Pau Amarillo/Yellow heart for "Backing a bow"

[Marc St Louis]

Hi Marc, I'm sorry but I didn't ignore Marc or DC. I stated,

"2. I did machien the boo flat and then machined a taper."

and

" 1. I machined the boo flat to 4.5 mm
2. Using the taper sled, I tapered the boo tips to 3mm. The handle section was 4.5. It fades from tapered to constant thickness somewhere vague in the middle.
3. Prior to machining the boo I took some scrap boo, machined it flat, then tried to break it around the nodal areas. The boo refused to break at the nodal points. I tried around 10 node areas. The boo would fail outside the node area but close to it. This data caused me to think that machining the boo flat would provide a homogeneous material to play with. If it did let go then it would be between the nodes not at the nodes. Ero sanding the nodes would be cool."

What's going on is, I'm learning from others who are more experienced and knowledgable than me, but at the same time as experimenting proving things to myself in order to gain a thorough understanding and confidence in what I'm doing.

Thank you and kind regards,
Andy

Well that's your whole problem then.  Leave the back of the boo alone and it will stop breaking on you.  Don't even touch the nodes

[gutpile]

I agree with Marc as stated earlier... when you flatten the boo you are destroying its power fibers basically violating it... and BOOM... there is the problem.. flatten boo on belly ONLY... taper your belly wood... if inducing reflex deflex in glue up... get the video and watch it.. gut

[mmattockx]

I'm only going to change one variable at a time. The next obvious choice is the backing material. For me personally boo is not practical. I'm sure its great when you get the hang of it, or maybe I just got a bad batch as someone suggested.

Bamboo is a superb backing wood, you have destroyed its properties by machining the outer surface flat. Leave the outer surface and nodes intact and you will never break a piece again.

In terms of the core wood. IPE is very popular. If you look at the performance numbers on the wood database then I can see why. On paper it performs better than Osage and Lemon wood. I can't find anything better.

You are getting your terms mixed up. Ipe is a superb belly wood. The core is the bit in the middle between the belly and the back and it doesn't do much in terms of carrying the load.

I don't understand why it's good for strong bows and not light bows too. I've managed to thin it down to ball park performance requirements and on the bows that have shot it felt great. Why would you use a lower performance wood?

It's not that ipe is bad for light bows, but it is unnecessary and you can use a cheaper wood that is easier to work and get the same results on a kids bow. The other issue with it is that you end up super thin on the limbs and it is hard to tiller them when they get that thin as even a small scraping ends up having major effects.

..more IPE, Lemonwood & Hickory. Something should work! 

If you have decent, straight grained hickory available to you it will work much better for what you are trying to do, just make sure to put the tapered face in towards to the belly wood and keep the back face intact.


Mark

[AndyTurner]

Marc, Gut & Marc. Thank you chaps. Have a great weekend, Andy.

[AndyTurner]

If you have decent, straight grained hickory available to you it will work much better for what you are trying to do, just make sure to put the tapered face in towards to the belly wood and keep the back face intact.

Mark

Just one last thing Mark - it doesn't seem intuitive to me to glue tapered surfaces together to preserve the back face. The back would have been machined anyway.

For me it makes more sense to glue the flat surfaces together as per attached.

Please can you explain.   

Thanks in advance,
Andy

[mmattockx]

Just one last thing Mark - it doesn't seem intuitive to me to glue tapered surfaces together to preserve the back face. The back would have been machined anyway.

For me it makes more sense to glue the flat surfaces together as per attached.

Please can you explain.   

You bet. If the grain runs parallel to the flat face (a big if in a lot of cases) then the tapered face is cutting across the wood fibers at an angle, exposing the end grain similar to other grain violations. If you put this face on the back of the bow where it sees maximum tension then those exposed end grain locations are more likely to lift a splinter than the flat side with the theoretically continuous fibers running end to end of the lam. This only matters on the back lam, the belly is far less sensitive to exposed end grain and other grain violations.

I don't know that this is much of an issue when you are taper grinding lams as you are, as the taper is very gradual, but stresses are high enough in a bow that I always do everything I can to tilt the table in my favour and doing it this way costs nothing extra but may help deliver a functional bow in the end.


Mark

[DC]

The back would have been machined anyway.

I'm not following you. Why would the back have to be machined?

[willie]

I don't know that this is much of an issue when you are taper grinding lams as you are, as the taper is very gradual, but stresses are high enough in a bow that I always do everything I can to tilt the table in my favour and doing it this way costs nothing extra but may help deliver a functional bow in the end.

In fact, if you are getting the backing lam out of a thicker board, you would actually want to prep the back facing surface of the lam to best follow a ring  (or the grain if not flat sawn.)

[AndyTurner]

You bet. If the grain runs parallel to the flat face (a big if in a lot of cases) then the tapered face is cutting across the wood fibers at an angle, exposing the end grain similar to other grain violations. If you put this face on the back of the bow where it sees maximum tension then those exposed end grain locations are more likely to lift a splinter than the flat side with the theoretically continuous fibers running end to end of the lam.

Hi Marc. I see clearly now! Guess who put his tapered surface on the back facing the target?!  (LOL)

I'm not following you. Why would the back have to be machined?

Hi DC. Because when I make lams I flip the boards during the thickness process to make sure everything is flat and square before I taper it.

In fact, if you are getting the backing lam out of a thicker board, you would actually want to prep the back facing surface of the lam to best follow a ring  (or the grain if not flat sawn.)

Hi Willie. Noted - thanks. I didn't think of that!

I was on the phone to the nice man selling me the wood. He assured me that you can't back a bow with Lemonwood and that I needed Hickory. I read somewhere on the web that you can use Lemonwood on its own because the grain is always straight and tight. I bought both in the end just to play with & see for myself.
 
On the wood database (https://www.wood-database.com/lemonwood/) the Modulus Of Rupture, which I'm using to estimate tensile strength, is 22,100 lbf/in2 (152.4 MPa). Hickory on the other hand is ballpark less, e.g. Water Hickory is 17,800 lbf/in2 (122.8 MPa), Shagbark is 20,200 lbf/in2 (139.3 MPa). Bamboo is between 11,020 lbf/in2 (76.0 MPa) and 24,450 lbf/in2 (168.6 MPa). It doesn't mention species. IPE for reference is 25,660 lbf/in2 (177.0 MPa).

I'm guessing MOR alone is not the deciding factor in choosing a wood for backing. Looking the very popular boo - I'm guessing the rind itself must naturally seal in the grain preventing the splinters from lifting. That said most people scrape that stuff off. Looks to me now like its the best and cleverist bit for backing material.   

Do you have any favourite reading on making wood backings?

While you're there, do you have any favourite reading on making wood laminated bows?

Thanks,
Andy

[willie]

I wish I knew of an authoritative reference for lam bows to recommend, and there may well be one out there, but I am not aware of it.

searching this site with google works better than the forum search.  for example...

hickory backed  site:http://www.primitivearcher.com/smf/

[Tommy D]

Hi Andy... this thread has kept me on the edge of my seat ... but I can’t decide if in part it’s like watching NASCAR for the crashes! Keep going you are nearly there and clearly persistent ... but some thoughts that might really help...

Have you read any of the Traditional Bowyers Bibles? Vol 1 and Vol 4 have some very useful chapters that I think would solve many of your issues. Along with the Dean Torges video on bamboo backed bows as suggested earlier. Or some of the great you tube videos on making a board bow?

There is some world class advise you are being given by some truly gifted bow makers on this forum, but sometimes it pays to take the time to learn the terms and basics... 

I would really focus on making a few straight board bows - especially if they are just for kids.

I don’t know where you are based - and I know it’s hard with the dreaded virus - but if you can find a timber yard and pick through the lumber - oak, hickory, ash - and pick your own wood with the correct grain orientation and start tillering and making bows, you will learn a lot about wood and the process of tillering.

Once you have a few tillered working board bows, you can always glue a bamboo backing onto them and start playing around again. I am not sure that this “destructive testing” is that helpful - better to learn to make them so they stay together and then start pushing those limits...

Do you have a band saw and a belt sander? You can thin a bamboo back with these two tools in about 10 minutes. Even a hand held belt sander you can clamp upside down in a vice. You really don’t need to be worrying about thickness tapers and stuff like that right now.

Draw the profile of your bow on the bamboo and cut it out. Then turn it sideways and cut it to within a few mm of the back.  Put some 40 grit sandpaper in your belt sander and get a piece of wood to hold the bamboo down against the belt which helps avoid pruning your finger tips. Pull the bamboo strip towards you against the rotation of the belt whilst pushing down with the wood.  Sand the bamboo until the edges are nearly sharp. Use the wood to put extra pressure where you need more bamboo removed. Sanding till the edges are sharp once the back profile is cut out  will naturally taper the bamboo towards the tips anyways.

DO NOT touch the shiny back of the bamboo ... and if you do it should be with sandpaper right at the end and only enough to take the waxy rind off if you plan to stain/ finish the bow.

If you glue this onto an already tillered board bow you will up the poundage, and you can even start playing with shapes at that stage like gluing in R/D and you will understand what is happening along the way.

A bamboo backing is an amazingly simple and easy thing to do if you don’t overcomplicate it!! You are doing something very wrong to break this many bamboo backs. Even poor quality bamboo is very strong in tension.

If you do like grinding lams and tapers and gluing things up in a way that is pre-tillered, you may do well to visit Binghams store online and buy a kit for one of those bows we aren’t allowed to mention here! The kits come with instructions for the bowyou choose, the correct tapers and parallels for the poundage you want and if you follow the instructions step by step you get a pretty decent bow! Albeit the kind we cannot mention here...

But the process will teach you very little about how to tiller a wood bow - which is an art in its own right...

[Pappy]

I generally don't read through all these long threads but did this one, all I can say is Andy, you have the patients of Job, good luck.
 Pappy

[AndyTurner]

Hi,

this forum could use a "like button" function. So many of you have been so kind and useful. Thank you.

Ok, so while waiting for my new wood to rock up I built another IPE/Bamboo bow. I reused the handle, a disgarded Belly&Core (its just one bit of wood, the profile wasn't perfect for an end bow), and tapered up a new Bamboo back. I baptised it "Franken Bow". I had it on the tiller board and for one brief glorious moment in time it was all symmetrical, pretty & beautiful. It truly was awesome!!! The only problem was it was pulling like 20b at 8". I'm not sure who said it but I concur. You were right - I was wrong. Its a learning experience. IPE is no good for light bows. I sanded & sanded. In the end the IPE was ridiculously thin, like 1-2mm, and in a couple of spots I ground down to the boo. Please see attached.   

On a more cheerful note, the Lemon wood and Hickory rocked up. Let me tell you...
 
1. Lemonwood is "absolutely gorgeous" to work with. Really, truly, its like a seductive butter by comparison. you just want to stroke and admire it. It's beautiful. That said it gives ZERO warning when it "lets go". By comparison, Ratan will send you a courtesy email 2 weeks in advance, then reminders. In the end it just gives in with no drama or danger to the user. Fab for kids bows. Unbacked IPE - the limb, thankfully, shot past my eye and entered a new timezone before I realised what had happened. I never did find the broken limb. Testing scraps of Lemon wood verses IPE, well less just say that Lemonwood will give about 1/10ths notice compared to IPE Great. At least you can hear the IPE splinter first then boom. The Lemon wood is just like "Boom baby"!!! That said it's so seductive & bends so nicely compared to IPE! :0)

2. The Hickory looks to be your flexible friend and I can see why people recommend it for a backing. Please see attached!

I'm really looking forward to seeing what happens! :0)

Thanks again for all your help & patience,
Andy