Machine lash, acceleration, or what?

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Jeremy Schiffer
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Machine lash, acceleration, or what?

Postby Jeremy Schiffer » Wed, Mar 21 2012, 9:09AM

Look at the attached photo, and you can see what looks like machine lash causing the ends of this stretcher to be pretty sloppy looking. As I watch the machine cut, it seems to start (accelerate) and stop (decelerate) pretty abrubtly, which is causing what you see here, particularly noticible around a dado like this, because the movements are small. This seems to have cropped up only over the last couple of months.

Should I be concerned that the bearings or leed screws are wearing out? The machine (CS41-48) is just three years old, and prettly lightly used... I would hope it would last longer than that. Or, has something changed in a THM software update to change the acceleration and deceleration numbers? Would fiddling with those numbers help this problem? If so, how do I fiddle with them? I've never messed with them before. Using version 5.66 THM software.
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Josh Rayburn
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Re: Machine lash, acceleration, or what?

Postby Josh Rayburn » Wed, Mar 21 2012, 9:22AM

Jeremy, what is your tangency factor set at?
G09F__ ?
jnr
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Re: Machine lash, acceleration, or what?

Postby Forrest Chapman » Wed, Mar 21 2012, 9:54AM

It could be something else. I see that its only where the tool crossed the top of the tenon at the start and stop point. If your tooling is a little dull from running the mdf and you are cutting in climb cut it could be flexing out in the center but relaxing when it stalls on the ends of the cut. Forrest

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Re: Machine lash, acceleration, or what?

Postby Jeremy Schiffer » Wed, Mar 21 2012, 10:03AM

Hi Josh,

Tangency factor is 1.00, arc speed factor is 1.00, axis 1 acceleration is 25.00, axis 2 acceleration is 25.00, axis 3 acceleration is 100.00.
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Re: Machine lash, acceleration, or what?

Postby Josh Rayburn » Wed, Mar 21 2012, 10:12AM

That all looks good to me Jeremy, that was just a guess anyways.... Sorry I can't be of more help on this one. I bet Forrest is right - have you had the same result on VC material as well, and when cutting conventional?
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Re: Machine lash, acceleration, or what?

Postby Jeremy Schiffer » Wed, Mar 21 2012, 10:34AM

Here's another photo, this is a mortise cut. The arrows are the cut direction.

See how it seems to "whip" as it stops and makes the turn after the end of the slot? As if it accelerated too fast, and then stopped too abruptly, causing the machine to whip. I can see it happening if I watch the leg of the gantry on the X axis (the bearing on the rail), it seems to "bounce" a bit as it stops and changes direction.

Any other ideas? I'm thinking of changing the acceleration number, but not sure what to change it to, higher, lower? I don't even know HOW to change it... :oops:
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Re: Machine lash, acceleration, or what?

Postby Scott G Vaal » Wed, Mar 21 2012, 11:07AM

Jeremy,

You can lower the accelerations by adding in a ramp/acceleration macro. G800 through G809.

G800 is factory settings and each one above drops the acceleration by 10%. So, the G801 will reduce the accels by 10%, the G802 by 20% etc. until G809 by 90%.
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Re: Machine lash, acceleration, or what?

Postby Jeremy Schiffer » Wed, Mar 21 2012, 11:33AM

Thanks, Scott. I'll give it a try and see what happens!
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Re: Machine lash, acceleration, or what?

Postby Neville Bastian » Thu, Mar 22 2012, 7:52PM

Jeremy, We have had same result and just put up with it. Would like to correct it so will be interested in your findings.
If you could post your results that would be of interest.
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Re: Machine lash, acceleration, or what?

Postby Georgi Baltov » Sun, Mar 25 2012, 11:16AM

Scott G Vaal wrote:Jeremy,

You can lower the accelerations by adding in a ramp/acceleration macro. G800 through G809.

G800 is factory settings and each one above drops the acceleration by 10%. So, the G801 will reduce the accels by 10%, the G802 by 20% etc. until G809 by 90%.


Scott, where can we add that and how. We have the same issue.

Thanks

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Re: Machine lash, acceleration, or what?

Postby Jeremy Schiffer » Sun, Mar 25 2012, 10:04PM

I inserted G803 into the program after the G901 at the beginning. It definitely made a difference, almost totally got rid of the apparent lash. I also tried G805, but it wasn't noticeably different than the 803. I'm still cutting on this job, so tomorrow I'm going to fiddle with it some more, might even try some higher values and see what happens.

Does the G80X command stay active until the machine is reset/homed? What resets it? I'd like to know what to look for so I can make sure it is not being deactivated by another code during the program.
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Re: Machine lash, acceleration, or what?

Postby Scott G Vaal » Mon, Mar 26 2012, 7:51AM

Jeremy Schiffer wrote:I inserted G803 into the program after the G901 at the beginning. It definitely made a difference, almost totally got rid of the apparent lash. I also tried G805, but it wasn't noticeably different than the 803. I'm still cutting on this job, so tomorrow I'm going to fiddle with it some more, might even try some higher values and see what happens.

Does the G80X command stay active until the machine is reset/homed? What resets it? I'd like to know what to look for so I can make sure it is not being deactivated by another code during the program.


Jeremy,

A home will reset this back to factory settings. Also, a G990 will also set this back to factory. The G990 is called at the end of the program and between each sheet. You could use the sheet macros option on the settings dialog to get this added at the top of each sheet automatically for you. You can add the G803 as the header macro and you do not need to turn it off as it will do this automatically in the G990 called at the end.
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Re: Machine lash, acceleration, or what?

Postby Jeremy Schiffer » Mon, Mar 26 2012, 2:32PM

Here is the result of adding a G803... much better!
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Re: Machine lash, acceleration, or what?

Postby Neville Bastian » Sun, Apr 15 2012, 8:11PM

So Jeremy, have you done any more fine tuning or was the last post the answer to the problem?
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Re: Machine lash, acceleration, or what?

Postby Jeremy Schiffer » Mon, Apr 16 2012, 3:41PM

In CN preferences, I put G803 in the header macro so that it appears at the beginning of every sheet. The machine isn't quite as "jerky" now. I have also slowed the feed rate overall for most materials. Takes longer, but in the end there is less bit deflection, and less machine lash. Mind you, I already ran it slower than a lot of people do, I think. But anyway, I'm happy with it, now.
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