RE: SLS Somos problem

From: Long Phan (
Date: Thu May 14 1998 - 22:08:31 EEST

I have to agree with David Leigh. The problem is mainly due to the roller bumping into the part. Changing the layer thickness somewhat reduces the problem, but decreases part resolution. Currently, at Plynetics Express we are building SLS Somos parts between .005"-.007" layer thickness with a fairly good success rate. I believe the key to prevent the roller diameter from increasing in size during the build is to start out with a super clean roller and scrapper. Therefore, during the machine preparation make sure to dress the roller and have the scrapper sit "water-tight" (hint: you should not be able to see between the scrapper and the roller) against the roller. This will help cut down the powder from accumulating on the trailing side of roller during build.
The bottom line, this is a roller issue and until the problem is fixed, don't count on the build to come out every time.

Long Phan
Plynetics Express Corporation
Tel 503-531-2701
Direct 503-531-2707
Fax 503-629-6208

Sent: Thursday, May 14, 1998 3:36 AM
Subject: Re: SLS Somos problem

Somos Problem . . .

The issue is that the roller is bumping the part . . . This is why
DTM recommends .008" layers. This doesn't do much for part
definition in a material that is not real good for definition to
begin with.

So, why is it bumping??

I have not noticed any curl in the parts, so the parts are not
"jumping" up in front of the roller. So, what could it be?? The
roller is hitting the part, not vice versa. The roller has not
changed and the powder is not sticking up out of the bed, so . . .
the powder is sticking to the roller. If you notice, the part starts
fine, but as static or adhesion starts, the build will crap out
because the effective roller diameter has increased and is now
interfering with your part.

Building a base won't work because the part is not curling. Lower
laser power won't work, because the roller is the issue. So, fix
your roller issue, and you've fixed the problem. That's about all
the free advice you'll get from this here yocal.

David Leigh
Harvest Technologies
Rapid Prototyping Services
(254) 742-1822

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