[RodrigoFarias]

I'm a chilean user of CNC router, sorry bad english.
In my area (small workshops) this technology is very rare in Chile and I have no references to evaluate my work. I have learned for myself.
Please help me telling me from the photos, if it is possible to improve this result. For me it is certainly unsatisfactory but the best I get by trial and error.

Attachment 252970 Attachment 252972 Attachment 252974

Wood: Pinus radiata (i think "Monterey pine" in USA, not secure).
Width: 15mm, profile cutting down 3mm each pass.
Tool: 4mm HRC40 carbide flat endmill (2 flutes)
RPM: 10.000
Speed: 1200

The piece takes 1 minute aprox., but requires many time after with sanding and polishing, to get a satisfactory product.

Is this that obtain normally with CNC profile cutting or I need change parameters to get fine cut?

Thanks in advance.

[awerby]

There are some things you could do. First off, the cut quality isn't really that bad. You're only seeing some hanging threads in certain areas, which is due to the way the cutting direction and the grain direction interact. If you were cutting this wood with a knife by hand, you'd change directions when approaching it from different angles, but if you're going all the way around it without changing direction, then some areas are going to cut worse than others. I suppose you could rewrite your toolpaths to take this into account.

More usual, though, is to do a roughing cut, like you've done, but to leave a mm or so for a finish cut. If there's less wood to remove, the cut will be cleaner. A sharper tool might help. Carbide wears out slower, but it doesn't take as sharp an edge as HSS or cobalt steel, which are also cheaper. Another thing to do would be to change wood species. Monterey Pine won't cut as cleanly as some hardwoods, like walnut, cherry, or maple. I'm sure there are some South American species that would also work better; you might find some scraps and do some experiments.

[ger21]

Looks to me like your spindle is not perpendicular to the table. Also, it looks like the wood may have moved, or there is a lot of flex in the machine?

Your feedrate is on the slow side, and I suspect that your tool is not very sharp.
Try cutting at 2000mm/min, and cut at 2mm/pass, with a full depth finishing pass removing about .5mm.

[Christian Knüll]

Hi,

I'd say dull or generally unsuitable tool - can you show a photo of it?
Try larger diameters (6 or 8mm) and straight instead of helix flutes.
Maybe even steel instead of carbide (often much sharper).

Christian

[RodrigoFarias]

Really thank you very much for taking the time to answer me.

The vertical is correct, it is perfectly perpendicular. It's just a defect with the zoom of the picture.
The tools we use today are of Chinese origin, but I've also used some more expensive tools available in my country with similar results, always carbide. My alternative would be an import, I'll try.
I only use the rule inside - clockwise, I would not have thought to use different path direction in a same piece, thanks for the tip.
I will also consider lowering less material per pass, thanks. (sometimes I down 5mm or plus...sorry).
Increasing the feedrate I've had problems with breakage of the tool. And with increased rpm spin generally wood burns.
I know this is really basic, but I have not had acces to this information:
- Is there any table or formula I can use to calculate the optimal setting for certain woods and cuts, or is it just trial and error?

And about a quote from awerby:

More usual, though, is to do a roughing cut, like you've done, but to leave a mm or so for a finish cut.

- Could you please clarify what you mean by this?

[cpr]

A roughing cut meand to split the operation in two parts, roughing and finishing.

Let's say you want to cut a 10mm radius. You cut 10.1mm at first, and then remove the last tenth in a second pass. You could use a better tool for that pass, and dust will be easier to remove, and you could optimize RPM and feed rate.

[awerby]

I don't know what you're using to generate your toolpaths, but most CAM software will allow you to set up a finishing pass as well as a roughing cut. You cut out your part roughly, like you've done, but you leave a little material - a millimeter or, as Ger suggests, half a mm - for a second cutting path to remove. Since it's not removing as much material, or trying to cut on both sides of the tool, there's less deflection and vibration, so the cut quality will be smoother.

If you could feed faster, you'd be able to sustain the higher RPMs without burning. Wood generally likes to be cut pretty fast, with a high-RPM spindle. If you're using a smaller tool, you need to spin it faster to get the same results. Until you're getting good results and feel more confident, don't drop the tool more than half its diameter in a pass. I don't know of any charts that break down feeds and speeds by wood species, but if you find one. please let us know. There's so much variation in people's machines, though, that it would be difficult to come up with one that would be truly universal. In the meantime, give the trial and error a trial, and report back.

[kostas1]

Hi Rodrigo,
have you finally managed to solve this problem, because I have a very similar one here ?

Thanks.