Use of epoxy for levelling

[Boyan Silyavski]

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.

[Rich]

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.

Silyavski,
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?

[Boyan Silyavski]

Rich,

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.

[Rich]

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.

Neil,
Hence the need to run a bench test in advance and track the behaviour of the epoxy you have chosen.

[Clive S]

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

[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.

[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

[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.

[njhussey]

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 thunb 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.

Silyavski,
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?

Rich, you need to leave the epoxy until it is totally set. If you bolt the rails to it before its totally set they'll sink into it. Eddycurrent had just this thing happen to him, he corrected it by filling the marks/dents with more epoxy.