plastic Double bass bridge

Discussion in 'Luthier's Corner [DB]' started by scouse2000, Oct 31, 2016.

  1. Hi All

    As i have gone through many bridges while trying to find the best setup i like with different strings, I was going through bridges every few week.
    So a friend said he could make me one with his 3D printer.
    He copied the dimensions and shape perfectly, (i also got him to add a few mm to the total height to allow for adjustments) 3384385-12cb7f70afe0df548e32e367536fe977.jpg this is the prototype, (for fun he even put the band name in)
    I started by sanding the feet to fit the body of the bass but the plastic is so hard it took hours to shape.
    Next i will start on the curve and cut the string slots.
    I will keep you posted on how it goes, It might just collapse under the string pressure, i dont know.
     

    Attached Files:

  2. I know a few rockabilly weirdos who have Perspex bridges. There's only one way to find out if it works.
     
  3. Hi KUNGfuSHERIFF
    My only concern at this stage is the bridge seems a bit......Brittle and may snap under tension, but time will tell
     
  4. Ortsom

    Ortsom Inactive

    Mar 23, 2016
    Yes indeed...

    Maybe tension-up the first time with the whole lot on cardboard, to give some protection to the top. Wrap cloth around your TP.

    I have a coaster of that material (if it is the same?) and offhand I'm not sure it is very suitable. Feels heavy & sounds dull. But maybe it works well; please keep us posted!
     
  5. Hi Ortsom Yes copious amounts of cardboard are called for when testing.
    It took 3 days of shaping for the feet and almost a whole night to file the slot for the E string.
    Last night i did the A string slot (took 2 1/2 hours of filing with a rat tail file.
    Tonight.....I attack the D string

    Edit The 3D printer can print in different mass weights. At 90% it is 90% plastic and 10 % honey come (That is, A solid slab of the printed plastic is actually hollow like a honey come)
     
    Last edited: Nov 1, 2016
  6. Ortsom

    Ortsom Inactive

    Mar 23, 2016
    Big bike for the Gold Coast...:thumbsup:
     
  7. Hi Ortsom, Yes the beautiful Gold Coast. Shorts and Tee shirts all year round..

    last night I managed to cut the slot for the D string, man its killing me. the bridge is so hard.
    if you see in the photo, the position for the piezo is like spread out to fit all of the shape of the piezio. I hope this may help to reduce feedback.
     
  8. robobass

    robobass

    Aug 1, 2005
    Cologne, Germany
    Private Inventor - Bass Capos
    Just curious, Did you guys take a 3D scan of a bridge, or just work up the CAD drawing with tracings, etc.? If you have access to a scanner you could put the foot contour and bridge slots right into the printed part. I'm looking into this technique myself, but for a different aspect of bass luthiery.
     
    Last edited: Nov 3, 2016
  9. Ortsom

    Ortsom Inactive

    Mar 23, 2016
    Yes. I don't want to hear it. Last weekend put my winter tires, we'll have snow coming weekend...

    Are you sure you're using the right kind of tool for this material? It shouldn't be like hardened steel, and even in that you'd make progress, with the proper tools. The coaster I have doesn't seem that hard at all, so it's probably different material.
     
  10. robobass

    robobass

    Aug 1, 2005
    Cologne, Germany
    Private Inventor - Bass Capos
    I have to agree. This plastic can't be that hard.
     
  11. gerry grable

    gerry grable

    Nov 9, 2010
    Just off the top of my Polish head, I would try using a pair of lock-jaw pliers, an assortment of various sized finishing nails, and the gas burner on my kitchen gas range. Fine tune later with the rat-tails.
     
  12. Ortsom

    Ortsom Inactive

    Mar 23, 2016
    The material might be PLA or ABS, which are both thermoplastic (and with PLA loosing its strength above 50°C that may be an issue for a DB bridge, if you leave it in a car in the sunshine), but apparently there are also modern 3-d printers producing ceramics. That would be very hard & difficult to work. And it might be something else again.

    Honeycomb structures are used to reduce the amount of feed material, and will also reduce weight. It would be interesting to see how much your bridge weighs, before you mount it. Bridge weight has quite an effect on the sound, in addition of course to the acoustic properties of the base material & bridge structure.

    At any rate, with the strings pushing the bridge onto the top with some 50-60kg (depending on strings & geometry), I'd be careful with such a bridge, and avoid higher temperatures if it's a thermoplastic.
     
  13. Hi All
    Yes. there are some interesting points as described above but I finally managed to mount the bridge and...it works but the sound is very bright. I am not sure if this is due to the material used or the fact that where a piezo would normally fit in to the wing with a small amount of physical wood to piezo contact, The area on my bridge is flared out to produce a shape exactly the same size as my piezo so i have 100 % plastic to piezo contact (if that makes sense)
    The apparent hardness to sand and file is to do with the way the printer lays the plastic in layers, I am sanding "across the grain" as it were. i have experimented on a left over piece and its certainly easier to sand and file in the other direction

    I will try and add some sound files (but only have a Iphone for recording, so poor sound quaility will be expected)
    but a comparison of the wood and plastic bridges will still be possible.
    Hi ortsom, try sanding your coaster in one direction and then turn it 90 degrees and the difference is startling.
     
  14. Ortsom

    Ortsom Inactive

    Mar 23, 2016
    Hi Scouse2000, not sure what piezo you use, but often the sound coming from a piezo very much depends on the way it is loaded & actuated by the vibes in the mounting. Depending on the PU construction, a point-load, or a bending actuation, can give quite a different result from a pure pressure (compressional) actuation. And then of course the vibes the piezo is exposed to depend on the compliance of the mounting method and the vibrations occurring in that mounting. Optimising the piezo output is yet again another can of worms.

    But it does sound like previously, in the wooden bridge, you had something closer to a point load (which, in combination with a piezo crystal supported in the PU by a compliant material below, results in a bending actuation), while now, in the printed bridge, you go for compressional actuation. The piezo is then likely to give lower output, with a stronger high-end bias, as the lows are not seen by it. But that is probably separate from how the bridge performs acoustically. I suggest to first focus on how the bridge performs acoustically, and thereafter on optimising PU output. Or the other way round, if gigging is a prime driver. Just saying that the 2 are separate issues.

    Yet the printed bridge might also sound very bright if played acoustically. The conventional maple bridge has a geometry & all sorts of ornaments which act as tone filters, and by using a substantially different material (in the same geometry) the balance is quite different, and the filters will be different. And high-end emphasis may be the result. In other words, it might just be too 'hard'. Weight is quite important too; how much does the bridge weigh?

    If you plan to use the bridge in earnest, it would also be quite useful to know what material it is made of, because really from what I read about PLA, I would be quite worried over a bridge made from that. I understand PLA is more rigid than ABS, and more difficult to work, but has much lower thermal stability. ABS is soluble in acetone, which I don't see mentioned for PLA. And it might be something else again; PLA & ABS are just mentioned as the 2 currently most common materials for 3-d printers.

    On working & machining the material: I believe you. I have no experience in working these materials, and my coaster is a commemorative one which I like to keep undamaged (and the material probably different from your bridge anyway). As Gerry said, maybe try a hot nail or a soldering iron if further shaping is required.

    Looking forward to some sound comparisons.
    Thanks for sharing this interesting journey!