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Routing using a template: Bushing v. Bearing?

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Forum topic by JesseTutt posted 02-24-2013 06:18 PM 1046 views 0 times favorited 3 replies Add to Favorites Watch
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JesseTutt

811 posts in 856 days


02-24-2013 06:18 PM

Topic tags/keywords: question router bits pattern bits bushings

I was reading an article in FWW magazine and for one piece the author instructed me to create a template.

I am supposed to drill a 3 1/2” hole in the template so that I can use a bushing in the router to make the hole in the final piece (drill an undersized hole and route the hole to the correct size). Then he goes on and tells me to make the curve part of the bottom of the leg using a router bit with a bearing on it.

Why would I use a bushing for a round hole and a pattern bit with a bearing on it for the curve?

How do I decide when to use each one?

-- Jesse, Saint Louis, Missouri


3 replies so far

View Loren's profile

Loren

7822 posts in 2394 days


#1 posted 02-24-2013 06:39 PM

A bushing offsets the cut and does not interfere with
bit depth settings. Bearings are simpler to work with
in a lot of situations because you don’t have to make
the template over or under-sized. However, the
bearing, top or bottom, must be in contact with the
template, so sometimes that obliges you to take
a pretty big cut using the full length of the cutter
(which can cause tearout).

-- http://lawoodworking.com

View RogerInColorado's profile

RogerInColorado

306 posts in 700 days


#2 posted 02-24-2013 07:16 PM

Edge treatments are done almost exclusively with bits with a bearing on the bottom of the bit. The bearing rides against the edge below where the edge treatment is being cut. The bearing insures that the cutting edge follows the surface as exactly as possible. A radius on the edge of the leg is an example of this approach. Without the bearing, the bit would make its own path into the leg.

Following a template can be done with EITHER an exact template of the desired shape and a top (or in some cases bottom) bearing mounted bit, OR a template that is sized to the desired shape and size of the desired shape (minus the bit to bushing OD dimension) with a bushing guide and using a straight bit to do the cutting. It is usually a matter of preference, comfort level and ease of implementation. It might be as esoteric as the author wanted the final hole to be slightly under the 3.5 inch hole initially cut in the template. In the example you cited, it could have been done either way. There are many ways to put holes in things. This is simply the way the author chose to make his on this particular project. It is fairly common for woodworkers to use alternate techniques from those in the instructions. Sometimes we take different approaches because it saves us a trip to the store to buy a top mounted pattern following bit.

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MonteCristo

2098 posts in 934 days


#3 posted 02-25-2013 03:46 AM

The bushing method has the advantage that, unlike the bearing, it is not part of the spinning bit assembly. This, and the fact that often the bushing is a larger diameter, means the bushing method should yield a cleaner cut.

-- Dwight - "Free legal advice available - contact Dewey, Cheetam & Howe""

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