So, I've destroyed two router bits.. help!

[fjhuerta]

Router? Check.
Jasper jig? Check.
Perfect circles? Check.
Broken router bits? Check!

I've broken two bits so far. Does it have to do with the depth I used with the plunge router? I used a 3/8" depth. Is it far too much?

[eyekode]

3/8" is a little deep. I probably have gone this deep before with a 1/4" bit, but usually I do more than 2 passes to get through 3/4". I probably do about 1/4" a time. And have never broken a bit...

I have used MLCS's 1/2" katana plunge and 1/4" whiteside spiral up cut. Thankfully never had problems with broken bits. How are they breaking anyway? Chips on the cutters? Shaft broken?

[cjd]

1/4 at a time, yup. Take it easy. Probably overheating the bit and binding it.

Only ever broke a flush-trim bit, and that because it got hot and the bearing self-destructed. 1/4" shank. I only use 1/2" shank now for that kind of thing.

C

[Paul H]

I agree using a 1/2" bit wherever possible.

My rule of thumb is 1/4" max cut depth, and I always cut the last 1/16" with a last pass to provide a smooth final cut.

[Cataclysm]

I am not saying it's smart to do, but if I have a ton of holes to batch cut in 3/4" mdf, I just grab the big 3.25hp Makita plunge router with a 1/2" carbide spiral cutting bit and blow through in a single pass. Honestly, it creates little event; no chatter, just need a good even feed matched to the correct spindle speed, and a good way to evacuate the dust so it doesn't clog or burn the bit.

I would wager the issue lies in either the cutting speed, bits not being tough enough, too small of a shank, or excess clogging of the cutter.

[cjd]

1/2 inch bit can take 4x the pressure.

[Lurkalot]

Broken Router Bits

As a younger man, I was in the wood and metal working cutting tool business for 20 odd years.

If you are using a 1/4" shank bit, I would limit the cut depth to 3/16" or so per pass. Even with 1/2" shank bits, which I use extensively in larger routers, I normally keep the depth of cut to 1/4" or so per pass. The pitch of the router motor is a good indicator of how hard the router-and the router bit are working. By limiting the depth of cut, you will extend the life of your power tools and cutting tools, and it does not add a lot of extra time to the job either...

[---k---]

You didn't say, but I'm guessing that this is with an spiral upcut bit. I broke a pair of upcut bits from MCLS. I don't know why or how. But, I bought some Bosch ones from the local Lowes, and haven't had any problems. They are worlds better. I use MCLS bits for almost everything else, and never a problem. Don't know. Maybe I was doing something wrong. But, I like the Bosch spiral bits. And, they are cheap.

[Face]

No wonder I'm going through so many bits! A 3/4" cut is a little much for a 1/4" bit eh?

[John_E_Janowitz]

I will typically do a total of 4 passes on 3/4" mdf. My Porter cable router has a depth stop so i set the bit flush with the surface of the mdf then set the stop. I turn the dial to make the first cut at 1/4", second cut at 1/2" and then a third cut at just under 3/4". I leave a thin layer on that last pass. Then I go around with a 4th pass but pull the router up, move over about 3/4" then plunge back down. I do this 4 times to leave 4 small tabs that can be cut out easily with a knife. This holds the piece from dropping in and prevents the bit from gouging the side if the piece does drop. It also goes quite fast. On a 15" diameter hole you are spending maybe 10seconds per pass so the whole thing is done in less than a minute and the small passes don't wear on a bit badly either.

John

[jbateman]

I wonder if it has anything to do with direction of cut? I always go clockwise for circles cutouts, but never tried it the other way to see what would happen.

It also bugs me that cutting 1/4" at a time means you're only using the end of the bit to do all of the work.

[eyekode]

I will typically do a total of 4 passes on 3/4" mdf. My Porter cable router has a depth stop so i set the bit flush with the surface of the mdf then set the stop. I turn the dial to make the first cut at 1/4", second cut at 1/2" and then a third cut at just under 3/4". I leave a thin layer on that last pass. Then I go around with a 4th pass but pull the router up, move over about 3/4" then plunge back down. I do this 4 times to leave 4 small tabs that can be cut out easily with a knife. This holds the piece from dropping in and prevents the bit from gouging the side if the piece does drop. It also goes quite fast. On a 15" diameter hole you are spending maybe 10seconds per pass so the whole thing is done in less than a minute and the small passes don't wear on a bit badly either.

John

John,
I like this idea. It is just like you would program a CNC machine. I typically cut till there is ~1mm or less then use a chisel but I will use your technique next time.
Thanks!
Salem

[David_D]

In order to generate that much heat to where the bit becomes brittle & snaps. Those cutters must have been screaming in pain. The first rule to using any type of cutting tool is not to force the cut. Allow the tool to do the work. This is all a balance between cutting depth & feed rate.
It kills be everytime I get something cut at Home Depot and the kid on the panel saw is pushing the blade through the panel as fast as he can muster. Then they wonder why they're changing blades every two days and saw motors each month.

[ibilisi]

Do you happen to have a variable speed router? If so, I would check the rpm that you are using. You could be building up too much heat and snapping bits. When I switched from my Ryobi to my Bosch I snapped two bits before realizing that the rpms were too high for the bit. Once I backed off the rpms no more breakage and still smooth cuts.

Just a thought.

[fjhuerta]

3/8" is a little deep. I probably have gone this deep before with a 1/4" bit, but usually I do more than 2 passes to get through 3/4". I probably do about 1/4" a time. And have never broken a bit...

I have used MLCS's 1/2" katana plunge and 1/4" whiteside spiral up cut. Thankfully never had problems with broken bits. How are they breaking anyway? Chips on the cutters? Shaft broken?

The shaft is broken.

Both tips broke the same way. As I was expanding the circle cut I was doing, I felt as if the router pulled to one side. The wood was "bitten" on the edges where the cut was made, and the bit looked a bit burnt where it broke.

[fjhuerta]

You didn't say, but I'm guessing that this is with an spiral upcut bit. I broke a pair of upcut bits from MCLS. I don't know why or how. But, I bought some Bosch ones from the local Lowes, and haven't had any problems. They are worlds better. I use MCLS bits for almost everything else, and never a problem. Don't know. Maybe I was doing something wrong. But, I like the Bosch spiral bits. And, they are cheap.

I bought a "double flute up" and a "2 flute down" from Amazon (I really don't have a clue as to what the difference is, and perhaps that's part of the problem). The bits are from Freud.

[fjhuerta]

Do you happen to have a variable speed router? If so, I would check the rpm that you are using. You could be building up too much heat and snapping bits. When I switched from my Ryobi to my Bosch I snapped two bits before realizing that the rpms were too high for the bit. Once I backed off the rpms no more breakage and still smooth cuts.

Just a thought.

Thanks... I do have a Ryobi, but I don't think it has a variable speed setting. At least I don't remember reading about that in the manual. I need to check, though.

Off I go to buy a couple more bits today. :T

[Cataclysm]

I bought a "double flute up" and a "2 flute down" from Amazon (I really don't have a clue as to what the difference is, and perhaps that's part of the problem). The bits are from Freud.

The flutes have opposite helix's to them (if they're spiral type cutters).

-an "up" cutter shears in such a way that it pulls all the chips up and out of the hole. Tends to lift grain and cause chipping, but they're ideally suited to doing plunge cuts, mortises, stop dados, or really any heavy type of work where you need good chip evacuation as well as a cutter, that by nature, will keep the router pulled down against the work surface.

-"down" cutters work in the opposite manner. They're ideal for cleaning up the edges of veneers, or making through-holes in thin substraits that you can't afford to have pull up, or blister. They really aren't ideal for plunge cuts with a router.

[CraigJ]

I wonder if it has anything to do with direction of cut? I always go clockwise for circles cutouts, but never tried it the other way to see what would happen.

Is there a "correct" direction? I've had good luck cutting circle holes with 1/2" carbide up-spiral bit. I move the router counter clockwise, lowering the depth 1/4" at a time. I then use a rabbeting bit in a clockwise direction. No broken router bits "yet".

Craig

[Cataclysm]

PDF on routing, bits, the two ways to cut (straight and climb cut), etc.

http://www.taunton.com/finewoodworking/FWNPDFfree/011129070.pdf

[---k---]

The bits are from Freud.

Those are respected bits. They shouldn't be breaking. Hummm...
Lots of good suggestions above.

[cjd]

You rather clearly described an overheated and binding bit. That could be caused by trying to feed it too fast for the work you're giving it.

Also, check the main bearing on the router, make sure it's not shot, and everything is snug. Especially if you've broken a couple bits, things can come loose or worse, the main bearing can be damaged from the vibrations. It could be loose from something else and the actual cause of your problem also.

C

[fjhuerta]

PDF on routing, bits, the two ways to cut (straight and climb cut), etc.

http://www.taunton.com/finewoodworki.../011129070.pdf

Another error I made. It describes how the router felt when the bit broke.

6 START THE ROUTER WITHOUT WOBBLE
I start a router with its base casting flat on the edge of the
workpiece. I find it troublesome and risky to set down an
already running router on the workpiece. However,
starting the router on an edge isn't completely risk-free.
Some machines will jerk from the torque of the motor
and possibly push the bit into the workpiece. Worse,
starting a cut before the bit reaches full speed can break
the bit. I prefer soft-start machines because they don't
twist on start up.

The things I don't know about woodworking are more than the things I don't know about speaker building! I thought that would never happen. :rofl:

[Bill Schneider]

Those are respected bits. They shouldn't be breaking. Hummm...
Lots of good suggestions above.

I have had problems with Freud 1/4" spiral upcuts breaking. Like you, I found the Bosch spiral upcut bits to last longer and to cut smoother.

I always take small 3/16" passes with any 1/4" spiral upcut bit no matter the brand.

MLCS recommends that the cutting depth be equal to or less than the diameter of a spiral upcut. http://www.mlcswoodworking.com/shops...TM25spiral.pdf

[Cataclysm]

If you want a seriously well made bit, albeit spendy, check out the solid carbide cutters from Onsrud.

You can even get them in configurations tailored to more aggressive, or roughing cuts:

[eyekode]

The fact that it looked a little burnt means it was running too hot. I don't see how a 1/4" spiral bit could get too hot from too fast of a speed so I bet the issue is dust evacuation. If the chips/dust cannot get away from the bit they continually get crushed and heat up. This heats up the bit too and leads to early failure.

You said you used a jasper jig? There is plenty of room around a 1/4" bit in a jasper jig right? My only guess is depth of cut is way too deep. Also pay attention to where the dust is going. If it isn't going then you need to stop and figure out why.

Good luck!

[Dennis H]

If you have a good jigsaw like a Bosch, there's another method I like for deep cuts, say a double baffle. Take a shallow pass with your circle jig and router. I like a hinge mortising bit for that but a regular straight or spiral bit will work. Cut out the circle with the jigsaw, staying a 1/16-1/8 away from the outside of the router cut. Clean up the cut with a flush trimming bit. Net result is a fast, clean cut and not so much dust.

[fjhuerta]

OK.. my router doesn't have a variable speed.

And it says in the manual I shouldn't try doing cuts deeper than 1/8"

I just bought a 1/2" and a 1/4" bit. I'll try again this Thursday!

[Amphiprion]

I go all the way through 3/4" MDF in two passes (5/8 and then 1/8 roughly). I'm still on my solid carbide spiral upcut 1/4" diameter bit that I bought... years ago? It's a Bosch that I bought at Lowes if I recall correctly. I use a Dewalt DW621.

[fjhuerta]

1/4" works perfectly.

I bought a set of chinese router bits for $15. 15 BITS!

The surfaces look bad, but the borders are perfect, which is exactly what I needed. I even got a chamfer bit, so I did the chamfer underneath the baffles.

Thank you for all your help! I finally made a good set of baffles!