# HOW TO:Chemical Polishing the inside of demonstrator pens



## BradG

Hi Chaps
Today I've been playing with polishing the inside of acrylic. This process works for many types of plastics, so by all means give it a go on what you're using.

I've heard many people cuss about having to polish the inside of transparent pens using sandpaper as it can be quite awkward to get all the nooks and crannies within. Flame polishing generally isnt possible due to the narrow inside diameters we're dealing with.

This method uses the vapour produced by a cheap chemical called Dichloromethane, or DCM for short

*The beginning*





I wanted this to be as rough as poossible to test just how effective this method would be. so, I used a blunt 9mm drillbit and forcefully bored it through a piece of acrylic rod, which has left lots of tooling marks within as you can see.









The next step was to build the high tech apparatus. A jam jar with a piece of stainless tube hot glued through the lid.









I added around a tablespoon of DCM to the jar and screwed the lid on tight.










It's important that the stainless steel tube does not touch the walls of the inside of the pen piece, otherwise it will smudge. To ensure this, I mounted the piece of acrylic into the chuck of my drill press, and placed the jar on the bed. I will mention that at no point is the drill press turned on.. we're purely using it's quill action only.










simply placing a hairdryer next to the jar is all it takes to heat the liquid enough for it to begin emitting vapours. this is a little slow with regards to the amount of vapours it puts out, but nevertheless it does work. A better approach i found was to wave a blowtorch around the base of the jar (use caution not to shatter the glass by having the blowtorch blasting on it) to create small bubbles on the DCM. you could of course also use a hotplate.










Once the vapours are being produced, simply pull the handle of the drill press to lower the quill, which in turn inserts the stainless tube all the way into the pen piece. slowly raise it back out again, and repeat until its clear. the whole process is likely to take about 60 seconds. overdoing it and the surface will become wavy.. a bit like looking through water, but nevertheless still clear.










And here's the end result. those drill gouges have vanished and the piece is nice and clear.






*Summary*
This process is great. the chemical is cheap. the litre bottle cost me £10 including delivery ($13). the other stuff I had laying around, despite stealing SWMBO's hairdryer and a jam jar. I should mention this works by melting the surface of the plastic.. so by touching it with anything you will leave a sticky fingerprint on it and ruin the surface.. then you sure will be sanding it back to normal, but not the end of the world. I would recommend mechanically polishing the outside because its easy to do anyway.

The better the surface is before you do this process, the better the result will be. the key is to do this as little as possible, so obviously having a better surface finish, by for example reaming the piece after drilling, would significantly reduce the amount of time required to chemically polish it internally, thus yielding a much better result.


So, hopefully that's another string to your bow 

This should be done in a well ventilated space. in the garage with the door open is adequate.. or as I do, I have a movable extractor fan on a tripod. Inhaling this stuff, apart from generally not being healthy, will make you dizzy, and give you headaches... so don't skip the ventilation part.


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## D.Oliver

That's awesome, Brad.  Thanks for the info!


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## TonyL

Thank you. I have watched the process used on large sheets of acrylic. The videos did emphasize ventilation and other precautions: https://www.youtube.com/watch?v=7na8kQ78vkQ


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## magpens

Thanks for this, Brad ... nice to know about this technique.


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## Curly

Brad is this the same product used to glue Plexiglass (Perspex)? Thanks for the tip.


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## BradG

Curly said:


> Brad is this the same product used to glue Plexiglass (Perspex)? Thanks for the tip.



It is indeed used for plastic welding


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## SteveG

I stand amazed at the variety of creative, useful pen ideas that issue from your brain. I may never get to use this due to difficulty/expense of getting hazardous materials to my small island, but will be checking it out. Thanks!


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## SteveG

Oh...BTW, I noticed you have contracted: Purple Finger "Industrial" Disease.   

Is it contagious? :tongue:


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## Curly

Oh! Oh! He better watch out for the purple people eater!
https://www.youtube.com/watch?v=DL1ZH0Ke92A


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## BradG

Yes this was my stubbornness of wanting to fill up a piston converter with ink, but only having ink cartridges instead of a bottle... and a scalpel :biggrin:  

il post that pen in a couple of days once I've made the stand


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## Jim15

That's a great idea. I learn something new everyday here. Thank you for sharing.


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## Sylvanite

Dichloromethane, a.k.a. methylene chloride, is nasty stuff.  Besides being a carcinogen, it's highly volatile, highly flammable, causes chemical burns, and when inhaled, acts like carbon monoxide poisoning.  Symptoms include dizziness, nausea, confusion, and asphyxiation.  A man died from DCM poisoning last year (see https://www.osha.gov/Publications/OSHA3883.pdf)

[size=+1]Use DCM only in well ventilated areas!

Wear protective eyewear and clothing.

Be very careful when heating it to avoid explosion![/size]

I use methylene chloride to weld acrylic in my trophy business, but try to limit my exposure as much as possible.

I hope that helps,
Eric


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## BradG

Thanks for contributing Eric 

For ayone curious on the health aspects of DCM, you can read a toxicology report here.

As mentioned, used ventilation, and you'll be fine. 


https://toxnet.nlm.nih.gov/cgi-bin/sis/search/a?dbs+hsdb:@term+@DOCNO+66


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## PatrickR

Organic solvent vapor is heavier than air, so it drops. If (?) that is true of DCM, a device that allows the vapor to drop into the void may be more effective. May explain the need to heat it. Which would scare the hell out of me!


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## Woodchipper

The school where my wife taught many years ago had an aquarium in the lobby.  Someone used an abrasive to clean off the algae.  Guess what?  Scratches galore on the acrylic!  Check with a pet supply store.  There is a compound that you can wipe on the acrylic and it clears up the scratches.


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## gtriever

Cerium Oxide (CeO2) is the compound used for removing fine scratches in aquarium glass. I haven't tried it on Acrylic. Usually applied with a felt bob at high speed, it's a friction polish. It's like Aluminum Oxides in that it's measured in microns instead of grit, but unlike some other polishing compounds it has a peculiar property of polishing much finer than micron/"grit" size would indicate. The typical "grit" size comparison is 8,000 but I've heard reports that it polishes equivalent to up to 50,000 "grit". But, the manufacturers all say that if you can feel the scratch with your fingernail, it's too deep and you have to start removal with a lower grit (400-600 or so).


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## Woodchipper

gtriever, thanks for the info.  50K grit would be finer than talcum powder.  Wow!


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## gtriever

Woodchipper said:


> gtriever, thanks for the info.  50K grit would be finer than talcum powder.  Wow!


 
That's what it looks like - pink talcum powder. And it's one big mess to use... you usually make a slurry of around 2-4 parts water to 1 part CeO2, and it flies everywhere!


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