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Thread: Luthier CNC

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  1. #1
    Following on from my introductory/ideas thread - http://www.mycncuk.com/threads/12712...r-big-hardwood

    I have now finished an initial design for my CNC for guitar building. I had the following requirements:

    - Optimal performance for fast and smooth cutting of hardwood with large bits
    - Minimal machine weight (1 person carry, or easy to dismantle)
    - Minimal tooling required to produce - I have access to a CNC but no experience and little desire to work with Aluminium
    - Adequate size to produce guitar bodies and necks - bass necks and neck-throughs are not part of the core requirements
    - Relies on low-risk mature technologies (parallel port, Mach3)
    - Sensible cost

    I drew inspiration from two existing machines:
    1) Wal's build - http://www.mycncuk.com/threads/11266-3-Axis-900x500mm
    I liked the simplicity and robustness of the mechanics on this machine. It is for bass guitars, so similar requirements.
    2) The obsolete K2 CNC 3925 - https://www.youtube.com/watch?v=LLNeA1oUCGc
    I have seen quite a few videos of this machine performing wonderfully in guitar building. Seems to have been a popular choice for woodworkers and particularly luthiers in its heyday. Nothing else I've seen compares (short of a HAAS). Not impressive mechanically but has fully convinced me that a servo drive is what I want.

    Attached are some pics of the mechanical CAD model. There are a couple of features which aim to meet the requirements:
    - Performance is met using servos, and gearing for all axes is required. 1605 ballscrews used throughout with pulley drives. 20mm linear rail throughout. heavy duty 45x45 extrusions throughout.
    - 3kW air-cooled spindle. Mainly decided on due to the K2 machine. I'm reluctant to use water-cooled as don't want the faff of pumps and water near my dried woods - after VFD control I'm also running out of capacity on the basic parallel port breakout board. I'm a bit worried about the noise - I use handheld routers a lot - I hope that an air-cooled spindle will be a lot more quiet - does anyone have any experience with one?
    - For weight, I rely mainly on extrusions, using plates only where necessary. All plates are 15mm thickness. Machine size is kept as small as possible.
    - The work envelope is big enough for all guitar bodies and necks, including angled headstocks etc. It is not big enough for most bass necks or neck-through guitars. If I have the spare space and the need I will upgrade the machine - easily done, until then I will be tiling any occasional bass build - I wanted to ensure I could easily tile work so avoided a raised support around the work area.
    - I'm using openbuilds steel Nema 23 mounts as these allow me to get easy belt tensioning without requiring me to make bespoke aluminium components. Apart from the side supports, only rectangular plates are used so they can be bought pre-cut. Everything else can be done with only hole drilling and tapping.

    The electronics and motors are based on my research into the K2 machine. I will be looking to use this 3 axis servo kit from the US as it uses the same drivers and slightly higher spec servos as the K2. Not a bad price and contains most of what I will need.
    https://www.automationtechnologiesin...-gecko-driver/

    I already acknowledge a few limitations/challenges:
    1) Using servos will not be straightforward however I am ready for the challenge and have some relevant control systems education
    2) I gather 2 ballscrews for the major axis would be preferable. Unfortunately I am reluctant to take on the challenge of synchronising the control loops of 2 servos, and the belt tensioning complexities and mechanical synchronisation of a single servo driving 2 screws. I'm therefore sticking to a single screw - it seems to work fine on the K2 at least.

    Would love to hear any feedback or suggestions at this point as I'm feeling about ready to jump in!
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    Last edited by bluesking; 24-04-2019 at 12:09 AM.

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