How long should PR be under pressure?

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spiritwoodturner

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As much as I've read on this site, I don't remember seeing anything about how long PR castings should be under pressure. Hours? Days? I'm using 5 drops of catalyst pen ounce for the blanks I'm doing now, and after 8 hours they were still quite wet, and obviously not close to ready.

Thanks,
Dale
 
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I use 3 drops per ounce and usually cast in the evening and leave them in the pot overnight and they come out ready to turn. When I'm rushed and need to cast several, I take them out after 4 hours and start another.Are you using colorant? Sometimes colorant affects the cure time and I've even had some colors not cure at all. I mostly cast snakeskins which uses clear. I'm sure someone will have some info for you. I've started using only colors recommended for PR. Several I know use Mixol tints.
Do a good turn daily!
Don

spiritwoodturner said:
As much as I've read on this site, I don't remember seeing anything about how long PR castings should be under pressure. Hours? Days? I'm using 5 drops of catalyst pen ounce for the blanks I'm doing now, and after 8 hours they were still quite wet, and obviously not close to ready.

Thanks,
Dale
Click to expand...
 
You only need to leave the PR under pressure until it gels. Once it begins the solidifying process, it can be removed from the pressure. Once the gelling begins to take place, there should be no more opportunity for bubbles.
 
Temp. makes a big difference. Don being in Texas probably has a faster set up time than you up in Colorado, 'specially this time of year. Here in Michigan, I use 5 drops and leave under pressure 24 hrs. May be overkill, but they turn out nice.
 
My shop is heated plus I heat the resin to about 175 (I'm guessing) prior to adding the MEKP and pouring into the molds.
Do a good turn daily!
Don

CaptG said:
Temp. makes a big difference. Don being in Texas probably has a faster set up time than you up in Colorado, 'specially this time of year. Here in Michigan, I use 5 drops and leave under pressure 24 hrs. May be overkill, but they turn out nice.
Click to expand...
 
I used to use drops. I changed recently after realizing the only thing I wasn't really controlling was the measurement of the MEKp. What size are your drops? It depends on the aperature you cut in the tip of the bottle. The recommended amount of MEKp for Silmar 41 is 1% +/- 0.5% depending on your ambient temp and humidity. I have been using 0.5% for most things since going to direct measurement.

I like to leave my casts under pressure a minimum of 6 hrs, longer is better. I have had some casts that were under pressure longer that I undercatalysed (using the drops method) and after being under pressure 6 hrs, upon depressurizing the pot the surface of every cast erupted in bubbles.
 
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its_virgil said:
How do you measure?
Do a good turn daily!
Don
Click to expand...

I use one of these and a disposable plastic cup(s). Just got the new HF flyer and they are on sale w/coupon. You just tare the weight of the cup and your off and running

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I also heat my resin in a small toaster oven. I heat for 30-40 min at 150 degrees. This will do 2 things first it thins the resin making it much easier to mix the mek and second it speeds up the hardening of the resin. I use 3 drops per oz and as Don I mostly do clear castings of cactus and snake. I leave in my pot for 2-4 hours after that there's no need to leave in the pot as the resin has hardened to the state that no more air could escape. If the outside of the blank is still tacky I will put the blank back in the oven at 150 for 45 min. and I've had no problems turning right after taking it out.
 
For me, a PP is useless as my casts are ready to turn in just under an hour from the time of pouring them. By the time I would get the casts into the pot and press/vac'ed they would be set. The last pour I did was 40 blanks and they were all ready to turn in 57 mins. Had 6 pens finished an hour later.
 
OK, gang, my first lot of blanks came out of my pot after being in for about 20 hours. I did coffee beans in one mold, plain in the other mold. I used 5 drops per ounce, my shop is a comfy 55 although at night the thermostat drops it down to 45, I used Pearl-X. Plus, I have to say I wonder if my mixing is up to speed. I mixed yesterday by hand with a popsickle stick, but yesterday my wife found some big tongue depressors at Hobby Lobby to use as a drill paddle a la Chub's video. I think all these factors combined to give the following results.

They came out of the molds fine, solid but quite sticky and not ready to drill. I think I'll pick up a toaster oven today, because this could take a while otherwise. Don and Roy, very interesting you heat the resin first. No danger of fire or explosion there, inside a toaster oven with an exposed heating element? I just spent 100K building this shop and her art studio above it, I'll be in a tent if I blow it up!!!

All of you have been so very helpful! I could figure this out just like you did, but the learning curve is a heck of a lot faster with you folks around.

Thank you,
Dale
 
I heat the resin in hot water. The ultrasonic cleaner I have has a heater to keep the water hot. The PR is in a glass jar and is heating as the ultrasonic cleaner does its job.

Tents are made really nice these days...some have several rooms.:biggrin:

Good luck and ...
Do a good turn daily!
Don


spiritwoodturner said:
Don and Roy, very interesting you heat the resin first. No danger of fire or explosion there, inside a toaster oven with an exposed heating element? I just spent 100K building this shop and her art studio above it, I'll be in a tent if I blow it up!!!

Thank you,
Dale
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Don, you have some very cool toys! Where'd you get the cleaner, and do you remember how much? And Buddy, YOU may be able to live in a tent down there, but up here?!!!

Dale

its_virgil said:
I heat the resin in hot water. The ultrasonic cleaner I have has a heater to keep the water hot. The PR is in a glass jar and is heating as the ultrasonic cleaner does its job.

Tents are made really nice these days...some have several rooms.:biggrin:

Don
Click to expand...
 
150 degrees is really not that hot, remember that in most of the warehouses that PR is keep in they are not air conditioned, my shop in the summertime before I installed AC was upwards of 120-130 when the outside temp was in the 90's and in july and aug with the temp 100 and above, well you get the picture. I heat them in the toaster oven in the 9 oz. plastic cocktail glasses and @ 150 degrees the glasses only get warm, but then I only spent a couple of grand on my shop building.:biggrin::biggrin::biggrin::wink:. Also the toaster oven is great to finish the job.( Harden the exterior).
 
Dale, you can get a toaster oven at goodwill or salvation army store for $10.00. Put your sticky blanks in at 150 for an hour and sticky be gone.
 
The ultrasonic cleaner I purchased was from Harbor Freight. This is it: http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=95563

I went in to buy the smaller one but this one was on sale for $49.99 and I had a coupon for 15% off. The smaller ones will work fine but I'm not sure if they have the heater.

some guys bought them off of Ebay and got some really nice ones for $25. You may want to check there or some of the surplus equipment websites.

Do a good turn daily!
Don

spiritwoodturner said:
Don, you have some very cool toys! Where'd you get the cleaner, and do you remember how much? And Buddy, YOU may be able to live in a tent down there, but up here?!!!

Dale
Click to expand...
 
its_virgil said:
How do you measure?
Do a good turn daily!
Don
Click to expand...

I'm using 1cc syringes with 18ga needles that I have ground flat on my grinder.

1 cubic centimeter = 1 milliliter

1% of 240ml (approx 8 oz) of resin is 2.4ml(cc).
0.5% of 240ml of resin is 1.2ml (I fill and dispense the syringe twice with 0.6ml of MEKp)
0.25% of 240ml of resin is 0.6ml

Since I changed over a few months back I have found more controllability with the cure. Time is more managable. Everything passes the drop/toss test and I still get ribbons when I turn them after making them round.
 
Thanks Charles. Do you use this method with clear casts as well as those with pigmnents? I may have to try the 1% mix next time.
Do a good turn daily!
Don

Glass Scratcher said:
I'm using 1cc syringes with 18ga needles that I have ground flat on my grinder.

1 cubic centimeter = 1 milliliter

1% of 240ml (approx 8 oz) of resin is 2.4ml(cc).
0.5% of 240ml of resin is 1.2ml (I fill and dispense the syringe twice with 0.6ml of MEKp)
0.25% of 240ml of resin is 0.6ml

Since I changed over a few months back I have found more controllability with the cure. Time is more managable. Everything passes the drop/toss test and I still get ribbons when I turn them after making them round.
Click to expand...
 
Yep, got my toaster oven for 18 bucks at Wally World (blanks are in them right now), and wouldn't you know it, went to Harbor Freight today and didn't know they had the ultrasonic cleaners! We have a little one for jewelry, but no heat, so I ordered one from Amazon. Got another vacuum pump at HF but pots weren't on sale. Where are you guys getting the discount coupons for HF? I haven't seen one in a long time, and they said at the store today they haven't done them for a long time.

Thanks again,
Dale

UPDATE: After an hour in the oven at 150, they're perfect! Already cut and epoxied tubes in a few, now tomorrow the fun REALLY begins! I can already tell tools need to be ultra-sharp and I'll have my gallon jug of thin CA handy. I would think they have to be soaked as soon as round, and maybe again as you go. The dry beans go everywhere. I also am casting a new batch with Mixol camel (cappuccino) and white head (cream). Next time I'll mix a little cinnamon powder into the white!

The Mixol works great, a little does go a long way.
 
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its_virgil said:
Thanks Charles. Do you use this method with clear casts as well as those with pigmnents? I may have to try the 1% mix next time.
Do a good turn daily!
Don
Click to expand...


I haven't done any clear since I changed over. I have done transparents with Pearl-ex, and they have come out beautiful. One of the local turners saw one of the recents tests with a new gold powder I am trying and he had to have the turned and polished cylinder to make a pen or use as bands or something. It was really pretty. Pitty I didn't get a photo before he snagged it.

After I get all the present castings out of the molds, I will give a clear cast a go and let you know, but I don't know why there should be a problem.
 
its_virgil said:
I heat the resin in hot water. The ultrasonic cleaner I have has a heater to keep the water hot. The PR is in a glass jar and is heating as the ultrasonic cleaner does its job.

Tents are made really nice these days...some have several rooms.:biggrin:

Good luck and ...
Do a good turn daily!
Don
Click to expand...

I just started getting into casting. What "glass jar" do you use? Is it completely submersed in the ultrasonic cleaner? We have a Bronson B200 Ultrasonic cleaner for jewelery but its small and does not have a heater. After reading this thread, I'm off to buy one at HF today.

Any help would be greatly appreciated!
 
These HF coupons are for particular items in the store. I check these websites all the time, but haven't seen a 15-20% off coupon for any one item in a long time. I'm on their mailing list and just don't see them like I used to.

Guess I'll keep looking...
Dale
 
Just got back from HF, purchased the same ultrasonic cleaner as recommended in this post. The price for this item on-line said $72.99, I didn't see a sale advertisement or coupon on-line or in the flyer. Thought I might take a look at the product since I had planned on going there any way. Much to my surprise and chagrin, the price tag for the item said $49.00, the discount (although not advertised, was still in effect)!!!! Also picked up a nice digital Metric/US dry/wet scale for $19.00!!!!

Thanks for the recommendation!
 
I save glass jars from the kitchen .... jelly, peanut butter, etc ... and fill it with PR (or the amount needed) and place it in the water in the cleaner. The water in the ultrasonic cleaner is about 2 inches deep. A heater in the cleaner is probably not necessary. Use hot water from the tap and change it a few times to heat the resin a little. Or, do like Roy and use a toaster oven if you have one. Roy uses the small cleaner that HF sells if I remember correctly. But, having the resin thin makes the casting go much better in my opinion. And, the air moves out easier and quicker.

Do a good turn daily
Don

JFeagans said:
I just started getting into casting. What "glass jar" do you use? Is it completely submersed in the ultrasonic cleaner? We have a Bronson B200 Ultrasonic cleaner for jewelery but its small and does not have a heater. After reading this thread, I'm off to buy one at HF today.

Any help would be greatly appreciated!
Click to expand...
 
Just a thought, although I havent cast yet. Could the elevation have something to do with Dales' cure time compared to everyone elses'?
 
Tim, I wondered about that too, but other batches have been much slower to cure. The unique thing for this batch was the heated water ultrasonic cleaner. Charles's theory about how old the resin may have been would have had weight if it was a new can I was into, but it was from the same can that I made the last batch that took 3 days to cure, and they were goopy when I took them out.

I'm going to write a journal with every single particular factor until I get to the point I can count on this. And then I'm going to continue journaling.

Thanks for the thought,
Dale
 
its_virgil said:
I save glass jars from the kitchen .... jelly, peanut butter, etc ... and fill it with PR (or the amount needed) and place it in the water in the cleaner. The water in the ultrasonic cleaner is about 2 inches deep. A heater in the cleaner is probably not necessary. Use hot water from the tap and change it a few times to heat the resin a little. Or, do like Roy and use a toaster oven if you have one. Roy uses the small cleaner that HF sells if I remember correctly. But, having the resin thin makes the casting go much better in my opinion. And, the air moves out easier and quicker.

Do a good turn daily
Don
Click to expand...

So when you put the jar of PR in the UC do you put the catalyst in before or afterwards?
Thank you
:cool:
 
Glass Scratcher said:
I haven't done any clear since I changed over. I have done transparents with Pearl-ex, and they have come out beautiful. One of the local turners saw one of the recents tests with a new gold powder I am trying and he had to have the turned and polished cylinder to make a pen or use as bands or something. It was really pretty. Pitty I didn't get a photo before he snagged it.

After I get all the present castings out of the molds, I will give a clear cast a go and let you know, but I don't know why there should be a problem.
Click to expand...

I've never counted drops, I use pipettes like these http://www.barnesonline.com.au/product.asp?strProdFamily=Dispensers

It's easy to eyeball in .1 of a ml increments up to 3 mls, although the markings are every .5ml from memory. As I'm usually casting about 250mls at a time, it's the perfect size. I bought a pack of 50 for something like AUS$3, but I just keep using the same one over & over, as the MEKP has no effect on it.

I've done clear casts, coloured casts, embedded things etc all the same way, no problem.

Russell.
 
Okay, not trying to hijack the thread here or start a war, but is it good to heat up alumilite before casting as well? I use PR and alumilite but have never heated either. I may try though as I just kidnapped the toaster oven from the kitchen (permanently, it's not going to be used for food again!).
 
MesquiteMan said:
NO NO NO NO NO NO DO not heat up Alumilite before casting! You will not be able to get it poured and into the pot before it cures.
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Thanks Curtis....yeah now that I think about it, that's the stupidest question I've ever typed. That would be like heating up 2 part epoxy before you tried to do a glue up....:clown:
I guess I would've figured out REAL quick that it wouldn't work!
 
GouletPens said:
Okay, not trying to hijack the thread here or start a war, but is it good to heat up alumilite before casting as well? I use PR and alumilite but have never heated either. I may try though as I just kidnapped the toaster oven from the kitchen (permanently, it's not going to be used for food again!).
Click to expand...

Alumilite kicks over fast (5 minutes of open time) compared to PR at room temp. You can extend the open time of Alumilite 30 - 60 seconds by cooling the "B" side in the fridge for 3 - 5 hours: http://www.alumilite.com/FAQ.cfm#8
 
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