Finishing question

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lfox

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May 12, 2020
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6
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Missouri
Sure it is a sanding error but there is a spot that doesn't look like it took the finish. It is walnut and a CA finish. Didn't notice when I was sanding and didn't seem to feel different.

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Dehn0045

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Mar 19, 2017
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sanded through the finish. Sometimes you can reapply CA directly without any issues and try again, but sometimes the part that was sanded through will take a slightly different color (may have to turn all the way down to wood and restart if this is too bad). I find that CA with flex tends to be quite a bit softer and I sand through much easier (I actually stopped using flex for this reason). Also, if the blank is not perfectly cylindrical (which is actually surprisingly difficult to do with wood due to the varying hardness) then I am a lot more likely to sand through. Your options are to either sand less aggressively or apply more CA prior to sanding. My personal method is to apply a pretty heavy layer of CA, then turn with a sharp skew using a scraping or planing cut. If the blank wasn't out of round too bad (noticeable high/low spots in the CA while turning) then I will proceed to finishing, but if it seemed out of round then I'll add a couple coats of CA and then turn with skew again and proceed to finishing.
 

leehljp

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Agree with Sam.

That is called sand-through. You are not the first one to experience this and you are not even in the first 1000. To be honest, I can't tell you how many times this explanation has been rejected at first. It doesn't seem possible, but it is.

Do you have calipers? Measure a area on a blank before adding CA. Measure After putting CA on and before sanding. (mark it down) You will find that you don't have very much CA thickness. And then after you sand it smooth, you will find you are back to the thickness of the blank before you applied CA. This is common when just starting out.

CA layers need to be built up for a bit of thickness before sanding.

IF you don't have calipers, get some. You can get a decent set from Harbor Freight on sale for about $10 to $12 occasionally. Don't get the composite ones but the metal ones. Metric/inch. There is one that is Metric/Inch/Fraction that is good too.

What part of MO are you located? I'm headed to Springfield for the Memorial Day Weekend to visit a Daughter and visit Grizzly.
 

lfox

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Joined
May 12, 2020
Messages
6
Location
Missouri
sanded through the finish. Sometimes you can reapply CA directly without any issues and try again, but sometimes the part that was sanded through will take a slightly different color (may have to turn all the way down to wood and restart if this is too bad). I find that CA with flex tends to be quite a bit softer and I sand through much easier (I actually stopped using flex for this reason). Also, if the blank is not perfectly cylindrical (which is actually surprisingly difficult to do with wood due to the varying hardness) then I am a lot more likely to sand through. Your options are to either sand less aggressively or apply more CA prior to sanding. My personal method is to apply a pretty heavy layer of CA, then turn with a sharp skew using a scraping or planing cut. If the blank wasn't out of round too bad (noticeable high/low spots in the CA while turning) then I will proceed to finishing, but if it seemed out of round then I'll add a couple coats of CA and then turn with skew again and proceed to finishing.
What kind of ca do
Agree with Sam.

That is called sand-through. You are not the first one to experience this and you are not even in the first 1000. To be honest, I can't tell you how many times this explanation has been rejected at first. It doesn't seem possible, but it is.

Do you have calipers? Measure a area on a blank before adding CA. Measure After putting CA on and before sanding. (mark it down) You will find that you don't have very much CA thickness. And then after you sand it smooth, you will find you are back to the thickness of the blank before you applied CA. This is common when just starting out.

CA layers need to be built up for a bit of thickness before sanding.

IF you don't have calipers, get some. You can get a decent set from Harbor Freight on sale for about $10 to $12 occasionally. Don't get the composite ones but the metal ones. Metric/inch. There is one that is Metric/Inch/Fraction that is good too.

What part of MO are you located? I'm headed to Springfield for the Memorial Day Weekend to visit a Daughter and visit Grizzly.
about 50 miles from Springfield, was at grizzley the other day. About what thickness before sanding is common?
 

lfox

Member
Joined
May 12, 2020
Messages
6
Location
Missouri
sanded through the finish. Sometimes you can reapply CA directly without any issues and try again, but sometimes the part that was sanded through will take a slightly different color (may have to turn all the way down to wood and restart if this is too bad). I find that CA with flex tends to be quite a bit softer and I sand through much easier (I actually stopped using flex for this reason). Also, if the blank is not perfectly cylindrical (which is actually surprisingly difficult to do with wood due to the varying hardness) then I am a lot more likely to sand through. Your options are to either sand less aggressively or apply more CA prior to sanding. My personal method is to apply a pretty heavy layer of CA, then turn with a sharp skew using a scraping or planing cut. If the blank wasn't out of round too bad (noticeable high/low spots in the CA while turning) then I will proceed to finishing, but if it seemed out of round then I'll add a couple coats of CA and then turn with skew again and proceed to finishing.
I see my first response got cut short. What kind of ca do you use.
 

Dehn0045

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I use Bob Smith Industries Thin only. I apply using open cell foam (similar to the foam in furniture cushions), this allows a longer work time and I get about 0.0005" to 0.001" of increase diameter per coat. I can't get nearly that thickness per coat when using paper towels. Some guys like to use craft foam (closed cell) or plastic baggies to achieve similar result, just a matter of preference. But I do recommend getting away from paper towels if you're using thin CA. I agree with Hank on calipers, they are a very important tool in penturning, I use them a lot when turning to final diameter and finishing. I usually turn down past the final diameter by about 0.004" to 0.006" then build back up to about 0.001" to 0.002" over the final diameter. This gives me a little room for turning and sanding back down to match the final diameter. The final finish thickness is about 0.002" to 0.003", which I don't think is too thick (some have noted that if the CA finish is too thick it will tend to crack, I haven't noticed an issue with my method). Some folks like to use medium or thick CA for building thickness, I did so when I first started penturning, but I have settled on thin-only as my method. I tend to go through about one 8oz bottle of thin per year, so its a little more cost effective for me to only use one type -- my first year I had to trash 1/2 bottle of thin and 1/2 bottle of medium that got old.
 

leehljp

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Feb 6, 2005
Messages
7,312
Location
Tunica, MS,
There are dozens or hundreds of methods. Sams is great and works for many. The main thing is to learn to measure and build up what is needed for you. Having said that, I turn my blanks down about .005 below the size needed and then build up CA to + .005 and sand or turn back down to the precise size. BTW, with very sharp tools, one can turn the CA to a smoothness with the tools only - that is equal to and even better than 600 - 800 grit sand paper. But, I use calipers to determine the sizes.
 

TDahl

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Joined
Dec 11, 2019
Messages
36
Location
Brentwood
I use Bob Smith Industries Thin only. I apply using open cell foam (similar to the foam in furniture cushions), this allows a longer work time and I get about 0.0005" to 0.001" of increase diameter per coat. I can't get nearly that thickness per coat when using paper towels. Some guys like to use craft foam (closed cell) or plastic baggies to achieve similar result, just a matter of preference. But I do recommend getting away from paper towels if you're using thin CA. I agree with Hank on calipers, they are a very important tool in penturning, I use them a lot when turning to final diameter and finishing. I usually turn down past the final diameter by about 0.004" to 0.006" then build back up to about 0.001" to 0.002" over the final diameter. This gives me a little room for turning and sanding back down to match the final diameter. The final finish thickness is about 0.002" to 0.003", which I don't think is too thick (some have noted that if the CA finish is too thick it will tend to crack, I haven't noticed an issue with my method). Some folks like to use medium or thick CA for building thickness, I did so when I first started penturning, but I have settled on thin-only as my method. I tend to go through about one 8oz bottle of thin per year, so its a little more cost effective for me to only use one type -- my first year I had to trash 1/2 bottle of thin and 1/2 bottle of medium that got old.
What is the shelf life of Medium and Thin CA?
 

Dehn0045

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Mar 19, 2017
Messages
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Location
Houston, Texas
I find that shelf life is about 1 year. Towards the end the CA will take longer to cure, this is an indication it is going bad. I find that thin has a little longer useful life than medium, but 6 months to a year is a good guess. Moisture and heat are both bad for CA. Manufacturers recommend to only store unopened CA in refrigerator -- if an opened bottle is stored in the refrigerator it might generate condensation inside the bottle when it is removed, which is really bad (moisture is worse than heat). Manufacturers also tend to hedge their bets by saying the shelf life is for unopened bottles only. My understanding is that when CA goes bad it doesn't cure quickly/completely, this causes some uncured CA in the finish, when this does eventually cure it causes the a slight shrinking that results in cracking of the already cured material. It is a pretty common problem for old/bad CA to cause a spiderweb cracked finish after a few days. Another thing that I have learned is that accelerators use either acetone or naptha as the solvent but basically all use the same (or very similar) active ingredient (N,N Dimethyl-P-Toluidine). Acetone will dissolve CA, so it doesn't seem to be the best thing to use on a finish. I use BSI Insta-set (pump spray), but I only apply prior to application of CA to the blank, if I apply the accelerator to uncured CA it will cause a dimpled surface. Here is a good write-up with more information: https://www.claypenblanks.com/what-is-polymer-clay/ca-finishing-101-html
 
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