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View Full Version : Bill Young's Extruder, Take II - molding done!



johnm
05-27-2006, 03:34 PM
Bill -

Thank you SO much for this program! Rose got it dialed in and we cut one section of molding on Thursday night, chickened out about "where to start" mid-run, and started the job up again on Friday, finished it, and delivered it.

We cut eight 8' long sticks of molding 4" wide, with a profile over about 2+". Rose accepted the default stepover of .050, I think, and we were able to cut the remaining seven pcs. The material was a panel of Azek PVC trim board 3/4" thick.

We ran the spindle at 14k with a 1" ball nose bit at 6ips for the profile portion, and a 1/4 end mill for the cutouts and rabbets at 4.5 ips for most of the job - we've NEVER run that fast a feed rate, but the finish was fine and the bit never got over 80 degrees (f).

Even at that, though, the job took FAR too long for it to be profitable. Each section of molding took about a half-hour total - 20 min for the profile and 10 for a rabbet. We did have a couple of duplicate toolpaths, but nothing serious.

The question in our minds is how large a stepover we can get before we start to see some scalloping. I guess we could speed the feed rate up some more, but we are a bit chicken... nonetheless, it would be nice to find a way to speed the job up.

The only other issue is that the shop is FULL of snow... The chip collector was working, but the static was repelling the shavings all over the place.

Anyway, here are some photos of the work.

Thanks again SO much for all of your help!

John Moorhead
Rose Davidson
Sleeper Woods Design



4858
4859
4860

Brady Watson
05-27-2006, 07:40 PM
John,
A good rule of thumb for 3D stepover values is between 8-12% of the bit diameter. This of course depends on the shape you are cutting. (A raster tp on a donut shape would require a tighter stepover because of the scalloping in the XZ plane)

On the question of speed, if you are running in the Y direction you are going to be pretty limited since the tool will go into 'ramping mode' and never get over 4IPS (guessing). If you ran the tool along the X direction, then I would say that you could probably run @ 8 to 10 IPS. There would be no change in Z during the move, until the tool came to a stop, moved the stepover distance in Y and then ran down the other end of the workpiece.

Using the extruder you are limited in this aspect...but I suppose it is better than not being able to do the job at all! They look good!

-Brady