Thread: Use of epoxy for levelling
Have you considered whether the fault lies with poorly mixed resin? The cure is a polymerisation. If the relevant components aren't available in sufficient quantities, the density of the film may change, leading to variation in final thickness?
Epoxy resin tends to be quite sensitive and there's little mention of preparation in this thread.
Using a good set of scales will ensure the right amount of resin and hardener is used. Really important if you want to resin to perform per manufacturers specifications e.g. hardness
Mixing. Spend at least five minutes mixing before use. Hand mixing is fine, an electric mixer is easier, but a slow speed. Avoid mixing in air. Once you have mixed for a minute, use a pop stick to ensure the resin sitting on the side and in the crease of the cup is integrated properly. Mix for the remaining four minutes. Once the batch is mixed, poor into a separate cup - leaving a little behind, so as to avoid any un-mixed resin transferring across.
The surface to be coated needs to be clean and dry.
The video was helpful in some respects. Personally, I wouldn't put a heat gun near epoxy without wearing a mask - air bubbles or no. But he's right epoxy loves heat and it does affect the viscosity of the poured resin. Personally, I'd lift the temperature of the resin prior to mixing using a water bath, especially here in the UK. I'd also be more interested in ensuring the ambient temperature of the room remained constant - especially in a hot climate.
I understand the target thickness for the film is 3-5mm. There's no reason why this need to be done is one pour: http://www.westsystem.com/ss/epoxy-chemistry/ A second layer can be applied once the first layer has started to gel, sufficiently. This might well be the best approach, assuming the underlying cause is human error
I'm not entirely certain what steps are taken after the film has been applied, but if the variation remains say 0.3mm i.e. human error is not a factor, could a high viscosity resin/compound then not be used to seat the rail? I believe that what is taking place here? http://www.moglice.com/ . You'd need to wait around a week before seating the rail. Ambient cure epoxies take a while to reach a state of final cure, which could be a problem, as you don't want an ultra thin layer of epoxy being exposed to pressure, when not chemically bonded to the layer below .... all my epoxies are heat cure, so I'm not in a position to run any tests. So lets hope its human error and applying two layers to create the desired thickness produces a lower error rate.
Oh yes. Vinegar is a good solvent for any split epoxy.
Personally, for this job, I'd been thinking about urethanes - but I'm not any way near needing to do this yet.
Last edited by Rich; 15-03-2015 at 02:58 PM.
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Mixing definitely is not the error if you mix the epoxy 10 minutes. Though i agree that it could be if not careful.
I believe i showed all already how to arrange and pour epoxy properly on even very big table, + saving 1 liter mixture at least on doing it with one bridge only. i hope my experiments and waste of money was not a waste, so people repeat the same mistakes over and over again, just because they want to do it their way or reinvent the hot water.
We could speak and speak, but - the errors are the following below. Only one of them or a mixture of them. Nothing more, nothing less.
-poor choice / epoxy not fit for casting/
-shrinkage /not pure epoxy, cheap epoxy/
-cast thickness -ideal 5mm, no less than 3mm
-less than 15C or max 35C, ideal 22C
-differential between material temperature / heating the room shortly before, bringing the epoxy from other room/
-not weighting precisely the mix parts
-too much air in mix
-mixing less than 7-10 minutes
-not changing the mixing bowl with new, just before pouring
3. Surface preparation
-not cleaning the surface with acetone prior to pouring
-dust on the surface or hidden at the corners
-varying distance between dams on same rail
-too flexible dams
-dams from different material at different places
-hidden leaks between dam and material that don't show outside leak -not impregnating and check beforehand with thin epoxy layer for leaks
-dam leaking or absorption due to wrong dam material
-not positioning it right so when it shrinks it sucks from channel
-not making extra long dam structure at the long rails
-not making bridge and dam extensions strong enough
-wrong bridge and extensions material,
-heating too much/too slow pass with the torch/
-making more than 2 separate passes /leads to orange peel/
-heating from different angle,not trying to be 90 degree with the torch
-heating too much the dams if they are from plastic
-accidentally heating the bridge more than the epoxy mixture
-dust when drying
-checking with finger if the epoxy is dry, during the first 24h
-laying the rails on top during the first 3 days to check how it looks
-mounting before a week has passed from pour
-not checking for dust particles that integrated during drying and scraping them with the straight edge
-not cleaning properly the rails and epoxy from dust before mounting, seat with the edges and scrape when laying down so no dust gets trapped
-heating the epoxy during drilling
-not chamfering the holes properly to clean the raised epoxy
-knocking the epoxy when dropping something or checking with the rails, and so making invisible raised points
Exposing the machine to >50C/ direct sun when outside temp is >25C/ will lead to problems.
Thats all folks. Do it properly and you will have 0.01 precision. Do it right and you will have great machine. Miss one point and you will have woodworking machine. Miss 2 and you will have a problem. Though of course people could lie to themselves and believe they have done it ok.
Last edited by Boyan Silyavski; 15-03-2015 at 07:28 AM.
Thou as they say in Yorkshire " Proof is in eating the pudding" so when your machine is finished let us know if your machine can surface two faces parallel to each other across it's full length & Width then surfaces hold ONE hundreth millimeter parallelism over the whole length.? . . . Then I'll be impressed and Don my Flat Cap to epoxy and You Sir.!
Last edited by JAZZCNC; 15-03-2015 at 11:32 AM.
Its relatively speaking. I did not mean to brag or mislead, just to encourage and lay down the points that should be followed to the letter, if one wants to achieve what could be achieved at home.
Yes Dean, its more like a wishful thinking. Of course it could not be measured, especially at home. I agree its not real 0.01mm. Maybe even not real 0.05mm at some places. But may be it is between 0.01 and 0.05mm if lucky and done right/. I was able to discover bigger than 0.05mm gaps using the edge and strong led torch.
Lets say i am happy when with the straight edge i could not find a spot where it did not look perfect and tight fit to the edge. Thats my criteria for straightness for my machine. Obviously on a 3000mm travel, that's something, when done right and at home.
Having in mind that the straight edge itself is not so straight over 3000mm , table below, that on paper it should be supported/handled at a special length for the measurement to be right i would say there is no way that something could be proven right or not.
That means though that there is still a small chance in a million that in fact is that straight. . Who knows, when its not measurable.
So i say, better do things right with the idea that all must be perfect. Yeah the result may not be. But what would happen if one even does not even strive to do it right.
Thanks Silyavski, its good to have all the detail laid out like that.
When thinking about the issue last night, I had in mind UK conditions and the tendency, recorded within various logs, to complete this task at below 25oC i.e. circa 10oC. This is relevant because as a general rule of thumb, a 5 degree F increase in cure temperature will half the time taken to cure, which is a thought I'd like to carry forward.
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.
However, as per the original posts #1, it took 72 hours to reach a state whereby it was possible to mark the epoxy using a finger nail i.e. the epoxy was still in a very plastic state at this time. So I am thinking, is this not the time to be thinking about mounting the rail?
The sort of procedure I have in mind is detailed below, but then I don't know how long it takes to mount the rail accurately? How much tinker time is needed?
Broad brush, the process would be as follows:
- Set up a bench test for the epoxy you are using. Dam an off-cut from the material used to make the supporting axis, circa 30cm in length?
- Before testing the epoxy, measure the ambient temperature, it needs to be below the manufacturers recommended cure temp, let say 15oC instead of 25oC. This provides for a much long gel and cure time.
- Mix and pour. One layer or two, depending on your view.
- Measure the hardness of the epoxy at regular intervals during the cure. A cure schedule can be drawn up based on the manufacturer specs in any event. Once it becomes evident that a thumb print can be made, start measuring the hardness of the cure by dropping a ball bearing from the same height and recording the difference in the diameter of the depression made.
- At a point to be determined by the dropping of the ball bearing i.e. while the epoxy is still relatively plastic, seat the rail using pre-drilled placement holes.
- There is where there is a balance to be struck, or not, depending on tinker time and ambient temperature. The rail needs to be seated on epoxy that is able to resist the the weight of the rail, but unable to resist seating of the rail when lightly bolted into place i.e. such that there is insufficient upward force to cause a deflection in the rail at the mid-point, between the two bolts.
Clearly it would help to run this experiment a few times. Removing a test sample isn't an issue.
Like you clearly suggest, the right epoxy system is key. I would be concerned about using the West System if the ambient temperature is above 25 degrees C. Mixing - don't just stir the components together, mix the top into the bottom. Acetone will affect the chemistry of the resin system, so clean the frame well before the dam is constructed. Personally, I would do any final wipe using IPA. Heating/Degassing ... don't mix bubbles in. I wouldn't put a heat gun near epoxy, random application of heat? Use a brush and wet out the steel - like they did in the video. If you must, use a hair dryer set at min heat until you have a level. Heat the resin as a whole should you need to lower its viscosity prior to pouring. A water bath is the safest method - just be sure to dry the cup, as water and liquid epoxy need to be kept apart. Has anyone used a syringe to transfer the epoxy into the dam - 100ml every 40 cm or so?
Last edited by Rich; 15-03-2015 at 08:01 PM.
its proven that's its better to drill when epoxy is dry, not before pouring it and then messing with masking the holes.
The epoxy should be same temperature as the table to avoid shrinkage. yes you de-gass it by slightly heating it, but you pass with the torch very fast and as i said if you heat it further here by mistake, you will end with orange peel surface .
i dont insist on that, but its my feeling that the epoxy should be same temp. I took care of that and it worked. Why waste 100euro pour, just to see if it can be done as you say.
IMO it's much better to give the details of how it's done and leave out any claims of accurecy unless can be verified to avoid dissapointment and instead show results of your labour with work produced.
Don't take me wrong here i'm not taking anything anyway from your build and I'm quite sure your machine will give very good accurecy and results. But to me the whole point is what gets spit out the other end, so IMO build to the best of ones abilty and be happy in the knowledge that what comes off the cutter is the best it can be given each persons Skills/equipment.! . . . . THE POINT. . . . Don't get hung up on pointless details that can't be proven or seen.!!!
I'm advocating a bench test in advance of pouring! Surely that saves money Sil?
I would leave the bolts in and if they were a little resistant, I'd heat gently using a soldering iron to release them. That's if I hadn't applied mold release.
Shrinkage is a post cure issue ... you might be seeing a change in viscosity due to temperature disparity between the resin and the table, which is affecting flow. The resin will quickly adopt the temperature of the table in any event, hence the suggest to paint on a thin film in advance of a pour - but in reality the impact on flow will be negligible.
Syringes, reminds me of these: http://uk.rs-online.com/web/p/epoxy-...zzles/0503385/ If you want belt and braces on the mix.
The resins I use are heat cure epoxies, so I don't have anything suitable for running a test. Once I've sold a few more things on Ebay, I look at finding a suitable resin system for the job.
Hence the need to run a bench test in advance and track the behaviour of the epoxy you have chosen.
Last edited by Rich; 15-03-2015 at 10:11 PM.
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
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