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Hello everyone, I am putting a small PCB into an SMA filter housing made of nickel-plated brass -- https://www.crystek.com/microwave/spec-sheets/enclosure/SMA-KIT-1.5MF.pdf. According to the housing manufacturer, it can withstand reflow temperatures but they would not give guidance as to the...

Hi Compositepro! >Using three more temperature controlled rods or bolts is a well established method of making high-force micrometer actuators. But if you want to maintain parallelism rather than to control it, then one large solid rod is desired rather than several smaller ones. I imagine...

Hi EdStainless! Thanks for the info. I think maybe even Solidworks can do a thermal stress analysis. http://help.solidworks.com/2012/English/SolidWorks/cworks/IDH_Analysis_Background_Thermal_Stress_Analysis.htm?id=43e4391fc5ba49c1b6e4bffc0ab5983e

Hi Compositepro! That makes a lot of sense about the thermal gradients. I am seeing 8 W/m/deg C for Alloy 72, and 235 W/m/deg C for Al. The current design has a cylindrical Al heat shield. I will try to servo the crap out of it at several points and try to keep the Peltier arrangement...

Thx Magben. That seems reassuring that the stresses can be annealed. @IRstuff, I don't understand. How is this better? 150mm of annealed Alloy 72 with less temperature shift seems to do the same job without an additional mechanical joint? I'm not a mechanical engineer, but it seems like you...

Hi IRstuff! According to my optical simulations, if I reduce the interferometer length to 60mm then the required displacement range goes up to something like 1200um.

Hi MagBen! I did not know about those alloys. Thanks that is very helpful. You are correct that a shorter rod would be easier but there are optical requirements which make longer rods require less length tuning. I chose 150mm as a compromise. By "all cold works done" do you also mean...

Interesting! I suppose that a larger rod spacing makes any small differences in expansion between the rods less important.

Hi MintJulep! In general I agree that simply forcing tolerances tighter is a sign of laziness or lack of creativity. I'm not trying to achieve a high parallelism between the alumimum faces though. They are just to hold the interferometer mirrors. The standard technique to make them parallel...

Hi arunmrao! Yes as I mentioned, the other option is choose a stable material like invar or glass and then tune the total length with a piezo stack. But then that just pushes the "maintaining parallelism while expanding" problem onto the piezo stack. Interferometers with small piezo...

Hello, I am designing a mechanical system which uses an aluminum rod as a temperature dependent length tuning element. With the exception of machinability and long-term stability I do not care about the mechanical properties. The main problem is that I need the end faces of the rod to stay...