band saw speed for metal?

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  1. pishta

    pishta I know I'm right....

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    Its very low compared to wood, ie 250-300 FPM when wood is 2800 (stock speed on a Craftsman 12" wood) I've cut 1/8 at 2044 FPM with an 18 tpi bi-metal cobalt blade but was curious why metal takes such slow speed. Does the faster speed just make the teeth bounce off the metal like trying to use a 3/4 holesaw at 1600 RPM? Does the faster blade speed work harden the metal on front of it..I found It would stop cutting sometimes unless I really pushed it past the point and laid into it. Speed reducing a bandsaw down to <300 would involve 2 10" to 2" pulleys in series using a 3500 RPM motor (stock motor was anemic 1/2 horse 1750 RPM) Now I have a 2HP 3500 RPM monster under there.
     
  2. Hyper_pak

    Hyper_pak Old School Chrysler Fan

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    I have having problems also with my Craftsman. I bought a metal blade but have no way to slow mine done without a lot of work. First cuts were as you said, had to push. I was told it hurts the blade at too much speed and then your done. I picture a hack saw, sloooow cut speed. I think I am going to buy a cut off blade and put it in my miter saw to cut header tubing.
     
  3. abdywgn

    abdywgn dismantler

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    rheostat to control speed?
    I have a "table" that mounts a hand held band saw...just need the band saw. The table comes from a Jeep enthusiast out west.
     
  4. pishta

    pishta I know I'm right....

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    Cut header tubing with a chop saw and a metal disk, gets straight cuts every time and is fast. You want straight cuts so when you butt weld, there is no gaps. Ill post up my Craftsman gear arrangement when I get something going.
     
  5. pishta

    pishta I know I'm right....

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    no, wont work as its an A/C induction motor. 3 phase can be changed, single phase not so much without killing torque. changing it to DC would work but finding a beefy 1HP DC motor would be $$$ as well as the inverter needed to run it. treadmill motor/Newer washing machine motor with its speed control would be awesome.
     
    Last edited: Jul 12, 2020
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    • RedFish

      RedFish Well-Known Member

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      Wood is porous. Doesn't generate or retain nearly as much heat as solid material like metal. Steel will expand and pinch the chips and the blade. You'll cut steel faster with coolant.
      It varies with what type of metal too. I worked at a shop where we made thrust washers for aircraft landing gear actuators. Material was called aluminum nickle bronze. We had to ask how to saw the stuff. Set up like steel, coolant on, blade just sat there, hardly scarred it. The right tpi, blade speed and pressure, with coolant off got it done. every aspect of machining this stuff was different from anything we had ran before.
       
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      • krazykuda

        krazykuda Well-Known Member FABO Gold Member How-To Section Editor

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        Metal has a higher friction than wood which can heat up the blade more and make it dull, so the slower speed helps keep the blade from overheating and loosing sharpness....
         
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        • AJ/FormS

          AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s

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          Just like drilling with ever larger bits, the tip-speed has to be reduced
           
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          • Ager

            Ager 72 Demon 340

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            Best speed for cutting steel can be 180 - 250 using a 18 - 20 tooth blade.
            Cutting at high speeds causes the blade to chip teeth (shock vibration)
            I'm a machinist :)
             
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            • 67Dart273

              67Dart273 FABO Gold Member FABO Gold Member

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              Other than jackshaft and more pulleys I got nuttin. Any high torque output electrical speed reduction for a single phas motor is going to be expensive, and might not be that efficient. Some motors might not work at all without problems.

              An example is, "when I was a kid" and first got into amateur radio, there was still a fair amount of aircraft 400hz AC stuff around. You can NOT use those items on 60hz ac, the core structure just won't hack it. They heat up and die. I would imagine the same thing would happen to a 60hz motor operated way below design frequency
               
            • damraider

              damraider FABO Gold Member FABO Gold Member

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              Just look for a Delta Rockwell 14” wood/metal saw. They have an internal 20-1 reduction gear. Can usually find them for around $500.
               
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              • brian6pac

                brian6pac Well-Known Member

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                You just need a power inverter variable frequency drive. I got mine of ebay and it works great. I put it on my milling machine that was 3 phase, this unit is under $100 is programmable variable speed, very nice unit.

                1.5KW 3HP VFD 8A 220V SINGLE PHASE SPEED VARIABLE FREQUENCY DRIVE INVERTER | eBay
                 
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                • pishta

                  pishta I know I'm right....

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                  C'mon...none of our consumer shop tools are 3 phase 220.
                   
                • brian6pac

                  brian6pac Well-Known Member

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                • brian6pac

                  brian6pac Well-Known Member

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                • pishta

                  pishta I know I'm right....

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                  5. Input phase: 1 phase or 3 phase
                  6. Output phase: 3 phase

                  white model said the same:
                  Suitable motor type: for
                  3-phase Motor

                  So...you still need a 3 phase motor? Not sure if I'm reading that right...
                   
                  Last edited: Jul 12, 2020
                • pishta

                  pishta I know I'm right....

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                  Well, I stumbled upon a complete treadmill 5 miles away for $60 so I jumped on it (gear box or step down pulleys would cost that much for the original AC motors) . I got a working treadmill but I gutted it just for the 2.5HP DC motor, PWM speed control and controller board. Not as complicated as I thought it was going to be..just a DC motor running a belt to a roller, and the electronics to supply the DC and the PWM. As I did the math, the motor will go from 1mph to 10 mph...that computes to about 550 to 5500 RPM before the 4:1 pulley setup. I plan to use the flywheeled 1.5" drive to a 8" pulley for a 8:1 reduction then onto the 12" wheels. It uses a 5 rib belt and I have a crank pulley from a Chevy truck that may be the same pitch. That would be a stroke of luck but Im well on my way to a fully controllable band saw as well as a drill press if I can adapt the motor to that as well.
                   
                • RustyRatRod

                  RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                  Sure you do. Get a foot control like for a dremel too. Done.
                   
                • pishta

                  pishta I know I'm right....

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                  induction motor can't use a foot control like a brushed motor.

                  Here's the guts of the treadmill. That flywheel weighs about 10 lbs.

                  20200712_165621.jpg 20200712_180527.jpg 20200712_173634.jpg
                   
                  Last edited: Jul 12, 2020
                • RustyRatRod

                  RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                • pishta

                  pishta I know I'm right....

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                  Try it. I think it may work to a point but the motor will stall out or buzz and get hot or something weird. They make fan controls but those brushless motors are 1/15 HP.
                   
                • RustyRatRod

                  RustyRatRod I was born on a Monday. Not last Monday. FABO Gold Member

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                  I have an old Rockwell drill press I can try it on.
                   
                • pishta

                  pishta I know I'm right....

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                  here is pretty much what I ended up with. Turns out DC motors are not that expensive after all? If I can get away with using a DIY controller, I may be able to sell the stock controller board and recoup some money. Seems a $2.50 bridge rectifier can give you 115V DC to the motor.
                   
                • nevjr

                  nevjr Well-Known Member

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                  few important points:
                  all materials have an ideal cutting speed range usually measured in surface feet per minute. in your case, the blade is probably high speed steel and the material is mild steel? google " mild steel HSS SFM" and see what comes up. I get 10-125 sfm. this means that your 12" wheel on the band saw needs to spin in the neighbourhood of 40 RPM. this sounds reasonable, as thats the RPM of the metal cutting bandsaw at my local makerspace.
                  next, each cutting tool has a feed rate. in the case of a drill bit, it is very high. in the case of a band saw it is very low. an ideal situation is to have 3-5 teeth of the saw engaged in the cut at any given time. lower than this and the blade will skip and bounce, then it will tear off teeth and then the blade is not long for this world. more than this and the blade will clog. the gullet between the teeth is where the chips go as the saw cuts. if its fine toothed in a long cut, the gullet fills up with cuttings then it is just adding drag while not cutting until it leaves the work piece and can be cleared. this also kills blades. the same goes for holesaws. most people ram the hole saw through and after the first 1/8th of an inch the saw just burns and overheats. you have to drill a few revolutions, lift the hole saw out to clear then repeat until you get through.

                  this also means that thicker material needs coarser blades. a 1" bar needs 3-5 tpi, a tube with 1/4" wall needs ~10 tpi
                   
                • nevjr

                  nevjr Well-Known Member

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                  oh yeah, as you noticed, most 120v motors are actually universal motors and run happily of 115v DC
                  they can also be speed controlled by a PWM circuit and a big mosfet
                   
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