Problems with the Bio epoxy resin and other stuff...!

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robutacion

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Joined
Aug 6, 2009
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robutacion
Member

JoinedAug 6, 2009Messages6,278LocationAustralia - SA Adelaide Hills
Friday at 11:37 PM
Hi,

I also do some 3D printing and I made a honeycomb based from where I cast 5 blanks from but I didn't like the amount of time it took to print a slab 22mm high x 130x130mm square about 13 hours to complete the other issue that I didn't like was the fact that the honeycomb pattern does follow the round contour of the blank so it looks different as you turn it, I know there are designs where the same pattern is made in a circle where every hollow is the same but I didn't bother to look for it. 002.JPG

I was expecting that you would find a brass tube to the size you need from that mod I sent you to but that didn't happen, sorry. You may don't need to print the insert as I don't think that any of filaments available are strong enough to prevent the blank from bending, I haven't done any research on them but I just thought of something that could also do the job, I don't think they are expensive, I'm talking about the curtains down rods to help you open and close the curtains they are made of a clear solid and strong plastic, normally about 2' long or a little more, any curtain places should have them, I don't really know the technical name but I'm sure you can explain what they are if you know/seen what I'm talking about, in fact, I recall seeing them in older houses. and the best way to handle them is to actually centre them in the mold and pour the resin around it, any drilling will be done after turned, just an opinion.

The one thing that I keep forgetting to tell you is, for the epoxy resin blanks that tend to become a bit softer while turned on the lathe, one trick that works wonders is to put the blank in the freezer overnight to turn it the next day, the slow loss of temperature maintain a good stiffness on the blank and by the time you finished sanding, the blank should be back to ambient temp. Also, remember that most of the heat introduced to a resin blank while on the lathe is on the sanding stage particularly the dry sandpaper most of the sanding should be made with wet and dry sandpaper and lots of water after that is polishing. Keep the lathe at low speed the faster you more the more heat it will generate in a short period of time.

Now, I have tested your blank the only test I couldn't do what the hardness test on my Durometer, I used it some time ago and I probably left if on so today it didn't turn on, I thought that was the battery but I replaced it and still didn't work so I will try to find out what the problem is in the mean time you can see some tests I done for IAP so time ago with this instrument. Sothe tests I did was first the hand band test and that felt solid little movement, my temp was about 22C so fairly cool in a hot day that would be a different story.

I then tried the turning on half blank up to 19mm diameter and I noticed something that did show me that, there was far too much grey powder on that mix, which is called liquid saturation so, what it is is that any liquid only accepts a certain amount of powder, sugar, salt, flour and so many other possibilities but with powder what happens is some of the powder particles no long can mix/dissolve so, the undissolved particles float in the resin and set where they are but when you turn the blank, you start seeing the silverish powder spots that got embedded in the resin but not in liquid form, they stayed a solid material covered all around with the resin so cutting through it you see these unmixed bits of powder, 001.JPG that is one of the results of too much powder, the others are taking a lot longer to set and be less rigid/solid. The resin composition becomes altered/compromised somehow as a result, however, liquid dyes in excess tend to almost spoil the whole mix it may never dry.

I have sanded by hand with 120 dry sand sandpaper tom remove those pits/spots but after 1mm removed they were still there well not really, I have removed to ones showing in the pic buy more were underneath, this can show throughout the whole blank. When I finished sanding it I could start feeling the blanks to start wobbling slightly the temp from the dry sanding was enough to soften the resin, that was resolved when I went with the wet sanding with cold water I did only 4 grits 600, 100, 1500 and 2000 and then spread a bit of the Novus 2 polishing compound (only I use) and took it to the polisher and while it didn't shine as some other blanks I make but it was quite acceptable in my view, what do you think...?
002.JPG 003.JPG

So, apart from the issue of too much powder, this blank came out as it should hardness wise.

Hope this helps.

Cheers
George
 

robutacion

Member
Joined
Aug 6, 2009
Messages
6,493
Location
Australia - SA Adelaide Hills
JustLookin'

Well I had a rather slack today really. Have been 3d printing orders and getting stuff packed up to send, but did not go out to the workshop at all today.

I'm wondering if you can help me locate a set of TBC bushings. I did post on the forum, but no answer so far.
I'd like to get them locally is possible, and need them to be 5mm to fit inside the holes. Thought I might be able to get 7mm ones and cut them down, but can only seem to find the type that goes on a mandrel.
 
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