Avoiding Tear-Out in Arched-Top Cope-and-Stick Door Machining
I have better luck with doing the arch (rail) first on an oversized piece, then cut to length, then do the ends. Make sure your router or shaper bits are super sharp. When cutting the rail ends the problem, if it occurs, is always at the trailing edge if you're feeding into the cutter. I always make two passes, cutting about 95% on the first pass, very slow, and the remaining on a faster pass. That means the wood will burn on the slow pass, but the fast pass will clear that away.
Last of all, if that doesn't work, I'll feed backwards (with the grain) the last little bit first, then go back to feed most of it into the cut. You have to be real careful with this, but it usually prevents tear-out. For me, with cherry, the two-pass method works fine. You're having a problem with cherry I'd suggest your blade isn't sharp enough.
From contributor G:
Don't cut the arch until the end. First cut the angles on the pc that will form the arch. The board should be wide enough to have the arch cut out of it (obviously). Set up your coping machine a using a miter jig cut both end copes. Then cut out the inside arch, sand and do whatever to make it good. Then run it through your stick profile. Then you will glue the door up leaving the outside of the arch flat/straight. After the pair of doors is glued up lay them together with the proper spacing in between them and draw your arch and cut and sand it.
From the original questioner:
Thank you for your replies. Contributor G I'm not quite sure you understood me or I'm not understanding you! Contributor S you were correct on what I was getting at. However, the wood is beech not cherry (or alder which machines well like cherry and wouldn't be a problem). The beech is kind of like oak in that it is brittle (hard and brittle). I think what I've resigned myself to do is lessen the arch on the rail as it comes to the stile. 95% eyebrow arch with just a hint of a cathedral! I checked out my local big box store and it looks like 2/3 of the manufactures out there do this with their eyebrow arches. Thanks so much. If anyone else has advice please chime in and again thank you to those who have.
From contributor S:
Hopefully I'm understanding your question correctly.
1. I first cut the rail the exact length and oversize the width.
From contributor R:
How about cutting all of your arched top rails an inch too long? You can also cope the right side. Cut/shape the arch off-center by one inch. Cut off the left side to final length, removing the blow out from shaping the arch profile and groove. Then cope the left side. By coping in this order, you can use a simple flat backer board to avoid blow-out.
From contributor S:
I just want to add something to the info I posted earlier. This is reference to cutting the "cope" in the ends of your arched rails, after the arch itself has been profiled. If after proceeding in the steps I outlined above you are still getting tear-out on the bottom corner of your arch you may have to "protect" that corner while cutting.
This is accomplished by first cutting a mirror part for at least part of the arch. This would be for the right side of your arch, since that is normally where the tear-out occurs. The idea is to cut a cope into the mirror arch, then fit it tightly into the true arch. You now have two parts fit together: your arch for the door and the coped mirror arch. You then run the pair together into your router or shaper. While you are coping the arch end the trailing edge is protected by the mirror.
Note that the mirror arch can be used to protect all arch rails with the same arch profile. At the end the mirror arch is discarded, so it can be made of scrap material. If you have more than one arch profile you would make a different mirror arch for each one.
From contributor O:
Hope this message reaches you in time to prevent the afore-mentioned "hair pulling" event. I work for a woodworking machinery manufacturer. We manufacture machines which can produce an arched panel or an arched rail from a piece of stock, without being pre-shaped, and also manufacture machines which require that the substrate be pre-shaped. In the latter case, we've found that a backer-board eliminates most of the blowout, but the style of backer board varies with the species of wood, the type and depth of cut, and the feed rate, As previously suggested, making a sacrificial "mirror image" piece to fit into the arch may cure some of the issues, but there is a simpler method which cures almost all of the issues.
Cope the ends first. Cut a board approx. 6" wide, and 45 degree one end of it. Then, cut your stick cut on the 45'd end. When you cut the arch, plug the two pieces together. An added advantage to this method, is that the 45'd board can be used repeatedly, and (if you play with the angle of the cut a little) can be used as a push stick.
From contributor S:
There are all kinds of alternatives. The only problem I would have with contributor O's method is that for my use I use a sled that holds the wood piece and the template in place, and there is no way (in that sled) to hold the piece he describes. Other than that, it seems like a workable solution.
From contributor J:
I have a weaver sled that holds the pattern and the piece to be milled. Back the piece into the cutter-climb cutting and go about two inches then cut the rest from the front. This has limited the rejects when making a set of doors.
From contributor O:
The method I described applies strictly to feed-through machinery, not single-spindle stationary shapers. Sorry for not clarifying in the previous post. I guess I was assuming the Larick was their model which has a floating, rub-collared first station shaper.
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