Good ways to prevent movement in a scarf joint glue up?

PeteC

I've got several necks on the go at the moment after starting a single build then deciding to do multiple necks while I had the gear set up a particular way in the shed. 

One of these is my first crack at a multiple laminated neck.  
It's not quite deep enough to do a single neck cut in profile, so I am scarfing it. Its come up really well on the scarf jig and I've been careful to get everything very flat and very square. 

I'm looking for a good way to do the scarf and have the laminate joints meet up precisely without having to resort to inserting some veneer in the joint to hide any inaccuracies between the edges of the laminates when glued up. 

I'm thinking of dry clamping it when perfectly aligned then drilling a couple of 3mm holes in the waste areas and inserting a couple of old 3mm drill bit shafts as locating pins to stop it moving when I come to the glue up. 

Is there a better way of approaching it ?
Any suggestions welcomed. 
cheers

WezV

Just as you describe, pin it.   But I would use cocktail sticks or BBQ skewers

PeteC

Ah - yes, Thanks @WezV , that way I can leave em in the glued headstock and just cut them out as part of the waste wood. 

I did think about using double stick tape to secure the dry joint before drilling the locating pin holes but having mocked that up its still too thick to ensure an accurate match.  I'm wondering whether I could do a weakly bonded glue up to prevent any movement when drilling the pilot holes and then separate the joint ready for the proper glue up. Not sure.....

ICBM

I would use bolts through the waste areas. Make the holes slightly oversize to allow movement so you can get the alignment perfect before you tighten them up to lock it, and then apply the full clamping pressure.

more

Tap in a couple of  pins and cut them off just above the wood . The small metal spikes will bite into the other half , when you gently clamp the join together, and stop it from slipping .   

WezV

ICBM said:

I would use bolts through the waste areas. Make the holes slightly oversize to allow movement so you can get the alignment perfect before you tighten them up to lock it, and then apply the full clamping pressure.

my concern would be that the twisting of the bolts as you tighten can be enough to throw the alignment off... but that is also a risk to look out for when tightening the clamps

ICBM

WezV said:

my concern would be that the twisting of the bolts as you tighten can be enough to throw the alignment off... but that is also a risk to look out for when tightening the clamps

I think you're right... in that case I would refine it - bolts in oversized holes first, get them tight enough to hold the pieces in place (you should be able to see the alignment of the laminates at each end and move them until they're perfect), then when you've got it exactly right and locked, drill two more accurate holes through both pieces and use tight-fitting pins. Then disassemble, add the glue, and reassemble using the pins and clamps - you probably don't need the bolts.

PeteC

Thanks gents , this sounds like a bombproof plan - which is what I was hoping for !!   I'll try that.  Off to the shed......

Corvus

I've used pins but favour plain old wood screws; mock up joint, drill pilots; glue/screw & whizz them out when you're ready. Two screws is enough, easy and solid.

PeteC

Thanks.   Just cleaned up the joint and it’s such a clean match dry fitted that I might miss the bolts and just go for the pilot holes on this one.   I’m sure the bolt idea will come in sometime though knowing my luck !   Hopefully I won’t regret missing that extra step @ICBM !   

ICBM

PeteC said:

Thanks.   Just cleaned up the joint and it’s such a clean match dry fitted that I might miss the bolts and just go for the pilot holes on this one.   I’m sure the bolt idea will come in sometime though knowing my luck !   Hopefully I won’t regret missing that extra step @ICBM !   

If you can clamp it into place dry without it slipping it will work. Just make absolutely sure it is locked in the correct place before you drill, and it doesn't move while you do, or you'll guarantee a *mis*alignment.

PeteC

Yep - I know what you mean    Left it for tonight so might still go the bolt route Tomorrow if I’m uncertain about the pilot holes.  

MattNovak

I’ve used an industrial stapler on the waste areas in the past.... 

GSPBASSES

A way to strengthen your head stocks and scarf joints.

In the first photo the two white lines represent two pieces of quarter sawn Maple 5mm X 9mm that's inserted across the staff joint, in the drawing I haven't taken them up to the nut but that could be done to strengthen up the headstock as well.

In the second photo same size Maple is inserted either side of the trust rod through the scarf joint and beyond the nut into the headstock.

Both these methods we have the scarf joint together for longer but more importantly will strengthen up the headstock so it's less likely to snap off.

The video below is well worth having a look at, the quality isn't that good but watch it through to the end and you'll see just what a difference inserting these two pieces of Maple make to a neck.

PeteC

very interesting @GSPBASSES ;
- thank you for sharing this. 

PeteC

In the end there was so little slippage in the dry joint that it was fairly easy to drill pilots and use wood screws ( starting with 1.5mm and working up to 4mm so as not to risk vibration disturbing the clamps ) 

Glue up was then very easy with a few small clamps and the wood screws left to bond for about 4 hours.   Curing overnight now.   
You can see the alignment of the laminates in the shot of the back of the neck. The front will be hidden by the fingerboard. 

Another lesson learned - thanks for all the help and advice as ever. 

A few necks on the go now. 

MattNovak

Those all look great Pete, have you gone for a couple of different scarf methods too? 

PeteC

Cheers @MattNovak       Yes , I have done a couple with the scarf in the neck and with blanks deep enough that the final visible part of the joint will be well away from the nut, and one neck with the scarf in the headstock, which  will be veneer covered. 

MattNovak

PeteC said:

Cheers @MattNovak       Yes , I have done a couple with the scarf in the neck and with blanks deep enough that the final visible part of the joint will be well away from the nut, and one neck with the scarf in the headstock, which  will be veneer covered. 

Nice. Assume you use a bandsaw to get the headstocks down to thickness, removing material from the back? My Aldi affair isn't up to that, it only has a 90mm throat and the stock I've been using is 100mm...   

PeteC

I will do since buying a decent bandsaw,  but previously I have taken taken the back down to thickness with a router jig and used a small riser glued to the top edge of the headstock face to get a slight taper on the back.