Square coner parts being created with round corners

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hlyman
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Square coner parts being created with round corners

Post by hlyman »

Vcare Wizard, or anybody.

When I load a dxf part with square corners it shows correctly in 2D. When the toolpath using outside machine vectors is created it shows square corners but saved in Sherline (mm) the g-code is always created with rounded corners. I need square corners, how do I fix this bug? Attached is the Cut2D file.

hlyman
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Adrian
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Re: Square coner parts being created with round corners

Post by Adrian »

I think you're getting the toolpath confused with the result. The toolpath shows rounded corners because a round tool has to move that way to create square corners. The actual part will have square corners when you cut it.

If that's not the case and you mean you are actually getting rounded corners on the part you physically cut out then the problem is most likely the acceleration/ramping settings on your machine and it's not slowing down enough on the corners.

JimG
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Re: Square coner parts being created with round corners

Post by JimG »

hlyman wrote:Vcare Wizard, or anybody.

When I load a dxf part with square corners it shows correctly in 2D. When the toolpath using outside machine vectors is created it shows square corners but saved in Sherline (mm) the g-code is always created with rounded corners. I need square corners, how do I fix this bug? Attached is the Cut2D file.
That looks correct. The toolpath on an external corner (270 degree) will take the path of an arc with the centre of the arc radius on the point of the corner and the result will be a square corner cut on the material. There will be a radius on the internal corners (90 degree) dependign on the radius of your cutter.

Jim.

chrismartin
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Re: Square coner parts being created with round corners

Post by chrismartin »

I have a glitch, well two glitches actually, that I'd like some advice about.

1. when pocketing, on two corners of the four, the machine rounds out the corner, and on the other two goes into the corner as it's supposed to. I have to do a climb and conventional cut one after another to get all four corners cut out square. What's happening here?
2. The machine will arbitrarily either gain or lose about 5mm of z height once you've pressed start. I have to press start, wait for the machine to begin the move, then press stop, go to zero and check the z... every time I start a move. You can imagine it's pretty annoying! Sometimes it drives straight into the material...which is not catastrophic on most materials, but when I'm using aluminium and a small bit... that's the end of the bit. Any ideas?

I use cut 2D with Mach 3

Chris

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glenn
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Re: Square coner parts being created with round corners

Post by glenn »

Hi Chris,
You have a mechanical issue. It could be the router bit is slipping in the collet, the motor linkage (lovejoy couplings) is slipping,
or you have the z axis motor losing steps. It sounds like you are losing steps to me. To fix this, you should first go into mach , config, motor tuning, z axis, slow down its' velocity -waaay down 50% or more to find a speed that absolutely misses no steps.
Run through several files cutting air, then return home, check z axis for accuracy, then repeat the process 10% faster each test until the z axis fails (this is what you need to find out!)- then back it off maybe 20%.
Now, this is probably the fastest this axis should ever run. If you need it to run faster, you may have to replace this z axis motor with a stronger(larger) one until you are happy with its' speed.
I never get the speeds from my z axis that I would like, but I settled for a slower speed that never misses a step- after all, accuracy is more important than speed. The speed can be fixed when I upgrade my cnc router or its' components.
Glenn

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zeeway
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Re: Square coner parts being created with round corners

Post by zeeway »

Regarding your corner issue...you should be able to get square corners on the external side. If you cannot (and you are using Mach3), you should make sure under the General Configuration scree, that you have exact stop checked and not constant velocity.

Angie

chrismartin
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Re: Square coner parts being created with round corners

Post by chrismartin »

Hi Glenn,
I don't think it can be a mechanical issue, at least nothing like slipping linkages or collets. This is a problem I've been working around for quite a while and meaning to find a solution to. I don't think I can be losing steps because the motor only does it at the point where I start a new job, and never again until I get the next new job into the system. On the occasions that I have lost steps in the past, it's been because I've pushed the acceleration/speed on one of the other axis, and you get a horrible noise that goes with it. The Z axis never makes any noise when it does this... However, I'll try what you say and see if it helps....It may be that the free running speed at that point is higher than at any other time.
Thanks for your speedy feedback, very much appreciated and I'll let you know if you're right.
Chris

chrismartin
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Re: Square coner parts being created with round corners

Post by chrismartin »

Hi Angie,

I am able to get square corners on the outside cuts... no problems. As I said, the weird thing about this is that it's only on two of the four sides of a cut... I wonder if that's got something to do with acceleration and deceleration?

Thanks for your speedy response Angie, I appreciate that.

Chris

chrismartin
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Re: Square coner parts being created with round corners

Post by chrismartin »

Another thing that just occurred to me Glenn is that if it was 'losing' steps, it wouldn't sometimes 'gain' 5mm instead would it?

Chris

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Adrian
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Re: Square coner parts being created with round corners

Post by Adrian »

If you're running Mach3 a lot of people seem to have issues with the CV settings rounding off corners. Might be worth searching for that.

chrismartin
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Re: Square coner parts being created with round corners

Post by chrismartin »

Thanks Adrian, what are CV settings? Is the problem within Mach 3 then do you think?

Chris

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Adrian
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Re: Square coner parts being created with round corners

Post by Adrian »

CV stands for constant velocity. I'm not a Mach3 user myself but I've read several threads on the forum from people who have had similiar issues to yours and changing the CV settings solved it.

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glenn
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Re: Square coner parts being created with round corners

Post by glenn »

Hi hlyman,

Did you get all sorted yet?

If not, It looks like what Angie and Adrian are suggesting with the cv option could round off your corners-

ScreenHunter_01 Jun. 18 08.11.gif


http://www.machsupport.com/forum/index. ... 959.0.html






Chris,

You have me stumped on why your axis loses 5mm. Is there something causing friction or rubbing near home position- a vac hose, wiring, or bolt head?

Glenn

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Adrian
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Re: Square coner parts being created with round corners

Post by Adrian »

Oops. Didn't spot that Angie had already suggested it.

KatoCNC
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Re: Square coner parts being created with round corners

Post by KatoCNC »

zeeway wrote:Regarding your corner issue...you should be able to get square corners on the external side. If you cannot (and you are using Mach3), you should make sure under the General Configuration scree, that you have exact stop checked and not constant velocity.

Angie
Glad I found the post...same issue I was having...I"m buyin what your sellin...lol...thx

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