Shop Doc – Tapered Out

Today’s Machining World Archives October 2008 Volume 04 Issue 10

Dear Shop Doc,

We’re using a horizontal band saw with automatic feed. Until recently we were cutting 12L14 RD material and we had a nice, straight cut. Then we changed to cutting 6061 aluminum SQ material, and we keep getting a tapered cut. What can we do to get rid of the taper when cutting the new type of material?

Tapered Out

Dear Tapered Out,

There are a few possible contributing factors related to your question. 12L14 is a relatively hard material, so if you were sawing too fast it could have led to premature dulling of your blade. So perhaps when you started sawing 6061 aluminum; the blade was already dull. To prevent premature blade life the saw operator must use their eyes and their ears.

First, you have to look at the chips. They should be the same color as they were when you started cutting. If they’re thick to the point of turning to a blue or brown color that indicates you’re overfeeding. On the other hand, if the chips are really skinny and resemble rice kernels that indicates that you’re not using enough feed pressure. This can do additional damage, as it can actually work harden the material and eventually cause premature dulling of the blade.

Second, you must listen to the cut — the harmonics should be pleasant sounding. If it’s “screaming” during the cut, that tells me that there’s too much vibration, which will also lead to premature wearing of the blade.

The other factor that’s very critical is the coolant, or cutting fluid ratio. We recommend using a water to cutting fluid ratio of 10 to 1. Use 2 quarts of cutting fluid to every 5 gallons of water. Cutting fluid has three functions in bandsaw applications. It flushes, cools, and most importantly provides lubricity (viscosity). You need a little slickness so the chip doesn’t adhere to the gullet of the blade itself. If the cutting fluid is too weak, you’ll get the flushing and the cooling action but you won’t get the lubricity needed. That can lead to chip weld along with premature dulling of the blade. When you mix the cutting fluid, always add the fluid to the water or it won’t mix properly. Just remember the acronym O-I-L: “oil in last.” It’s the same as dressing a salad. You have to pour the oil on after the vinegar; otherwise the vinegar will just slide off.

Another thing to remember is making sure the chip brush is adjusted and working properly. The chip brush itself should not be positioned any deeper than the shallowest gullet on the blade. If you position and align the chip brush too deep, the saw blade will cut the bristles and render the chip brush useless.

Hope this solves your problem,

Al Terronez
DoALL Sawing Products

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