Chace Randolph

Blog Post 69

Written and uploaded 10-06-2023

I have been surprised on a couple of occasions, looking for information on the internet, and the information just doesn’t exist. Or at least is not available or distributed for public consumption. Perhaps I am digging into to niche of topics. One example was my recent attempt to start a pod cast about the history of the Soviet Space program. I didn’t find anything too good online, lotsa of specific things, but nothing broad covering the program as a whole and not a specific event. Even physical information was hard to find, none of the book stores in my area had any books related to the Soviet Space program. I was very disappointed.

But that’s not what I am talking about today. This week, for both personal and professional reasons, I was doing some research into CNC machines and bits and tooling and stuff. I have purchased a small desktop CNC machine for myself, and will be using a similar sized machine, in addition to a massive CNC machine at my place of employment. I was designing a small duct with some cad software to add a 60mm fan as a cooling unit to the upgraded spindle of my upgraded desktop CNC machine. Buy upgrade, I mean I bumped it up to a bigger power supply, some external transistors to feed it, so it’s not pumping all that power straight through the little circuit board, as well as a bigger more powerful spindle motor, in hopes that I will be able to cut through not just wood, foam and plastic as advertised but also, I hope to make it work (albeit slowly and carefully) in aluminum. I’m not sure what I am going to do with that, but I will do something.

That’s not the point of this post though. I have a 60mm cooling fan, I picked up a couple of them, from amazon for cheap. And I have designed or was attempting to design a duct to mount this 60mm fan onto the head of my small machine to cool the upgraded spindle motor. Now because I purchased this fan from amazon, I have all the specs for it. I know its RPM, its CFM, its voltage, and amps and watts and even the air pressure it puts out. I was hoping to find a mathematical formula for the optimum diameter for this duct, so that I can get the highest possible air velocity output from the tip of my duct, to try and jet the air straight into the standard cooling ports on the spindle motor. In short I was trying to turbo charge the cooling fan, with another cooling fan. Anyway, I couldn’t find the formula I was looking for. It shouldn’t be that hard to find a formula with a constant or two, where I can plug in my CFM, and out put air pressure to calculate the smallest diameter duct I can use for peak air velocity without reducing airflow with excessive back pressure. Sounds pretty easy, but after four hours of company time, I could not find said formula. In the interest of time, I instead designed a duct with interchangeable tips. So I can through trial and error find what tip/nozzle works best. Started with a 4mm output. I also have a 6mm tip, so well see if the 10:1 version works better. But it would have been nice to see a simple formula to plug in the specs I had for the fan and get the duct diameter I needed, but no, everything wanted to be about HVAC ducting or air compressor nozzles and orifices

If you have, know, or know where I could find such information as nice formulas that could help me with this, or even related kinds of formulas that could help me with future designs of a similar nature, that would be great to know, and I would greatly appreciate it, if you reached out to me to share that information, because apparently the internet doesn’t want to teach me about it…