Technical Tutorial - Low cost automation
Drawing Basics For Multiple Screw Holes And Threaded Holes
Many tapped holes are made on parts such as machine bases and cover frames. If careful design considerations are not given to the tapped hole placements, the results may lead to problems such as positioning/alignment errors and excessive machining time. Therefore, the bolt placement layout is not to be taken lightly, as a designer's technical ability can be measured by how the design was developed.
Case 1: Through hole and tapped hole design in round objects
- If reading error of the drawing is not anticipated, the hole placement layout can be represented with the first hole and the last hole (one pitch pair) in actual hole drawings, and the rest may be drawn as radial hole pitch lines and pitch circle diameter line [Fig. 1].
- The hole property and the number of places to be machined are shown with a leader line extending from the hole location, written as: number of holes followed by a dash (hyphen) and the hole dimensions and/or screw size [Fig1].
Design basics for screw holes in round objects
* Equally divided pitch placement
* Placed on a common pitch circle diameter
Case 2: Screw hole design for rectangular covers
When drawing multiple holes on a common center line, intersecting pitch lines on the center line can be omitted if all the cross points are clearly understandable by the first dimensioning entry. In such cases, the quantity of repeated holes must be clearly indicated within the dimension text, or as a notation entry [Fig. 2].
- of Fig. 2, the end hole location is at a intersecting point of center lines of two sides of the rectangle. This makes the hole positioning a single easy task, contributing to an economical design.
- of Fig. 2, the end hole location is on the cover's corner radius.
Design basics for rectangular objects
* Place all holes on a common straight line
* Place all the holes at a equal pitch distance
