We have a metal gazebo in the back yard, and in the summer it was like an oven until I started stringing up a tarp in the late spring. If it's 95 out, then it's 95 out, but without the tarp it felt like 125 or more under that open sided metal roof.
I think that a lot of your heat discomfort is coming from the radiated heat from your metal roof. For a test, get a large umbrella and open it and stand under it for a few minutes (at least 2), then quickly close it and see if it suddenly feels much warmer. As a second test, get the largest silver plastic tarp that you can, say from HF, and string it up across the ceiling on the side of the shop that gets the most sun as close to the ceiling as you can
(preferably without blocking airflow to the ridge vent). Then by just standing under it and then not standing under it see if you notice a significant difference. You could also get a cheap laser thermometer to check temps of the tarp vs the ceiling.
If that helps
(meaning you are getting a lot of radiated heat) and there is no way for a more permanent solution
(too many air lines and hanging lights in the way maybe) to install across the ceiling, then maybe you can get/fabricate some large cantilevered umbrella stands on rollers to move to the work area of the moment.
Perhaps something like
this on rollers only cover the fabric with mylar and add some lighting and small personal sized fan underneath it. Perhaps put a box on the stand and throw in your old brake discs as ballast to make it more stable, or better maybe a big cooler with Gatorade in it.
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Now, not so much about discomfort as just just about safety and health, if you must work under these conditions to put food on the table and it's getting to become a safety hazard, you might want to consider a cool shirt system (
I use a similar Veskimo {chilled water pumped through} on my motorcycle in the summers here in Texas) or phase change vests. If your air supply is good I believe they also have cooling vests that use an air hose. Not easy to wrench in maybe but perhaps needed in your case just to live through the day?
Best wishes, work safe.