gr/ml of red:cherry?

A 1:1 mix of Red and Cherry, yielding a lost wax capable resin tuned for 30 - 70 micron slice thickness
Chris Botha
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gr/ml of red:cherry?

Post#1 » Wed Jul 13, 2016 6:10 pm

Hi All,

I followed a few threads which indicated that resin has a gr/ml of 1.10 (pic100 is 1.187 for example)

However... in a few experiments i find this number 25% low at about 1.375... Can anyone confirm the actual gr/ml?

If it is in fact 1.10 then i have to go grumble on the Rhino forum about their volume routines... I say this because our calculations on this same part in a different resin where also about 25-30% out.

Alternately there is a wall thickness bleed making parts heavier than than they should be and we need to account for that in the original model.

See video for one of our experiment parts.

https://www.youtube.com/watch?v=3P3nRML ... e=youtu.be

Thanks :)
Matrix8.0, Rhino5, 3DCoat4, 5 Axis MinitechMinimill2, Envisiontech Perfactory, B9 1.2.
Be the Shepherd, or be the Wolf... Just never be the Sheep.

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Robert Howle
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Re: gr/ml of red:cherry?

Post#2 » Wed Jul 13, 2016 10:15 pm

You can get bleed from the MSM being a little to high. Actually the best and most accurate prints come with really great focus and zoom settings (projector calibration), and the minimum MSM to get good table attachment and subsequent layers to bond.

As far as specific gravity (weight per unit volume) of the B9 resins go, I use 1.1 as sort of a standard SG to calculate metal weights (wax being 1.0, or same as water). All SG numbers are just comparisons to the SG of Water.

I have always found the metal weights calculator in Matrix/Rhino to be off. Also is the most accurate if every intersecting solid is booleaned to make one solid. I just weigh my cured prints and X .9 to get a wax/water equivalent, then X specific gravity of the metal to be used. Then sprues and drive weight of course.

Here is the metals chart I have been using for over 35 years. Just sharing this info and charts again for the newbs at casting in the group. Chris, I am sure u are aware of all this.

Robert Howle.

metal 1.jpg

metal 2.jpg
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Chris Botha
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Re: gr/ml of red:cherry?

Post#3 » Thu Jul 14, 2016 12:29 am

Hi Update

The part is now fully cured, and separated from supports now. still 1.23x too heavy from cad weight. so not build platform thickness issue. Focus is good, size is within 1% from design.

Our pic100 works out fine at advertised 1.17 on our ET's.

I will simply adjust my setting up to 1.2 for b9 and move forward..
Matrix8.0, Rhino5, 3DCoat4, 5 Axis MinitechMinimill2, Envisiontech Perfactory, B9 1.2.
Be the Shepherd, or be the Wolf... Just never be the Sheep.

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Robert Howle
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Re: gr/ml of red:cherry?

Post#4 » Thu Jul 14, 2016 9:51 am

When u cast and clip the B9 print would u take the time to weigh and compare to the cured print. A larger piece like that would certainly tell us more. Would be curious. Might give all of us more insight on larger stuff.

Thanks,
Robert
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Chris Botha
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Posts: 90

Re: gr/ml of red:cherry?

Post#5 » Fri Jul 15, 2016 8:39 pm

not sure where the error is, but moving my script to 1.2 seems to have gotten a more accurate result.

we are a mass manufacturer (2 million pieces per annum, and at least 400 new models being printed each month) so our general weight category for gold goods is under 3.5gr.. a 10% at that weight is negligible and easy to rectify in cleanup.

We havent really paid attention super accurate weights until this thing started with these bangles and we had a cad weight of 45gr but a part weighing 61 grams... its my job to isolate and fix that discrepancy, so its part rhino volume calculation factor (which i believe is accurate in "simple" geometry, but can induce as much as 5-10% error in more complex parts with internal convolutions)

Our magics install and our rhino report different volumes on the same parts -but- to qualify, the difference is noted AFTER we clean the models in magics fixer. so some degree of difference of weight in nurbs volume, vs the weight of the horrific mesh rhino spits out vs the cleaned mesh from magics. We now use 3dcoat exclusively to voxelise the mesh, then bring back into rhino to volume and the error is marginalised at about 1.5 to 2% on large parts and a negligible amount on smaller models.

next up is the values used in Matrix as "standard" SG. of course the software is written to use the most common SG's but they do make provision for editing the sg to match your actual sg. so an exercise to measure volume on parts cast was started and our own SG's fixed. now output weight is closer than ever.

the last part of this exercise was determining why the weight goes up in the resin.. for both the pic 100 and b9 resin i added roughly 10% to SG and now we are withing total error <2%.

I dont imagine the SG of the b9 resin is innacurate, i ascribe the error to small difference in scaling and bleeding. Again in small parts >4gr this will have gone unnoticed previously.

to speed up the process of calculating these things i wrote a grasshopper script to adjust a master list of YG, 925, brass and resins, and the team are tracking predicted vs actual. once they values on these are locked down we will add SG for white and rose golds, (we have 4 rose golds and 3 white golds... every step a step closer to dialling out errors... as you might imagine a 0.1gr overshoot is nothing when you selling that one ring at retail, but on a delivery of 50 000 pieces it will add up..

script is available in my grasshopper thread in 3dcad, cannot claim ownership as its assembled from bits of scripts scrounged from GH forum. looks like so. I wrote it because the designers/cad operators are too busy to have to leave rhino to use my excel sheet calculator. Script will eventually update to factor cad>resin>cast>vulcanise>cast>cleanup weights. aim is to get under 0.1% error margin.

https://www.youtube.com/watch?v=GUJTfoqmJhk
Matrix8.0, Rhino5, 3DCoat4, 5 Axis MinitechMinimill2, Envisiontech Perfactory, B9 1.2.
Be the Shepherd, or be the Wolf... Just never be the Sheep.

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Metalcaster
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Re: gr/ml of red:cherry?

Post#6 » Fri Jul 15, 2016 9:35 pm

I have noticed discrepancy in weights depending on which software is used ... I get a different weight in Rhino then I do using 3Design. Which one is correct :?:
Ah!
To Know that.... you need to know the alloy used in the original software calculations... and that software as written, will only be exactly correct when the Jewelry is cast with that exact alloy.
So the work you are doing is definitely beneficial.

In the 1980's I was casting around 100,000 pieces a week in gold... Mostly super light stuff/ high volume. Also around 40,000 ++ in sterling... We weighed the metal going in and coming out of casting, after cleaning etc...
I built filters/ traps all over to recover any gold/precious metals....

Went to using a waterwheel grinding system so that all grinding was washed into a recuperation bucket... allowing quick gold recovery. The other benefit is the piece does not get hot when grinding. If you are not doimg that, you should give it a try.

Sounds like you a have a lot of work ahead ! Good Luck!

Chris Botha
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Re: gr/ml of red:cherry?

Post#7 » Fri Jul 15, 2016 10:21 pm

..and complicated, because our current scale factors allow for pretty accurate lightweight model weights once you factor shrinkage and cleanup removal.. so i have to setup categories of product by weight with sliding scale factors otherwise those model all come out underweight.. sigh :roll:
Matrix8.0, Rhino5, 3DCoat4, 5 Axis MinitechMinimill2, Envisiontech Perfactory, B9 1.2.
Be the Shepherd, or be the Wolf... Just never be the Sheep.

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Metalcaster
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Re: gr/ml of red:cherry?

Post#8 » Sat Jul 16, 2016 11:01 am

Another issue I have found is occasional trapping of air or gas in the printed prototype... not sure how that is happening... That could account for the Printed piece not weighing exactly what it should. Seems to happen more often when I print flat on the table.

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akgold
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Re: gr/ml of red:cherry?

Post#9 » Sat Jul 16, 2016 2:19 pm

Metalcaster wrote:Another issue I have found is occasional trapping of air or gas in the printed prototype... not sure how that is happening... That could account for the Printed piece not weighing exactly what it should. Seems to happen more often when I print flat on the table.


I too have ran into this recently
It makes me wonder if there are air bubbles trapped in the layers but I just don't see how it could happen with the movement it should release them unless when the Z raises after clearing the window it is going above the resin and coming back down through the resin with a air being pressed down on the surface of the window. Maybe the resin levels would be better to be higher than the Z lift so there is no clearance between the last cured layer and the resin
I'm so far behind I think I'm First !!

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Robert Howle
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Re: gr/ml of red:cherry?

Post#10 » Sat Jul 16, 2016 4:29 pm

The only time I have seen the gaps or missing partial layers is on flat, snapped to the floor items. I'm wondering is it is a slicing thing. Usually small spot do just wax it up, but would like to know what causes it. The mystery is that it is not in the early layers.

Robert
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