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Proper pewa positioning

Alan Weinberg

Alan Weinberg

Joined
Feb 18, 2023
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Orange, CA
From what I see, pewa, or bowties, are usually placed perpendicular to the crack with the narrow waist over the crack. I placed a couple parallel to the crack and I think it looks pretty good also. I was just experimenting. What are your thoughts on pewa placement? Is it artist choice?

Traditionally, corners are sharp but I also like the softness of the rounded corners.
IMG_8806.jpeg
 
I have never been a fan of rotten wood or radial checks or ring shake so I don't have a need for butterfly keys to hold a piece together. The light colored key on the left looks like it may be on a ring shake crack and as such makes no sense at all because it does not hold the two sides together. As far as Hawaiians historical use of PEWAS I thought I had read that it was for the repair of existing bowls, since they were difficult to make new replacements with the tools available so they were still valuable.
Hope you don't think I am being nasty but I am just expressing an opinion contrary to the current fad of trying to get something out of overly decayed timber. There is an abundance of good solid wood available even in large metro areas as you have already proven in a previous post, but it might be a good idea to transport it in something other than a two seat sports car.
 
Pewa or butterflys have long been used to bind cracks together. The reason for the shape is that the "wings" lock across the crack and resist its widening.
Maybe you're repairing an old piece. Or a new piece had cracks in the wood. Or you want to make something that looks like it was repaired. Or maybe you're using pewa as some sort of artistic element. All that's fine with me.
But seems to me that if you are bridging a crack, you ought to respect the geometry and structural reason for the butterfly shape.
My $0.02 - maybe not even worth that.
 
Dave Landers said:
Pewa or butterflys have long been used to bind cracks together. The reason for the shape is that the "wings" lock across the crack and resist its widening.
Maybe you're repairing an old piece. Or a new piece had cracks in the wood. Or you want to make something that looks like it was repaired. Or maybe you're using pewa as some sort of artistic element. All that's fine with me.
But seems to me that if you are bridging a crack, you ought to respect the geometry and structural reason for the butterfly shape.
My $0.02 - maybe not even worth that.
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I’m not a structural engineer but the crack had no gap, the piece wasn’t in danger of falling apart, and I felt artistically that the way I arranged them looked better than the conventional placement. But I posted the thread to hear different opinions, so thank you!
 
Its your choice If you like them positioned the way you have them. But… @Dave Landers is correct, pewas are for improving structural integrity and are shaped accordingly. For purely decoration, any shape can be inserted any way you want.
 
Bill Boehme said:
Once wood has split due to internal stresses means that the stresses have been relieved so unless you tried to pull the crack closed and then hold it closed by installing patches the patches don't have any appreciable forces acting on them. Another way to look at your question would be to observe if the crack is essentially stable without a patch ... If so, the forces acting on the patch would be the minimal.

Concerning the pewa patch not going all the way through, assuming that the patch is glued in place, a lap joint is stronger than a mitered joint.

I am assuming that our normal use of a patch is an embellishment and not something that is intended to make the vessel watertight.
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Back a few years I posted about pewas asking if they go all the way through the bowl wall. And observed a 3/16" thick pewa doesn't have much holding strength once it's sanded down to match the curvature of the bowl. I did assume cracks were pulled together and held together by the pewa. The above was Bill's response.

Are any folks actually using pewas to hold a crack together after it's been forced closed?

Pewa cutting of the opening and the insert itself are a good use of CNC. No router guide templates needed and the corners don't need to be rounded. Picture below shows a random, non-symmetrical shaped bow tie I did using what's called v-carve inlay technique.

pewa.JPG
 
Doug Rasmussen said:
Are any folks actually using pewas to hold a crack together after it's been forced closed?

Pewa cutting of the opening and the insert itself are a good use of CNC. No router guide templates needed and the corners don't need to be rounded. Picture below shows a random, non-symmetrical shaped bow tie I did using what's called v-carve inlay technique.

View attachment 68242
Click to expand...
I have used dovetail keys as well as straight glued splines once or twice to stabilize cracks in turnings. If I were using a key to hold together a crack under stress I would want the mechanical advantage of a square-edged key as well as the glued surface. I hate the look of round-ended pewas but I don't think the v-inlay process is as strong as a standard routed recess with the corners trued up with a chisel. No offense, but that asymmetrical key doesn't appeal to me.

I think explicit crack repairs are ok to hold together an otherwise good form. They should be oriented with the length of the key perpendicular to the crack for strength. Strictly decorative pewas are not for me. I throw up in my mouth a little when they are made with open gluelines.
 
Sloppy glue lines are of course not appealing. I personally prefer the rounded corners which to me look softer, if that makes sense. I usually use pewa—and splints and round coins—just to highlight a crack which then gets filled with colored epoxy. As usual, this thread shows a variance of opinions, which is appreciated.
 
I recently did some experimentation and found that it in some cases* you can put in sharp corner pewa into a round pocket without doing any clean up of the corners.
I obviously messed up the angle of the middle one, so I began to play around and for the one on top I just tapped a sharp corner version into a pocket, no modification. I did this to several and it worked quite well. The corners are radiused for a 3/32" endmill, so there isn't really a lot there to clean up anyway.

20241019_201342.jpg

* this was a rough-out, and the pewa material (don't know what it is, but maybe osage orange) is likely harder than the work material.
 
Kevin Jenness said:
t I don't think the v-inlay process is as strong as a standard routed recess with the corners trued up with a chisel. No offense, but that asymmetrical key doesn't appeal to me.
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Never done any testing of the relative holding strengths between v-carve inlay and the template routed version. I kinda think the v-carve type might be a bit better because you have a longer glue surface around the perimeter of the pewa.

The asymmetric bowtie was to demonstrate for a class the inlay needed a mirror image profile when the inlay is not symmetric. V-carve inlays have usage in embellishment of all sorts of woodworking and woodturning pieces and many times they aren't symmetric which users frequently don't realize.
 
My point is that a traditional dovetail key has a mechanical lock independent of glue resulting from its shape. A v-inlay depends entirely on its glue bond to hold a crack together, and should be equally effective no matter its shape. That's not to say v-inlays or simple, well-glued splines are not effective, just that they don't work quite the same way and strictly rely on glue.
 
Doug Rasmussen said:
_MG_0060.jpegBack a few years I posted about pewas asking if they go all the way through the bowl wall.
Click to expand...
If you consider the gluing surfaces and factor in the amount of end grain gluing it would seem to me that if the pewa goes all the way through the bowl wall it’s relying on just the glue at the perimeter of the patch/hole. There may be an equal amount of face/end grain included. Traditional pewas that bottom out in the recess add the face grain glue joint that is inherently stronger (as I understand it) from the mating bottom surfaces.

I’ve done both. Doing fully pierced pewas is kind of a pain - I needed to source longer router bits to get the depth I needed, and the patch itself needed to be thicker as well. It works, but adds considerably to the process. I generally put in the patches with the outside finish turned and the inside rough hollowed.

Not entirely sure how much most cracks benefit from the additional strength, but where I’ve used the fully pierced versions it is usually spanning a wider crack/inclusion. I have had these pop out on two occasions when finished bowls were dropped…
 
Googling on bowtie splines and related terms, lots of hits. Most were related to flat planks rather than bowls. Surprise, no one showed any full thickness, through bowties. Also, lots of mention of the bowties being a decorative embellishment.

Here's sometimes that might be of interest, search Youtube for "Strength Testing Bow Tie Keys - Woodworking". Turns out they may have more strength than I would have thought.
 
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I saw a You Tube video last night about some one using a Batman bat form to make a pewa for a table. It looked pretty good.... I am guessing there are many shapes that can be used....

robo hippy
 
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