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Thread: Calculating the cutting speed through a block of material on a horizontal band saw

  1. #1
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    Default Calculating the cutting speed through a block of material on a horizontal band saw

    Hey guys,

    I was reading a thread on another board about a guy who was looking for equipment recommendations to cut a large amount of 1" long parts out of 1" 1018 round bar stock. I found the thread interesting and informative. It did bring up a question for me that I will pose here.

    Disclaimer: I am not and will not attempt to compete with the original poster for his project.

    Is there a way to calculate (estimate) the time it will take to cut through a bundle (or block) of stock with a horizontal band saw. What variables need to be taken into account. Also, is there a way to estimate blade life.

    My example is:
    My saw is your typical 7X12 1HP Chinese band saw with a geared drive, coolant and a 7/8 bimetal .75 blade that is .035 thick.

    The object to cut is:
    A bundle of 39 bars of 1" 1018 stock. The bars are arranged in a roughly triangular shape with 9 bars across the bottom and 6 rows high (bars nested). The top row is 4 bars wide.

    I found a speed & feed calculator on Sawblade.com that gave a result but it seemed awfully fast to me.

    Tim

  2. #2
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    Keep in mind that those figures are often a maximum value that takes into consideration "time is money" for a commercial shop and they want to get the stuff cut NOW and to heck with the blade cost. Also in a lot of cases it relies on really solid machines. Your 7x12 likely meets that need where my cheap 4x6 will make the blade jump off the wheels if I push it too hard.

    I really don't think that there is any way to predict the time per cut through that pyramid of steel. I think you'll have to set it up the best you can and time the first cut and then base the rest off that.

    Also figure that your feed rate WILL slow down as it cuts through to the longer engagement. With the span involved you very likely will not have enough tension in the blade to allow you to apply enough force to maintain the feed rate. If you try the blade may bend and jump off the wheels or cause the blade to flex and break sooner. So trying to calculate a time per pass based on a feed rate that ends up being a variable will be tough.

    On the longer engagement areas of the cut packing the gullets of the teeth with swarf can also lift the teeth out of contact. Or just as badly cause the tips to drag without really cutting. That does a real number on the teeth which dull rapidly. So be sure you pick a tooth pitch which will work with the feed rate such that the gullets don't fully pack up when moving through the wider portions. But that means you will need to hold back on the pressure for the peak of the pyramid of metal so you don't feed too fast and overload the few teeth that are engaged.

    All of which makes me think that running a 9 pc wide base with 6 layers might not be the best idea. It will certainly require a lower pitch blade to deal with the base layer. And that blade may not like the top layer unless you control the engagement manually and with care. What does Sawblades.com say about running through a 9" width of cut?

  3. #3
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    No chart that I have ever seen. There are too many variables involved like type of blade, tooth configuration, down feed force, type and hardness of material, shape, etc.
    Cut a bunch and you know exactly.
    Blade life.......... depends on what you cut. I cut a wide variety of materials and typically get several years out of a band. It fatigues and cracks before it gets dull.

    JL..................

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    how long? don't be making any big dinner plans

    For a cut like that, 9", you'd ideally have power downfeed, at least a 1.5" blade, 1.5 - 2 tpi, flood and 10+ hp.....that is if you want maximum time efficiency and could well be what the calculator you used assumed....hence the optimistic time.

    With your saw, gravity feed will vary with the angle, the blade isn't heavy enough to load it fully, and a blade that size that will mean there is lots of rubbing and skipping along vs cutting, so it would be a challenge to calculate.

    We do stuff all the time outside of the machine's comfort zone, so I I'm not saying the saw can't do it, just that if time is the big concern (like you have 100 cuts to make), that's not the saw for it and you might consider having the service centre cut them
    Last edited by Mcgyver; 08-12-2017 at 02:21 PM.
    .

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    BCRider, some good points. With the configuration that I described I was trying to maximize the amount I could get into my little saw. The semi triangular configuration was easier to constrain (I felt) than any other than a round bundle. I talked to a customer rep at Sawblades.com and she did not allude to any potential problems with the material configuration.

    Sawblades.com's calculator says that the cut time should be somewhere between 3 and 5 minutes per pass in the configuration I described. Does this sound reasonable?

    A few years ago (when the saw was new) I was cutting 3" round bar A36. It took approximately 5 minutes to cut a piece. There was no attempt at saw optimization as I only needed to cut about 75 pieces.

    I could use a 6X6 configuration and reduce the length of the bottom of the cut without substantially the reducing amount of pieces cut per pass.

    JoeLee, right you are sir. I asked the CSR at Sawblades.com the same question about blade life and she said the only way to tell was to try a blade and see.

    Tim

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    I'm not an expert, and only have the smaller brethren of that saw. But I'm glad to share a few thought in response to your query; What variables need to be taken into account.

    When cutting there is a point where the number of teeth that are cutting are just right for the pressure and ability to move the cuttings clear of the cut. If too many teeth are in the cut they will spread out the pressure and do more rubbing than cutting. Gullets that are too small will pack up and prevent further cutting.

    When cutting stock I normally try to set it up to cut the same cross section most of the time. That may mean that instead of putting square tube on it's side that I use a V block to put it on edge. The idea is to keep the same number of teeth in the stock so the bite is consistent.

    Your 39 bar bundle will cut more quickly at the 4 bar layer than they will at the 9 bar layer. They should also need more pressure, since at some point the teeth will be making a 9 inch wide cut with dozens of teeth spreading the load. Kind of hard to model it unless you can calculate time for each layer and add them up.

    Dan
    Measure twice. Cut once. Weld. Repeat.
    ( Welding solves many problems.)

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    Quote Originally Posted by Mcgyver View Post
    how long? don't be making any big dinner plans
    Ha, would that be a hot dog for dinner or a full blown steak with all the trimmings and wine dinner?

    danlb, great tip about blocking up the bundle so that the material width is approximately the same throughout the cut. Should improve the blade life and speed up the cut. (assuming a 6X6 bundle).

    Tim

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    Quote Originally Posted by tmc_31 View Post
    A few years ago (when the saw was new) I was cutting 3" round bar A36. It took approximately 5 minutes to cut a piece. There was no attempt at saw optimization as I only needed to cut about 75 pieces.
    I was doing something similar with a 4 inch aluminum bar. It was taking quite a while. My buddy took one look at it and said I was using the wrong blade ( a 14-10 variable pitch). I asked him what I should use, and he suggested the coarsest pitch that I had. I complained about wasting time by swapping blades, but did it anyway. The next cut took a fraction of the time. Since I had a dozen cuts to make that was a big deal.

    Dan
    Measure twice. Cut once. Weld. Repeat.
    ( Welding solves many problems.)

  9. #9
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    Quote Originally Posted by danlb View Post
    I was doing something similar with a 4 inch aluminum bar. It was taking quite a while. My buddy took one look at it and said I was using the wrong blade ( a 14-10 variable pitch). I asked him what I should use, and he suggested the coarsest pitch that I had. I complained about wasting time by swapping blades, but did it anyway. The next cut took a fraction of the time. Since I had a dozen cuts to make that was a big deal.

    Dan
    When I was cutting the 3" round A36, I believe I was using a 14-17 variable pitch blade as that was what I had on hand at the time. When I talked with the CSR at Sawblades.com she recommended a 5-8 variable pitch blade. Their calculator recommended a 3-4 tpi blade. Unfortunately that tpi was not available in a 3/4 in wide blade (it was available in a 1" wide blade. Hmm, I wonder if I could put a 1" wide blade in my saw?). I also asked her if increasing the blade pressure would decrease the cut time. She said it wouldn't as the cut time was determined by the blade speed.

    Tim

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    I would start at the 1 cubic inch per hp material removed. Should give you ballpark fiqure upper limit on this sort of sawing op.

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