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Thread: Tail piece angle

  1. #1
    Registered User CJFizzix's Avatar
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    Default Tail piece angle

    I am trying to replace my stamped tail piece with a cast Allen tail piece. The Allen tail piece has no angle adjustability, and it is at a much different angle that the stamped tail piece. The cast tail piece angle is larger than the stamped one if you measure the angle relative to the top. If I install it, the strings will angle down from the tail piece to the bridge rather than come out straight. This will likely result in less downward pressure on the bridge and an extra angle as the strings leave the tail piece.
    What are people's experiences with cast tail pieces?
    Should I give up on the cast tail piece?
    Should I not worry about the angle difference?

    Since it is cast, I am doubtful that I could bend it, and even if I could I doubt that I could do so with any accuracy.
    The only thought I have is to make a wooden shim that is wedged and shaped to the mandolin on one side and to the tail piece on the other. I could use this to get the angle approximately correct.
    Thanks for any thoughts,
    CJ

  2. #2

    Default Re: Tail piece angle

    Without a picture for reference, it sounds as if you're trying to put a tailpiece designed for an archtop mandolin on a flattop instrument. No, you definitely can't (nor should you try) to bend a cast tailpiece. Nor would I try to shim the tailpiece away from the rim, there's a considerable number of ft/lbs of pressure pulling there. You're best bet would be to get a tailpiece designed for a flattop mandolin. They're probably available out there in the celtic part of the unverse.

  3. #3
    Registered User sunburst's Avatar
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    Default Re: Tail piece angle

    Quote Originally Posted by CJFizzix View Post
    ...If I install it, the strings will angle down from the tail piece to the bridge rather than come out straight....
    I think some clarification is in order. I can't understand the situation because it is a physical impossibility for the strings to angle down (toward the top) from the tailpiece to the bridge more than a minimal amount.

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    Registered User CJFizzix's Avatar
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    Default Re: Tail piece angle

    Ok. Let me try again to explain this more clearly.
    It is an arch top mandolin. The side of the mandolin (at the butt end) is not square to the top. (it angles inward toward the mandolin from top to bottom.
    So when you press the tail piece against the side of the mandolin, the part of the tail piece along the top of the mandolin angles up away from the top of the mandolin at a larger angle than you would normally expect.
    If you run a straight edge across the top part of the tail piece it ends up way above the bridge.
    Does this clarify? I will try to take a photo, but the tail piece isn't attached and I am not sure that it will clarify. But I will try.

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    Default Re: Tail piece angle

    I would like to see this. As I understand it if the side comes in toward the mandolin it should make the tailpiece closer to the top not farther away. Was the tailpiece possibly made wrong? Does the angle match your old tailpiece at all?
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    Default Re: Tail piece angle

    A few points of clarification first. Some luthierspeak for the benefit of CJFizzix: What he is calling the butt end of the mandolin is called the tail end by luthiers (so the tailpiece is at the tail end); The other end of the mandolin is called the head end (so the headstock is at the head end of the mandolin. If I understand his description, the sides (aka "rim", aka "ribs") slope toward the tail from front (i.e., top plate) to the back (i.e., back plate). Which means that the angle of the sides to the edge of the sides at the top plate is <90 deg, while the angle of the sides to the edge of the sides at the back plate is >90 deg. That configuration would tend to point the portion of the tailpiece hanging over the top plate further away from the plate than if the top angle were 90 deg.

    Another clarification: Pressure has units of, e.g., lb/ft2, i.e., pounds per square foot, not pound feet.

    CJF seems to be worried about decreased down force on the bridge and in turn the top plate if the "breakover" angle (of the strings over the bridge is lowered by a tailpiece end that is higher. I would not be very worried about that. The breakover angle of the strings over the bridge results in a static down force on the bridge and in turn on the top plate. What sets the top plate - and ultimately the rest of the instrument - in motion are the dynamical forces at the string ends resulting from the string motions. The dynamical forces from the string depend more on the amplitude(s) of the string motion(s) than on the magnitude of the static down force. In the case of the Allen tailpiece, I would worry more about the much greater mass of that tailpiece hung on the edge of the body, and hence on the edge of the top plate. For more detail on this, see the Fletcher & Rossing text, "The Physics of Musical Instruments", 2nd ed., section 2.8 and particularly section 9.3.

  7. #7
    Registered User CJFizzix's Avatar
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    Default Re: Tail piece angle

    Dave's description is correct, I apologize that I couldn't describe this more accurately.

    The primary reason for my question is that I was told that I should be sure that the strings come straight out of the tail piece to the bridge. In other words, they should be parallel to the tail piece and not angle up or down as they travel to the bridge (relative to the tail piece). If this isn't a concern, then I won't need a shim and I'll just try it and see how it sounds.

    Rob, the shim would not push the tailpiece away from the rim. The tail piece would still rest against the rim, and the shim would go towards the bottom of the tail piece. I guess I really do need a picture to help explain this.

    Dave, thanks for the input. I have "The Physics of Sound" by Rossing, Moore and Wheeler. I will have to get "The Physics of Musical Instruments".

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    Registered User sunburst's Avatar
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    Default Re: Tail piece angle

    The strings should follow a line that projects from the top of the bridge to the edge of the top/rim at the tail end of the instrument. If they do not, because the tailpiece is deflecting them from that straight line, then there is a torsional load on the tailpiece and therefore the tail block that it is attached to. Over time, that can be a bad thing for the structure of the instrument, so if the cast tailpiece significantly deflects the strings from that line, whether or not the strings "come straight out of the tail piece to the bridge", it is probably not a good idea to use that tailpiece. Personally, I don't like the idea of using a shim to adjust the angle. I suppose it would work, but it would not be ideal.

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    Registered User darylcrisp's Avatar
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    Default Re: Tail piece angle

    I remembered this thread regarding your tailpiece:
    http://www.mandolincafe.com/forum/sh...ith-a-cast-one

    if you installed the tailpiece higher on the back rim edge than it should be, that may be why the strings are coming out and are lower than the tailpiece itself-just a thought.

    d

    ** a James tailpiece allows adjustment of angle so you can align it to the bridge-but I guess its too late to send the other back if you have altered it(with regards to the other thread).

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  11. #10

    Default Re: Tail piece angle

    Quote Originally Posted by CJFizzix View Post
    Since it is cast, I am doubtful that I could bend it, and even if I could I doubt that I could do so with any accuracy.CJ
    It is quite possible to bend a cast Allen tailpiece to change the angle and/or correct a slight twist. A number of years ago I received several tailpieces from Randy that were somewhat twisted. I sent them back, he corrected the alignment and all was well. Since then, I've had multiple occasions to do it myself without incident.

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    Registered User CJFizzix's Avatar
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    Default Re: Tail piece angle

    Thanks for all of the great input. From what John said, I definitely should not put the tail piece on has is because the straight line projection from the tail piece to the bridge ends up about a half inch above the bridge.

    Darylcrip, the tail piece is definitely resting on the rim.

    mandomentch, I would love to try bending the Allen tailpiece. How did you go about it? I do have access to a couple of pretty nice vices at work.

  13. #12
    Registered User CJFizzix's Avatar
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    Default Re: Tail piece angle

    ok...finally have some photos.
    Click image for larger version. 

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    Above is the photo when I press at the bottom of the tail end of the tail piece. The tail piece makes pretty good contact here top to bottom. (although the mando is more curved than the tail piece.) Notice that the angle of the tail piece ends up way above the bridge.

    Below is the photo when I press at the top of the tail end piece of the tail piece. The angle is just about perfect now. there is about a 1/16 gap at the bottom where the tail piece does not meet the mando.
    Click image for larger version. 

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    Default Re: Tail piece angle

    I don't see anything wrong with the top photo, in fact I like the angle better than the bottom photo. Sometimes the stamped tailpieces don't have enough angle, I have put a small shim under them right over the block to keep them off the top. The cast angle looks just fine to me.
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    Default Re: Tail piece angle

    Quote Originally Posted by sunburst View Post
    The strings should follow a line that projects from the top of the bridge to the edge of the top/rim at the tail end of the instrument. If they do not, because the tailpiece is deflecting them from that straight line, then there is a torsional load on the tailpiece and therefore the tail block that it is attached to. Over time, that can be a bad thing for the structure of the instrument, so if the cast tailpiece significantly deflects the strings from that line, whether or not the strings "come straight out of the tail piece to the bridge", it is probably not a good idea to use that tailpiece.
    John, the "torsional load" you are referring to has the same tendency to try to twist the ribs at the tail as does the string tension itself,..., except that it is really small compared to the string tension. What makes you think that the "torsional load" from the mismatched angle of strings and tailpiece is a significant problem?

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    Registered User sunburst's Avatar
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    Default Re: Tail piece angle

    Quote Originally Posted by Dave Cohen View Post
    John, the "torsional load" you are referring to has the same tendency to try to twist the ribs at the tail as does the string tension itself,..., except that it is really small compared to the string tension. What makes you think that the "torsional load" from the mismatched angle of strings and tailpiece is a significant problem?
    It seems to me that when the strings path is essentially straight from the edge of the instrument to the top of the bridge, the rotational pull on the tail block is the least it can be for the total bridge height. When the tailpiece is holding the strings higher than the straight line path, it seems to me that the rotational pull is increased simply because of the added leverage. I don't believe I said it was a "significant" problem, just an added amount of strain that might cause problems over time.

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    Registered User CJFizzix's Avatar
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    Default Re: Tail piece angle

    Hmmm. I guess I hadn't thought about it this way....
    If the rim is the pivot point, and the strings come straight out of the tail piece, then they won't exert any torque. They will exert approximately 100lbs of force, but it will be parallel to the tail piece. Since there is no perpendicular component to the tailpiece, there won't be any torque. However, if the strings come out at an angle even as small as 5 degrees, then they will exert approximately a 9 lb downward force where they come out of the tail piece. While 9lbs may be insignificant relative to 100lbs, I think I would like to avoid having this much force essentially pushing down on the end of the tail piece.
    I am going to try bending the Allen on Monday. If I can't bend it or do a poor job of bending it, I'll just put the stamped tail piece back and put an end to this adventure.

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    Default Re: Tail piece angle

    Quote Originally Posted by CJFizzix View Post
    Hmmm. I guess I hadn't thought about it this way....
    If the rim is the pivot point, and the strings come straight out of the tail piece, then they won't exert any torque. They will exert approximately 100lbs of force, but it will be parallel to the tail piece. Since there is no perpendicular component to the tailpiece, there won't be any torque. However, if the strings come out at an angle even as small as 5 degrees, then they will exert approximately a 9 lb downward force where they come out of the tail piece. While 9lbs may be insignificant relative to 100lbs, I think I would like to avoid having this much force essentially pushing down on the end of the tail piece.
    I am going to try bending the Allen on Monday. If I can't bend it or do a poor job of bending it, I'll just put the stamped tail piece back and put an end to this adventure.
    Except that 5 degrees would be quite an angle. That is about 8.4 mm in the 105 mm between tailpiece and bridge on a mandolin. Is your angle really that much? I would guess from what you wrote above that the angle in your case is more like 1 or 2 degrees at most. An extra 9 lb of force would be ~9%, but you have much less to worry about. Five degrees results in an extra 9 lb, but 1 or 2 degrees would result in much less additional force.

    I have seen quite a few ~100 yr old Gibson oval hole mandolins with the back plate pulling away from the ribs and heel block. I am pretty sure that that is due to the ravages of time, cycles of moisture and bacteria acting on the very old, very dry hide glue, & etc. If a modern instrument cannot withstand, say, 105 lbs of force vs 100 lbs of force, I'd say that something is wrong with its' glue seam as well. The shear in both hide glue and AR glue is pretty high. I really don't think that you have anything to worry about with your tailpiece as is. But as I posted earlier, what bothers me about that tailpiece is its mass.

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    Default Re: Tail piece angle

    Cast isn't very friendly to bending and should you bend it and get it where you want it may weaken it and at some point in the future break and I would think that would be worse than any minimal force it will exert while playing it as is.
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    Default Re: Tail piece angle

    What fun this is!
    Dr. Cohen, the 5 degrees was an estimation, so I measured it. The angle is around 5 degrees. 4.5" from the tail piece to the bridge and more than 3/8" above the bridge which gives an angle of about 5 degrees. (I said a half inch in a previous post, but it is a bit less than that and a bit more than 3/8"). So I do think the 9 lb estimate is pretty close, and it does worry me a bit.
    I know you have suggested that mass is a problem, but I don't have the book you are referring to. Are you suggesting that people shouldn't use cast tail pieces because of the mass? It seems to be a very common modification. What is the negative effect due to tail piece mass?

    Pops1, Some folks have bent theirs with success, but I am sure that you are correct, that it is a concern. How much of a concern it is probably depends on the particular alloy. I would think that if I damaged the tail piece that I would notice some cracking. It is an expensive experiment, but I can't send it back at this point anyway.

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    Default Re: Tail piece angle

    Good luck, let us know how it turns out.
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    Default Re: Tail piece angle

    Heavy, cast tailpieces are indeed a popular modification. One popular rationale for the mod is that the heavier tailpiece will increase sustain. Not only have I never seen any verification for that which is not entirely anecdotal, but I have measured characteristic decay times as a function of frequency for a few different mandolins. The characteristic time is the time for the amplitude to decay from its' initial maximum to 1/e of that value. Before anyone makes any claims about sustain, you should ask "Sustain for which note? Turns out that characteristic times decrease dramatically (by a factory of 3x or more) for notes that are close to the peaks frequency of a body mode., whereas the notes which are in between those body mode peak frequencies have much longer characteristic times. The body modes are effective at 'stealing' energy from the string for notes that are close by in frequency I showed a pilot of characteristic times vs frequency for two different mandolins - an arch top ff-hole type and a Neapolitan - in my chapter in Rossing's 2010 book, "The Science of String Instruments" The bottom line is that the mass of the tailpiece is way down the list of things influencing sustain.

    Wholly aside from the sustain argument, both experimental results and theoretical studies suggest that lower mass for plates is always a good thing. Evan Davis did some theory based on flexural plate models (presented at the 2008 GAL convention, and ??), and his bottom-line conclusion was "always build light". Physicist Bernard Richardson (Cardiff, Wales), came to the conclusion that a low effective mass for plate modes is always favored. The short version of his work (and of his grad student, Howard Wright) was published in his May, 2002 CASJ article, "Simple Models as a Basis for Guitar Design". Hanging a heavy tailpiece on the edge of a plate is not particularly good for low effective masses of the plate's modes. I am not completely sold on Richardson's model (maybe partly sold), but I do find in my builds that tailpiece mass is a crapshoot. It might help in some cases, but it will hurt in other cases, the difference being in the particular plate. For some plates, the heavier tailpiece might lower the main (i.e., the (0,0) or T(1,1)) mode frequencies and fortuitously increase coupling with the main air mode. In other plates, depending on their modal properties, the heavier tailpiece might have a completely negative effect. But in more cases, I think the heavier tailpiece is likely to have no effect (either positive or negative) at all. Finally, and completely anecdotal, in my own builds, I have been happiest with the response and feel of instruments with low mass in general, including low tailpiece mass.
    Last edited by Dave Cohen; Feb-15-2016 at 12:16am. Reason: typo

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    Registered User Ivan Kelsall's Avatar
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    Default Re: Tail piece angle

    The t/piece angle in the top pic. in the Op's post, looks to be at a very similar angle to the cast t/piece on my Lebeda. & i have no trouble with it at all. On the other hand,the Op's bottom pic.is similar to the angle on the Weber t/piece which IMHO, is way too close to the top of the mandolin @ 3/16". I've often wondered if the steep string angle behind the bridge, contributes something to the Weber's slightly 'bright' tone - maybe John Hamlett can answer that (please ),
    Dave - I'd tend to agree re. the 'added sustain' bit,but i did fit an Allen cast tailpiece to a Michael Kelly 'Legacy' mandolin,which did increase the sustain 'to a degree'. I strongly suspect that on a flimsily' built mandolin,a cast t/piece could add something extra in that department,but that on a 'luthier' quality instrument,the effect would be either little or none,
    Ivan Click image for larger version. 

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    Default Re: Tail piece angle

    In the FWIW category, I just bent a cast tailpiece to correct the same issue described in the OP. It is a cheap(er) Pac rim tailpiece (Ashton Bailey) which is described as cast bronze and has a mass of ~70 grams. I would assume that the Allen tailpiece is higher quality, and would be even more likely to survive bending unscathed. Of course that is merely an assumption. I just put the attachment end of the tailpiece in a vise (wooden jaws) & pushed down on the string end. It took a good bit of force, but it moved about .25" (measured at the end of the tailpiece) without any apparent difficulty. It seems that you require even less movement. Personally I wouldn't hesitate to bend the Allen tailpiece a small amount. I hope this helps; good luck.

    Earl Tyler

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    Registered User CJFizzix's Avatar
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    Default Re: Tail piece angle

    This is all so fascinating. The more we chat the more confused I am about the best thing to do! LOL

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    Registered User sunburst's Avatar
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    Default Re: Tail piece angle

    Quote Originally Posted by Ivan Kelsall View Post
    ...I've often wondered if the steep string angle behind the bridge, contributes something to the Weber's slightly 'bright' tone - maybe John Hamlett can answer that (please )...
    Dave Cohen already answered that when he said:
    "The breakover angle of the strings over the bridge results in a static down force on the bridge and in turn on the top plate. What sets the top plate - and ultimately the rest of the instrument - in motion are the dynamical forces at the string ends resulting from the string motions."
    In other words, the extra static pressure on the top does not translate to any difference in sound. People familiar with banjos often make the mistake of assuming that adjusting tailpiece height will do similar things to mandolin sound as it does to banjo sound. It does not because, in the case of the banjo, the added pressure on the bridge serves to tighten the head a little. That makes the top stiffer (the head being the top on a banjo, and when it is tightened it is stiffer). Added pressure on a mandolin top does not stiffen the top, so the sound does not change like it does on a banjo.
    (With banjos, we can adjust the stiffness to mass ratio of the top (head) "on the fly", while mandolin tops have their stiffness to mass ratio predetermined by the builder.)

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