Primitive Archer
Main Discussion Area => Bows => Topic started by: DC on December 05, 2019, 11:36:21 am
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I bought four 4" boo logs. I've made one bow that has survived so they seem structurally sound but they have minor scrapes and stains. How much can I scrape the outside without being risky? What is this "rind" I hear about? How thick is it? I see some remove that. That may get rid of the flaws.
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The rind is very thin, like a sheet of thin paper. Unless it's a light scratch in the rind only, removing the rind generally doesn't help with dings, bruising, and other flaws, and they are places where splinters can raise. Try to lay the bow out between them.
When you remove the rind, you can get some it well sharpened scraper, then sand. It is better to leave some of it behind in the creases than remove ANY of the good stuff below trying to get all of the rind off.
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Thanks DWS. Is there any use in removing the rind if it's that thin? In the past with boo I've left the back natural. I just give it a good wipe with lacquer thinner so the finish will stick. There are too many marks to go between them so I'll just live with it I guess. The only way I could get boo was online so you use what you get. I took some of the small scraps and tried to break them and couldn't so I'm hoping it's good. I know bending isn't a definitive test but it's what I've got.
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I remove the rind for staining ..use a scraper then sand.. it will change color so its easy to track..otherwise it wont take stain.. I take the nodes down a lil not flatten... I leave those a lil proud.. this is on a boo backed bow... gut
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Thanks Gut, I won't be staining so maybe I'm better off leaving it. I haven't touched the nodes in the past. Here's what I've got.
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DC, the rind is a thin protective layer over the bamboo. If you want to stain the bow, remove the rind like gut said but be very careful. It doesn't take much to nick the power fibers and that's where a splinter can rise. Anywhere those power fibers are broken or violated, either by you with a scraper or damage done before you got it is a potential splinter origin.
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Remoweing the rind is simple work, does not take much time. I allways take it of. Better is to do it afer glueing because then you can easy remove dried glue with rind together. On your backing is the rind partly gone allready, i would not leave it on. You will get much better look as well.
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Just playing with some scrap pieces. When I'm scraping and the colour changes is that the end of the rind? If I'm not mistaken the "wood" gets harder then?
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Scraping off the rind would be like scraping shellac off. It's a thin film that protects the fibers from the elements.
The fibers on the outside of the bamboo are the densest and strongest of the fibers that make up the bamboo. As you get down below the surface of the culm the fibers are less tightly packed and weaker in structure.
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I see the rind as a sort of waxy layer on the outside of the bamboo, and as you scrape away at it, you'll reveal a light yellow layer underneath. That is the part that I want as the back. I use a scraper and get most of the waxy part off in between the nodes, then carefully scrape up over the nodes and in the little crease in the upper portion of each node. I am careful to only remove the waxy stuff and not cut into the bamboo any further.
Sometimes the bamboo is furrowed and you get stripes of rind that are in the grooves. If there is a lot of rind stuck in the grooves, I continue removal of the rind with 120 or 150 grit, focusing on the areas where rind still shows and avoiding the other areas. If there are not a lot of grooves, I use 220 grit to smooth everything out. I never use anything less than 120 because it leaves deep scratches.
I imagine if you go much further into the yellow, you'll start to see those brown fibers that you can see on the ends of bamboo where it is cut. You probably don't want those exposed.
For reference, I've done 7 bamboo backed bows, all with the rind removed via the method above, and while several of them broke, only one was due to an issue with the bamboo (there was a crack in a node that I didn't see until it was almost done). The others were due to glue failure or crushing the belly.
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I measured it this time. I looks like what I'm thinking is rind is about .010"(.25mm) thick. Sound about right?
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Sounds about right to me
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It's not really a pure thickness thing. Just scrape a couple of scraps and observe them under a magnifying glass. The rind is sort of like a layer of waxy varnish over a chalky paint film.
The safest thing is to just sand the waxy part and leave the rest.
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Pat M nailed it, I have made over 50 bamboo backed bows, early on I scraped every bit of rind off, sanded and finished. I had a few bamboo failures, looked closely and could see some very tiny diagonal cuts across the bamboo back. I realised no matter how careful I was the rolled edge on my scraper would dig in ever so slightly when it touched the back and make a cut. You couldn't see them unless the back had been stained, stain makes every flaw pop.
I started scraping the rind partially off, only going through the rind at the high spots and leaving the nodes alone except for the crumbly part on top. I sand the part of the rind down that was left after my initial scraping but barely get to the power fibers on most of the back. I sanded the rind slightly at the nodes but most of it was still there. No more failures.
My local bamboo doesn't have a perfectly flat back and has tiny shallow creases that run out from the nodes some. In the past I would dig out the rind in these creases now I leave that rind intact.
The sanded rind absorbs stain more than the slick power fibers for a nice effect. I did scrub the stained bamboo with a scotch bright pad between the nodes to lighten it somewhat,
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(https://i.imgur.com/xZ7SpWW.jpg)
Left to right: Outer rind (waxy layer), inner rind (chalky paint layer), bits of inner rind in grooves with good back exposed, good back sanded with 220 grit.
It took about 10 seconds to make this sample piece, that's how little you will remove.
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Lots of useful info here.
I'll add... normally, I have plenty of bamboo here to choose from, so I can afford to choose a clean piece without deep scratches or dings, and then don't bother to remove the rind until part way through the tillering. But if I only had the two pieces pictured above, I would at least remove the rind around the scratches and nicks to more closely inspect them in those specific areas. If the damage reached into the power fibers at all in areas that would end up being in the bow, I'd hold off and order some new pieces from someone who is familiar with the needs of bowyers.
I would still leave the rind intact everywhere else because it helps protect the bow's back from glue and such.
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Use a razor blade and thick gloves. Not sandpaper. Razor blades remove the rind super fast and clean. It is the best tool in my opinion to work bamboo and you don't need to worry about the bamboo dust then. You also don't need to fret much about taking off too much. The stuff will hold together regardless if it is good boo, but the power fibres (the strongest most dense fibres) are right on the underlayer of the rind and don't go very deep. You can see them if you look at a cross section of it.
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Thanks guys I will be trying a boo backed soon. Can you just leave the rind on and have no affect. Will the rind take true oil?
Arvin
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It really doesn't like to let stuff stick to it without being at least micro abraded to knock the shine off. A scotch- brite scrub and acetone or similar wipe will "etch" it enough for an adequate grab to the surface.
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I've never removed the rind up til now. I've never used true oil but I've used tung oil and it went on OK after I scrubbed the bows back with lacquer thinner. If this boo wasn't so marked I wouldn't remove the rind. I'd just use lacquer thinner and leave the back absolutely natural. I'm a bit anal about natural backs though ;D
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Thanks Pat. Arvin