Simple Set-- Kerf and Shrink

widetrackman · September 09, 2021, 03:23:06 AM

I am not sure SS input drops include for the blade kerf ( could not find in WM manual but may have overlooked) I have only been adding 1/16 shrink only on bug kill pine and the dimension lumber is a little undersize. I think the kerf for the 747 .045 blades I have is around .095 but not sure. Sooo my question is if I do need to add the kerf, do I add 1/16 or 1/8. A 1/8 would make me about .032 proud, 1/16 would be undersize .032 if shrink was 1/16 ???. Probably makes no difference, however what would be prefered if I do in fact need to input the kerf? Sorry to ask dumb newbie questions but you guys are my life-line as Me and the old Gal are by ourselfs and don't know anyone to ask locally. The Forestry Forum is absolutely the best!!!!

WV Sawmiller · September 09, 2021, 06:15:18 AM

SS drops exactly what is displayed on the screen every time. The quarterscale on the mast of your mill allows for kerf but not SS.

I use .042 blades and allow 1/8" for kerf and have been well pleased with that. Once that is determined disregard SS and just determine how much you want to oversize your boards to allow for shrinkage, set and saw accordingly. I'd suggest you take a few boards you sawed on a known thickness and check them after they are dried and see the difference. I'd use several as I am pretty sure there are slight variances the closer or further from the pith you move. I could be wrong about that but it would be easy to check.

I have made me a cheat sheet for all the common lumber I saw and when I get to the 4th face I set on my nearest mark for the lumber I am sawing and then I end on my mark on the bottom board every time saving me one cut per log.

John S · September 09, 2021, 07:24:13 AM

As WV said, SS does not compensate for kerf. I used to add 1/8 inch and use the sliding scale to hit the target. I started using cheat sheets but my WM dealer suggested using the sliding scale, much more efficient, at least for me.

fluidpowerpro · September 09, 2021, 12:25:06 PM

John S. where can one get his hands on this "sliding scale". I assume its used to estimate shrinkage based on board thickness?

WDH · September 09, 2021, 12:44:34 PM

Yes, you have to add 1/8" for kerf. If you drop 1 1/4" on simple set, the board produced will be 1 1/8" thick.

widetrackman · September 09, 2021, 02:53:56 PM

Quote from: WDH on September 09, 2021, 12:44:34 PM
Yes, you have to add 1/8" for kerf. If you drop 1 1/4" on simple set, the board produced will be 1 1/8" thick.

Thanks much, that's what I wasn't doing. BTW as to shrink generally, does 1/16 for bug kill pine and 1/8 for green pine sound right.

Magicman · September 09, 2021, 04:01:31 PM

There are items other than whether it was a live standing tree or a beetle killed tree that can cause a variance in the amount of shrinkage. Whether the lumber was flat sawn, rift sawn, or quarter sawn can affect the individual boards amount of shrinkage. That being said, I saw framing lumber to my own dimensions that have proven as being reliable. I normally allow 1/8" over on widths up to 8" and 1/4" for 10" and 12" widths. Even then it is not "chiseled in stone" what the widths will be because a customer might want a full 4, 6, 8, 10, or 12" widths. The key is being consistent with a customer's cut list.

Virtually all of the framing lumber that I saw is 1 9/16" thick.

WDH · September 09, 2021, 07:11:58 PM

Depends on if you will use the lumber rough or if you will plane and finish the boards S4S after drying. For pine 1/4" over is generally enough to yield a finish planed board at 3/4" finished thickness. So sawing rough at a full 1" thick will generally give you a 3/4 " finished board. This assumes the lumber has been dried.

If you are sawing framing lumber that will be only air dried and used rough without planing, Magicman's 1 9/16" thickness will air dry to 1 1/2" thick and match up with store bought framing.

For hardwood that will be kiln dried and used for interior paneling, flooring, or furniture, the Industry standard is to saw an extra 1/8" over so green hardwood lumber at 4/4 would be sawn at 1 1/8" thick, 8/4 at 2 1/8", etc.

I saw beetle killed pine and green pine the same. You will be surprised how wet beetle killed pine logs are. They do not dry out as much as people think that they do in log form.

As to width, the shrinkage in width is a function of the amount of drying, i.e. if the lumber is only air dried or kiln dried. The wider the green board the more of that board will be lost to shrinkage. It is also important to know if the boards will be used rough or surfaced all 4 sides. Obviously if just used rough, you do not need to add as much for shrinkage loss as you would for kiln dried and surfaced 4 sides (S4S).