Brittle blanks

[Dorno]

I am currently making my blanks with clear polyester casting resin and my blank seem to be very very brittle . Does antone out there know how to make them less brittle is there a little trick or something else I can put in to make my blanks less brittle.
I am using aroung 9 drops of hardener per 25ml which works out to about 22 drops per blank. Is this right or can I do something else to soften them.

Thanks Ian

 

[lorbay]

I would think you are putting too much hardener in. On a single cast blank (about 1 oz) I am putting 4 drops in. I am no expert as I am learning also so I am sure some of my teachers on here will chime in.

Lin

 

[jttheclockman]

Ian cut it in half. Too much hardener.

 

[ldb2000]

4 drops per ounce will soften up the PR and make it less brittle , also don't post cure your blanks (if you are) . Too much heat will also make the blanks more brittle
Or you could also practice up on your turning and learn to work with them . The most brittle blanks also shine like glass when polished . Inlace blanks are a perfect example of this . I normally add 10 drops per ounce and will on occasion add as much as 20 drops per ounce for special pens .
A very sharp skew and feather light cuts and they turn well with no chipping . The main thing is don't rush it while turning .

 

[Dorno]

in that case I am using far to much hardener and will cut it by at least half and see how it goes from there.
I am keen to see how it all works I have been frustrated beyond belief.

Thanks Ian

 

[JohnU]

When you turn them, are they cold? That will make pr brittle also. I keep my pr blanks in the house closet because my basement shop is colder. I use 3 drops of catalyst per one ounce of pr resin. I put my molds in a pressure tank and inflate to about 30 lbs. Then I set it near the furnace vent in the back bedroom over night. The blanks come out of the mold a little tacky but I pop them out and set them by the vent for a few hours. After that theyre nice and smooth.

 

[Glass Scratcher]

What brand or type of polyester resin is it?

 

[LandfillLumber]

You are using way to much hardener for sure.I use .75-1% hardener with my polyester it seems to produce a strong blanks that turns easy and is not to brittle.I use a syringe to measure so I can be exact on my measurements it is important.Good Luck,Victor

 

[Glass Scratcher]

You are using way to much hardener for sure.I use .75-1% hardener with my polyester it seems to produce a strong blanks that turns easy and is not to brittle.I use a syringe to measure so I can be exact on my measurements it is important.Good Luck,Victor

Another convert to exact measuring! Yay! That makes 3.

 

[jason_r]

in that case I am using far to much hardener and will cut it by at least half and see how it goes from there.
I am keen to see how it all works I have been frustrated beyond belief.

Thanks Ian

Ian-

Check out the Resin Color Library. There's solid data there on how the amounts of hardener affect the resin gel time, etc as well as the color recipes.

And as always- the library's open for new submissions.