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How much bend is acceptable in a neck? (Read 5785 times)
Byggles
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How much bend is acceptable in a neck?
Apr 4th, 2009 at 6:09am
 
I picked up my neck after having left it while gluing braces  and patches on the front and back boards and found it was no longer flat.  It has a 1/2 mm convex bend in it, essentially a slight hump on the surface that  will be glued to the fret board.  Should I  try to sand this out or is it within acceptable limits?  Sometime my sanding makes things worse!  The pull on the strings will tend to take it out but the frets will be dressed before the strings are on.  This is my first instrument build so any help  you guys can provide will be appreciated.

Here is a link to the construction photographs.

http://picasaweb.google.com/Byggles

Thanks.
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Matt Blacka
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Re: How much bend is acceptable in a neck?
Reply #1 - Apr 4th, 2009 at 9:40pm
 
Hi Byggles,

I wouldn't hope to get much flex out of your neck due to string tension, especially if you use the standard fretboard and neck thickness that is used by Hana Lima 'Ia. Maybe in the long term you will get a bit of creep in the neck, and 0.5 mm is not much, but I wouldn't rely on it for a solution.

I know what you mean about making things worse when you sand. If I were you, I would stick a long length of sandpaper to your table saw table (or equivalent machined flat surface, I sometimes use a big piece of glass). Then, using long strokes in one direction only, sand the neck surface flat. Every 10 or 20 strokes, turn the neck around and go the other way. The trick is to not sand back and forward, but in one direction only at a time. Try to keep as even pressure as possible across the width of the neck.

Check very regularly to make sure that you are not making anything worse.

Good luck,

Matt
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Byggles
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Re: How much bend is acceptable in a neck?
Reply #2 - Apr 5th, 2009 at 3:09pm
 
Thanks for the sanding tip.  I noticed when trying to get a good join on the 2 top halves that when I used a single hand and a back and forth motion that the end result was a heavier loss of material on the ends.  I solved that problem by adopting a 2 handed technique that applied equal pressure.  The neck had a somewhat constant curve and I was finding it difficult to know where on the curve I was registering during the sanding operation.  Persistence pays of though.

Thanks for the help.
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Matt Blacka
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Re: How much bend is acceptable in a neck?
Reply #3 - Apr 6th, 2009 at 1:48am
 
In situations like that, cover the surface that you are sanding with pencil marks. It will give you a quick indication of where you are taking material away from.

Matt
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dochughes
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Re: How much bend is acceptable in a neck?
Reply #4 - Apr 6th, 2009 at 6:08am
 
I enjoyed going through your pics, Byggles.  Your laminated neck looks great!
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Byggles
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Re: How much bend is acceptable in a neck?
Reply #5 - Apr 7th, 2009 at 5:33pm
 
Good idea to use pencil markings.

Thanks for the compliment on the construction pictures.  I'm working up the nerve to glue the back to the sides.
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zog
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Re: How much bend is acceptable in a neck?
Reply #6 - Apr 8th, 2009 at 7:55am
 
Cool looking neck!
I use sand paper that has a self adhesive back it comes in rolls 80-120-240 grits, I also have a 5/8" thick piece of steel that is about 12" x 24" that is surface ground flat. I use it to clamp on pieces on and sand necks. It also works great to match tops and backs.
Smiley
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Byggles
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Re: How much bend is acceptable in a neck?
Reply #7 - Apr 8th, 2009 at 3:41pm
 
Does the 'sticky' on the sandpaper leave a residue behind when you peel it off the steel?  I have access to a very flat table saw surface but I don't want to leave a mess behind me.
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dochughes
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Re: How much bend is acceptable in a neck?
Reply #8 - Apr 9th, 2009 at 2:09am
 
I use a spray-on adhesive on the back of standard sandpaper when I need to adhere it to a flat surface, and it does leave a residue, but it is very easily cleaned up with paint thinner.
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lefty
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Re: How much bend is acceptable in a neck?
Reply #9 - Apr 9th, 2009 at 10:36am
 
Byggles,
 Great photos.

 I think that your neck flex
may
have been caused because of the lamination's.  Because the top and bottom portions of the neck itself are different thicknesses the thin lamination on the bottom is curling out and causing the bump.
 I would keep a close eye on it to make sure the hump does not get worse.

 Just my two cents worth,  Hope I'm wrong,
Lefty
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Byggles
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Re: How much bend is acceptable in a neck?
Reply #10 - Apr 9th, 2009 at 4:13pm
 
I might try the spray adhesive technique on the fret board.  Its going to be cherry, which is the same as the light wood in the neck lamination.  Hopefully that will stop any bend from getting worse.

Thanks for the help.
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Matt Blacka
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Re: How much bend is acceptable in a neck?
Reply #11 - Apr 12th, 2009 at 12:41am
 
Hello again Byggles,

I was using a spray contact adhesive to stick sandpaper down, and it left a sticky residue, but I just scraped it off with a stanley knife blade. about 30 seconds of scraping and all is clean.

These days I use the self adhesive sandpaper from stewart mcdonald. This is the fastest cutting sandpaper I have used, and has saved me hours of sanding time. I was a bit bothered by spending the money on whole rolls and getting them shipped to Australia, but it has been well worth it. I will do it again as soon as I run out.

Matt
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Byggles
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Re: How much bend is acceptable in a neck?
Reply #12 - Apr 12th, 2009 at 10:53am
 
I seem to be well stocked with sandpaper at the moment so am going to try the spray adhesive technique when I get to the neck.  I'm currently working on a jig to cut the binding rebate.  You guys must have nerves of steel!
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