Easy neck straightening with a Yamaha SB-5A

Bringing your older offset back to life.
Post Reply
User avatar
will
PAT. # 2.972.923
PAT. # 2.972.923
Posts: 720
Joined: Sat Oct 20, 2012 3:36 pm
Contact:

Easy neck straightening with a Yamaha SB-5A

Post by will » Sat Jan 27, 2018 9:02 pm

I've been wanting an early weird Yamaha for a while, and recently I picked one up on eBay when the biding didn't go too high. It looked pretty good in the pictures, at least!

It appeared pretty good when it arrived too, though I had a bit of panic when I saw that it was just shipped with its case in an open-face cardboard box covered in kraft paper, with no padding around the case and a big hole ripped in the kraft paper.

Image
Image
Image
Image

I played it for a bit just to make sure that nothing was wrong with the electronics, but when I disassembled it for a good cleaning, I found that the neck was held on by only one screw (...with a weird thread pitch that makes finding a replacement pretty tricky)

Image

Also, the height screws on the bridge were either missing, glued in place, or replaced with 4-40" allen screws. ...and one was drilled out so that no threads were left. I needed to drill out the stuck screws.

Image

I wound up drilling and tapping them in an easier to find M4 size - it turned out pretty well, I think!

Image

Another problem was that the neck had quite a bit of backbow - To get the strings to pull the neck straight, I needed to tune the bass to A-D-G-B! I checked out a bunch of videos on Youtube about straightening bowed/twisted necks, and the solutions all seemed pretty drastic - clamping a neck and putting it in an oven, pulling out the frets and putting in frets with a different width tang, pulling off the fretboard and planing the neck flat... I figured that I would try something a bit less destructive and see if it would work.


Here's what I tried on a test subject (Teisco bass with a twisted neck)

-I found a big flat board and clamped the bass's body down
-Using some shims and clamps, I clamped the headstock so that the neck was bent back in the correct direction (I bent it a bit past where I wanted it to go, expecting it to spring back when the clamp was released
-Next, I used a hair dryer on "high" to apply heat to the neck for an hour. At one point, the fingerboard popped off about an inch at the nut, but I glued and clamped it back in place.
-I let it cool down overnight before I removed the clamps

Image

When I removed the clamps, the neck didn't spring back as much as I thought it would - I wound up with a neck that was less twisted than before - but in the opposite direction! Also, the neck seemed to bend more where the wood was thinner - next time, I'd concentrate the heat more where the wood of the neck is thicker.

I tried this method again with the Yamaha - except I used shims to bend the neck up so that it had just a bit of relief. I didn't want to overdo it!

Image

...this time, the neck sprung back quite a bit when I took the clamps off the following morning - though, now the neck is perfectly flat when the strings are tuned to E-A-D-G. Hooray! I might try the hairdryer thing again, except with a bit more bend put into the neck.

User avatar
dylanafghjkl
PAT. # 2.972.923
PAT. # 2.972.923
Posts: 421
Joined: Fri Jun 13, 2014 8:59 am
Location: Melbourne

Re: Easy neck straightening with a Yamaha SB-5A

Post by dylanafghjkl » Sun Jan 28, 2018 1:31 am

did some very similar stuff during my guitar building and repair course with pretty positive results except without the heat - i guess not wanting to melt the glue on the fretboard. also had varying degrees of success clamping 1 side of the headstock to repair twists

nice save though! and super cool basses. always love seeing what comes through your workbench!

User avatar
mgeek
PAT. # 2.972.923
PAT. # 2.972.923
Posts: 827
Joined: Mon Mar 17, 2014 1:03 pm

Re: Easy neck straightening with a Yamaha SB-5A

Post by mgeek » Sun Jan 28, 2018 8:46 am

dylanafghjkl wrote:
Sun Jan 28, 2018 1:31 am
did some very similar stuff during my guitar building and repair course with pretty positive results except without the heat - i guess not wanting to melt the glue on the fretboard.
I've always thought you wanted the glue to soften to an extent, the idea being that when it re-sets it helps hold things in the new position.

Nice save and also: LOVE that Teisco bass, wish they turned up here in the UK

User avatar
will
PAT. # 2.972.923
PAT. # 2.972.923
Posts: 720
Joined: Sat Oct 20, 2012 3:36 pm
Contact:

Re: Easy neck straightening with a Yamaha SB-5A

Post by will » Sun Jan 28, 2018 12:13 pm

mgeek wrote:
Sun Jan 28, 2018 8:46 am
dylanafghjkl wrote:
Sun Jan 28, 2018 1:31 am
did some very similar stuff during my guitar building and repair course with pretty positive results except without the heat - i guess not wanting to melt the glue on the fretboard.
I've always thought you wanted the glue to soften to an extent, the idea being that when it re-sets it helps hold things in the new position.

Nice save and also: LOVE that Teisco bass, wish they turned up here in the UK

I'm surprised that Teiscos didn't wind up in the UK - it seems like so many (especially the later junky plywood ones!) of them were shipped the the USA!

I watched a few videos where people tried clamping necks without heat/moisture, but they all seemed to end with no real results when the clamps were removed. Is this used more for making small adjustments?

I figured that I'd need to use one or the other of heat/moisture, and I was worried that steam would wreck the finish. I used the hair dryer instead of a heat gun because I figured that the heat would be enough to soften the glue a bit (without delaminating everything completely and igniting the binding!)

User avatar
mgeek
PAT. # 2.972.923
PAT. # 2.972.923
Posts: 827
Joined: Mon Mar 17, 2014 1:03 pm

Re: Easy neck straightening with a Yamaha SB-5A

Post by mgeek » Sun Jan 28, 2018 1:33 pm

will wrote:
Sun Jan 28, 2018 12:13 pm


I'm surprised that Teiscos didn't wind up in the UK - it seems like so many (especially the later junky plywood ones!) of them were shipped the the USA!

I watched a few videos where people tried clamping necks without heat/moisture, but they all seemed to end with no real results when the clamps were removed. Is this used more for making small adjustments?
Oh some ended up here, just none of the cool ones bar a (very few) SS4ls etc. Those turn up on ebay here maybe once every two years ;)

I've actually done some bending without heat and had some results, but that was in the case of a really severe twist, with the fretboard removed. It got some of the way, which I wasn't expecting (I had just been doing a test clamp), but when I tried bending it more like that it didn't do anything so I steamed it up and that did the trick.

Post Reply