Trad Gang
Main Boards => The Bowyer's Bench => Topic started by: John Malone on March 10, 2018, 05:03:00 PM
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Hey Guys been awhile since I made a bow so here we go.
I need some tiller practice on a r/d so I'm going with boo and ipe at 72 inches #50. Ive always wanted a really long bow just because, and it will be easier to tiller.
Ive profiled the boo to 1 inch wide a 12 (14?) inch riser parallel to mid limb taper to half inch.
Question is were should I place the block and clamp that pulls it down into deflex? Looked at every ones set up but no specs on that that I could find. Should it be a third of the way up? mid way? is there a formula or general rule for that? Roy's looks half way?
Also, how much should I put in there?
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Also would a q/s red oak riser work? Not that crap from Lowes the good stuff, I have a piece that's one inch thick.
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John, you should take a look at Sam Harper's website (poorfolkbows.com). He has a BBI build along that is an R/D longbow that is fairly thorough.
As far as your handle goes, I don't see why qs red oak wouldn't work. I think you don't see it often because it's not purdy like those fancy exotic hardwoods. If you have it, use it!
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I normally place the mid limb posts half way between the flares and limb tip. The closer you place the mid limb post closer to the riser, the more deflex you get. And the more of the limb that will work.
Being that you want a 50# with a 72 inch bow, you better leave the ipe thicker. 1/2" at least, maybe thicker.
The red oak will work.
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Thanks Guys, I noticed BMorv seemed to have his closer to the flares in a pic he posted on the bow swap thread.
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So I should place the post midlimb because its so long??
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Ya that would be ok.
You just need to remember since the bow is so long and you want 50#, ya better make the belly lam a good 5/8th thick, or wider...
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Thanks Roy, I can get 5/8. I could shorten it if I really needed to but this piece of boo would be perfect for 72 inches. My other piece of boo is better, the nodes are all are pretty evenly spaced at 12-12.5 inches, I'm saving it for when I know more about what the heck I'm doing.
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Make it the 72. You can shorten it later if you want or need more weight.
Start keeping a journal of bow dimensions, lam thickness, etc. And the weight they produce.
Them gwass guys call it stack. LOL
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I'm ready to glue fellows. But I'm still trying to figure out how much. Should the tips be 2 inches higher than the handle and the deflex post be one inch lower than the handle?
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Any one?
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My center of handle post is 3 3/4", the mid limb posts are 2 3/4" and end posts are 5".
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Thanks Roy, I forgot it was Sunday.
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No problem, was at daughters for her birthday party.
(http://i.imgur.com/BGAAApR.jpg) (https://imgur.com/BGAAApR)
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Ipe is so dense, is there a chance that making it so long could give the limbs a bit too much mass creating a bit of thump?
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No idea Bob, but were gonna find out.
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Bob, ipe is dense but it's strength is in line with it's weight. What I mean by that is you end up with narrow thin tips that are super aerodynamic and close to the same weight as any other wood, assuming that excess mass isn't left there. The end result is a fast bow compared to other woods.
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Where are you on this one John?
I saw the comments made on PA about this bow and this length. I agree that you won't gain much from the deflex with this long of a bow, and it will make the tiller harder to figure out.
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BMorv, That ipe is now riser and power lam material. Going by what was said on PA like you mentioned I decided to cut it down to 66. Just go ahead and learn how to tiller a real R/D that I could get the full benefits from. I tapered it down some more to allow for the shorter length, but as I was cranking it down at the mid limb post, CRACK! So that's where I'm at on this one. I started and finished in all of 30 minutes.
No need to fear though I have more wood.
Goining to make a new post For advice on lemon wood core lam thickness.
Its 7/16 tapering to 3/8 and I have ipe belly lams wht do you think?
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Oh yea, I was able to save the boo backing strip so that's a plus.
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Sucks, but at least you weren't that far into the process. I've had 2 or 3 ipe boards break on me during test runs before glue up. Remember that thick ipe hates to bend; it will break; you can't force it. And it doesn't like tension as in when you crank down on the clamps for the reflex and deflex post.
If you do another ipe, pre-tiler the ipe and make sure it's bending decently before you put in on the form. If it's bending enough on the floor and is properly tapered, it should bend fine on the form. Another step that I do is to round off the belly side edges and sand them smooth before the form. It can handle a lot in compression, but is finicky when forced to bend in tension.
So you want to make a tri lam with lemon as core and ipe as belly?
I have zero experience with lemon wood.
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I tapered it, evidently not enough. It was fine on the dry run. Even had a nice pressure strip under it. Oh well.
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I've never had one make it through the test run and not through glue up. It should be bending the exact same amount, so that's confusing to me....
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Ive seen it before doing laminated rockers and other stuff for furniture. Doesn't happen often but not unheard off. It surprised the heck of me to.
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BMorv I made a bonehead mistake. I cut the midlimb post 2 3/4 tall they happened to be 2 inches wide. When I screwed them to the base I put them 2 inches tall. So I was cranking them down 3/4 of an inch further than what they were tapered to do. So that's why the dry run was good. When I glued them I was going 3/4 of an inch further and snap. Man I feel like a genius now.
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Remember that thick ipe hates to bend; it will break; you can't force it.
Yup ipe is tough stuff.
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Oh I can force it all right, it went right down in thar. Only not in one piece.
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In regards to your midlimb post question, a good place to start is where Roy mentioned, midway between your flares and tips. An inch or 2 one way or the other isn't all that critical, so you can adjust it to your liking on further builds. I moved mine in a few inches in from mid because I wasn't getting enough deflex off the form.
If you don't already have one, look into getting a .25"x 1.5"x6' mild steel flat bar. It gives you a pressure strip on the entire bottom and it also bends nicely from post to post. You can set the flat bar in your form with your proposed post locations and step back and see if you like the shape.
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Thanks BMorv, I use a 6 foot steel yard stick but its not thick enough. I got my cousin on look out for a piece of flat steel like you mentioned. Use to have one but it got repurposed for something else.
I thought yours looked closer to the riser in the pic you posted on the bow swap thread. I will go mid way, then ill know wht effect it has.
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The yard stick might work. It doesn't have to be a certain thickness. Let me double check the thickness of my bar. It may be less than .25".
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And yeah, I started mid limb like Roy described, but I kept inching my way towards the handle on subsequent builds. I just wasn't getting the deflex bend that I wanted in the handle. There's only so far I feel comfortable going though, considering that you are putting all of that bend in a spliced lam.
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There's only so far I feel comfortable going though, considering that you are putting all of that bend in a spliced lam.
Yup I've cracked a few before I got mart.. :)
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My flat bar is .135” thick, so I guess that’s what 10 gauge?
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Close, its actually based on weight. Stainless will be thicker than aluminum at the same gauge. I'm no metal expert but I remember that from some were.
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Here's pic of a riser I did with thin strips. If you like the look it's easier than fitting a one piece riser, IMO.
(http:// [url=https://imgur.com/GQxmxdj] [img]http://i.imgur.com/GQxmxdj.jpg)[/url] [/IMG]
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Nice BMorv, I may end up doing that this time. I thought I had a piece of 5/4 oak but its only 4/4 it wont be wide enough. So if I have to laminate two pieces I might as well do strips. Strips would look better plus I could use that ipe I busted on the last try.