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Chemical sanding to help in removing deep scratches from Tenite plastic

Started by TelePlay, April 04, 2018, 09:26:24 PM

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TelePlay

One more way to restore plastic. Others have their methods and end up with well polished housings. This is one more technique or method that can be used to remove scratches or dull surfaces resulting in a nicely polished surface.

Based on the pioneering chemical sanding work done by cihensley and recently modified by WEBellSystemChristian, those efforts were the basis for developing this technique to quickly remove deep scratches from tenite plastic. This work advances the concept of chemical sanding for scratch removal. Other topics for ABS and soft plastic restoration (different problems, different steps and different solvents) will follow in time.

To demonstrate this technique, a busted up WE 302 black tenite housing with deep scratches below the dial was used. This technique is applicable to any tenite housing but only tenite plastic, other plastics require other solvents.

This housing was used because the scratches were many and deep, so deep that they required about 5 minutes of sanding with 400 grit wet sandpaper. This, of course, left a very rough but even surface.

Chemical sanding was used to quickly move from 400 grit to 600 to 1000 and then to 2000 grit by removing or disolving the high ridges left by the last used sand paper leaving only the deep marks then easily removed by the next step up sandpaper.

The technique is reversible in that at any step, if prior sanding marks are seen, the restorer can go back to a prior step to remove those scratches and move forward to a final, nicely polished surface.

This technique can be used for a small spot (the size of a penny) or an entire side surface of a housing.

The first step is to select a sandpaper grit that will rather quickly remove the scratch. In this case it was 400 grit for the heavy scratches in the plastic. I have used 320 grit on some housings. Normally, light surface scratches can be removed with 1000 grit wet sandpaper and starting at that level greatly reduces the time it takes to get the surface back to a nice shine. 600 and 800 grits are good starting points for medium scratches. Best way to find out which is best to use is to start with 1000 and if the sanding is taking too long, drop down until the highest grit paper that does the job quickly is found.

The basic process for tenite is wet sanding, chemical sanding using a 2" square high bite cloth backed by a cotton ball soaked with 100% denatured alcohol and then moving to the next higher grit sandpaper. This is repeated until 2000 grit has been used. At that point, the high bite alcohol swab is used first and then a soft cotton patch backed with a cotton ball and soaked with denatured alcohol to put the final surface on the plastic. When that has been done, and before the alcohol completely dries out of the surface, a bit of Novus 2 is spread over the surface to keep the plastic alcohol damp. The Novus is immediately removed with a rotating orbital buffer. A second application of Novus 2 and orbital buffing takes the once scratched surface to a very nice, near new polished surface.

This complete process including information about the high bite cloth used is in a captioned YouTube video (no sound).

          https://youtu.be/LfSCLTnVvVo  (just under 15 minutes long)

During my last job, I noticed a special cloth was being used in hospitals to wrap instrument trays prior to sterilization. When unwrapping unused trays, I found this white cloth that was soft but abrasive and started to save them for chemical sanding. When asked recently if I found a commercial source for this cloth, I began to look. I knew the hospital cloths were made by Kimberly Clark. The cloth is completely synthetic (contains no pulp or organic materials) and made by Kimberly Clark under a patent. They call the cloth SMS for Spun-Meltdown-Synthetic. Commercially, is it referred to as Hydroknit and sold under the brand name of WypAll. They can be found as X-50, -60, -70 and -80. These are related to the thickness of the cloth. X-50 is the thinnest and X-80 the thickest. X-60 is the same as the hospital cloth I was using and is just the right thickness to work well as a high bite chemical sanding cloth.

The best source I found for low quantity (less than 10 boxes, a case) is Office Depot which currently sells them for $9 a box and if you order 3 boxes, they ship for free (a $9 cost saving). Each box contains 126 sheets. One sheet can be cut into 32 2" square patches. One complete phone housing can be chemically sanded with 2 to 4 patches so one box of X-60 is sufficient for 1,000 to 2,000 housings. I use one patch until I quit work and then toss it starting with a clean patch and cotton ball when I go back to the project.

Items needed or used in this tenite technique include

1 )  high bite chemical sanding cloth
2 )  soft cotton cloth
3 )  cotton balls
4 )  100% denatured alcohol
5 )  2000, 1000, 600 and 400 grit sandpaper
6 )  Novus 2
7 )  Rotating orbital buffer with terry cloth cover
8 )  Distilled water in a wash bottle
9 )  Cleaning rag

Below are images of the housing (before, after 400 grit sanding and when completed), comparison before and after images and an image of the WypAll X-60 box.

If anyone would like a few sheets, please send me a PM.

AE_Collector

So this process is for tenite only which is most North American "soft plastic" Phone housings....correct? You mentioned you would get to ABS hard plastic housings so will wait for that to make it out of the cutting room, hopefully not off the floor!

And of course this particular example is primarily to remove bad scratches and leave those housing perfectly shiny but can be adjusted to remove much more moderate scratches as well. How about discolouration of plastic?

Good step by step process!

Terry

kleenax

I swear I read an article about 10 yrs ago that detailed how Western Electric used to dip ABS plastic in a chemical solvent bath to "refurbish" them.  I remember that the process was timed precisely so that not too much plastic would be chemically removed in the process.

It may have been collector Jim Aita that told me about it though; can't recall. He used to work for WE, and he was a professional buffer of plastic housings for WE.
Ray Kotke
Recumbent Casting, LLC

TelePlay

Quote from: AE_Collector on April 04, 2018, 10:46:43 PM
So this process is for tenite only which is most North American "soft plastic" Phone housings....correct?

Yes, the steps, the materials and the solvents are specific to removal of scratches left by sandpaper. The point was to sand out a deep scratch and use chemical sanding to rapidly work up from the starting sandpaper to 2000 grit and then Novus and end up with a scratch free surface.



Quote from: AE_Collector on April 04, 2018, 10:46:43 PM
You mentioned you would get to ABS hard plastic housings so will wait for that to make it out of the cutting room, hopefully not off the floor!

Different plastic so different steps and different solvents.



Quote from: AE_Collector on April 04, 2018, 10:46:43 PM
How about discolouration of plastic?

Chemical sanding can be used to very effectively remove discoloration on ABS or soft plastic but the techniques are different, removal of discolored plastic requires no sandpaper until the very end and different solvents are used for different plastics (video to follow).



Quote from: AE_Collector on April 04, 2018, 10:46:43 PM
And of course this particular example is primarily to remove bad scratches and leave those housing perfectly shiny but can be adjusted to remove much more moderate scratches as well. How about discolouration of plastic?

Yes, a very small surface scratch in Tenite can be removed with this method starting with 1000 grit wet sandpaper, then chemical sanding, then 2000 grit, more chemical sanding and finally Novus 2. After the first 1000 grit sanding, the surface will show dull sandpaper marks. A small scratch uses the same process, just starting with a higher grit sandpaper and taking less time. No need to sand a whole side for one small mark but the sanding has to be large enough so as not to show a depression once back to a shine.


===================


This topic has nothing to do with refurbishing housings by chemical dipping or spraying. That has been discussed on the forum in 2011 in this topic.

     http://www.classicrotaryphones.com/forum/index.php?topic=5030.0

and this topic in 2015

     http://www.classicrotaryphones.com/forum/index.php?topic=14315.0

This topic is to show how one can quickly go from a coarse grit sanded surface to a shine in a very short period of time.


Dan/Panther

I found Acetone works on ABS.
For cracks I spread and clean the crack. Dry it well. I then use a Q-Tip to apply Acetone to the carefully Spread crack. After the Acetone fills the crack I let the crack relax back to it's original position, and hold it in place until the Acetone dries. Don't squeeze the crack,  you will squeeze out the Acetone.
Next after the crack has dried, I then add a thin line of Acetone along the crack. When that dries you can sand the spot smooth and polish it. You will not see a crack line if done properly.
Another trick, if I have a chipped or deep scratch I will find a donor area inside the case, scrape some ABS and collect it. Then I apply Acetone to the scratch, put enough donor ABS to fill the crack. The Acetone will dissolve the ABS and fill the scratch. You may need to do this step 2 or 3 times depending on depth of scratch.

D/P 

The More People I meet, The More I Love, and MISS My Dog.  Dan Robinson

TelePlay

Quote from: AE_Collector on April 04, 2018, 10:46:43 PM
And of course this particular example is primarily to remove bad scratches and leave those housing perfectly shiny but can be adjusted to remove much more moderate scratches as well.

Yes, the size of the small scratch or the total area scratched determines the starting point and the first grit sandpaper used. No sense doing a whole side for a small scratch.

If Tenite or soft plastic, use Denatured Alcohol between paper grits. If the scratch is in ABS, use solvents used in the ABS discoloration topic to work up from 400 or 600 grit to 2000 and then the finishing steps. With ABS, the swabs are used with gentle pressure between sandpaper grits to remove just the high sanding peaks, not with high pressure to remove layers of plastic.

I did a small scratch in Tenite video showing how a small scratch can be quickly removed from a polished surface. Depending on the scratch, use the appropriate grit sandpaper and work it back up to 2000 using the Denatured Alcohol chemical sanding method above and then the finishing steps.

Here is a link to that video (the scratch removed is so small it his hard to see in the shine):

     https://youtu.be/-vc4k-4bnSQ

If the scratch is in ABS, then the method used for ABS (different solvents) is used to work up from coarse grit to 2000 and then the finishing steps.


This looks a lot more difficult in words than it really is. Practicing on a junk housing is a good start to get these quick steps down the learning curve. The best thing going for these techniques is that if a mistake is made, recovery by going back a step or two to fixes the mistake and then moving forward only adds a few more minutes to the restoration.

TelePlay

The housing that was used in the first topic post was dropped and a small scratch appeared in the front center just below the dial.

The following video shows how quickly and completely a small scratch can be removed and the surface returned to its prior shine. This was a Tenite case so only denatured alcohol was used to chemically sand off sandpaper high marks to quickly move up in grit and prepare the surface after the 2000 grit sanding for the final polishing.

     https://youtu.be/QBEMV6XhF4I

Since it his hard to see the scratch in the video, the before and after still photos of the scratch and full front area is attached below.

This can also be done with ABS but the chemical solvents for ABS are different and fully described in this topic:

     http://www.classicrotaryphones.com/forum/index.php?topic=20168.0