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| Doolin Bender w/ Venetian Cutaway http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10102&t=15096 |
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| Author: | SniderMike [ Sat Dec 22, 2007 7:41 am ] |
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I'm planning on building a Doolin-style bender, and I'm curious if anyone has built a venetian cutaway section into theirs? I've got some ideas, but it would be great to see some pics if anyone has done it already. Thanks |
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| Author: | James Orr [ Sat Dec 22, 2007 8:36 am ] |
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I'm working on one right now, too. Mike clamps the butt then bends the lower bout, bends the upper bout, then bends and clamps in the waist bend before clamping the upper bout. I can see a venetian cutaway working similarly. Lock the butt in, make the bend, bend the upper around the point of the cutaway without clamping it, bend the waist, clamp it, then bend the actual cutaway. I wonder if you could use the spring assembly per the usual method until you need to bend the cutaway---at which time would release the spring assembly. |
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| Author: | Bruce Dickey [ Sat Dec 22, 2007 8:52 am ] |
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I just build one both ways. Others screw in a cutaway block the right shape into their standard mold. |
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| Author: | SniderMike [ Sat Dec 22, 2007 10:38 am ] |
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Thanks, guys. I'm not so concerned about the mold itself. I've essentially built the same mold with a removable cutaway, but it indexes off the waist and clamps there first, with no springs, sandwich, etc.. I'm more concerned with the clampage, but don't have a feel for how everything interacts with the Doolin-style. Got pictures, Bruce? |
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| Author: | Rod True [ Sat Dec 22, 2007 10:39 am ] |
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James, I would not bend it the way you mention. With the springs pulling the slats tight here is what I would do for bending a Venetian on a Doolin style bender. Lock at the tail end, bend the lower bout the slats should be tight enough at this point, the springs will not be totally stretched at this point. Than clamp the waist down than do the cutaway. The cutaway will really stretch the limits on the tight slats and the springs, I would think the rolling action of the slats and wood might not work out so well. The best thing to do of course is to get some practice pieces and try it a few different ways. |
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| Author: | SniderMike [ Sat Dec 22, 2007 11:42 am ] |
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Rod, thanks a bundle. That's exactly the kind of advice I was looking for without even knowing it. |
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| Author: | Rod True [ Sat Dec 22, 2007 1:22 pm ] |
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Mike, I'd really like you to know that I have made a Doolin style bender, but I don't make venetian cutaways, I'm a florentine guy myself. So I've given you my best guess as to how to bend a venetian cutaway with the Doolin style bender. 
I started a thread back in July regarding the Doolin bender and there was some discussion there about venetian cutaways. Paul Woolson was asking about it. You might try emailing him for any ideas too. Here's the thread from July |
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| Author: | James Orr [ Sat Dec 22, 2007 1:24 pm ] |
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Rod, I'm interested in your reservations with the bend order I mentioned. I spoke with Mike Doolin last week to see if that's indeed the way he bends, and he affirmed it. Pulling the waist down after the upper bout seems different to me, too, so I'm interested in hearing your thoughts on it. The beauty of Doolin's design is registering the side at the butt, and the springs pulling the slats tight give the side support from below. |
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| Author: | Rod True [ Sat Dec 22, 2007 1:25 pm ] |
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James, I just re-read your post again, [quote=James Orr]I wonder if you could use the spring assembly per the usual method until you need to bend the cutaway---at which time would release the spring assembly. [/quote] This could work but I really think you'd want to clamp down the waist after the lower bout before bending the cutaway. Just my guess. Sorry if my first post sounded belittling, that was not my intention. |
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| Author: | James Orr [ Sat Dec 22, 2007 2:11 pm ] |
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Hey, no Rod, not belittling at all! |
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| Author: | SniderMike [ Sat Dec 22, 2007 2:24 pm ] |
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Thanks, Rod. I was actually peepin that thread earlier. I'll try Paul. James, let me know how things go. |
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| Author: | Rod True [ Sat Dec 22, 2007 2:29 pm ] |
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James, just for the cutaway is all. Pulling the upper bout than the waist in the cutaway bending form, I would think you'd have a lot of stress on the horn of the cutaway when bending the waist. I bend on my Doolin style bender, just how Mike describes and does, so again, I'm just saying be careful to bend the upper bout on the cutaway after the waist is bent. I'm not saying it WON'T work bending the horn after the lower bout, I'm just saying be careful. Take a look at this, maybe it will help 
See with out the cutaway it's all a smooth bend and as you lower the waist, the side bears down on a smooth (and fully supported on a solid mold) curve where as if you bend the cutaway first, look at all the points the side will be stressed over not to mention the tight bend of the cutaway itself. For the cutaway side, I think it would be difficult to bend a venetian on a Doolin style bender. I know Rick Turner uses the same style bender and back in July he mentioned that they just bend the cutaway on the pipe instead of in the bending machine. I certainly could be wrong (it's happened many times before) so please, someone give it a try and let us all know how it turns out, good or bad we all will learn from it. |
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| Author: | SniderMike [ Sat Dec 22, 2007 3:23 pm ] |
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Well, what if you had a removable piece for the cutaway? Leave it in and bend just like you normally would. After it's cooled down, remove the springs/upper bout area, and remove the cutaway section, leaving the waist and lower bout clamped down. Then bend the upper bout into the venetian. Do you see any trouble with that? |
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| Author: | Rod True [ Sat Dec 22, 2007 3:59 pm ] |
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That certainly sounds like it would work Mike. Except for the fact that you'd have to pull the side out (I think) to remove the "removable piece" than put the side and sandwich back in. Maybe you wouldn't though, if the piece could be pulled out from the side. Than the springs will make the sandwich (and cool side) bare down on the sharper points as shown above. Check out this picture of the head end of the machine, 
the spring arm pulls the sandwich down (there's a lot of tension on those springs when the waist is clamped) if you were to add a venetian cutaway to the mold, the spring arm would have to be rotated 90* upward to ensure you don't kink the side or slats on the front edge of the body. Now for a venetian, I would think you might be able to make a different spring arm, longer and use some different springs to allow for a lot more travel during the bending of the lower bout and I think you'd have to move the pivot point down on the base. Than I would bend the waist, than the horn and cutaway. I'm going to draw a quick sketch to help explain what I'm thinking. be right back. I think it can be done, but this is something that I think might take a couple revisions on the design to get it right. Being a former mechanical technician, I've spend a lot of time designing machinery and "testing" those designs, I have to tell you not to many times a new design works the first time out off the plans. |
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| Author: | SniderMike [ Sat Dec 22, 2007 4:08 pm ] |
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I hear you, Rod. What I'm think though is after the initial "normal" bend, removing the entire spring assembly. Then the slats, blanket, and side can follow the cutaway without the kink. It loses the tight sandwich effect, but it's just for the cutaway. Does that make any sense? Anyway, I look forward to what you draw up. |
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| Author: | Rod True [ Sat Dec 22, 2007 4:10 pm ] |
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Ok, take a look at this, I think it could work. 
What do you think? |
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| Author: | Rod True [ Sat Dec 22, 2007 4:12 pm ] |
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The "Stop" would have to be adjustable I think, so that the slats would remain taut the entire bend. |
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| Author: | Rod True [ Sat Dec 22, 2007 4:27 pm ] |
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Just reading through the thread from July, here's something Rick said back than, I don't remember reading it before (maybe I did) and I came up with the same idea as he did, I just put it on paper. [quote=Rick Turner]We're still doing the cutaways on a Fox, but there's no reason why adding the Fox cutaway press to the Doolin wouldn't work just fine. In that case, we'd tighten the butt, then the waist, and then go in with the cutaway, maybe even with springs pulling the slats out horizontally instead of down vertically. [/quote] |
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| Author: | SniderMike [ Sat Dec 22, 2007 4:29 pm ] |
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Ok, I see. Looks like it would work great to me. This would be a separate pivot arm from the one used for non-cutaways, correct? |
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| Author: | Rod True [ Sat Dec 22, 2007 4:32 pm ] |
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The other thing you could do to make this work is to add a pivot point at the top of the spring arm where the springs are attached. How can you tell, I have nothing better to do. I'm waiting for the next feed for our new addition, we're sitting watching hockey, good Canadian girl she is 
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| Author: | Rod True [ Sat Dec 22, 2007 4:33 pm ] |
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You got it Mike, I think you'd need different springs too. |
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| Author: | SniderMike [ Sat Dec 22, 2007 4:42 pm ] |
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Hey, congrats! I definitely like the idea of the pivot on the springs. I'm going to marinate on this idea overnight. Thanks so much for your help. Very much appreciated. |
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| Author: | Rod True [ Sat Dec 22, 2007 4:50 pm ] |
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Thanks
Your welcome. It was fun to think this through some more. |
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| Author: | Rod True [ Sat Dec 22, 2007 5:15 pm ] |
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[QUOTE=Rod True] I know Rick Turner uses the same style bender and back in July he mentioned that they just bend the cutaway on the pipe instead of in the bending machine.[/QUOTE] Sorry, I miss quoted here. Rick bends their cutaway section on the fox bender not the pipe. |
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| Author: | Brad Way [ Sat Dec 22, 2007 11:59 pm ] |
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Mike and Rod... Here is a concept I have been kicking around. The drawings are missing some details but I think you will get the idea. Bending upper bout 
Bending the cutaway 
I am just about to finish a bender that uses a few pnumatic cyclinders rather than springs. This allows for more force but what I noticed when testing is that if the force from the springs/cylinder is pulling inline with the arms then it takes much less effort to make everything work. It will also minimize the movement of the springs. |
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