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Router bit question -- upcut vs. downcut

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Forum topic by Furnitude posted 12-21-2011 04:10 PM 5569 views 0 times favorited 11 replies Add to Favorites Watch
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Furnitude

346 posts in 2228 days


12-21-2011 04:10 PM

Can anyone explain the difference to me? I’m wanting to buy a simple 1/8” router bit for routing grooves to make boxes. I’ll be using it with a router table. I’m looking at Whiteside bits on Amazon and want to know the difference between these two:

Upcut:
http://www.amazon.com/Carbide-Spiral-Router-Diameter-Cutting/dp/B000K29JK0/ref=sr_1_22?s=hi&ie=UTF8&qid=1324476332&sr=1-22

Downcut:
http://www.amazon.com/Replacement-Downcut-Spiral-Whiteside-RD1600/dp/B000K2FI8M/ref=pd_sim_hi_5

Thanks,
Mitch

-- Mitch, http://furnitude.blogspot.com Also blog at http://www.craftsy.com/blog/author/mitch-roberson/


11 replies so far

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richgreer

4524 posts in 1796 days


#1 posted 12-21-2011 04:24 PM

Even though you will be using this bit in a table, it is easier to think about upcut versus downcut if you think of the bit in a hand held router.

The upcut brings the chips up and the downcut brings the chips down.

You should only use a downcut bit when you are running the bit all the way through the wood. The only purpose/advantage of a down cut bit is to minimize tearout on the top surface.

The upcut bit does a good job of clearing out the chips as you route. I always use an upcut bit when I am cutting mortises with a jig (Mortise Pal).

Of course, there are also, the more common straight cut bit, that is neither an upcut or downcut.

I’ve never seen a upcut or downcut bit as small 1/8”. The smallest I have is 3/8”. If you are dealing with an 1/8” diameter, you may be better served with a straight cut. I would expect an 1/8” upcut (or downcut) to be more likely to break than a straight bit of the same size.

-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.

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Furnitude

346 posts in 2228 days


#2 posted 12-21-2011 04:41 PM

Thanks, Rich. Very helpful.

-- Mitch, http://furnitude.blogspot.com Also blog at http://www.craftsy.com/blog/author/mitch-roberson/

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richgreer

4524 posts in 1796 days


#3 posted 12-21-2011 04:46 PM

You may find this site helpful – -

http://www.mlcswoodworking.com/shopsite_sc/store/html/smarthtml/pages/bt_solid.html

Here you will see that an 1/8” diameter upcut or downcut is available. I still think (but I am not certain) that the upcut or downcut design reduces shaft strength. In general, that is not a problem with bigger bits, but it would concern me a bit (pun intended) on a small bit.

-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.

View HorizontalMike's profile

HorizontalMike

6960 posts in 1635 days


#4 posted 12-21-2011 09:02 PM

I have been experimenting with both 1/4in upcut and 1/4in straight bits in my new mortising machine and in my router table. So far, from my limited experience perspective, I do NOT see much difference in the cuts other than to say that the upcut bit seems to cut faster than the straight bit.

Straight bits are much cheaper than upcuts. I am finding out that if you go slowly, straight bits do a fine job. Patience is a key.
Just my 2-cents…

-- HorizontalMike -- "Woodpeckers understand..."

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live4ever

983 posts in 1731 days


#5 posted 12-21-2011 09:07 PM

I believe it is the fact that most spiral bits are made of solid carbide that makes them fragile, not necessarily the upcut/downcut/spiral design.

FWIW, you can get spiral bits in HSS that don’t have the fragility issues of the solid carbide bits. Of course, they won’t stay sharp as long as the carbide ones.

-- Optimists are usually disappointed. Pessimists are either right or pleasantly surprised. I tend to be a disappointed pessimist.

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mcgriffith

87 posts in 1118 days


#6 posted 12-21-2011 09:28 PM

I do not have experience to share with you concering your question, but I got interested becasue when I read the question, I thought, what is the answer and what can I learn about this without asking the same question some day. As RichGreer answered and then showed the link in his second comment, I find it interestng that the upcut bit has the swirl of the cuting edge go up to the right while the swirl of the downcut bit goes down to the left – just interesting to learn that and notice it as a factor in the bits I never thought about.

Thanks for the question and help that I am learning from. ...mike…

-- Michael TX, Not even my wife understands my sense of humor.

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richgreer

4524 posts in 1796 days


#7 posted 12-21-2011 10:07 PM

I’m going to speak up to comment on Mike’s comment above. I have never sensed that the spiral bits provided a cleaner cut – but they are faster. In fact, they can be very fast.

On many occasions I have used my plunge router and a Mortise Pal jig with the doweling template to “drill” holes for dowel connections. I can “drill” a 1/2” x 2” hole in about 5 to 10 seconds depending on the wood with a upcut bit.. I cannot come close to that with a straight bit or with a drill press. Of course, a DP is running at about 1000 rpm and the router is running at 22,000 rpm.

-- Rich, Cedar Rapids, IA - I'm a woodworker. I don't create beauty, I reveal it.

View pintodeluxe's profile

pintodeluxe

3513 posts in 1535 days


#8 posted 12-21-2011 10:53 PM

1/8 spiral downcut bits are frequently used for template inlay work. They work great, with no tearout at all. You are removing such a small amount of material, I would go with the downcut.
For a 1/8” groove, I actually prefer the tablesaw.

-- Willie, Washington "If You Choose Not To Decide, You Still Have Made a Choice" - Rush

View GaryK's profile

GaryK

10262 posts in 2710 days


#9 posted 12-21-2011 11:43 PM

I did a post on this subject about a year ago.

http://lumberjocks.com/topics/24784

-- Gary - Never pass up the opportunity to make a mistake look like you planned it that way - Tyler, TX

View Furnitude's profile

Furnitude

346 posts in 2228 days


#10 posted 12-22-2011 07:18 PM

View DS's profile

DS

2132 posts in 1142 days


#11 posted 12-22-2011 08:34 PM

Tear out and application usually will determine the best type of spiral to use. If you are using a bit in a panel router (or router table) to cut dadoes in melamine, a downcut spiral will shear the melamine cleanly with no tearout at the edges. An upcut will run cooler, since it clears the debris easier, but it will tearout the laminate.
If you are routing a fairly hard, dense solid lumber, the cooler upcut may be preferrable since tearout would be negligable—though I would consider a chip breaking up-spiral cutter so the debris will clear easier.

In solid carbide there is also something called a compression spiral. This has an upcut for a portion and a down cut for the remainder of the cutting surface. This is usually used to cut two sided melamine parts on a cnc router, or with a collar and templates and jigs.
Since the debris is slightly compressed at the middle of the bit before clearing out, this type runs hottest of them all, but can cut cleanly at the top and bottom with no tearout.

-- "Hard work is not defined by the difficulty of the task as much as a person's desire to perform it.", DS251

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