Thursday, September 16, 2010

Dealing with detaching rafts



In which your narrator seems to have come up with a way to prevent raft peel for ABS on an acrylic print table.

About two weeks ago, the rafts for my ABS prints started detaching from the right hand side of my print table.  I was losing one out of two to one out of three prints that way.  At first I decided that my acrylic print table had simply got too warped and I had too much variation in level on the acrylic.  I removed the acrylic print table and checked its flatness with a milled straight edge.

Indeed, it was a little warped so I used a belt sander on it till if was as flat as the milled straightedge.  That seemed to work for about an hour but I was soon back to where I began.  I then decided that the table was now adjusted properly and went to a great deal of trouble getting it so on my Rapman.  Same result.

In desperation I began to print on the left hand side of the print table and the problem went away.  It was still troubling, though.

On Tuesday, I finally caught on.  In the last weeks the weather had cooled to where the outside temperature was in the teens more often than not and dropped into the single digits {Celsius} in the early mornings when I began to work.  I looked at the printer table and noticed that the window I used to ventilate the work area was on the right hand side of the printer.  The next time that I had a raft detach I measured the acrylic work surface temperature with my IR thermometer and discovered that whereas it was about 25-26 C on the left hand side of the table the draft from the window dropped that to 22-23 C on the right hand side.  I was rather shocked that I got that wide a variation in surface temperature over a few centimeters distance, but I certainly did.

I closed the window and the peeling instantly stopped.

That remedy wasn't workable because of the ABS fumes, so I rigged a portable heat lamp onto my camera tripod to shine on the print table.




The radiant energy keeps the acrylic print table at 34-40 C with the window open.

I haven't had a raft detach since then.  I've done a few dozen prints, mind.

6 comments:

Viktor said...

... a clear point for a tempered housing :-D

Viktor

Giles said...

Hold on a sec, In your Previous Post you said you didn't have trouble with warping, and you didn't know what all the fuss was about. It seems now that you think that you need a heated bed, heated chamber, or heat lamp!

Forrest Higgs said...

Viktor: I don't think so. A tempered enclosure places all sorts of design restrictions on a printer. A small heat lamp which can be turned off as soon as a print is several millimeters high is much simpler.

Giles: The weather had been considerably warmer for some months and I actually wasn't having any trouble with warping.

As well, when a raft detaches, you don't get warping because the extruder starts pushing the print object around on the print table, which is to say, it's immediately ruined, not warped.

BodgeIt said...

Brrr I think I need a heat lamp feel like I'm warping out in the Home office.. !

Temp says 15c fells like a lot less.

Stove fixing components delayed by a week

Forrest Higgs said...

I'd previously used this one to keep my legs warm under the table I keep my workstation on during the worst of the bad weather in Winter. :-)

Joel said...

There's an interesting essay by Paul Graham about the effects of cold work space on innovation.

I take all of his writing with a grain of salt, but the case made in that essay has me more convinced that your work to make RepRap printers appropriate for marginal spaces is really important.