# Router bit question -- upcut vs. downcut



## Furnitude (Oct 18, 2008)

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


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## richgreer (Dec 25, 2009)

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.


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## Furnitude (Oct 18, 2008)

Thanks, Rich. Very helpful.


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## richgreer (Dec 25, 2009)

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.


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## HorizontalMike (Jun 3, 2010)

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…


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## live4ever (Feb 27, 2010)

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.


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## mcgriffith (Nov 2, 2011)

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…


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## richgreer (Dec 25, 2009)

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.


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## pintodeluxe (Sep 12, 2010)

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.


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## GaryK (Jun 25, 2007)

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

http://lumberjocks.com/topics/24784


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## Furnitude (Oct 18, 2008)

Thanks, all.


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## DS (Oct 10, 2011)

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.


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