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Old 14-06-2005, 12:44   #1
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Hole Saw Tips and Tricks

This post was inspired by an article in “Good Old Boat” Magazine http://www.goodoldboat.com/ (Issue 43, July/Aug ‘05)
“Concentric Holes” 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.
See:
http://www.vermontamerican.com/NR/rd...SystChoice.PDF

General:

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.

Speed:
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.
See: http://www.vermontamerican.com/NR/rd...CuttingSpd.PDF

Feed:
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.

Lubricant:
Cutting oil 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 in water, 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.

Tear-Out:
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.

Stainles Steel:
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

Large Holes:
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”.
See: http://www.vermontamerican.com/Produ...e.htm?G=120076

HTH,
Gord May
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Old 14-06-2005, 15:34   #2
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Question Timely topic

Gord, I have to drill 3 holes to install our holding tank. What type of hole saw do you recommend for drilling fibreglass?

David
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Old 14-06-2005, 16:14   #3
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I like Carbide Tipped, or Tungsten Carbide Grit Hole Saws for cutting holes in materials too hard or abrasive for standard bi-metal saws, or so thin they would strip bi-metal or chip carbide teeth.
They're good for cutting fiberglass, ceramics, hardwoods, cast iron, composites, PVC, wood, and materials that are too hard and/or abrasive for regular steel hole cutters.
Goto:
http://www.lenoxsaw.com/ctholsaw.htm
http://www.lenoxsaw.com/grthlsw.htm
http://www.milwaukeeconnect.com/weba...tRefNum=127418

HTH,
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Old 29-11-2011, 11:03   #4
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Re: Hole Saw Tips and Tricks

best advice i can give u....

DONT skimp on these. a good quality hole saw (while painful at the cash register) makes a world of difference.
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Old 29-11-2011, 17:20   #5
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Re: Hole Saw Tips and Tricks

The last time I used a hole saw, cutting 3mm plate, I found it useful to pre-drill the pilot hole. I then used a cheap piece of rod in the hole saw in place of the drill.
I did this because I was scrunched up in a corner with limited access and the chances of ruining a pilot drill were high (dont' ask me how I know!!)
Regards,
Richard.
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Old 29-11-2011, 17:45   #6
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Re: Hole Saw Tips and Tricks

The poor guy forgot the most important "TIP" for drilling through gelcoat, marine ply, headliners etc..

START THE SAW IN REVERSE!!!!!! Drill the pilot hole then grind through the surface in REVERSE. No chipping and a beautiful clean hole.

I use only Lenox hole saws. The rest last about 1/10th as long including many "big name" products in red, yellow and that funkly tealish blue color...

Also use brad point drills in fiberglass and they can also be started in reverse. While installing a battery monitor on a customers boat I remembered to take some pics..


The only reason for tape was to mark my hole center and I get holes just as clean without tape:


I then drilled a 1/4" pilot hole, the same size as my hole saws arbor drill, using a brad point drill bit (not really necessary in the waste circle but prevents skating of the bit):


Started in reverse with the brad point and once through the gelcoat I switch to forward:


Then I busted out one of my trusty Lenox hole saws and drilled through about half way in reverse before switching to forward:


Hole done, no chips and perfectly clean:


I also saved the plug to show how easy this is:




The right tools and the right technique make for easy work..
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Old 29-11-2011, 18:22   #7
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Re: Hole Saw Tips and Tricks

If you use the nice carbide abrasive hole saws made for cutting glass Gord mentioned in post #3 way back in '05, there is no "reverse".
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Old 29-11-2011, 19:00   #8
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Re: Hole Saw Tips and Tricks

great tips main man. I checked out your how to's site as well. I need a battery monitor so I read the whole really well laid out tutorial. I'll probably buy one from you and install myself..cheers
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Old 30-11-2011, 15:09   #9
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Re: Hole Saw Tips and Tricks

Safety...

I came to respect the hole saw as the most dangerous tool used on a boat.

Used with a hand drill if everything is not perfect it can move, grab, jump and then bite out chunks of human flesh.

Even in a drill press if the work piece is not held very firmly the bit can grab leaving a rotating work piece that's ready to give a nasty wack to any body parts that get in its way.

Not to mention their ability to grab hold of any loose piece of string or cloth and then wind it and anything attached at high speed into those sharp blades.

Don't ask how I know all this...
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Old 30-11-2011, 15:36   #10
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Re: Hole Saw Tips and Tricks

Quote:
Originally Posted by Boracay View Post
Safety...

I came to respect the hole saw as the most dangerous tool used on a boat.

Used with a hand drill if everything is not perfect it can move, grab, jump and then bite out chunks of human flesh.

Even in a drill press if the work piece is not held very firmly the bit can grab leaving a rotating work piece that's ready to give a nasty wack to any body parts that get in its way.

Not to mention their ability to grab hold of any loose piece of string or cloth and then wind it and anything attached at high speed into those sharp blades.

Don't ask how I know all this...
Very true. The bigger the saw, the more torque and the more danger. Obviously, a bigger more powerful drill motor is also more dangerous. One of the worst shop injuries I have seen (I've seen a great many) was done this way. My friend Bob was cutting out the portholes in the hull of Cascadia when we built her. He was using a Hole Hawg with a 6" carbide abrasive hole saw to cut out either end of each porthole with perfect radii and then connect the dots. The hull had solid blockouts around each porthole, so it was 1 1/2" - 2" thick solid carbon fiber. He was doing this from a scaffold. He managed to get a little off balance and off center on a cut and cause a bind. The drill motor spun around and cracked him in the jaw. He had a fractured jaw and lost some teeth, looked just like someone hit him in the mouth with a bat. About a year later he died of a sudden brain embolism. Could have been totally unconnected but we all always wonder...
By the way if you are using a drill press with hole saw and haven't clamped your work piece down, you will be injured. Do not rely on holding it.


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Old 10-12-2011, 12:07   #11
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Re: Hole Saw Tips and Tricks

I find the best way to enlarge a hole is to put a plug into it. I have about half a dozen through hulls that have to be moved, so I'll drive a wood plug in from outside, and flush it with the disk grinder, then mark the center and cut. I agree, cutting free hand is dangerous, you need to really pay attention to what you are doing and try to keep the saw down on all sides. I am cutting 1/8 plate, so a lubricant is required, and it makes the hole go much faster.
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Old 10-12-2011, 14:12   #12
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Re: Hole Saw Tips and Tricks

A Lenox 3 5/8 hole saw fits the BLUE SEA SYSTEMS batt switch perfectly. I used it behind the companionway ladder when installing dedicated battery circuit.
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