I've forced them before as long as they were reasonably close and it didn't seem to be a problem BUT - it might not be "proper"
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| Forcing Sides to Shape http://luthiersforum.com/forum/viewtopic.php?f=10101&t=45134 |
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| Author: | George L [ Fri Feb 13, 2015 3:22 pm ] |
| Post subject: | Forcing Sides to Shape |
I'm working on an OM-sized guitar, with red gum (Liquidambar Styraciflua) for the back and sides. Never worked with this wood before and found it rather difficult to shape the sides. Even after two passes through my side bender and touching up by hand, the waists still won't fit my shape accurately without being forced into position. I'd say they are about 1/2" - 3/4" wide on each side. An exterior mold or clamps keeps them in place, of course, but I've never had sides that required this much force to match the final shape and I'm wondering if I'm looking at trouble ahead by continuing. Not having faced this before I just don't know. If you have insight or experience to share, I'm all eyes. Thanks, |
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| Author: | SteveSmith [ Fri Feb 13, 2015 3:25 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
I've forced them before as long as they were reasonably close and it didn't seem to be a problem BUT - it might not be "proper"
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| Author: | Glen H [ Fri Feb 13, 2015 3:34 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
Force is a relative term George. If you really have to exert effort to put them into position, I would try heating them again (I assume you a blanket heating element on your bender), putting them in hotter and longer. Nothing wrong IMO with a little coaxing to have them in position, but nothing near what I'd call a force. |
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| Author: | meddlingfool [ Fri Feb 13, 2015 3:36 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
I'd be comfortable letting the top and back plate when glued holding it in position. As long as you can get it in the right shape in the mold. |
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| Author: | kencierp [ Fri Feb 13, 2015 4:06 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
If you take the Martin factory tour you'll note that sides are so perfectly shaped they glue the tail and neck blocks to the sides and install the ribbon kerfing outside of the profile mold. At KMG we follow this example so --- the key is getting the waist curve correctly shaped, the best way to do that is to have a separate operation, in other words similar to the factory process. In addition I highly recommend style specific waist cauls. I want the sides to snap into the mold, not have to be crushed into the mold. $ .02 |
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| Author: | meddlingfool [ Fri Feb 13, 2015 4:08 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
Preferable but not strictly necessary IMO... |
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| Author: | Terence Kennedy [ Fri Feb 13, 2015 4:41 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
Won't help on this one but double sides are a good way to address difficult to bend wood as you can go much thinner. You can bend both inner and outer sides at the same time so they really match at the time of lamination. "If it doesn't fit, force it" is one of the cornerstones of my approach to woodworking. |
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| Author: | Pat Hawley [ Fri Feb 13, 2015 5:11 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
This is pertinent to me right now as I'm in the middle of trying my hand at my first contour cutaway. I was expecting to need some pressure to get the cutaway side glued to the curved and tapered neck block. What I didn't anticipate, and perhaps should have if I'd given it more thought, was that in forcing the side to the block, the horn would be pulled away from the form at an angle. I can push it back but I'm introducing all kinds of strain into the cutaway region of the side. I hope eventually the top and back will keep everything in place and it all doesn't go "boing" someday. Pat |
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| Author: | George L [ Fri Feb 13, 2015 5:38 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
Thanks for the replies! Yes, these were bent (twice) in my bending form using a thermal blanket. I've followed the same routine and used the same mold with other woods, achieving good results. This wood just seems a bit persnickety. I took the thickness to .080 and they felt extra flexible, so I chose not to go any thinner. They came out of the bender feeling remarkably stout, however, which I thought was interesting. After the second pass through the bender these are already showing signs of scorching, so I'm leery of running them through again. I think I'll just squeeze them in a bit and keep moving forward. I give my guitars away as gifts to friends--with no guarantees! If something goes haywire down the line, I can always just build them another one. Looks like I won't be the first to force things a bit. I'll embrace this approach then and accept it as part of my learning process.  Thanks again, |
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| Author: | meddlingfool [ Fri Feb 13, 2015 5:44 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
Don't forget, wood takes a set. That's why you can't leave a traditional longbow strung up. The tension will eventually relax. While we try to get perfectly bent sides, a little squeeze squeeze occurs from time to time. After 150+ guitars, I think I'd know by now if it caused problems down the road. I like to think that anyway. |
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| Author: | Hesh [ Fri Feb 13, 2015 5:57 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
Hi ya George: I'm not keen to force things much and although I agree that wood usually relaxes I think that we also have to consider the idea of what John Hall calls "case hardening" of the wood. Once it's been heated once or in this case twice even to the point of some scorching the wood becomes less plyable and more prone to breaking and cracking. As such I would consider asking the vendor of this wood for a new set of sides. Lots of exotics are sold to us for Lutherie purposes when the seller may not have direct experience with actually using this specific wood. This happened to me once and my vendor replaced my sides. With the replacement set I would use SuperSoft II and take the new sides to .070" prior to bending and see what that gets you. I'm OK with forcing sides maybe a 1/4" at most into the mold but beyond that I would question my side thickness and if perhaps SSII would have been helpful. I also agree with Ken that not having to force things at all is a very good idea too. |
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| Author: | kencierp [ Fri Feb 13, 2015 6:04 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
I will say that I constructed a couple of tight curved cutaways that we very uncooperative -- that was some time ago no reports of catastrophic or even minor failure. |
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| Author: | bluescreek [ Fri Feb 13, 2015 6:31 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
I have seen wood that was forced a good bit and never had an issue. If you can make it fit it fits. The pre stress is hooey , wood will take that shape and the stress releases pretty quickly. |
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| Author: | meddlingfool [ Fri Feb 13, 2015 7:33 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
Carry on George, it'll all work out ok. |
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| Author: | George L [ Fri Feb 13, 2015 8:21 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
Thanks again for all the replies. Yeah, I think everything will be fine. I assumed this wouldn't be the first time a set of rims needed a little coaxing to take their shape, just thought it best to check with the group. To be clear, I don't believe there is anything "wrong" with this wood, other than it doesn't seem to want to take a shape as readily as the few others that I've used in the past. At any rate, it was purchased from an individual and not the original tonewood supplier (a well-reputed dealer, by the way), so returning the materials is not an option. For the record, other than this bending issue, which may very well be due to my limited experience, I like everything about this wood. It's grown domestically in North America, presents beautiful figure, and doesn't appear to need any pore filling. I saw some big name builders using it, so thought I'd give it a whirl. The subject of stress introduced to the box during construction is an interesting one. I've read convincing opinions presented from contradictory positions, all of which seemed well-reasoned. I don't feel qualified to take a stance at this point in my journey as a builder. Perhaps that will start to change in time. I don't know. |
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| Author: | Pat Foster [ Sat Feb 14, 2015 4:29 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
George, Some woods will take a set and not bend after the first try, though most won't. The most stubborn set I ever had was EIR, if you can believe that. I could not get the waist tight enough on a single-0 shape. They've been sitting in an external form for three years now and still haven't complied. So yes, most woods will take a second bend, some will conform to stresses, some won't. If a pair of sides is under stress, a split along the grain is more likely to spread like wildfire. This I know. ![[headinwall]](./images/smilies/headbangwalluf8.gif "Mad") I've taken to bending the waist first on a pipe when in doubt. Pat |
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| Author: | bluescreek [ Sat Feb 14, 2015 6:21 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
EIR is usually easy to bend what thickness and what heat? I bend at about .075 in and start bending at 250 to 325F rosewood bends like butter if you waited too long the cells will set before the bend. |
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| Author: | Don Williams [ Sat Feb 14, 2015 6:36 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
A very prominent and successful builder once told me that he bends the waist first, and gets the curve right, and then the angle of the transitions to the upper and lower bouts correct before moving on to bend the rest of the side. He always felt that it was a pretty important step, and he is known mostly for his fantastic OM's in particular. For what it's worth, I think it can be worth the effort, especially when using valuable and brittle woods like Brazilian RW or other dense woods. I have no experience with red gum, so I'm clueless as to whether it applies other than sharing the same body type. LMI came out with a new side bender setup a few years back which has a special heating blanket just for the waist area, and perhaps it's important to get a better, more targeted heat at that area. Both Hesh and Pat Foster have said some things I agree with wholeheartedly. Don't ask me about the split thing. it is much too familiar an issue for me... |
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| Author: | Lonnie J Barber [ Sat Feb 14, 2015 7:51 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
George, I made a mandolin in 1991. Using water soaked Maple bent over a candle. It had to be forced into the mold. But it's in my closet the sides are fine. I think you'll be ok. If not lesson learned Sent from my iPhone using Tapatalk |
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| Author: | Jim Watts [ Sat Feb 14, 2015 8:25 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
IMO if it just takes light hand pressure to bring it in, it's ok. Anything thing more though and I'd be leery. |
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| Author: | George L [ Sun Feb 15, 2015 3:51 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
Thanks for the follow up replies. The results were greatly improved after the second time through my bender, so I don't think this wood is inherently uncooperative. It is far more likely that my technique is not fully evolved. I'll be the first to admit that I still have a lot to learn. :-) I'm moving forward with these sides as-is and will just have to wait and see how things turn out. I'm fairly confident all will be okay. If that weren't the case, I would not be proceeding in this manner. Best to all, |
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| Author: | Joe Beaver [ Mon Feb 16, 2015 1:56 am ] |
| Post subject: | Re: Forcing Sides to Shape |
I would recommend that you clamp the sides into the form, glue in the end blocks then use a 2 piece lining like the one's Paul Woolson makes. They are very solid and should hold the shape after the sides are removed from the form. He also sells the linings from time to time. |
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| Author: | jayluthier [ Mon Feb 16, 2015 7:14 am ] |
| Post subject: | Re: Forcing Sides to Shape |
Touching up the waist bend on a bending iron is always allowed and is often the cure for an uncoooperative set. |
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| Author: | Quine [ Mon Feb 16, 2015 1:28 pm ] |
| Post subject: | Re: Forcing Sides to Shape |
1/2 to 3/4" sounds like a bit much to me for the waist area. If you can squeeze it into shape in the mold with just hand pressure then its probably ok. I'd put the waist area on the hot pipe again with plenty of water. Not to really bend them but make them flexible. Then clamp it in the mold and let it dry overnight and it should set better. If that doesn't work....go with it as is. Some wood just doesn't want to cooperate |
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| Author: | George L [ Thu Feb 19, 2015 11:48 am ] |
| Post subject: | Re: Forcing Sides to Shape |
Thought I'd follow up with a report. With the rims squared away in the mold nothing felt or acted unusually stressed, so I embraced John Hall's approach of "if it fits, it fits," as well as the advice of the others advocating I move forward without further adieu. So, as the boss of my workshop, I went ahead and closed up the box. All seems to have gone well and I'm all set to continue with this guitar. We'll see how things go from here. Thanks again for all the input. Working through this obstacle was very helpful and taught me a few more things that will make me a better builder down the line. I greatly appreciate your willingness to share. Because we all love pictures, here's a shot of the back, which I find quite striking: 
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