PDA

View Full Version : Bandsaw accuracy?



gtslabs
12-29-2003, 08:02 PM
I am wondering how accurate of a cut can be obtained on a Bandsaw.

I want to make 5.5" Diameter by 1" Aluminum discs and have been searching for material
options. I have found 1" plate 12" x 12" and 5.5" rounds by 16" long.

I would think that with a lathe I could cut down the plate to my 5.5" diameter and keep the 1"
cast dimension.

But with a round I would need a bandsaw to get my 1" thick disc. I currently have an old craftsman bench bandsaw.

I know I have not provided any tolerances here but what are my options for the best precision?
Thanks
Steve

keithorr
12-29-2003, 10:03 PM
Try getting a price on having cut disks delivered. I use a stainless distributor that makes salami cuts on round stainless bar up to 24 inches in diameter. Used for bolt flanges on piping. Saves the machine shops a lot of time and money when they are making valve bodies. Maybe your local vendor can provide a similar service.

HuFlungDung
12-29-2003, 10:13 PM
Steve,

Cutoff bandsaws can give decent results. With a good sharp 1" wide blade, and a properly squared vice, I can get cuts that are square (in that 5.5" diameter) within the waviness factor of the cut. This would mean about .020" minimum facing allowance on each side of the blank.

It sounds like you intend to use a hand fed saw. That can get mighty strenuous, mighty quickly. You'll have big biceps and pectorals when you get done, though :D

Keith made a good suggestion. When you don't have a shop full of tools of your own, it makes sense to let someone handle it who has the proper equipment. Believe me, it is no sweat for a big bandsaw to cut that size of stock, although they might be a bit more rammy, and you might need 1/8" of stock allowance to guarantee cleanup.

lsfoils
12-29-2003, 10:26 PM
Hi gtslabs,

You can get amazing accuracy out of a well tuned bandsaw. But, your bandsaw must have the ability to be tuned. Rolling guides are a must and a good bi-metal blade will be a big help. I prefer a 10 pitch or coarser blade for aluminum and use A-9 or another parifin based cutting fluid. (You can get by with some of the home brewed things you see posted on the web but you will find a big difference in the stuff thats formulated for cutting aluminum.)

So, basic points:

1. Set the guide rollers so they pinch the blade just hard enough to guide the blade but not past the point that you can still turn the *clean* bearing by hand.

2. Use an agressive pitch blade. Make sure you have it properly tensioned. I like to twang the back side of the blade and get it to play E-flat above middle C. Seriously, as you strum the blade (don't get cut doing this) listen to the sound. When it starts to make a musical sound it is just getting tight enough. Tighten a little more but not to the point that it quits making a nice tone. Thats too tight.

3. Run your saw at least 150 feet per minute. I like to get mine going 280.

For what its worth, a word about bi-metal blades. They are pricey little devils and if not treated properly can sometimes break in short order. So, set the blade on the saw and tighten it just to the point below making the musical note. Close the blade guards (!) and start the machine. (The blade will normally stay on and if it doesn't its because it wasn't quite tight enough.) Let it run for 2 or 3 minutes and then tighten it further while its running. Let it run for another few minutes. Then turn off the machine and tension as listed above. Some manufacturers pre-stressed their blades, but not all. If it isn't done the blades will crack near the teeth and the crack will quickly develope into a failure. All this according to the blade guy that comes around our shop. I think he's right as I haven't had a new blade failure since he showed me how.

I have cut square plate into rounds with my lathe and I don't care for it. You didn't mention if you were going to have a hole in it or if you were going to rough it in with a jig saw and turn it round in 2 steps with the outside jaws.

Anyway, I hope this helps. -Doug

Sorry it got so long winded...