good experiment.
Any chance you could repeat for some different insulators?
and for a no insulator with metal to metal contact with and without thermal goop?
Any chance you could repeat for some different insulators?
and for a no insulator with metal to metal contact with and without thermal goop?
Hi bwaslo,
Just a data point for mica and goop would be nice. The mica is the universal constant everyone has. I'd be interested in how much the exotic insulator buys you.
I still use mica and goop. It works and I have the materials on hand.
Hey Andrew,
Do you have any idea how much work that would be. Even asking for one other is a fair amount of extra work for bwaslo.
-Chris
Just a data point for mica and goop would be nice. The mica is the universal constant everyone has. I'd be interested in how much the exotic insulator buys you.
I still use mica and goop. It works and I have the materials on hand.
Hey Andrew,
Do you have any idea how much work that would be. Even asking for one other is a fair amount of extra work for bwaslo.
-Chris
I still have to populate the other heatsink. I could use mica on it first, then swap to alumina later. But the only mica I have now are shaved-down ones (see above), so results might not apply if you only use the as-received thickness mica.
I do realise. But it is so rare to see a good experiment that is well reported.
measured thickness is good. It is an extra data point.
Hi bwaslo,
I don't know if the shaved insulators would actually change the numbers that much. Your greatest thermal resistance is the interface between the mica and other surface.
Many thanks!
-Chris
I don't know if the shaved insulators would actually change the numbers that much. Your greatest thermal resistance is the interface between the mica and other surface.
Many thanks!
-Chris
Hi Andrew,
Well, the experiment you proposed would take someone days to complete. I wouldn't want to scare anyone off.
-Chris
Well, the experiment you proposed would take someone days to complete. I wouldn't want to scare anyone off.
-Chris
I can't be choosy, so I would settle for as little, or as much, as Bwaslo would volunteer to do for us.
Hi bwaslo,
This ought to be interesting.
The torque applied to the mounting screws is important. Doing them too tight will increase thermal resistance.
Hi labjr,
Mica peels in layers. If one is careful, the surface will be as smooth as an insulator before splitting. This is something I do not do as a rule.
-Chris
This ought to be interesting.
The torque applied to the mounting screws is important. Doing them too tight will increase thermal resistance.
Hi labjr,
Mica peels in layers. If one is careful, the surface will be as smooth as an insulator before splitting. This is something I do not do as a rule.
-Chris
It is possible to pull off only part of a layer, though. Pretty hard to tell sometimes, also, even under the microscope. One of the things that made me think of alumina again.
I use mica a lot, but I only install thin mica.
I aim for less than 2thou (2mil) and often get around 1thou.
Many of the mica pre-cut isolators are around 6thou thick and I can get two, or three, thin isolators from each. Occasionally a layer breaks, or slices out, part way across, these small pieces become To220, or if very small To126 isolators.
I aim for less than 2thou (2mil) and often get around 1thou.
Many of the mica pre-cut isolators are around 6thou thick and I can get two, or three, thin isolators from each. Occasionally a layer breaks, or slices out, part way across, these small pieces become To220, or if very small To126 isolators.
How do you split them? With a very sharp knife, also? I loose approx. half my mica isolators when trying to split them. they are not expensive luckily.
And how do you measure the thin mica, I don't know how to measure micrometers.
And how do you measure the thin mica, I don't know how to measure micrometers.
I have to use strong glasses just to read resistor colour codes and solder where I actually want the joint.
I also use a magnifying lamp with the 3.5dioptre spectacles, when I need to see more of the small details, like soldering 603 smd caps/resistors to very fine tracks.
That combination let's me see the coloured fringes (Newton's rings) when I start to split a mica sheet.
The two difficult operations (at least for me) are getting the knife to "Start" at roughly half thickness. The second is getting the split to travel slowly and controlled all the way past a pre-punched hole. If a sheet is going to break it is usually at a hole.
The knife/scalpel has to be sharp. I use a diamond chisel sharpening "stone", grade 150 for reshaping, grade 300 for sharpening and grade 450 for very fine sharpening. My old hobby knife from about 45years ago still has it's second blade in it (it is getting quite short and won't last another decade). I lost track of all the spare blades about 40years ago.
Scalpel blades are brittle. They will not accept abuse.
A micrometer is needed to see if the thin mica is tapered. Micrometers can read down to <0.5thou and some to 0.1thou.
You can get away with a caliper that reads to 0.01mm for general thickness measurement.
I bought a digital caliper a few years ago and it has been a good workhorse. It reads down to 0.5thou, or switches to 0.01mm.
It can measure depth, or step, or diameter, or bore, or thickness.
I wish I had it when I was manufacturing my car.
I also use a magnifying lamp with the 3.5dioptre spectacles, when I need to see more of the small details, like soldering 603 smd caps/resistors to very fine tracks.
That combination let's me see the coloured fringes (Newton's rings) when I start to split a mica sheet.
The two difficult operations (at least for me) are getting the knife to "Start" at roughly half thickness. The second is getting the split to travel slowly and controlled all the way past a pre-punched hole. If a sheet is going to break it is usually at a hole.
The knife/scalpel has to be sharp. I use a diamond chisel sharpening "stone", grade 150 for reshaping, grade 300 for sharpening and grade 450 for very fine sharpening. My old hobby knife from about 45years ago still has it's second blade in it (it is getting quite short and won't last another decade). I lost track of all the spare blades about 40years ago.
Scalpel blades are brittle. They will not accept abuse.
A micrometer is needed to see if the thin mica is tapered. Micrometers can read down to <0.5thou and some to 0.1thou.
You can get away with a caliper that reads to 0.01mm for general thickness measurement.
I bought a digital caliper a few years ago and it has been a good workhorse. It reads down to 0.5thou, or switches to 0.01mm.
It can measure depth, or step, or diameter, or bore, or thickness.
I wish I had it when I was manufacturing my car.
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yes, the conversion is 1inch = 25.4mm
it was the thou that got him,
1thou = one thousandth part of one inch.
and the North Americans call it a mil, presumably because they think mil equals milli, again a one thousandths part of one.
But I did give two other references that linked thou to USA/Canada and metric values.
He just did not read.
it was the thou that got him,
1thou = one thousandth part of one inch.
and the North Americans call it a mil, presumably because they think mil equals milli, again a one thousandths part of one.
But I did give two other references that linked thou to USA/Canada and metric values.
He just did not read.
OK, one thousandth part of an inch. Sorry for being metric, I am just not used to such systems (and probably never will). A milli-inch so to speak 🙂 Google did not help me this time.
http://lmgtfy.com/?q=thou
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I am good at swapping back and forth between feet and metres and inches and millimeters and even from miles to kilometres. in either direction and virtually instantly.
But one I have not got used to is from thou to 0.01mm and back. I always have to think about this especially when on the lathe and have to divide by two to ensure I don't take off too much.
Yes, my cross feed read in thou of cut and that removes 0.0508mm from the diameter.
And when I am trying to work with something around 74.35mm diameter with an old head on my shoulders and an old imperial lathe that had a run out of ~1thou per 9inches of bed travel ???? I had to be alert to avoid mistakes.
But one I have not got used to is from thou to 0.01mm and back. I always have to think about this especially when on the lathe and have to divide by two to ensure I don't take off too much.
Yes, my cross feed read in thou of cut and that removes 0.0508mm from the diameter.
And when I am trying to work with something around 74.35mm diameter with an old head on my shoulders and an old imperial lathe that had a run out of ~1thou per 9inches of bed travel ???? I had to be alert to avoid mistakes.