Router flexing off perpendicular when using dust hood

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Router flexing off perpendicular when using dust hood

Postby Adwalker » Thu Jan 08, 2015 5:28 pm

With the Rockler 60th Anniversary Edition, has anyone experienced the router flexing off perpendicular when the dust hood is attached? I am simply drilling holes, .375 deep (3 pecks), in walnut. Everything is fine without hood, but hood installed causing router to flex off parallel on second and third peck when pushing down the brush perimeter of the hood. Not a loose router, the whole mount is flexing. No hood for me right now.
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Re: Router flexing off perpendicular when using dust hood

Postby monitoringpost » Thu Jan 08, 2015 10:00 pm

I have the KentCNC dust shoe and it does basically the same thing when the z-axis lowers down whereby the brush is pressed hard into the material. I find that best results are had when the brush is just making just enough contact to create a seal of sorts. When this is a problem I just don't use it. Drilling holes is one of those instances where I usually don't use it as the dust created is minimal. NWA didn't come out with a dust shoe until after KentCNC's dust shoes gained popularity - that makes me think that NWA didn't really take into account the flex that they might cause and engineer the gantry accordingly. You'll find some owners have elected to totally enclose the unit eliminating the dust shoe.
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Re: Router flexing off perpendicular when using dust hood

Postby 4DThinker » Thu Jan 08, 2015 11:48 pm

The back plate of the gantry will flex with the cantilever weight of the router. Mainly when it is in the center of the gantry or close. On the HD 2.0 version we bolted a 2x2 piece of angle iron across the top back of the back plate. We still have had some flex during aggressive X-direction cuts and will be bolting another piece across the bottom edge to see if that helps once the new college semester begins. IMO that back plate should have been a box or I beam to eliminate twist/flex.

I noticed the new model has an aluminum plate rather than the plastic that earlier models came with, but being still a flat plane it still will flex with the added weight up front.
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Re: Router flexing off perpendicular when using dust hood

Postby rungemach » Fri Jan 09, 2015 8:07 am

The problem can be lessened by trimming the length of the bristles so they all do not touch at the same time.

When they all touch at the same time, the whole group of bristles has a lot more strength. if you can get them to bend at various heights, the force required to overcome the "step" of causing them to bend is greatly reduced, as you are only trying to bend a few at a time. Once a bristle bends even a little, it loses most all its resistance to further down force.

You can also think about thinning down the number of bristles as well.

IMHO, the bristles only serve to stop the pieces that are coming off of the bit that are flying off parallel to the table top. Those pieces can get out of range of the vacuum stream pretty quickly.

My kent shoes have two lengths of bristles from the factory. a partial shorter set that helps hold the longer ones in place. I also cut the bottom edge of the longer bristles at slightly different lengths, so they do not have to all bend at exactly the same point. Having the bristles bend at different times can make a big difference. The length difference does not have to be dramatic. 1/2 inch between longest and shortest can make a big difference. The picture below shows a modified Kent shoe, it also shows the reinforcing row of short bristles that comes with that design.

When the router is moving sideways, the problem is lessened in that the movement helps the bristles bend more easily as it is "pulling the rug out from under them".

Of course, most of this problem goes away if you strengthen the gantry. (and the z axis assembly). 4DThinker is very correct in saying that bars or beams are better behind both bearing rods as they work as a pair to counter the torque of the pressure on the router assembly. A flat plate (plastic or aluminum) has much less resistance to being bent in that direction.

Bob
Attachments
Brush modification.jpg
Brush modification to tapered bristles
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Re: Router flexing off perpendicular when using dust hood

Postby Adwalker » Fri Jan 09, 2015 11:17 pm

Thanks for the replies. All make sense.
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Re: Router flexing off perpendicular when using dust hood

Postby milo30 » Sun Jan 11, 2015 9:40 pm

I always found that if you left a little gap between bristles and work surface, it would deflect the router and it would allow better suction for dust control.
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