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Thread: Hide glue strengths

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    Default Hide glue strengths

    I went to my local 'finishes' supplier today and bought some hide glue. I asked about glue strength as I thought I remembered reading about it somewheres. They phoned the manufacturer and told me that the hide glue had a "bloom gel factor" of between 130 and 140 grams at 12.5% concentration. Is this ok for instrument use. I'm looking to repair a very small crack that has appeared in the maple back of my IV kit and also to mix with some Lycopodium power kindly sent me by another forum member. I'm not sure if I'd be confident to use it for actual assembly as I haven't used hide glue for decades. All the hide glue I have seen does not mention glue strength.

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    Mandolicious fishtownmike's Avatar
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    Default Re: Hide glue strengths

    Not an expert on hide glue but have used it on occasion and the gram strength usually used is 192 grams for guitars building and violin makers use somewhere around 315 grams. 315 grams is stronger and tackier then the weaker 192 and sets faster which has benefits in repairs. The smaller the gram strength the more working time it allows. The 130 is more for things like furniture building where much longer set up time is needed.

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    Registered User sunburst's Avatar
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    Default Re: Hide glue strengths

    There doesn't really seem to be any particular correlation between gram strength of hide glue and joint strength in wood. Gram strength is a measure of firmness of the jelled glue and not a measure of the strength of the dried glue. A properly made glue joint in wood, under normal conditions of temperature and moisture will not break at the joint, but will break in the wood, so what good is more glue strength anyway?
    As gram strength goes up, working time get shorter, so higher gram strength glues are more difficult to work with because of time limits.
    There is a lot of good information about hide glue here at Frets.com.

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    Default Re: Hide glue strengths

    As I understand it, the main reason for using hide glue in Musical Instruments is that it gives great strength but should the instrument sustain damage, the glue will break before the wood. This ensures that the wood of the instrument is less likely to be damaged, but the joint can easily be repaired. The glue works best when it is thin, unlike other glues where thicker is better. Otherwise you could just use any woodworking glue - but you wouldn't be able to repair any damage without further damage to the instrument.

    A properly made glue joint in wood, under normal conditions of temperature and moisture will not break at the joint, but will break in the wood
    This is precisely why hide glue is used, what good is an instrument which breaks in the wood rather than at the joint? It can't be repaired and is no use to anyone as a bunch of splinters

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    Registered User sunburst's Avatar
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    Default Re: Hide glue strengths

    You can try it yourself. It will break in the wood.
    Some makers of violin family instruments use a weaker or more dilute mixture of hide glue for attaching tops and/or backs so that seams can be separated more easily.
    And then we can get into sheer strength vs. tensile strength vs shock resistance. Hide glue is amazingly strong in tensile strength but not particularly strong in sheer strength and not very shock resistant, so some joints can be reversed through applying a sheer or shock load.
    It is correct that the strongest glue joints are thin, in theory a glue line one molecule thick would be strongest, and that is true for all glues that I know of and for most adhesives, the notable exception being epoxy. The reason is that most glues and adhesives are stronger in adhesion than in cohesion, or, they stick to wood better than they stick to themselves, or, the dried glue itself isn't as strong as wood, so a thick layer can break leaving dried glue or adhesive on both wood surfaces. Epoxy is generally stronger in cohesion than in adhesion.

    As I see it, the main reasons for using hide glue in instruments is it's resistance to dry heat and it's resistance to creep.

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    Registered User grandcanyonminstrel's Avatar
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    Default Re: Hide glue strengths

    Whenever I get a new batch of any kind of glue, I ALWAYS glue up a half dozen test pieces of similar size materials, vary the glue mixes in measurable increments, and then bust up everything with a mallet on the workbench 24 hours later to see how they each hold up. Then I pick the one that seems to best meet my needs. As much as my mechanical engineering background and those seven years of college love the numbers, nothin' beats a little whack, whack, thunk, thunk with a good mallet to let me know if the real world working conditions are where I need 'em...much to the dissappointment of all my dork professors who would talk and crunch numbers for years, but were terrified beyond measure to actually do something with their hands...

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    Hester Mandolins Gail Hester's Avatar
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    Default Re: Hide glue strengths

    For the past couple years I've been using 192TG, a super clear highly refined grade of glue recommended by Frank Ford. Before that I used Behlen amber from StewMac which I have seen referenced in different places as 164, 192, 250 and 350 strength. What does it all mean? I've never had any problems with hot hide glue but I always do some test pieces as James suggests.
    Gail Hester

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    Default Re: Hide glue strengths

    Hey, James, careful with the namecalling. I resemble that "Dork Professor" moniker!

    http"//www.Cohenmando.com

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    Default Re: Hide glue strengths

    I bought a small barrel of 192 high clarity from M&H in 2000 or 2001. Frank Ford gave it high marks, as did other luthiers who were persuading me switch to HHG. No regrets, no failed joints. Great glue. The big benefit(other than the considerable price break) of buying a large amount at one time is that you get used to your glue, how to mix it, how it will work, how long you have, all that good stuff. When buying by the pound, you're using a different glue every year or so(depends on how much you build), and even the same grades will vary from batch to batch, as it is a natural product.

    I store the dry glue in my basement which is dry and cool; so far, no critters have found it.

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    Default Re: Hide glue strengths

    Mario, that is the same glue I am using. Plenty strong, and cleans up nicely when soft.

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    Default Re: Hide glue strengths

    And you're one of the fellas who was persuading me to use HHG about 10 years ago, remember?

    I good student, I is.

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    Default Re: Hide glue strengths

    Yes, you are!

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    Default Re: Hide glue strengths

    Quote Originally Posted by PollyCymru View Post
    As I understand it, the main reason for using hide glue in Musical Instruments is that it gives great strength but should the instrument sustain damage, the glue will break before the wood. This ensures that the wood of the instrument is less likely to be damaged, but the joint can easily be repaired. The glue works best when it is thin, unlike other glues where thicker is better. Otherwise you could just use any woodworking glue - but you wouldn't be able to repair any damage without further damage to the instrument.



    This is precisely why hide glue is used, what good is an instrument which breaks in the wood rather than at the joint? It can't be repaired and is no use to anyone as a bunch of splinters
    The thing about hide glue is that it comes apart with heat and that the heat required to melt the glue is less than the temperature that would burn or hopefully, not char the wood. I have a little set up made out of a hotplate for heating knives when I'm taking an instrument apart. I have marked on the knob the temperature that works to do precisely that. I'm not exactly sure what that temperature is but I think that it is about 220 degrees F or just over 100 degees C. What hide glue does it let you take an instrument apart for repair. A proper hide glue joint will, under undo stress, break the wood before the joint separates. Maybe a hide glue joint will come apart under sheer but I don't think I'll be trying to knock any instruments apart anytime soon. If someone else wants to try it I'd like to hear the results. I'm not so sure about it's resistance to dry heat either. I have deal with to many old parlor guitars that have been stored in attics and sometimes what you get is a guitar case with a pile of boards in it.
    Last edited by barney 59; Mar-08-2010 at 8:15pm. Reason: grammer

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    Registered User sunburst's Avatar
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    Default Re: Hide glue strengths

    Attics can get humid, humidity isn't good for hide glue, and humidity promotes the growth of fungus and fungus can ruin hide glue.

    As for sheer, here are my results (different from the experience of some others, I might add).
    I had an old Martin guitar in the shop with the bridge cut down to nearly nothing by someone trying to avoid a neck reset. I heated the bridge until it smoked and I was starting to worry about other glue joints like the top center seam, but try as I might, I couldn't get a blade started under it to remove it.
    I had read that the repair folks at Martin used to lay a drift against bridges and give it a sharp rap to remove them, so after this one cooled, I put a hard wood scrap against the end of the bridge, took a mallet in my right hand and started to feel uneasy. I took a deep breath, decided if I was going to try this I'd better do it like a mean it, and swung the mallet! The bridge frisbeed across the room and bounced off of the wall with barely any spruce splinters attached. It was one of the cleanest bridge removals I've ever done.

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    Registered User Bill Halsey's Avatar
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    Default Re: Hide glue strengths

    Violin tops are (hopefully) put on with diluted glue. When a well-maintained instrument requires top removal, it is a pleasure to be able to pop it off with your thumbs. However, this is rarely the case in the real world.
    ~Bill~
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    Default Re: Hide glue strengths

    John, actually the old official Martin repair manual (for warranty stations) suggests not a drift, but rather a 1" chisel at the end of the bridge and then a whack with a mallet. I never have had the cojones to try that, but I do understand the theory. Not for Titebond though! I'll try to dig my old Martin book up out of some dusty box or other.

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    Default Re: Hide glue strengths

    I tried the hammer trick on a junked top that had a hide glued(my 192g glue) bridge. I also had a witness. We braced the top against my table saw fence(bad idea, BTW...) and with a flat, steel drift and ball peen hammer, I gave it a really good shot. The top broke, and the bridge had a big dent in it, but the joint held. Now, this joint was less than a year old, so it can very well be that an old(er) joint that is already loosened or has been weakened by heating like John did will release, but this one absolutely did not. I'd not recommend the technique based on this experience. If I'm replacing a bridge, I rout it off the top; zero chance of damage.

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    Registered User David Newton's Avatar
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    Default Re: Hide glue strengths

    Martin didn't mean the hammer and chisel to work on every bridge joint, just Martin bridge joints.

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    Default Re: Hide glue strengths

    Martin is of course a factory and the time factor for labor seems to be to be a major concern in any factory I've ever been to. I have never been to the Martin factory but I doubt that it's that much different. Martin is in a much better position than most to cover themselves when "Oops, sorry, your guitar blew up!" happens. If 90 + times out of 100 the guitar doesn't blow up it may be worth it to them. I wonder if the popoff method is used when someone brings them a 1930 OM 28. If I ever screw up one it's a major embarrassment and a financial disaster. I've had it happen and the feeling I get when it does can't be that much better than the feeling someone has standing in front of a firing squad. I much prefer owning them myself,fixing them and turning them over than working on somebody elses instrument. If I want to try something new out and I own it and it doesn't work out the way I hoped than I pull the tissues out, cry a little and swear alot . Then I go about my business realizing that I may have cost myself alot of time and probably money or maybe it goes to the "later" collection. So, I have a Martin here that could use a bridge replacement---hummm! So, "Poppers" do you score around the bridge before you whack it?

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    Registered User sunburst's Avatar
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    Default Re: Hide glue strengths

    Martin doesn't "whack" bridges anymore, nor do they use hide glue on most production models, so it wouldn't work for most of them anyway. ( I won't go into how they glue their bridges now, but getting the newer ones off for repairs is going to be... interesting.)
    Last I heard, Martin's repair department's method of removing bridges from valuable old guitars is routing them off.

    Martin, by the way, is a very well run factory, and while they are a factory and saving time is important, it is surely not a sweat shop. The repair department is separate from the manufacturing part, and the time pressure is not intense in there. I've spent a day in the Martin repair department observing and interacting with the folks working in there, and it's a pretty good place to work, in fact.

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    Default Re: Hide glue strengths

    I didn't imply that Martin is a sweatshop, just that, working in a timely manner may matter and that they are in a better position to do some risky procedures that may save time. Martin must be doing something right to be probably the oldest company in the country to be run by the same family and that would probably include good employee relationships. I knew Dick Boak when he was teaching school in Vermont and working for Martin seems to have worked out pretty good for him. I do know that they can and do restorative work on rare and valuable instruments and I always figured that they have a special arrangement for that. If Martin were to kill a guitar that was on warranty and it's not a collector item they can just give the customer a new one. Not so easy for me. I would think that would be part of the guarantee. If by some chance your guitar turns out to be a lemon they could give you another or repair yours and at their discretion. I would think that if you have to work for someone, working for Martin would be pretty good, would sure beat Hormel or Walmart.

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    Default Re: Hide glue strengths

    Quote Originally Posted by barney 59 View Post
    The thing about hide glue is that it comes apart with heat and that the heat required to melt the glue is less than the temperature that would burn or hopefully, not char the wood. I have a little set up made out of a hotplate for heating knives when I'm taking an instrument apart. I have marked on the knob the temperature that works to do precisely that. I'm not exactly sure what that temperature is but I think that it is about 220 degrees F or just over 100 degees C. What hide glue does it let you take an instrument apart for repair. A proper hide glue joint will, under undo stress, break the wood before the joint separates. Maybe a hide glue joint will come apart under sheer but I don't think I'll be trying to knock any instruments apart anytime soon. If someone else wants to try it I'd like to hear the results. I'm not so sure about it's resistance to dry heat either. I have deal with to many old parlor guitars that have been stored in attics and sometimes what you get is a guitar case with a pile of boards in it.
    We take violins apart almost every day. Nobody in the shop uses heat to undo a hide glue joint. The joint always breaks well ahead of the opening knife, so heat would never get to it. We just find (or create) a weak point and slide a very dull blade down the joint. The end and corner blocks require additional effort, but if your technique is good and the joint is old it takes very little time.

    The way it works is that the wedging action of the knife creates a stress riser at the discontinuity between the wood and glue, just as a crack in a machine part would do, and the glue fails. Hide glue is brittle when old, and fails pretty easily in this mode. I hate taking new joints apart. A little alcohol in the joint will make the glue brittle and ease opening, but it's not compatible with most violin varnish.

    If an instrument comes apart with thumb pressure the joint is too weak, and sound suffers. One of the first things I do when I check an instrument out is to check for open or weak joints by tapping.

    Biggest advantage of hide glue is repairability. Joints are easy to open with good technique, and you don't have to clean off the old glue - it will bond to new glue, making re-assembly a lot easier. The other advantage is rigidity - resistance to creep.

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    Registered User Joe Mendel's Avatar
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    Default Re: Hide glue strengths

    I had heard that Martin took bridges off with a "WHACK", but I've never had the nerve to try it & doubt that I ever will. I did have one bridge that simply was not going to come off, I routed it off. It is amazing how little of the original can be left on the guitar doing that way, with due care.

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    Default Re: Hide glue strengths

    If you are going to use a chisel to take off a bridge, you need to round off the chisel behind the sharpened edge so it doesn't damage the top. After heating the bridge, don't strike the chisel hard, but small taps moving all around the bridge will put pressure straight up on the bridge. Actually works quite well. Was the way i was taught 20 or so years ago.
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    Registered User David Newton's Avatar
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    Default Re: Hide glue strengths

    Violin tops should be mounted with a thin, weak glue.
    There is a world of difference between violin methods, and guitars and mandolins.

    There isn't a joint on a guitar or mandolin that I want to come apart easily. I want all my joints to last forever. The main reason I choose hide glue is because it is harder and won't creep apart.

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