Tip for using hole saws and other large hole makers

[LCHIEN]

Today's tip for using hole saws:

Hole saws are good for big holes, more efficient than forstners because they only cut material around the rim and not the entire circle.
The tradeoff is that The hole is not as clean as you get with fortners. They're great for cutting circles for toy wheels and knobs and such where you need to retain the center piece instead of turning it to dust.

One problem with hole saws is that there's typically no exit for the cuttings. If you cut, you need raise the bit frequently and clear not only the teeth but also the partially cut kerf. If you don't do this then what happens is that the cuttings fill the area under the teeth and when full it keeps the teeth from cutting the bottom, the packed cuttings form a hard ball in the gullets between the teeth and just get very hot and burn the hole and destroy the temper of the teeth. And it takes forever to cut the hole this way.

One trick I learned is to cut a relief hole - say a 1/2" hole with a forstner or an spade bit. The relief hole must intersect the kerf of the hole saw. If you are interested in a hole as the final product, then cut the relief hole in the inside of the hole saw area, or if you want to cut a wheel, the the relief hole should be on the outside of the hole saw.

The relief hole should intersect the kerf as much as possible without cutting into the part that's important to you. This is pretty easy - hole saws usually have a big kerf.

After the relief hole is cut, then the hole saw can be used... and the cuttings under the teeth will neatly fall out of the hole saw kerf into the relief hole quite readily if you've done this correctly. You will find that the extra time to cut the relief hole is easily made up in efficiency of cutting the big hole - you may have to raise the saw only once or twice instead of nearly continuously.

There's two disadvanatges - one is that if you need a hole and a circle then one will be ruined. The other is that you will need two setups and you will need to mark where the big hole will fall accurately so you can position the relief hole effectively.

But, you will be really surprised at how well this works.

[cabinetman]

That is a good tip mentioned by a member in this thread:
http://bt3central.com/showthread.php...highlight=hole
It's good information and new members may not have been privy to that tip. Thanks for the detailed description.

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[cabinetman]

Not to hijack the thread, but adding another hole saw tip. Buy one that has the slots on the side. They may be straight or on an angle...like this one. They will permit access to being able to work loose a stuck piece after the cut. The saw may be warm after use and may have expanded slightly to give an advantage to getting the wood out. I try to discharge the waste as soon as possible.

Just a note, that whatever probe device is used not to damage the side of the saw.

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[sweensdv]

Also, keep in mind that a hole saw is primarily a carpentry tool and not a woodworking tool. For the cleanest results use a forstner bit instead of a hole saw for fine woodworking projects.

[Russianwolf]

The other is that you will need two setups and you will need to mark where the big hole will fall accurately so you can position the relief hole effectively.

Not hard at all. Use the hole saw and make a scoring cut (I usually do this in reverse so it doesn't grab and mar the face). You can then position the relief cut very accurately since the hole saws' kerf is visible.

Once the pilot bit comes through the back, I flip sides and again go in reverse to score the surface and prevent damage to the faces. Then complete the cut.

[leehljp]

In the past, I needed to make a number of 3 inch holes with smooth sides in some 3/4 thick boards. Of course this required a Forstner bit. I did the first 1/8 in with a Forstner; then drilled a pin hole through the center and reversed to the other side with the Forstner for scoring the back side surface, as Mike mentioned above. Next, I used a 2 1/2 in hole saw and cut the center. From there, with the first 1/8 inch recessed as a guide - the Forstner cut the rest with ease.

That sounds like a lot of steps, but when you need to cut about 20 three inch holes with smooth sides, the Forstner 3 inch size is slow go and soon to dull the Forstner . . . unless one has a carbide Forstner.

I could have used a 3 inch hole saw and used a good drum sander that I don't have.

[sweensdv]

In the past, I needed to make a number of 3 inch holes with smooth sides in some 3/4 thick boards. Of course this required a Forstner bit. I did the first 1/8 in with a Forstner; then drilled a pin hole through the center and reversed to the other side with the Forstner for scoring the back side surface, as Mike mentioned above. Next, I used a 2 1/2 in hole saw and cut the center. From there, with the first 1/8 inch recessed as a guide - the Forstner cut the rest with ease.

That sounds like a lot of steps, but when you need to cut about 20 three inch holes with smooth sides, the Forstner 3 inch size is slow go and soon to dull the Forstner . . . unless one has a carbide Forstner.

I could have used a 3 inch hole saw and used a good drum sander that I don't have.

That's a great tip, thanks for sharing that. I can see that in a mass production situation how that would really speed things up.

[L. D. Jeffries]

Another good sub for a hole saw is to use a "circle cutter". Does the same as the hole saw but leaves a nice smooth surface cut. With the double sided cutting bar you can cut either smooth sided holes or profiles that look like toy wheels. For one thing it is far cheaper than a big forstner bit as they are really expensive. My 2 bits worth!

[LCHIEN]

In the past, I needed to make a number of 3 inch holes with smooth sides in some 3/4 thick boards. Of course this required a Forstner bit. I did the first 1/8 in with a Forstner; then drilled a pin hole through the center and reversed to the other side with the Forstner for scoring the back side surface, as Mike mentioned above. Next, I used a 2 1/2 in hole saw and cut the center. From there, with the first 1/8 inch recessed as a guide - the Forstner cut the rest with ease.

That sounds like a lot of steps, but when you need to cut about 20 three inch holes with smooth sides, the Forstner 3 inch size is slow go and soon to dull the Forstner . . . unless one has a carbide Forstner.

I could have used a 3 inch hole saw and used a good drum sander that I don't have.

A trick for cutting real clean holes of say a 3" size when you don't have or can't spin (it takes a fair amount of power and low speed to turn a 3" forstner) is to cut a 2" forstner hole, then use a 1/4" rabetting bit and a flush trim bit to alternately make a stepped rabetted hole of 2.5" and then flush trim to 2.5", then rabbet again to 3" stepped hole, and finally to make a 3" clear hole with the flush trim bit. It really works well to make clean, clear smooth accurate holes this way. You can step up to much larger holes using rabbet bits with larger rabbet and more steps, if you plan the sizes right.

[leehljp]

A trick for cutting real clean holes of say a 3" size when you don't have or can't spin (it takes a fair amount of power and low speed to turn a 3" forstner) is to cut a 2" forstner hole, then use a 1/4" rabetting bit and a flush trim bit to alternately make a stepped rabetted hole of 2.5" and then flush trim to 2.5", then rabbet again to 3" stepped hole, and finally to make a 3" clear hole with the flush trim bit. It really works well to make clean, clear smooth accurate holes this way. You can step up to much larger holes using rabbet bits with larger rabbet and more steps, if you plan the sizes right.

That is a great idea! And as you said, it does take some planning. For the project that I referenced, the size was not critical as it was more decorative for a kids room. And I have rabbet bits an flush trim bits.


I forgot to add that on mine, I did use my radial arm DP and a fence to help in alignment.

[LCHIEN]

That is a great idea! And as you said, it does take some planning. For the project that I referenced, the size was not critical as it was more decorative for a kids room. And I have rabbet bits an flush trim bits.


I forgot to add that on mine, I did use my radial arm DP and a fence to help in alignment.

its practical to make holes up to about 4-5 inches this way.
Using bearing guided bits make several passes on each hole when you've reached the full bearing contact to make sure you leave no bumps as they'll be copied each pass.

Finally the planning - if you have a rather common Forstner set in 1/8" out to -1/8" then you can make practically any hole. The rabbet bit kit sets have different bearing sizes to make most rabbets in multiple sizes, for example, 1/2", 7/16", 3/8", 5/16", 1/4", 1/8" (MLCS #8366 kit).

the easiest way to do it know the final diameter, like 4"
pick a rabbet size (say 3/8")
So each pass will take add 3/4" (2 times 3/8" radius expansion) diameter.
The step before the last pass will be 3.25"
The 2nd to last step will be 2.5".
The 3rd to last step will be 1.75"

so you can drill a 1.75" hole, take three passes, or a 2.5" hole and take only two passes, to get to 4" final diameter.

You can also change one pass to a different rabbet depth to be able to start at any reasonable starting hole you may have a forstner for, if you have an incomplete set.

[cwsmith]

Great tips, thanks for the posts.

Regarding the post recommending a "circle cutter"... I really don't like those (with respectful apologies to LDJ). I see they have some two-point cutters and perhaps they are better, but I've never tried one.

I've seen the single, adjustable width kind in use and find them a bit "scary", as it's difficult to see the cutter and they seem to vibrate a lot as it was way off balance.

I have a Ridgid 1550 drill press and it definitely says NOT to use this kind of cutter with it. In consideration of the taper mounting of the chuck, I'd almost guarantee that the cutter would vibrate the chuck loose.

Perhaps some of the members have had good luck with "circle cutters", but I thought I should mention my perception and warning statement for my particular drill press.

CWS

[LCHIEN]

CW, I have a single-bit circle cutter I picked up somewhere, but I've never really had the gumption to use it, for reasons like you describe.

[cabinetman]

A trick for cutting real clean holes of say a 3" size when you don't have or can't spin (it takes a fair amount of power and low speed to turn a 3" forstner) is to cut a 2" forstner hole, then use a 1/4" rabetting bit and a flush trim bit to alternately make a stepped rabetted hole of 2.5" and then flush trim to 2.5", then rabbet again to 3" stepped hole, and finally to make a 3" clear hole with the flush trim bit. It really works well to make clean, clear smooth accurate holes this way. You can step up to much larger holes using rabbet bits with larger rabbet and more steps, if you plan the sizes right.

The planning for that type of an enlargement procedure does take some planning from the start. Once you get past the forstner stage, and run the first rabbet depth, it has to be high enough to accommodate the bearing of the flush trim. Then you need a landing for either the rabbet bearing and the flush trim bearing. The last run may have to be done with a flush trim with the bearing on the top. Whether you can access the backside of the subject piece may also play into the planning.

Some of the enlargement holes may not be accessible to a router, or a drill press. JMO.

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[cabinetman]

Another good sub for a hole saw is to use a "circle cutter". Does the same as the hole saw but leaves a nice smooth surface cut. With the double sided cutting bar you can cut either smooth sided holes or profiles that look like toy wheels. For one thing it is far cheaper than a big forstner bit as they are really expensive. My 2 bits worth!

+1, I agree. A good circle cutter, AKA 'fly cutter' (not a cheap one) does cut a clean hole, and if operated at slow speeds runs very smooth. Either a single or twin cutter will work.

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