenza

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Re: TS55 Cuts Wider in the Middle
« Reply #33 on: September 28, 2018, 12:21 AM »

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

Offline GoingMyWay

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Re: TS55 Cuts Wider in the Middle
« Reply #34 on: September 28, 2018, 09:41 AM »
Ah I see.  Thanks for clarifying that.
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Offline Sparktrician

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Re: TS55 Cuts Wider in the Middle
« Reply #35 on: September 28, 2018, 10:21 AM »
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. 
- Willy -

 "Remember, a chip on the shoulder is a sure sign of wood higher up." - Brigham Young