Fig. 1: Cylindrical Recess or Recess With Chamfer
A ball-type nosepiece with an extension sleeve is the best tooling solution if the gap between the outside diameter of the screw head and the internal diameter of the cylindrical recess is larger than 0.8 millimeter on all sides, or if the diameter of the screw head is smaller than 8.5 millimeters.
If the gap is too small to be accessed by an extension sleeve or if the screw head diameter is larger than 8.5 millimeters, we recommend the use of a split-type nosepiece. In this case, the length of the screw shaft must be 4 to 5 millimeters longer than the depth of the cylindrical recess.
Fig. 2: Recessed Screw Location With Partial Wall or Screw Located in a T-Slot
If the gap between the outside diameter of the screw head and the radius of the wall is larger than 0.8 millimeter and the diameter of the screw head is smaller than 8.5 millimeters, a ball-type nosepiece with extension sleeve is recommended. For a larger screw head diameter, a split-type nosepiece with a support ring must be used.
Fig. 3: Freely Accessible Screw Location and Flat Surface
Generally, a split-type nosepiece (possibly with locking jaws for self-tapping screws) is the preferred tooling. The split-jaws can additionally be equipped with a support sleeve to prevent scratching of the product surface.
Fig. 4: Using a Template
Templates, or masks, should be used, if a screw location does not allow the positioning of the nosepiece on its outer geometry. Templates can also be used to speed up the assembly process if many individual components have to be installed in the part.
Another application for a template is the assembly of parts with sensitive surfaces, such as an expensive coating or a control board. Using a template will prevent the screwdriver from touching the surface of the part. Templates can also help with error-proofing. By numbering the through-holes sequentially, a template can tell the operator the sequence for installing the screws.
The geometry of the template will simplify the positioning and alignment of a ball-type nosepiece. The chamfer will guide the nosepiece into the hole. The chamfer for positioning the nosepiece should have a 90-degree angle. The gap between the template and the part should be as small as possible, and the internal diameter of the hole should be equal to the maximum diameter of the screw head plus 0.2 millimeter.
If the application requires the use of a custom-made template, the manufacturer of the autofeed system will need to know the maximum distance from the top of the template to the rim of the screw hole (see dimension H in the sketch). This distance will determine the stroke of the screwdriver and the length of the bit.
Lori Logan
Marketing Manager
DEPRAG, Inc.640 Hembry Street
Lewisville, TX 75057
(800) 433-7724 Toll Free
(972) 221-8731 Phone
(972) 221-8163 Fax
www.depragusa.com
