Best way to make a guitar body thinner?

Milk

Hi, I’ve currently got my mind on an idea for a scratch build guitar which is something I’ve never done before,

im At the stage of planning every details down to what I need to do, what tools to buy and what materials to buy,

if I wanted to remove 3-5mm of the top of a guitar how can this be done accuratly without buying expensive and impressive machines to do so?

Danielsguitars

Make a box sled for your router to go on, it's easy with mdf, you'll need a more rigid piece of wood going across the box that the router sits on then a cheap orbital sander to smooth it out.

Google routing box sled

Milk

Thank you I’ll look into it, I’d presume it will leave a few marks but should be easily sanded out ?

Danielsguitars

Milk said:

Thank you I’ll look into it, I’d presume it will leave a few marks but should be easily sanded out ?

The cheap orbital sander from screwfix will take care of the marks no problem, start at 80, 120, 180, 240, 320 to finish.

Funkfingers

Milk said:

if I wanted to remove 3-5mm of the top of a guitar, how can this be done accurately without buying expensive and impressive machines to do so?

CAUTION:
5mm is approximately the thickness of the top of some guitars, with rear access control cavities, in the area where the shafts of the pots emerge. Removing that much material from the front of such guitars risks rendering the control cavity "open plan".

If you remove 5mm from the top of a Stratocaster, the recessed jack socket cavity would no longer be deep enough to accommodate the Switchcraft socket.

Milk

@Funkfingers thank you! my plan is roughly at the moment 

Buy slab of wood
make slab of wood thinner via the slab method mentioned
glue on a nice maple top
make it guitar shaped
route out all cavities needed


It in my head is the logical order of things but there might be a better way, what i am going to do is buy some scrap wood and practice thinning it to the thickness first

Corvus

You might have all this covered already but also-
A side jack hole won't be central any more. May not matter though doesn't look pretty.
If the guitar already has pickup/neck cavities routed you'd likely need to deepen them, def the neck pocket.
If you're planning on adding a fancy top then there's another job in re-chopping the cavities out. That's perfectly doable with the right cutter but clearance for the bearing+screw head can be tight, just needs a bit of planning re cavity depths though.

If you make a router sled, make the sled rigid or it'll sag in the middle with the router's weight. Bowl cutters are good for surface planing, they have radiussed corners so you don't get the plough marks (if sled is meaty enough).

Milk

@Corvus as it will be a blank all the pickup routing and side jack holes won't be there so i can ensure they are where they should be

also I'm thinking of making a sled out of metal maybe to make sure it is solid enough

Sporky

I think normally you machine the cavities before the top goes on. 

Milk

@Sporky so i would machine the cavities in the base wood then add the top and re machine into the maple ?

Danielsguitars

Sporky said:

I think normally you machine the cavities before the top goes on. 

No the only thing you normally machine is a wiring channel then route everything from the top.

Sporky

Ah - fair enough. Seems a missed opportunity. 

Milk

Thank you all. Best make a shopping list 

Funkfingers

Milk said:

@Funkfingers thank you! my plan is roughly at the moment 

Buy slab of wood
make slab of wood thinner via the slab method mentioned
glue on a nice maple top
make it guitar shaped
route out all cavities needed

My mistake. The wording of the third paragraph in your opening post led me to think that you were going to modify an existing guitar body.

Milk

my fault with my illiteracy  @Funkfingers ;

TJT1979

Agree with router sled. Mine is made from wood and OSB and is very rigid. I had thought about welding something instead, but having made it like this, I really wouldn’t bother. 

mooncat

Would it not be easier to buy the slab of wood in the correct thickness?

WezV

mooncat said:

Would it not be easier to buy the slab of wood in the correct thickness?

Yes.   It would also be easier to buy a ready made guitar

idiotwind

I did this recently as a rank amateur piecing things together with minimal kit.  Here's my effort



It worked, but there's definitely some things I'd do differently next time.  The biggest problem was caused by using offcuts I had to hand rather than properly measured stuff.  So the MDF is only just wide enough - I hadn't factored in that the router bit being in the middle of the router.  Sounds obvious in hindsight, but it meant I had to place the rails further apart.  I had a minor accident where the sled slipped sideways and fell off the rail, causing the router to dig in a bit.  Also my support pieces ended up a bit short, but I didn't notice any sag.  My rails were from an old cot bed, so they were factory cut for consistent size and straightness.

I used a 20mm bottom trim bit from Wealdens - a compromise fitting my router (1/4") and budget (small). Wasn't too bad, just more passes needed.  In general I found that I didn't get too bad lines, but it did help to finish with a very light pass moving up less than the width of the bit, as it would mean you go over the line left by the previous pass. Depends how much time you want to spend.

I used this on both the body and the neck fairly successfully.

Milk

@mooncat it would probably be easier but i fancy a challenge

@idiot wind, that's really helpful information, I'm in no rush for this project to be completed so if it takes a month or 2 years im not too fussed. how much material was you removing each pass?

idiotwind

Milk said:

@idiot wind, that's really helpful information, I'm in no rush for this project to be completed so if it takes a month or 2 years im not too fussed. how much material was you removing each pass?

I think the first pass was around 1.5mm. This was too much for this setup. It was harder to move the router and this is when the slip happened. In the end I found it quicker to do two small passes rather than one big pass. By the end I was just skimming the surface. I took 4mm off in total. Probably took a couple of hours. If I had a 1/2" router and a bigger budget then a 52mm diameter surfacing bit would no doubt have flown through it.

If I was doing this again, my main change would be to make the sled wider enough to overhang the rails, with some extra pieces going down to make sure the sled couldn't move side to side.