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Spiral up or down cut router bits?

 
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tugboat1980



Joined: 17 Jan 2012
Posts: 378
Location: Savannah, GA

PostPosted: Thu Nov 15, 2012 8:47 am    Post subject: Spiral up or down cut router bits? Reply with quote

So I'm getting close to cutting and routing the wood for my scratch build Les Pauls (DC Special and a Standard). Do spiral and shear up and downcut router bits reduce tearout compared to straight bits? I plan on cutting close with a bandsaw and sanding down as close as possible to the lines to keep the amount of material for the router to take off down to a minimum and reduce tearout. But if these make a noticeable difference, all the better.
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dougk



Joined: 11 Dec 2007
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PostPosted: Thu Nov 15, 2012 8:59 am    Post subject: Reply with quote

Besides the top or bottom of a piece, yes spirals seem too (and do) work better for reducing tearout.

If you are using it in a router table, an upcut bit will be a better choice (keeps the bottom edge clean). If you are routing down from the top and upcut bit will run faster but will fuzz the top edge, a downcut bit will run a bit slower but keep your top edge clean.
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tugboat1980



Joined: 17 Jan 2012
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Location: Savannah, GA

PostPosted: Thu Nov 15, 2012 9:16 am    Post subject: Reply with quote

Specifically I'm wondering about flush trimming sides, control cavities, etc... Sounds like it might be worth it to use them?
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RolandR



Joined: 03 Sep 2003
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PostPosted: Thu Nov 15, 2012 9:17 am    Post subject: Reply with quote

pretty much what doug said, he's always right ... Laughing

from what I read, if you are routing "free hand" with a router, a down spiral bit is recommended. It keeps the wood down on the work table (use a router mat). Upcut spiral bit are used for work clamped down or the router table method.
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Vic Vega



Joined: 15 Mar 2010
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Location: SW Idaho

PostPosted: Thu Nov 15, 2012 9:41 am    Post subject: Reply with quote

I've only used binding bits with bearings. So basically what you're saying is it depends on the direction of the cut: down=down and up=up. Is that right?
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Heavy Air



Joined: 04 Aug 2008
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PostPosted: Thu Nov 15, 2012 9:44 am    Post subject: Reply with quote

I always used upcuts for things like cavities/edge routing etc. Downcuts for inlays etc as the edges are usually fuzz free.

But yeh, what Doug said
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dougk



Joined: 11 Dec 2007
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Location: About to lose his head in Sacramento

PostPosted: Thu Nov 15, 2012 11:48 am    Post subject: Reply with quote

tugboat1980 wrote:
Specifically I'm wondering about flush trimming sides, control cavities, etc... Sounds like it might be worth it to use them?


I use an upcut spiral to flush trim my bodies but keep in mind when I do this I've cut 95% of the material away with a downcut spiral on my CNC. Then I just flush trim off the rest.

(this is because I don't want to mill into the table on my CNC).

If you are using a template and trying to flush trim the entire side of a guitar than really either one would work, one edge will likely be fuzzy regardless. I'd prefer down so it pulls the part against your router table (or up cut if using a top bearing and hand held router).
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Bob_Kennedy



Joined: 16 Jul 2012
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Location: Gilbert, AZ

PostPosted: Thu Nov 15, 2012 1:20 pm    Post subject: Reply with quote

To route the perimeter of bodies, you want a 2" long upcut spiral flush trim bit. It'll leave a very smooth edge. No fuzz. However, only use this bit in a router table & sand to the line on the body before you use this bit. This is a scary router bit & you must use extreme care or your workpiece & your fingers will be trashed! Do not attempt to use it in a handheld router!!! For the control cavities & neck pocket, I just use a 1/2" template bit.
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tugboat1980



Joined: 17 Jan 2012
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Location: Savannah, GA

PostPosted: Thu Nov 15, 2012 1:22 pm    Post subject: Reply with quote

Thanks for the tips Doug! I'll pick up a downcut for the sides (router table) and an up cut for cavities and the top carve.
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Tom Pettingill



Joined: 04 Jan 2010
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PostPosted: Thu Nov 15, 2012 1:56 pm    Post subject: Reply with quote

tugboat1980 wrote:
Thanks for the tips Doug! I'll pick up a downcut for the sides (router table) and an up cut for cavities and the top carve.

Just to clarify, when using a big honking 2" cut spiral bit in a router table, its best to use an upcut bit as the natural tendency of the bit will be to pull the work towards the table, not lift like a down cut would do.
Here is what you would want http://www.amazon.com/gp/product/B0012JI870/ref=oh_details_o01_s00_i00
And heed Bob's warning, these bits are scary monsters and not for hand held use!
Another point when using a spiral bit, feed into the cut. If not it can grab and toss your work across the room in a heartbeat.
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Mr. Clevername



Joined: 08 Dec 2006
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PostPosted: Thu Nov 15, 2012 2:07 pm    Post subject: Reply with quote

+1 what Tom said - upcut spiral in the router table.
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tugboat1980



Joined: 17 Jan 2012
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Location: Savannah, GA

PostPosted: Thu Nov 15, 2012 2:30 pm    Post subject: Reply with quote

Or...what about the complete opposite approach, at least with shaping the body? Still use a router for cavities but for the body use rasps and surforms, and finish it with sandpaper? I'm not on any schedule and, while not as quick as a router, shouldn't take a heckuva long time. Especially if I bandsaw properly.
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Bob_Kennedy



Joined: 16 Jul 2012
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Location: Gilbert, AZ

PostPosted: Thu Nov 15, 2012 3:06 pm    Post subject: Reply with quote

If you already have a 1/2" diameter, 1" long pattern bit for the cavities, you can use that for the body as well. You'll just have to make multiple passes. On the first pass, the bearing on the bit will be riding on your template. Take the template off for your second pass around the body, as the area you routed on your first pass will now act as your template. At this point, depending on how thick your blank is, you may have to change to a 1/2" diameter flush trim (bottom bearing) bit & flip the blank over to make the last pass.
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dougk



Joined: 11 Dec 2007
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PostPosted: Thu Nov 15, 2012 3:31 pm    Post subject: Reply with quote

Mr. Clevername wrote:
+1 what Tom said - upcut spiral in the router table.


Ya thanks Tom I meant to clarify that you need to do the "opposite" if its mounted in a router table. Tom nailed it
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