MFT stopped a speeding router bit today

[Cannuck]

I had my first (and hopefully last) router bit escape the collet on me today. 

Thank goodness for my MFT. 

I was using a small router to do some copy work today - making baltic ply drawer inserts for my kitchen.  I had my work pieces clamped onto the MFT.  The darn router (non-festool) was giving me some grief tightening the collet - one of those one wrench jobbies, and I guess its getting worn.  Should have listened to that little voice in the back of my head, which was to grab a different router.

Anyway...pushing away through about my 10th piece when all of a sudden I hear this whine and a clatter.  I shut the router off, to find the router bit embeded in my MFT top.

When it let loose, the darn bit shot right through a second piece of 12 mm baltic ply  (plus the one it was cutting), and buried itself about 1/2" in the top of my MFT before it stopped.

Scared the bezeezus out of me.  I can't imagine what that would have done to my leg?!

Needless to say, that router's going to be replaced real soon with another Festool router.

 

[jaegerhund]

Whoa!!!  That'll wake you up in the morning --- bugger of a router  --- cool that it turned out alright for you.  Take it easy,

Justin

 

[poto]

I was once routing a circle out of some maple and cherry laminated (horizontally) together. I was using my OF1010 with a 1/4 inch straight cutting bit. I was taking shallow passes as I went around. Unfortunately I wasn't using the knob to lock the plunge depth. As I was making a pass through some end-grain, I heard a "ping", and the router suddenly sped up. I turned it off, to find only the stub of the router bit still in the collet. The bit had broken and shot off. I never found it. It scares the **** out of me to think that it could easily have gone through me. Probably about the same speed and size as a bullet. Now I wear a leather apron in the probably vain hope that it'll protect me from speeding bits of router bits.

I discovered later that as I had been leaning into the curve, the router had plunged, and I was putting too great a load on the bit. Hopefull I'll know better for next time.

Still gives me the willies.

 

[Per Swenson]

That would make me consider a change in apparel.

A pair of these, oversized, so there is some room for the Depends.

[attachimg=#]

Per

 

[dltflt]

I'm with Per, I think I would have to clean out my pants after that.  Glad everything turned out for the best.

 

[Jim Metzger]

I don't know your experience level but when I have had problems tightening a bit it is because the shaft was bottomed out in the collet. Insert fully and pull out about an 1/8". Oops, I mean 3.175 mm.

Hope this helps.

Jim

 

[minimal]

As mentioned, if you've accidentally put your cutter all the way in so it's shank is seated, it will NOT
tighten correctly: this is because the collet requires the shank to move slightly "in" to get locked down.
If the shank is seated, it cannot move in that direction and so will not be able to be locked down.

Someone can correct me on this if I'm wrong: I've been told (and follow) that you should make your
collet tight, but not super-tight. Friction on the cutter works to keep the collet as tight (or tighter) than
you set it. Overtightening a collet just wears it out quickly.

 

[greg mann]

As mentioned, if you've accidentally put your cutter all the way in so it's shank is seated, it will NOT
tighten correctly: this is because the collet requires the shank to move slightly "in" to get locked down.
If the shank is seated, it cannot move in that direction and so will not be able to be locked down.

Someone can correct me on this if I'm wrong: I've been told (and follow) that you should make your
collet tight, but not super-tight. Friction on the cutter works to keep the collet as tight (or tighter) than
you set it. Overtightening a collet just wears it out quickly.

Sorry to challenge you, Minimal, but this simply is not true. In metal machining we use collet chucks, often grabbing shanks as large as 1 1/2 inches, and intentionally bottom the shank against an adjustable screw that is specifically designed for this purpose.  We then use that tool to take very heavy cuts, sometimes over 50HP, on materials that make the hardest wood you know seem like styrofoam.

You are right that the collet needs to move slightly as it locks down, but this slippage can occur along the shank of the tool or the taper of the spindle. If the shank is bottomed out it will happen along the taper of the spindle and the shank of the tool simultaneously. You are also right that a collet can be overtightened. In the case of a router it is possible to stress the spindle enough to crack the taper open, although this would be very rare. I have seen it happen to other collet chucks when someone uses a cheater on the wrench.

The most important thing is to have a clean fully engaged shank in clean collet with a clean nut. A very light lube on the threads of the spindle will greatly increase the efficiency of the grip. 

 

[minimal]

As mentioned, if you've accidentally put your cutter all the way in so it's shank is seated, it will NOT
tighten correctly: this is because the collet requires the shank to move slightly "in" to get locked down.
If the shank is seated, it cannot move in that direction and so will not be able to be locked down.

Someone can correct me on this if I'm wrong: I've been told (and follow) that you should make your
collet tight, but not super-tight. Friction on the cutter works to keep the collet as tight (or tighter) than
you set it. Overtightening a collet just wears it out quickly.

Sorry to challenge you, Minimal, but this simply is not true. In metal machining we use collet chucks, often grabbing shanks as large as 1 1/2 inches, and intentionally bottom the shank against an adjustable screw that is specifically designed for this purpose.  We then use that tool to take very heavy cuts, sometimes over 50HP, on materials that make the hardest wood you know seem like styrofoam.

You are right that the collet needs to move slightly as it locks down, but this slippage can occur along the shank of the tool or the taper of the spindle. If the shank is bottomed out it will happen along the taper of the spindle and the shank of the tool simultaneously. You are also right that a collet can be overtightened. In the case of a router it is possible to stress the spindle enough to crack the taper open, although this would be very rare. I have seen it happen to other collet chucks when someone uses a cheater on the wrench.

The most important thing is to have a clean fully engaged shank in clean collet with a clean nut. A very light lube on the threads of the spindle will greatly increase the efficiency of the grip. 

Challenge away! But let's think about this for a second: we tighten the collet to a certain torque (whether by "feel" or by measurement with a torque wrench).

In one instance (shank NOT bottomed out), the resistance is provided solely by the force of the collet perpendicularly to the shank, i.e. a clamping force.

In the second instance (shank bottomed out), as you say: the resistance comes from two components: 1- clamping force as above, AND 2- a sliding force of the collet along the shank (as the shank is fixed).

If we are tightening to the same torque at the "wrench end" in both circumstances, it seems to me that the first method will result in a greater clamping force (unless the sliding force is zero, which it would not be under any normal circumstances).

You thoughts on this?

(p.s. we're only talking about collets here, not chucks that only apply forces perpedicular to the shank, right?)

 

[greg mann]

In your first instance force is not solely perpindicualr as the nut is still forcing the collet further down into the taper as you tighten it, which is a sliding action. In either case the perpindicualr force is generated by the sliding action of the collet in the taper, and the force of the nut needs to overcome that friction. I know it seems counter-intuitive and I can think of one case where it would not be good to have a shank bottomed out. This would be where the bottom of the bore does not run true to the ground taper of the collet. This could cause a slight radial load on the end of the shank which could cause distortion in the spindle. I could see this possibility in a cheaply made router. That doesn't define a Festool, thankfully. Usually, the bottom of the bore is slightly conical in shape. This would actualy give another level of stability as the end of the shank is forced into that cone. Think of a flag pole in your hands. If the wind is blowing it around what do you do? You stick the end into the ground to increase stability.

 

[minimal]

In your first instance force is not solely perpindicualr as the nut is still forcing the collet further down into the taper as you tighten it, which is a sliding action.

If the shank moves *with* the collet (as it does when the shank is *not* bottomed out) it only sees the clamping force. Only when the shank is
fixed and the collet is moving do frictional forces add to the clamping force, as is the case when the shank is bottomed at the start.

We may be at an impasse here, or at least til we can get in front of a chalkboard and work
out the vectors.

So, in short, you are suggesting that it's an equally strong mount when the collet is tightened down with the shank
bottomed out as not?

 

[greg mann]

I am suggesting that in an equivalent exercise, writ large, there is no evidence to suggest that bottoming out the bit is a problem. I have alluded to a possible negative consequence and a different possible positive consequence. When I put it that way, I guess there is nothing more I can add.  : : :