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Sawing nails with lower blade speed?

Started by Bluejay27, November 27, 2016, 07:00:58 PM

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Bluejay27

Has anyone had any luck sawing metal with their sawmill? I have a customer who needs flooring stock sawn from every bit of reclaimed lumber he can get, which includes a lot of basically nails with wood holding them together. I'm sharing what we've learned and some ideas and just hoping someone else is as crazy as I am to saw stuff like this and offer their insights.

We've figured out that an 0.055" blade on an LT70 with HP blade guides will do 50 nails but that gets us around 200-300 bdft/blade with a lot of flex life used up. We learned that a sharp blade cuts poorly because the sharp portion causes the mill to speed up and overload the dull portion, so keeping the blade intentionally dull was key to cutting that many nails. Plus all the cuts are under 12" making waviness less of an issue.

We cut a lot of poles, so we do a rough denailing, square up four sides and split the pole in half, denailing where the middle cut goes. It's a lot easier sawing through rather than along a nail. Then we denail fully and run the halves through a resaw, although we find a nail often enough to be a headache since the resaw blade is sharp and hoping to saw faster. We're running 0.045" blades and HP guides on an LT40 head, so a little less tolerant of nails. We'd run 0.055" but the blade life would be a lot lower on the smaller blade wheels.

That's how we currently do it, but we need to get more production out of the LT70 as a breakdown saw, which is largely lost to the dull blade and having to denail on the mill.

So my "crazy" idea is that the key to cutting faster is to cut slower. Sawing at 5000 fpm means the corners of the blade teeth are being heated and worn right off, which is why wood bandsaws can't cut rebar even with the exact same blade as a metal resaw. So if I lower blade speed, I expect it can cut metal without damaging the teeth. I already tried it once just by unhooking the throttle, but it's still too fast (2700 fpm) and going slower by messing with the idle speed makes the motor run too rough to cut.

Which is where a 6:1 gear reduced Honda motor comes in. I should be able to mount it outboard of the drive side of the LT40 and just swap the drive belt over and get as low as 500 fpm. Mild steel needs lower speeds (300 fpm), but there's so much more wood that there should be a happy medium well above that. I'm hoping around 1000 fpm.

And since it'll be running as a resaw, I just set the belt speed low and babysit. I know a sharp blade will do at least 30 ft/min at 5000 fpm, and should saw proportionally as well at 6 ft/min at 1000 fpm (same units, I know it's weird).

And to take the pole breakdown load off the LT70, cutting 2 perpendicular cuts is all the resaw needs to cut the other 2 faces off, get the pole denailed out of the way of either mill, and get split into smaller pieces to make final denailing easier. Then I don't know if I should run the "clean" pieces at full speed, or plan for nails and cut at half speed or so.

I know I got really long winded, but I've run it through my head enough and need to stop before I blow a bearing in the old hamster wheel. So thank you for reading this and any opinions, insight, etc is greatly appreciated.
'98 Wood-Mizer LT40HDD42 Super, '08 LT40HDG28, '15 LT70HDD55-RW, '93 Clark GPX25 Forklift, '99 Ford F550

4x4American

The only luck I've had sawing metal with my sawmill has been with .055" blades...but on an LT40 the 19" bandwheels are too small and the blades don't last long enough.  So now I've been running .045".  That is a good thought on slowing the blade down to make it saw metal better, but, how well will that saw wood?  Have you thought about slowing the blade down using a longer pitch tooth?  Instead of 7/8" pitch maybe 1" (or longer) pitch might be better?  Something to experiment with, maybe. 


I thought WM was coming out with carbide tipped blades, not sure where they got to with that, last time I checked they were still in the R&D process.


On a side note, I like how you space out the paragraphs on a longer post, makes it easier to read.  When there is 20 sentences all in one paragraph, it makes it really difficult to read and often times I just don't read it!
Boy, back in my day..

bandmiller2

BJ, the big thing with nails is how you hit them, and your right about slowing down. Common nails hit at a right angle most of the time will be cut clean if your not cutting too fast. Nails hit almost parallel will mess up the set and usually cause a dive. After a nail is cut their will be small curls of steel just under the tip. If those curls are removed with a pocket knife most of the time cutting can continue. Drywall screws are pure poison to a band. I'am not sure about cut nails never hit one. Frank C.
A man armed with common sense is packing a big piece

Kbeitz

Collector and builder of many things.
Love machine shop work
and Wood work shop work
And now a saw mill work

sandsawmill14

i have never run a carbide tipped blade on a bandsaw but from the way it works on circle blades it will not work AT ALL  :o it would have to be some kind of high carbon bimetal  blade  :) when the carbide tip hits metal it will break the tips off and its scrap if the 1/4-9/32 carbide tips on the big mills cant handle it i dont see any way a .045-.055 blade could take it :)  but i imagine the carbide tip would be great on dirty logs or really hard stuff such as dry hickory :) 
hudson 228, lucky knuckleboom,stihl 038 064 441 magnum

never finished

  I may be missing something, but don't this leave a lot more pieces of metal to get out ? Before it goes through the shaper. I would rather pull whole nails. I think?

redprospector

Hmm. Maybe a blade made for dismantling pallets. ???
I spent today sawing some more power poles. I found a few pieces of metal dispite a metal detector. Didn't matter much how fast my blade was turning. Hit a nail, change a blade. I ruined 2 blades, but I may be able to save the other 4.
Thankfully that's behind me.
1996 Timber King B-20 with 14' extension, Morgan Mini Scragg Mill, Fastline Band Scragg Mill (project), 1973 JD 440-b skidder, 2008 Bobcat T-320 with buckets, grapple, auger, Tushogg mulching head, etc., 2006 Fecon FTX-90L with Bull Hog 74SS head, 1994 Vermeer 1250 BC Chipper. A bunch of chainsaws.

longtime lurker

Quote from: sandsawmill14 on November 28, 2016, 07:59:20 PM
i have never run a carbide tipped blade on a bandsaw but from the way it works on circle blades it will not work AT ALL  :o it would have to be some kind of high carbon bimetal  blade  :) when the carbide tip hits metal it will break the tips off and its scrap if the 1/4-9/32 carbide tips on the big mills cant handle it i dont see any way a .045-.055 blade could take it :)  but i imagine the carbide tip would be great on dirty logs or really hard stuff such as dry hickory :)

THIS!!! Tungsten carbide is very hard but quite brittle.

I don't know that you could slow it down enough and still be cost effective but in principal you're correct.

Common wisdom here has always been that you can't cut Spotted Gum with a Bandsaw. Big band, little band - same result. Well you can but not real well.
Anyhow... you can. Cut steel, or cut Spotted Gum, or marble, or granite. Its just a matter of getting the band speed right for the material at hand.
Mild steel cutting bands run at around about 150 fpm.
Spotted Gum cuts well with band speed at around 600-900 fpm.
I think a Woodmizer as standard runs at around 5500 fpm.

Only question is how do you slow it down, If you had electric drive it'd be easy with a VFD (I know a guy that mostly cuts granite and marblem but he'll cut a log for himself occasionally just by turning the dial up) but other then that you'd maybe need to look at a gearbox or a whole heap of belts and pulleys.
The quickest way to make a million dollars with a sawmill is to start with two million.

terrifictimbersllc

It's been my impression that hitting metal going fast dulls fewer teeth, but the downside of going faster is that if the blade cant cut straight after hitting metal, and  climbs or dives, then either the top or bottom board will be ruined faster, before I can stop.

So if I am cutting a lot of old beams into 1x, or other situation where ruining wood is an acceptable risk,  I will go faster than if I am resawing just one prize piece of lumber.

If I am sawing a prize beam in half or other highly valuable wood where metal is suspect, I will go slower and stop if the kerf is not straight.

If in any wood where I have already hit metal, I keep going slowly and sight the kerf on both sides as I saw, watching for and stopping if kerf straightness becomes an issue.
DJ Hoover, Terrific Timbers LLC,  Mystic CT Woodmizer Million Board Foot Club member. 2019 LT70 Super Wide 55 Yanmar,  LogRite fetching arch, WM BMS250 sharpener/BMT250 setter.  2001 F350 7.3L PSD 6 spd manual ZF 4x4 Crew Cab Long Bed

Bluejay27

A lot of the nails we hit are actually cut nails. The modern ones will ruin a blade, but these century old ones luckily aren't from good steel. I don't think carbide is an option either, it would chip, but the bimetal blades should saw a lot longer than doublehard. But either blade should work since the nails are softer than the blade steel.

To lower the blade speed, I have a 6:1 reduction Honda that will fit to the left of the drive wheel, I'm actually planning to take out the 3/8 spacer under the up/down gearbox and put a longer one in as the motor mount. I'd have to leave the blade brake off, but I could swap belts between the motors as needed. Things wouldn't go wrong as fast, so I won't have a clutch mechanism on the Honda.

And I actually tried a Lenox Palletmaster, but after that failed miserably, I learned that you want only a few teeth engaging the workpiece at a time to saw efficiently (gullet size, torque, feed pressure). I know the 1/8" nail throws a wrench in things, but the 7/8" spacing should be roughly correct. At 1000fpm blsde speed and 6ft/min feed rate, that's 190 cuts per inch or about 5 thousands. That's not much at all, even for steel.

And I think the enemy isn't hardness, it's heat. Metal takes more energy per unit to saw, meaning the blade sawing so fast puts too much power into one tooth. This makes the tip heat up and lose hardness, wearing it away because it becomes softer. Just like when I get heavy handed with a hole saw and start making sparks out of the teeth. So my options are either cooling (impractical) or lower the cutting power, which just means lowering the cutting speed. And since the tooth only makes a short duration cut in metal, I can probably saw way above metal sawing fpm without overheating the tip of the tooth.
'98 Wood-Mizer LT40HDD42 Super, '08 LT40HDG28, '15 LT70HDD55-RW, '93 Clark GPX25 Forklift, '99 Ford F550

5quarter

Theoretically, you could run the engine at idle with the blade engaged and cut all the nails you want. even at that, you may still be running too fast. the other problem is that it would take you 5-10 minutes to make a board.  :-\ Tell him to de-nail his lumber BEFORE you resaw it. if he won't do that, he's either lazy or doesn't need it badly enough.  ;)
What is this leisure time of which you speak?
Blue Harbor Refinishing

Brucer

I grind my metal lathe tools at about 5° for cutting steel. I wonder if a 4° blade would work well in this application. Just a thought.
Bruce    LT40HDG28 bandsaw
"Complex problems have simple, easy to understand wrong answers."

DMcCoy

Have you tried a blade made for cutting metal, 10-14 TPI?
You are already talking about slower blade speed and slower feed I don't see where this is much of a leap.

If your customer wants a reused look you could also take nice lumber drive nails in it, leave it out in the rain for a couple of months until it stains.

Also it's ok to say "no" to some customers or jobs.  There are a few customers I want my competition to have.


Bluejay27

It's less about saying no to the job and more about taking a job we can already do adequately and making it faster. It would take half an hour (on them) to denail and we'd still hit something, whereas we can saw off most of the outside face and leave them with fewer and easier to get at nails to pull in 5 minutes.

My brother sawing on his own gets enough done but the problem is I'm not able to help effectively and the LT40 resaw setup goes unused until we have enough denailed. So running the resaw slow (6 ft/min, 2 minutes per piece, and fed continously) would still just about double our production and I'd be free to denail between cuts, although we have at least 2 helpers provided to do most of it.
'98 Wood-Mizer LT40HDD42 Super, '08 LT40HDG28, '15 LT70HDD55-RW, '93 Clark GPX25 Forklift, '99 Ford F550

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