> On Feb 18, 2018, at 6:53 PM, Chris Albertson <albertson.ch...@gmail.com> > wrote: > > Question: What would be the preferred timing belt for a new design? > > Here is the application. I'm making a z-axis control for a Harbor Freight > mini mill (Sieg X2). In this design a 5/8 diameter, 0.200 pitch ball > screw is fixed and the nut spins. The nut is driven by a timing belt > "about" 50 teeth and the motor has an about 25 tooth pulley. I'm thinking > a 400 in/oz. NEMA 23 stepper should work. Assuming the 2:1 reduction > each 1.8 degree step lifts the head 0.0005 inches. By 1/4 stepping I get > 0.000125 per pulse. > > When looking for a good design for the mini mill I was looking for a good > place to put the ball screw. This design places it very close to the dove > tail, almost touching it. Maybe 0.1 inch in front of the dovetail. The > ball screw goes right where the current rack it the original design. I > will have to remove the rack to fit the screw. > > So I need to select a belt type and size. My initial guess at this a the > GT2, 3mm pitch and 9mm wide. > I’ve used almost the same configuration on my scratch built mini-mill and it has worked fine for 8 years. The GT2 belts are superior in most respects, particularly because they have an involute profile. This reduces noise and increases effective stiffness.
> Some one else used a XL type 3/8 wide and 0.2 pitch but I'm reading that XL > is not the best for new designs as GT2 has a much improved both profile > that eliminates backlash. The XL doesn’t really have backlash, but does have more compliance for a given belt tension, as the profile allows the teeth to generate higher separation loads which allow them to ‘ride up’ some under high loads. As such, you end up needing higher tensions to transmit a given torque. > > I started to calculate torque and load on the belt then thought "Why > bother?" the actual force is going to be whatever the motor can do as I'll > set the acceleration limits until it start skipping steps then back up by > about 30% or so. The real reason to calculate the forces is to make sure you have sufficient static tension so that under max load the ‘slack’ side of the belt never actually goes slack. If that happens the belt will unwrap from the slack side of the drive sprocket and might skip a tooth. According to the literature, this represents a belt drive failure and will rapidly destroy a belt by overload the cords and breaking strands in them. Broken strands lead to lose of tension, and the cycle rapidly repeats until the belt either looses sections of teeth or falls apart. > I might go with a NEMA 34 1100 in/oz motor if I need > to. So I might choose a belt that can handle whatever the 1100 in/oz motor > can do. Just looking to double check GT2, 3mm pitch and 9mm wide is > reasonable. > > So I guess the best way to ask the question is what kind of belts are > working well with motors in the 400 to 1100 in/oz. range. > > If there is any interest I'm modeling this in Fusion 360. and can share > the CAD files > > -- > > Chris Albertson > Redondo Beach, California > ------------------------------------------------------------------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
