Official Luthiers Forum!

So, In the research I've been doing, I'm finding that there is an awful lot I don't know about the CNC world. I"ve been working wood for a long time, and I keep finding myself drawing parallels between the two worlds.

I can see that building a machine can be a relatively straightforward process, and there is tons of information about that process, kits, and lots of DIY info on that topic, but what happens when the machine is built? There's the software end of it, but also other questions, like:

Spindle or Router? Aside fromt he noise issue, what other advantages?

Collets - If I go with a spindle, now the collets are "ER" size - I can get an ER20 collet that can take up to a 1/2" shank - will that also accept the smaller bit sizes as well?

If I'm only cutting hard wood for necks, fretboards, and perhaps the occasional plywood piece for other projects, will a 1.5 hp spindle be sufficient?

Where can I learn how to use the CNC for other processes, like Inlay? tooling, materials, processes, etc.

Anyone have some good resources on how to get up to speed more quickly?

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Mitch

Spindle - quieter, full speed control while maintaining torque if used with a VSD, which can be controlled in software from your CNC controller. Collets are also more precise, as a rule. Routers are loud and fast and tend to have more runout.



Yes. My future spindle will have an ER25 collet, and I've got collets ordered for 1/8", 1/4", 1/2" and 5/8" shafts. They have all sizes from 1mm to 16 mm in metric, and a broad variety in imperial. check usshoptools.com for example.



Should be fine. I'm getting a 2.2 kw spindle because it's only a little bit pricier.

Thanks Mattia - BTW - did you see that George is offering spindles now on his machines?

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Mitch

I would buy a premade machine if you can. Even the folks who do this professionally do not get it perfect on the first try...with any equipment there is a prototyping phase.

I always suggest that anyone who is interested in CNC get into CAD first. CAD is a great tool even without the CNC...! If you find that you catch onto CAD pretty quickly then that bodes well for getting into CNC work.

Best,
Trev

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http://www.PeakeGuitars.com

As Trev said, CAD is step 1 for sure. You can't cut something without a drawing.

Spindle VS router has been covered

Go to Maritool to see what you can get for collets in a certain ER size (or collet holders in a certain taper size, for those with ATCs)

Horsepower tends to be cheap when it comes to spindles, since the bearings are most of the cost on any spindle. 1.5HP will bog down with a 1/2" cutter, whereas a 3HP shouldn't in most cases. You actually need a bit over 6HP to run a 1/2" cutter in hardwood 'ideally' at 18K RPM.

I would go further than insane if I had to listen to a router running all the time so I'd go with a spindle, barring complete deafness. They're cheap from Keling and other places anyhow.

So far as cutting goes, speeds and feeds for aluminum are a good safe place to start from on dealing with wood. Wood doesn't melt and stick to cutters, so you can get away with things in wood that you can't in aluminum. Experimentation pays off when it comes to technique; everything I've learned about cutting has been a result of experimentation or reading up on things on Modern Machine Shop, Practical Machinist, CNCZone, etc.

So far as inlay goes: PreciseBits and hide glue (those are all the commonly known 'tricks', right on one line!) There are even better ways, but I haven't seen them outside my shop yet

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

Yeah, but I don't want watercooled, and his pricing on European-made spindles is good, but after shipping and import duties the price difference is minimal. Rather have a local place get that piece of my business and have stuff supplied that I know works on 220V without me having to think about it too hard. I'm getting a TeknoMotor 2.2 kW 24Krpm spindle.

I would add that your spindle speed requirement is very DIRECTLY related to the rigidity of your entire frame. For setups that are not altogether rigid...MUCH higher rpms are needed to reduce the propensity of resonance within the system. Basically, higher rpm means less side load on the cutter and therefore, less pressure on the spindle and the held part, both of which could have instability, depending on your system.

Rigidy is everything when it comes to machining anything.

For instance, I have a Haas TM-3 I use for cutting wood. This machine is about two tons and has a heavy, cast frame. Its accuracy is in the .0003" range and the thing is QUITE stable. Using a .023" diameter end mill I cut fret grooves into maple at a feed rate of 10 ipm, stepping down .005", .01", and .02" on successive passes to finally achieve a final depth of .07". A 22 fret board takes about 20 minutes to cut. I don't know how that rate compares to other setups, speed wise, but I dont care. When the part comes off it requires only the slightest brush of fine scotchbrite and the grooves are pristine and sharply defined. In the meantime.....I'm doing something else. Once setup....I make 25 parts.

The spindle speed is 4000 on these cuts......significantly less than.....up to 25,000 I've heard about when using cnc machines on wood. I've used this type of profile with wenge, purple heart, and other brittle woods with difficult, open grains and have done very fine wooden inlays using this machine.

So for any machine you might consider....take a look at how rigid and how accurate it claims to be. Although "rigidity" isn't something that is spec'd easily, there is a very direct relationship between rigidity and the "accuracy" and "repeatability" spec that you may find on a machine you may be considering.

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I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

The reason higher RPMs are used on wood isn't usually to do with rigidity requirements, it's because it allows higher feeds and because wood cuts better with a higher surface speed. The feed forces required vary linearly with horsepower used, regardless of RPM, though higher RPM at the same feed (ie: underfeeding) can help with deflection in a less rigid machine.

You can definitely run the fret slots at much higher speeds and feeds and get equally good results; the fuzzing you're seeing at the top of the slots is most likely from the low edge speed of the cutter. I think I'm tied with Taylor on slotting speed, but they cheat and use a saw (and I do blind slots )

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Bob Garrish
Former Canonized Purveyor of Fine CNC Luthier Services

+1 on Trev's statement. I compared building verses buying and I didn't have the time to build so buying was the better option for me although I would surely had loved to build my own machine. That said, if you go the pre-made route, look at what kind of support you will receive. I researched this topic for about 5 years before I took the plunge and ended up with a ShopBot. They have one of the best forums around with lots of generous help to bail you out of a jam, and there will be lots of jams, believe me! They have been in buisness for many years with a proven track record of building quality machines for the cost. Looking back with hind site, I would buy another Bot in a heart beat. Mine does everything I need. It isn't a Haas or Fadal but it is an awesome tool that has an endless amount of potential for my applications. Just my $.02

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tim...
http://www.mcknightguitars.com

I appreciate everyone's comments on this. I have wanted to build a machine for a long time but didn't want to lost in space on the process and left on my own to learn and know everything there is to know before taking the first step. I've researched the DIY options out there and have found that the Joe's 4X4 hybrid machine is probably the best bet. I can build the machine for about $2500, way cheaper than buying a similar commercial machine, and the forum is very very good - lots of folks that have made mods like rack and pinion drives and adding a 4th axis. The hard work has been done already, and the design appears to be very solid and well vetted out, with over 80 machines built on this design and another 100+ builds in process. So I'm not necessarily starting from scratch...

That being said, I have some limited experience with G-code, but not really a lot with CAD/CAM software. I'd be looking for files to use as a starting point to learn how to do my own from scratch, like necks, bridges, fretboards, etc.

what would really be helpful is if someone who has this experience would put together a tut on designing a bridge or neck in TurboCAD ( or some other CAD Package) and post it up so we could learn from that...

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Mitch

already done...I highly recommend Rhino as the best bang for the buck for this type of work

http://www.luthiersforum.com/forum/viewtopic.php?f=10106&t=13037

Best,
Trev

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http://www.PeakeGuitars.com