Quote Originally Posted by tkms002 View Post
I have a 16 tooth motor pulley driving a 48 tooth reduction pulley and that drives through a shaft a 16 tooth drive pulley. I understand all your math up until "You double that with the 1" pulley, and you get 130lbs of force from each motor.". Where does the double that with a 1" pulley come from? Are you saying double it because of 2 motors?
If I understand you correctly I have to stay under 400 ipm to get much torque. But that gets me from one end of an 8 foot table to the other in something like 14 seconds. Is that a reasonable speed?
Thanks again.
Reasonable speed is up to you.

At work we have extractors that pull parts from mold machines literally in the blink of an eye. They make use of linear motors and have a tendency to ruin a set of linear bearings once a year. I do mean ruin as the linear bearing end up so torn up they aren't even worth taking home as scrap!!! (i throw out more linear bearing rails per year than I carte to admit to -sobs-)

So speed is really subjective, given enough money you could move that gantry at some really incredible speeds. Now here is a little gotcha, the ability of your CAM software to optimize moves minimizing the need to use high traverse rates is an important aspect of the impact of slow rapids. Or to put it another way the more rapid moves, that are unjustified, the greater the impact of slow rapids. The type of work you are doing is also a factor as is your ability to manually adjust G-Code if the CAM software really fumbles.

I feel I'm not relaying this idea well but if your cutter is in contact and doing work a good portion of a run, slow rapids don't really matter. On the other hand if you have G-Code that takes the tool out of contact constantly and jumps around the work piece, then slow rapids can have a huge impact on run times.

Beyond all of that we can hope that your cam software does not generate many full length rapids. Generally that seldom happens so your actual rapids will generally be covering less than 8 feet. Beyond that a return to home after the end of run generally isn't a big factor either as that is also a time to cleanup, get ready to remove the work piece and what ever else needs to happen. 14 seconds might sound like a long time but sweeping or vacuuming the work piece can easily cover that time.

Perhaps the most important thing here is to realize that you now have a robot working for you. A robot that works dirt cheap really. A slow rapid might look sad to you but frankly you should NOT be looking at the robot, instead you can leverage that time to do something else.