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| Top losing radius !! http://www.luthiersforum.com/forum/viewtopic.php?f=10101&t=26404 |
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| Author: | Gregg C [ Sun Mar 07, 2010 8:45 pm ] |
| Post subject: | Top losing radius !! |
I have two Dred Sitka tops that are braced but not yet glued on, they both have lost most of there radius. Is there a way to "re radius" a top without disassembling it ? The best I can remember I assembled them at about 25% RH and now its below 16% RH. Gregg |
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| Author: | Mark Groza [ Sun Mar 07, 2010 9:00 pm ] |
| Post subject: | Re: Top losing radius !! |
I would get the humidity back up to where it was when it was braced and they should be ok. |
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| Author: | Gregg C [ Sun Mar 07, 2010 9:06 pm ] |
| Post subject: | Re: Top losing radius !! |
Excellent suggestion, However I recently put a RH gage in my house where my guitar will live and my house has never gone above 16% RH. That is why I wanted to "re radius" at 16% |
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| Author: | MRS [ Sun Mar 07, 2010 11:22 pm ] |
| Post subject: | Re: Top losing radius !! |
Where did you assemble them? Is your shop separate from your house? You said it was around 25% and now its 16% and your house never goes above 16%. If for some reason the humidity does rise in the house this can cause problems too. 16% is to low in my opinion. You may develop cracks in the body sides and backs at that low. |
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| Author: | peterm [ Mon Mar 08, 2010 12:12 am ] |
| Post subject: | Re: Top losing radius !! |
"assembling" any guitar related stuff at 25% humidity is a recipe for disaster. You should be gluing up stuff at around 45 to 55% |
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| Author: | Howard Klepper [ Mon Mar 08, 2010 1:17 am ] |
| Post subject: | Re: Top losing radius !! |
peterm wrote: "assembling" any guitar related stuff at 25% humidity is a recipe for disaster. You should be gluing up stuff at around 45 to 55% Not if its going to live at 16%. Gluing up at 45% would just make it worse. It should get better (but not necessarily the same as it was) when you bring humidity backup to 25%. It's generally a bad thing to brace a top or back and leave it around for any length of time. If you have to do that, clamp it with some go bars to your radius dish. |
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| Author: | Gregg C [ Mon Mar 08, 2010 9:09 am ] |
| Post subject: | Re: Top losing radius !! |
Thanks guys, I live in Albuquerque, My house has radiant floor heat and refirgerated air, these two systems combined are a recipe for a dry inside environment. Plus Albuquerque has an average RH of approx 20%. I build in my garage so the RH can fluctuate between 15% and 35%. I'm thinking I should brace up in my shop at the lowest RH (approx 16%) and then store my parts temporarily in my house which I've never seen above 16%. Then when my guitars live in my house the RH is the same. Yes / No ?? Gregg PS....I think my rookie mistake was to allow these parts to stay in my garage and be subject to the garages RH changes. I've seen many postings about the problems associated with high RH, apparently low RH is going to be a challenge also. |
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| Author: | Gregg C [ Mon Mar 08, 2010 10:00 am ] |
| Post subject: | Re: Top losing radius !! |
I just placed another RH gauge in my house rght next to the original, its reading 21%. The original still reads 16%, I guess there is going to be a differance in reading from one $10 wal-mart gauge to the next. Anyway, my house where my guitars live is definitely dry !! Gregg |
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| Author: | runamuck [ Mon Mar 08, 2010 10:21 am ] |
| Post subject: | Re: Top losing radius !! |
Gregg C wrote: Thanks guys, I live in Albuquerque, My house has radiant floor heat and refirgerated air, these two systems combined are a recipe for a dry inside environment. Plus Albuquerque has an average RH of approx 20%. I build in my garage so the RH can fluctuate between 15% and 35%. I'm thinking I should brace up in my shop at the lowest RH (approx 16%) and then store my parts temporarily in my house which I've never seen above 16%. Then when my guitars live in my house the RH is the same. Yes / No ?? Gregg PS....I think my rookie mistake was to allow these parts to stay in my garage and be subject to the garages RH changes. I've seen many postings about the problems associated with high RH, apparently low RH is going to be a challenge also. In my opinion, the reason most people need to build at 45%+-RH is because that represents an average. A guitar will have as good a chance at not coming apart in California as it does in New York. New Mexico though is awfully extreme. If the guitar is going to live its life between 16% & 35%RH than it's best to build it at the average of those readings. |
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| Author: | Gregg C [ Mon Mar 08, 2010 10:24 am ] |
| Post subject: | Re: Top losing radius !! |
" If the guitar is going to live its life between 16% & 35%RH than it's best to build it at the average of those readings " Thanks for the reply, I agree, it just makes sense. |
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| Author: | Hesh [ Mon Mar 08, 2010 10:33 am ] |
| Post subject: | Re: Top losing radius !! |
I have yet to find and measure a digital hygrometer that is worth using and I have tested a number of them now against a wet bulb standard and they all have been off. Some have been very off...... The only way to really know for sure what the RH really is is to do a wet bulb test or use a sling psychrometer which is the same basic idea as a wet bulb. It's cheap (price of two lab thermometers), only takes a couple of minutes to do, and its accurate. Once you know how off your hygrometer is AND, very important...., in the range that we care about you can make a mental note or write on your hygrometers what ever you need to add or subtract to the readings. Most people are very surprised when they find out how inaccurate digital hygrometers are. I recently tested a case hygrometer and it was 18% off. That 18% off is enough to have the owner have a piece of mind while in fact their guitar is being seriously damaged from dryness. |
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| Author: | Gregg C [ Mon Mar 08, 2010 10:46 am ] |
| Post subject: | Re: Top losing radius !! |
Hesh, Very interesting, Do you have anymore info on this "wet bulb test" ?? Maybe a link or a tutorial ?? Thanks Gregg |
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| Author: | thomas west [ Mon Mar 08, 2010 11:04 am ] |
| Post subject: | Re: Top losing radius !! |
Right on Howard...!!! 40 to 45 is not etched in stone.It depends on the RH of the location where the guitar will live. Tom |
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| Author: | WaddyThomson [ Mon Mar 08, 2010 11:35 am ] |
| Post subject: | Re: Top losing radius !! |
Hesh is right on! Get yourself a wet/dry bulb thermometer, or make one and see what the RH really is. Go on line and look up Wet/Dry bulb thermometer or Sling Psychrometer. There are lots of web pages devoted to the subject, and the charts are available. There is a source on Ebay that sells an inexpensive Wet/dry bulb thermometer, and it works just fine. I, now, only rely on analog hygrometers, which I check a couple of times a week with the wet/dry bulb thermometer, and calibrate as necessary. The key is to draw air across the thermometer, or hang it where it is in a constant draft. I keep a fan going in my shop 100% of the time to help keep things even in there, so I just add water to mine and hang it in the draft. In 10 or 15 minutes I check the temps, and read the difference on the chart. It's very simple and takes only a few minutes. |
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| Author: | Gregg C [ Mon Mar 08, 2010 12:16 pm ] |
| Post subject: | Re: Top losing radius !! |
Thanks guys, My questions on RH have been answered, as a beginner I dont know what I would do without the help and support of all of you !! Thanks again Gregg |
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| Author: | JohnAbercrombie [ Mon Mar 08, 2010 1:30 pm ] |
| Post subject: | Re: Top losing radius !! |
WaddyThomson wrote: Hesh is right on! Get yourself a wet/dry bulb thermometer, or make one and see what the RH really is. Go on line and look up Wet/Dry bulb thermometer or Sling Psychrometer. There are lots of web pages devoted to the subject, and the charts are available. There is a source on Ebay that sells an inexpensive Wet/dry bulb thermometer, and it works just fine. This topic comes up quite often, generally with a conclusion that the wet/dry bulb method is far superior to using a digital RH meter /hygrometer. I was a high-school science teacher for 30+ years, and one of the 'standard' introductory junior science labs was to heat water and plot a temp vs time graph. I've seen literally thousands of lab reports, tablulated class results, etc etc for such experiments. What's the point?? The cheaper 'lab-grade' thermometers are not all that accurate. Even with thermometers from the same lab supply company there was often +- 2 deg C variation in boiling point measurements in a group of 15 measurements. (e.g. BP results from 97 to 101 deg). So, those cheaper alcohol-filled thermometers are not guaranteed to be accurate. You should definitely 'match' your thermometers when they arrive to make sure they actually have the same temp reading. Also, the 'immersion level' on lab thermometers is specified (and usually marked), so you should take this into account as well. Looking at a RH chart http://weather.nmsu.edu/Teaching_Material/soil698/relatium.html shows that quite small temp differences affect the RH calculation in a big way. For example, at 20 deg shop temperature, a temp diff of 2 deg indicates 59% RH, 3 deg 41%RH and 4 deg 24% RH. So you do need to consider the accuracy of your temp measurements carefully, since few readily-available thermometers have subdivisions smaller than 1 degree C. The very best possible RH measurement you can make with a pair of 'standard' thermometers could be 'off' by 10-20% absolute RH. If you are interested in building a wet/dry bulb hygrometer, a nice homebrew device is described at http://www.digitemp.com/wetbulb.shtml I think I'll stick with my Caliber III digital unit for now! Cheers John |
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| Author: | Hesh [ Mon Mar 08, 2010 2:06 pm ] |
| Post subject: | Re: Top losing radius !! |
Gregg you are very welcome. Here is a link to a post that I did on the ANZLF forum regarding calibrating hygrometers. Interestingly John's comments about the accuracy of alcohol filled thermometers and inexpensive thermometers in general are very important and he has my attention. I would still like to know a good source for lab quality alcohol filled thermometers. Anyone know a good vendor? The thermometers that I received (4 of them) were very difficult to read AND only two of them matched readings..... Here is the link: http://www.anzlf.com/viewtopic.php?t=2116&highlight=hygrometer |
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| Author: | JohnAbercrombie [ Mon Mar 08, 2010 2:27 pm ] |
| Post subject: | Re: Top losing radius !! |
The 'problem' I see (all the time) with things digital is that just because there are 'accurate-looking' results on the display, it doesn't necessarily mean that the device is particularly accurate. (Heck, I still distrust my 'digital calipers'.) So even though my Caliber III hygrometer is reading 44%, I try to remember to interpret that as 'in the acceptable 35-55% range'. When I crank up the heat in the shop a few degrees, I expect to to see the RH reading to drop -and I do- so I assume things are working OK, especially if the RH reading correlates with the info from the local weather service. Taken in that light, probably any reasonable RH measuring device would do the job for me. Cheers John |
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| Author: | WaddyThomson [ Mon Mar 08, 2010 3:27 pm ] |
| Post subject: | Re: Top losing radius !! |
That's interesting, John. My CaliberIII reads 32% when my shop is at nearly 45%, and 35% when it gets to about 50%. I check my thermometers, with a Mercury lab thermometer, which I also happen to have, and they are always dead on. I do keep my shop in the low 70* temperature range, as I find it easier to use HHG when it's comfortable in the shop. When it drops below 70 the open time suffers greatly. I do agree that measuring accurately is very important, but to the same degree, depending on a digital hygrometer guaranteed to be within 1%, which is off by 12 to 14 points, an error of nearly 25%, seems a little strange to me. I bow to your obvious superior knowledge on this matter, though, and I'll keep checking my wet/dry bulb, and using my analog hygrometers on a daily basis. |
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| Author: | Michael Dale Payne [ Mon Mar 08, 2010 4:22 pm ] |
| Post subject: | Re: Top losing radius !! |
Assuming you shaped the braces to have a radius in them tht was glued to the top whine in the mold, this created a stressed skin (the top plates) about the radiused braces. Now this stressed skin want to pull back to its natural state. The edges of the braces have been thined down so the top plaes can over come the stiffness of the braces of the outer edges but the inner section it is not likely that the top plantess can deform the bracing. My guess is the outer portions of the top has pulled the braces outward a bit but the skin is still formed around radiused plane of the braces. You can put the top asssembly back into the radial dish and reclap it usiung go-bars ina constant RH equal to that you glued it up at. within a day or two it should be back to normal Now if you used flat bracing forced into a radial shape by the the shape of the mold the the braces will want to return back to straight and this will flatten the dome shape you had. but I doubt this is the issue. |
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| Author: | Michael Dale Payne [ Mon Mar 08, 2010 4:23 pm ] |
| Post subject: | Re: Top losing radius !! |
Assuming you shaped the braces to have a radius in them tht was glued to the top whine in the mold, this created a stressed skin (the top plates) about the radiused braces. Now this stressed skin want to pull back to its natural state. The edges of the braces have been thined down so the top plaes can over come the stiffness of the braces of the outer edges but the inner section it is not likely that the top plantess can deform the bracing. My guess is the outer portions of the top has pulled the braces outward a bit but the skin is still formed around radiused plane of the braces. You can put the top asssembly back into the radial dish and reclap it usiung go-bars ina constant RH equal to that you glued it up at. within a day or two it should be back to normal Now if you used flat bracing forced into a radial shape by the the shape of the mold the the braces will want to return back to straight and this will flatten the dome shape you had. but I doubt this is the issue. |
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| Author: | Rene [ Mon Mar 08, 2010 4:29 pm ] |
| Post subject: | Re: Top losing radius !! |
Wonderful, First digital hygrometers are bad so I decided to make a wet/dry hygrometer because they are supposed to be the real deal. Come to find out now that your standard cheap walmart garden thermometer sucks too. Anyway, I made this quick, easy, and cheap hygrometer from: http://retirees.uwaterloo.ca/~jerry/orc ... t&dry.html Works great, at least that's what I choose to believe. René |
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