Thread: Making horns.

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  1. #1

    Hi Everyone,

    Just joined the forum in hope of some advice on machines that may suit my purpose.

    I make loudspeakers and at present the mid range horns are commissioned, here is a picture of how they come in.

    DSCN1737 by mearssimon, on Flickr

    They are made from 18mm layers of ply, joined on dowels and glued then sanded back. The sanding takes some time to get the steps out before they are sufficiently smooth.

    The top 2 123d make images are the horns that I am now looking to make (different shape). I have had quotes to have then done on a 5 axis machine (expensive) and also on 3 axis in 2 halves joined down the center and smoothed inside and out.

    I want to cover all my options and may consider buying a machine, I have a budget of 7-8K.

    Any advice would be most welcome,

    Many Thanks,

    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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  2. #2
    Sorry for the double post. Please feel free to remove the other one mods.

  3. #3
    Is wood your best option ?
    Also are they that shape for acoustic reasons or just for the looks ?
    Last edited by EddyCurrent; 05-02-2015 at 04:02 PM.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  4. #4
    The inherent problems of acquiring 5 axis machine is: price and software, so i would forget about that.

    It seems to me what you need is precise and sturdy machine, which is well within your budget. Size wise it will be good idea to make all loudspeaker parts with it.

    So if you make the part from 2-3 pieces machined cleanly with ball nose bit and glue them together, you will be left with only minor finishing job.

    Or once you know that the shape is right you can machine yourself molds and make the parts from epoxy for example, or whatever. There are many many things that come to my mind. MDB or wood and then epoxy impregnate and so on...

    PS. Of course i would start doing it the way you have done it till now. Just use 3d paths and ballnose. So when all goes together it will need only minor sanding. If i am not mistaken looking at your photos, it was used 2.5D path not 3d. On your pictures it looks like a 2.5D path or 3d roughing pass, not 3d finishing pass which would leave all super smooth

    Last edited by Boyan Silyavski; 05-02-2015 at 04:45 PM.
    project 1 , 2, ...

  5. #5
    Thanks for the replies, the horns are machined in wood as it offers the best sound and the profiles are specific for drivers used. The other loudspeaker parts are run through saws and veneered but it may be an option to consider as the biggest panel is 1000 x 520mm.

    Sturdy, precise, that's what I am after as it will mainly be used for machining the horns, I have had a brief look through the site here and EXEL seem well though after. I am a novice with regards to CNC so is the consensus that it is possible to make these horns leaving say a 240 grit sand and finish or am I asking too much. Any advice on particular machines they may recommend for this purpose?

  6. #6
    I'm not sure you would get away with 240 grit and here's why. If you think about the cutting tool, probable a ball mill where the end is rounded, and imagine it cutting tiny furrows in the material, then the amount of stepover you give it will determine how far it moves across to cut the next furrow. So if the furrows are very close together it will take a very long time to cut and at some point there is a trade off between time to cut and desired finish. There's not a great choice of UK made machines, Exel was the one I was going for before deciding to make one.
    Spelling mistakes are not intentional, I only seem to see them some time after I've posted

  7. #7
    Thanks Eddy, I am going to contact Exel tom. with similar info to what I have posted here to see which of their models they would recommend for machining these things and off course the price. I thought it might be asking a bit to much to go straight to 240, I don't mind a bit of elbow grease.

  8. #8
    why does the horn have to be split to do it on a 3 axis ?

    if you run a .3mm or .4mm stepover you will have very little sanding to get to smooth

    whats the dimensions of the horn ? width and depth ?

  9. #9
    On the other hand the stock is so light you are not going to have issues with torque so you could opt for a larger diameter cutter (for all convex work) which would keep the scallop height pretty low so if nothing else you could go with a 3 axis machine with a decent CAD/CAM package. You might still have to make it out of a number of blocks to optimize step over with different gradients but it might be 4 or 5 instead of the 3D jigsaw.
    Best of luck with it

  10. #10
    I will be making several different sized horns the biggest at about 500mm wide 400mm high and 500mm deep (roughly). As I said I am a total novice and my comments on machining in two halves are simply taken on face value from this e-mail,

    1. True 5 axis machining is complex and expensive, and should be avoided if possible
    2. Cutter lengths are limited. Your item in one piece exceeds this. The cutter length for optimum machining is 50mm.
    3. To accommodate 1. & 2. the machining solution is a hybrid 3 axis one. The first 48mm of material is positioned and bonded up. The surface is machined from 0 to 48mm in the height with a 12mm ball ended tool stepping over 1mm per pass, cutter orientated vertically. The next 48mm of material is bonded on, and machined from 48mm to 96mm in the height. Etc, etc, up to 216mm.
    4. The inside surface of your horn could be machined using this technique. The outside will be the edge in plan projected down to the same plane as the small hole (ie not 25mm thick). Is this an option?
    5. To cut the outer surface at 25mm thick the item need to be inverted. As it no longer has a flat bottom this way up it will require a male support jig, increasing the nominal cost by 50%. The item is now too deep for the 50mm cutter vertically, so has to be cut full 5 axis (expensive).
    6. Another option would be to split the model into 2 halves. Each half could be machined front and back using 3. above, as there are flat joint surfaces for support when inverted. The outer surface would require some limited cutting with a 100mm long 12mm ball ended cutter, run at a slower feed rate to avoid it snapping off.

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