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| Self-centering neck fixture http://mowrystrings.luthiersforum.com/forum/viewtopic.php?f=10106&t=40965 |
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| Author: | Sheldon Dingwall [ Wed Jul 24, 2013 7:33 pm ] |
| Post subject: | Self-centering neck fixture |
I've been working on this fixture for a LONG time. We'll use this fixture to hold necks for fretboard radiusing, slotting and inlays. I've found for us the best way to not distort the fretboard plane while holding it is to grab the neck from the edges. Two self-centering vises mounted on plates that index onto our master vacuum table. The soft jaws have a slight curve to them to accomodate various neck tapers. There are two dowel pins that set the heel height. An adjustable gauge transfers the Z height of the fingerboard at the headstock end. I haven't found a need for it yet, but there's room for a 3rd vacuum fixture in the middle to mount support pins. |
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| Author: | Mike Lindstrom [ Wed Jul 24, 2013 10:31 pm ] |
| Post subject: | Re: Self-centering neck fixture |
Pretty cool. What do you do for FB radiusing? I find I need support in the middle of the neck or I get flexing, ending up with a not flat fret plane. |
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| Author: | Bob Garrish [ Thu Jul 25, 2013 3:06 am ] |
| Post subject: | Re: Self-centering neck fixture |
I think you'll want to grab it in the middle just to mitigate vibration; I've never had good experiences with long pieces supported at the ends. Definitely a spiffy fixture, and I dig the versatility. I've generally built fixtures to be modular, with rigid components, so I can swap out this bit or that depending on the headstock/bridge/etc I'm working on. I tend to fear moving parts in fixtures, but those vises are pretty sweet. That's the problem with having a 'real' machine like the Fadal, your fixture-making ability is just too great to resist! |
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| Author: | Sheldon Dingwall [ Thu Jul 25, 2013 9:12 am ] |
| Post subject: | Re: Self-centering neck fixture |
Mike, we're using a copy mill (button cutter) to radius the FB. It doesn't have a "dead" area in the center like a ball mill so doesn't try to displace the material in the center of the cut. We've been testing out the concept using vacuum to hold the heel and back of the headstock. So far we're not noticing any unwanted distortion from the cut, just distortion from the vacuum fixturing if the headstock and heel aren't 100% co-planar. Bob, I never thought about a third vise in the center. That would be cool. What would you think about a Y shaped piece with two pins that come in at 45 degrees or so to support the middle in both the Z and Y directions? |
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| Author: | Bob Garrish [ Fri Jul 26, 2013 12:32 am ] |
| Post subject: | Re: Self-centering neck fixture |
Sheldon Dingwall wrote: Bob, I never thought about a third vise in the center. That would be cool. What would you think about a Y shaped piece with two pins that come in at 45 degrees or so to support the middle in both the Z and Y directions? Vibration works both ways, so you'd need to support it 'top and bottom' to stop Z-axis vibration. The fact that you're using a button cutter means you're going to have a pretty low-vibration cut, so perhaps just wedging a piece of foam rubber or something under the middle of the neck would be enough to take care of it. Since you've got a truss rod in there at carving time, you can always flatten the middle again if the rubber pushes it up, right? |
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| Author: | Sheldon Dingwall [ Sun Jul 28, 2013 5:34 pm ] |
| Post subject: | Re: Self-centering neck fixture |
Bob Garrish wrote: Sheldon Dingwall wrote: Bob, I never thought about a third vise in the center. That would be cool. What would you think about a Y shaped piece with two pins that come in at 45 degrees or so to support the middle in both the Z and Y directions? Vibration works both ways, so you'd need to support it 'top and bottom' to stop Z-axis vibration. The fact that you're using a button cutter means you're going to have a pretty low-vibration cut, so perhaps just wedging a piece of foam rubber or something under the middle of the neck would be enough to take care of it. Since you've got a truss rod in there at carving time, you can always flatten the middle again if the rubber pushes it up, right? I think the best way to level the board is to tension the rod to the point where you'd like the FB to eventually read straight, then mill off the surface. It would probably be a compromise but the neck could be pinned in the middle and then the truss-rod loosened to apply pressure against the pin. It wouldn't be much, but if the vibration is minimal it might be enough. |
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| Author: | npalen [ Tue Jul 30, 2013 11:09 pm ] |
| Post subject: | Re: Self-centering neck fixture |
Sheldon, tell us a little more about the vises. Did you convert conventional vises to self centering? |
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| Author: | Sheldon Dingwall [ Wed Jul 31, 2013 1:35 am ] |
| Post subject: | Re: Self-centering neck fixture |
There are a few self centering vises available. My budget only allowed for the import variety. The best deal I found was a Canadian Supplier called Busy Bee tools. They'd be similar to a smaller version of Grizzly. They seem pretty solid with minimal backlash. Quality would be similar to Shars or slightly better. |
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| Author: | Stuart Gort [ Wed Jul 31, 2013 11:15 am ] |
| Post subject: | Re: Self-centering neck fixture |
Bob Garrish wrote: Sheldon Dingwall wrote: Bob, I never thought about a third vise in the center. That would be cool. What would you think about a Y shaped piece with two pins that come in at 45 degrees or so to support the middle in both the Z and Y directions? Vibration works both ways, so you'd need to support it 'top and bottom' to stop Z-axis vibration. The fact that you're using a button cutter means you're going to have a pretty low-vibration cut, so perhaps just wedging a piece of foam rubber or something under the middle of the neck would be enough to take care of it. Since you've got a truss rod in there at carving time, you can always flatten the middle again if the rubber pushes it up, right? I have a similar idea for supporting the center on a universal neck jig. so far...I've made new jigs for every neck model and I can't keep doing that. My idea for a universal fixture: 1. Affixes and supports the heel at a hard angle with screws. 2. Supports the headstock with a plane that will lock to the position the headstock takes after cutting. 3. An adjustable center support with a fairly hard foam pad as you describe. The screwed down heel is obviously the hard point (and a "boss" of sorts) since that is going to fit to the body. Any subtle misalignment of the rear headstock, due to the stress relief of the rear cut must be accommodated for with a locking plane. Variable height must also be accounted for. I have several ideas on this but they are in the thinking stage...not really gelled yet but it could be something as simple a three point locking post assembly. Honestly though? I screw the headstock to an angled plate now and haven't noticed any real problem with this method using shims to accommodate subtle issues. The center support is key I think. I worry about z-axis vibration too so I'd make this and then maybe find out later that it wasn't necessary. Once the neck and headstock are affixed to the jig a height gauge would be placed over the top of the wood in the center. Then the center support would be adjusted upward until it deflected the needle above. Then adjusted down again until the needle returned to his initial position. One might have to mess with various hardness on the pad until the support was ideal. |
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| Author: | Sheldon Dingwall [ Fri Aug 02, 2013 4:47 pm ] |
| Post subject: | Re: Self-centering neck fixture |
I'm in agreement on a neck support, but not foam or rubber. Maybe cork gasket or just a wooden cap on a steel pin. |
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| Author: | Fleck [ Sat Aug 24, 2013 11:29 am ] |
| Post subject: | Re: Self-centering neck fixture |
That is very cool. It almost seems like with that setup you could possibly simulate a bit of tension while milling. |
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| Author: | Sheldon Dingwall [ Sun Aug 25, 2013 10:02 am ] |
| Post subject: | Re: Self-centering neck fixture |
You probably could. We weren't seeing any benefits so haven't done that in a long time. |
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