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Offsets

This topic has 6 replies, 4 voices, and was last updated 18 May 2015 at 12:28 by Bowber.

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17 May 2015 at 10:08 #190237
Bob Rodgerson
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@bobrodgerson97362
As far as I understand things the machine has its own memory of where zero is and in order for it to successfully machine a component from a programme it has to know where the zero point on the work piece is. Armed with this information It compensates for this difference with every move the table makes below the spindle relative to the X,Y & Z coordinates.

At the moment I am more concerned about the Z axis as this one can cause disasters if it goes wrong.

The machine is referenced prior to starting by Zeeroing all axis, Then, in theory, using either a reference tool or the first tool to be used the tool is bought down until it touches the top of the work piece and the Z axis is set to zero. This should then enable the machine to compensate for the difference between it's z zero and the Zero of the start of the job. Similarly if I am using a tool table all the tool lengths in that table are compared with the referenced tool so that their different lengths are automatically taken into account.

I have referenced the tool several times and always with the same result in that the machine immediately takes off upwards and trips the Z stop. Why?

The only way I have been able to run my programme has been to reference the first tool at the bed of the machine and fiddle about by stopping the programme and re-referencing the X & Y axis until eventually the table moves to the correct position under the cutter, not an ideal situation by any stretch of the imagination.

However I have manage to get the programme to run until the the second tool change where the tool is left cutting air. I once again interrupted the programme at this stage and referenced this tool Z axis to the machine bed and it continued to do the right thing.

Obviously I am doing something fundamentally wrong but I can't figure out what.

Anybody able to help? It's doing my head in!

I will be out for most of the day but I will respond to any replies later in the day.

P.S I am using Sprutcam as my CAM programme and the machine is a Tormach PCNC 1100 series 3
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17 May 2015 at 10:08 #15071
Bob Rodgerson
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@bobrodgerson97362
Problems positioning tool to start at the correct place and depth
17 May 2015 at 11:52 #190257
Ady1
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@ady1
I have referenced the tool several times and always with the same result in that the machine immediately takes off upwards and trips the Z stop. Why?

Doing it the wrong way round? Try it the other way

Mess around with different systems, while cutting air of course

focus on messing with the z axis only, a milling drilling milling drilling toolchange with no bed movement only z axis work
17 May 2015 at 22:06 #190372
Anonymous
For several years I ran my Tormach without referencing the axes with no issues. However, now that I have started to use tool tables properly this is what I do:

1. After power up and 'reset' I hit the ref all command and let the machine test out the limit switches – I do not alter the values in the axis windows on the display.

2. I use the master tool (tool 0) and touch it on the table and set the Z axis on the screen to zero.

3. I use the Tormach electronic tool setter, which is 3.15", or 80mm, high to automatically touch off the other tools and populate the tool table.

4. With the workpiece in the vice or fixtures I then set the zero point on the work, which can be anywhere depending upon where it is set in the CAM program. Often it is the back left corner, but equally it can be a convenient hole or the centre of the workpiece. The Z = 0 point can be either at the top or bottom of the workpiece, or can just stay as the top of the machine table. Where ever it is I touch off on it using the master tool and set Z = 0 on the display.

5. My post processor file inserts a number of commands on the first line of every G-code file including G90 which ensures absolute mode.

6. I set the X = 0 and Y = 0 points either by touching off a tool on the work or using a Haimer Zero Master or Centro depending on the precision I need and the type of feature I have chosen to be my zero point.

Andrew
18 May 2015 at 08:16 #190408
Bob Rodgerson
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@bobrodgerson97362
Hi Andrew,

thanks for taking the time out to reply. I am short on time to give a proper response as I am about to take one of my newer Motorcycles for an MOT. When I get back I will respond properly.

Thanks,

Bob
18 May 2015 at 10:52 #190428
Bob Rodgerson
Participant
@bobrodgerson97362
Hi Andrew,

I took my Velocette for an MOT this morning, peeing down with rain and nose to tail traffic all the way there and back and as usual when I go for an MOT, something goes wrong, either on the way there or back. This time on the way there the starter motor decided to kick in due to water in the starter switch. I could hear the damn thing whirring away while I was stationary in traffic. I had a job turning the thing off but after a few jabs of the starter button it stopped and I was able to stop the engine. (Bike is retro fitted with ab French made E-start system that gives nothing but problems). Any way all was well with the MOT so that's it for another year.

On To my problem with the mill: I think that I am doing all the right things to get the programme to work and the problem may be down to my 3D drawing, when I skip through the various views of the milling machine in SprutCam I can see an outline profile in 2D that seems to be sitting on the machine table (Under the vice) and I think that the work reference is being taken from here and not the top of the 3D part in the vice, hence the reason for me having to reference the table to get the machine to arrive at the right place. I can't be sure if this is what is the cause but I will take another look at my drawing and try to eliminate the 2D image and see what happens when I rerun Sprut Cam and generate the G code.

I am seriously considering doing one of Tormachs Courses but the earliest that I could do it would be August. Has anybody on the site been on one who can tell us what benefit it was to them?

Stupid thing is that I am off to the States next week for a month but I couldn't convince SWMBO that it was essential to detour from New Mexico to Wisconsin.

Regards,

Bob
18 May 2015 at 12:28 #190443
Bowber
Participant
@bowber
Sounds like you need to make sure your CAM program is using the top of the material as Z zero, it may not be automatically set to that point.

My CNC mill uses the top right corner to ref all to machine zero, I set it up this way because of the convenience of mounting the switches there.
I then normally use the bottom left corner of the part and material for the work X, Y zero with the top of the material as Z zero. This is also setup in my CAM programs, I normally use this method so I'm not messing with minus figures which can lead to errors if I have to add any hand coding.

I don't use the tool table or tool offsets because I have to change all my tools by hand anyway so I just re zero the Z each time I change tools

Steve
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