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Spiral Upcutting vs downcutting router bit

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Forum topic by Josh posted 1592 days ago 5356 views 0 times favorited 11 replies Add to Favorites Watch
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Josh

99 posts in 1647 days


1592 days ago

Topic tags/keywords: question

Can someone help me understand when I would use one vs the other. I watched a woodsmith shop that said they use the downcutting bit when working with plywood so that it wouldn’t rip/chip the veneer. When would you use an upcutting bit then?

-- Josh, South Jordan Utah


11 replies so far

View woodworm's profile

woodworm

14124 posts in 2216 days


#1 posted 1592 days ago

For cutting mortises & tenons, I use upcut. Clean bottom (and for through mortise on the exit opening).

-- masrol, kuala lumpur, MY.

View Michael Murphy's profile

Michael Murphy

448 posts in 1630 days


#2 posted 1592 days ago

Upcut or upshear bits will pull the chips up and out of the cut. Downshear leaves a crisper, cleaner edge on the top surface of melamine and plywood for dadoes and mortises. It cuts with a downward pressure and tends to pack the chips down. There are also compression bits that combine the two for through cutting of plywood or melamine or any two sided material so it elimiates chipping on both sides. The bottom portion is upshear and the top portion is downshear. These are usually used more on CNC machinery than with the hand held router.

The cutting edges are either spiraling down or spiraling up or both (compression).

-- Michael Murphy, Woodland, CA.

View live4ever's profile

live4ever

983 posts in 1635 days


#3 posted 1592 days ago

It’s all about which way you want the bit to pull the chips.

Upcut bit pulls them “up” – towards the router.
Downcut pushes them away from the router.

As Masrol said, if you’re cutting a mortise, you want the chips being pulled out of your hole, hence upcut.

Downcut bits exert more downwards pressure (in addition to forcing chips away from the router), so that might be better for smaller workpieces. They are also good for reducing tearout on the upper edge as your vid mentioned.

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

View closetguy's profile

closetguy

744 posts in 2517 days


#4 posted 1592 days ago

Upcut – faster chip removal. Downcut – cleaner edges on top. Just pick the right one for your application.

-- I don't make mistakes, only design changes....www.dgmwoodworks.com

View Brad_Nailor's profile

Brad_Nailor

2531 posts in 2583 days


#5 posted 1592 days ago

I use a compression bit in my router with a straight edge to rough cut plywood down to a manageable size. It works better than a circ saw and leaves a much cleaner edge.

-- http://www.facebook.com/pages/DSO-Designs/297237806954248

View TomHintz's profile

TomHintz

207 posts in 2023 days


#6 posted 1592 days ago

At times it comes down to personal preference but there are some basics to making gthe choice. I have a story on this at the lin below that shows some examples if that would help. When you remember the direction of the spiral cut you will find other uses in the shop for cleaning up cuts that can cause chipping.

http://www.newwoodworker.com/updowncutbits.html

-- Tom Hintz, www.newwoodworker.com

View Josh's profile

Josh

99 posts in 1647 days


#7 posted 1592 days ago

thanks for the link and thanks everyone for your quick responses

-- Josh, South Jordan Utah

View richgreer's profile

richgreer

4522 posts in 1700 days


#8 posted 1591 days ago

Please note that if you are using an upcut bit on a router in a router normal router table the chips are actually being pulled down (towards the router). For me, it gets confusing.

Nonetheless, I use an upcut bit frequently. I just used it today with a handheld router to cut a groove for an inlay. It clears the chips away very nicely. I also use it frequently in the router in my router table.

I virtually never use a router on a piece of plywood. I understand that, with plywood a downcut bit can be useful. However, from my perspective, I see no need for a downcut bit.

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

View Ger21's profile

Ger21

622 posts in 1756 days


#9 posted 1591 days ago

Also, an upcut will leave a much smoother bottom than a downcut.

-- Gerry, http://home.comcast.net/~cncwoodworker/CNC_Woodworker.html

View widdle's profile

widdle

1377 posts in 1624 days


#10 posted 1576 days ago

Im a little late on this topic ..but was just in the shop using a 1/4 ” down cut bit in my new little router table with a 1 horse motor cutting slots in 3/4’ poplar and the bit seemed to devolop a slight wobble . Was a little concerned with the bit breaking ? Should i be ? Was really looking forward to making some much needed jigs with that bit …But the bit also created a high pitch whine ..didn”t sound too happy..Any feedback would be great
thanks

View Ger21's profile

Ger21

622 posts in 1756 days


#11 posted 1576 days ago

Down cut is probably a poor choice in a router table, as it’ll want to lift the wood off the table.

1/4” bits will frequently scream, unless you’re taking very light cuts. Very common.

If the bit is carbide, it won’t bend, it’ll just snap. If it’s wobbling, check the collet.

-- Gerry, http://home.comcast.net/~cncwoodworker/CNC_Woodworker.html

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