How to measure bore size

Discussion in 'Trumpet Discussion' started by Blind Bruce, Jul 12, 2009.

  1. Vulgano Brother

    Vulgano Brother Moderator Staff Member

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    Machinists hate it when we do our own measuring. A cheapo set of calipers works perfectly for comparing "same or different" kinds of measurements, but two people with the same set of (even great) calipers can get different readings.

    Since (as Brekelefuw pointed out) the inner diameter of the slides should be equal, it is easy to compare bores by sticking an old mouthpiece in the third valve slide. The slide the mouthpiece goes farther in is the bigger of the two.
     
  2. rbdeli

    rbdeli Mezzo Piano User

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    So, if the bore size is the inner-part of the 2nd valve slide and the soldering doesn't count, that would mean it's much more difficult to measure on certain horns depending on how the 2nd valve slide is made?

    I would also think this lends credence to how important it is to have your valves aligned properly.
     
  3. Brekelefuw

    Brekelefuw Fortissimo User

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    A good solder doesn't show on the inside of the tubing.
    Yamaha Student trumpets (I don't know about the xeno line) are all solid tubes. The ferrules are just for decoration, which as a tech makes removing stuck slides on them really really annoying.

    I don't understand your reasoning about bore size and valve alignment.
     
  4. Bob Grier

    Bob Grier Forte User

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    You can also measure the inside of the inside slide on the main tuning slide.
     
  5. veery715

    veery715 Utimate User

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    Measuring the ID of a tube accurately to a thousandth of an inch is difficult. WIth tubes this small you first need to make sure your measuring device is expanded to the full inside diameter, and you must wiggle it about to ensure that. You can repeatedly measure the ID of .460" and .464" tubes and get roughly the same reading.

    VB's idea of using the mouthpiece taper is a good one, and a very small difference in ID will yield a large difference in how far the taper enters before stopping. Each increase of .001" in ID will let the mouthiece enter .020" further - a visible to the eye difference. So if you make a mark in pencil where the MP stops in one tube, it will either disappear or stand proud when inserted in a larger or smaller one.

    veery
     
  6. rowuk

    rowuk Moderator Staff Member

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    I am trying to figure out why bore size is so important - except to the ad people that lie when they say that bore size makes the instrument more "free blowing". If they know ANYTHING about trumpet design, they are aware that leadpipe and bell taper determine the impedance/reactance of the horn which directly translates to efficiency and perceived blow.

    Last time that I checked, the valve cluster on a Bach Strad was the same bore for the ML and L sizes. I guess that puts this into relation better than anything we could guesstimate on.
     
  7. Vulgano Brother

    Vulgano Brother Moderator Staff Member

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    Yup--the difference is in the tuning slide.
     
  8. Dave Mickley

    Dave Mickley Forte User

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    as a machinist and machine repairman we always called them very-nears because they are not all that accurate. when we needed an accurate measurment we used either id or od mics.
     

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