Starting out in guitar building - There will be questions!

SteveF

General question that's popped up for future reference rather than this build: 

When dimensioning parts, how close do you go to the final desired dimension and how much do you leave for sanding etc.  e.g. if you wanted a 45mm body and you thickness the blank, I assume you wouldn't go all the way to 45mm with the router/thicknesser but would leave a small allowance to be taken away when rough and finish sanding so as not to end up smaller than the final dimension in the end?  Is there a rule of thumb? 

WezV

As a very rough concept, what sanding takes away, finishing adds back.

Also, how crucial is body thickness?   If it ends up 44 or 46mm will it matter?

BillDL

SteveF said:

.....  Is there a rule of thumb? 

Yes, make sure to move it to the side when using sharp, pointy or dull-thuddy hand and power tools 

TTony

SteveF said:

Is there a rule of thumb? 

Stop just before you go too far.

And what Wez said.  

Unless you're trying to make vintage replicas to within fractions of a mm, body thickness isn't a critical dimension.

If you are trying to make vintage replicas, you'll probably find that dimensions of one example differs by more than a few fractions of a mm from another example!

SteveF

Thanks all, makes sense.  I guess body blank was a poor example - I was more thinking about things that are more specific e.g neck thickness at the nut etc.  The guidance about finishing basically replacing what is sanded away helps though. 

SteveF

Getting there. Brief pause to cobble together a spray station and we're away.  Body is all sanded and first coat of sanding sealer is on (picture is before that happened).  

SteveF

Sigh. 

A temperature drop and a rainy day (presumably, at least from what I can gather from googling) and there’s white patches in my clear coat. Any advice? (Beyond don’t spray on a cold, rainy day - I got that now) 

davros

Are you spraying nitro? I tend to use MGT nitro and it has anti-bloom thinners in it. Otherwise, a light sand and spray another coat in better weather should release it.

WezV

Do a light sand now,  spray a light coat on a dry day

SteveF

Yes it’s MGT nitro clear gloss over LPB. 

I’ve brought it in from the garage to the house to see if it releases when properly dry but it’s been in a couple of hours now and it’s no better - worse if anything. 

If it doesn’t improve I’ll wait for a better day and try as you suggest. Dry sand with 600 do the trick? 

SteveF

Presumably sand until all the white has gone? 

WezV

Yeah, or even a hard rub with a cloth now... just something to break the surface enough for the moisture to release.  Success will depend on how deep the moisture is

SteveRobinson

Another light coat should fix it.

WezV

SteveF said:

Presumably sand until all the white has gone? 

Not necessarily.... it needs to come out, it can be quite deep. 

If sanding or a rub down now doesn't clear it, the next coat should, if sprayed light

SteveF

Cloth didn’t seem to do too much but a quick rub over with some 600 seemed to sort it I think. It’s supposed to be dry tomorrow afternoon so I’ll give it a light coat then and see how it goes. 

SteveF

Well, first attempt at wet sanding was disastrous.  I think some of it was actually down to my prep not being quite as good as I had perhaps thought.  I have a couple of areas where I sanded right through to the primer and some patchy areas that I think is where I have gone through the clear to the colour and therefore there are lighter areas where it's just colour and darker areas where there is some clear still.  

Count to ten. Learning process.  I think I'm going to go ahead and finish for now and then I think I'll try and respray when I do the next one.  

SteveF

Managed to sand through completely at the edge here: 



And again here. I think as the light patches appeared I thought they were low spots, so kept sanding.  I actually think it's where I had gone through the clear and into the colour coat, so the light patches are where there is colour only.  Keep sanding til the low spots disappear... whoops.
 


On the plus side, I kind of like how my heel looks.   



More patchiness.  Again where I think I have gone through the clear. Also near the ferrule block rout, I had some kind of high spot I think.



A few factors at play here I think.  Preparation first of all.  I don't think I had sanded nearly as well as I thought I had.  Also, poplar seems to be REALLY soft and dings up easily, so more care required in general.  Obviously second is my lack of experience with wet sanding.  I thought I was being safe by starting at 800, but it was still really easy to go through. I think too much pressure perhaps was a factor too. The large area of sand through on the upper front section was the first area I did.  I reduced the pressure after that and it seemed to help a bit.  

I figured I would carry on and see what I could get the "good" bits looking like.  I did 800, 1200, 1500, then used some autosol and then t-cut and it seems to have come up ok.  Not sure if I should have gone even higher with the sandpaper first?  I also think I will need some kind of buffer to get much better shine. 

I think I am going to get the guitar built, nut cut and see how it plays and then move on to the next project for now.  It will need a refinish, but I need to work out how I am going to do my spraying going forward first.  My makeshift spray area worked fine for keeping direct spray off everything that it should have, but the garage with no extraction is not ideal - There was a thin film of blue dust over EVERYTHING in there as it had obviously just been in the air.  I'm going to still be wiping that off stuff come Christmas!

I'm going to have to do it outside or get some kind of pop up spray booth or something.  Having hit October in Glasgow, I don't think I will get string of suitable days to do it for about 6+ months though. 

BillDL

That's a shame Steve.  I had a similar disappointment with a guitar I just finished a few weeks ago, but that was down to the dye continually separating into creamy streaks and being unable to achieve a consistent opacity and shade.  I made the best of it and sanded it back to a kind of "beach washed" finish and it came out OK.  You're right about the weather though.  Even if you managed to install a powerful enough extractor fan and an improvised filter, the air from now until Spring is likely to be either too humid or too cold (condensation) for any guarantee of a decent finish.

I used to have to spray paint industrial machine components and finished parts in an open fronted booth.  All they used was relatively cheap double-layer concertina paper filters similar to these that are really just a baffle with offset holes in the front and rear layers to trap the particulates:

https://spcb.co.uk/products/cardboard-spray-booth-filters

You could probably knock up a small booth frame from ordinary lengths of pine and just make a "lip" around the open area for the filter to sit in.  The area behind with the extractor fan needs to be enclosed and vented to the outside air though.  You could use plastic, aluminium of galvanised flexi-piping for that.  You would need a fairly strong fan behind the filter, but I think you could easily get by with a large diameter domestic pedestal fan running at full speed.  You would obviously have to be well aware of the potential of a spark from switches or the motor when you are dealing with volatile solvent fumes.  A guy down the road from me fixes up motorbikes and has to spray paint them.  He has an old and fairly wide perspex half circle shower enclosure that he modified into a spray booth in his Marley lock-up garage, and he uses those paper baffle filters and a large fan ducted through a corrugated flexible drainage pipe.

SteveF

Thanks Bill.  It is disappointing, but I am fairly sanguine about it.  This is my first build and I fully expected there to be some learning experiences.  I had expected to have made half a dozen bodies and necks by now  

I will work out what to do with the spray booth at some stage.  I see plenty of people who seem to get decent results by doing it outside, so it might just be that I need to wait on some decent weather - I am struggling for space as it is.  As long as I can get a full day's spraying in without rain etc, then I should be ok.  If I have to have gaps between each spraying day it's not the end of the world. 

It will come.  I am confident that I can learn from the errors and get better as I go on.  As long as I have a playable guitar at the end of the first build then I have met my aim (and surpassed my expectations! ) 

TTony

I remember my early builds, and thinking that I was almost there when I'd finished the woodwork part.

Then I realised that it can take 5x (or more) as long to get the finishing done!

One "experience" was with a no-longer used stain-based finishing kit that didn't turn out how I wanted, so I decided to strip and re-do.  But the stain had penetrated into the wood.  I ended up taking 1mm off the thickness of the body (with my surfacing bit in the router) to get back to bare wood to be able to start again ...

Finishing is a definite skill!