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post #1 of 10 (permalink) Old 08-15-2012, 08:35 PM Thread Starter
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Default Template beginner question

I have experience using a router but I am getting ready to use a guide bushing for the first time. Is there a difference in a guide bushing and a bit with a bearing on it? Won't they do the same thing if you used a template?
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post #2 of 10 (permalink) Old 08-16-2012, 06:27 AM
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Yes they will with this important difference.
The bearing is the same diameter as the bit,usually, so it cuts to the shape of the template exactly.
The guide bushing, however, has to be wider than the cutting edge and therefore the cut is offset from the template by the difference between the outside diameter of the guide bushing and the diameter of the router bit, divided by 2.
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post #3 of 10 (permalink) Old 08-16-2012, 06:30 AM
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Nearly but not quite. They do different things with some overlap.

A straight cutting (non profile) normally has a bearing the same size as the cutter at either the top or bottom of the cutter. If the bearing is following a template the cutter will trim the work exactly to the template provided that there are no internal corners with a smaller radius than the bearing. A bit with a lower bearing (flush trim) cannot plunge into the job. The primary exception to the same size bearing and cutter is rabbet bits, where you deliberately use a bearing smaller than the cutter to produce an offset cut.

Using a template guide allows you some more freedom, like plunging with a profile bit, but at the expense of being forced to deal with offsets.

Because the template guide must be clear of the cutter parts it encloses in its cavity, and must have some wall thickness for strength, the outer diameter is normally at least 1/8in (generally more) bigger than the cutter, so to make a template you must predetermine the cutter diameter, the guide diameter, calculate half the difference as the 'offset', and make the template smaller all round by the offset for external cuts or larger by the offset for internal cuts. Not too much of a hassle for straight cuts, circles or ellipses, but quite an issue for complex shapes.
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post #4 of 10 (permalink) Old 08-16-2012, 06:53 AM
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I like using the bearing. You can get a bit with the bearing on the top or the bottom. The bottom is easier to use because you are looking directly at what you are cutting and not looking at the top of the template.
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post #5 of 10 (permalink) Old 08-16-2012, 09:33 AM
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"Won't they do the same thing if you used a template?"
***************************
Essentially, yes.
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post #6 of 10 (permalink) Old 08-16-2012, 11:13 AM
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A bearing guided bit seems like the easiest solution for template work. It trims wood to the template shape, doesn't have any offsets to figure. So why use guide bushings? The first reason is you can not plunge cut with an end mounted bearing guided bit. To use a shank mounted bearing guided bit you must fully extend the cutter and that wont work in many situations. Using guide bushings is safer because you only need to expose the amount of cutter required by the cut. Working with offsets allows you to custom tune your cuts to additional sizes. Most people end up using both bearing guided bits and guide bushings for different jobs.

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post #7 of 10 (permalink) Old 08-16-2012, 11:48 AM Thread Starter
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Thanks folks. I am going to experiment with different size bearings and different size guides to see if I like one better than the other, or both. Now back to play...
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post #8 of 10 (permalink) Old 08-17-2012, 03:01 PM
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Quote:
Originally Posted by malb View Post
A bit with a lower bearing (flush trim) cannot plunge into the job.
I never have to worry about that, as I always drill a hole the bit goes into. Works great for me.

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post #9 of 10 (permalink) Old 08-17-2012, 08:17 PM
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Quote:
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I never have to worry about that, as I always drill a hole the bit goes into. Works great for me.
That's pretty limiting as you can't do a non-through cut. ie, a serving tray with recesses for glasses.

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post #10 of 10 (permalink) Old 08-20-2012, 12:15 PM
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Quote:
Originally Posted by jschaben View Post
That's pretty limiting as you can't do a non-through cut. ie, a serving tray with recesses for glasses.
Yes, true. I should have said that I don't do any non-through cuts, just use templates, or masters as I call them, and rout 1/2", or occassionally 3/4", plywood. For now, if I wanted say a serving tray with recesses for glasses, I would just rout round holes thru a piece of wood/plywood, and laminate it on a base.

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