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Thread: Cast Blanks Brittle
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13th October 2013, 07:53 PM #1
Cast Blanks Brittle
Hi All
Ive been reading the casting threads and have tried a few myself.
Give me an excuse to hide in the shed ...
The only problem is the casting is brittle or not very strong compared to other plastic acrylics Ive brought.
What I do:
- Polyester resin and hardener from Fiber Glass International (called something else now)
- Pearl Ex
- Slimline pen kits
- Resin and hardener new and fresh.
- make 2 x 180mm long blanks at a time
- I cast and cut blanks and drill holes for barrels on the drill press
- glue in with industrial superglue
I use a plastic mould which I made out of old PE breadboards cut up and screwed together
When I drill the hole for the pen barrels on the drill press, I have to be so careful. Easily blows out ...
If I drop the blanks they can fracture or break
When I machine on the lathe it chips and fractures really easy
Very hard to machine on the lathe
- temp when casting 27-15C (Gold Coast Weather, September)
- Hardener - I don't do hot mixes, I find it takes about 2 hours to go gluggy
and 24 hours to be totally hard. Because of the sunny weather here I let them
finish off in the sun.
Any suggestions or is this normal for Polyester resin ?
PS Ive tried the same with no Pearl Ex - little difference
RandalIf it looks to good to be true it probably is !!
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13th October 2013, 08:59 PM #2
Basically yes. Sounds like you are on the right track. Less catalyst makes them less brittle, but by the sound of your times for setting, you are using the right amount.
Turning them is an art to a great extent. I tend to sand them roughly round first, using a disc sander, that helps. I DO NOT use CA to glue them in, I only use epoxy for all my pens. Although CA does work, it doesn't take too much of a catch or edge to chip out, especially if not glued all the way along the tube for support. CA also take a long time to go off at depth, the fast setting is only at the surface.
Sharp tools are a must.Neil____________________________________________Every day presents an opportunity to learn something new
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13th October 2013, 09:18 PM #3
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13th October 2013, 10:07 PM #4
+2 on this, also lathe speed should be high and tools sharp. I only use a sharp skew on my PR castings.
Regards Rumnut.
SimplyWoodwork
Qld. Australia.
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13th October 2013, 10:17 PM #5
howdy doody Randal
i agree with Neil but there is another thing that may have got you
when i first started casting i purchased some "Quality Casting Resin" instead of "Clear Casting Resin", hey i thought well if its quality it must be better, BEEP, Wrong answer, it had all the characteristics of what you described to the letter, this could be the problem, the resin had a blackish tinge to it straight out of the can
other than that i use 2% MEKP, you may get away with a little less but i don't think that will make a great deal of difference
check out the type of resin though i am guessing thats the prob
i hope this helps
all the best
MIKNo Result Without Effort
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14th October 2013, 07:29 PM #6
They are all on the Money with there comments when it comes to casting Neil has done plenty and has it down to a fine art also trevor (tdrumnut) has done a fair bit as well so it is all good information and it is just practice. As for the blanks being more brittle than the ones you have been buying the reason they are like that is they are a completely different product and type of resin. we are using a type of polyester resin and I am not sure what the other stuff is ? someone here may know more ?
Cheers Ian
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15th October 2013, 08:37 PM #7
Thanks
Everyone
Many thanks. Yep I do have a can of the Clear Casting Resin (not good one ) and one from Fibre Glass International - not sure what this one is .... I suspect Clear Casting as that is what I asked for (nothing on the can)...
Funny about the CA V Epoxy ... I agree I have had alot of failures with CA/wood and Acrylics over the years and have moved to the two pack structural epoxy - really annoys me when pens let go at the machining stage.
OK will try and let you know.
Also, about a month ago when I started I tried casting with different coloring things to see what it looked like. I tried lots of different stuff to see what colours etc worked - I tried everything from watery acrylics to nail polish .. some really interesting results. At the end of the day I found the cost of proper pigments etc where just as good for price and effect eg polyester pigments, pearl Ex I want to try adding power coating powder which seems to be used a bit by some of the posts on UTUBE ... still trying to get some from the local powder coaters..
Thanks for the links .. prices are good .... might buy some ....
RandalIf it looks to good to be true it probably is !!
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18th October 2013, 06:27 PM #8
Don't forget the full eye protection. You'll be using a white cane if you get MEKP in your eyes.
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19th October 2013, 08:19 AM #9
Thanks + more
Nasty stuff - will get the goggles
Randal
Also, a mate of mine has some clear epoxy which he uses for boats Kintrix 104 (I think) .. will see how that works. Apparently, Epoxy is alot cheaper these days - Alot has changed since the old Araldite ... shows my age...If it looks to good to be true it probably is !!
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