This post was inspired by an article in “Good Old Boat” Magazine http://www.goodoldboat.com/
(Issue 43, July/Aug ‘05)
by John Spier (page 73)
“HOLE SAW TIPS”
Using a hole saw is the fastest and easiest way to create a hole up to several inches in diameter. A hole saw has three parts
- an arbor or mandrel that attaches to a standard drill,
- a pilot bit,
- and the hole saw itself.
Drill at slow speed until the hole saw has penetrated the work
. Retract the hole saw frequently, to clear waste from the hole. Doing so makes cutting more efficient, and lessens the chances of overloading the drill. If stock jams in the saw body, pry the piece free with a screwdriver.
Each hole saw is packed with a table showing recommended RPM's for each size saw cutting specific materials. Operating at higher speeds than those recommended will shorten the life of the saw, and produce very inefficient cutting.
Sufficient feed pressure to take a chip must be applied. Variables in material, work
configuration, etc. should be considered. Generally, apply 80-100 pounds per inch of hole saw diameter when sawing in metals. Insufficient feed pressure will dull tooth points prematurely. Too much pressure can destroy teeth.
serves two purposes when sawing in metals. It cools the saw and the work, reducing heat and abrasion which can shorten cutting life, and it removes chips from the kerf. An exception is cast iron, which is cut dry.
Sandwich a sponge between a couple of boards. Use the saw to cut through the sponge. Lift
the saw and remove the sponge from within, and soak the sponge plug
, cutting fluid or machine oil
. Push the sponge plug
back onto the saw, and the lubricant will seep from the sponge and lubricate the saw - keeping the saw cooler.
Pilot Drill Placement:
The point of the pilot drill must not extend beyond the teeth points more than the thickness of the material being cut. If the drill pierces the work before the saw teeth are in contact, the saw can hit the work with sufficient shock to break the saw or the teeth.
A common problem when using a hole saw is that it tends to tear out, as the saw exits on the opposite side. To prevent this from happening, begin drilling from the first side as usual, but before the saw goes all the way through, go around and finish the hole from the other side. The result is a clean hole on both sides.
Placing a "backer" board behind the hole also helps prevent tear-out, and if you are hole-sawing metal less than 1/16" thick, the backer prevents flex.
You’ll typically want to cut at a slower rpm
than seems intuitive. We think of stainless steel
as being a tougher metal, but it’s really more of a gummy (high ductility) material. Stainless steel
gets extremely hard near the drilling area as heat builds up during drilling. Slower rpm
reduces work-hardening effect caused by drilling
Cutting a large-diameter hole through a door or other thick workpiece with a hole saw can strain your wrist and the drill motor
. Using the hole saw, cut just enough to score the surface of the wood
. Next, remove the saw and bore four or five ¼-inch-diameter holes around the inside edge of the scored circle. Then continue cutting with the hole saw. The holes provide chip-clearing spaces, which keep the saw cutting cooler, cleaner, and easier with less chance of binding.
Enlarging Existing Holes: (Concentric Holes)
The best way to get an enlarged hole is to use two hole saws on one arbor. You'll need one smaller hole saw the size of the original hole, and a larger hole saw the size of the new hole.
Install the two hole saws, the small inside the large one. The small one should protrude at least a 1/2" beyond the larger one. Insert the smaller saw into the old hole, and carefully guide the saw through the hole. Keep the drill on a straight, steady course as the larger saw cuts the new hole around it.
Another way to enlarge an existing hole is to fasten a piece of 1/2-inch plywood
over (or under) the existing hole. Then bore into the plywood
and through the hole behind it. The plywood will hold the pilot bit on track until the saw starts cutting.
Smaller holes can be re-drilled (up to 1-1/4") using a “step-bit”.