WOn't cut square!

[Ed_R]

Add not cutting square to the list of things my machine won't do. It's a deepgroove, from eBay, they come with no documentation whatsoever.
I'm just getting the hang of the design side, drawing a 4-inch square in a cad prgoram and converting it to gcode and watchign it go on the sim and then... big moment, run it on teh machine and... out pops something that's not a square. A 4-inch square is about a 16th out of square.
So I think, 'Hmmm, what's causing that?' And I start tweaking the carriage frames a bit. Got them shimmed up for some compensation, let's see.... nope, still out of square.
I'm cutting half-inch plywood with quarter-inch passes, it ought to cut through like butter, but it's not square. SO I redce both speed and depth and make more passes. Better but still nto square. I can get about a 64th of an inch out of square for a 4-inch square.
And then just for grins I decide instead of cutting conventional, I'll cut climb.
And it's square.
So wassupwidat? Frame torque? Huh? What? Bit deflaection? Huh? How the heck do I handle THAT? THe spindle's a Bosch Colt, it's extremely securely mounted, so of course, it's probably moving.


Anyone got any Hints? Tips? Donations?

[ger21]

I doubt it's bit deflection, you're not pushing the bit very hard. Are all the sides perfectly straight? You were on the right track adjusting the machine to get it square. The small deviation from conventional vs climb cutting might be due to backlash.

[Madclicker]

I know what climb cutting is, but it was my understanding that routing direction only had relevance in manual routing for operations like patterns, templates and edge forming using bearing bits.

Is there a "conventional" direction for cnc cutting and if so what is it?

[lakeside]

Is there a "conventional" direction for cnc cutting and if so what is it?
Cutter outside of frame travel clockwise or cutter inside of frame travel counter-clockwise

[Madclicker]

Is there a "conventional" direction for cnc cutting and if so what is it?
Cutter outside of frame travel clockwise or cutter inside of frame travel counter-clockwise

Why? This opposite the way you route with a handheld.

[lakeside]

if you cut the other way its called climb milling G41 and G42

Climb Milling
Cycle: Pocketing

In the Pocketing cycle, the tool path moves always in clockwise direction. If this option is turned on, tool path movement is counter-clockwise.

[Madclicker]

So, is this just convention, or is there a reason to cut one direction verses the other?

[lakeside]

when you climb mill there is little tool defection but if your cutting wood that not an issue chip of edge may occur in a climb mill more than a convention path

[ger21]

So, is this just convention, or is there a reason to cut one direction verses the other?

Whether hand routing or CNC routing, Conventional cutting would be going around the outside of your part CCW. Climb cutting is going around the outside of the part CW. You should never climb cut with a handheld router, for safety reasons. The bit will grab and want to pull the router out of your hands.

What I've found when CNC routing wood, you usually get a much better cut when conventional cutting. But there are a few circumstances when climb cutting is needed. When cutting hardwoods, and cutting along the grain going CCW, if the bit is cutting along the edge of the wood, it's very likely that you'll experience tearout. Some woods are worse than others, with oak being about the worst. Climb cutting will allow you to make the same cut without getting tearout, almost all of the time. One exception is cutting arcs. Its possible to get tearout along an arc with both conventional and climb cutting, due to the grain direction changing during the cut.

The best way to avoid tearout all together, is to always leave a little material on the waste side of the bit when cutting. This will always keep you from getting tearout, but depending on bit size, can waste a lot of material.

[ger21]

if you cut the other way its called climb milling G41 and G42

Climb Milling
Cycle: Pocketing

In the Pocketing cycle, the tool path moves always in clockwise direction. If this option is turned on, tool path movement is counter-clockwise.

Apparently your talking about a specific software here. G41 and G42 are tool radius compensation. With a standard spindle rotation, G42 (offset to the right) is always conventional cutting and G41(offset left) is climb cutting. It doesn't matter if your cutting pockets, or the outside profiles.

[ger21]

when you climb mill there is little tool defection but if your cutting wood that not an issue

Tool deflection CAN be an issue when routing wood. But, it's not very likely on a homebuilt machine unless your using bits smaller than 1/8".

[Ed_R]

Backlash would be an issue, wouldn't it? In a climb situations, bi deflection could be countering it. I took all backlash compensation out of the config after I was cutting circles and getting fun offsets And removing the backlash comp did make the squares a bit more square too, but after thinking about it, it would still be a factor. DAngit.
Guess I need more brass shim material. ( sigh )
Trust me, this deepgroove machine ain't all that.