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Old 12-18-2017, 12:51 AM   #1 (permalink)
 
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Default Ambient Temperature

Are there any fact-based or experience-based guidelines for minimum ambient temperatures when using CA or WTF?
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Old 12-18-2017, 07:15 AM   #2 (permalink)
 
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Single digit outside, 45ish inside the garage and reactions (as forecast in Chemistry and other classes) are much much slower. (November conditions in Alaska)

Your mileage may vary.
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Old 12-18-2017, 07:30 AM   #3 (permalink)
 
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Experience showed me temps in the fifties the CA has difficulty curing. I sat a forced air heater on the floor directing the blast towards the lathe and cleared up the problems I was having. Take care to avoid wood dust and shaving getting into exposed elements, a ceramic heater is ideal in this regard.
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Old 12-18-2017, 12:09 PM   #4 (permalink)
 
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I've never used WTF, so can't comment on that. Obviously "thickness" of the CA will be the most important factor in cure time. Not all "thin" and "medium" CA are created equal. My understanding is that CA is generally ethyl 2-cyanoacrylate and the thickness is determined by how much "thickener" is used, methyl methacrylate (the monomer for PMMA or plexiglass) is one thickener that is used. For example, I use Bob Smith Industries CA and their Thin CA has no methyl methacrylate, Medium has about 5% and Thick closer to 10%. Interestingly, when CA is modified with methyl methacrylate it has slightly different properties, it is less stiff and has better impact resistance, but I digress. The age of the CA will also play a role. My understanding is that there are two major contributors to reduced activity of old CA: 1.) gradual polymerization of the CA results in a more viscous liquid with less reactive, longer chain molecules, and 2.) water in the CA will slowly react to form acids that are not neutralized when the CA is exposed to ambient conditions, this acid inhibits the polymerization reaction. There are also a whole slew of inhibitors, stabilizers, and viscosity modifiers that are added to CA adhesives intentionally to change their properties, each brand/product will respond slightly different in the conditions in your shop and the exact application.

After composition, I would argue that temperature is probably not the most important factor when finishing pens. Humidity plays a more important role, but as you would expect higher temperatures generally mean higher humidity. Water consumes the acidic inhibitor in the CA which allows the polymerization to occur rapidly. Without any water (humidity) the inhibitor remains in the liquid and no polymerization can occur (like what happens in the storage container). This is why the manufacturer recommends not storing the CA in a refrigerator after it has been opened, the heat cycling forces humid air in the container and degrades the CA.
Next, the substrate plays an important role. I notice that the first couple coats of CA cure very fast, but the substrate is wood and the CA chain reaction is initiated by the moisture in the wood. After that the subsequent CA coats are on top of prior CA coats, so it needs to search for moisture in the air to cure.

As for temperature, Cyberbond states that the rule of thumb for temperature is that cure time halves with each 10 degC increase in temperature and the ideal is 20 to 24 degC. Therefore, you can expect it to take about 4 times longer to cure at 32 degF versus 70 degF (pretty sure I'm never gonna work in a shop that is below freezing...). One approach might be to add heat to the blank prior to applying CA by using some good old friction, then you don't need to heat up your entire shop. But it is my opinion that increasing temperature alone probably isn't going to significantly change the cure time (or amount of time needed to finish a pen).

The moral of the story is "its complicated". If you think your CA is bad, buy some new stuff or change brands. If you think its too dry, use some accelerator. If you think its too cold, wait a little longer...
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Old 12-18-2017, 01:14 PM   #5 (permalink)
 
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Great answer, Sam. This one should be added to the tips section of the site.


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Old 12-18-2017, 02:58 PM   #6 (permalink)
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Sam, I agree with you. And you and I are giving somewhat ambiguous answers as opposed to the OP, however that is all we have.

As to Temp and Humidity, Humidity does play a huge role where it is present. My experience in living along coastal Japan and now in North West Mississippi (near Memphis, TN) high humidity around and above 80 produces less fogging for me than the equivalent humidity at 50 - 70. I don't finish pens below 60. One thing that I noticed about cooler temps was that in the curing with high humidity, it seems to draws more moisture out of the air, similar to cold glass on a table sweating. I haven't seen that at 80 and above. The colder temps with humidity makes a mess of cloudiness. After learning this, I turned on a heater and heated the room up for a while before finishing.

Back to Nebens original question: "fact-based or experience-based guidelines"
. . . That (fact based) would be good to have. All we have is experienced users and in my years here, I have noticed a wide variance of results - due to dry regions vs higher humidity regions, with temp changes altering it some.


The two pictures below were done about 9 or 10 years ago (Toyota City/Nagoya area) and I did them in winter with about 55 - 60 in my shed, I let it cure overnight and the next morning it was white. It dropped down into the lower 40's overnight. It did not turn cloudy on the inside. It did have a thick coat of CA on it. Oh, and the bottom one was not polished at that point, only sanded with about 2400 MM to get the "frost" off. Of course that was not REAL frost, but something that happened in the curing process in cold humid weather.


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Old 12-18-2017, 03:12 PM   #7 (permalink)
 
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Quote:
Originally Posted by leehljp View Post
Sam, I agree with you. And you and I are giving somewhat ambiguous answers as opposed to the OP, however that is all we have.
Yeah, after posting my answer I read the OP again and was thinking "damn, I should've just typed no and yes" (no for the 'fact based', I think everyone who has used CA has their own 'experienced based' guideline). Unfortunately there is a lot magic in the additives that different CA manufacturers use. I think most of the formulations are trade secrets or otherwise undisclosed, which makes things harder. In this way I think that CA finishing is more of an art than a science, I've done about 150 and no 2 have been exactly the same.
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Old 12-18-2017, 08:30 PM   #8 (permalink)
 
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Go below 50 and pretty much all urethanes and poly-urethanes start to have serious trouble. This time of year I regularly have customers tell me 'I used brand X poly I bought at big box store to finish item two months ago and it is still tacky.' First question, what temp and humidity did you finish at? The answer is almost always, 'IDK, whatever it was in my garage. I could see my breath.'

I don't get the same complaints about our products, but our customers generally know what they are doing, and we try to give those who don't enough info to have a fighting chance.
I try REALLY hard not to finish anything below 60.

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Old 12-18-2017, 10:55 PM   #9 (permalink)
 
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Thanks everyone, I'm a newbie struggling with finishing. Have had some success with CA but will probably experiment with acrylics until it warms up. Love this site, spend tons of time here.
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