What is the Thickness of a CA Coating

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DrD

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Turning/Finishing Pen Blank to Pen Component Dimensions

Someone had asked about knowing how much thickness is added to the pen barrels by applying a CA coating. That was a question I wanted answered. There are many, many variables which impact any such answer. Thus, your mileage will vary.

I designed a simple experiment, controlling as many variables as possible. The answer to the question though will most certainly vary from one technique to the next, and more importantly will vary with your ability to consistently execute your particular technique. All this includes such things as type of CA, type of accelerator, technique used for application of both, type of sanding medium, length & pressure of application of sanding medium – just to name a few.

For this exercise I took a scrap blank and glued (2 part epoxy) it to a length of 7mm brass tube as seen in the attached photo. The end opposite my hand is the "A" end, the middle is "B" and the end next to the extended tube (end I am holding) is "C.'

Step 1 With the lathe set to ~1700 rpm, the turned pen blank was first dry sanded with Abranet 320, MirlonRed (~360 grit) and Mirlon Gray (1500 grit). The sanding is done on the lathe. For radial sanding, the lathe is turning; the lathe is stopped and the mandrel is turned by hand through 360 degrees for longitudinal sanding, followed by dust removal with a cotton rag before advancing to the next grit.

Step 2 Next the lathe is turned down to ~360 rpm and the CA is applied following the materials and methods shown in the Craft Supplies USA blog “Applying a CA Finish”. In short, using a blue shop paper towel I first apply 2 coats of thin CA, followed by 10 coats of medium – or as CSUSA says, Pen Finish. In between each coat of CA the blank is lightly sprayed with a quick burst of accelerator.

Step 3 Sanding out the CA by sanding, following the procedure outlined in step 1. The lathe is turned back up to ~1700 rpm. The gloss is completely removed by wet (water) sanding with Mirlon Red, followed by Mirlon Gray. Remenber to remove the watery swarf before moving to the next grit, and sand radially and longitudinally. If any shiny spots remain repeat the sanding with the Mirlon grits before advancing to the MicroMesh pads. Because I inspect all my finished barrels with a 20x lighted loupe, I start with 1500 MM and go all the way thru 12,000 MM, radially and longitudinally sanding, and removing swarf between each grit.

Step 4 Final polishing begins with apply 3 separate coats of 20/20 Plastic Polish, buffing each on the lathe with clean cotton cloth with the lathe running at ~1700 rpm. Next is the application in the same manner of 3 coats of Renaissance Wax. Finally, the inspection with the loupe. For those of you familiar with statistical process control (spc), the loupe inspection is unnecessary because the preceding steps are designed to ensure no noticeable sanding marks.

A​
B​
C​
Prior to Coating (1)
0.679”​
0.668”​
0.665”​
After CA Coating (2)
0.687​
0.675​
0.674​
After Sanding (3)
0.684​
0.674​
0.673​
After Polishing (4)
0.684​
0.674​
0.673​


As you can see, in this case after all is said and done the applied CA coat adds 0.005” to 0.008” thickness to the uncoated turned & sanded blank. Again, your mileage may vary. By way of example in this case, if the od of my Receiver Connector Nib was 0.674”, I would turn that end of the blank to ~ 0.668”. Or stated differently, in this case the CA added ~0.006” in thickness to the barrel. I hope this helps.
 

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1080Wayne

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Just a minor terminology quibble . The 5-8 thou is an increase to the diameter . The actual CA thickness is half that . A very good experimental approach , that more would benefit from adopting .
 
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DrD

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Good pick up. What I'm measuring is increase in DIAMETER of the barrel, and the thickness of the CA would be half that delta. Too much celebration last night Geaux Tigers!
 

monophoto

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Minor point - the increments you quoted (0.005 - 0.008") are the difference between the final diameter (4) and the initial diameter (1). But the thickness of the CA coating is half that increment - when you measure the diameter, the CA coating is included twice.

But the conclusion is still interesting - twelve applications of CA results in finish that is 0.0025 - 0.004" thick.

It would be interesting to take the experiment further to measure the incremental thickness as additional coats are added. I suspect that the first coat, and perhaps the second, tend to soak into the wood and don't actually result in any significant coating thickness. Also, I suspect the final sanding and polishing affects only the final coats in the finishing sequence. Ultimately, I think most people are mainly concerned about the final thickness of the finish, and simply assuming that each additional application adds one twelfth of these increments would lead to an incorrect answer. But if you were to take the experiment further, you could eventually determine the approximate effect of each additional coat of CA.
 
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DrD

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Minor point - the increments you quoted (0.005 - 0.008") are the difference between the final diameter (4) and the initial diameter (1). But the thickness of the CA coating is half that increment - when you measure the diameter, the CA coating is included twice.

But the conclusion is still interesting - twelve applications of CA results in finish that is 0.0025 - 0.004" thick.

It would be interesting to take the experiment further to measure the incremental thickness as additional coats are added. I suspect that the first coat, and perhaps the second, tend to soak into the wood and don't actually result in any significant coating thickness. Also, I suspect the final sanding and polishing affects only the final coats in the finishing sequence. Ultimately, I think most people are mainly concerned about the final thickness of the finish, and simply assuming that each additional application adds one twelfth of these increments would lead to an incorrect answer. But if you were to take the experiment further, you could eventually determine the approximate effect of each additional coat of CA.
Absolutely correct - see comments of 1080Wayne. My intent was to measure increases in diameter as that's the resulting measurement from the calipers. My laziness substituted thickness of the barrel for diameter of the barrel....
 

DrD

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Columbus, Mississippi
It would be interesting to see the results from other techniques, different types & brands of CA, different numbers of coats, different sanding and polishing protocols, etc.

I had to do something similar to determine the plunge depth to set on my TS75 track saw, taking into account the height (thickness) of the guide rail, etc to keep from cutting into the support table. Once that was determined, assuming Festool extruded all their different lengths of guide rails to the same thickness (not necessarily a good assumption I found out), take that delta and add that to the thickness of the board being cut, and you could cut thru the board leaving barley a scratch on the work table beneath.
 

leehljp

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It is entirely variable for me concerning how much is added on a specific blank - as it (thickness added) changes as the need changes, such as if I go from thin to medium and on a rare occasion thick. And not using PT (which soaks up more than is added to the blank) and instead using mostly latex gloves and occasionally foam type spreaders, the depth varies as I need it. I have accidentally (not paying attention) turned blanks .01 too much more than once over the years, and just apply one or two layers of thick or 3 to 4 layers of medium to more than make up for it. Then there is the temp and humidity - when it is about 60° or less and higher humidity in low temps, setting and curing are slower, so I add thinner coats for quicker curing.
 
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