Yes.. the blue stuff is some nice silicone from Loctite. On the tube says: Flächendichtung, Loctite 40ml. Just some stuff i found lying around in a garage :shrug:
I tried a thin rubber as a seelant, but the stuff leaked like crazy and it was very hard to cut.

@Puzdre: The shakes were my concern too, but then I used two metal profiles that restricted movement of the block to left and right... and it worked pretty well. And if there are still too much shakes, try not to go so deep in the material with mill bit. That helps too, although it takes some extra time.

As Mondoshawani said, "time not important...only life important":D

I saw in your earlier post what you used to stabilise the workpiece, and I must admit, it was nice idea! Gonna try that soon. One more thing, how many flutes was that mill bit? I got some with 2 and 4 flutes, just wanna know (without trying;) ) what would be easier to use (I guess 4 flute will be steadier, but I don't really know)?

Mine had 4 very very sharp :D

Superb....... I was looking at it as a mill made block until I got the where you showed the pillar drill. realty excellent and it shows just what you can do with limited tooling and a little bit of true ingenuity ;)

I made my early ram blocks with a pillar drill and an old lathe as X-Y but is was not up to any sideways milling at all, so joined holes a-la-rotor was the order of the day.

I know its' the way you had to do it, but the only thing that makes it look a little home made is the blue sealant IMO. What you could do is take the clear tops and get a machine shop with CNC to mill you an thin o-ring grove, (should be pretty cheap), then get the appropriate size o-ring...... spend an evening with t-cut & polish on the copper parts and they would look better than production quality, (it is easy honestly) :p ........don't forget some pics of the cooler on the card later on btw,

A really super job, and I'll have to watch out if you get a mill :cool:

Thx, BladeRunner

I already made the groove for o-ring but it's now covered with blue silicone sealant. I know it doestn't look that great, but that was the only thing I had in the reach of my hands ;). I'll try to spend some quality time with them... polishing and stuff :p

That's what i call pushing the machine over the edge ;)
Sometimes I can do wonders with my drill. Once i even used it as a lathe :shrug:

@Puzzdre: Sorry I overlooked that you were asking what material is the top off.

It is made of 10mm thick polycarbonate.
I got a nice piece (500mm x 500mm x 10mm) for around 15 EUR (17 USD). I think that was a pretty good deal.