School me on the best machine for big hardwood

[bluesking]

Thanks again Clive,

Something has been sitting uneasy with me about all of this and I think I may have finally figured it out. When I'm seeing various machines cutting guitars on Youtube I'm generally left underwhelmed. I think it is most likely that I come from a purely woodworking background and metalwork is a foreign world to me. But what I actually need is a woodworking machine, I couldn't care less about aluminium (above and beyond any I need to machine to produce the CNC itself).

The only truly satisfactory results I've seen to date have been on HAAS-type machines. I've obviously been managing my expectations and ruled out anything in that league. And then suddenly I see this:

https://www.youtube.com/watch?v=LLNeA1oUCGc

This is the first time I've seen a desktop machine doing exactly what I hoped I could do. So I start trying to pick it apart - why is this machine doing what I require while I see no evidence that others are? Hard to see on the video, and the manufacturer K2CNC is now kaput. I follow some breadcrumbs and find some images of the machine:

https://www.hmres.com/site/images/pr...-8e6f-87f6.jpg

Looks OK, but pretty unremarkable. Yes its got square rails, yes, its probably using ball screws, yes it doesn't use steel, yes, its only using a single screw for the long axis, yes, it doesn't look all that sturdy. The only two remarkable things I notice are:

1 - Monster spindle - I don't know what power, but looks to be at least 3kW
2 - SERVOS!!!!

You can probably guess where my mind is going - and it does relate to my earlier whinging about everyone else using what I consider to be "small" cutters. I really want to use the cutters that I understand, and these are mostly big, multi-flute affairs. Now, my understanding is that I need to have substantial feed rates to generate good chips in such situations. My early research suggests steppers can certainly yield the same torque as servos, but also that servo's reach peak torque at high speeds, while steppers reach peak torque at low/zero speeds. Servos match my personal experience of hand-routing wood - a certain minimum feed rate is necessary to achieve controllable and clean cuts.

I get the impression that servos are a little rarer in most builds here and I understand they bring lots of extra cost and complexity. I'm particularly concerned that if I go down the servo route I may be out in no-man's land and perhaps less able to rely on the expertise of people here. Is there anyone here who can hold my hand a little and give me some advice about servos?

I may well be wrong, maybe steppers are perfectly sufficient, but I can now only convince myself of this if I can see them producing similar results to the above youtube link. At the end of the day, if I can't expect that sort of performance, I don't think I can justify investing so much time in a custom build!

[Clive S]

I may well be wrong, maybe steppers are perfectly sufficient, but I can now only convince myself of this if I can see them producing similar results to the above youtube link. At the end of the day, if I can't expect that sort of performance, I don't think I can justify investing so much time in a custom build!

Yes bigger more powerful spindles like 3 kw you can use bigger cutters. If you want more motor power then use nema 34 but then you need higher voltage drives (mains voltage type).

The machine like Wal's in my opinion is far more sturdy than the one you linked to. Modern tool paths can out perform with greater speed and less spindle power. Why not have a look at some feed and speed calculators.

using 10mm pitch screws with steppers you can easily get 10mts/min You will be surprised how fast 5mts/min is on a small machine.

[bluesking]

Yes bigger more powerful spindles like 3 kw you can use bigger cutters. If you want more motor power then use nema 34 but then you need higher voltage drives (mains voltage type).

The machine like Wal's in my opinion is far more sturdy than the one you linked to. Modern tool paths can out perform with greater speed and less spindle power. Why not have a look at some feed and speed calculators.

using 10mm pitch screws with steppers you can easily get 10mts/min You will be surprised how fast 5mts/min is on a small machine.

Thanks Clive, good food for thought.

Wal's machine certainly looks more sturdy than this K2. In fact, almost all machines I've seen look more sturdy than the K2. In my mind, this begs the question, why have I not seen any desktop machine performing as well as the K2 in this scenario?

It doesn't look like the timings will work out for me to see Wal's machine in action before pressing ahead with mine as I do need to get going. I'm sure you're right about 10/5 m/min, I couldn't even tell you what numbers the K2 is running at - all I can see is that the cuts look exactly what I want to be doing and I've not seen anything else that doest - leaves me with quite the risk of going down a dark path!

Compare the rickety K2 taking nice deep cuts with big cutters:
https://www.youtube.com/watch?v=LLNeA1oUCGc

To these much more sturdy machines, seemingly taking their sweet time scratching away:
https://www.youtube.com/watch?v=F5Jy5cJscXU
https://www.youtube.com/watch?v=WatC-mihuoA
https://www.youtube.com/watch?v=Psr9Yt49grw

[Washout]

Hi bluesking

I can see why you want to go for larger cutters and for roughing I would agree, however there is another factor to maybe consider dependant on the guitar design/type you are looking to machine. I'm sure you're aware that most routed pockets on say a Les Paul or Telecaster are a. imperial, but b. also are designed for a set of cutters that have certain corner radii e.g. 1/8 inch which means using a 1/4 inch cutter for most humbuckers. So you may be able to rough out the pockets with an 8-12mm cutter, but will have to do a tool change and a clean up operation with a smaller cutter to clear out the corners.

Also I am using 70v nema 23 steppers on my machine and it easily goes to 15mm depth per pass and I could make that 20mm without too much if any additional tool wear - see here: https://youtu.be/WVf5J8XytSA

BTW if you want the CAD for a "normal" Tele I have that linked in video #9 of the series above. There's a thread on here somewhere as well, as it was a kind of community project.

Chris

[Voicecoil]

Your requirements are not a million miles away from what I want to end up with, except mine will be used for building high-end loudspeakers rather than guitars (hence needs to be a bit larger); I've also had to think about the relocation issue. My advice if you're going to build your own is to go for a "raised side rail" arrangement, as then it's pretty easy to make the gantry detachable which would obviously help with moving the thing. But even so, I wouldn't be expecting the base part of anything that's properly rigid to be a one man lift - however if you're making one yourself you can of course build in handles/lifting points and provision for mounting it on a dolly or similar. I've also had a word with my pal Mike Vanden, one of the best archtop luthiers in the country, and he said don't get too hung up on feed rates as with some fancy hardwoods you can get a poor cut if you go too fast - he tends to work his Isel machine at 2000mm/min tops on standard wood and less if doing fine work on brittle stuff. A lot of the problem is that wood isn't a completely even material and some hardwoods are a bit on the brittle side; if you hit a hard spot/twisty bit near a corner on the end grain you can easily take a wee chip out of the edge. Using downward spiral cutters and machining the end grain first can help obviously, but won't solve everything all the time.
Regarding your comments on the K2CNC machine, it's difficult to say exactly what size that spindle is, but assuming the square rails are 20mm, I guess it could be a 2.2KW aircooled thing. Although servos have better torque at high rpm than steppers that doesn't mean you can't make a machine that goes fast enough for your kind of work using steppers, it's just a matter of getting the design right, there's a very useful motor/ballscrew calculator on this forum. And then there's now the closed-loop steppers available which are kind of a half-way house.