So you’re on your 20th something notch of your latest tubing project and the 3rd hole saw in a row binds up, twists your arms like a pretzel, and distorts to the point you can measure the cutter’s run out with a yard stick. Hole Saws are for the birds, right? They’ll never work! Well, maybe there are a few things we can take a look at to get a little better life out of those inexpensive cutters and save your wrists from drill-induced torture.
First thing – let’s check out the brains of this operation – yes, you the operator! I’ve lost more hole saws than I care to admit by getting in a hurry or not paying close enough attention to what I’m doing. The number one killer of hole saws in my shop has been not removing the little slug that breaks off on the first half of the notch. When you pass through the first side of the tube, a little hole saw-slaying slug will break off, often inside the cutter itself. STOP! Back the hole saw up and take that piece out of the hole saw before continuing. If you don’t, more often than not, it will poke its devilish little head out of one of the vent holes in the side of the cutter and wedge itself against the tube. Game over for the saw and the use of your right hand for awhile.
Next up is drill choice and cutting speed. We don’t need anything real special to get good life out of a hole saw. A quality 1/2 inch corded drill does the job well. Preferably something on the slower end speed wise with good torque. I personally use a Milwaukee 0300-20 drill with a max speed of 850 RPM, and I don’t think I’d want anything slower, but not much faster either. When I’ve tried to run the drill at half speed or less the cutter tends to catch and bind more often and can cause it to chip off teeth. Start relatively slow, and ease the cutter into the tube, then when the teeth are engaged into the material, you can open up the drill and let the cutter do the work.
The next item on our checklist to notching nirvana is the depth of the cut. Don’t plunge the hole saw into the tube 6 inches from the end and use the notcher to cut your tube to length! I’ve done it, it’s dumb, and you’ll wear out a hole saw faster than you can imagine. A good notch depth should just barely leave the long edges of the “fish mouth” shape untouched by the hole saw. Any deeper and you’re engaging too many teeth into the material, and building too much heat, which will wear out the cutter faster than normal. If you’re notching to the proper depth, that little slug we talked about earlier will break off inside the hole saw. Don’t forget to stop and get him out! Beware at this point as you break through the first half of the tube that you are easing up on the pressure so as not to ram the hole saw into the opposite wall. This is sure to ovalize your hole saw which will also end it’s life prematurely.
Finally, if you’re heeding at least some of the wisdom from above, you should be making some good notches, and getting your money’s worth out of these $12-$15 hardware store heroes. The last items to take a look at are the hole saw itself and lubricant.
No matter what, every once in a while the cutter is going to bind up, the drill will stall, or something else will happen that puts a huge load on these thin steel constructed cutters. Some hole saws are constructed with a thin stamped sheet metal base. This thin base can distort and ruin a hole saw long before the teeth ever wear out or break off. I prefer to use hole saws that have a thick steel base plate. This more rigid design seems to be less prone to binding, and when the cutter does bind up, it’s less likely to destroy the hole saw.
A good quality cutting lubricant can also help to reduce heat in the cutter and extend blade life. WD40 and similar products are probably not the best choice for this, as they are primarily solvents, and you’ll have to use some type of weld-safe cleaner to remove the residue left behind. I prefer water based cutting lube that can be simply wiped off with a rag when finished.
While the number of notches per hole saw can vary based on a lot of factors, with a little practice you should expect to get 50+ notches in mild steel and somewhere around 20-30 in chromoly. Once you’re in-tune with your notcher, the drill, hole saws, and the proper notching procedure, you won’t cringe when it comes time to take on that next tubing project.
-Written by Christian Huffman – Inside Technical Sales