Ash's acoustic rabbit hole

[ADFinlayson]

Got the 8th coat of lacquer on the mahgoany one at the weekend. Hopefully that is enough to start levelling it properly in a couple of days. 

The lacquer has really popped the tortoise shell

Made a good bit of progress on the next one. Thought a splash of colour inside would look cool so I stuck a maple veneer on the end block, dyed it red and gave it a coat of sealer. I made a special effort to get the linings glued in neatly this time with no gaps, particularly on the back linings as they're visible through the sound hole. I used small clamps to do a lot of it rather than relying on the rubber band reinforced clothing pegs.

The top and the back of the sides have been sanded on the dish, I just need to notch out the sides before I can close the box, but I might just plane down the neck block a bit, it's a bit chunky. 

[Andyjr1515]

The first one looks splendid.  Nice touch on No 2 also with that splash - it's those little things that make all the difference.  Very cool!

[ADFinlayson]

Thanks @Andyjr1515

Had another go with the labels, tweaked the design a bit. I stained some parchment paper to yellow it up a bit with a wet tea bag, dried it with the mrs hair dryer and printed out the design. I wasn't expecting much from this, especially with my £30 HP printer but I think it came out ok. Stuck it down with some Titebond brushed on very sparingly. Installing the label on the mahogany one will not be quite so enjoyable, I expect.

and finally I closed the box tonight. Glued the back down first in the gobar deck, then after an hour I took the spreader out, flipped the dish and the guitar over and glued the top down. The cool thing about the dish is it makes the perfect caul for the back which remains under clamping pressure while the top is getting glued down, so it will stay like this over night.

 

 

 

[Andyjr1515]

5 hours ago, ADFinlayson said:

The cool thing about the dish is it makes the perfect caul for the back which remains under clamping pressure while the top is getting glued down, so it will stay like this over night

Good tip.  Consider it stolen! 

[Crusader]

On 9/9/2023 at 5:52 AM, ADFinlayson said:

Really happy with how this has come out. 

I would be too, looking good!

 

On 9/13/2023 at 2:03 AM, ShatnersBassoon said:

When you start building acoustics, it’s serious business!

Totally agree with that!

[ADFinlayson]

15 hours ago, Andyjr1515 said:

Good tip.  Consider it stolen! 

I've stolen a fair few of your ideas so, seams fair!

[ADFinlayson]

Got it out of the clamps and trimmed up this eve. Wiped some thinned down lacquer around the edge first to help protect the end grain from the router

Then I had a play with one of my new toys

This thing is a real time saver, had the sides sanded flat in no time at all with 120g on the bobbin. Definitely a mask on kind of job though!

I also got some curly maple strips through the drum sander and down to 6.5mm x 2.3mm, they're ready to go in the bender, then it's on to the scary bit.

 

[ADFinlayson]

Well I didn't enjoy that much, fortunately I had some rope and wedges hanging around for a bit of reinforcement. I think 2.3mm for flame maple binding must be a bit too chunky - Even though I bent it in the bending machine, it still didn't really want to conform without some manhandling. Luckily I used titebond instead of superglue this time so I had time to mess with it. 

I have mixed feelings about this machine. I'll start by saying it's at least 10x better than my previous method. It does cut a perfectly parallel with sides channel and it does feel quite natural to use after a bit of playing around. It doesn't use traditional bearings but will cut any channel to the thickness of the binding/purflling so binding doens't have to be an exact thickness.

The accuracy of the channel really relies on the guitar side riding on that back bearing farthest away from the cutter. The trouble with it is that once the first channel has been cut, the side is too thin by the neck block to ride on the back bearing, so I had to bind the back before I can route the channel for the front.

Elevate do a an upgrade with a bigger bearing surface for thinner instruments so I might get that, pretty annoying it doesn't come with it as standard though.

My other gripe is that although the channel is perfectly square with the sides, the channel seams to be imperfect with a little ridge in the bottom, Here's a little diagram of the profile so you can see what I mean.  

So I had to spend an age with a small file and chisel to carefully remove that little ledge all the way round, then I sanded a small bevel into the underside of the back of the binding to help it sit flush. I'm sure this is probably down to how I've set the binding jig up, or perhaps I just need some more practice to get the knack, but it is annoying.

I want to have a go at purfling along with maple binding on the front to tie in with the rosette, but I had such a pain in the butt getting the binding in on the back so I'm not sure if I want to add the extra complexity. I suppose I'm going to have to dive in and try purfling at some point.

[Bizman62]

Based on all the videos and stories I've seen about binding it seems that there still isn't a fool proof tool that gives perfect results in one go. There'll always be a ledge in the bottom, or the cavity is angled, or the depth isn't the same in all places, or you'll have to do some places by hand, or...

Then again, I can't help but wonder how tedious it must have been before power routers!

[Prostheta]

Even CNC cannot do it to the point of what I would call geometric perfection. The objectives as I see it are to produce crisp edges. Internally, they can be cleaned by hand for areas that are missed or left to fill with glue in voids.

An example that I rolled about my head was the binding channel over the curved arm contour of my Mirage bodies last year. If done by CNC (I did them manually in the end) with the cutter following an XY path around the perimeter with adjustment in the Z, the nature of the cutter would leave it inconsistent. The ideal path would be a rectangle swept around the profile with the direction changing perpendicular to the profile in a pure XY shape. With a cutter being cylindrical, it cannot be perfect. The exact same issue that you are describing.

The small ridge left if acceptable in my view, since it can either be cleaned manually as mentioned, or the inner edge of the binding can be scraped. Either or both. The main objective is for the seams to be tight and clean. Any slight deviations internally are neither here nor there, and have to be accepted at some point as a consequence of geometry.

I like that machine, but really it seems like something that may still need to be supported by a Schneider Gramil or even manual cutting. My jig is literally like the Z axis of a CNC with my Makita palm router fitted, and using a modified white plastic Thor hammer face as the bearing. In the extremes of curvature, the channel reduces in depth significantly compared to the flat areas. It works, but needs final tuning.

[ADFinlayson]

Yeah I guess you could never really CNC cut a binding channel on an acoustic anyway because no matter how good you or your machines are at side bending, the sides will never be identical to what is in the CNCs path. A gramil is a good idea, I don't know why I didn't think of using that to tidy up, would have been a lot easier than a chisel, even with my gramil being made of chocolate metal - I could really do with getting a decent one. 

I was keen to see what it looked like so I got the tape off first thing this morn

It's not bad, probably my best effort at binding but I've chosen a pair of quite unforgiving woods - Gaps I was able to just fill on the mahogany one could do with some improvement. We're zoomed right in here so these gaps aren't anywhere near as bad to the naked eye but I can see them now and they're annoying me. I think I'll see if I can press them in a bit more with a hot iron before attempting to scape anything flush.

if I was using a darker wood here I would absolutely be filling with dust and glue instead.

I probably could have avoided this if I had done more wraps but alas I ran out of rope. Time to invest in something more suitable than tow rope

[Prostheta]

That being said, I bet you Taylor cut their channels on CNC....because that's the sort of thing they seem to see as a challenge to best.

I agree about a hot iron. It might be useful in the long term to make a brass block with a threaded handle to judicious application of heat. Similarly, a nice brass Gramil or one made from say, African Blackwood or other wood that takes a thread nicely may be in your future.

[ADFinlayson]

Had a go with the iron, worked pretty well to soften the glue and I was able to push the binding into place, so I wrapped it up again and left it for a few hours. 

Got it all scraped flush and it came out pretty good, I've still got a couple of hair lines which I've filled with blacklimba + titebond as woodfiller. I'm especially happy with the joint on the back. 

Will have a go at the front binding channels tomorrow. 

[Prostheta]

Have you tried epoxy as a pore filler yet? Pacer Z-Poxy Finishing Resin is pretty amazing.

[ADFinlayson]

3 hours ago, Prostheta said:

Have you tried epoxy as a pore filler yet? Pacer Z-Poxy Finishing Resin is pretty amazing.

Actually I ordered some z-poxy PT-40 last week. I was contemplating grain filling the other day - I don't want to do a coloured fill on this and the only clear stuff I've got is aqua coat which I don't like. I was also thinking about when I would do grainfillng, might make my life easier to do prior to routing the mortise

[Prostheta]

You'll love it as long as you do small quantities and keep the process under control. A bunch of wooden forks for mixing, precision scales and plastic or paper shot glasses. The thing that always bothered me about epoxy was me not being organised enough or able to mix small batchs of a few grams at a time. Done over multiple sessions and taking off as much as you can each time, and it's magical.

[Andyjr1515]

15 hours ago, ADFinlayson said:

Had a go with the iron, worked pretty well to soften the glue and I was able to push the binding into place, so I wrapped it up again and left it for a few hours. 

Got it all scraped flush and it came out pretty good, I've still got a couple of hair lines which I've filled with blacklimba + titebond as woodfiller. I'm especially happy with the joint on the back. 

Will have a go at the front binding channels tomorrow. 

That looks good. 

I think I've mentioned in some of my build threads that after bending to shape, I use a hot iron to  actually glue the bindings.  I do it like I do my veneering - I apply a decent PVA to all relevant surfaces, let it dry and then use the iron to melt the joint progressively round, holding in position with a leather-gloved hand as it cools.  The advantage is that I know it's spot on before I move to the next inch or so and therefore don't suffer from accumulated positional error.  And it's quick...

[ADFinlayson]

1 hour ago, Andyjr1515 said:

That looks good. 

I think I've mentioned in some of my build threads that after bending to shape, I use a hot iron to  actually glue the bindings.  I do it like I do my veneering - I apply a decent PVA to all relevant surfaces, let it dry and then use the iron to melt the joint progressively round, holding in position with a leather-gloved hand as it cools.  The advantage is that I know it's spot on before I move to the next inch or so and therefore don't suffer from accumulated positional error.  And it's quick...

I remember you talking about that technique, but tbh that idea scared me a bit for binding. 

[Andyjr1515]

I'll be using it for the dinky acoustic if all goes to plan.  I'll see if I can document it

[ADFinlayson]

I spent the morning on front binding, that was a high stress operation towards the end. I cut my channels and they seemed to come out pretty well. The binding channel was easy, the perfling channel was scary but seemed to manage it without hickup or noticable tearout.

tested both pieces

You can see the inperfection in the channel I mentioned before, although it was only a couple of patches that was like this, most areas came out clean

So I had a go with my gramil, but it was fairly useless so I just went back to a sharp chisel 

Another test fit all round after tidying up the channels

And a couple of hours and some swearing later 

Touch wood it seams to have gone quite well though the oversized purfling does cast a bit of a shadow so it's difficult to see gaps.

I spent some time hand bending the binding prior to installing even though it was machine bent, that made the fit a lot better and not as much clamping force was needed. Will see what it looks like in a few hours. 

 

[Prostheta]

It'll work out fine. When you scrape back the purfling, the black outer lams tend to spread out into any hairline cracks. The main thing is always the downpressure on the binding itself so there are no gaps around the perimeter of the sides. That's always caught me.

[henrim]

1 hour ago, ADFinlayson said:

So I had a go with my gramil, but it was fairly useless so I just went back to a sharp chisel 

Maybe it would work better with less stick out on the blade. Also I find it odd that the sliding surface is knurled. I can’t see the whole tool in the picture but if there is a flat surface on either arm that would make a better support. Round tool tend to rotate in unwanted ways. 

[Andyjr1515]

2 hours ago, ADFinlayson said:

So I had a go with my gramil, but it was fairly useless so I just went back to a sharp chisel

After similar trials and tribulations, I now just use a 30mm x 10mm piece of 10mm ply with some 120 emery cloth stuck to one of the faces with double sided tape, and razor cut flush with the bottom face. I can then run that bottom face of the ply  along the ledge of the rebate and sand off any imperfections square

[Prostheta]

1 hour ago, henrim said:

Maybe it would work better with less stick out on the blade. Also I find it odd that the sliding surface is knurled. I can’t see the whole tool in the picture but if there is a flat surface on either arm that would make a better support. Round tool tend to rotate in unwanted ways. 

It looks upside down, perhaps. Yes, most Gramil-like tools that I have seen are something like a 20 x 30mm block with a radius of say, something like 3-5cm on the bearing face. Round looks difficult to dial in.

[ADFinlayson]

It's not upside down, it's just shite. I'll take a better picture when I'm out in the shop next.