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Mach Discussion => General Mach Discussion => Topic started by: SDConcepts on November 23, 2008, 11:17:31 PM

Title: making parts to size on customer prints
Post by: SDConcepts on November 23, 2008, 11:17:31 PM
i am new to using mach 3 and was playing around with cutter comp on my cnc mill.  i am currently trying to cut an arc with cutter comp and it doesn't seem to be working.  i would hope that i could ultimately use cutter comp to be able to run the job with multiple different sized endmills.   so far though i haven't had any luck and i've had to go back and manually fix the parts because the cutter just wouldn't take enough material.  i guess is was lucky that it was not enough and not too much.  i'm just wondering how good of luck people are having making parts to print? 
Title: Re: making parts to size on customer prints
Post by: jimpinder on November 24, 2008, 03:59:18 AM
Cutter compensation is one of those subjects that comes up very regularly.

Yes, you are quite right. Using cutter compensation yOu should be able to program the machine to cut as per the drawing, and the machine should then make allowance for the width of the cutter, according to the tool table.

If you search this forum, a complete explanation with diagrams was given by Graham Waterworth as to how it should be applied, i.e. left or right hand, depending on what result you wanted to achieve.

Having said that - and I am sure someone will tell me - HAVE WE LOST THAT WHEN WE UPGRADED THE FORUM - ANYBODY?? :-\
Title: Re: making parts to size on customer prints
Post by: jimpinder on November 24, 2008, 04:12:24 AM
If you are experimenting, you must remember that Mach 3 must run into cutter compensation, In other words, it is no good lining up your work, then switching on cutter compensation and expecting Mach 3 to jump to one side or the other to apply the compensation.

If you are cutting, say, a circle in a plate, then start at the circumference of the circle (without cutter comp). Your first move should be to apply cutter comp - G41 or G42. The second move is move round the circumference of the circle a short distance - say a quarter turn G2 or G3. This is the move that Mach uses to apply the compensation. The third move should be then to cut the circle, drop z, then   - G2 or G3 Bear in mind that the tool table must have the cutter diameter, and the correct tool must be selected.

G41 and G42 depends on whether you are using G2 or G3 (which direction your tool is travelling) and whether your tool is inside or outside the circle.

Try replacing your cutter with a felt tip pen, and drawing it out on a sheet of paper, you will be able to see the different paths, particularly if you try doing the circle first, then using compensation. The way Graham drew it, I am quite sure he has it in his head as a fixture, but to us lesser mortals, it could be a good reminder to then pin the diagram on the workshop wall.

Title: Re: making parts to size on customer prints
Post by: RICH on November 24, 2008, 07:10:02 AM
I have done many pieces to size using cutter compensation. Let me make a few points without getting specific on programing  or the tool tables and such. A lot of my mills are regrinds done by me on a Darex end mill sharpener.
I measure the end mills using 3 or 5 flute anvil micrometers to determine the endmill diameter. I think one should do some testing of their machine to see just how well it can hold dims. Try milling an outside circle as a test and maybe at
 a few different diameters or an inside circle. That will quickly tell you what to expect as it takes into account
the "whole system" ie; tool, depth of cut, feeds /speed, table movement, material, cutting fluid  etc..  If the system doesn't have the ability in movement or cutting to begin with you can't expect software to make up for what is lacking. With some testing done and knowledge of what can be expected, you can appropriately try to make up for those shortcomings to some tolerance.
In summary do some testing and apply to your machining.
RICH


Title: Re: making parts to size on customer prints
Post by: SDConcepts on November 24, 2008, 07:46:59 AM
ok a little back ground on me... i have run mills in the past so i'm familiar with lead ins for cutter comp.  i guess what i'm really after is the limitations of the software.  i have an IH mill and with that i have cut plenty of circles using the wizards and they were right on within .0005 of the actual diameter.  the current print i'm working at needs me to put an arc at the base of the part.  basically i need to remove about .100 of material and then throw an arc profile on the part so it can be welded onto a tube. 

in mach when starting cutter comp is it necessary to have both an x and y move?  or will just one of them suffice set cutter comp? 
Title: Re: making parts to size on customer prints
Post by: jimpinder on November 24, 2008, 02:52:27 PM
I will put my hand up and admit, that after I wrote my last post, I went into the workshop to try it, with a pen in the spindle chuck. No matter what I put in, in what order, I was still getting the pen to describe the arc, circle, or line, without any compensation. I am at a loss.

If you look on the GCode tag on the milling 1024.set, there is now a description of many of the  codes, including 41 and 42

Rich - gives us a clue in what order to put the code in. Does it only work in a GCode program, or can you access it from the MDI line. The codes at the top of the display change as you enter them.

Are there any settings in Config that I am missing.
Title: Re: making parts to size on customer prints
Post by: SDConcepts on November 24, 2008, 03:12:04 PM
i agree this is a serious problem with Mach 3.  i am having doubts of running customer parts on what i have to believe to be hobby equipment now.  even with tool paths generated in a cam program, how does it offset correctly?  what if your using reground end mills?  what if your end mills aren't spot on the diameter?  how can you compensate for this?  i've run a few jobs on this setup and basically all of them i had to rewrite the path when i swapped end mills.  this really should not be the case. 
Title: Re: making parts to size on customer prints
Post by: RICH on November 24, 2008, 08:06:52 PM
You can cut my head off on this one!
I used a different control program and controller for many of those pieces that were made. So stupid me 
just ass..u..me..d it worked the same way in MACH. You had to have a move before the compensation
and the compensation lagged one move in the program before it was implemented as it needed to know how long the next move was before it compensated for it with the same amount applied for all the next moves until canceled.
So just forget what i just said as it may not apply to how MACH implements it.

I also found that things worked better if i just let the CAM program generate compensated code rather than use compensation. So in using Mach i continued to used that system.  Which is fine if almost everthing you make is a onezy like me, but would be a PITA for a lot of parts to do and tool wear was involved.

I may have saved Graham's post as it was a good one. Let me look rather than confuse.
RICH
Title: Re: making parts to size on customer prints
Post by: RICH on November 24, 2008, 08:25:58 PM
Here is the link to the post by Graham

http://www.machsupport.com/forum/index.php/topic,7862.msg50220.html#msg50220

RICH
Title: Re: making parts to size on customer prints
Post by: SDConcepts on November 24, 2008, 11:08:04 PM
I may have been a little to hasty...  i sat down and looked through my programs, it looks like mach is trying to compensate, but i can't tell without actually running a part.  i will try draw some tool paths tomorrow using cutter comp with different sized tools as per the tool table.  i am also under the impression that the wear offsets don't work.  is this correct?  ultimately i'm not that worried about it, but its just good to know.

thanks

Jerry
Title: Re: making parts to size on customer prints
Post by: Hood on November 25, 2008, 05:13:01 AM
I think Brian is about to do a major reworking of cutter comp but this could take a while as I would imagine its not an easy part of Mach to mess with.
Hood
Title: Re: making parts to size on customer prints
Post by: RICH on November 26, 2008, 11:20:37 PM
Jimpinder,
Wanted to try out cutter compensation using my mill along with MACH & the SS so here are some screen shots.
The code contours a 1" x 2" rectangle and was generated with an .3" arc entry and exit and .2" dia mill.
I added the G40 & G41 as shown below. The tool paths were drawn onto paper using my tacer pen ( picture attached) while attached to the mill. By just adding a P value after the G41, ie; .001, .050, .1 you will get the different compensations.They are all plotted in attached picture.
RICH
Title: Re: making parts to size on customer prints
Post by: jimpinder on November 27, 2008, 03:15:07 AM
Rich - yes - that is what I anticipated I would get, but, as I say, I kept getting the original without the comp. I notice you are using  a Px.********* command after the G41/42. Does G41/42 not pick up the cutter diameter from the tool table, or do we have to add this each time.

I was trying to use the tool table.
Title: Re: making parts to size on customer prints
Post by: RICH on November 27, 2008, 06:34:01 AM
Never used the tool table, but will try it out. Currently have V3.042.015 installed and been meaning to upgrade
it to the lockdown. So will try with both. First wanted confirm the Gxx Pxx worked. Will repost tomorrow as no time to fool around today.
RICH

BTW: With no tool changer it would seem just as easy to add or change the P value.
Title: Re: making parts to size on customer prints
Post by: ger21 on November 27, 2008, 08:56:04 AM
# different ways to use comp:

G42 by itself uses the diameter in the tool table of the current tool

G42 Dx use the diameter in the tool table of tool #x

G42 Px.xx where x.xx is the tool diameter.

It looks like in Rich's example code above it calls Tool #0, so I don't think you'd get any comp with tool #0 being the current tool. Unless you used the D or P option.
Title: Re: making parts to size on customer prints
Post by: ger21 on November 27, 2008, 09:00:08 AM
i am also under the impression that the wear offsets don't work.  is this correct?

No, the wear offsets in the tool table don't do anything.
Title: Re: making parts to size on customer prints
Post by: ger21 on November 27, 2008, 09:33:14 AM
in mach when starting cutter comp is it necessary to have both an x and y move?  or will just one of them suffice set cutter comp? 

Just one should be fine, but make sure the lead-in move is at least as long as the tool radius, and preferably in a location where the comp can be easily applied.

Here's how I'd code a simple arc with comp.

G40
G20
M3
G0 Z0.1250
G0 X0.0000 Y0.0000 Z0.1250
G1 X0.0000 Y0.0000 Z-0.2500 F50
G42P0.125
G1 X0.0000 Y0.3750 Z-0.2500 F150
G2 X3.0000 Y0.3750 Z-0.2500 I1.5000 J-1.8670
G40
G1 X3.0000 Y0.0000 Z-0.2500
G0 X3.0000 Y0.0000 Z0.1250
G0 X0 Y0
M5
M30

Just a note. Mach's comp has been constantly evolving over the past few years. In it's current incarnation, it can behave differently in different situations. Notice in the pic and code that I posted, how comp is applied. The tool moves along the programmed path, until it's diameter is tangent to the arc. At this point, comp is applied. Then, notice that comp is turned off when the tool's diameter is tangent to the lead out move. At one point, comp was applied the same way it is turned off in this example. The tool would move from the programmed start point, to a point where it was tangent to both the lead-in move and the first comped move.

Now, I did a little testing. Basically the same code, but without the arc. Notice now, the the way comp is applied and removed is exactly the opposite of the way it is with the arc. Now, comp is applied during the lead in move, moving to a point where the tool is tangent to the lead-in and the first comped move. But during the lead out move , the tool actually travels along the programmed path. Here' the code:

G40
G20
M3
G0 Z0.1250
G0 X0.0000 Y0.0000 Z0.1250
G1 X0.0000 Y0.0000 Z-0.2500 F50
G42P0.125
G1 X0.0000 Y1.1045 Z-0.2500 F150
G1 X3.0000 Y1.1045 Z-0.2500
G40
G1 X3.0000 Y0.5698 Z-0.2500
G0 X3.0000 Y0.5698 Z0.1250
G0 X0 Y0
M5
M30

Now, the last pic is a drawing I did showing how comp used to work, and how I hope it works again at some point. I believe that the comp should be applied during the lead-in move, and removed during the lead-out move, as shown in the pic. And hopefully it works the same whether the first comped move is a straight line or an arc, NOT diffeent as it apparently does now.
Title: Re: making parts to size on customer prints
Post by: RICH on November 27, 2008, 05:50:40 PM
Gerry,
So i quess the best thing to do is take a look in a dry run as to how the compensation is applied by MACH.
OR     Is there a simple way to remember it all.
RICH
Title: Re: making parts to size on customer prints
Post by: ger21 on November 28, 2008, 07:53:28 AM
   Is there a simple way to remember it all.
RICH

For right now, I'd say just be sure to program the lead-in the same all the time. If you need to lead in to an arc, just you two lead in lines and two lead out lines. That should get you consistent results.

We'll see what happens when Brian changes the comp code. :)
Title: Re: making parts to size on customer prints
Post by: SDConcepts on November 29, 2008, 11:01:56 PM
i have to run a few sample part by the end of the week so i will see how close i can get to the prints with the tolerances and the current mach setup.