Quite an Unusual one

[Boyan Silyavski]

Today started soldering the bed frame and bought the epoxy. As i stopped working at all except on the machine, money flows like water through my fingers. So i bought at the end the Spanish epoxy with very similar properties like the WS. from choice of three i choose the most similar. There were seemingly better though some data was not clear, from the one that could concern, i mean. 125eur with shipping for 5kg pack +1.6kg hardener.

Basically 90 min gel time, max isotherm 40C, compression strength 580kg/cm2, yellowish, contraction 0.1%, density 1.08 gr/cm3 which roughly translates to 6.5l so ~20eur /lit mix, I cross my fingers that it works ok.




It seems that the machine will lay on the floor with no legs. have to figure where to fix some hooks for the future and most importantly some plates to lift it using car jack. To level it for the epoxy pouring. Cause now it is unliftable already.

Now going cheap was really bad idea. Ok, it would have saved me 100euro on this size of structure...

But here is what happened:
The epoxy poured extremely well. It leveled well. And for 4 hours it was perfect. As gel time was 90min, i thought well, i cheated destiny. But no. After the 4rth hour it shrank in volume and there was not 20mm wide flat area in the center to munt the rail. I did the test 50mm wide channel, instead of the 40mm normal with WS 105+209. Read a lot why and it seems the reason is that the epoxy is low quality and contains non reacting solvents that vaporize when the hardening starts. On the long axis it was straight, so its not a mixing problem, anyways i mix it at least 5 minutes and change the can before pouring, so not my mistake. Repeated twice the test-same result.

So i took a risque and lost. My reasons were not that i am greedy, but the price difference multiplied by the future machines is quite some money. However i just returned the 5_1.6kg epoxy so the loss is about the cost of shipping, the time and 1 lit of epoxy.

Conclusions:
1.Seems the biggest unaccounted problem for that purpose is the shrinkage, in other words the purity of the epoxy. Hence the price of good epoxies :-). Otherwise flatness and surface quality is more a result of good mixing and following exact mixture to the gram and temperature when pouring.
2. Judging epoxies from their technical sheets means nothing. It can seem on paper right but poor in reality
3. Epoxies with very high viscosity >700 cps of mixture maybe contain something that will evaporate later

Left on the picture is WS 105+209 at the time of pouring and cured. Also the spanish epoxy untill 4h. Right is the shrinkage when 8h passed



At the moment of pouring till 4h



The problem after 8h of curing, a bit difficult to be seen but the drawing above shows it better. On the second picture the shrinkage lines can be seen at the reflection distortion . Not that it could not have worked as we are talking about 0.3mm here and on the long axis was straight, but not worth the additional fiddling.

[Neale]

I don't think that you can blame the quality of the epoxy. It did what it was designed to do. I think that epoxies containing solvents are typically used for coating, so that they spread well - which is what your epoxy did! They are definitely not recommended for use as adhesives or fillers, mainly because of the shrinkage as the solvent evaporates. However, I didn't know this either until a couple of days ago when I read an article on the use of epoxies for adhesives and coating! Something to watch out for if anyone is looking for an alternative to the usual named brands.

[Boyan Silyavski]

I don't think that you can blame the quality of the epoxy. It did what it was designed to do. I think that epoxies containing solvents are typically used for coating, so that they spread well - which is what your epoxy did! They are definitely not recommended for use as adhesives or fillers, mainly because of the shrinkage as the solvent evaporates. However, I didn't know this either until a couple of days ago when I read an article on the use of epoxies for adhesives and coating! Something to watch out for if anyone is looking for an alternative to the usual named brands.

Hi Neale,
This is specifically a casting epoxy, its not a coating epoxy. It specifically says 0.1% shrinkage in its technical sheet, and by no means its a cheap epoxy , its simply cheaper than imported WS epoxies.
I also read a lot of documents about epoxy and all say the same- 3 types of shrinkage, and exactly this type is due to non reacting solvents. This is not shrinkage due to temperature cause it happens after the initial hardening. From the company started to argue with me, saying this is not possible, it never happened, until the moment they understood that i know a lot of sh^t about epoxy and they agreed that this was because of the cheap solvents. That was the moment they agreed to break their policy of no return, once its opened.

[ba99297]

Hi Neale,
This is specifically a casting epoxy, its not a coating epoxy. It specifically says 0.1% shrinkage in its technical sheet, and by no means its a cheap epoxy , its simply cheaper than imported WS epoxies.
I also read a lot of documents about epoxy and all say the same- 3 types of shrinkage, and exactly this type is due to non reacting solvents. This is not shrinkage due to temperature cause it happens after the initial hardening. From the company started to argue with me, saying this is not possible, it never happened, until the moment they understood that i know a lot of sh^t about epoxy and they agreed that this was because of the cheap solvents. That was the moment they agreed to break their policy of no return, once its opened.

Syliavski i thought that a solvent free epoxy is a must at this procedure. Why you choose to buy an epoxy that contains solvent ( or i missaunderstood something?)

Vagelis

[Boyan Silyavski]

What about adding a filler like ATH ?

I thought to do it , only had graphite at home. But truth is i want it perfect, so bought the West system epoxy at the end.

Syliavski i thought that a solvent free epoxy is a must at this procedure. Why you choose to buy an epoxy that contains solvent ( or i missaunderstood something?)

Vagelis

I chose to buy epoxy sin solvents but they sold me one with solvents :-)

[ba99297]

You mean the solvent was in the epoxy before you make the mix?
Good for you that they admit their mistake and you finally get your money back.

[Boyan Silyavski]

Hi,

The build is going on but i am stuck with epoxy problems. Mean BIG problems .

Second time casting epoxy on the long sides and same problem. The area near the connecting bridges is sunk checked against straight edge. about 250mm wide visible inclination, not measured cause still not perfectly hardened but say 0.1-0.3mm . Each pour cost me 100euro 2.5kg of WS epoxy mix.

Now for a woodworking machine this will not matter, but spending so much money on it i would like to be as Perfect as possible. Hell, at least 0.05 precision or better, real life, not exaggerated. I was striving to something like the first machine i made 0.01mm, knowing that on such a big scale it would be difficult but worth to try.

So to achieve this i depended too much on the epoxy.

Whats the f---g problem then? Everything is perfectly prepared. 21C in the garage, 45mm wide dams, 10min careful epoxy mix, all by the letter. First time i thought the dam was flimsy and contracted at certain points. Not so the second time, everything is reinforced with steel/the bridges/ and hot glue / the 10x10mm dams.

I gave it a lot of thoughts and the conclusion is : the 1600mm long bridges are the culprit. The epoxy contracts , so the bridge epoxy contracts and takes away epoxy from the rails at the exact moment when its solidifying. cause i looked 100 times after 1 hour of pour, 2, 3 hours of pour -it was ok. It happens on hour 4 to 6. Or maybe it was my mistake that the connecting bridges had to be both ends, so when all contracts , contracts equally, like a ring i mean. No money though for further experiments . I believe though that even if ring is formed the right angle between them is the culprit.

So yes, there is a problem with 3000mm rails and 1600mm distance between them. Inherent problem i mean. Not reported by any body till now but hey, did anybody who made such a big machine take care to measure it against DIN 874 straight edge? Possibly no.

I blamed the air trapped, blamed the supports, blamed this and that, but on a smaller scale i did not have any problem before, +fixed all possible doubts. So yes its inherent, until somebody prove me wrong.

I see only 2 possibilities from here on.

1. Will wait to dry for 3-4 days and mount the rails using the straight edge/ 1m/ and shim. Then will have to buy the 2000mm straight edge to continue with the build and check the rails against each other. But if there is a twist , 2000mm straight edge will not be enough or at least would be very difficult to straighten things up. To the precision i would like, i mean.

2. I knew it when pouring second time, but was not sure. . So may be third pour from scratch or half pour over this one. And on minute 45 / 21C/ cut the bridges simultaneously by some previously prepared method. Say a sliding plate or similar. The way in actual water channels the water flow is cut. Cause at this moment everything is perfectly leveled .