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Flush trim cutting (i.e. template routing) with a spiral bit

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Forum topic by RS Woodworks posted 03-21-2011 03:47 AM 1751 views 0 times favorited 4 replies Add to Favorites Watch
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RS Woodworks

533 posts in 2716 days


03-21-2011 03:47 AM

Topic tags/keywords: router bit flush trim spiral cutter

Hey all, I haven’t asked a question on here in some time, but I have something that I just can’t seem to find the answer to.
I’ve been using a flush trim router bit, the type with a bearing, to template route some curved pieces for a current project. The material I’m routing is maple, and as soon as the grain changes direction, I’m getting some tearout that I’d prefer to avoid. The bit’s I’m using are double fluted Freud bits.

I’d like to try a bearing guided spiral bit, in hopes that the spiral action will help reduce or eliminate tearout. Will that help? And if so, which bit do I choose, an upcut spiral or a downcut spiral? I’ve read about the differences and I think I have a grasp on that, but I can’t seem to figure which one will be better for template routing? I’m thinking I want an upcut to move the chips down towards the router and away from the bearings otherwise the chips may interfere with the bearing riding smoothly along the template. Is that correct?

Thanks for your help.

Here is what I'm considering...

And here is what I currently have...

-- I restore the finest vintage tools! If you need a nice plane, saw, marking tool or brace, please let me know!


4 replies so far

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drewnahant

222 posts in 2554 days


#1 posted 03-21-2011 03:53 AM

upcut definitely, you dont want chips between the template and the bit, but be ware, you can still get tear out, though it is less likely, but you are likely to get splintering along the top edge, remember upcutting instead of crosscutting, but still a shearing cut, so a backer board is a good idea.

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RS Woodworks

533 posts in 2716 days


#2 posted 03-21-2011 04:08 AM

Thanks drewnahant, what do you mean by a backer board, in this application?
Upcut was the way I was thinking for sure for that very reason.

-- I restore the finest vintage tools! If you need a nice plane, saw, marking tool or brace, please let me know!

View drewnahant's profile

drewnahant

222 posts in 2554 days


#3 posted 03-21-2011 04:15 AM

I mean that your tearout will be along the edge, because there is nothing behind the grain to support it and get a clean shear, so it just splinters off. you should clamp a board down to the surface, probably 1/4 in hardboard will do, just something so that your edge behaves as if it were the middle of a larger board.

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RS Woodworks

533 posts in 2716 days


#4 posted 03-21-2011 04:21 AM

Ah, yes I see exactly what you mean, on the edge that’s against the table, I may get some tearout there. I may run a rough round-over on that bottom edge first to avoid that problem then.
Thanks very much.

-- I restore the finest vintage tools! If you need a nice plane, saw, marking tool or brace, please let me know!

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