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; 23-04-2019 at 11:09 PM.

  2. #2
    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.
    Air cooled spindles are generally very noisy. Not sure why you think the water cooled ones are going to put water all over the place as they are fed with 6mm tubing and the pump and water container can be anywhere off the machine. They are also quiet .

    Re the plates I would use 20mm and if you don't want to machine it use cast as that will be flatter.

    Have you checked out if any of the bolts clash with each other ie on the bearing blocks for Z and Y
    ..Clive
    The more you know, The better you know, How little you know

  3. #3
    Quote Originally Posted by Clive S View Post
    Air cooled spindles are generally very noisy. Not sure why you think the water cooled ones are going to put water all over the place as they are fed with 6mm tubing and the pump and water container can be anywhere off the machine. They are also quiet .

    Re the plates I would use 20mm and if you don't want to machine it use cast as that will be flatter.

    Have you checked out if any of the bolts clash with each other ie on the bearing blocks for Z and Y
    Thanks Clive,

    Point taken re the air-cooled spindle. Water cooling seemed like one extra thing to worry about but perhaps the noise issue will make it worth it. I spent some time with a local CNC machine today which was using the Kress 1050 spindle - air cooled. Whilst not particularly loud (certainly compared to a router) it could certainly have been quieter. I don't see many people using 3kw water-cooled spindles, nor that many places to buy - I wonder why?

    Re the plates, what if I used 20mm just on the gantry sides? That seems to be the critical point - surely the z-axis won't matter too much (if anything, the thicker plates will move the spindle further away, creating more torque on the gantry?). Another idea I had was just to bolt some extrusion vertically to the 15mm gantry sides to stiffen them up a bit.

    I was going to buy my plates from here: https://www.aluminiumwarehouse.co.uk...e-cut-to-order
    I can't see cast here - is there somewhere I can go to specifically buy cast aluminium?

    Also I see 2 alloys - 5083 & 6082T6 - but I don't know the difference and which is best for machining. Biggest machining job I really want to take on is drilling holes on my drill press and tapping them.

  4. #4
    If I were you I'd stick with 15mm (or even 12mm) on the gantry sides and add some reinforcement ribs (say 40mm tall) all the way up along the edges (40x15mm flat bar for instance) - if you do the sums it works out much stronger than thicker flat plate. Aluminium Warehouse are not bad for plate, even if not the cheapest and having had a slightly checkered history with some of us on here, at the moment they are giving good service, cutting plate VERY square and generally 1...2mm oversize: to select the cast stuff click on "grade" and select the bottom item from the drop down box.
    If it were me I'd also be adding some plates top and bottom of your bed frame members to form like a "sandwich" structure and tie it all together in X and Y - though I can see that might have some weight problems for you.
    Last edited by Voicecoil; 24-04-2019 at 08:38 PM.

  5. #5
    Quote Originally Posted by Voicecoil View Post
    If I were you I'd stick with 15mm (or even 12mm) on the gantry sides and add some reinforcement ribs (say 40mm tall) all the way up along the edges (40x15mm flat bar for instance) - if you do the sums it works out much stronger than thicker flat plate.
    That was my feeling too - If I can spread the cross sectional area of those gantry sides that would be better than basically just adding more mass. I was just going to bolt some 45x45 extrusions to the outside of the plates. Easy to align and not a lot of extra weight.

    Quote Originally Posted by Voicecoil View Post
    Aluminium Warehouse are not bad for plate, even if not the cheapest and having had a slightly checkered history with some of us on here, at the moment they are giving good service, cutting plate VERY square and generally 1...2mm oversize: to select the cast stuff click on "grade" and select the bottom item from the drop down box.
    Very useful information - I didn't expect the cuts to be oversize - hell, when I have bought pre-cut sheet wood/mdf I expect much better than that! May not prove to be that critical though if I can at least drill all the holes accurately relative to each other. Even if the measurements are out, maybe they will be consistently so, such that two pieces of the same spec are the same size, even if its not the right size!

    I do have a table saw and maybe if I buy the right blade I may have to take the plate cutting into my own hands - but I'm a little concerned about cutting it square enough - its not a precision table saw by any means! I'm scared enough of the table saw when cutting hardwood - don't know what to expect with aluminium!

    Quote Originally Posted by Voicecoil View Post
    If it were me I'd also be adding some plates top and bottom of your bed frame members to form like a "sandwich" structure and tie it all together in X and Y - though I can see that might have some weight problems for you.
    Yes, I may just plonk a single plate on top. I was going to use a couple of layers of 18mm MDF here but might make the lower one of them aluminium. Putting one below the frame will mean some redesign and yet more gantry height plus hinder what little access I have to the drive mechanism - I'm already worried about how I'm going to retension the pulley belt under there.
    Last edited by bluesking; 24-04-2019 at 08:57 PM.

  6. #6
    Quote Originally Posted by bluesking View Post
    I don't see many people using 3kw water-cooled spindles, nor that many places to buy - I wonder why?
    Just to attempt to answer my own question - it seems not many people are using 3kw spindles full stop.

    From what I can tell, a 2.2kw ran off the common huanyang VFD is often rated around the 8A level for current draw - this means you can plug it into a normal mains socket without worries (assuming you use and appropriate fuse).

    The 3kw spindles I'm looking at, when run from an appropriate VFD will likely draw in the region of 18A. You're not going to find a mains socket fuse for this type of current. Still, the ring circuit from your consumer unit will probably allow currents up to 30A, so providing you can get beyond the mains plug you might be fine. One thing worth noting is that 13A fuses may not actually be designed to blow until 20A (go figure....) so it may be possible to get away with it (that's what I read here https://www.pat-testing-training.net...cteristics.php).
    Last edited by bluesking; 24-04-2019 at 11:42 PM.

  7. #7
    Quote Originally Posted by bluesking View Post
    I do have a table saw and maybe if I buy the right blade I may have to take the plate cutting into my own hands - but I'm a little concerned about cutting it square enough - its not a precision table saw by any means! I'm scared enough of the table saw when cutting hardwood - don't know what to expect with aluminium!
    Cast plate cuts quite nicely with the appropriate blade if you keep it lubricated (WD40 works OK) - just take it steady. Provided your saw is rigid enough you can do quite good work if you spend the time to get it set up square.

  8. #8
    Quote Originally Posted by bluesking View Post
    I spent some time with a local CNC machine today which was using the Kress 1050 spindle - air cooled. Whilst not particularly loud (certainly compared to a router) it could certainly have been quieter.
    Don't worry about the noise generated by air cooled spindles. It only makes a difference if you will be cutting air. ...and you'll be surprised how quiet an air cooled brushless spindle is compared to the Kress or a router...

    I have been using air cooled spindle for some years now, though it is only 1.5kW, but it is that noisy before cutting starts. If it must be replaced I'll buy another air cooled spindle, that's for sure.

  9. #9
    Quote Originally Posted by Voicecoil View Post
    Cast plate cuts quite nicely with the appropriate blade if you keep it lubricated (WD40 works OK) - just take it steady. Provided your saw is rigid enough you can do quite good work if you spend the time to get it set up square.
    I've gone through the design with a fine tooth comb and it seems there is only one plate where the dimensions are critical. If any of the other plates are cut a mil or two oversize it won't make any difference.

    Also, costings show that I would pay more for uncut plate of adequate size than I would pay getting aluminium warehouse to cut everything for me.

    I'll probably just go with the precut cast plate.

    I've given up on a plate for the tabletop - aside from the weight - it'll cost rather a lot. A piece of well attached MDF will suffice I think.
    Last edited by bluesking; 25-04-2019 at 11:22 AM.

  10. #10
    1
    Last edited by bluesking; 25-04-2019 at 11:14 AM.

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