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End checking in sipo back plates
http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10101&t=50821		 Page 1 of 1
Author:  J De Rocher [ Wed Jul 18, 2018 3:10 pm ]
Post subject:  End checking in sipo back plates
I cut a 3/4" wide strip off the end of one of the sipo back plates I was planning to use for the current guitar so I could make tiles for a segmented rosette. As soon as I picked the strip up off the band saw table it simply fell apart into six pieces from cracks with the grain. I then cut a 3/4" strip off the corresponding end of the other back plate and it did the same thing. It spooked me that only one of the cracks was at all visible before cutting. The others were completely invisible. I cut a strip off the far end of the first plate and it was fine. It held together and it didn't crack under bending.

The plates were extra long so I cut a second 3/4" strip off the ends of each plate. Those strips did not fall apart, but they did break under bending in to three and four pieces. I cut a third strip of each plate and those did not break or crack under bending.

I also cut a 3/4" strip off the end of a back plate from a second sipo set I have with the same sort of figuring and it was fine so the cracking in the first set doesn't seem to necessarily be a characteristic of sipo in general and may just be a quirk of that particular set.

Am I safe to assume that I have now removed the end checks from that end of the plates and they are safe to use for the guitar?

Attachment:
Cracks in end of sipo back plate 1.jpg

Attachment:
Cracks in end of sipo back plate 2.jpg
Author:  meddlingfool [ Wed Jul 18, 2018 3:54 pm ]
Post subject:  Re: End checking in sipo back plates
I'd say so. You can flood it with water thin CA and any cracks will show by wicking it up...
Author:  Michaeldc [ Wed Jul 18, 2018 3:56 pm ]
Post subject:  Re: End checking in sipo back plates
Hi Jay,

What happens if you flex that last intact strip? I think I'd try flexing the plates also and if they hold together run with it. It wouldn't take long to brace it and reevaluate it again then also. I had some padauk sets that I resawed do the same thing. Unfortunately I didn't notice the problem until I started finishing. I went through the stack and gave them all a little crossgrain tweak and ended up with a couple failures that turned into ukes.

Best, M
Author:  jfmckenna [ Wed Jul 18, 2018 4:06 pm ]
Post subject:  Re: End checking in sipo back plates
I would think so too and I would also flood the end grain with CA. It's nice looking Sipo.
Author:  J De Rocher [ Wed Jul 18, 2018 4:09 pm ]
Post subject:  Re: End checking in sipo back plates
Michaeldc wrote:
Hi Jay,

What happens if you flex that last intact strip? I think I'd try flexing the plates also and if they hold together run with it. It wouldn't take long to brace it and reevaluate it again then also. I had some padauk sets that I resawed do the same thing. Unfortunately I didn't notice the problem until I started finishing. I went through the stack and gave them all a little crossgrain tweak and ended up with a couple failures that turned into ukes.

Best, M


Both of the last strips I cut off stay intact when I flex them. Each of the second strips I cut off broke with very slight flexing. The first strips fell apart on their own. I'm not seeing or hearing any signs of cracking when I flex the plates.

The plates are about 0.150" thick now. I'm thinking I'll go ahead and glue the plates up and bring them down to final thickness and see how they are holding up then. At that point, I'll also try wicking thin CA into it to look for cracks as Ed recommended.
Author:  jshelton [ Wed Jul 18, 2018 4:58 pm ]
Post subject:  Re: End checking in sipo back plates
What you did is exactly what I do when I get ready to re-saw tops off cedar billets. It's worked fine for me for over 50 years so I assume you're good to go.
Author:  Haans [ Wed Jul 18, 2018 5:04 pm ]
Post subject:  Re: End checking in sipo back plates
You might be OK, but that is not saying that there won't be some cracks in the middle.
Here's a good check. Flood the piece with mineral spirits and flip it over after you glue the center seam and sand to close to final thickness. Circle the cracks and wick as Ed said. If the wood is that brittle, you might want to flood the inside and out with thin Cya. Let it cure without accelerator, then sand down to final dimension. This is what I did with my 90 year old brittle BRW and it works very well. The key is to sand it back down till you get wood dust again.
Wood was probably not originally end grain sealed before drying.
Author:  J De Rocher [ Thu Jul 19, 2018 3:15 pm ]
Post subject:  Re: End checking in sipo back plates
Here's what the sipo looks like after thicknessing, wiping one side down with naptha, and marking the spots where the naptha came through on the opposite side. Maybe this is why it's called sipo. laughing6-hehe

Based on the distribution, shape, and the grain, I'm thinking these spots correspond to pores that go all the way through rather than cracks. It's reassuring that there was no sign of crack-shaped seepage at either end of the plates, particularly at the neck end which is the end shown in the two photos in my first post.
Author:  Haans [ Fri Jul 20, 2018 8:14 am ]
Post subject:  Re: End checking in sipo back plates
Is that sipo or sieve-o?
Author:  jfmckenna [ Fri Jul 20, 2018 1:42 pm ]
Post subject:  Re: End checking in sipo back plates
Wow! On second thought idunno

The flooding with CA and sanding back sounds liek a good idea to me.
Author:  J De Rocher [ Sat Jul 21, 2018 1:50 pm ]
Post subject:  Re: End checking in sipo back plates
Why does it sound like a good idea?
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