#1 I’ll help you if I can but, this is your project, not mine. You’re the Engineer, I’m just the Machinist.
#2 Like the Boy Scouts; “Be Prepared”. Bring a drawing, sketch, or SolidWorks file with you when you see me. An invention comes from your head, to your hand (for the sketch), then to me for the actual model. Don’t come to me and say something like “Well, I want it to kind of look something like….., well I don’t know…..”.
#3 You can build a rough model out of corrugated cardboard or plywood. Cardboard assembled with hot-melt glue is a cheap and easy way to build a prototype. Plywood assembled with drywall screws is a close second for visualizing then working out the bugs in a design.
#4 Don’t over-engineer a device. Simpler is always better.
#5 I like 80-20 https://8020.net/product-basics#
#6 No welding.
#7 I’d make everything out of aluminum and Delrin if you’d let me.
#8 Countering rule #7, steel is the best material for rotating shafts. Nylon or bronze bushings are easier to incorporate in a design than ball bearings.
#9 Use Lexan, not Plexiglas.
#10 Mounting rotating gears and pulleys with setscrews to the shaft is usually an acceptable way of transmitting torque. Keys with keyways is the strongest way but takes extra time and energy for me to fabricate.
#11 Don’t bring 3-D printed parts expecting me to modify them. Instead modify the file and reprint them.