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Author Topic: How do I clear a fixture?  (Read 5429 times)

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How do I clear a fixture?
« on: November 10, 2011, 11:12:17 AM »
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

Offline Hood

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Re: How do I clear a fixture?
« Reply #1 on: November 10, 2011, 01:56:21 PM »
Usually called rapid Z in CAM programmes I have used as its the height that any rapid moves can take to clear obstructions.
Hood
Re: How do I clear a fixture?
« Reply #2 on: November 10, 2011, 05:28:51 PM »
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:



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

Offline ger21

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Re: How do I clear a fixture?
« Reply #3 on: November 10, 2011, 05:43:24 PM »
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.
Gerry

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Re: How do I clear a fixture?
« Reply #4 on: November 10, 2011, 05:48:42 PM »
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
« Last Edit: November 10, 2011, 05:50:15 PM by mhackney »
Re: How do I clear a fixture?
« Reply #5 on: November 10, 2011, 06:04:57 PM »
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

Offline BR549

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Re: How do I clear a fixture?
« Reply #6 on: November 10, 2011, 06:21:24 PM »
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

Offline ger21

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Re: How do I clear a fixture?
« Reply #7 on: November 10, 2011, 06:36:52 PM »
Quote
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.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html
Re: How do I clear a fixture?
« Reply #8 on: November 10, 2011, 06:47:35 PM »
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

Offline ger21

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Re: How do I clear a fixture?
« Reply #9 on: November 10, 2011, 06:55:17 PM »
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.
Gerry

2010 Screenset
http://www.thecncwoodworker.com/2010.html

JointCAM Dovetail and Box Joint software
http://www.g-forcecnc.com/jointcam.html