Router use question and tearout - Woodworking Talk - Woodworkers Forum
 
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post #1 of 18 Old 01-08-2013, 11:35 PM Thread Starter
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Router use question and tearout

Hello,

I am making a simple 35" x 44" mirror frame out of poplar (as it's gonna be painted) and today I was routing out the rabbet on the back where the mirror will be set. The rabbet is approx 3/8" deep by almost 1/2" wide. Several places it is not smooth and the router tore out big chunks. When I was done I was quite concerned and wondered what I did wrong. After thinking about it, I think I should have done this in at least 2 but maybe 3 passes before I got the final depth. The bit is an Amana rabbet bit and is brand new so it is very sharp.

Am I correct in my assessment or something else that I should have cut the rabbet in several passes? Also, if I am correct, should the passes be done going deeper or wider in each pass?

- Bob
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post #2 of 18 Old 01-08-2013, 11:54 PM
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You are correct, more passes will reduce the tear out. I just cut a 1/2" rabbet 1/4" deep a few days ago. I set the depth to 1/4" and made 3 passes with different bearings, gradually cutting with each pass. I was cutting some hard maple.

I just have to remind myself to not get in a rush....and that's a challenge for me!

Hope this helps.
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post #3 of 18 Old 01-09-2013, 12:18 AM
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I think you've got the ticket with more gradual passes. It never hurts to test the operation you have planned on some scrap of the same material before hand. If there are any peculiarities in the grain (knots and other crazy stuff), this can also cause some problems. Were you routing clockwise or counterclockwise around the frame?
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post #4 of 18 Old 01-09-2013, 01:03 AM Thread Starter
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Quote:
Originally Posted by Phaedrus
I think you've got the ticket with more gradual passes. It never hurts to test the operation you have planned on some scrap of the same material before hand. If there are any peculiarities in the grain (knots and other crazy stuff), this can also cause some problems. Were you routing clockwise or counterclockwise around the frame?
I was going clockwise. Was that the correct or incorrect direction? Thanks - Bob
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post #5 of 18 Old 01-09-2013, 01:09 AM
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If you are holding the router, the outside of the object should be clockwise, and inside an object should be counter-clockwise.

If the router is in a table, these would be opposite because the router bit is essentially turning the opposite direction.

Please correct me if I am wrong.
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post #6 of 18 Old 01-09-2013, 01:42 AM
(clever wood pun here)
 
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An easy way to think about it is that you want to always be pushing the router against the direction that it is turning so that the cutters are moving toward the wood.
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post #7 of 18 Old 01-09-2013, 06:58 AM
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As everyone else has said, you got it right. If you can choose your timber and have an option on how to machine it, it is preferable to machine with your grain direction so that it naturally 'tears' or 'splits' in the direction you are removing the timber.

There is another process called 'back feeding' where you deliberately feed the material the wrong way. Again it needs to be done a bit at a time and very carefully. There is a high risk of the material being grabbed by the blade and thrown out. If you are not experienced at wood machining I would not recommend this method at all. If you are experienced and feel confident but have not tried this method I would say proceed with caution.

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post #8 of 18 Old 01-09-2013, 08:01 AM
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here's some diagrams

http://www.dekalbsaw.com/bitkickback.html

Feed against the rotation or into the cutter. If you feed with the rotation, it may/will grab and shoot the work in the direction of rotation.

The wood grain direction may also be a factor. If you are feeding INTO the cutter AND the grain is tearing out because it's being lifted up rather than cut/sheared off THEN you have to climb cut or feed with the grain. It's OK if you bump cut it, taking small partial depth cuts every 1/2" or 3/4" or so. You must have a good grip on the router and the work must be secured to the bench.


The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 01-09-2013 at 08:33 AM. Reason: wrong link
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post #9 of 18 Old 01-09-2013, 08:05 AM
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Quote:
Originally Posted by avewads View Post

Am I correct in my assessment or something else that I should have cut the rabbet in several passes? Also, if I am correct, should the passes be done going deeper or wider in each pass?

- Bob
Two maybe three passes can give a very clean rabbet. It's not necessary to change bearings (to increase width of the rabbet). Just make depth changes. Your last pass can be just a skim pass to clean off the edge.

Quote:
Originally Posted by DaveTTC View Post

There is another process called 'back feeding' where you deliberately feed the material the wrong way. Again it needs to be done a bit at a time and very carefully. There is a high risk of the material being grabbed by the blade and thrown out. If you are not experienced at wood machining I would not recommend this method at all. If you are experienced and feel confident but have not tried this method I would say proceed with caution.

Dave The Turning Cowboy
+1. It's also called "climb cutting". Here is a simple guide for router direction.
.






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post #10 of 18 Old 01-09-2013, 08:27 AM
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I agree climb cutting will reduce the amount of blowout when routing. You should make sure the router bit is especially tight in the router as the reverse direction can cause the router bit to start comming out of the router and make a deeper cut then you wanted. I normally set a router to the finished depth and more or less gently freehand a climb cut to a depth of about 1/8" and then route the rest of the cut forward.
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post #11 of 18 Old 01-09-2013, 08:36 AM
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Quote:
Originally Posted by cabinetman

+1. It's also called "climb cutting". Here is a simple guide for router direction.

.
I thought you guys might have a different term for it, just didn't know what it was, thx.

Also we don't call it a rabbet, I was taught 'rebate'. That's what you get talking with an Aussie lol

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post #12 of 18 Old 01-09-2013, 08:40 AM
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Quote:
Originally Posted by avewads View Post
Hello,

I am making a simple 35" x 44" mirror frame out of poplar (as it's gonna be painted) and today I was routing out the rabbet on the back where the mirror will be set. The rabbet is approx 3/8" deep by almost 1/2" wide. Several places it is not smooth and the router tore out big chunks. When I was done I was quite concerned and wondered what I did wrong. After thinking about it, I think I should have done this in at least 2 but maybe 3 passes before I got the final depth. The bit is an Amana rabbet bit and is brand new so it is very sharp.

Am I correct in my assessment or something else that I should have cut the rabbet in several passes? Also, if I am correct, should the passes be done going deeper or wider in each pass?

- Bob
Hi Bob - I concur with everyone else, that should have been a minimum of two passes. 1/2"x3/8" is a pretty good size hunk of tree to remove. As for going deeper or wider to change depth, either will work fine. I prefer going deeper each pass with a rabbetting bit as you don't need to change the bearing. Most of the time I do frame rabbets on the table. Works fine with mitered or half-lapped frames as the rabbets get hidden in the corners. If you are butt-jointing the corners you need to use stopped rabbets. I never butt-joint frames anyway.
I'm pretty sure you were going the right way with the router. On that large of a frame with that deep of a cut, you would have known fairly soon if the direction was wrong.

John

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post #13 of 18 Old 01-09-2013, 08:47 AM
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Quote:
Originally Posted by DaveTTC View Post
I thought you guys might have a different term for it, just didn't know what it was, thx.

Also we don't call it a rabbet, I was taught 'rebate'. That's what you get talking with an Aussie lol

Dave The Turning Cowboy

This is a rabbEt:



This is a rabbIt :


This is a rebate...in the USA:

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #14 of 18 Old 01-09-2013, 09:34 AM
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Priceless. Thanks for clearing that up!!

Sent from my DROID RAZR MAXX using Woodworking Talk
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post #15 of 18 Old 01-09-2013, 11:55 AM
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All very good information. I also try to take a minute before I start and gauge which direction the grain runs. It can give you a good idea of the side you need to take gradual cuts on. Doing the same thing right now on poplar cabinet doors with a glass panel.
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post #16 of 18 Old 01-09-2013, 12:07 PM
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Take a scrap piece of wood and a sharp knife. On a long edge corner of the wood try to shave off a 45 chamfer. On the same corner go the opposite way with the knife. In one direction the knife should be able to cut the chamfer cleanly. In the opposite direction the knife will dig in and a chunk may be lifted. This demonstrates grain direction.

Experienced woodworkers learn to see and work with grain direction. The visual can be different with each species. In some, it's easy to see, others not. The grain I'm speaking of in this case is related to the medula rays and the way a tree grows, not necessarily to the annual growth rings which are more often the visual we see on the face of the board, such as the cathedral arches seen on red oak, for example.

By seeing the "grain", we can plan ahead for operations like routing and position the work pieces so we cut with this "grain" whenever possible. This will do much more to eliminate tear out than any other tactic. Incremental cuts, leaving the last pass very light, are always a good choice for the best surface finish.

Unfortunately for us, boards don't always have consistent grain running in the same direction. When we need to rout both sides of an edge, one will have grain going the opposite way from the other. Many boards will have sections where the grain reverses and figured species will have grain going in all directions. Sometimes, "climb cutting" going opposite the way you should with a router, works. This is a tactic often used in doing curved work, where the grain runs opposite each side of the curve. On handplanes, jointers and planers, different sharpening angles are often used when working with figured grain.

Here is a picture of a pile of parts I'm working on. On the left is a cabinet top, 15"x42". This required a rounded bull nose around the perimeter, red oak. I used three tactics to deal with grain going the wrong way as well as end grain. I used a hand held router and a 3/8" roundover bit, which could have been sharper. I made the cut in four incremental cuts, I used climb cutting on the edges where the grain ran the wrong way and I replaced the standard round bearing with a square Euro style bearing to prevent bearing marks on the edge. This is fairly typical for me, using any "trick" I know to get the results I need without having to do extra work or risk a piece being ruined. It's an important part of woodworking, taking it slow and staying in control.
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post #17 of 18 Old 01-09-2013, 12:21 PM Thread Starter
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Thanks y'all! Lots of great information. Now, if I can just remember it all.

Woodnthings - I got a good laugh out of your reply on the pictorial of the different "rabbets". On that note, I will leave you with this, if you say "raise up lights" quickly, you are saying "razor blades" in Australian. ;-)
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post #18 of 18 Old 01-09-2013, 12:24 PM Thread Starter
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Hammer1 - very good explanation of what goes on with the wood grain. Thanks.
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