Pump
Roger,
I used the Europa balance, but modified by using 20 lb breaking strain nylon
fishing line as the pivot, rather than the nail as described in the manual.
The nylon line goes through the brass tube, and is stretched tight across
the frame. This was a suggestion from Dr Martin Armstrong, technical
director of SP systems (now Gurit) who make Ampreg resins. He pointed out
that if you use a nail for the pivot, the brass tube tries to roll on the
nail, resulting in a slight movement of the pivot point, and it also causes
significant friction, both resulting in inaccuracies.
I tested the balance against accurate pharmacy scales and found it was
accurate to less than 0.02 g when balancing a 100 g weight with a 25 g +-
small weights using the 4:1 ratio (ie 40 cm to 10 cm on the balance). In
practical terms, I can easily detect the effect of 1 drop of hardner when
nearly balanced. I expect that using digital scales would take longer, as
you have to accurately measure quantities of both resin and hardner, whereas
with the ratio balance you just pour roughly the amount of resin you want,
then add exactly the right amount of hardner. Having now got close to the
end, I have been amazed at the number of resin mixes needed - far more than
I initially envisaged - so any time saved here is significant.
I also always mixed the resin and hardner back and forward between the two
cups, rather than simply pouring the resin into the hardner as suggested and
then reusing the resin cup next time. I had thought, and Martin Armstrong
confirmed, that this can result in significant inaccuracies, depending how
long you spend draining the resin from the cup each time, as well as
allowing water (vapour) and CO2 into the residual resin in the cup.
I'll be interested to hear what others have found.
Regards,
Keith Hickling,
New Zealand.
Engine in, working on cowls.
----- Original Message -----
From: "Roger Lowe" <rlowe@speedway.ca>
Sent: Thursday, January 31, 2008 3:53 PM
Subject: Europa-List: Epoxy Measuring - Balances vs Digital Scale vs Ratio
Pump
>
> Hi, I've purchased a partially complete Europa a little over a year ago
> and had to put it storage until my garage/workshop was re-vamped in order
> to build the kit. It is now to a point to where I can start moving my kit
> into it and start working on it.
>
> I have question about the different devices used to measure the epoxy and
> wondering what most builders have done in the past. The cheapest of course
> is to make the Europa mechanical balance which should be no problem (is it
> quick and easy to use during a layup?) but I'm leaning towards either a
> Ohaus / Sartorius digital scale with a resolution of 0.01gm (do I need
> that much precision or can I get away with a lower cost 0.1gm unit?) OR a
> ratio pump like a Glenmarc Portionator MBT-JR from A/S which is the most
> expensive of the all the options (is it worth the cost for ease of use?).
>
> I live in Canada so I will be using Aeropoxy resin (100:27 by weight or 3
> to 1 by volume).
>
> I would appreciable any feedback/experience that you have that would help
> me make up my mind!
>
> Thanks, Roger
>
>
> Visit - www.EuropaOwners.org
>
>
>
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