Thread: Some experimenting

Originally Posted by guitstik

Where do you guys get knots that aren't made in China?

All Knots are chinese,at least all badger hair comes from china,They are considerd a pest and do alot of damage to crops.
All is not wasted tho,they are also an important food source.

Mycarver has made some excellent plastic scale material - as I recall, he uses acrylic, not polyester. I have made a number of poly brush handles from rod that I cast. As you found, it is very brittle, and you have to be extremely careful turning, or it will "explode". I haven't done any for a year or so, but as I recall using a tool with a very small contact point worked best. And, I haven't tried making scales from it. I like the semi-transparent look you are getting. Good luck with your projects.

Originally Posted by skipnord

Mycarver has made some excellent plastic scale material - as I recall, he uses acrylic, not polyester. I have made a number of poly brush handles from rod that I cast. As you found, it is very brittle, and you have to be extremely careful turning, or it will "explode". I haven't done any for a year or so, but as I recall using a tool with a very small contact point worked best. And, I haven't tried making scales from it. I like the semi-transparent look you are getting. Good luck with your projects.

Thanks for the tip! I'm going to be turning that piece probably next week. I'll post how it goes...

Originally Posted by HARRYWALLY

Funny you say 1700 rpm. That's my go to speed for turning.

You turn by hand? I would try "riding the bevel" with this material. It creates more of a shearing cut rather than a scraping cut. Less chance of a piece breaking off or chipping. It's a technique used to achieve very smooth cuts.

Riding the Bevel - NewWoodworker.com LLC

Thank you! I have been hand turning for almost 70 years and no-one has shown me that. Always used scraping as my dad taught me.
~Richard
I have eaten more than one chunk of broken plastic caused by internal stress. Acrylesters are pretty good without extra care.

If you notice variations in the force needed to make a cut, then you might do as we did for years with plastic rod and sheet:
If there are hard spots or internal tension, there will be surprises in the turning and machining.
Put it at about 280 degrees F raising to that temperature slowly for a few hours to anneal all the parts of the rod to the same hardness and relieve internal tension. Let it slowly come to room temperature. I do not know if home cast is the same as purchased cast acrylic but the difference between cast and extruded was significant in hard spots.

From Carville Plastics
How to stress relieve acrylic and other plastics

All cast and extruded plastic materials will carry internal stress. To ensure stable dimensions and a long life for precision component parts, it is essential that materials are correctly heat treated to remove all material stress.

On material such as acrylic, it is necessary to heat treat the material to a temperature of 140⁰C and to cool slowly under controlled condition. This initial heat treatment, or normalising process, will result in material shrinkage of between 2% and 4%.

All plastic materials used by Carville are fully heat treated before any machining operations take place. Subject to the material or component size, these heat treatment processes can require anywhere between 24 and 96 hours.

There is a lot more information on line as to the timing etc.
Be safe!
~Richard

Nice idea I really like the look and have not seen it before, good work!
Rob

Curious,How are you geting the casting out of the PVC,or are you just turning it off?

Originally Posted by pixelfixed

Curious,How are you geting the casting out of the PVC,or are you just turning it off?

It comes out with a little tap. Since it's not a real mold, I spray a mold release to help it a little. The molds that are slightly flexible seem to work great without the spray.

Originally Posted by JimmyWetshaver

Very cool. Have you contemplated simply painting the isiude of the knot hole black (or any color of your choosing) like they used to do with the old clear acrylic brush handles? Might be cool especially if you get creative with your color selections. Just a thought.

Yes that's a good one and I may try that with that green sample. Like you said you could probably do some neat color combinations...thanks for the suggestion

One way to have a bubble free casting is to make the mold at least twice as high as necessary and use a vacuum generator to drop the pressure as close to "0" as possible. The mix will foam up a lot and then will subside and the bubbles from mixing and moisture retention will be on the surface of the pour. Do this about three times to assure all the trapped gas is removed.
I have been mixing and casting resins at a workplace from 66 until 2002. This is the same routine that the folks use for stabilizing wood where the vacuum pulls the mix into the wood's pores and removes moisture while doing so.
A Urethane is particularly bad at absorbing moisture during mixing.
~Richard

Thanks Richard. I found a good article online with the pros and cons of esters, urethanes and epoxies and it notes that same sensitivity for urethanes to moisture. So far for what I've been doing the polyester has behaved nice without bubbles and fairly user friendly.
I love learning new processes and materials - thanks for the info!