Double bass rebuild - not for the faint of heart!

[Stub Mandrel]

On 08/05/2025 at 16:12, The Guitar Weasel said:

Alcohol seems to soften the finish as stands,

 

French polish?

[The Guitar Weasel]

9 hours ago, Stub Mandrel said:

 

French polish?

It's possible ... I may try some 99% acetone on an odd area to see if that gets it off. 

[bass_dinger]

On 08/05/2025 at 16:12, The Guitar Weasel said:

Suggestions on a postcard please ... 

 

I looked up suggestions on Google.  Artificial Intelligence told me to use a heat gun, or a sander.  I think that AI confused "double bass" with "floorboards ". Easily done. 

 

My money would be on talking to a violin maker, or a luthier, to ask how they would remove a finish. 

[Hellzero]

1 hour ago, bass_dinger said:

 

I looked up suggestions on Google.  Artificial Intelligence told me to use a heat gun, or a sander.  I think that AI confused "double bass" with "floorboards ". Easily done. 

 

My money would be on talking to a violin maker, or a luthier, to ask how they would remove a finish. 

I think @The Guitar Weasel is some kind of a luthier. 😉

[bass_dinger]

On 02/05/2025 at 16:31, The Guitar Weasel said:

These other basses I looked at were all fixer-uppers, as I am fairly handy - owning a guitar pickup company helps .

 

On 10/05/2025 at 08:40, Hellzero said:

I think @The Guitar Weasel is some kind of a luthier. 😉

You are right - and I am embarrassed!

 

I once tried to clean my 120 year old violin with surgical spirit, which made the finish go all sticky.  When I mentioned surgical spirit to my tame violin repairer, he knew exactly what the problem would be. From that day, I decided that I would leave this work to the experts (like @The Guitar Weasel)

[The Guitar Weasel]

So the neck pocket has gone from this: 

To this 

The shorter end to the left cheek of the neck socket is to allow for a piece of ply to be let in to repair the top. 

Looks a bit neater now  

[The Guitar Weasel]

7.00am this morning - in the cool of the yard outside our Oil City workshop - I took off the extra unwanted neck heel - bringing the neck angle to 90 degrees. This was a bit of a 'brown trouser job' as a cock up here could ruin the whole neck. 

I am getting used to the Japanese saw ... it's very strange cutting on the draw stroke - but by the Lord Harry it razors through maple like soft wood! That's a huge slab of American oak everything is clamped to - somebody just fly-tipped down the road from my house a few weeks ago - amazing what some folks throw out!  

 

I got thing mostly bang on - with a bit of end grain No4 Stanley plane work which was pretty soon sorted. 
The only slight downer is that I now find out the base of the neck pocket itself is a tad out of true with the bass centre line - clearly their production tolerances were a bit iffy - so a little bit of extra plane work will be needed.

 

The lower part of the heel also needs tapered down a lot ... but that's not so 'mission critical'.

[The Guitar Weasel]

I was resisting sticking even low tack tape down the front of the bass to establish a centreline as the finish comes off on masking tape as easily as the finish comes off a Murphy Labs Les paul neck! And that's bloody easily.

I could 'Chinagraph' pencil or wax marking crayon a centre line - but there are so many check lines that go all the way to the wood I'd probably be left with a permanent 'ghost line' - unless of course I strip the whole finish - sigh, that's looking more and more likely. But with a wayward floor to the neck pocket I will have to be a bit more proactive in lining stuff up, so I think the tape is the way to go. 

 

The plan is for the neck to be bolt on - and I'm already coming up with a jig to drill the neck bolt holes exactly in parallel with each other and with the neck. 130mm x M8 high tensile steel Allen key cap bolts (nickel or chrome plated if I can get them) with captive nuts inside the bass - these nuts have 'prongs' that are dragged into the wood when tightened and will be permanently fixed inside.  I plan to mount the nuts on the cap bolts by way of a long rod (and some Blu Tack) through the end pin hole - probably with an auxiliary positioning arm through one of the F holes. Yes it's keyhole surgery (well F hole actually), but the alternative is to cut an access hatch - and I don't do bodges like that! 

 

Yes I could glue the neck joint - but I may well be doing some travelling, and a  bolt on neck double bass is an attractive proposition. The cap bolts will be sunk into the neck heel so they won't be visible.   

[Rosie C]

On 08/05/2025 at 16:12, The Guitar Weasel said:

Suggestions on a postcard please ... 

 

Feel welcome to send villagers with pitchforks and lighted torches, but my first thoughts are a small power sander for the main body and a dremel for the detail  😈

[Beer of the Bass]

I reckon nobody would look askance at a neatly done access hatch on a removable neck bass. Some very well-respected luthiers do them, for example;

https://www.talkbass.com/threads/nz-non-standard-cleveland-removeable-neck-and-sound-post-hatch.562329/

[Hellzero]

19 minutes ago, Beer of the Bass said:

I reckon nobody would look askance at a neatly done access hatch on a removable neck bass. Some very well-respected luthiers do them, for example;

https://www.talkbass.com/threads/nz-non-standard-cleveland-removeable-neck-and-sound-post-hatch.562329/

Very clever, indeed.👌🏻👍🏻

[The Guitar Weasel]

9 hours ago, Hellzero said:

Very clever, indeed.👌🏻👍🏻

That's fascinating ... interesting to see the single neck bolt too. My plan is two bolts - to my mind it makes it easier to shim the pocket securely if there is a need at a later date. I quite like that circular access panel - it looks way better than the square ones I've seen - and the neodymium button closing magnets are easy - I always have hundreds of those lying about the workshop - bears thinking about. 

[The Guitar Weasel]

 

Started to shape the neck heel to the same size as the original - lots of rasp work needed. Huge amounts of maple biting the dust! 

I've drilled the neck bolt holes too ... well the 6mm pilot holes at least 🙂 

[itu]

Couldn't you use a DIN7965 type of "screw" (threaded insert) in the body as an anchor? Then there would be no need to reach the insides of the bass? Maybe two M6s would be strong enough. M8s could be overkill.

 

I use similar inserts in my electric bass bolt-on necks. To get more area under the bolts (DIN 7991), I have used spherical washers (DIN 6319).

 

https://www.fasteners.eu/standards/din/7965/

Reminder: The slotted head is to go in first.

[The Guitar Weasel]

8 hours ago, itu said:

Couldn't you use a DIN7965 type of "screw" (threaded insert) in the body as an anchor? Then there would be no need to reach the insides of the bass? Maybe two M6s would be strong enough. M8s could be overkill.

 

I use similar inserts in my electric bass bolt-on necks. To get more area under the bolts (DIN 7991), I have used spherical washers (DIN 6319).

 

https://www.fasteners.eu/standards/din/7965/

Reminder: The slotted head is to go in first.

The problem I have with threaded inserts is that a double bass neck is two or perhaps three times the weight of an electric bass neck, and even with low tension strings the pull on that neck is prodigious. In order to get a full and stable fixing on the 30mm thick heel block you would need close to 30mm of threaded insert - and they ain't common - and when you do see them they are intended for furniture and relatively softwood. The heel block is hardwood and some of the long fasteners appear to be fairly dubious alloy. Most of the pro conversions I've seen done seem to use M8 - so that's why I intended to go that route.  I've used threaded inserts on guitar and electric bass before ... but this is a magnitude bigger enginearing. I'm deffo open to looking mind. 🙂

[Stub Mandrel]

An interesting fact about internal threads... all the strength is in about 4 threads. That gives more metal cross section than the core of the screw, plus elastic deformation concentrates the stress in a tiny portion of the engaged threads.

 

This is why screws strip far more frequently than nuts.

 

You will find that inserts with a deep external thread are very strong, however as they put the wood in tension they may not be ideal.

 

Your idea of using spike nuts, that will spread the load over more timber and put it in compression is sound.

[Stub Mandrel]

I found this...

 

 

 

[Matt P]

I've been watching this and am impressed by your skills and craftsmanship, I'm no luthier but as a mechanical engineer i thought I'd offer some ideas as an alternative to the spike nuts.

 

I've used the spike nuts before and have never been impressed with how they hold into the wood when the bolt is removed (or the quality of the metal but that might just be the cheap ones I've encountered.)

 

for this situation the standard engineering solution where i work (engineering R+D department) would be a nut plate, for this particular case a small plate of steel with 2x M8 tapped holes would be used, 10mm thick by about 20 wide would be plenty, and to hold it in place a third smaller tapped hole (M5 is probably enough) could be added to hold it in place when the neck is removed (a recessed bolt in the neck pocket of the body)

 

for materials I'd go with mild steel and grade 8,8 bolts, a coat of paint on the steel would be enough to keep corrosion at bay, I'd avoid Stainless steel as it is prone to galling and difficult to drill and tap compared with mild steel.

 

i will try and make a sketch to show the arrangement

 

Matt

[Matt P]

Hopefully this makes it clear enough (you'd never guess I worked as a draughtsman for 18 months!) 

 

Matt

[The Guitar Weasel]

3 hours ago, Matt P said:

Hopefully this makes it clear enough (you'd never guess I worked as a draughtsman for 18 months!) 

 

Matt

That's a super elegant solution  - and I may yet go for that (especially if I cut an access panel in the cutaway, as the only other way of getting it in would be via an F hole.

If you don't mind me saying this - and it's a compliment - that's the sort of solution my father would have come up with - apprenticed in the REME and finally a Staff Sergeant instructor - before finishing his time (I think it was 21 years back then) and joining Westland on the Black Knight and Black Arrow rocket projects (and launching the Prospero satellite) - and moving on to British Hovercraft - before being made redundant and buying a hardware shop! 

The only issue I see is I'm not super convinced the heel block doesn't taper towards the bottom slightly ... of course that would mean that the drilling angle on the plate might not be exactly 90 degrees. I shall do a bit more measurement and find out. 

PS my grandad was an engineer too - my dad used to say he'd be surprised if lathe cutting lubricant didn't run in my veins. As it happens though I wound up as a feckless musician - though all that changed when I started my pickup manufacturing business fifteen years ago - now I design music electronics - so a bit light on the full on enginearing practise these days 🙂 

[Matt P]

getting the bar in via the f-holes shouldn't be too difficult if you use the string method (similar to getting pots and jack sockets into hollow bodied guitars,) drop a string into the hole in the neck pocket and then fish it out through the f-hole, then run it through the threaded hole in the bar and tie a stop knot, a string through each M8 hole should allow you to pull the nutplate into position so it can be fixed with the m5 screw.

 

of course if the profile isn't nice and square inside then the block becomes more difficult to shape, but once the block is in place you shouldn't ever need to remove it so the access panel wouldn't be required.

 

Engineering runs in our family too, my Paternal grandfather was an engineer and my brother was also an engineer before he moved into computing. (the other side of the family is all fairly practical too, mostly in various manufacturing industries.) I've married an engineer and our son is showing pretty good technical abilities at age 8.

 

Matt

Edited 2 hours ago by Matt P

[Hellzero]

Remember that without any pressure on the top, the soundpost will have a tendency to fall, so you would need an access (hole) or the skill to put the post in place like the classical luthiers.

 

Unless you use this adjustable soundpost (start at 2:20 to avoid the presentation):

 

 

 

https://www.anima-nova.de/english-1/the-soul/

 

[Stub Mandrel]

Don't forget,  the M8 screws need washers in their pockets to spread the load. The force will be equal to the load on the inside so spreading it over a greater area than those two washers is redundant.

[The Guitar Weasel]

6 minutes ago, Stub Mandrel said:

Don't forget,  the M8 screws need washers in their pockets to spread the load. The force will be equal to the load on the inside so spreading it over a greater area than those two washers is redundant.

I did physics at school - but preferred chemistry - as you could lean to blow stuff up 😁 I discovered ping pong balls dissolved in nitric acid can be used to make make 'gun cotton' - it's amazing how long it took for my eyebrows to grow back even with all the hormones of a fifteen year old at the time.