Hole Saw Horrors

[Rick Hubbard]

This weekend I needed to cut some 2 ½ inch holes is some ¾” MDF. My router with its nifty little circle cutting base is on loan, so I trotted up to the local hardware store and bought a Lennox hole-saw and mandrel. I assembled the unit and chucked it into my DP (set to 300 RPM) and was flabbergasted at the result. The cutting process was excruciating. The MDF got so hot it was smoking. I tried to cut as slowly as possible, but it was just an unbelievable pain to finish 4 of these holes.

What’s with this? Should I not cut MDF with a hole-saw? Surely I did not need a faster DP speed, did I? I doubt that I will ever need to use this saw again, but if I did need to, I might be out of luck it is so badly scorched!
:confused:

[Mike Heidrick]

Did you try at a faster speed like you get using a hand drill?

[David Duke]

Rick, one trick is to begin drilling the hole, after you have scribed the cut stop and drill a small (3/16") hole through just on/inside the scribe line. What this does is allow the dust to fall out preventing a "rubbing" affect, its amazing the differnece this makes.

[Doug Shepard]

I'd have just used the first one as a template to make the rest of them with and switched back to the router.

[Matt Benton]

Rick,

I do this alot. Stop drilling every once and a while and clean the buildup off of the teeth. The longer you go without doing this, the harder it will be to remove.

[Rick Hubbard]

I'd have just used the first one as a template to make the rest of them with and switched back to the router.

Yeah, that would have made good sense- I guess the thick pall of smioke in the shop must have addled my brain.

Here's the question though- is this characteritic of hole saws in general or just hole saws and MDF?

Rick

[Philip Giangarra]

Hi,

I always clean the teeth constantly (every 10 sec. or so) when I am using a hole saw. You get a much better cut, it is quicker, and you don't get any smoke. Since the "blade" is buried in a circular grove with no where for the saw dust to go, it is only natural that it will clog up and stop the cutting.

Phil Giangarra

[Jamie Buxton]

Yeah, if you're boring down, there's no place for the sawdust to go. If you can stand the workpiece up so you're boring horizontally, the dust falls out naturally.

[Mike McCann]

When I use a hole saw it is always with a hand drill. I try not to let the teeth sit flat on the board but rock it a little so about a quarter of the saw hits the wood at a time. This also prevents it from kick out the wood.

[Byron Trantham]

I think WD40 is the answer!:D

[Rick Hubbard]

Rick, one trick is to begin drilling the hole, after you have scribed the cut stop and drill a small (3/16") hole through just on/inside the scribe line. What this does is allow the dust to fall out preventing a "rubbing" affect, its amazing the differnece this makes.

Hey David-

This sounds like a terrific idea. If I ever need to use one of these contraptions again, I'll try to remember this tip.

Thanks,

Rick

[Jim O'Dell]

I experienced the same thing with MDF this weekend and two 1 1/4" holes. Cleaning off the teeth often helps. It is mostly a problem because of the MDF, but plywood can go slow sometimes too. Jim.

[Rick Hubbard]

I experienced the same thing with MDF this weekend and two 1 1/4" holes. Cleaning off the teeth often helps. It is mostly a problem because of the MDF, but plywood can go slow sometimes too. Jim.

OK Jim-

Now I know its not just me, FOR SURE. I wonder if I completely torched the hole saw? It sure did get hot! Guess I'll try soaking it in some blade cleaner and see how bad it looks afterward.

Rick

[Jim Becker]

Funny...I was just talking with the plumber who is...well, plumbing...our addition about hole saws. He's switched over to a version that uses just a single carbide tooth and they cut like butter. The problem with hole saws is friction...which causes heat...which causes the metal to lose its temper...which causes the hole saw to become, well...an ex-tool. MDF is extremely abrasive and you guessed it, it's going to cause even more friction. I prefer a fly cutter on the DP for cutting holes in just about anything over a hole saw.

[glenn bradley]

Yeah, that would have made good sense- I guess the thick pall of smioke in the shop must have addled my brain.

Here's the question though- is this characteritic of hole saws in general or just hole saws and MDF?

Rick

Its also common in oak and other easy-burn woods. The tip for drilling a relief hole just inside the edge helps a lot.

[Jeffrey Makiel]

I second the fly cutter on a drill press. Use it very slowly (~100 to 200 rpm) and touch up the cutter's edge on a grinder when dull.

-Jeff :)

[Jim Kountz]

Another vote for the fly cutter. When I was making my blast gates I used some melamine for its nice "slickness" and experienced the same thing until I went to the fly cutter. Its like others have already said, theres just no place for the dust to go.

[Brian Kent]

I hate the thought of anything cutting my fly.

I've never heard of this tool before - checked it on google and now it makes sense. What brand or source do you recommend?

[Doug Shepard]

General makes a few different versions that handle different ranges of diameters that work well. They're sold pretty much everywhere and you can get replacment cutters for them, although I've never spotted the cutters locally - just online. I've never noticed any other makes in stores. They're for DP use only though, so if you're forced to drill something with a hand drill, the hole saw is probably the way to go, or even better - a Forstner.

[Randy Denby]

I've seen the fly cutters at sears and Lowes.I bought mine 25 yrs ago and its been really handy . Just be really careful and clamp down any work. That big wing swinging in the air looks treacherous. I will not allow anyone, 'ceptin myself to use it at my shop.....not that theres been that many that wanted too.

[Jules Dominguez]

Drilling the relief hole is a good tip which I wasn't aware of. I drilled some 2 1/2" holes in white oak recently using a hole saw and the drill press, and I got by with using light pressure and raising the bit frequently to clear some of the sawdust out and let the bit cool off. I'll use the relief hole next time.

Rick, the slower the cut, the more heat builds up. The faster you can make a clean cut with a power tool, the better, in order to minimize heat buildup, which can burn the wood and "draw" the temper from steel.

[Jim Becker]

Rick, the slower the cut, the more heat builds up. The faster you can make a clean cut with a power tool, the better, in order to minimize heat buildup, which can burn the wood and "draw" the temper from steel.

True to a certain extent, but there are limits. Sometimes it's best to take a shallow bite, pull it out, let it cool and then do a little more. If the workpiece is clamped down, that shouldn't alter the quality of the hole but will help preserve the tool a little longer.

[Ed Beers]

I doubt that I will ever need to use this saw again, but if I did need to, I might be out of luck it is so badly scorched!

Quite likely the saw is toast. As others have mentioned, you must provide a way to remove the sawdust from the gullets. A small hole drilled through the work is easiest when possible. Otherwise withdraw the bit every 1/16" and blow out the dust.