CNC services in China

This topic contains 8 replies, has 4 voices, and was last updated by  Shannon M 1 year, 1 month ago.

Viewing 9 posts - 1 through 9 (of 9 total)
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  • #7401
    Daren Banarsë
    Daren Banarsë
    Keymaster

    I thought I’d try getting a reed chamber made up with a CNC router, as I have a few reed experiments to try out. For anyone that doesn’t know what a CNC router is, it’s basically a cutting machine controlled by a computer.

    Like 3D printing, you do all the design work on your computer, but it works in the opposite way to 3D printing. Instead of building up a model from nothing, layer by layer, you start with a block of plastic, wood or metal, and cut into it.

    I found a company in China that was much cheaper than those in the UK or US, so I decided to send them my files. They promised a tolerance of ± 0.1mm, but better still, said I wouldn’t have to pay until they’d finished the model, and had sent photos.

    Well the photos arrived, and unfortunately it wasn’t accurate at all. There’s curves in the reed chamber, where the reeds would have to lie flat. And many of the straight lines are a bit wavy…

    melodica reed chamber CNC

    Melodica reed chmaber China CNC

    They also sent some production photos which are quite interesting:

    melodica CNC

    Melodica CNC China

    #7413

    Tatu Salmela
    Participant

    Are you sure the chamber surface is curved, not the reed channel cuts? With small-diameter router bits there can be some “stretchiness” to pattern edges, especially when removing too much material per pass. Usually milled surfaces tend to be flat and clean. Some of the waviness in the reed channels can be explained by hand finishing, the mill bit can’t cut sharp corners in a hole. On my cnc-milled reedplates, I had to hand-finish the reedholes by squaring the corners with a file.

    Always when outsourcing a process, make very clear what is important in your design. If exact tolerances on the shape of the reed channels is not as important as the flatness of the surface, the round cornered rough channels in the lowest photo would do. If the shop has to do additional hand finishing, it shows in the price.

    If I were you, I’d perhaps just ask if the surface was straight. Then I’d just pay for it, and test it once it arrives.

    #7414

    Melodica-Me
    Participant

    I have to agree with Tatu, when the piece is milled it should be flat and true when the final cut is completed. Unless the end mill is heating up the material enough to distort the material as it is cutting, then once the material cools down the true cut will then be visible. Also if the original material used is not flat or is held down with different pressure points, this can create uneven cutting surface as well. Parts that do not sit firmly to the bed will over cut or push the material as it cuts and create an uneven surface too. Another issue is that when cutting polymer/plastic/acrylic from one side only can cause a bowing effect due to heat stress build-up on one side only.
    Melodica-Me

    #7415
    Daren Banarsë
    Daren Banarsë
    Keymaster

    According to the company:

    “The parts are a little bit curved in the middle.
    But the curve is unavoidable for plastic parts with such a long length.”

    They’re actually very helpful, and suggest possibly using PMMA plastic or aluminium instead.

    #7417

    Tatu Salmela
    Participant

    Hey, that’s wonderful!

    If you use aluminium, you should get it anodized once you get the finish right (there might be some sanding and polishing). If you can go trough the trouble, it should resonate quite well, and give some weight to the sound. If you can afford it, order at least one in each material (you are experimenting, right?). Stainless steel or brass could do without coating, but they are much heavier.

    This is the reason I joined this forum, it’s really nice to see some development on this instrument of humble origins!

    #7418

    Tatu Salmela
    Participant

    Untreated aluminium tends to oxidise with spit, creating a white foam which is not healthy. Motorcycle shops and hobbyists are helpful with anodising, it needs some equipment and good ventilation. You can do some small-scale anodising in a well-ventilated workshop or garage, but you need a large container of non-reactive material which can stand heat (glass or ceramic perhaps), and I haven’t found a 50 cm tall glass jar yet.

    #7419

    Melodica-Me
    Participant

    Daren, Tatu, If you want to keep the aluminum look, you can use a product called Everbright coatings. It is used to coat a clear finish on metal with no effects or discoloration to the metal finish and keeps moisture away from the metal and avoiding oxidation. It can be wiped on with a rag or sprayed and it needs no maintenance once applied. It is also non toxic and is safe after it drys. Anodizing is better if the finish if clear aluminum or if a colored finish is acceptable, if you want a polished aluminum finish then the Everbright coating is the way to go and you don’t need a professional to apply it for you. I used this product for a moisture issue on a radiation cooling system that had condensation build up and caused Oxidation on an aluminum fitting panel, worked perfect.
    Melodica-Me

    #7421
    Daren Banarsë
    Daren Banarsë
    Keymaster

    Yes Tatu, I am experimenting! I will try a few materials. I’ll have to thin it out a bit before I get it made in aluminium, as it could add too much to the weight. Thanks for the anodizing tip, and thanks MM for the Everbright tip. This will eventually be out of view so I don’t mind what it looks like…

    #7706

    Shannon M
    Participant

    Hi Daren,

    Any further progress with your experiments?

    Thanks,

    Shannon M

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