View Full Version : Do you account for climb cutting in G code?

11-03-2003, 05:56 PM
Hi all,

Do you write/produce your g-code accounting for climb cuts (side cut on a flute mill bit) ? If so how?

I'm trying some simple 3d cutting with multiple levels of toolpaths with finishing cuts on my homebuilt. Using ball end two spiral flute bits, one large to rough out, smaller to finish. For the curious it's purely amateur cutting of half hull models of sailboats in poplar.

The machine is mostly mdf construction so its not hugely stiff (!). I've noticed that when cutting test pieces that there's different loads, vibrations and quality of cut between cutting on the climb ('right') side and the other side of the cutter. Much the same effect as hand routing in woodworking.

I've found that if I code a G-code file to avoid climb cuts I can run faster and get much better results without as much vibration from the toolbit. For me that means cutting one way over the piece.

Anyone else seen that?

Since I'm doing this on the cheap - Rhino / turbocad / Aceconverter / Turbocnc - that means hand modifying the cut file, which is a bit (pardon the pun) tedious to say the least, and of course giving huge opportunity to screw it.... er for error...

Is this something to worry about,? do more serious software packages account for climbcuts when producing a toolpath?


11-03-2003, 06:16 PM
Yes, fyffe555

"Real" cadcam software does give you this kind of control.

In some software, such as Bobcad, you will be responsible for picking the direction of the chains to be cut, but at least you can choose.

In Onecnc, this becomes more automated, as the software creates toolpaths, it asks you which direction is your preference.

Its just a matter of spending the money :)

There could be a whole range of software in between the above two that I have not mentioned (because I lack exposure to them) that will also work.

11-03-2003, 07:20 PM
I have not noticed a big difference in cut quality in wood when climb cutting. The largest tool I have used is 1/4". Perhaps a larger bit would produce a more noticable diference. Right now I don't really care which way it cuts.


11-03-2003, 07:26 PM
That screw....er error thingy is what a friend of mine calls "a prime time to de-excel".


btw I run in wood and like balsaman it doesn't make a lot of difference unless you are using the bit to make a side cut that is going to show and I then slow everything way down and use a stepping cut.

11-03-2003, 07:50 PM
What is a stepping cut?


11-03-2003, 07:55 PM
I don't believe climb milling works as good in "real" wood. Even planars are designed to "conventional mill" lumber. I believe this creates a burnishing effect on the wood, that improves the finish, without unduly damaging the cutter.

A stepping cut? That would be more than one pass required to get to full depth, would it not? In 3d milling, the rough cut creates plateaus that look like steps as the rough mill cuts each level on its way down to the bottom.

11-03-2003, 09:25 PM
If you're cutting solid woods, not plywoods or composites (mdf, partical board), sometimes you need to climb cut to keep from getting tearout. Especially if you're just trimming an edge with the grain. Climb cutting can put a larger load on you're machine, because the bit will try to pull the router along with it. But, if the bit is not very sharp, you'll tend to get a fuzzy edge. Generally, I would say the only reason to climb cut wood is if you're having a tearout problem. And sometimes climb cutting can still tear out, depending on the grain direction.
You also might want to look at roughing with staight bits, you'll probably be able to cut faster than with the ball nose bits. Some great bits can be found here: http.www.vortextool.com
I believe you get a 30% discount if you buy 3, too.
Also, if you have Rhino, have you looked at Meshcam to generate toolpaths. Right now, the beta is free with no expiration or limitations, and if you have models in rhino, you can get full 3D toolpaths. http://www.robgrz.com


11-03-2003, 10:25 PM

Thanks for the meshcam link. New to me but it looks like it could save me loads of time I currently spend with turbocad making multiple layers for ace... My Rhino is an older v2 acedemic version so I'll have to see if mechcam works with it.

I don't appear to need to climb cut to avoid tearout thankfully, because it really does pull the machine about. Version 2 will need to be a lot more ridgid I think!



11-03-2003, 10:31 PM
Just export your Rhino models as .stl files. I have a copy of Rhino 1 and it does it, so yours should as well. Meshcam is really easy to use, as there are only a few different settings.


11-04-2003, 12:51 AM
balsaman stepping cut is what I was told was the oppposite of climbing. It may very well be the wrong name for it but someone told me that several yrs ago and that is what I have called it since then. Please tell me I haven't been looking like a moron for several yrs!!:o :D

ger21 I downloaded meshcam a couple of weeks ago and have not had time to tinker with it yet. Does it just do 2d or can you write a 4 axis program with it where the part rotates or probably better description would be to index as it will actually be cut on four sides?


11-04-2003, 08:51 AM
Meshcam does 3 axis only, but I believe the author said he would like to add 4th axis cabability in the future.


11-04-2003, 08:55 AM
If you're not climb cutting, it's usually called conventional cutting.


11-06-2003, 09:21 PM
Climb cutting definately has it place, but if you are doing predominantly linear cuts, ( really 2 d cuts ) on a half hull, you can probably gain as much advantage by looking at the grain path on the individual slopes, Isolate individual areas with similar grain direction and mill each one in a path that accomodates the grain. Quite often cross grain cutting forgives the soft wood.
It has less to do with cnc experience than it does with woodworking experience.
Often in a wood that appears "stringy" you can get a cleaner surface on a first rough ( read that as deep ) cut than you do on a final shallow cleanup path. When this appears as though it is happening, you might try going to finish cut with a greater amount of wood left from your rough in passes.

If you do climb cut, tend to your bit edges and watch for blowouts when going "downhill" They will come out as deeper tears.

When doing human faces we usually ( if we are having tearout problems) do a finsh cut that leaves about 0.02" material, do a quick coat ( while still on the machine)
with a very weak cut ( if you buy pre-mixed shellac, cut it by 75%)of shellac. This will dry very rapidly and stabilize the surface wood. A carbide bit wont mind and your tearout is reduced by 90% if not totally.

No matter how it goes, don't throw away your sandpaper.

I don't know if Rhinomill is available on an academic deal. If it is, it will cure most of your programming problems. ( it is basic Visual mill packaged with Rhino )

Best of luck,

Phill Pittman