Marshall Burns wrote:
>
> Phil,
> Your numbers below seem to suggest that the SLA is much more accurate than the Sanders and that the Actua is almost as accurate as the Sanders. Do you agree with this interpretation of your data?
Marshall,
I believe that SL is more accurate than Sanders or the Actua at the
moment.
> There has been little if any discussion on this list of the difference
between precision and accuracy. Precision relates to the ability to make
fine details; accuracy relates to the correctness of dimensions. They
are related but they are not the same thing. It may be that the forte of
the Sanders machine is not accuracy, but precision. Yet I wonder why
this would be the case. Are there internal stresses induced during
drop-on-drop deposition that are resolved through creeping distortions?
Internal stresses used to cause terrible inaccuracy in SLA models but
improved chemistry and process dynamics have drastically reduced those
stresses. Is there similar work needing to be done on drop-on-drop
techniques such as in the Sanders machine? But still, why is the Actua
coming out ahead?
Marshall,
I would agree that the Jetting machines are generally more suited to
fine features but as we have small spot work being done by Norma Jean
Iveson and Paul Bernard this is now changing.
In the long run I see the jetting techniques being as accurate if not
more so than SL. I think it is more a case of machine design rather than
the nature of the process itself.
The Actua did look better than the Sanders but this may be due to the
machines used. I do not think you can say that Actua is more accurate
than Sanders or vice versa.
In the long term I see Jetting machines taking over!!
Phill
>
> Marshall Burns
>
> Professor P M Dickens wrote:
>
> > Marshall,
> > It might be worth looking at a paper that we published at the Rapid
> > Tooling & Manufacturing conference in Denmark last year. - "The accuracy
> > of RP models for Investment Casting of Injection mould Tool Inserts",
> > Heather Almond et. al.
> > I give a few results of accuracy tests:
> > Sanders
> > epsilon 90 = 0.35mm, 39% of error values within +/- 0.1mm, max deviation
> > = 0.7mm
> > Actua No.1
> > epsilon 90 = 1.0mm, 38% of error values within +/- 0.1mm, max deviation
> > = 1.6 mm
> > Actua No.2
> > epsilon 90 = 1.2mm, 26% of error values within +/- 0.1mm, max deviation
> > = 1.7mm
> > SLA QuickCast 1.1 No.1
> > epsilon 90 = 0.05mm, 82% of error values within +/- 0.1mm, max deviation
> > = 1.1mm
> > SLA QuickCast 1.1 No.2
> > epsilon 90 = 0.05mm, 86% of error values within +/- 0.1mm, max deviation
> > = 0.02mm
> > SLA QuickCast 2.0 No.1
> > epsilon 90 = 0.2mm, 44% of error values within +/- 0.1mm, max deviation
> > = 0.4mm
> > SLA QuickCast 2.0 No.2
> > epsilon 90 = 0.1mm, 70% of error values within +/- 0.1mm, max deviation
> > = 0.3mm
> >
> > Phill
> >
> > Professor Phill Dickens
> > De Montfort University
> > Leicester
> > England
> >
> > Marshall Burns wrote:
> > >
> > > Dear Dan,
> > >
> > > Okay, but it would be interesting to know what are the tolerances that
> > > you guys who are actually using the various machines are accustomed to
> > > getting from them? Some people say that an important reason for choosing an
> > > SLA today is that the machine is mature and gives good accuracy. How good?
> > > And can it be as good as Sanders?
> > >
> > > Marshall
> > >
> > > DANIEL CHARLES DAVIS wrote:
> > >
> > > > Marshall,
> > > >
> > > > That's what I get for answering before my morning coffee. Two
> > > > thousands......twenty thousandths.......what's a few thou between
> > > > friends. Sorry for any confusion caused by my brain failure.
> > > >
> > > > This thread is timely for me as I was just going over tolerances here
> > > > for some plastic parts. I'm sure you realize that in the auto industry,
> > > > especially Asia, our tooling is held to 0.1-0.2mm (or even looser) for
> > > > 90+% of what we make. That leads me to wonder: how many consumer
> > > > product industries REALLY need to hold accuracy to 0.05mm overall? Of
> > > > course that can get us into a whole debate regarding engineering
> > > > practices ala Taguchi methods and "robustness." This is the wrong forum
> > > > for that although I would be happy to discuss in private.
> > > >
> > > > Regards,
> > > > Dan Davis
> > > > Head, RP&M Division
> > > > PROTON Berhad
> > > > Hicom Industrial Estate
> > > > Batu Tiga, PO Box 7100
> > > > Shah Alam, 40918 Selangor MALAYSIA
> > > > +60 3 515-2380
> > > >
> > > > > ----------
> > > > > From: Marshall Burns[SMTP:marshall@ennex.com]
> > > > > Sent: Friday, June 05, 1998 10:36 AM
> > > > > To: DANIEL CHARLES DAVIS
> > > > > Cc: 'James Theoharris'; 'RP-ML'
> > > > > Subject: Re: Too many SB's & a little late
> > > > >
> > > > > Dan,
> > > > >
> > > > > Would you please clarify? You seem at first to be implying that
> > > > > machines
> > > > > other than the Sanders can hold 0.002 inch tolerance. But then your
> > > > > data
> > > > > talks about holding 0.010 to 0.014 inch. Accuracy has always been a
> > > > > complex
> > > > > issue. What point are you actually making here?
> > > > >
> > > > > Marshall Burns
> > > > >
> > > > >
> > > > >
> > > > > DANIEL CHARLES DAVIS wrote:
> > > > >
> > > > > > Hmmmm, two thousandths of an inch. Are you saying that all RP
> > > > > equipment
> > > > > > except Sanders is only accurate to that or is this only the Actua?
> > > > > >
> > > > > > Of course the Actua (and Z-Corp and other concept modelers) will not
> > > > > > hold tooling tolerances. If we are talking about SLA & LOM, we
> > > > > > consistantly hold 0.25-0.35mm (0.010-0.014 inch) tolerance evben on
> > > > > full
> > > > > > envelope parts. I have many CMM printouts to support that. Maybe
> > > > > the
> > > > > > folks in question just don't know how to dial in their machines?
> > > > >
> > > > >
> > > > >
>
> --
> Marshall Burns
> Marshall@Ennex.com
>
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