honza992

6 hours ago, Andyjr1515 said:

It will be fine

Thanks Andy, I love your opptimsm🙂 Let's hope it's ......founded.

23 hours ago, Si600 said:

Is that all the bracing it gets? From my recollection of looking in sound holes acoustic guitars are like a boat inside, ribs and frames everywhere. 

20 hours ago, JPJ said:

My thoughts exactly - I was expecting a bass bar or similar plus a reinforcement under the bridge?

Don't forget this is an archtop with a tailpiece so most of the string tension is absorbed by the sides.  It's only the downward forces which need to be resisted by the top (something like 15% of total string tension).  A normal guitar has all the string tension pulling on the bridge itself which is glued to the top.  The arching itself also provides strength. 

Having said that, I shall be sh_tting bricks when the time comes to string it up!  My best guess is that it will be fine, but it's hard to know. 

Today I finished the braces. There are huge differences in the heights of braces that other builders use.  Benedetto goes from 12mm in the centre to 4mm at the sides.  Ken Parker goes from 5.5mm (!!!!) in the middle to virtually nothing at the edges.  I've decided to aim for 8mm in the middle, to 1.5mm at the ends.  This is really significantly less than most acoustic bass guitars have.  But it seems to me that for bass frequencies you need flexibility.  I'm flexing it with my hands all through the process, trying to memorise how it feels so that during the next build I've got a comparison already in my muscle memory.   Anway, here's my carving station:

Here are the braces at their final heights.  I found it really usefuly to write the heights every 30mm all along the braces.  They ended up being 8mm (16mm for the flyover) in the centre, thinning to 1.3 & 1.6mm at the ends.  It's pretty flexible.  Will it withstand the downforces of the strings? Ummm.......not sure.  Let's hope so!  For this bass though, that's as far as I dare go. 

The top needs a bit of cleaning up, sanding etc but we're pretty much there.  I'm excited!

In the short breaks between eating fresh pasta and drinking prosecco, I started on carving the brace(s).  There only one glued on for the moment:

My plan is to have one jump over the other, rather than an X-brace which is glued together.  Having shaped the first brace into a sort of conical shape, the handle of an iwasaki file was the perfect shape for the corresponding hole in the other brace:

So they fit together like this:

Clearly, that second brace has still got some work that needs to be done.  Just a tad oversized....

Those iwasaki file are the nuts by the way.  Hands down the best files I've used.  Much better than the Dragon files that Stewmac sells.  They create shavings rather than dust and leave a ridiculously smooth surface.  Even the handles are the perfect shape. 

Just now, Owen said:

Wait! He can do all this with wood AND he gets to live in Italy? Wow. Lots of good things in one place there.

Yep, I realise it's entirely unjust.  Nor deserved.  I've led a terrible life being unkind to the young and infirm and listening to progressive rock.  Just goes to show that there really is no justice in this world. 

While the glue malarkey kafuffle was ongoing, I cracked on with the sides.  First job, trim the kerfing back with a spokeshave.  The best job in luthiery.  It's like popping bubble wrap but much better

The back is dome shaped, with a radius of 12 feet.  So that same radius needs to be sanded into the sides & kerfing. Straightforward to do on the radius dish, even if it takes quite a while.  Any time I'm doing sanding I try to do it inside my hi-tech sanding cubicle.  A quick n easy downdraft table.  Or sidedraft I suppose.  Works a treat.  

Next I need to carve channels through the kerfing so that the braces sit nicely inside.  I used a dremel, again in my sidedraft cubicle.  (I must get that patented, pronto). 

The idea being that the ends of the braces go into the kerfing, like this:

The gaps will get filled with epoxy when the back gets glued onto the sides.  And here they are, not glued yet as there's another job to do first......(ooh mysterious!)

4 hours ago, JPJ said:

Fantastic work, really stunning, but could the problem with the epoxy be a reaction with the acetone you used for clean up?

Thanks JPJ, a very good suggestion!  But the mixing pot was the same.  There's something odd about the hardener.  It's got a skin on the top which I've never seen before, despite years of using exactly the same epoxy.  Anyway, it's in the bin and new ordered. 

This morning the glue is hard. Hurray! That was close to being very annoying. 36 hours to cure is a loooong time though. I'm throwing away the containers, and have ordered more West System. 

It's a good reminder to measure exactly the two parts of the epoxy mixture, and to stir them together really really well. It's also a reminder to keep the mixing pot so you can check each batch has hardened. I use a paper espresso coffee cup. 

Phew😅

2 hours ago, alittlebitrobot said:

Oh no! I'm new to the epoxy game but this has definitely happened me, thanks to my devil-may-care approach to measuring ratios. With this build, why go with epoxy over wood glue?

Yeah, getting the ratios right is key, as is stirring...a lot.  Epoxy has got lot's of advantages.  It's got a long open time, so you've got lot's of time to set up clamping etc.  it's incredibly strong, it doesn't creep, and it gap-fills better than wood glue.  Also, it's not water-based meaning that I'm not introducing moisture and possible warping into my very thin piece of wood.  The disadvantage is that if it doesn't cure properly....yer buggered.  Up until now West Systems has been spot on....

I generally use Titebond for most things.  But for critical joints and anything designed to never come apart, epoxy is great. 

2 hours ago, Si600 said:

Is it particularly damp or cold in Italy at the moment? I don't know how epoxy works or if it's affected by the weather. 

It was suddenly colder last night, but this is Italy, it's not the arctic....Cold for us is anythng below 15C !!  Fingers crossed tomorrow morning it will be rock hard and all my hair pulling will have been for nothing...

Ok this is a bit frightening. The epoxy hasn't completely hardened. It's hard but I can still push my finger nail into it. I've had failures before with epoxy, but never with West Systems and my way of measuring out exact amounts with syringes. Fingers crossed it just needs more time. This is why it's always good practice to keep the mixing pot so you can check it's completely hardened. We'll see how it is in a few more hours. 

I've started on the bracing.  The blanks I've got are very oversized, so by cutting some off at the line I can end up with a brace which is almost perfectly quarter sawn:

Putting it onto the platform, I use a biro sticking through a Gibson selector switch washer to mark out the shape of the top onto the blank.  You can chose either Rhythm or Treble depending on whether you want thundering lows or blistering highs.....It also means you can get a pretty much exact contour. 

Because the top is arched in both directions I mark both sides of the blank. With a spokeshave I then carve down to the line...

...

My makeshift 'go-bar deck' is ugly but very effective.  I find myself using it all the time either for gluing or just holding stuff down.  Here I'm using it for both.  The brace get's held in position on top of a piece of sandpaper (150G).  You can adjust the go-bars very quickly so they apply just the right amount of pressure so the brace is held in place but you can still slide the sandpaper back and forth to get good fit. 

Finally the brace can be glued down in the same way.  I use West System epoxy.  I use the Ken Parker method (as usual).  Which is wet the brace, put it onto the top, then remove it so you have an imprint:

The idea is to let the epoxy soak into the wood as much as possible.  I've got a silicone brush which I use to go back and add more epoxy to any parts that soaked it up.  Finally, clamping in the go bar deck.  One of the (many) good things about epoxy is that it needs very little clamping pressure, just enough to stop anything moving.  Squeeze out I clean up with a cotton bud soaked in acetone.  

Tomorrow, brace number 2...

Sides are nearly finished.  The final kerfing was glued in this afternoon....

Top carving continues.  I've hummed and ha'd long and hard about final thicknesses.  Ken parker thins his tops to between 2 and 3mm, he mentions D'Aquisto tops were 2.5mm to 4mm thick.  Obviously those were guitars but the string tension is actually very similar.  The arch is a bit flatter on mine and the wood is certainly cheaper...so plugging all those variables into the scientific calculator, my finger in the air came back with the following: 4mm around the bridge, 3.5mm around that thinning to 3.2mm at the periphery.  

I don't know if you can read any of these numbers, but here we are, getting close:

Post #2 in my world's uggliest jigs compilation....

I'm planning on thinning the top till it's quite flexible.  Holding firmly without cracking it is therefore a problem.  I've taken Ken Parker's beautiful work holding platform which takes several hours of video to explain, and made my own version which took about half an hour to make.  It's basically a 6mm sheet of MDF, with a 15mm piece of ply with the shape of the guitar cut out.  Some more scrap pieces of 4mm MDF on top of that cut to the shape of the top ensure that the top goes back in the same position.  Because the top is still slightly oversized it can sit upside down on the rim.  The thing is as it get's thinner an more fragile it really needs support from below.  Sooooo......I then filled the space with 3.5-5.5mm polystyrene balls - the ones you use to fill bean bags and such like.  So far it's worked really well.  The balls are soft enough not to scratch or dent the top, but it seems for the moment to provide enough support.  We'll see as the top get's thinner how it works out, but so far I love it!

I love building guitars.  I hate building jigs.  It's a personality defect I know, but I resent having to do it.  So I thought I'd show you a couple of my fuuuugly jigs, that seem to work just well enough that probably I'll never upgrade them. 

First is the top thickness guage.  The guage itself was a cheapo from Amazon.  A piece of scrap clamped above the table, and a piece of threaded rod going through a hole in my table.  A plastic knob thingamy stops the top from getting scratched.  

I then write in pencil on the top what the thickness is at each point.  It's pretty much a consistent 5mm, so I'm going to go back to the drill press and do another series of holes at just over 4mm.  Which strangely is what I thought I did last time, but there you go.  That's why you measure twice.....

I should also say that pretty much everything I'm doing with this build is copied directly from Ken Parker.  He's done an incredible series of videos called Archtoppery, which if you are interested and have a spare 30 hours or so, they are amazing.  He's hands down my favourite builder, an absolute genius.  Here if anyone is interested:

https://kenparkerarchtops.com/archtoppery

I'm working on the inside carve.  At the moment I'm doing it all with a gouge.  It's probably a bit small (Sweep 5, 18mm in case anyone is interested), but it's an utter utter joy.  

The grain is tricky.  The middle section (marked in pencil) runs opposite to the areas either side.  I wake up sweating in the middle of the night just thinking about tearout.....

OK, the carving of the top I'm calling finished.  There's still a bit of refining to do, particularly on the cutaway, but I'll do that with sandpaper once the top is on.  

Turning over I use the drill press to mark a 4.25mm depth everywhere (4mm mdf and a 0.25mm feeler gauge).  I use a simple wood dowel with a thin piece of cork on top.  Without that the top will get dented from the force of the top being pushed against the dowel. 

I then drill several million holes to within 25mm of the side (note to self, template #8).  Several million more to go tomorrow.   I'm exhausted.....

OK round one of the carving is complete.  I left it 1mm thicker everywhere on purpose in order to give me a chance to see how the carving was going without risking it getting too thin.  Time to get serious.  I routed the perimeter down to 4mm, it's final thickness.

Time to crack out the gouge and mini plane again.  I'm not finding it easy planing it without getting tearout.  Wood is like cats fur, it want's to go in one direction.  Get it it wrong and the blade can get out under the fibres and pull out a chunk.  Carving it is like butter, till suddenly it isn't.  It's also a second grade piece of wood, so there's lot's of grain runout, making tearout even more difficult.  So far so good though....

3 hours ago, Hellzero said:

The best and very expensive piezos are the RMC's with their dedicated preamp: you'll get all the low end lacking usual piezos.

 

I also have the Fishman BP-100 twin piezo on my Leduc U-Basses: it's glued under the soundboard at two strategic places.

 

If you add the Fishman PowerChip buffer-preamp to the BP-100, you'll get an amazing full sounding system.

Thanks Hellzero for those suggestions.  I wondered if anyone had put the BP100s into a bass rather than double bass, there's my answer.   I may well come back to you to explore this a bit more.  But it's a non-permanent install, is that right?  The trouble with the K&K is that it's permanent - they're superglued to the inside of the top.  These are prototypes I'm building so it would be good to know I can chop and change the electronics around. 

Also, I may drop RMC a line and see what they would recommend for an archtop bass.  Cheers!

22 hours ago, Andyjr1515 said:

I haven't used Ghost stuff for bass guitars but I've used both Acoustiphonic and Hexpander units and piezo elements on a number of my own solid and semi 6 string guitars.  Pricey but very competent - other than the 'collector block' that the connectors for each of the piezo wires plug into.  Shockingly bad bit of tat that can (and does) stop the show.  If they've changed that design/supplier then fine - it makes a good but flawed system great.  If they are still supplying it, then shame on them.

 

Ok thanks Andy, good to know. Any instinct as to whether the Ghost saddle units are less susceptible to feedback than the more normal piezo strip that goes under the saddle?

Carving in progress. I'm not sure how it's going. It's definitely going to take some practice...

😬

Does anyone have any views on what piezo pickups I should use with this one?

The last one has a K&K glued on the inside of the soundboard.  I want to try something different to contrast.  The obvious options are:

Fishman Matrix piezo element under the saddle:

https://www.thomann.de/it/fishman_matrix_infinity_vt_narrow.htm

or 

https://graphtech.com/collections/ghost-pickup-systems-kits/products/ghost-bass-acousti-phonic-kit

coupled with these elements which I could fit into a handmade bridge:

Any one with any thoughts?  I know Rob Allen uses a version of the Fishman matrix....The Ghost, I've no experience of....

Contours done, upside down on the router table. Next, carving..

16 hours ago, alittlebitrobot said:

🤐

 

Love the progress. What's going on here, though? It's intriguing

It's basically a moxon clamp adapted to hold guitar bodies.  Two outer pieces of 18mm MDF, then two inner pieces of 4mm MDF held in a curve.  It means the clamping pressure is applied to the edges not the top/back of the guitar.  Other than the MDF it's two 1 inch diameter pieces of pipe, two flanges which I've just screwed into the table, then pipe clamps.  Like all my jigs it's ugly, but works really well.  

Here it is holding the last build:

15 minutes ago, Si600 said:

I've heard worse ideas 🤣

 

How does the template work?  Presumably there's some sort of scale reduction because that looks a very big dish, more like one of those medieval spoon shaped instruments than a carved top.

Yep.  The total thickness of the top is 16mm.  The dome will be 12mm.  So dividing 12 mm by 9 templates, means each template will be used to only take off 1.3mm.  Archtop guitars I think have a much bigger dome - 16-18mm, but my complete finger-in-the-air guess is that that's too much for a bass.   I've never done this before though, so it will be a voyage of discovery for all of us!