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post #1 of 24 (permalink) Old 07-10-2012, 01:24 PM Thread Starter
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Default new member - question on avoiding this problem in the future

Hello everyone,

I'm new here and I have a question. I was routing 1/4" dados across the grain on a set of 5" wide boards for drawer joints, when the 1/4" in bit broke and went into the router, destroying the fan and armature and tripping the breaker. Needless to say the router is ruined (and I just had the bearings replaced). I've broken off bits before but they've never gone inside the router causing all this damage.

I'm scared to use another 1/4" straight bit, so how can I prevent this in the future? I suspect that 1/4" depth was too much for the bit so it overheated and snapped off, perhaps going in 1/16"s or even 1/8"s depth would help?

I had the router mounted on a table where I've had trouble free use for years.

Off to buy a new router now... looking forward to your replies.
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post #2 of 24 (permalink) Old 07-10-2012, 02:31 PM
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On the bright side, n/a, nobody got hurt, eh? Better a shopping trip for a new router (1/2" collet this time?) than a trip to the ER!
On a much happier note, Welcome!
Cheers,
-Dan
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post #3 of 24 (permalink) Old 07-10-2012, 02:31 PM
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Usual rule of thumb is 1/4 inch a pass on soft wood with a sharp bit. I usually adjust the less for some harder hardwoods.

More important than the rule of thumb for tellling me- is what I feel, what I hear, what I see and what I smell.

If the feed rate feels like it is dragging.... If I hear it dragging... If I see smoke other than from moisture... If I smell other than the smell of cut wood, such as burning...

On large diameter bits, I test to see how much I can take off at a time. On knots and burls, I take off less at a time and crawl.

Even after all that, for some reason, after routing often for so long, it still might happen. About 4 times in 20 plus years, routing almost every day. I'll never get used to that sound. I think over half of them was my fault, thinking I could go a few more time with a dull bit, going too deep with too fast a feed rate.

Next, I use a bit insert ring somewhat close to the size of the bit. The main reason for that is to keep excess sawdust off... Secondary, (has happened with me, so) is far safety. If the bit breaks it'll slow down the pieces as it rips apart the insert ring.

I can't say that any of my router's exhaust ports have an opening large enough for a 1/4 bit to enter, like your's did.

Last edited by MAFoElffen; 07-10-2012 at 02:35 PM.
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post #4 of 24 (permalink) Old 07-10-2012, 04:44 PM Thread Starter
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Thanks all. I ended up buying another Porter Cable 690 for $184 + tax. I was using a 1/2" shank, 1/4 straight bit. IMO they make those things too long. If the bit was 1/2" tall only there would be less torque on the metal.
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post #5 of 24 (permalink) Old 07-10-2012, 05:10 PM
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N/a, my guess would be the bit may of been dropped creating a hidden defect? Other possibilities are you were trying to feed the bit too fast, hit a knot or started the router in contact with the material? Any of these could cause the bit to break, it sometimes happens.

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post #6 of 24 (permalink) Old 07-10-2012, 05:48 PM
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Hi N/a......

The "square" rule stated above is correct, but there are several other facrors to note: you can generally feed slightly quicker with dust extraction than without (and the bit stays cooler), single flute cutters clear waste better than 2-flute cutters - which is why they were used for production pin routing from the 30s to the 80s (albeit the quality of the cut is not as good as two flutes) and spiral upcut bits clear waste better and can be fed much faster than other designs. Spirals are the one cutter design which may allow you to exceed the "square" rule (i.e. depth per pass must NOT exceed diameter of cutter), but not by much

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post #7 of 24 (permalink) Old 07-10-2012, 06:07 PM
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G’day

Welcome to the router forum.

Thank you for joining us.

That also happened to me, once. I am still not sure why. I was using a 1/4" cutter with 1/2" shank and only taking a 1/4" bite in soft wood.

Mine was an older cutter from a cheap set.

How was your feed rate? Sometime, if we have a few to do, we tend to push through a bit quicker.

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post #8 of 24 (permalink) Old 07-10-2012, 09:39 PM Thread Starter
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I started feeding it at a normal pace, but I fed it a bit faster near the end. The wood was hard maple too, something I've never routed before, so you could say these two factors caused it. The bit and router were hot to the touch when the breaker tripped, unlike now that I reduced the depth to 1/8" and reduced my feed rate. That also helped with tearout on exit.

Its 12 drawers with lock joints so its 24 boards with 1/4 grooves for the front and backs.
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post #9 of 24 (permalink) Old 07-11-2012, 06:08 AM
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Quote:
Originally Posted by jw2170 View Post
That also happened to me, once. I am still not sure why. I was using a 1/4" cutter with 1/2" shank and only taking a 1/4" bite in soft wood.

Mine was an older cutter from a cheap set.

How was your feed rate? Sometime, if we have a few to do, we tend to push through a bit quicker.
I've done exactly the same, though with a 1/4" shank bit. I suspect I was feeding too fast too, though it didn't feel like it was straining. I guess it doesn't take much excess force to break a cutter that small, so best to err on the side of caution with the feed rate.
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post #10 of 24 (permalink) Old 07-11-2012, 07:16 AM
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I have found that the router takes too long for just the reasons mentioned. When I need a dado I reach for the dado blade and do the job in a fraction of the time on the table saw. I learned the hard way by burning out the speed control on my router.
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