[neeboy]

Noob question here...I'd like to get into machining small wooden blocks with intricate architectural details. I know that every tool has a "radius", and obviously that means a 90 degree inside corner can't be machined easily (at least not in one step). Knowing that, what is the smallest size tool I could use in a small 5-axis CNC router?

[pfred2]

Wood machining speed appears to be somewhere around 3300 Surface Feet Per Minute so a 1/16th diameter bit turns 200,000 RPM, an 1/8th bit 100,000.

It doesn't cover wood but everything else should be the same:
http://en.wikipedia.org/wiki/Speeds_and_feeds

[spoiledbrat]

I just tried using a 1/16" ball mill to machine some wood. Basically, high detail, 3d carving. I was carving sepelli, a variant of mahogany (not sure about that spelling!). I found that that is the limit for my machine. I started to see that the wood would simply not hold more detail; splinters began to occur on even the simple flat planes on my carving (when viewed up close!).

I would submit that the 1/16" ball mill is the limit for 3d carved detail. Now, if you were to use a 1/8" ball mill, and use the 1/16" to pencil-trace or clean up some details, it should do fine. Maybe even smaller bits would work for small details, but not for carving everything.

Just my opinion. I am sure that more will follow mine soon.

Good luck with your application.

Rob

[ger21]

I've gotten excellent results with a 1/16" ballnose bit in birch. No splinters at all, and glass smooth right off the machine. Stepover between .005-.008.

I think you need to use a harder, less porous wood like maple or birch. I've cut mahogany with an 1/8" bit and got some splintering there as well.

I plan on trying a 1/32" bit, because I'd like a bit more detail than the 1/16" provided.

[spoiledbrat]

Ger,

Thanks for the tip. Your results speak for themselves!
I was using 0.006" step-over, and yes, my wood is porous compared to maple.

What software did you use to draw the head? Is that ZBrush?

I wish I had about 1000 hrs to invest in that software. Phenomenal art is created with that program. zbrushcentral dot com. Crazy!

Rob

[Drassk]

My smallest are 0.01" flats and 1/32" balls. The flats are used for pocketing when I need really fine detail, and I've only use the 1/32" balls a couple times on some small parts with tiny details carved into them. Wood is far from a homogeneous material, there are a lot of mechanical properties that vary widely across different species (compare ebony and balsa!)

[RomanLini]

Ger21- Nice woodwork!

Is that oiled/laquered or straight off the mill? And if you don't mind me asking how long did the final cut take, and if you used a roughing cut(s) how long did that take? Thanks!

[pfred2]

But then there's this:

http://blog.metmuseum.org/cloistersg...sary-bead_324/

I saw it once when I was a kid pictures just don't do it justice!

[ger21]

It's laquered, but no sanding was done prior to spraying the laquer. The model is a sample that comes with Aspire.

I use an 1/8" ballnose for roughing, with a 1/8" stepover. It splinters much less than larger tools.The carving is about 5" diameter. I think the roughing was only about 15 minutes, at 175ipm, and the finish pass was around 2 hours? 1-1/2 to 2 hours, can't remember.

And, btw, I got the bits on Ebay. $5 for the 1/8", and $7.50 for the 1/16".

The biggest problem with small tools is the very short cutting length. The 1/16" is only 1/4" cutting length. Smaller ones are typically less.

[Drassk]

I've been using Ridiculous Carbide for my wood and aluminum tooling, unless I have specific reason not to, and I've found their stuff to be pretty good. I find, their grinds are a little sharper than others, and the prices are as good as eBay without the need to shop around. <$5 for 1/8", <$7 for 1/16" ballnoses, and they make a lot of long/extended length tools at good prices

For micro stuff, <1/16", PreciseBits is the only real game in town. I run everything under 1/16" at 65K RPM, though. They'll get through wood at 10K, but it takes forever and the edge speed isn't there to get them to cut well. I haven't run anything smaller than the 0.025" ones at 10K, and they have to cut at far less than 1/6 of the feed they'll do at 65K.

[LazyMan]

I've gotten excellent results with a 1/16" ballnose bit in birch. No splinters at all, and glass smooth right off the machine. Stepover between .005-.008.

I think you need to use a harder, less porous wood like maple or birch. I've cut mahogany with an 1/8" bit and got some splintering there as well.

I plan on trying a 1/32" bit, because I'd like a bit more detail than the 1/16" provided.

Ger21,

What is the overall size of your nice carving?

[pfred2]

Whats bad about carbide, other than how brittle it is, is the fact that the stuff never gets nearly as sharp as HSS does. Of course whats great about carbide is it takes a really long time to get any duller than it starts out as. That, and it can take a heck of a lot more heat than HSS can too.

As long as you aren't setting the wood on fire I'd imagine you could run small carbide tools about fast as possible. 300,000-500,000 RPMs if you could do it. You can generally push carbide about 4 times faster than HSS.

So, your 65K RPM isn't even breaking a sweat for your tools. The fastest spindle I have is a swiss high speed pneumatic die grinder and I think it tops out at around 120K RPM. Its cute though, it sounds like a little jet engine when it runs.

One thing I find a bit odd is that you say they charge more for smaller bits, usually with carbide more costs more, not the other way around. But then again their name may be Ridiculous Carbide for good reason!

[ger21]

Ger21,

What is the overall size of your nice carving?

About 5" across.

[RomanLini]

Thanks for the carving infor ger21 (and also thanks Drassk).

[Drassk]

Whats bad about carbide, other than how brittle it is, is the fact that the stuff never gets nearly as sharp as HSS does. Of course whats great about carbide is it takes a really long time to get any duller than it starts out as. That, and it can take a heck of a lot more heat than HSS can too.

As long as you aren't setting the wood on fire I'd imagine you could run small carbide tools about fast as possible. 300,000-500,000 RPMs if you could do it. You can generally push carbide about 4 times faster than HSS.

So, your 65K RPM isn't even breaking a sweat for your tools. The fastest spindle I have is a swiss high speed pneumatic die grinder and I think it tops out at around 120K RPM. Its cute though, it sounds like a little jet engine when it runs.

One thing I find a bit odd is that you say they charge more for smaller bits, usually with carbide more costs more, not the other way around. But then again their name may be Ridiculous Carbide for good reason!

Some of your information is dated, and some of it's short on important details. Carbide today isn't what carbide was 20 years ago. The grains are small enough now to grind a razor edge onto the tools, and I have tools so sharp that they're dangerous to handle by the flutes. There are very few good reasons to ever use HSS tooling anymore except for a custom grind; the only HSS in my shop is in drills.

Surface speed formulae are a good basic guide on regular cutters, but micro-sized mills are a whole different animal. There aren't spindles available that I know of that will drive a 1/8" cutter at over 100K RPM, and its ideal edge speed in even aluminum would need 180K for a high-end cutter. When you get into micro-mills, the beam strength of the cutter starts to be a big concern, and they can't take the side load that would be required to cut at full surface speeds.

A die grinder has so much runout that you wouldn't even get a 1/64" mill all the way into the cut in anything harder than softwood before you stopped having a 1/64" cutter. A milling spindle in that RPM range will only handle a tiny ball nose, and will cost some serious change. A few thousand for a turbine spindle over 100K, and a few thousand more for a compressor and air dryer that puts out enough clean air to run it. And the bearings generally cook every few months, which adds up in rebuilds. I've got 90K spindles, but only use them on special occasions because of their limited bearing lifetime.

So far as the carbide costs, the material isn't very expensive anymore. The cost is mostly in the grinding until you get into big cutters and even then the prices aren't insane. $130 retail for a 1" ballnose and $100+ for a coated HSS ball the same size. The more you need to grind off, the more time it takes to make a cutter, so the prices go down until 1/8" shanks and then increase as the grinding time increases and the size of the grinding wheels decreases to cut smaller flutes.