Use of epoxy for levelling

[Neale]

Thanks to various contributors, I have been able to get a lot of useful information about using epoxy for rail levelling. However, it is usually buried deep within build logs, so I wanted to start a thread just for this topic, if only to make it easier to find later!

After reading lots of views on the subject, I ended up with Reactive Resins Syntac EPAFD low-viscosity resin and matching Synamin 201-c slow hardener. I calculated the required volume based on width/length of area to be filled and a guess at a sensible depth (5mm), and based on 1ml weighing 1g (which I now realise is a big assumption and not based on any known density...) I mixed up 500g of resin and 250g hardener, which should have filled the required area with a bit left over. To my surprise, this is exactly what happened.

This is an overall view of my machine (very much work-in-progress).



Top rails are about 1800mm, spaced at about 1000mm. Construction is all-welded, a mix of 50x50x3 and 100x50x3. As far as I can judge, the X rails dip in the middle by about 1.3mm. I don't know if this is welding distortion, or if the original box section was slightly bent.

I used a single central bridge, an odd length of MDF that was about the right size. It is screwed to some odd bits of batten, clamped to the rails so it is level with the rail surface.



The dam uses Screwfix thick draught excluder, which stuck well. To avoid leaks in the corners, I used small dabs of hot-melt glue. I tested this first, in case it melted the draught excluder, but it seemed OK and worked well. The only leak, in fact, was over a couple of the plug welds that hold a 25x5 strip in the top of the rails (to take the tapped holes later). There was clearly a very slight weep through these. This shows the hot-melt glue, and the sink hole close to one end over a plug weld.



I don't expect this to be a big problem later.

There were a couple of things that were worrying me before I started. One was the horror stories of shrinkage, especially at rail/bridge joins. I didn't see any evidence of this.



One thing that I did do was to run up and down the epoxy with a small stick once I had poured it, to encourage it to find its own level. I think that that might explain the visible stripes in the epoxy at the join, although you can't feel them on the surface. I could also remove almost all the bubbles by poking them with the stick.

The other main worry was whether the epoxy would set or not, given the drop in UK temperatures over the last week or so. I decided to go ahead anyway, and for a small part of the time built a tent over the machine and blew in hot air from a small fan heater. However, I wasn't happy running this when I wasn't in the garage, so it didn't get a lot of this. In practice, this only took it up to 15C or so. However, as far as I could tell, the temperature in the garage varied between about 8C and 12C; the minimum temperature for the resin is given as 8C so it wasn't too bad. After 24hr, I could leave a fingerprint on the resin which largely disappeared over a few hours. After 72hr, it would mark with a fingernail. After 6d, I peeled back some of the dam on the bridge and tried scraping the meniscus as an experiment and it seemed pretty hard.



I'm now feeling fairly comfortable about being able to start drilling/tapping and mounting the rails.