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mikeyb2
12-18-2016, 02:01 AM
So far I have completed 1 mahogany tenor build which was reasonable but had very slight telegraphing, but you would have to look for it, to see it.
Recently I've been building 3 more tenors concurrently in different woods. Cherry, Makore and Mahogany. The bracing was as the first and taken from the Stewmac plans(3 fan braces and bridge patch), and all tops were thicknessed to around 1.8mm. The lower transverse brace radiussed to 25' approx.
They were all glued up around 45% humidity and boxes were closed a couple of months ago. All was fine. Now it seems after being stored in the garage workshop, which has recently reached 90% humidity, the mahogany build has developed quite bad telegraphing. I was hoping this might disappear when the body was brought into the house which is around 55%. I'm going to leave it a few days and if it doesn't improve , I'm tempted to scrap it or replace the top.
Questions. the other 2 builds are ok, so why the mahogany?
What should I do to prevent it happening again?
what would be the best and easiest way to remove the top, if I have to do that?
Thanks in anticipation. Mike.
Forgot to mention that all are unfinished apart from being stained and shellac sealed( the cherry and mahog builds, but the makore is still raw wood)

Michael N.
12-18-2016, 06:49 AM
Different woods react in different ways to changes in humidity but you also have the combination of the struts and the top. Gluing up in 45% RH and then placing the instruments in much higher humidity is asking for the effect that you describe. You should also be careful of clamping pressure, it shouldn't be overdone.
I wouldn't worry about telegraphing too much though, you are going to get the effect come what may. It's simply a matter of trying to minimise it.

mikeyb2
12-18-2016, 10:08 AM
Thanks Michael, although you say don't worry about it, I couldn't live with it the way it is. I try and look at it as though I was a buyer( although I don't do this to sell), and I wouldn't touch anything with such a top. If it doesn't even out, I'll have to replace it and do things differently so I'm not faced with the same problem. Maybe make it a bit thicker, say 2mm for starters, and think about do the braces differently. When I built the top, I radiussed the transverse brace and also the 3 fan braces(not sure whether I should have). I also fitted the bridge patch(1.3mm) so that the grain was perpendicular to the top grain, which I think was correct but not sure. The fan braces were about 12mm by 4mm tapered at each end, maybe I should reduce the height? Like you say, I want to do what I can to minimise the telegraphing on the replacement top. Cheers Mike.

Michael N.
12-18-2016, 01:56 PM
Well I don't know how bad it is. I've literally seen hundreds of guitars that show this effect, some of them very expensive instruments. Some of mine show it, especially those with thin tops. I've tried to eliminate it but I've only really succeeded in lessening the effect. A much thicker top helps but of course you might pay the price in terms of response. Using very little clamping pressure helps, just enough to get the job done. Humidity control is important too.

Allen
12-18-2016, 04:20 PM
Thin tops are always going to show telegraphing with most bracing patterns. If you don't see it to some extent, then your top is most likely too thick. It's a trade off with thickness and bracing to get "your sound".

Drastic changes in humidity of course are going to exacerbate this. And a high gloss finish will show everything off to full effect.

My advice is to let it stabilise for a month before getting to carried away. In fact I'd live with it for some time just to observe the effects of temperature and humidity over time. You might learn a thing or two.

sequoia
12-18-2016, 06:33 PM
Thin tops are always going to show telegraphing with most bracing patterns. If you don't see it to some extent, then your top is most likely too thick. It's a trade off with thickness and bracing to get "your sound". And a high gloss finish will show everything off to full effect.
.

Yup and yup. A guy I know was performing with his incredible sounding 58' Martin D-28 the other day and watching from the audience when the light hit the guitar it was liking looking at an X-ray of the bracing. As matter of fact I found myself thinking more about mid-fifties Martin bracing styles than I did about listening to the music. You could see every single brace pushing up. The instrument is fine and from what I could tell has no cracks and it sounds incredible.... Yeah, thin tops sound great, but they move and shiny top shows all flaws.

One thing you didn't include with your posts was pictures. Pictures help so much. There is telegraphing and then there is TELEGRAPHING!!!

mikeyb2
12-18-2016, 11:06 PM
Thanks everyone, just had a look this morning and it does seem to be lessening, so I'll do as Allen suggests and wait a while. In fact, I'll continue with it and see how it looks with a finish, which won't be high gloss but a Tru-oil sheen. Mike

Yankulele
12-19-2016, 03:05 AM
I built a nice cherry uke that I now consider a good part of my learning process. I glued up the bracing when the rh was too high, and not long after closing the box, the top dished. In my case, I went pretty far with the thinning of the top, and I'm pretty sure I got it too thin. The final instrument acts like a hygrometer: it bows in and out with the relative humidity. And the braces telegraph horribly. It sounds pretty good and has good volume, but its flaws are undeniable. I generally try to learn from other's mistakes, but sometimes I get to learn from my own first-hand. I have replaced tops on the first two ukes I built when they cracked, and I considered that a good learning experience. But this uke still plays well and has binding, which makes for a bigger job. For now, I think I'll keep it as it is. But I don't think I could give it away. Unless you have a home already planned for your uke, you might be happier keeping an eye on it as it is at home.

Nelson

mikeyb2
12-19-2016, 05:20 AM
Nelson, I thought I had learned from my first build mistake, similar to you glueing in high rh, so this time I made sure it was around 45%. I think the problem was leaving it in the garage as humidity rose gradually over a couple of months. It is getting better now it's been in the house for a few days, so fingers crossed.

I would still like to know from anyone, whether the fan braces need to be radiussed as the transverse brace is, or do others keep them flat? Thanks Mike.

Michael N.
12-19-2016, 07:20 AM
They don't need to be anything. 99.9% of makers shape them in some manner though. That could be a radius or shaped like a pitched roof. I've come across flat but it's rare, almost always on cheap instruments. At least that's the case with guitars. Not to say that flat isn't a viable approach. Who's to say that it doesn't work? You'll only really find out by doing it and if you can make extremely near identical instruments (shaped and flat) you might be able to come up with a strong case either way. Unfortunately that kind of thing is rarely done, costs too much, takes up too much time, no one gets paid.

mikeyb2
12-19-2016, 12:17 PM
They don't need to be anything. 99.9% of makers shape them in some manner though. That could be a radius or shaped like a pitched roof. I've come across flat but it's rare, almost always on cheap instruments. At least that's the case with guitars. Not to say that flat isn't a viable approach. Who's to say that it doesn't work? You'll only really find out by doing it and if you can make extremely near identical instruments (shaped and flat) you might be able to come up with a strong case either way. Unfortunately that kind of thing is rarely done, costs too much, takes up too much time, no one gets paid.
Michael, I was referring to radiussing the bottom of the brace along it's length to give the lower bout a 25' radius. The lower transverse brace is done this way, but I'm not sure whether the fan braces need to be thus shaped or is the transverse brace radius sufficient to give enough radius to the lower bout area? Thanks Mike

sequoia
12-19-2016, 04:41 PM
I do not radius my top braces this way because of issues resulting in a convex radiused top (cutting binding, rosette issues, bridge issues, structural issues, etc. etc.). However, Pete Howlett does radius his tops I believe and claims it enhances the response. Shrug. I don't know. My tops are flat and plenty responsive. Guitars are built with flat tops so why not ukuleles? Although I believe the old Martin ukes had a slightly radiused top, I don't know for sure. I do know for sure that doing this would seriously challenge my uke building chops. Backs I can radius no problemo and I put a pretty radical radius on my backs. Tops: Nada.

spongeuke
12-19-2016, 05:12 PM
None of my vintage (Pre WWII) Martin Sopanos have an arched top, however the Vita Ukes did.

Moore Bettah Ukuleles
12-19-2016, 06:17 PM
Nelson, I thought I had learned from my first build mistake, similar to you glueing in high rh, so this time I made sure it was around 45%. I think the problem was leaving it in the garage as humidity rose gradually over a couple of months. It is getting better now it's been in the house for a few days, so fingers crossed.

I would still like to know from anyone, whether the fan braces need to be radiussed as the transverse brace is, or do others keep them flat? Thanks Mike.

My fan braces are straight, flat and pretty low with the highest point being just behind the lower transverse brace and tapering to zero at its termination. I'm not convinced that profile shape matters much. The type of wood chosen does though (I use red spruce) as does keeping it on its quarter.

greenscoe
12-19-2016, 09:44 PM
I don't use a radiused top. However those guitar and uke makers that do so often achieve this using a dished workboard/solera (and go deck).

The flat soundboard is place on the dished workboard. The glued flat braces are added and the pressure applied to hold each brace in place is enough to allow the soundboard to take on the slight curve of the dished workboard. The dimensions of the fan braces are such that they bend to conform to the workboard. The transverse brace is obviously more substantial and therefore needs to be radiused as you mentioned.

If you spend some time watching videos on Youtube of classical/flamenco guitar makers or uke makers you will see and learn many different techniques which you may choose to adopt. A couple of minutes on YouTube took me back to this clip where there is mention of the use of a dished solera at around 1.20-1.50. It will take you less time to watch the whole clip than its taken me to reply.

https://www.youtube.com/watch?v=6KuL31w-Qy8

Michael N.
12-19-2016, 09:52 PM
Michael, I was referring to radiussing the bottom of the brace along it's length to give the lower bout a 25' radius. The lower transverse brace is done this way, but I'm not sure whether the fan braces need to be thus shaped or is the transverse brace radius sufficient to give enough radius to the lower bout area? Thanks Mike

I see what you mean. Normally they are press fitted to the soundboard and take on the dome given to the solera (the dish). All Spanish guitars are built with that doming. Earlier guitars were not. I've tried both but I couldn't possibly tell you which was better, too many variables. Some people seem to think that the doming insures against cracks but I'm not convinced. I've seen plenty of instruments that had doming and also cracks. I've seen 200 year old flat tops that had no cracks.

mikeyb2
12-20-2016, 06:36 AM
Thanks again everyone, your help and information will help me on any future builds. I think I'll be doing things differently. Cheers Mike.