Sumi von Dassow on sun 11 oct 09
I have a North Star Extruder with an expansion box, which was a new desig=
=3D
n
just released in April 2009. It uses the Big Blue dies. I have used all t=
=3D
he
dies successfully except for one. The large hollow square die produces an=
=3D
extrusion with a ragged tear on both corners, where the clay splits as it=
=3D
goes past the bracket holding the center piece onto the outer piece. It
appears that the bolt holes are just too close to the edge of the die
opening and the clay splits around not only the bracket but the bolts and=
=3D
this split doesn't rejoin as the extrusion exits the die. Has anyone else=
=3D
experienced this problem - if I have even described it in such a way that=
=3D
you can understand it! - and is there a solution? I emailed North Star an=
=3D
d
got no response.
David Hendley on mon 12 oct 09
Hi Sumi, and welcome to Clayart.
Yes, it sounds like the clay is not healing back together after being
split by the bracket. I do not like the North Star die design because
it does not allow enough space between the bridge and the die
for clay to be compressed back together. Sometimes pieces that
look fine will come out of the glaze kiln split along the lines where
the clay was cut by the bracket. I would prefer to have at least
an inch of space between the bridge and the die, which is why I
use U-bolts as the bridge in the dies I fabricate. Unfortunately,
the barrel of the North Star is so short that there is not enough
room to use this design.
Short of fabricating a new, taller bridging bracket, the only possible
solution I can think of would be to use softer clay and hope that
the soft clay joins back together more easily. I would certainly
try to contact North Star again.
David Hendley
david@farmpots.com
http://www.farmpots.com
----- Original Message -----
From: "Sumi von Dassow"
I have a North Star Extruder with an expansion box, which was a new design
just released in April 2009. It uses the Big Blue dies. I have used all the
dies successfully except for one. The large hollow square die produces an
extrusion with a ragged tear on both corners, where the clay splits as it
goes past the bracket holding the center piece onto the outer piece. It
appears that the bolt holes are just too close to the edge of the die
opening and the clay splits around not only the bracket but the bolts and
this split doesn't rejoin as the extrusion exits the die. Has anyone else
experienced this problem - if I have even described it in such a way that
you can understand it! - and is there a solution? I emailed North Star and
got no response.
Larry Kruzan on mon 12 oct 09
Hi Sumi,
There are a lot of variables with this problem so I'll just try a couple
suggestions I use the most and let others who own this rig address others.
This being Clayart I'll add a personal observation or two as well - only
worth what you pay for them!
First of all, clay body could be the problem if you work with a stiff or
course clay. Softening the clay will help it to heal together after passing
the brace. Slowing the extrusion can also help - I think it allows the clay
more time to compress together after it passes the brace.
Corner tearing is almost always a sign of a stiff clay.
You also may need to make a longer extrusion. Short, large diameter
extrusions also just don't have time to heal. I typically make a long first
extrusion to get past that "fish mouth" you see in the beginning.
I own the Northstar 4" extruder without the expansion box and a Bailey Powe=
r
Extruder (with 9" chamber). I have found the Bailey and Northstar make fine
hollow extrusions but I had to adjust my clay density in the beginning in
order to get the best forms.
Softer seems MUCH better for extrusion than the way I prefer my clay for
throwing. The Northstar dies have a brace that is nested into the die body
giving very little time for the clay to heal after passing the brace.
Lastly I'll put a plug in for a series of DVDs by one of our own. David
Hendley has produced the finest DVDs covering extruding that I have seen.
Some of the best produced videos around, very professional. Not only does h=
e
cover a lot of great techniques but he address many problems that we have
with these machines and clay. I consider them a "must have" for anybody eve=
n
thinking about buying an extruder. Plus you get some really good non
commercial music. Music, drama, comedy, gratuitous clay sex (not really),
it's all in there!
Larry Kruzan
Lost Creek Pottery
www.lostcreekpottery.com
-----Original Message-----
From: Clayart [mailto:Clayart@LSV.CERAMICS.ORG] On Behalf Of Sumi von Dasso=
w
Sent: Sunday, October 11, 2009 7:50 PM
To: Clayart@LSV.CERAMICS.ORG
Subject: problem with North Star Extruder expansion box
I have a North Star Extruder with an expansion box, which was a new design
just released in April 2009. It uses the Big Blue dies. I have used all the
dies successfully except for one. The large hollow square die produces an
extrusion with a ragged tear on both corners, where the clay splits as it
goes past the bracket holding the center piece onto the outer piece. It
appears that the bolt holes are just too close to the edge of the die
opening and the clay splits around not only the bracket but the bolts and
this split doesn't rejoin as the extrusion exits the die. Has anyone else
experienced this problem - if I have even described it in such a way that
you can understand it! - and is there a solution? I emailed North Star and
got no response.
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