Cut alignment issue

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Cut alignment issue

Postby Olle » Mon Jun 24, 2019 6:26 pm

This has had me tearing my hair out this morning: I'm trying to cut a sharp corner by running two 1/8" passes and then cleaning it up with a 1/16" pass. I have tried different ways of doing this, but no matter what I do I end up with the 1/16" cut being slightly offset. The lines align perfectly in the drawing, but the 1/16" pass ends up being slightly offset. To make it more interesting: It's only offset in the X direction, and I can correct it by moving the square cut about 5/1000" to the right. Does anybody know what's going on here? :?:
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Re: Cut alignment issue

Postby Olle » Mon Jun 24, 2019 6:27 pm

...simulation...
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Re: Cut alignment issue

Postby Olle » Mon Jun 24, 2019 6:27 pm

...and a copy of the file. I have tried to offset the long lines by 1/16" and use the "cut on line" option, I have checked the tool diameters etc, etc, but nothing but moving the square seems to help. There must be something wrong with the 1/16" cut, I just can't figure out what it is.
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Re: Cut alignment issue

Postby dealguy11 » Mon Jun 24, 2019 8:49 pm

Looks fine when I try it. Try setting your simulation resolution (it's under the Toolpaths dropdown on the menu bar) to "Maximum" and see if it looks better. I think you may be seeing simulation artifacts.
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Re: Cut alignment issue

Postby Olle » Mon Jun 24, 2019 8:58 pm

You're right, this seems to line it up perfectly. This is just a small part of a larger model, ran a prototype this morning and I could swear the 1/16" bit didn't hit that corner... I guess I have to try again and pay closer attention to what happens. :D
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Re: Cut alignment issue

Postby dealguy11 » Mon Jun 24, 2019 9:13 pm

If you're seeing an offset in a real cut but not in the preview at high resolution, then there's probably some slop in your machine. I do cuts like this all the time - on an older machine that had some flex in the gantry, I'd see differences. My current machine does not flex and has imperceptible backlash, so they come out exactly as shown in the preview. If you continue to have problems then you should look at what needs to be tightened/adjusted.
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Re: Cut alignment issue

Postby Olle » Mon Jun 24, 2019 10:33 pm

It's tight and usually very accurate, haven't had any problems related to backlash. Not too long ago I cut some Delrin pieces to fit inside each other, and it worked great. However, I have noticed that some used bits can be off by several 1/1000" sometimes, and beech is especially bad at wearing them down quickly. I might have to load up with fresh bits and try again, but it's really not a huge issue since that corner is easy to clean up with a knife. I was just wondering why it didn't come out right in the simulation, but it seems like it actually does. And of course, trying to cut a material like wood with high precision is kinda futile anyway :D
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Re: Cut alignment issue

Postby martin54 » Tue Jun 25, 2019 10:58 am

Have you measured the 1/16" bit to make sure it is actually on size,? Although I guess if it weren't then you would see the same condition in the y axis. Have you tried slowing the cut down a little? Might be some tool deflection.
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Re: Cut alignment issue

Postby Olle » Thu Jun 27, 2019 6:36 pm

martin54 wrote:Have you measured the 1/16" bit to make sure it is actually on size,? Although I guess if it weren't then you would see the same condition in the y axis. Have you tried slowing the cut down a little? Might be some tool deflection.

Didn't think about that since the same thing showed on the screen, but now when you say it... Sometimes (like when doing very small, engraved letters) I need to slow down quite a bit to get a precise cut, so I might just try that. Haven't had time to make another run yet, but I'll definitely keep that in mind.
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Re: Cut alignment issue

Postby Olle » Wed Jul 03, 2019 5:01 pm

Got it all squared away (no pun intended), and it seems like martin54 was spot on: It's necessary to slow it down for this cut. It lines up nicely now, and it only takes a few seconds to make it perfectly square with a sharp knife. And for those who were wondering what this was all about: These are reproduction grips for an MBA Gyrojet rocket pistol: https://guns.fandom.com/wiki/MBA_Gyrojet
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