Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: BIGWING on July 18, 2007, 02:46:15 PM

Title: Near crash
Post by: BIGWING on July 18, 2007, 02:46:15 PM
Dear All

I am new to cnc and still on a steep learning curve. Today I produced a pocket with island using Autocad 14, loaded it in to  Lazycam pro 2.08 then ran it with Mach 2.065. All was well until near the end the cutter did a rapid speed through  the workpiece. Thankfully I was using a soft plastic so no harm was done.

N1050   G0
N1055   X225.7769  Y35.6699
N1060   Z10.1
N1065   G1 Z-1.000 F50

It looks to me as though Z10.1 needed to be before the G0 command. The programme did several repositionings prior to this without incident.

 Am I doing (or not doing) something stupid?. Is this a common error I need to be aware of.?

Any help would be greatly appreciated as my underpants can only take so much trauma

Cheers George
Title: Re: Near crash
Post by: jimpinder on July 19, 2007, 05:27:06 AM
If the Z command is the one that lifts the cutter then YES.

You can still use a G0 to lift the cutter.
I try and write my code with the command and the co-ordinates on each line - so I can easily see the co-ordinates the command refers to.
I repeat the command code - so what - at least I can follow what is going on easily without having to remember what the last command was.

G0 Z10.1 - (lift the cutter)(although we don't know what co-ord the cutter was at before)
G0 X225.7769 Y35.6699 (rapid move table - both co-ords move at once if on the same line, all three move if three co-ords)
G1 Z-1.000 F50 (move cutter down 11.1 at the above position at feedrate 50) (assuming +Z is up and -Z is down)
You could put another G0 code in to fast move the cutter down to the workpiece, before doing the G1 cut.

Just think about what you want the machine to do - bit by bit - and write the line of code for that bit.
If you want to make it simple, like programming a computer, write each line in English first, then run through it again, filling in the appropriate lines of code from your cribsheet.

e.g Lift cutter to safe height.
      Fast move to position B
      Drill hole to depth  at B

Hope this helps - I'm not an expert - but thats how I do it.
I wouldn't worry about your underpants - I got some steel railway wheels (for our miniature railway) cut at a professional machine shop about a month ago.
I took in the appropriate number of blanks - but I should have taken in a couple of extra ones. The first one had chew marks all over where they had forgotten to pull the cutter up !!!  The other favourite is forgetting where the clamps and other bits and pieces are.

Even the experts make mistakes - and some of their stuff weighs 300 Kgs

Title: Re: Near crash
Post by: BIGWING on July 19, 2007, 06:00:17 AM
Thanks for that Jim. This programe was written automatically by lazycam. I did a dry run on the screen and thought yip that looks like the right shape. When I ran it in anger the tool moved in the correct sequence most of the time ie( lift, rapid, drop ) no problems but one time it went (rapid,lift,drop) and I dont know why. It was quite a complicated shape (lots of blended curves)  with hundreds of lines of programe and I did have to up the connection tolerance to get the pocket to work. Do you think this is where the error has come from?
cheers George
Title: Re: Near crash
Post by: BIGWING on July 19, 2007, 11:24:24 AM
Hip Hip Horray

Think i've cracked it. Yes it was pilot error.

Spent today trying to retrace my steps. Think what i've done is forgotten to enter any details into the cut parameters box as I do remember having to manually edit the cut depth line from 0 to -1.0 which means the rapid height box will also have been 0.

Only thing I can't get my head around is why did it rapid travel at Z-1.0 and not Z0.0. Any ideas anyone?

Also I did another dry run in mach. The simulation showed the rapid movement (dotted line) well above the work surface. However when I did a line by line run through is clearly shows it moving across at Z-1.0 level. when the programe ends all trace of the faulty cutter path disappears making you think all is well.

Does anyone know of an idiots guide for checking this? (programe verification software etc)

Cheers George
Title: Re: Near crash
Post by: jimpinder on July 20, 2007, 04:56:47 AM
George - checking lines of code is a bit of a ****. Again all I can say is get the program into an editor and try and paragraph it so that it makes more sense and is easier to find particular parts of the program. Name each paragraph.

The trouble with Lazycam ( and don't get me wrong, I think it is a good program) it doesn't speak English.

As far as the Z -1.0 is concerned, the reason it did that is because that is what it was set at. Identify that point in the program and then trace back and see what the LAST setting for Z was. That is where the trouble lies, because that is where Z will stay. You need to lift Z by putting in another command before the rapid move. Looking at it if you swap lines 55 and 60 it will rapid up and then traverse instead of the other way round.

If you use an editor like WORD, you can use the search facility to quickly identify all the mentions of Z or even identify the Z-0.1 and Z10.
If you change the font colour for them, and you can do this for X and Y as well,  as well as G0 and G1 commands, it will make it much easier to read the printed version of the program and see what is happening if each has a different colour.

It sounds like a bit of a **** but if you do it once, and read through it you will find it is not all goobledygook, but is in a very logical sequence.
Title: Re: Near crash
Post by: BIGWING on July 20, 2007, 05:27:06 AM
Thanks jim ,
your rapid height explination makes sense now and thats a great tip about the search facility.
I am now older but wiser.
once again many thanks for your help