Use of epoxy for levelling

[JAZZCNC]

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

How do you get that I never added any heat or kept a consistant Temp just from me saying waited nearly a week before fitting rails.?? . . You know what they say about Assumption.!!
My workshop is fully heated and Temp controlled with a Thermostat. The frame was slowly brought to room temp of approx 17deg over 3 or 4 days before applying epoxy and then workshop was kept at this temp for constant 3 days 24/7 afterwards then rails fitted after 6 days of curing.
This was using West systems 206 Slow hardener not 209 but still it caught me out, which I should have known better after doing several machines with epoxy.

[Rich]

From experience I know my elevated cure resin will harden in cold well, just add time. Excluding the 205 hardener, a workable cure should be achieved within 2.5 days (72oF cure is 15 hours max, 67oF equates to 30 hours, 62oF should be 60 hours). They quote 'thin film'. It tends to be 1mm or so. Thicker films, shorter time periods. I guess you must have been unlucky, or the hardener is getting old.

Matthewb,
I agree, polyurethane has potential with some additional benefits, including vibration dampening. I had a quick look at the website you posted. There were some reasonable numbers, attractive numbers on shrinkage, however, they tend to require elevated post cure. Quite expensive in my opinion. Have you thought of looking to the industrial floor coating industry - they might entertain a few free samples. Help you get your eye in before you pour.

Just noticed this website: http://www.resins-online.com/ I'd contact the underlying manufacturer for clarifications.

[Boyan Silyavski]

How do you get that I never added any heat or kept a consistant Temp just from me saying waited nearly a week before fitting rails.?? . . You know what they say about Assumption.!!
My workshop is fully heated and Temp controlled with a Thermostat. The frame was slowly brought to room temp of approx 17deg over 3 or 4 days before applying epoxy and then workshop was kept at this temp for constant 3 days 24/7 afterwards then rails fitted after 6 days of curing.
This was using West systems 206 Slow hardener not 209 but still it caught me out, which I should have known better after doing several machines with epoxy.

Thats what i meant before, but could not explain it better. Machine,epoxy and room should be same temperature from the moment of pouring to the moment ready to mounting.

I have done some experiments and epoxy will even cure at 5C though not advisable.

[JAZZCNC]

Lets be getting real here.? Epoxy method isn't rocket science and doesn't need to be made so.!! . . .It's just a matter of using correct Resin/hardner mixing it correctly and applying in clean enviroment at sensible tempreture with-in Manufacturers recommendations. . . THEN . . . Leaving alone until it cures FULLY.

By far the Hardest part for most is being patient enough to leave for couple of weeks but it really is best if your unsure because if rails are bolted on and they Sink it's all been for nothing and correcting is hassle.!

Silyavski as highlighted some good points and made sensible suggestions which for anyone building a Large machine with lots oof expensive epoxy would do well to follow but for smaller machines where Epoxy settles quicker and easier to handle then it really is quite simple if some common sense is applied.!

Clean, Warm, Dry with leak free dams and it's a doddle. .

[Rich]

Jazz, so you're saying the epoxy method, as described by Clive and Silyavski is the best way to go because it achieves what level of accuracy?

[Boyan Silyavski]

Jazz, so you're saying the epoxy method, as described by Clive and Silyavski is the best way to go because it achieves what level of accuracy?

Let me respond instead.

It achieves the level of accuracy of your straight edge + your intention of accuracy.

You need a straight edge that should be at least as long as your machine is wide, to check the result and later square the gantry. Your intention of accuracy will help you see small mistakes if any and using shimming and checking against the edge will help the desired accuracy. Anyway you will need the edge to mount the rails straight in the other direction. The more accurate you want it to be, the more you will check and adjust and generally the more time it would take you.

For an example i did 3 separate pours of epoxy on my 3m long rails, when happy with the epoxy i mounted and dismounted 2 times the left rail and 4 -5 times the right one until i was happy. It took a week with helper, only adjusting the rails. The only reason to do that was because i will use that machine to surface other smaller machines and gantries in it and not mess in the future with epoxy if not building something huge. If this machines purpose was not meant for that, i would have shimmed the first unsuccessful pour and finish with that stage.

So if you mean all day doing precision aluminum milling is one thing, other thing is if you do all day wood.

Even so, the bigger the machine the difficulty to achieve precision multiplies. It not only the epoxy, it how many times you check all and if you take your time to repair all that you have found.

Its difficult to explain but at the end the precision of the machine depends how precise are you or how precise you want it to be. All else is means and ability to achieve it.

[Jonathan]

Per Jonathan's data, the suggestion must be that even with careful construction and preparation, the process retains a relatively high error rate, when compared to the required outcome. My addition is to suggest that the impact of the error rate, regardless of cause, could be halved by taking a two pour approach. I think that's relatively sound logic. But that not good enough.

At risk of repeating myself, the error I got with the epoxy was exceedingly small (according to my surface plate) - the large deviation you see at the end of the graph was caused by the bearing seal/lower surface rubbing on the aluminium epoxy boundary. That error went once the rubbing problem was alleviated. The other graphs with large errors were false readings caused by accidentally measuring roll not height. I'm not mentioning values here lest they taken out of context - see the original post for a proper explanation.

I heated the resin in a water bath before pouring. It clearly lowered the viscosity, but I can't comment on what effect this had overall as I have nothing to compare with.

[Rich]

Thank you Jonathan. What a mistake. I couldn't understand why everyone was so relaxed.

[Procato]

Apologies if degassing has already been mentioned.
Although I haven't got to the epoxy levelling stage on my build yet, I have had a bit of experience of some resins and silicones used for mouldmaking- After mixing and before pouring resins should be degassed thoroughly. It is very surprising how much air is trapped in the liquid even after careful mixing. I don't think you can achieve the figures on the data sheets without this process. Pouring/flow and shrinkage qualities are much improved.

https://www.youtube.com/watch?v=9sN0KT-tRsY

[routercnc]

Not done it myself but the 3 processes usually mentioned to reduce bubbles are:

1. Pouring the final mixture into another pot with a sealed hole near the bottom (e.g. duct tape), then opening the hole and pouring from the lowest part of the mixture, leaving the bubbles near the surface.

2. Once poured into the moat on the frame, flashing over any remaining bubbles with a hot air gun.

3. Not stressing over the odd bubble or two which gets trapped unnoticed.