I was thinking hi-temp bearing grease. Over time, it won't cake up like anti-seize compound or thermal paste....
Tomorrow, we'll see if this guy drilling the holes can pay attention to detail or not. He didn't have a 6" bit, so he asked if he could drill from both sides. I said yes, that the holes didn't necessarily have to "meet" perfectly, but they had to be absolutely parallel to the surfaces. I had only marked off a "+' on the one side where to start drilling 2 holes... I gave him a full day to do what he needed to do, instead of 1/2hr like he said he needed. He seemed pleased with the larger time margin. Needless to say, I'll walk in there tomorrow morning, take it outside to my truck and inspect his work with a micrometer. If it's decent, I'll have him drill the second block.
The guy did a great job drilling the holes. I measure 9.54mm for the holes, and 9.45mm for the elements. This leaves a .045mm (.0018") gap on either side. Nice and tight! I will use him again, he said he was able to do the job again if needed. It was just a tad bit tight on the one side, so I had to run a bit through to clean it up abit. The toelrance is so tight even the raised part # stamping on the stainless steel elements interfered with them going in smoothly. After a gentle sanding, and some heat sink goop they are now fitted in the block. I decided on heat goop because caking would actually be good to help keep them secured. Now I'll drill the holes for the 4 legs...
Excellent. I used 3" stainless round-headed bolts for feet. I haven't had any issues with heating the enclosing tray. I was thinking about enclosing the entire device in an upside-down baking tray with a rectangle cut out for the plate and a fan for cooling the unit after turning off.
I prefer my layout with all the wiring in the back - it gives me 3 clean edges. I find myself with my eye close to the edge, level to the surface (with a magnifier), monitoring the balls during the heating process. I am sure yours will work fine.
The guy who inspired me to build this did another cool mod: drill a small hole into the side, at an angle and fill it with solder for tinning wires by just dipping.
One thing to watch out for: the device is a lot like 'The Cornballer' in 'Arrested Development'. You probably have a longer attention span then I do; I burn myself quite often, leaving a trail of singed hair and expletives in the air.
In theory, there is no difference between theory and practice. In practice, there is. ...Jan van de Snepscheut
Instead of getting real close with a magnifier, maybe a USB microscope would be a safer option. I have one very similar to the one displayed here. I used it for the pictures earlier in this thread. If you can mount one close to the hotplate, you can watch the action safely on your computer screen. As an added bonus you can take pictures, or make a movie to post on YouTube.
...The guy who inspired me to build this did another cool mod: drill a small hole into the side, at an angle and fill it with solder for tinning wires by just dipping...
Very cool idea!
I don't have all the tools needed for tapping holes for the legs, so I drilled holes for some 3" wood screws I had. The holes were .010" smaller than the screw threads and it was still a battle to screw them into the 6061 Al block. I find myself using the micrometer all the time... It's now level and I've finished the wiring of the elements and powered up the PID controller. The 4 300W 120V elements are in parallel and will be wired in series with the 25A SSR. A couple more wires and I fire this baby up and watch the lights dim. Oh, I still have to drill the TC hole...
One thing I'll be watching is the time it takes to get up to temp. I've tried to outdo you enso!
Ive drilled the TC hole too deep by mistake. Looks like it's over by about .090". I'm going to fill it with some leftover metal shavings and thermal paste. This may be a blessing in disguise as now the PID TC feedback sensor is reading data through similar barriers as the elements.
Hmm, not working... I hear the internal PID controller relay clicking after reset, but no voltage to the SSR. TC is reading correctly and rises in temp to the touch
LOL @ Arlet. Once one gets stung by household AC voltage, one won't forget it! 230 even more so!
So I was reading up on this POS PID controller I got from EBAY. I need to modify it. Shouldn't be too difficult. The internal control signals that operate the internal relay need to be brought out to the SSR.
So, I made the most rudimentary modification to this PID board, by removing the internal relay and routing the 2 signals offboard, and the SSR is lighting up. Now time to hook up the load. And just 1 more beer...
EDIT:We've got heat! I love modern digital electronics. PID controller, element wires and SSR very cool. Hotplate up to 145deg Celcius. About 1 degree per sec, steady.
SSR getting warmer after 15 mins. Shutting down and putting device on a cookie tray to cool down. Success! Tried to show some steam, it floated to the left of monitor. Legs were getting too warm on the wooden desk. Had to shut down
Oh, I still have to drill the TC hole...
