Casting polyester resin balls

[Ueee]

Hi,
rather than tacking this onto the end of Marks thread here: http://www.woodworkforums.com/f65/whats-good-material-making-round-knobs-154846/ I thought i would start a new thread.
On Wednesday i set to casting some knobs for Freddies table support adjustment handles and i would make some spare knobs and rod while i was at it.
I used Diggers brand casting resin and black oxide from Bunnings.
I mixed up 300g of resin and 100g of oxide. The mix was not quite the honey that Mark describes, but it was certainly "peaky". It been pretty cold here, well it was cold during the week but freezing yesterday (like 3 deg at 10am) and today, so i went for the recommended cold weather mix-2.5ml per 100 grams- that worked out to be 450 drops of catalyst- but i run out at 400 :((.
Now for the problem....80 odd hours later the mix is still tacky....overnight and i could have (slowly) pored the mix out of the molds. ###:? The resin was less then a month old, i thought i used plenty of catalyst, but no success. No spare toaster oven to be had.....and my only other option is my heated seedling tray.......which is full of seedlings right now:doh:.
Not sure what went wrong....i just hope that they end up hard enough to use eventually.

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And lastly, just to show you how cold it is here....Arthur and i went for a drive today, to about 1200m altitude (1/2 hour from home)....froze our, um, well not our resin balls off!

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[Stustoys]

Hi Ewan,
Cant sit them in front of a little fan heater for a few hours?
I know heat has a lot to do with the time taken, maybe there is a point below which it pretty much stops completely?
Good luck.

Stuart

[Neil317]

One thought... wonder if the Bunnings "black oxide" is actually carbon black? Unlike iron oxide, it may prevent polyester curing. Not sure how to test it, maybe try burning a small sample?
Neil

[Ueee]

Thanks Stu and Neil,
It certainly is cold here, there is every chance it is cold to a point that the reaction has slowed to almost a stop. I shall set up a hot box or something and bake them for a few hours.
As for the oxide, it is the same diggers brand that Mark (graziano) used, and he had no problems, although of course he lives in a slightly warmer climate:D

[Michael G]

Box with an incandescent light bulb in it?

Michael

[Ueee]

Exactly what i did Michael. 50w hallogen in a box, sat at about 50deg for 6 hours. Nice and hard now! (oh dear:D)
There is good and bad news, the good is the pp balls came out ok, as did the rod, it just slid straight out of the pipe. The pp's on the end of the handles though shrank back to much and had to be removed.....bounced a hammer off them a few times before they cracked too!
I drilled the balls on the mill with the RT, only cause it was already on the table. cleaned up one on the lathe with some 120grit, looks pretty good, just needs a polish.
I have also recast the handles in small lengths of 38mm pipe. I have made them over length to allow for some shrinking. I think the size will be more suited to the shaper (the pp balls where a bit on the small side) and it gives me an excuse to use my yet untouched ball turning tool.

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[Ueee]

Ball turning tool worked a treat, although i think i should have sharpened the cutter differently. I polished the knobs to 400grit on the lathe then hit them with a loose calico buff. They came up fairly well, except for some tiny air bubbles:? I put some heat on them as soon as i had cast them and i think maybe they set too fast for all the air to come out. Once i have the forge set up and am casting i might do some brass ones.....one day.....

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[Steamwhisperer]

Nice job Ewan, :2tsup: but,
I seem to be drawn to that ball turning tool. May I have permission to copy it. Please:D I love it.

Phil

[Ueee]

Nice job Ewan, :2tsup: but,
I seem to be drawn to that ball turning tool. May I have permission to copy it. Please:D I love it.

Phil

Go for it! Worked well on the soft stuff.....The only thing i did to it was machine the hex on the end of the handle to fit a 3/4" spanner. If you want any finer details just let me know, its all pretty simple though.

[Steamwhisperer]

Thanks Ewan,
I should be ok, but then, they are my famous last words:-

Phil

[shedhappens]

your balls are....um..... nar I won't say

Great job Ueee :2tsup:

Did you cast those balls over a thread ?

and have you thought about making a couple of grunty washers with lugs that key into those slots ?

[Ueee]

I just cast them over flats milled about 1/4" in off the end of the bar (which is 5/8) There is actually 2 washes there see this post here: http://www.woodworkforums.com/f65/all-hail-shaper-gods-151294/index13.html#post1534632
Just need to make a jib now....