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Thread: 3 tooth rule for bandsaw blades, but what if your cutting multiple bars?

  1. #1
    Edster is offline Titanium
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    Default 3 tooth rule for bandsaw blades, but what if your cutting multiple bars?

    I was cutting 24 bars of 4" x 1/8" 6061 Aluminum today on the horizontal band saw. I was cutting the whole bundle at once so it was like cutting a 4" x 3" bar. I was talking (more like arguing) with one of the guys at the shop about the three tooth rule for bandsaw blades. He was trying to say that it didn't matter that I was cutting 24 pieces at once, what mattered was the material was only 1/8" thick and I should have minimum of three teeth in each piece of material.

    I know that the bundle won't act like a single piece of stock would, the chip will break between the individual bars. But there is still the fact that the blade is passing through 3 inches of material and there has to be enough space in the gullets of the blade for the chips. A blade with less teeth will have more room for chips. My theory is to use a blade somewhere in between what would be used for one bar 1/8" thick and one bar 3" thick. I ended up using a 6-8 tpi blade and it worked good. I have also used 4-6 tpi blades with good results on this job in the past.

    So what do you guys think? The three tooth rule seems to work good for cutting individual pieces, but what about cutting multiple bars?

  2. #2
    usmachine is offline Stainless
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    Just like when we were kids and some wise guy would ask which weighed more a ton of bricks or a ton of feathers

    Seems like you did just right to me as you don't want the gullets to fill up or the blade stops cutting.

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    LKeithR is offline Hot Rolled
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    Three teeth in a 1/8" thick piece of material? That would be an absurdly fine blade for cutting any aluminum. The three tooth rule is a guide at best but you have to be practical in applying it. For virtually all of our cutting--in a job shop where material can vary from 1/2" round to 6" square tube--we have found that a 1" x 5-8 vari-tooth blade cuts well and lasts for a reasonable length of time. If you're cutting a lot of one size of material a better matched blade may be appropriate but if you're constantly changing materials--and operators--blade changing gets old in a hurry...

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    Keith Krome is offline Stainless
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    For a stack of aluminum like that, you could use a wood band saw. I agree with the rule of thumb, but you have to take into account the material.

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    I would have cut the whole bundle as you did and wouldn't have thought twice about it. The 3 teeth rule more applies to cutting thin sheet or rod. When the work piece can fall between two teeth is when you can have a problem. The blade will want to sheer the material instead of cut and make a chip. For example, a lot of blades get trashed when someone tries to run a piece of 1/16" steel sheet on the vertical bandsaw that's equipped 4-6 tpi blade. "I'll just zip off a few pieces of shim stock real quick........."

    I gave up years ago trying to get people to change blades for the material they're cutting and focused my efforts on being able to change out a trashed blade really quickly. Part of my job is changing out blades after non machinists use the saw. It's impossible to stop the blade trashers.

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    peterve's Avatar
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    What matters a lott is what type of feed you have
    with manually downfeed your saw can sort of fall over the material with a coarse saw
    But with powerfeed the saw lowers no more as set for, so you can use a much coarser saw

    peter from holland
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  7. #7
    Ironman50 is offline Plastic
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    To answer your question, yes, it works both. Even if you’re cutting multiple bars at a time, the three tooth rule still apply. Let’s take your situation as an example. You’re first cutting individual 4”x 1/8” aluminum bars. Then you bundle all 24 pieces at once. It wouldn’t really matter. It is just like you’re cutting two aluminum bars with different dimensions. One is a 4” x 1/8” aluminum bar and the other one is a 4” x 3” aluminum bar. The only thing that will matter is the tpi of the blade that you’re going to use. A vari-tooth blade’s average tpi multiplied to the bar stock size should follow the engagement rule of a minimum of 3 teeth in the cut and a maximum of 24. The optimum number of teeth engaged in one cut is 6 – 12 teeth. The best blade to use with the aluminum bars that you’re cutting is a 2-3 tpi blade because it will yield an optimum no. of teeth engaged in one cut which is 10 teeth engaged. Plus, a 2-3 tpi blade has bigger space for the chips.

  8. #8
    Rawleigh is offline Aluminum
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    Quote Originally Posted by John Welden View Post
    I would have cut the whole bundle as you did and wouldn't have thought twice about it. The 3 teeth rule more applies to cutting thin sheet or rod. When the work piece can fall between two teeth is when you can have a problem. The blade will want to sheer the material instead of cut and make a chip. For example, a lot of blades get trashed when someone tries to run a piece of 1/16" steel sheet on the vertical bandsaw that's equipped 4-6 tpi blade. "I'll just zip off a few pieces of shim stock real quick........."

    I gave up years ago trying to get people to change blades for the material they're cutting and focused my efforts on being able to change out a trashed blade really quickly. Part of my job is changing out blades after non machinists use the saw. It's impossible to stop the blade trashers.
    Maybe a padlock on the power switch!!

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    Ironman50 is offline Plastic
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    Edster, this blog could help you with your questions: The Mathematical Calculation for Determining T.P.I. | BandSawBlogBandSawBlog .

  10. #10
    Verticut is offline Aluminum
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    If the material is firmly clamped together at the cut then I would consider it a solid and use a coarse blade.

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    Ironman50 is offline Plastic
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    The material should be firmly clamped to achieve straight cuts and not crooked ones.

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    sniper1rfa is offline Cast Iron
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    Quote Originally Posted by peterve View Post
    What matters a lott is what type of feed you have


    Agreed. The "three teeth engaged" rule is to prevent you, the terrible collection of pathetically inaccurate muscles, from jamming the part into the blade and ending up with an excessively large chip load. If you have a feed mechanism that has a set feedrate then it doesn't matter.

    If the feed mechanism has a set feed *pressure* then it does matter.

    Incidentally, i've never heard anyone say you have to have exactly 3, as if that was a magic number. Just that 2 or 1 is unacceptable. 3 teeth engaged is the minimum.

  13. #13
    david n's Avatar
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    Treat the stacked pieces as a solid. Every blade rep I've ever talked with takes the amout of material in the cross section and that gives you your material thickness. Take structural 12ga tube. One piece will destroy a 6/8 blade, but stack up 10 pieces or so(2X5), and you can cut all week long. .1" wall thickness x 2walls x 5 pieces= 1". The more you can cut at once the better. I used to work for a place that cut a few tons of 10, 12, and 14ga tube per day with 6/8 and even 4/6 pitch blades with no problems.

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    Ironman50 is offline Plastic
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    For best results, a minimum of 3 teeth engaged in one cut and a maximum of 24 should be observed. It doesn’t have to be exactly 3 and 24. The three tooth rule serves as a guideline.

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    motion guru's Avatar
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    Quote Originally Posted by John Welden View Post
    I would have cut the whole bundle as you did and wouldn't have thought twice about it. The 3 teeth rule more applies to cutting thin sheet or rod. When the work piece can fall between two teeth is when you can have a problem. The blade will want to sheer the material instead of cut and make a chip. For example, a lot of blades get trashed when someone tries to run a piece of 1/16" steel sheet on the vertical bandsaw that's equipped 4-6 tpi blade. "I'll just zip off a few pieces of shim stock real quick........."

    I gave up years ago trying to get people to change blades for the material they're cutting and focused my efforts on being able to change out a trashed blade really quickly. Part of my job is changing out blades after non machinists use the saw. It's impossible to stop the blade trashers.
    I think this is pretty funny - sounds just like our shop.

    We did a big fish bbq at our place a month or so ago and I used the bandsaw to rip a bunch of cedar and alder planks from 3/4" thick to half that so that I could cook the fish on wood planks. Filled the bandsaw with wood sawdust. When I was done, I opened up the saw to find that it hadn't been vacuumed out or chip bin emptied since the last time I was into the saw about a year ago.

    So if you are in there changing the blade . . . clean the damn saw while you are at it!!
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  16. #16
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    Likely only the gal's noticed the slight ferrous flavor to the fish.

  17. #17
    Ironman50 is offline Plastic
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    Quote Originally Posted by motion guru View Post
    I think this is pretty funny - sounds just like our shop.

    We did a big fish bbq at our place a month or so ago and I used the bandsaw to rip a bunch of cedar and alder planks from 3/4" thick to half that so that I could cook the fish on wood planks. Filled the bandsaw with wood sawdust. When I was done, I opened up the saw to find that it hadn't been vacuumed out or chip bin emptied since the last time I was into the saw about a year ago.

    So if you are in there changing the blade . . . clean the damn saw while you are at it!!


    With the saw turned off, of course.

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