Author Topic: R/D Tiller Discussion Continued  (Read 11049 times)

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Offline Bayou Ben

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R/D Tiller Discussion Continued
« on: March 23, 2018, 03:59:40 pm »


Badger: "On an R/D bow you have several angles going on at once,"  Yeah, this is it, too.  They are interrelated and at different stages from resting to brace to draw they effect each other.

BayouBen, that doesn't sound like cheating to me, but good planning.  Probably took me longer, but I do the same.  I  thickness taper my belly or cores on a table I made using my power hand planer, then add kind of long reverse wedges to the tips.  MY biggest problems came from bows that were WAY stiffer than intended draw weight so that by the time I got it down under ridiculous, I'd messed up somewhere.

Ben, what do you recommend for thickness taper?  I never got very scientific about it, but say I take a healthy 70" long x 3/8" lam and I'm adding a 1/8"-3/16" backing and a powerlam.   Do you taper it to half the thickness?  Or,  until it bends evenly to an arc? 

 I'll leave a foot untapered in the middle (so my fades will come off about where the limb taper starts) and thickness taper from there to just under 1/4" thick at the tips.   Then, I may add back 1/8" tip wedges 10" or so long.  Can you add anything to improve my method?




I'm reluctant to share how technical I get with taper, because I know so many make excellent bows without measuring much at all.  But I guess this style of bow is technical enough with all of the gluing and forms and reflex and deflex, so why not get technical with measurements.  I normally use a 0.006"/inch taper rate total.  If I'm making a tri lam, I like all 3 lams to be close in thickness, and taper each to 0.002"/inch.  That will give you a nice arch tiller then add your tip wedges, powerlam, and reflex/deflex to give you a shape you like.  If you rather stiffer outer limbs I would go 0.004-0.005"/inch. 
Leaving the 12" untapered in the middle is a good idea it's just hard to do with the way I taper each lam.  I use a standard cheap belt sander with a box built around it to grind my lams to spec. 
I'm no expert, but like I've mentioned I've experimented with a few different designs.  Here's one I glued up last night.  It's maple back, walnut core, ipe belly.  This is the 1st time I use maple as a backing, so once again I'm experimenting  ;D








Offline Stick Bender

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Re: R/D Tiller Discussion Continued
« Reply #1 on: March 23, 2018, 04:15:59 pm »
 Benton I'm glad you posted this, I'm all ready learning I never reliesed those bows had that shallow of tapper rate , Hum! I have a lot of 0.002 lams hanging around in different woods , I like your home made grinder preety creative , I'm following this one paticurly sense your using maple back !
If you fear failure you will never Try !

Offline JWMALONE

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Re: R/D Tiller Discussion Continued
« Reply #2 on: March 23, 2018, 04:39:00 pm »
Ben I've been meaning to try that with my bench sander, got one just like it. How does it work as far as consistency, also did you make a sled for it or a jig?
Red Oak its the gateway wood!

Offline Dances with squirrels

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Re: R/D Tiller Discussion Continued
« Reply #3 on: March 23, 2018, 05:06:53 pm »
I seem to remember encountering some resistance here on this 'primitive' site about trilams and such, so I've not talked about it much, here. It's nice to see it now. I know glass bows are taboo, but if you're as particular about grinding the wood for an all wooden bow, whether a simple two lam backed bow, or a trilam, or whatever... as folks are about grinding glassbow lams, the rest of the build is a lot easier, more straightforward, and better bows result. I've ground lams and cores for all sorts of bows, and I'm set up to do it with variability and accuracy. I too grind tapers from just outside the dips to the tips for most all wooden lam bows. I don't mess around with power lams or tip wedges, I find them unnecessary. Instead, I rely on good design and shaping, good glue joints, and vary the placement and amount of taper, and wood removal, depending on how I want the limbs to act. The extensive groundwork is warranted, and should ultimately be trusted... not fought. In other words, the "let it show you what it wants to be" statement I read in the other thread is something I learned years ago and have been trying to impress on folks who are able to bring the blank to that place, and then comprehend the inherent value in it.

Like I said, it varies depending on other aspects of the design, but for a run of the mill d/r bow, I usually start closer to a .004/1" taper rate, which allows me a little something to work with while tillering.
Straight wood may make a better bow, but crooked wood makes a better bowyer

Offline Springbuck

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Re: R/D Tiller Discussion Continued
« Reply #4 on: March 23, 2018, 05:13:00 pm »
 Ben, technical is ok!  Often you are just putting numbers and method to what other guys are already doing.

Can you describe how your tapering jig works?  I think I get it, but want to really understand.

 Also, can we share this thread?  Should I post the rocking table I use with my power planer to do my tapers?  It's super simple, but probably less precise.

 If I understand, you might taper a 36" lamination starting 0.375" thick or about 3/8" thick in the middle,  0.006 thinner for each inch of length?  Down to about 0.216" on the far end.   That sounds about right.

Same taper for a different length bows?

Offline JWMALONE

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Re: R/D Tiller Discussion Continued
« Reply #5 on: March 23, 2018, 05:50:41 pm »
Next time I do one ill show you guys how I do it by hand. Its time consuming but it works.
Red Oak its the gateway wood!

Offline Springbuck

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Re: R/D Tiller Discussion Continued
« Reply #6 on: March 23, 2018, 06:49:52 pm »
DWS:  "I don't mess around with power lams or tip wedges, I find them unnecessary. "

  Me neither, I just find them convenient, and sometimes attractive.   I've developed a couple of ways to make them quickly and easily, and there is always scrap lying around.   

I honestly started using them more to get all the lams I could out of a board than anything else.  Finding a perfect tropical hardwood board at McBeath's is rare enough, and considering what they cost, getting one or two more bellies out of it is worth it.

Offline gfugal

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Re: R/D Tiller Discussion Continued
« Reply #7 on: March 24, 2018, 11:56:57 am »
Benton I'm glad you posted this, I'm all ready learning I never reliesed those bows had that shallow of tapper rate , Hum! I have a lot of 0.002 lams hanging around in different woods , I like your home made grinder preety creative , I'm following this one paticurly sense your using maple back !
So the 0.002" taper rate is multiplied by 3 from the 3 separate lams that are each tapered to 0.002". Therefore the end result is a 0.006" taper. I'm just barely getting into laminate bows but I think that's a pretty aggressive taper not shallow. But if you do have a bunch of 0.002 you can add them together like he did.
Greg,
No risk, no gain. Expand the mold and try new things.

Offline Stick Bender

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Re: R/D Tiller Discussion Continued
« Reply #8 on: March 24, 2018, 12:39:43 pm »
 Well the taper rate that Ben posted was 0.006 total stack taper, I would imagine you could use any rate per lam as long as you arrived at 0.006  I was mentioning the shallow taper rate compared to a self bow ! But maybe Ben could comment on that ?
If you fear failure you will never Try !

Offline Badger

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Re: R/D Tiller Discussion Continued
« Reply #9 on: March 24, 2018, 01:29:12 pm »
Set tapers are much more reliable than the eye on these bows. I use a slightly less precision method but I do pre tiller my belly on the belt sander and it gives me a nice shape to start with when I start bending the bow. My eye will always tell me to get it bending more right in the curve and that aint always so.

Offline gfugal

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Re: R/D Tiller Discussion Continued
« Reply #10 on: March 24, 2018, 02:45:18 pm »
Well the taper rate that Ben posted was 0.006 total stack taper, I would imagine you could use any rate per lam as long as you arrived at 0.006
Yeah, the total taper is what matters from my understanding. But I guess different stiffness of materials could throw that off.  For example, a 0.006" taper on IPE, in an IPE, Maple, boo trilam, will affect the tiller more than if that 0.006" taper would just on the maple. But generally speaking, most woods are similar in their stiffness relatively so this can be ignored.

  I was mentioning the shallow taper rate compared to a self bow ! But maybe Ben could comment on that?
Has anyone measured the taper rate on a self-bow? That would be interesting to know. It would seem that it wouldn't be the same as a laminate mainly because we tend to leave our tips thicker. The only way fiberglass-laminate-makers can really accomplish that is with tip wedges (since you don't really tiller the belly. take too much off and you don't have glass anymore). So if you were to measure a self-bow you would have to measure to the thinnest point before it starts thickening around the tips. Crowned backs and bellies, as well as knots and other irregularities, would also make it difficult to measure an accurate taper rate.
« Last Edit: March 24, 2018, 03:52:29 pm by gfugal »
Greg,
No risk, no gain. Expand the mold and try new things.

Offline Badger

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Re: R/D Tiller Discussion Continued
« Reply #11 on: March 24, 2018, 03:06:57 pm »
    .006  would be pretty close for a self bow as well without the irregularities. The tips are usually thicker as mentioned. I use thicker tips on my lam bows as well, I don't like them bending at all. I only use a power lam if my belly slat is too thin to start off with.

Offline Stick Bender

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Re: R/D Tiller Discussion Continued
« Reply #12 on: March 24, 2018, 03:21:39 pm »
That is a hard question to answer depends a lot on working limb and design  the tapper rate changes but I just measured 1 of my osage lever bows with a 20 in. working limb  68 in TTT and the average taper rate is  0.012  I'm seeing a average more like 0.010 for my self bows maybe I'm wrong Steve ?
« Last Edit: March 24, 2018, 03:54:32 pm by Stick Bender »
If you fear failure you will never Try !

Offline BowEd

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Re: R/D Tiller Discussion Continued
« Reply #13 on: March 24, 2018, 03:47:47 pm »
Parallel limbs will have a more aggressive thickness taper on my self bows.It's hard to judge.When width taper takes over taper thickness wise slows down a little.
BowEd
You got to stand for something or you'll fall for anything.
Ed

Offline Springbuck

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Re: R/D Tiller Discussion Continued
« Reply #14 on: March 24, 2018, 03:54:56 pm »
Greg:  "But I guess different stiffness of materials could throw that off."  It could, and I'm pretty sure variations in bow length and working limb length will affect it too.  But, we still have to TILLER wood bows, so the idea is to get close.

"Has anyone measured the taper rate on a self-bow?"  THIS is going to vary a lot by style.  Pyramid bows, hardly at all.  Longbows (which I'm no expert at) I START by roughing out so that the tips are half as thick as whatever the handle is.  And that's that's just to see what I really have in the stave and work TOWARD floor tiller, before rounding or faceting anything or narrowing at all.

« Last Edit: March 24, 2018, 04:21:11 pm by Springbuck »