Mk7 with pla
Chris Gray
Sent from my Windows Phone
doug metzler
bearing as your pressure plate. I've got bearings the perfect size
and would be happy to donate a few, but you'd have to heavily modify
the housing and adjustment mechanism.
You might try replacing the delrin plunger with a UHMW plunger or
maybe Nylatron.
the PLA is much higher density than ABS so maybe you need to dial in
more pressure than you're used to. Also it might be possible that
you've gummed up your drive gear and need to open it up and clean it
out?
DougM
Vadim
got new a shiny makerbot kit with mk7 and was planing to put all it
together this week end :)
Paul Connor
suitability for injection molding (and perhaps ease of assembly), I
don't see the advantage of switching from a threaded - and therefore
adjustable - plunger to what amounts to a fixed plunger. Looking at
the the released model of the Mk7, it appears that the original intent
was to have a spring-loaded plunger which at least acknowledges the
requirement for tuning the plunger force and/or gap between plunger
and drive gear. I would be tempted to try modifying one side of the
injection-molded drive blocks to accept either a cut-down plunder with
a setscrew behind it or a swivel-ball setscrew such as 92123A103 from
Mcmaster-Carr. If it doesn't work you can always revert back to the
unmodified side and the standard plunger stack. I'd think it might be
as easy as drilling and tapping the assembled blocks or using a
threaded insert. Better yet, modify the printable drive block and
leave the stock block unchanged.
On the other hand, I I'm not sure I follow the objection to delrin as
a material for the plunger. Delrin (polyacetal) is rigid,
temperature-stable at the temps we care about, and fairly low
friction. Why would UHMWPE or Nylatron be a noticeably better choice?
Paul
doug metzler
work very well, so UHMW might be ever so slightly better than delrin,
but maybe not.
But I think the root of the problem is that the PLA being an
inherently harder material will not allow the roller to bite in as
much and therefore will require more pressure to create reliable
travel, and thus increase the stiction problem.
Ball bearings, which are cheap and abundant, have zero stiction, and
are not substantially more difficult to implement. The UP! print head
uses a fixed ball bearing and the stepper is fixed, and the
flexibility between the two is provided by reliefs cut into the
housing itself.
I have a selection of the swivel-ball setscrews you mention below and
the ball does not roll freely. They are designed more as stops - for
instance in the case where you've got something that you want to lock
in place, like a drawer when it closes. But because the ball is
stainless steel I think you are correct that they would be better than
the Delrin.
I don't have an MK7 handy to try it on but I'd be interested to see if
that solution solves the problem. I'll even loan one of them out to
someone if they want to try it, but unfortunately I'd have to get it
back as it belongs to work.
I personally think we as a group should design our own custom Seattle
print head with spring loaded driven rollers on both sides. We have
the advantage of not having to mass produce them so could spend a
little more time on design and money on parts :-)
Thanks,
DougM
Matt Westervelt
Chris Gray
Sent from my Windows Phone
From: Matt Westervelt
Sent: 10/28/2011 5:17 PM
To: seattle...@googlegroups.com
Subject: Re: Mk7 with pla
