Machsupport Forum
Mach Discussion => General Mach Discussion => Topic started by: mhackney on November 10, 2011, 11:12:17 AM
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Firstly, I use CamBam for my cam app. I am milling the perimeter of some aluminum disks and have a fixture that clamps the disk through its center hole. Imagine a 2" diameter washer on top of a 3" diameter part held with a 1/4" socket cap screw. I would like to zero my at the part's top surface and X=Y=0 at the center of the disk. But, there is a cap screw and the large washer there! If I move my Z up to .25" above the surface of the disk (which gives me the clearance I need), it takes forever as the mill cuts air through that 1/4" to get to the part (which is .062" thick). There has to be a way to program this but I don't even know what this is called to be able to google it!
Help greatly appreciated.
Cheers,
Michael
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Usually called rapid Z in CAM programmes I have used as its the height that any rapid moves can take to clear obstructions.
Hood
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Maybe my procedure is not normal? Basically, I have an X2 minimill with not limit or home switches. All my work is done in a 3" x 3" x 1" work envelope so I've never really needed them and I am actually producing parts for my business so I don't have a lot of extra time to spend. Here is what I do...
I have a fixture plate mounted to my table. It has a 1/4" post that is at x=y=0 - that is, I set the x & y to 0 at the center of the post. My fishing reel parts have a pre-drilled 1/4" hole and I simply slip the part over the post. the post is threaded so I can position a cup shaped "washer" over the part and screw it down to hold the part in place. The screw head and post protrude above the top surface of the part by about 1/4". The part is .062" aluminum and I reference z=0 at the top surface. My program cuts the perimeter of this part - which looks like this:
(http://www.eclecticangler.com/product_images/m/532/AluminumRaisedPillar__92122_zoom.jpg)
The problem is, when I do a goto 0, the tool would collide with the screw head that is holding the part to the fixture. If I set my z=0 above the top of the screw I wasted a lot of time cutting air. There must be a way to have a safe xy plane to move the tool around and not worry about colliding with the fixture while also getting the bit down to the part quickly so I am not wasting cycles cutting air as the tool slowly steps down?
thanks again,
Michael
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Your Z zero should be the surface of the part, and your g-code should have your rapid moves above your mounting post.
If you enable Safe Z in Mach3, Goto Zero will use the SafeZ height and lift the Z axis first, before moving.
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Thanks Gerry. Ok, so that is what I do - the z=0 is the top surface of my part and in CamBam I set the clearance plane to say .25". That works fine EXCEPT, at the end of the operation, the tool returns to x=y=z=0, which would break the bit (1/16" end mill).
I'll take a look at the Safe Z again. Maybe I misunderstood it when I looked at it earlier. I thought it would just raise the bit to the safe z height first, move x & y and then lower z to 0? If so, that would collide with the fixture screw. See what I mean?
cheers,
Michael
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I may not have been clear earlier. The problem I have is when I click "Goto Z". I guess I am just in the habit of clicking that since it is on the main display and seems like a reasonable place to go to start an operation, or go and then raise the tool for a tool change, etc. I think my programs (generated by CamBam) return the tool to 0,0,0 too.
regards,
Michael
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That is easy enought to solve.Move the 0,0,0 away from the center of the part.
Use the lower LH corner of the part extents. Then use a rapid clearance plane setting in the CAM to avoid the head of the screw.
(;-) TP
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The problem I have is when I click "Goto Z"
Then don't click it. Why do you need to got to 0,0?
If CamBam is adding it, configure it not to. It should be fairly easy to have it move wherever you want after the code is run.
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It might be a (bad) habit thing since it is on the main screen and I have to move the tool somewhere to get started. My pendant has it programed on one of the buttons too. So an accidental move might happen, which I would like to avoid if possible. What do most people do?
cheers,
Michael
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I never use Goto Z. I usually want to move away from the workpiece when finished, and 0,0 is usually over the workpiece.
My screenset has a Park position that my spindle moves to when finished cutting.
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THAT is why you use the LH lower extents for 0,0 (;-) It is not over the part.
(;-) TP
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What do most people do?
I for one will always look at the gcode at the beginning and end of the program to confirm the tool pathing is correct.
Don't care what program generated the code or how I may have input the settings.
Under Clearance Plane in Cambam if default is chosen as a setting, then it is to a safe Z location before a rapid to a new location.
That takes care of a collision. But as noted leaves you with a slow movement for some distance.
In some programs you can also define at what postion of the Z travel the cutting will start to occur. So you would have a rapid to some point
above the surface and and then a different feedrate there after into the material. If not available, one could add it to the code if the CAM dosen't provide for it.
A manual code entry would seem very reasonable if the code is used manny times as in your case.
You can set the start point in CamBam to say 1" above the face and have the clearance plane set at say .001 such that you will get a rapid (G0)
to a distance above the surface and then the slower feed rate will be applied for the plunge in. FWIW
Where i start or end depends on what i plan on doing afterwards, but most work done is a one of a kind. Sometimes it has to be done more than one time
and having the machine return to a chosen position is preffered. That position may be above or to the side of the material.
All is not just plug and play when one wants to do something specific.
RICH
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Ok, I just finished a session cutting some parts. Firstly, all is well if I don't click the Goto Z button. The gcode is doing the right thing and the clearance Z is working fine. I zero on the center of the part because it is easy to position my fixture and zero at its center. I guess I had just developed the habit of clicking Goto Z to position the tool. Most of my fixtures hold the parts from the edge and 0,0,0 is at a corner of a sheet of stock or centered along one edge. In those cases, I just clicked Goto Z and I was ready to cut. This is a new fixture that clamps from the center and I was just clicking Goto Z like I always do/did.
But, I am still concerned that the button is so prevalent that I might accidentally click it. How should I deal with that?
cheers and thanks for all the info.
Michael
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Edit the screen and remove the button.
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Thanks ger21. I haven't messed around with editing screens so maybe that's what I'll do.
In thinking about it some more, I think I default to using Goto Z because I do not have home switches and that seemed like a reasonable place to go. Maybe I should create a replacement button that takes me to a safe Z and x=y=0.
Thanks all,
Michael
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put a small peice of post it note over the button on the monitor when your doing the parts that wont allow the move.
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As silly as that sounds, that is basically what I did. I'm weaning myself go the habit to press that button. So far, 100s of parts and no accidental tool breakage.
cheers,
Michael