Pattern routing

[Dennis McDonaugh]

I'm making a set of chairs and wanted to use a pattern and router to make all the backs the same size and shape. I'm get lots of tearout going against the grain and can't figure out a way to always route with the grain short of taking the pattern off and putting it on the other side of the back. Am I looking at this correctly or is there another way to do it? (besides switching from a top bearing to a bottom bearing bit)

[Chris Barton]

Have you considered climb cutting?

[Dennis McDonaugh]

Chris, its not the direction of the feed that's causing the tearout, its the rotation of the cutter. When the blade spins into the grain, it splinters.

[Richard Wolf]

Well you know the answer, you just don't want to hear it, switch to a bottom bearing bit. This is why shapers have forward and reverse.

Richard

[Mike Vermeil]

Have you considered climb cutting?

No offense Chris, but I have never had any success with climb cutting, and despite my best efforts to avoid it, have had a couple near-misses with injuries due to the bit grabing a hold of the workpiece. No matter how little of material I leave to remove with the climb cut (I'm talking 1/32-1/64"), the router bit always seems to find a way of grabbing the wood & shooting it across the shop.

I highly recommend switching bits, or moving to the spindle sander for against-the-grain stock removal.

[Dennis McDonaugh]

Well you know the answer, you just don't want to hear it, switch to a bottom bearing bit. This is why shapers have forward and reverse.

Richard

I know Richard, I was hoping someone had a magic bullet. I guess I'm off to woodcraft in the morning.

[Joseph N. Myers]

Chris,

Popular Woodworking, June 2005, #148, page 20, Tricks of the Trade, "Double-sided Router Template Jig". Basically, make 2 identical templates glued to a spacer stock that is 1/16" thicker than the stock to be shaped. Stock is placed in the middle held in with wedges. Uses a top bearing straight bit in a router table. When the grain changes, just flip the template. In the example, the guy had 24 of them to do so worth the effort of the jig. And besides, he had to do both sides, so really 48 sides.

If you don't have the article, I can send it to you (e-mail, fax, or whatever),

Regards, Joe

[Ian Barley]

Can you clarify "tearout". Do you mean fibres of the grain being raised giving a rough edge or do you mean timber getting deep splinters around curves on the cut?

I use an inverted router (onsrud) to router cut patterns all the time. Generally the technique is to make sure that either the complete width of the bit is buried in the timber with a waste portion also equal to the diameter of the bit OR that the waste portion is less than 1/2 of the diameter of the bit. Basically that means that if you are using a 1/2" bit the waste needs to be either at least 1" or less than 1/4". Try bandsawing your piece to a rough dimension and shape and then use the router for the final dimensioning.

Even with the above you are still liable to get some lifting of the grain but this should go with a light sanding.

[Lynn Sonier]

I had trouble with tearout on a project once. I set up two routers - a router table mounted with top bearing bit and a handheld with a bottom bearing bit. I just switched back and forth as needed. Came to this arrangement after I screwed up some good (and expensive) wood.

[Byron Trantham]

I use a piloted, solid carbide, spiral cut router bit for pattern cutting. The shearing action pretty much eliminates tear out.

[pat warner]

Tearout can be severe with full thickness cuts, whether with or against the grain. If the cuts are staged, say 10-20%/pass, the tearout & adversity can be substantially reduced, climb or anti-climb cuts notwithstanding.
That will require:
1) A Plunger
2) A sharp cutter
3) A well centered collar guide-bush
4) A smaller templet to accommodate the offset in the cutter/collar ensemble and
5) The work has to be fenced in and clamped to its templet, no tape. Tape allows the work to squirm and the work cannot move.
A lot of work but consistant & good results and you get smarter.
Routers

[Dave Richards]

I attach the pattern to the work with carpet tape and cut what I can with a pattern trimming bit, bearing nearest the router. Then I switch to a flush trimming bit, bearing at the distal end of the bit, and flip the work over to get the last of it.

I've seen that somebody, CMT?, Freud?, has a bit with a bearing at each end. I haven't bought one yet but it seems like a great idea.

[Dennis McDonaugh]

Can you clarify "tearout". Do you mean fibres of the grain being raised giving a rough edge or do you mean timber getting deep splinters around curves on the cut?

I use an inverted router (onsrud) to router cut patterns all the time. Generally the technique is to make sure that either the complete width of the bit is buried in the timber with a waste portion also equal to the diameter of the bit OR that the waste portion is less than 1/2 of the diameter of the bit. Basically that means that if you are using a 1/2" bit the waste needs to be either at least 1" or less than 1/4". Try bandsawing your piece to a rough dimension and shape and then use the router for the final dimensioning.

Even with the above you are still liable to get some lifting of the grain but this should go with a light sanding.

Big splinters Ian. I bandsawed the blank to 1/16 to 1/8 over sized so I'm not taking much of a cut. The pattern routing bit is 1 1/4" in diameter so I'm using the middle speed on the router.

[Dennis McDonaugh]

I use a piloted, solid carbide, spiral cut router bit for pattern cutting. The shearing action pretty much eliminates tear out.

Byron, I looked at those bits, but didn't want to spend the extra $$, I may be regretting it today.

[Dennis McDonaugh]

I attach the pattern to the work with carpet tape and cut what I can with a pattern trimming bit, bearing nearest the router. Then I switch to a flush trimming bit, bearing at the distal end of the bit, and flip the work over to get the last of it.

I've seen that somebody, CMT?, Freud?, has a bit with a bearing at each end. I haven't bought one yet but it seems like a great idea.

Dave, do you know what the difference is between a pattern cutting bit and a flush trim bit?