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"Shallow cuts with the router", but how shallow?

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Forum topic by KnickKnack posted 04-11-2012 09:51 AM 1674 views 1 time favorited 13 replies Add to Favorites Watch
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KnickKnack

992 posts in 2290 days


04-11-2012 09:51 AM

Topic tags/keywords: router depth of cut shallow passes

I do almost everything with my router – mostly in the table, sometimes hand-held.
I’m familiar with the mantra of “many shallow passes”, and I do that.
I’m also a subscriber to the idea that “if it works, it works”.
I also suspect that I have a tendency to be ultra-conservative, and take more passes than I need to be, or “should” be, taking.

My question though, is about what the considered opinion of the more expert router users is as to “how shallow is shallow”.
Let me pose the question(s) in specific terms…
Presuming you have a decent router, and decent quality, sharp bits…
  1. If you’re cutting a simple slot with a 6mm (1/4”) bit in pine, at what depth of cut would you start to consider taking 2, rather than 1, pass?
  2. If you’re cutting a simple slot with a 6mm (1/4”) bit in something harder like oak, at what depth of cut would you start to consider taking 2, rather than 1, pass?
  3. If you’re cutting a simple slot with a 12mm (1/2”) bit in pine, at what depth of cut would you start to consider taking 2, rather than 1, pass?
  4. If you’re cutting a simple slot with a 12mm (1/2”) bit in something harder like oak, at what depth of cut would you start to consider taking 2, rather than 1, pass?

Do the answers differ depending on whether you’re cutting cross, or with, the grain?

I know there are no hard and fast rules, and that each piece of wood differs from every other, and that how it’s feeling should be the main guide, I’m just looking for some idea of what I “should” be doing, if I knew what I was doing.

Thanks in advance.

-- "Do not speak – unless it improves on silence." --- "Following the rules and protecting the regulations is binding oneself without rope."


13 replies so far

#1 posted 04-11-2012 10:36 AM

Knick Knack,
Cutting with the grain or across does indeed make a difference. Cutting across the grain usually is more difficult and may result in a breakout at the end of the pass.
But there are no rules or math that will answer the questions about depth of cut and number of passes. Not in my poor judgement, that is.
The method of making trial cuts in scrap is the best way to determine the answers. Even the differences between one board of the species to another can be significant.
So I offer this idea. Always have extra material for trial passes.
If it feels unsafe, for you or the material, don’t do it.

Finally, I offer this, don’t do anything you wouldn’t want to explain to emergency medical personnel.

Best regards,
Don

-- Will trade wife's yarn for tools.

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MoshupTrail

298 posts in 1205 days


#2 posted 04-11-2012 10:51 AM

Listen to the wood and listen to your router. If the router slows noticeably then take less. If you can hear that crackly sound like planer tear-out, then take less. It should be a nice, smooth, not complaining sound. (Sorry, that’s really subjective, and I think you might have preferred a more concrete answer)

When doing end grain I always go around the piece in a counter-clockwise direction. So if there is any breakout on a side, I’ll be going over it when I rotate the board to the next side. But that only works when you’re doing all 4 sides.

-- Some problems are best solved with an optimistic approach. Optimism shines a light on alternatives that are otherwise not visible.

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AaronK

1398 posts in 2188 days


#3 posted 04-11-2012 11:17 AM

you shoul;d be telling US, roger!

View Viktor's profile

Viktor

448 posts in 2143 days


#4 posted 04-11-2012 09:17 PM

Using ~ 1500 W router going along the grain I would start with approximately:
1. 10 mm
2. 7 mm
3. 7 mm
4. 5 mm
Probably little less across the grain.
But I also agree with what MoshupTrail said in post #2.

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RickRogers7

39 posts in 1762 days


#5 posted 04-12-2012 01:52 AM

I’m with Moshup Trail. I usually go by sound and the amount of force required to make the cut. Charles Neil does have a nice you tube video on bump cutting (another form of clim cutting) for dealing with end grain.

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Tennessee

1524 posts in 1238 days


#6 posted 04-13-2012 05:06 PM

I use mainly a 2HP Bosch router running a 1/2” shaft, 1/2” X 1.5” long round twin carbide cutter to rout out the tonal chambers in my guitars. My rule of thumb is anything over 10MM, two passes. If I have to rout out say, 28MM, I would take three passes. I am mostly going both ways, against and with the grain since the tonal chamber is the approx. size of my pickguard. My router does not bog down at all.
I have taken as much as 15MM a pass, but only on softer woods, like walnut or ambrosia maple.

-- Paul, Tennessee, http://www.tsunamiguitars.com

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KnickKnack

992 posts in 2290 days


#7 posted 04-15-2012 03:43 PM

Thanks for the replies.
I think I’m maybe being a little on the conservative side of expert wisdom, which is the right side.
What brought this issue to my attention was watching a few videos where the cuts they made just seemed effortless – like a knife through butter – mine seem more like the wrong side of a blunt knife through butter frozen down to almost absolute zero.

-- "Do not speak – unless it improves on silence." --- "Following the rules and protecting the regulations is binding oneself without rope."

View Dan Lyke's profile

Dan Lyke

1488 posts in 2849 days


#8 posted 04-15-2012 04:12 PM

In pine, I might try for a quarter inch per pass, in harder woods I go for about 1/16”. I’ve tried more (like trying to cut a sliding dovetail in a hard wood in a single pass) and just destroyed the bit (in one case, shearing off the shaft). Now, for a sliding dovetail I’ll rough out with a straight bit first.

So about half of what Viktor posted.

-- Dan Lyke, Petaluma California, http://www.flutterby.net/User:DanLyke

View Rutager's profile

Rutager

27 posts in 1027 days


#9 posted 04-15-2012 04:26 PM

Hello,

I’ve always heard that a good rule of thumb is not to go deeper than the diameter of the bit on each pass, so bigger bits can go deeper, of course at a certain diameter the horse power of the router may come into play. I myself tend to be much more cautious on my cutting depth and usually try and do a final pass of 1/32” or less to get a cleaner finish.

Best,
Rutager

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gavinzagreb

210 posts in 1044 days


#10 posted 04-15-2012 08:41 PM

Roughly, I’d say I do 5mm at a time in most cases. If it’s a really soft wood like pauwlonia, I might do 10mm at a time.

View Monte Pittman's profile

Monte Pittman

15157 posts in 1062 days


#11 posted 04-15-2012 08:53 PM

guess I am a conservative. I don’t go more than 1/8 to 3/16 of an inch at a time.

-- Mother Nature created it, I just assemble it.

View eddie's profile

eddie

7493 posts in 1338 days


#12 posted 04-15-2012 09:01 PM

may be a stupid question ,i,m new and like to use my router dose motor speed play a part in this ?

-- Jesus Is Alright with me

View a1Jim's profile

a1Jim

112544 posts in 2301 days


#13 posted 04-15-2012 09:08 PM

Lot’s of good answers, I wouldn’t have a problem cutting a 1/4” with the grain in one pass or even across the grain in pine,as long as I’m not using a 1/16” router bit. Like the others have said listen to you router and check to make sure it’s not bogging down and what you cut looks like.It also has to do with what your routing(type of cut) and what shape your router bit is in. If I’m routing a profile along the edge of a board I’ll almost always take to passes just to insure a good clean cut. I would suggest taking some time to just experiment to see the results you get using different router bits on different woods .

-- http://artisticwoodstudio.com Custom furniture

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