Use of epoxy for levelling

[mekanik]

Hi Guys
Have been following the progress of this thread and think there might some advantage in using trace heating cable on the bed to provide a stable temperature prior to resin pour, bed can be uniformly heated then knock off the power and let the bed cool to the desire temperature and do the pour.
Regards
Mike

[njhussey]

Well I'll be watching with interest to see the results of all this...

[Rich]

Clive - a soldering iron to the head of the bolt should stop that. Apply just enough heat to let it dissipate from the thread.

Cheers Mike, like you suggest, if you are going to apply heat to lower the viscosity of the resin, it needs to be applied uniformly. A heat gun is a little too intense and random IMHO. Adding an aluminium plate to the nozzle would certainly help the situation - a more consistent heat over a wider area.

Heating the frame with trace heating ... that's a lot of metal? Have you seen this thread: http://www.mycncuk.com/threads/6565-...dy-Eddy/page18 , photograph 6, you'll see a piece of flat bar below the film. There's no reason why this bar couldn't be used as a heat shield - held at a prescribed height above the dam (pre-drilled holes and placed back below, once the film had set). Ideally, it would be a little wider, but this approach would put the heat gun back on the menu, switch to full power with little risk of over-heating the surface ) I'd be inclined to test that last comment, especially as the thread of the bolt holding the bar is sitting in epoxy. If you are happy to keep waving the heat gun around in a consistent fashion, it would have the desired effect - reducing the viscosity of the resin and if you are patient and consistent i.e feet per second, you'd be well on you way towards curing the epoxy within specs. This assumes a thermometer, temperature gauge or such like between the flat bar and dam and the bolts don't become the focus of any heat build up.

Anyway - thanks for entertaining these ideas. If someone could let me know how much tinker time should be allowed for setting up the rail, it would help.

[gavztheouch]

I would be hesitant of leaving the bolts in as you will get miscues around the bolts like you will get at the edges of the moat. I used West System very slow cure 10 - 20 hours. After I had a long conversation with them on the phone they suggested that I flash the surface with a hot air gun (just a very quick flash) 5mm one pour. ..Clive

Clive I have some West systems slow cure coming on Monday, after the pour when should I flash the surface? Straight away? Is a hair dryer hot enough or do I need a proper industrial hot gun?

Cheers

[njhussey]

Clive I have some West systems slow cure coming on Monday, after the pour when should I flash the surface? Straight away? Is a hair dryer hot enough or do I need a proper industrial hot gun?

Cheers

Gav, a hair dryer will just blow the epoxy and splash it everywhere....i believe (I didn't do it myself as I didn't have many bubbles) the time to do it is when you're happy that you've got the epoxy evenly spread out and are just about to leave it to cure but I'm sure Clive will tell you when he did it.

[Clive S]

Ok This has all been said before. The system I used is this http://www.westsystem.com/ss/209-extra-slow-hardener/ this is the pdf. http://www.westsystem.com/ss/assets/...%20105_209.pdf
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It is very important to measure and mix well. it is important to make the moat water tight as any small leaks will spoil the job. I used a thin bead of silicone all round the inside edge. Just make sure that the frame is least at about 18C .
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Mix the epoxy with a flat paddle ie not a round dowel and mix well slowly so as not to introduce air into the mix then let it settle for a couple of minutes. If you have another prepared container with a hole near the bottom about 6-8mm with some tape over it you can then pour the epoxy into the prepared container.
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Then take the tape off the hole and let the epoxy pour from the hole into the moat. (this will get rid of most of the air as bubbles rise and you are pouring from the bottom)

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Don't just pour all the epoxy in one place but try and get it even all the way round. Then if you see any big bubbles you can just flash them with the hot air gun they instantly disappear. (you are not trying to heat the epoxy up it is a quick flash)
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The epoxy is almost like water and will flow very easy.
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Rich There is no way a soldering iron will stop the surface tension miscues thing from happening all around the edges of the moat AND around any bolts you have put in.
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When the epoxy has cured at least a week then remove the moat sides etc and with a rasp bastard file carefully remove the miscues. If you are using 20mm rails you want the moat at least 40mm wide (mine was 55mm)

I used two dams from one rail to the other and was more than happy with the result.
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This has all been done to death and is not rocket science I think in a hot country you may have to be a bit more careful. The epoxy may feel hard to touch but DON'T play with it until at least 7 Days have past and has been said already make sure that the base is clean and oil free. You can rub some oil around the inside of the moat edges to stop the epoxy sticking to the sides (make sure it is sealed first though). ..Clive

[JAZZCNC]

Clives spot on and speaks from experience so anyone going to do this would be advised to listen. Esp about the time to leave and longer the better I find.
It's very easy to get caught out thinking it's cured fully when it's not and then get sinkage, I've had it happen to me recently after leaving nearly a week and should have known better but was rushing. so don't think it's a rookie mistake because you will get caught out if you try to rush.!

One way good way to test if fully hardened is to make separate test piece same width about 12" and pour to same depth. (the moat will work for testing) Then pour at same time and leave.
Then when you think it's cured check the test piece by bending, if it just bends and doesn't snap then your not cured enough, if it snaps then your ready.

[Clive S]

Then when you think it's cured check the test piece by bending, if it just bends and doesn't snap then your not cured enough, if it snaps then your ready.

Yes I forgot that bit .. Clive

[matthewb]

I wonder if anyone has tried polyurethane casting resins instead of epoxy for levelling?

The stuff i have used in the past ( for casting not machine levelling) has the viscosity of milk and is designed to run and fill all the voids in a casting, i would imagine it would be better than most of the epoxy resins i have come across.

Its tough too and will take fillers and reinforcements if you want to use them.

http://www.benam.co.uk/products/plastic/

just a thought...

[Rich]

Thanks Clive, I will go back and edit, so it's clear that I am talking about the threaded bolts. The residual meniscus would be of a nominal thickness using this method and subject to removal once the drilled hole was opened out.

These guys might be worth a shout: epoxies start at page 58: http://www.swiss-composite.ch/scs4/h....shtml?lang=en (selling on behalf of: http://www.r-g.de/en/ ) I've never had cause to deal with them directly, but they are known to have a good reputation. Supplier to light aircraft industry, so quality is a priority.

Using the west system 105/209 as a point of reference, viscosity of the mixed resin @ 22oC is 650mPas. This figure will increase as the temperature decreases, so the resin will become more viscous, the lower the temperature gets. Minimum recommended temperature for the 209 is 18oC. Physical properties once cured are really important, so its good to have this datasheet as a reference point.

Possible alternatives:

- low viscosity resin system 100 mPas @25oC, cures at 10oC
- low viscosity resin system 250 mPas @25oC, cures at 15oC

There are some other low viscosity resin systems in there, if your ambient is higher.

Jazz, you're waiting 7 days? You're not adding any heat, not even ensuring a consistent 15oC?