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Old 07-23-2018, 12:04 PM
kjoiner kjoiner is offline
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Default Creating a fixture for low volume production

Hello,

One of the things I'll be using my Stinger 1 for at work will be to make low volume parts in house vs. having to send them out. I'm working on make a small run of some UHMW guide bars for one of our machines. The parts are .688 thick so I'll be selectively skimming down 24 x 24 x 3/4" UHMW plate. Since the parts are long and thin, I want to use screws to hold the parts in place while I cut the profiles. I tried using tabs on the prototypes but they rock somewhat during cutting which resulted in gouges.

I want to make a fixture with threaded inserts to I can hold the bars in place after cutting the holes and countersinks. I plan to use 1/4-20 flat head screws.

Since this will be my first fixture, I have a couple of questions:

1. I'll probably use MDF for the first trial of the fixture. My machine is in an air conditioned space so should I anticipate any swelling over time?
2. I want to confirm the process for establishing a repeatable XY zero for future runs - 1. Drill locating holes in the spoilboard that match the locating holes in the fixture. Save whatever location I use as a zero in Win CNC.
3. Locate the fixture to the spoilboard using dowels then run the program to drill the insert holes in the fixture board
4. Question - I use the FTC on my machine. Should I calibrate the switch to the new height of the fixture whenever I run the program, or should I build the fixture thickness into my material in V Carve?
5. Any other tips or suggestions?

I'm attaching a screen shot of what my setup looks like in V Carve.

Thanks!

Kyle
Attached Images
File Type: jpg Guide Bars.jpg (92.9 KB, 112 views)
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  #2  
Old 07-23-2018, 12:23 PM
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Gary Campbell Gary Campbell is offline
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Kyle...
1. I'll probably use MDF for the first trial of the fixture. My machine is in an air conditioned space so should I anticipate any swelling over time?
Most likely

2. I want to confirm the process for establishing a repeatable XY zero for future runs - 1. Drill locating holes in the spoilboard that match the locating holes in the fixture. Save whatever location I use as a zero in Win CNC.
Yes, as a "Home" position

3. Locate the fixture to the spoilboard using dowels then run the program to drill the insert holes in the fixture board


4. Question - I use the FTC on my machine. Should I calibrate the switch to the new height of the fixture whenever I run the program, or should I build the fixture thickness into my material in V Carve?
Save the Z reference difference with your home position, leave the FTC set to the spoilboard

5. Any other tips or suggestions?
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Old 07-23-2018, 03:42 PM
Charlie_L Charlie_L is offline
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Like Gary said, I'd create my design to the spoilboard surface. I'd write the thickness that the template fixture adds onto the spoilboard. Then when using the template fixture I would measure the first tool using the FTC, then tweak the Z setting on the WinCNC screen to show the template z=0. You will have a green box on Z now. After that, all FTC tool measurements will be based on the Z=0 of the template fixture. So, if you design is created to the top of the spoilboard, it will now be cutting correctly to the template fixture zero.
I'm not sure that this makes sense. I know there are other, maybe easier ways to do it.
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Old 07-23-2018, 04:14 PM
kjoiner kjoiner is offline
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Hello,

I think I understand it but I better check. So if my fixture is 3/4" thick, do I bring the cutter down to touch the top of the fixture and then hit the Z zero button on Win CNC? Then do I go into the home positions and save it?

I already have a home position saved that has the correct X and Y locations. Can I type in the Z and then re-save?

Thanks,

Kyle
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Old 07-23-2018, 04:24 PM
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Gary Campbell Gary Campbell is offline
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Yes. It will work great if its the correct number
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  #6  
Old 07-23-2018, 05:25 PM
kjoiner kjoiner is offline
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See if I have this right:

1. Design my fixture in V Carve using 3/4" material (for convenience). Design the fixture off of the machine bed (spoilboard). Create locator holes in the fixture
2. The front left hole becomes the XY zero location on the fixture.
3. Drill holes in the spoil board that match up with locator holes in the fixture
4. The front left hole becomes a new saved XY home position on the machine
5. Measure the actual thickness of the fixture board and enter that value as the Z home position then re-save the home position. (This is where I'm uncertain)
6. Set the fixture on the spoilboard and locate using the dowels
7. Call up the home position I saved
8 Run the toolpath. (When I run the toolpath, it will measure the tool. Does it automatically calculate the difference between the new, higher Z zero and the tool in a similar manner to how it does it for the original spoilboard zero?)

Thanks!

Kyle
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  #7  
Old 07-23-2018, 06:03 PM
Charlie_L Charlie_L is offline
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For what it is worth... Thoughts in BLUE below.

Quote:
Originally Posted by kjoiner View Post
See if I have this right:

1. Design my fixture in V Carve using 3/4" material (for convenience). Design the fixture off of the machine bed (spoilboard). Create locator holes in the fixture
2. The front left hole becomes the XY zero location on the fixture.
I would write the absolute table locations on the fixture too in case I lose the home position.
3. Drill holes in the spoil board that match up with locator holes in the fixture
Perhaps install a hardwood plug in the MDF if you will use these holes often. You can do this later after it is working.
4. The front left hole becomes a new saved XY home position on the machine
When saving the home position, delete the Z value. It will never be the same when you put in the next tool.
5. Measure the actual thickness of the fixture board and enter that value as the Z home position then re-save the home position. (This is where I'm uncertain)
I always save the home position with a blank Z position. So this step is not needed.
6. Set the fixture on the spoilboard and locate using the dowels
I would add a step here, G92 to clear all green boxes.
7. Call up the home position I saved
8. Use the Measure Tool button to get the z set to the table top.
9. In WinCNC type is the z value for the fixture thickness.
10. Push the zero Z button.

Now it would be set to a Z zero at the fixture surface. Green box on all X, Y and Z.
8 Run the toolpath. (When I run the toolpath, it will measure the tool. Does it automatically calculate the difference between the new, higher Z zero and the tool in a similar manner to how it does it for the original spoilboard zero?)

Thanks!

Kyle
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Last edited by Charlie_L; 07-23-2018 at 06:12 PM.
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  #8  
Old 07-24-2018, 12:05 PM
kjoiner kjoiner is offline
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Thank you for all the tips. Now my next step is to try it out. Before I make the fixture, I'' experiment with stacking a part on a spacer to simulate a fixture and make sure I understand the Z axis.

Kyle
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  #9  
Old 07-26-2018, 09:44 PM
rcrawford rcrawford is offline
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If I were making those parts, I would simply cut the whole sheet of parts out to a depth of 0.688" using a vacuum hold down, then flip the sheet over and surface the whole thing down to 0.688" with a fly cutter to release the parts. No jig would be needed then.
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  #10  
Old 07-26-2018, 10:12 PM
drummerjg drummerjg is offline
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Very clever, Russell. Thanks for posting!

I do have a question. For those of us without vacuum hold downs, would it be ok to use four locating holes drilled into the spoilbord and then use dowels as the holding agent? That way you could still fly cut because you would only be cutting a dowel. Im kind of excited to try this technique out.
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Last edited by drummerjg; 07-26-2018 at 10:27 PM. Reason: Added text
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