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View Full Version : For small-scale doming, 2-part or UV curable?



John Noell
06-01-2011, 8:49 PM
We get only a few requests a year for doming. I tried some 2-part but it was okay but it has gone bad with age (tropical weather). For those who do small-scale doming, do you prefer UV curable or the 2-part?

Rodne Gold
06-02-2011, 1:50 AM
You will get yellowing with 2 part and with uv curable , you might as well use the easiest (2 part) if you are doing small scale. if you want to avoid yellowing , you need special (read very expensive) resins. You will find 2 part urethanes better than 2 part epoxies in regard to yellowing, delamination and degradation but urethanes are more finicky to use. It is better to use a resin that is not rock hard when it gels , the ones that dry semi soft look better longer as they dont show scuff or scratch marks and dont shatter.

Gary Hair
06-02-2011, 2:00 AM
You will get yellowing with 2 part and with uv curable What kind of timeframe are you talking about Rodney? I have some uv curable pieces that are almost 4 years old and they look as good as the ones I did last week. Granted, they don't see much outside exposure, they are lapel pins, but I would think that over 4 years is a pretty good lifespan.

Gary

Rodne Gold
06-02-2011, 3:40 AM
Completely indoors and lapel pins are generally not problematic as the lifespan of the badges etc are short , however some resins are worse than others , I have seen some lapel pins demonstrate severe yellowing in a year or 2 indoors , but this is really only that relevant when you have a lot of white background. For outdoor , well I have seen even the good stuff (not the special stuff) yellow significantly within 6 months , so for eg if you were doing car or motor bike decals and doming them , you have to use special resins.
The biggest issue is with hard epoxies , as you have 3 problems , 1) Aline migration where the surface gets a milky haze after time , 2) Delamination off the domed substrate and 3) Cracking and shattering. This depends on lots of things but can happen quickly.
Thing is, short runs normally mean that doming isnt a core element of your business , and even if you do have the odd problem , it won't really affect your reputation or cost you an arm and a leg to rectify (like rerunning 10 000 items)
In terms of UV curables , the ones that use the blacklight type boxes and are quite viscous seem to be the worst offendors re yellowing outdoors , odd as one would think the uv curable stuff isnt. You get another uv curable that is not all that viscous , so you cant build high domes , but it uses a very high intensity flash type lamp to cure (like in 5 secs) and remains very clear , problem is the dome is too low for that really good domed effect and the lamps are expensive.

John Noell
06-02-2011, 4:11 PM
Mostly we get asked to dome stuff like RowmarK MetalGraph so it already has a yellowish look. Plus, these are almost entirely for indoor use. We've had trouble measuring and mixing very small quantities of 2-part. (Labor here is cheap but the quality is really low. Accurately measuring anything is not well understood by the locals here. It takes a LONG time to even get workers to SEE differences in quality, even when you hold pieces side by side. Because we are mostly selling to resorts run by ex-pats who DO see the levels in quality, it is a tough situation when your labor doesn't. I am getting more business because the ex-pats love dealing with someone who understands the quality they want.)

We also have an issue with the tropical weather hastening the demise of our epoxy supplies. Don't know how comparable the UV-curables are for storage life. Additionally, the quick cure time of the UV type is very appealing compared to the 2-parts.

Chuck Stone
06-02-2011, 5:26 PM
If you can find it locally, you might try a clear polyester resin. It won't dome as high as an epoxy or
poly, but tends to yellow less if you get a 'water clear' or 'crystal clear' resin.. and it is
probably easier to polish out.

The main disadvantage is that it doesn't want to dome on it's own, so you need to
dam around the edge and pour it. (I use tape, works fine) then shape with sandpaper
and polish out with sandpaper, micromesh or plastic polish. But with a wood block and
a sheet of 220 you can shape an 8x10 in about 30 seconds, polish in a couple of minutes.

Dane Fuller
06-02-2011, 6:13 PM
John,
I've never done any doming but used to build custom fly rods. When a customer wanted epoxy finish on the wraps I used Flex Coat Ultra V (no affiliation) in the Lite Build formula. It is pretty low viscocity stuff but, you can get it in the High Build formula that is fairly viscous. I don't know what you want for curing times. This stuff can take a while to cook off but it has a longer pot life. I kept the bottles in the fridge too. That seemed to help keep it from going bad as quickly. If you do that, don't forget to warm it up with a hair dryer before mixing. Also, after mixing, if you blow on it thru a swizzle stick/straw, the carbon dioxide will cause it to release the trapped bubbles quicker.

John Noell
06-02-2011, 9:06 PM
Thanks guys. Yellowing is not an issue but cure time and height of dome are. The fridge is usually pretty packed and I doubt my wife wants chemicals stored in it (but it sounds like a good idea for the tropics). :)

Dan Hintz
06-02-2011, 9:19 PM
John,

What about one of those mini fridges people keep at their work desks or in dorm rooms? Small enough to keep out of the way, large enough to hold quite a bit of epoxy-type stuff.

John Noell
06-02-2011, 10:38 PM
The problem with living on a beautiful tropical island with great fishing and diving, is that there isn't much else here. No one here sells such things. I might be able to get one from the capital (another island) but to get anything close to what I ask for I'd have to go there. And did I mention we pay more than 20 US cents per KWH? Ultimately that is a good idea. And that way I could have a few beers closer to hand. :)

Rodne Gold
06-03-2011, 1:07 AM
The killer for most doming compounds and when doming is humidity , we use dehumidifiers in our doming room , resins shouldnt readily absorb water unless you open and close a partially empty container a lot.