Downtime

[zorlack]

I'm in between shows right now, but I just had some new gear show up. A collet from Precision Bits and some new round-nose bits.

I'm not the kind of person that can have new toys and then wait for an occasion to use them.


1773

So I carved reddit (http://www.reddit.com)'s alien mascot out of pink foam.

Shot some video (http://www.youtube.com/watch?v=44xemf1CYhY) just for the heck of it.

-D

[david_gardner]

Watching your video I realized how smooth your prt runs. Mine seems to "slam" at each end of a raster pass with enough force to shake the table. Yours seems to change direction very smoothly.

Any ideas what could be causing my "slamming"?

Care to share your ramp values?

[zorlack]

Hmm... I'm afraid I don't have any magic to share.

I'm using the default values out of the 48x96PRT config file that ships with the Shopbot software.

I was running the bot flat out during this cut. I had the XY speed at 6IPS and the Z speed at 3IPS. There was definitely no slamming...

Are you using more aggressive ramping values?

-D

[david_gardner]

I've tried everything from the default values to Brady's aggressive values and it just bangs back and forth. I don't think the banging is hurting the machine but it is definitely hitting hard enough to leave marks in the workpiece.

[cutitout]

I have a bounce at the end of the raster also but I am on a wooden table and it has had it share of "G" pulling it in all directions.

Was the video run at a faster speed? I am running at 6IPS and it does not look as quick.

what software and post did you use?

Thanks

[zorlack]

David, if you rotate the raster direction by 90 degrees do you get the same shaking?

Eric, Yeah the video is sped way up... I didn't want to bore people by making them watch two hours of machining hehe.

I'd say its probably running the video at 4x to 6x.

[cutitout]

thought it was fast -- to bad I was hoping you had the magic settings for foam cutting speed.

[david_gardner]

Yes, it slams in both directions.

[magic]

change your ramping speed.

[zorlack]

Well, I'm not an expert on these matters, but it brings to mind a few questions:

Does changing the ramping speed have any noticeable affect on tool movement?

Is it possible that the ramping values are being ignored for some reason?

If you used a ridiculously slow ramping value, would the tool obey, and would the slamming stop?

[david_gardner]

I have never tried a ridiculously slow ramp speed. I've tried the factory default and Brady's supped up ones with no noticeable difference.

[coach]

David, I was cutting 3D files in foam. I was getting a lot of the banging you mention. I was moving x and y at 7 IPS and Z was 1.7 IPS.
Ryan at shopbot told me I could try 10 in x & y and 10 for the Z. I could not believe how smooth it cut. Literally no banging.
I don't know what you should run your machine at. I have an alpha.
David

[david_gardner]

I also have an alpha. I usually run my 3D files at 2-3 ips in x and y and .5 - 1 ips in Z but I'm cutting hardwoods. I'll try some test pieces where I run the Z speed closer to the x and y speed and see what that does.

[cutitout]

WOW -- would love to get speeds up that fast

I most of the time have a +/- 1/16 tolerance -- and would love to have the speed.