Bandsaw Conversion

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Brian Rupnow

Design Engineer
Project of the Month Winner
May 23, 2008
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Barrie, Ontario, Canada
I don't know of anyone who enjoys much time on the end of a hacksaw. You can buy a self feeding pivoting horizontal bandsaw for about $500, but they leave a lot to be desired in terms of having a decent cutting table to work on. On the other hand, woodcutting bandsaws go for less than $200 in the local "buy and sell" adds. Trouble is, they commonly travel at a blade speed of 1000 foot per minute, which is fine for wood or aluminum, but far too fast to cut steel or iron with. The "ideal" speed in feet per minute for cutting steel is 100 to 150 fpm blade speed. I have a customer who has asked me to modify a bandsaw for him, and since I am just beginning the project, I thought I would post a "step by step" of how I do it. The motor commonly found on these bandsaws is 1/2 horsepower 1750 rpm. That will work fine, as we are going to gear the blade speed down, which will give us a much higher torque at the lower band wheel. The saw pictured here is a typical 14" saw, and I do not recommend going to anything with a smaller diameter wheel. The reason for that is that metal cutting blades are wider and thicker than wood cutting blades, and they don't like the tighter radius of a smaller diameter wheel. These saws commonly have an idler shaft between the motor and the lower wheel to get the speed reduced to the 1000 fpm area. I will be adding a second "jackshaft" to reduce the blade speed to about 17% of that. The current woodcutting blade is 3/8" wide by .020" thick. The new metal cutting blade will be 3/4" x 0.040". It will be a "bi-metallic" blade, and no, it won't cut curves--at least not the kind that people think of when they hear "bandsaw".

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These are the new parts I will be adding to the saw. Two bearings, two v-pulleys, one or two shaft collars, and a piece of 5/8" shaft. The large pulley shown is 8" diameter. In a perfect world, I would have opted for a 10" or even 12" diameter pulley, but due to space restrictions, this is about as large as I can go. I know it works--I modified the bandsaw I use every day about 4 years ago, and used a 6" diameter pulley on it, and it cuts steel just fine.
It seems that I will be able to fit everything into the bandsaw base as shown. Last evening I modeled the new pulleys, shafts and bearings. This morning I modeled the bandsaw base and motor and motor pulley and assembled everything together. The slots in the original motor mounting plate will serve to tension the bottom belt. The top belt may have to be tensioned by placing spacers between the pillow block bearings and the original motor mounting plate.
So, here we are, 90% finished. I have to add a couple of slots and probably a couple of tensioning adjuster screws, but other than that it is finished. You will see that I flipped the new jackshaft to the other side of the mounting plate to gain a bit of belt clearance, but other than that it is the same as the model. I have to buy a metal cutting blade on Monday, and then I will post a short video of the saw cutting steel.---Brian
Fellows--Don't rush out to convert your old wood cutting bandsaw and expect it to cut 10" billets or drill rod (even unhardened drill rod). They work very good when converted for anything aluminum---I have cut 3" thick aluminum on mine, but be prepared to stand there for a while. I have likewise cut 1" thick 1018 steel plate, and up to 1 1/2" diameter cold rolled round stock. If you really push hard on the work, then yes, you can make the belts slip. I never said that this conversion would compete one on one with a store bought metal cutting bandsaw. However, it is very cheap, reasonably easy, and great for most things a hobby machinist would get involved in. In my customers case, the saw will be dedicated to cutting 1/2" 316 s.s. tubing with a .062" thick wall.---occasionally. A-bi metal blade is an absolute must, for longevity. A standard carbon steel metal cutting blade will work, but they get dull so fast it's just not a good idea. I get four to six months out of a $50 bi-metal blade. I run my saw without coolant and don't seem to have any real problem with that. Sometimes if the saw teeth are "picking up" from cutting aluminum I give the work and blade a shot of WD40 or cutting oil. A couple of years ago I passed on a dead lawn tractor that somebody wanted to give me, and have kicked myself ever since for not taking it to salvage the transmission for my bandsaw drive.----Brian
Yesterday I finished the main components installation and test run the saw just to make sure everything went round and round with no clearance problems. It did!!! Today I make up the first belt tension adjusters for the top v-belt.
Just for fun, I took my laser tachometer out and checked the rpm of the band pulley on the saw I just converted, and on the saw I converted 4 years ago and have used almost every day since. Converting RPM to foot per minute, I found that the saw I just converted has a blade speed of 200 foot per minute. This is a result of using an 8" diameter pulley instead of a 12" diameter pulley. On my 4 year old saw, where I just used a 3 step 5" max diameter pulley, the blade speed is a whopping 278 foot per minute. My old saw cuts steel very well. It will be interesting to see the results when I buy a new blade for the newly converted saw tomorrow.---Brian
Here is the video as promised. As you can see, it cuts steel and aluminum with no problem. At 200 fpm blade speed, it cuts noticeably slower than the saw I converted 4 years ago which cuts at 278 fpm blade-speed. I think if I ever do this again, I would just go with a 5" o.d. 3 step pulley instead of the 8" pulley I used here. I mis-spokle at the end of the video, I should have said "Light years ahead of HACKSAWING".---Brian
This is a picture of the tube which my customer will be cutting, in a fixture I designed, on the bandsaw I modified. The tube is 1/2" o.d. 316 stainless steel with a .062" wall.
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