What caused this to happen??

[Lester Sak]

I'm building a desk from African Sapele for a friend and began rough cutting the wood to size a few weeks ago. It got really cold (teens) for a week and I got sick following that, so I just got back to it this week. He bought the boards already surfaced, 3/4".

Thursday was unseasonably warm, almost 70 degrees so I went out to the shop as soon as I got home from work to continue. 2 of the boards developed a twist (they were stickered), so I'll try flattening them on my jointer.

I started ripping a 14"L x 7"W board. About halfway through, I couldn't push it anymore. I stopped the saw and realized the kerf pinched my MJ Splitter and it was being pulled out of the saws throat plate. When I tried removing the board, I saw the kerf was also pinching the blade, although not as tightly as the splitter. Luckily I was also using JessEm Clearcut tablesaw stock guides. I'm sure if I hadn't been the board would have been thrown.

What caused this to happen? Is this due to change in humidity/moisture level in the wood, or internal stress that was already there in the board? I checked the board with a moisture meter and there was over 1% difference from 1 end of the board to the other. I've never had this happen and want to avoid it going forward. The wood is stored in the shop which is not climate controlled and is heated when needed. Here's a link to a few pics.

https://goo.gl/photos/21zgmE5RqSjmLCNPA

[Jim Becker]

Is this due to change in humidity/moisture level in the wood, or internal stress that was already there in the board?


"Yes" is the most accurate answer. Unfortunately, since the lumber has already been surfaced, you don't have much to work with since correcting bows and twists is going to reduce the thickness further once you joint it flat and the plane it to even thickness.

[Jamie Buxton]

Sapele is sometimes strange stuff. I can buy six boards, have five that will behave, and one that will turn into a propeller. It seems that flatsawn is more likely to misbehave, but I've had flatsawn boards that were perfectly reasonable. Despite the strangeness, it is sure is pretty lumber.

[Frank Pratt]

Sometimes, even if properly dried, a board will have internal, opposing stresses that don't show themselves until cut in two.

[pat warner]

The very reason I only rip on the band saw.
(Un)fortunately, you've answered your own question.
Better you catch it now, rather than a year later when your project is all bent up.

[Wayne Lomman]

It doesn't matter whether using a bandsaw or a circular saw, the timber will end up the same. The bowing etc is from relieving internal stresses, not from incorrect machine usage. Lester had a problem and got out of it with everything intact. Good work. Tell you friend what happened and next time hopefully he will purchase rough saw so you have something to work with. Cheers.

[pat warner]

The band saw does not prevent the misshaping. But it does make it a lot safer.

[Art Mann]

It must be a huge amount of trouble to rip a 10 foot long plank with a band saw when the table is 24 inches square at most. Do you make an elaborate infeed and outfeed structure to accommodate? That would take up more space than a table saw.

[Wayne Lomman]

A band saw is only safer if the circular saw is correctly guarded. The 3 injuries that spring to my mind were all bandsaw inflicted, and all to do with unsafe practice. The only circular saw injury I can think of is yours truly with a drop saw. As noted elsewhere on a recent thread, I have a fair bit of workplace safety experience. Everyone has their preferred method of rip sawing. Do what you enjoy and feel comfortable with. To me, band and rip saws are different tools for different jobs with limited overlap. Cheers

[Steve Demuth]

A band saw is only safer if the circular saw is correctly guarded. The 3 injuries that spring to my mind were all bandsaw inflicted, and all to do with unsafe practice. The only circular saw injury I can think of is yours truly with a drop saw. As noted elsewhere on a recent thread, I have a fair bit of workplace safety experience. Everyone has their preferred method of rip sawing. Do what you enjoy and feel comfortable with. To me, band and rip saws are different tools for different jobs with limited overlap. Cheers

I disagree. There are plenty of ways to injure yourself, and very seriously too, with a bandsaw. But for ripping, particularly ripping rough lumber that does not yet have two flat square reference sides, or for lumber that may have reaction to being cut (which is to say, most real, noncomposite material), a properly set up bandsaw will rip through even fairly severe reaction without binding, while providing good operator protection. It won't under any circumstances that I've seen, throw wood at the operator.

For Lester's particular case of a 14" board, it's way safer, in my opinion, because a board that size with unexpected reaction on the table saw is a kickback waiting to happen.

[Al Launier]

I also agree with Pat & others that the BS is safer than a TS. Not only do you not get the potential for something sever to happen in a TS with a pinch, the kerf in a BS is about one third that of a TS (0.035" vs. 0.95"). If one is concerned about having to salvage a warped board on a jointer & planer, the narrow kerf width from a band saw could be a deciding factor. This has saved a number of small boards for me.

[Lester Sak]

Hey guys, thanks for all the feedback.

The place where the wood was purchased didn't have any rough sawn Sapele, just 3/4" and 5/4" S4. The thought was let's take a chance and save the extra $$$ on the 5/4" and if we have to buy a few extra boards due to problems like this, we'd (hopefully) still be ahead, rather than planing (and paying for) 1/2" off everything.

With regards to tablesaw vs. bandsaw, I too agree the bandsaw is inherently safer for ripping (and more economical due to the smaller kerf), but with my setup it's easier to use the tablesaw. In the past I've experienced kickback and being hit by the board a couple of times, the 2nd time hit in the abdomen breaking the skin and bruised for a couple of weeks. So safety quickly became a priority, and I can't recommend the JesseEm Clearcut tablesaw stock guides enough. That board didn't budge, but I'm sure without them it would have been airborne.

I'll be back at it today and hopefully, have minimal wood movement problems going forward. The pieces that have a twist are to be used for frame and panel assemblies (1/4" Sapele faced ply for the panels), so even if flattening them takes them down to 5/8", they will only be seen on one side so maybe still usable.

Wish me luck :)

[Wayne Lomman]

As I said above, everyone has their preferred method for rip sawing.

It also doesn't surprise me that there is a common perception that table saws are unsafe because the guarding and riving knife/spliter set ups that seems to be acceptable in USA are considered unsafe in Australia. Quite simply, I would be in jail if I allowed a table saw with a splitter to exist is a workshop and someone was injured. Cheers

[Dale Murray]

Several years ago some magazine published a few paragraphs on the merits of dropping your wood on the floor a few times before final dimension.

The idea is wood has internal stresses, and drying amplifies these stresses. As material is removed the likelihood of the stresses getting released in the form of warping increases.

Dropping the wood to a hard surface a few times will shock the stresses thus releasing them; this will allow you time to correct them before the wood is final dimension.

I have not done this personally, but I have on a few occasions stressed pieces of wood with a side load and have heard the sounds of tension being released in a board. The board was far to thick for me to break, but I could bend it very slightly.

This could be malarkey, or it could be effective. I cannot say, conclusively.

[Rod Sheridan]

351898351897351896



Hi Art, yes I made clip on in-feed and out-feed tables for my saw, each are about a metre long.

It makes handling timbers, logs or long boards much easier.

Shown are the two tables, using a log sled to make quarter sawn boards from a 20 inch diameter log, and breaking down old growth Douglas Fir beams for furniture components.

Extension fences increase the capability, and safety of using the saw.

Mine are 19mm Baltic Birch with 1/2" pipe flanges underneath and EMT legs that I've turned a wood foot with a nutsert in. This allows me to use a cap screw as the leveler for wherever in the shop the saw gets moved to. (Extensions are only on the saw when needed).

My brother has a Hammer band saw that uses their clip on aluminum extension tables, they're handy as they have a T shaped grooved in them for securing blocks, circle jigs etc.

regards, Rod.

[Steve Demuth]

Wayne,

I'm curious - are table saws significantly different in Australia from those sold in the US? I looked at a couple of web sites with .au addresses, and mostly I saw the same saws that are for sale in this country. I saw only one I didn't recognize (and which, interestingly, had the shorter rip fence you see in UK saws - a very good idea for many ripping jobs). Are there differences we don't see in the Australian versions?

[Malcolm Schweizer]

I concur with those saying sapele likes to move and has internal pressures that show up when you cut it. In regards to your situation, could it be that the board was wider at one end-perhaps due to movement- and therefore it was binding against the fence as you pushed it, and that made it push tighter against the blade? I will explain further- the board appears straight, and you start making the rip cut, but as you progress into the cut, suddenly it gets harder to push. The board could not have a flat jointed edge against the fence due to poor machining from the seller, or due to movement in the wood. All was well until you hit that slightly wider part of the board, and the board binds against the blade.

Edit- I drew a diagram on a post-it note. Very crude, but hey- it's a post-it note. Very exaggerated but in real life even 1/8" off would make a difference.
351906

[Kevin Jenness]

Yes, it is important to drop your wood on the floor to relieve internal stresses and guarantee future stability. Credit: Steve Latta, FWW. To save time you can stack your pieces on the edge of the bench and accidentally dump them all at once. I have successfully completed a number of projects using this method.

[Wayne Lomman]

Steve and all, rip saws here are more like the English ones. The main physical difference is that splitters basically do not exist. The rest of the differences with the use of guarding could be attributed to tradition. I am absolutely serious in saying that some of the practices that appear commonplace on this forum would see me in jail if injury resulted from allowing them in the work place. The laws seem draconian but the end result is that we are free to do what we want to make a profit provided that others are free to go home in one piece and nothing will save you if you deny someone that freedom.

Purely as an observation, it seems as though the USA has pursued it's own path in woodworking over time and resisted to some extent the influences of Europe and the UK. The USA appears to find European cabinet design and machinery somewhat of a novelty. Australia has been adapting to other styles forever. I would be interested to hear other views on this. I can't travel so this kind of discussion is a way to exchange culture. I spent a fair bit of time at Woomera and had great discussion with some of your compatriots on cultural differences. Cheers

[Robert Engel]

Yes, it is important to drop your wood on the floor to relieve internal stresses and guarantee future stability. Credit: Steve Latta, FWW. To save time you can stack your pieces on the edge of the bench and accidentally dump them all at once. I have successfully completed a number of projects using this method.This is quite interesting. Can you elaborate on exactly how you drop the wood and if you know why it works?

To the OP: What you're experiencing is internal stress relief, probably not moisture since the wood was probably kiln dried and surfaced.

It is quite easy to set up infeed/outfeed for the bandsaw using a couple roller stands.

Another technique that helps a bit is to rip a little over 1/2 the thickness flip the board and re-rip. This way if there is binding, the full thickness of the board is not causing it.

[Kevin Jenness]

" Can you elaborate on exactly how you drop the wood and if you know why it works?"

I was attempting to be facetious. When my parts wind up on the floor it is due to clumsiness. If the idea works it is probably because the wood that hits the floor has also been acclimatized to the shop/destination and roughed out somewhat oversize prior to final milling.