Hi everyone, As I mentioned in a previous posting I'm expecting a Bergerda AC Servo to replace the Stepper motor on the knee of my mill. http://www.autoartisans.com/mill/KneeDrive.jpg The photo shows how the stepper is connected. The L type pulleys were a gift from a friend who salvaged them from some equipment. The ratio is 3:1 with the smaller pulley having an insert for the 1/2" shaft on the stepper motor. With 3:1 the 7NM motor can work up to 300 RPM before the torque falls below about 3.5NM and it stalls. That 3:1 reduction puts 100 RPM works out to 25ipm. The 80SM-M0320MAL I've ordered will handle the 3.5NM all the way to the 2000 RPM max speed will give 166 ipm which is probably way more than the vertical ACME screw can handle on a regular basis but I'll be more likely to do a quick move to a tool change position than right now where it appears to take forever to get out of the way. http://www.autoartisans.com/mill/80SeriesACServoMotor.pdf I'm right on the edge though. I'd like to change to 4:1. Currently the upper pulley at 36T, as shown in the photo, is slid onto the 25mm shaft and anchored onto the square handle drive part. The lower pulley at 12T has a steel insert with a single set screw on the stepper motor 1/2" flat. Making a new lower pulley with 9 teeth is out of the question. It's too small for only 9T and definitely won't fit on the 19mm motor shaft. And that's the kicker. At almost 3/4" the pulley that goes onto it has to be large enough to have a decent grip with set screws onto a 6mm key. And so here's the problem. A large enough pulley from say Misumi, in L Type, makes for too many teeth to get 4:1 without a huge driven pulley. I've been using the various pulley calculators and I can't seem to come up with a different belt size that will work. My thinking is as follows: 1. A 4:1 ratio implies driven pulley is 4x the diameter of driving pulley 2. A driven pulley of 6" diameter means 1.5" max for the driving pulley or a Pd of 38mm driving 152mm Pd. 3. 38mm - 19mm shaft diameter leaves 19mm or a hub thickness of 9.5mm. 4. Minus half the key width of 3mm I'm left with 6.5mm set screw length. That's enough right? 5. Circumference of 38mm Pd pulley is about 119mm. 6. Using an XL size belt with a pitch of 5.08mm suggests about 24 Teeth and a Pd of 38.8mm. 7. So I need 96 teeth or circumference of 487.68 gives 155.23mm diameter (6.11") which is just at the max size. Will an XL series 9.5mm wide belt be strong enough turning a 24T 39mm pulley at 2000 RPM which drives a 96T 155mm pulley at 500 RPM? Do I have enough 'meat' on the driving pulley? Is there a better more appropriate belt style? Thanks John Dammeyer "ELS! Nothing else works as well for your Lathe" Automation Artisans Inc. www dot autoartisans dot com
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