Crosscutting long boards in half w/ circular saw - overthinking it again

[Scott H]

What is the best way to crosscut a long piece (~12 ft) of rough lumber in half with a circular saw?

Normally when I am cutting off smaller pieces I always keep the larger section supported by two sawhorses or a workbench and let the smaller unsupported offcut drop free. If I am at a workbench I can sometimes contrive that the keeper part is supported by 2 blocks so the offcut only drops a couple inches too.

When it gets to cutting a 12ft board into 6ft halves outside I always worry about the much heavier weight of the offcut:

• Heavier offcut = offcut might start drooping when cut is nearly done due to weight on small remaining uncut portion = possible blade pinch potential?
• Heavier offcut = more tendency for the last portion of the wood to break under weight instead of cut = splintered corner on one or both sides
• Heavier offcut = more momentum = if it drops onto pavement or concrete, much more damaged corners (can be avoided sometimes by dropping onto dirt or grass)

The simplest approach I can imagine is just to put 4 supports on the ground (say 2x4 sections), two per side of the cut, and loosely shim under any bow/twist in the board so it cannot hinge closed on the blade. (I guess you could use 4 sawhorses or 2 sawhorses with a 12ft plank underneath but that is very bulky to transport.) Is that a goofy way to do it? Any safety concerns?

I have to do this occasionally, mostly to fit things in my car for transport, but not often enough to experiment a lot.

 

[Bas]

A popular technique for cutting plywood is to use a sheet of insulation foam underneath the sheet, then cutting just deep enough to barely score the insulation. You could use a similar technique for cross-cutting a board. That way, you have support across both the pieces and no to minimal binding. It's not the most comfortable position to work in, but it's simple and bringing a sheet of foam is probably less work than a bunch of saw horses.

 

[Scott H]

I like the foam idea the more I think about it. I've seen it done for plywood. I could probably cut an 8'x4' sheet into 1'x4' sections and just stack them in the trunk, still keep some shims around if the board is really badly bowed/twisted.

 

[tvrgeek]

A cordless saw makes it all portable.

 

[Hmerkle]

The foam idea is GREAT. But, if you already have and use two saw horses, clamp one board with an "F" clamp to the saw horse and let the off-cut fall on the other saw horse.
(This is where two saw benches come in handy, the wider face makes it easier to "drop" the off-cut.)

 

[Roy G]

Or you could have 4 pieces of a 4x4.

Roy G

 

[chris_goris]

A chopsaw on a stand with outrigger support?

 

[RedBeard]

However you do it make sure the board isnt going to pinch the blade. Even on foam it could pinch and kick back if there is a bow and it’s not oriented correctly. Have the bow smiling at you, not frowning. If you have one section hanging off that will fall it won’t pinch. It’s only when the top side of the board closes on the blade. Could also use a jig saw instead of a circ. At least then You wouldn’t have to worry about kick back.

 

[Scott H]

Thanks for the suggestions everyone. I am glad to hear I wasn't that far off but there are a lot of good suggestions here.

Have the bow smiling at you, not frowning. If you have one section hanging off that will fall it won’t pinch. It’s only when the top side of the board closes on the blade.

@RedBeard Thank you for this in particular. Can you point me towards any info that explains some of the physics of why the top side will pinch but the bottom side doesn't? Does it have to do with the blade being wider front-to-back near the top of the cut or the entering/leaving teeth being farther apart near the top?

 

[FredP]

Thanks for the suggestions everyone. I am glad to hear I wasn't that far off but there are a lot of good suggestions here.



@RedBeard Thank you for this in particular. Can you point me towards any info that explains some of the physics of why the top side will pinch but the bottom side doesn't? Does it have to do with the blade being wider front-to-back near the top of the cut or the entering/leaving teeth being farther apart near the top?

The board will flex downward if not supported closing in on the rear teeth.

 

[Scott H]

The board will flex downward if not supported closing in on the rear teeth.

It seems like some rear teeth would get closed in on regardless of whether the top side of the board or the bottom side of the board is pinching, is it more a problem with the top side pinch because the rear teeth have more "downwards" motion to them at that point in their rotation so they're more likely to buck the saw up and out of the cut?

Not trying to be dense, I've just been worrying myself about pinching on the top or bottom side this whole time + now I'm trying to understand thoroughly.

 

[FredP]

It seems like some rear teeth would get closed in on regardless of whether the top side of the board or the bottom side of the board is pinching, is it more a problem with the top side pinch because the rear teeth have more "downwards" motion to them at that point in their rotation so they're more likely to buck the saw up and out of the cut?

Not trying to be dense, I've just been worrying myself about pinching on the top or bottom side this whole time + now I'm trying to understand thoroughly.

When the board flexes it will move forward due to the pushing of the circular saw. It closes in upon itself. Support the board and don't allow it to move away from you as you cut. I usually just set the good end on my foot and let the other end drop being careful not to loose any toes....

 

[RedBeard]

Blade width is the same. Circular saws cut from bottom to top not downward. As the waste side falls off it falls away from the blade. If the wood is bowed and the crown is on the top side it will potentially pinch the top side and kick back. I did a quick sketch. You can also do a search on YouTube that should give better visuals. If it were me I’d just let the waste side fall and be done. That’s what I was always taught. If you are really concerned I would do Hanks suggestion but really any of them would work. If you start cutting and the saw gets really hard to push and blade starts screaming stop and try to figure out why. Just noticed my sketch shows clockwise but basically

 

[JimD]

For me, it depends on where I am and how important the wood is. I was cutting up old 2x12s today to throw them away. I removed them from my dock months ago and just didn't bother to take them to the collection center. Value was 0. I just used my little Skil cordless circular saw and cut them where they laid on the ground. The long pieces I needed to cut were on top of smaller pieces that were on the ground. Sometimes the blade bound and sometimes it didn't. Depended on how it was supported by the other scrap.

I've also done this on wood I wanted to keep in the parking lot of the big box store. Typically for stick lumber, I would put part of it in the truck, hold the offcut and cut it off. That lets me support it and avoid the binding. On sheet goods, I don't know that there is a good way to do it in the parking lot. So I don't. I have a pickup now and before that I had a little trailer and either will carry a full sheet.

In the shop, I can move my outfeed table away from the table saw a few inches and cut hardwood to rough length in the gap between them. So something supports both sides.

 

[Scott H]

Blade width is the same. Circular saws cut from bottom to top not downward. As the waste side falls off it falls away from the blade. If the wood is bowed and the crown is on the top side it will potentially pinch the top side and kick back. I did a quick sketch. You can also do a search on YouTube that should give better visuals. If it were me I’d just let the waste side fall and be done. That’s what I was always taught. If you are really concerned I would do Hanks suggestion but really any of them would work. If you start cutting and the saw gets really hard to push and blade starts screaming stop and try to figure out why. Just noticed my sketch shows clockwise but basically

I appreciate the diagram, that is basically what I got from your original post but I think I made it more confusing with my terminology in the mean time.

I was referring to rear teeth as B (not A) and the blade width difference on the top side of the board vs the bottom side as W1 vs W2. Maybe confusing, as blade width could also be "kerf size" or "saw plate size" and rear could also mean "away from operator."



Anyway I think I got where I was twisted up, I appreciate the input everyone.

I usually just set the good end on my foot and let the other end drop being careful not to loose any toes....

I've seen framing guys do this on youtube, I don't think I'm that brave yet!

 

[pop-pop]

Two saw benches and a sharp crosscut handsaw will do this cut safely in less time than it takes to read this thread. Just sayin’.

 

[Scott H]

Two saw benches and a sharp crosscut handsaw will do this cut safely in less time than it takes to read this thread. Just sayin’.

Yeah, but that's not gonna help justify the cordless brushless circular saw I already bought last week

In all seriousness that is probably what I would do if I had just a few pieces to cut. If I have to do a lot of pieces and it's 90 degrees out and 80% humidity I might do the circular saw. I need more sawhorses too, the two I have do not fold (so they need another trip to transport by themselves) and are currently tied up holding something up in the garage anyway.

 

[pop-pop]

Yeah, but that's not gonna help justify the cordless brushless circular saw I already bought last week

These days, your saw may have been cheaper than enough SYP 2x to build the benches would have been.

 

[RedBeard]

If you’re not totally comfortable with it yet I’d suggest just get a few 2x and cut them up into a bunch of pieces. Best way to learn is through practice.

 

[Scott H]

I am pretty comfortable, I have been using a corded one for several years. Mainly just wanted to learn from others if there's a better alternative to dropping an offcut hard + maybe damaging it that is still considered safe.