Using Top-Bearing Guided Bits - Router Forums
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post #1 of 17 (permalink) Old 11-15-2014, 08:09 AM Thread Starter
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Default Using Top-Bearing Guided Bits

I have a plunge router. In the future I am going to cut some hatches and inspection ports out of plywood. I sort of understand about cutting patterns out of scrap plywood, clamping or screwing them to the ply I am going to cut the hatches from. I have purchased a couple of top-bearing-guided router bits. The bits are longer than the depth of my patterns. I can sort of understand that I start off with the bit alongside the pattern however I'm concerned about the bit running off-line before the bit gets far enough down that the bearing is alongside the pattern. I need to get this 100%. Could I have some suggestions and comments?

Thank you for your help.
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post #2 of 17 (permalink) Old 11-15-2014, 08:22 AM
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Is it possible to build up underneath the template (temporarily) to accommodate the long bit until you get far enough down, then remove the extra wood underneath the template...?

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post #3 of 17 (permalink) Old 11-15-2014, 08:59 AM
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Switch to collars. They have essentially no cutter extension limitations. Moreover, the straight bit inventory is 10x that of trimmers. And the collar guide bush is much safer, easier on the cutter and the router.
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post #4 of 17 (permalink) Old 11-15-2014, 09:31 AM Thread Starter
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Default I know nothing of collars

Oh dear! Straight away I'm in to something I know nothing of! Could you post a photograph of a collar and a correct bit for what I'm asking that is suitable for this? Thank you.
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post #5 of 17 (permalink) Old 11-15-2014, 09:55 AM
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Just click on the "collar guide bush" text in Quillman's post and it will take you to a full explanation with photo.

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post #6 of 17 (permalink) Old 11-15-2014, 12:29 PM
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Mike if you are cutting holes out then you don't have to start next to your template. Also if you are cutting holes out I would try to cut the bulk of the material with a jig saw and use the router to finish to a smooth edge. It's much easier on the bits and the router that way.

Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.
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post #7 of 17 (permalink) Old 11-15-2014, 12:37 PM
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I use a pattern bit, which only has a 1/4 inch cutter under the bearing. Make several passes around the template and adjust the cutter deeper as you go. Three or four passes should be enough to cut through 3/4 inch plywood.

The bearing rides against your pattern until you start cutting deeper than the template. then the bearing rides against your workpiece.

As mentioned above, you could make temporary shims to rais the template but I think it could possibly a disaster in the making. Been there, done that.

Note: In the pic I have attached, I have the pattern bit installed in the router. I was cutting dadoes in drawer sides. Your situation would probably be the same...follow the template as you make your cut.

Hope this helps.
Mike

Edit: I like Chucks method a lot better if you already have the bit in hand.
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post #8 of 17 (permalink) Old 11-15-2014, 06:07 PM
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Quote:
Originally Posted by Cherryville Chuck View Post
Mike if you are cutting holes out then you don't have to start next to your template. Also if you are cutting holes out I would try to cut the bulk of the material with a jig saw and use the router to finish to a smooth edge. It's much easier on the bits and the router that way.
Even if using bearing guided cutters or collars, I would definitley use Charles' method.

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post #9 of 17 (permalink) Old 11-16-2014, 06:52 AM Thread Starter
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Thank you for the replies and expertise. Chuck, I do not want to use a jigsaw as I am not confident of getting smooth corners, runs etc.

I had clicked on the collar guide bush link on Quillman's post, however I have only ever used router bits that go directly into the router (collet?). The Collar Guide Bush concept is new to me and until I see it in practice, I do not really understand it.

Mike (of Mt Stringer), the Pattern Guide Bit sounds good in that it is of shorter length than the Top Bearing Guided Bits I have.

I really love the smooth finish that I can (sometimes!) achieve with my router. I hope I can get this to work!

I'm away from home for a while, however when I return I shall work on your lines.
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post #10 of 17 (permalink) Old 11-16-2014, 07:05 AM
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Chuck and James are recommending you rough cut the piece over size before routing,therefore no need to plunge and no need to worry about accuracy with the jig saw
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