incremental vs absolute in simple hand code program

MwTech Inc · Dec 11, 2021

Ok understand the difference between the two, in my other posts it was explained and i got it.

BUT, i have a very simple part to make, a 3.5" dia. disc located in a fixture and I just need to mill a square pocket in the middle.

It would be so much easier, I think, just to tell the mill where to go incrementally.

In reading other posts it appears that subprograms are in inc so why not a simple part??

Thoughts on this???

Booze Daily · Dec 11, 2021

Call the center of the disc X0 Y0 and program in absolute. Incremental is hard to keep track of.
I only (mostly) use incremental to mill a circular pocket in MDI.

kustomizer · Dec 11, 2021

I have done both depending on the way the drawing came to me, I would prefer absolute but a time or two the drawing made inc easier.

706jim · Dec 11, 2021

For manual programming, I find that a mix of the two worked the best. Absolute to locate the starting point of feature and incremental to follow the profile.

Your machine could care less which system you use but this is what worked best for me.

And yes, an incremental sub can be a powerful tool for effectively shortening a program.

Johnhudson · Dec 11, 2021

Switching back and forth between will always lead to mistakes,
Either by you or some one following behind you,
Especially when using finger cam.
Kiss is the best practice.

Vancbiker · Dec 11, 2021

Johnhudson said:
Switching back and forth between will always lead to mistakes,......

For what reason? When hand programming using a mix of absolute and incremental and looping code results in much smaller programs. Small programs are less likely to have typos than a large program. I started programming before CAM. Using incremental moves where advantageous was a great tool to reduce programming time. It was used frequently with no increase in mistakes that I recall.

CarbideBob · Dec 11, 2021

Vancbiker;3854618... Using incremental moves where advantageous was a great tool to reduce programming time.[/QUOTE said:
Unsure this except for real amateurs where the big world is confusing.
Yes I use it but only special cases and comment the hell out of it.

Johnhudson · Dec 11, 2021

Was kinda reading between the lines, Op was having a hard time understanding the two methods.
I agree there is always benefits to both but when your really green
KISS

MwTech Inc · Dec 11, 2021

Yep i'm green

but lots of help here.......

I was thinking to do the center as xoyo........

Since i'm only doing a .812 square pocket it seems that a inc move over to the edge and around the square,( taking into account tool dia) would be easier than plotting out abs figures.

And i do get the problems that mixing would do...read a lot of posts about that....

What I have done so far is to use a wooden dowel in the tool holder, with a wooden "block" for my part
sitting loose in the vise which is also loose on the table..I guess that is my method of "dry run"...lol

How's that for cnc lingo...haha

So far have only had to hit the big red button once. :eek:

kustomizer · Dec 11, 2021

I like to start squares in the corner, but I spent a lot of time there as a kid, here's my first square

Booze Daily · Dec 12, 2021

(Absolute)
G0 G90 X0 X0
G1 G41 D1 X.406
Y.406
X-.406
Y-.406
X.406
Y0
G40 X0

(Incremental)

G90 X0 Y0
G91 G41 G1 D1 X.406
Y.406
X-.812
Y-.812
X.812
Y.406
G40 X-.406

Your choice.

MwTech Inc · Dec 12, 2021

What is the D1 ???
Google not helping......

Dang...... its easy to do abs....I just need to remember that in abs xoyo is the "center" of the graph,,,,,,, :willy_nilly:

Got to get my brain to make that stick..

Booze Daily · Dec 12, 2021

Diameter compensation. In my example the code is from the center of the tool. The D value would be either half the end mill size or full end mill size depending on how the parameter is set.

Some people (like me) program with the endmill already allowed for, in which case the D comp is really just a wear amount.

CarbideBob · Dec 12, 2021

If you really want to confuse yourself use a bunch of G92s with a mix of G90 and G91 tossed in for fun.
I've run across such code on old machines.
I only use incremental when there is a real good reason and that is rare and as I said a comment to alert others or myself to pay attention here.
More than once I have run an old program and it is off. I look at the line for the cut and think this move makes no sense at all. ....Oh, oh, I am in incremental here. :dopeslap:

Absolute is easier for me and and those I have taught to wrap your head around.
Now one can do G54, G55.. etc and that itself can add to being confused so I try to keep that to minimum also with only one used to bring some sensible datum on the part to zero-zero.
For someone without many years in just keeping track of where the heck in the world I am is hard enough.
Learn to crawl before walk or run.
Bob

mhajicek · Dec 12, 2021

IMO absolute is better unless you're trying to fit things in a tiny, antique control. With incremental, rounding errors compound (you will have rounding errors any time you have angles other than 90 degrees).

706jim · Dec 12, 2021

mhajicek said:
IMO absolute is better unless you're trying to fit things in a tiny, antique control. With incremental, rounding errors compound (you will have rounding errors any time you have angles other than 90 degrees).

Or multiple holes spaced in 64th's.

mhajicek · Dec 12, 2021

706jim said:
Or multiple holes spaced in 64th's.

Or metric dimensions on an inch control, or vice versa.

woodsrider845 · Dec 12, 2021

I'd rather do abs than legs. Leg days suck. Actually, they dont. Its two days after that suck. But that goes for whatever.

Both have their advantages. Using both in the same program, are even better. Depends on how you're feeling that day.

Greg White · Dec 13, 2021

I thought that G91 was what gave cnc the "Power"
I use it quite often,da loop/do again/repeat?no?
Gw

incremental vs absolute in simple hand code program

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