# Threading PR



## ldb2000 (May 25, 2008)

Hi All
This ones for the casting gurus out there .
How does adding pigment effect threading of PR .
I have found that the amount of dry pigment seems to make a difference in tne quality of the threads I have been cutting in PR and am wondering if anyone is having similar results out there .
Do you think that tinting with liquid coloring and less mica powder makes a difference .
Also how does the amount of hardner effect the PR as far as threading is concerned , I like a very hard almost brittle acrylic as far as turning is concerned but am wondering if this is also effecting the quality of the threads as well .
As an experiment I'm going to cast a Clear blank with the normal amount of hardner I use and a blank with a much lower amount of hardner then see if they thread any differently , being theres no pigment involved this should answer the first question too .
Time to chime in with some ideas and answers and even some questions , let's go everyone !


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## Chuck Key (May 25, 2008)

Ok, I have a question.  

What are you using for threading?  Tap & Die?  Lathe?  CNC? What tooling if other than tap & die?  What size threads?  Single start? Multi Start? 

I have been expermenting with cutting threads with a router and router bit.  No conclusions on that yet.

Chuckie


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## ldb2000 (May 25, 2008)

Oppps sorry 
Yes I'm using a multi start tap and die but seem to have more problems with the single start taps (the ones for the nib assy) , I think it has something to do with the corser threads taking a bigger (or deeper) cut then the multi start
Oh yes I'm using spray cooking oil to lube the taps and dies and must say it make a big difference in the cleanness of the threads .


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## scubaman (Jun 11, 2008)

According to machinist friends the best lubricant for plastics is soap and water...  dish detergent and water!

I tried cast resin and found it to be way too brittle to cut with a die.  This specific blank has a high mica content I think - I do not cast my own.  My suspicion is that for me, who would buy cast polyester resin blanks, the processes are too uncontrolled.  Different suppliers will use different amounts of hardener, different amounts of colorants etc.  I'd be very interested in hearing others' experience.

Lastly, I think these could be cuttable single-point.  I just wonder abnout material strength.


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## BRobbins629 (Jun 11, 2008)

I have cut multi start threads in home brew PR colored with Mixol liquid pigments.  Works fine.


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## ldb2000 (Jun 12, 2008)

OK let me preface this by saying that I'm not a materials engineer so this only my opinion .
After doing some experimenting I've had good results with clear PR (more about this at a later time) and mixed results with blanks with dry pigment as a colorant .
 I mixed as much as 1/2 teaspoon of dry pigments and mica and as little as a bit on the end of a mixing stick in 2 oz to make some 3/4" blanks , the blanks with more pigments were much harder to get a clean thread and most of the blanks with just a little pigment threaded much better .
So as far as I can tell the type of colorant and the amount of dry pigments has a large impact on the quality of the threads cut .
I also experimented with the amount of hardner and found that low amounts (3 to 4 drops) of hardner the tap and die seem to melt the PR while threading (the threads are rounded and and not cleanly defined) and high amounts (20 drops) seem to chip out to the point of becoming unusable .
The good news is that 7 to 12 drops seem to thread very cleanly which is a large enough range that almost anyone who likes turn PR can find a mix that can work for them .
Thank you Rich I will try dish soap and water to lube the cut , and thank you Bruce ,
I was hoping that someone had tried liquid colorant (as I have none) and had the same results as my clear PR that I was threading , it seems like the dry pigments are causing the PR loose some of it's cohesion ability (sorry if I'm not explaining this right)


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