Guidelines For An Optimal Engineering Drawing That Will Save You Money And Time. While it is true that engineering drawings are a fantastic method to express design intent, a drawing with your request-for-quote prototype can incur in longer lead times and even make your quote more expensive.
This is due to the nature of the optimal engineering drawing, which is a legally binding document. Experts carefully double-check and review the call-outs to guarantee this actually takes longer to quote a full-scale dimensioned drawing in comparison to a more simple drawing with only a few inspection call-outs.
On top of this, machine shops and expert providers will increase the quoted price further when they have to work with drawings with restrictive tolerances and full of dimensions because they are aware that they will need to invest much more time inspecting the part and discard finished parts which do not meet the specs.
In certain cases, some requirements need to be communicated through an engineering drawing, however, it is a must for engineers to convey the critical requirements. This can help you save both times when producing as well as drawing time, which eventually results in lower prototype production expenses. If you are having issues with the printing and production of drawings, a great alternative is to outsource the work to an external provider who can take care of printing engineering drawings for you. Trusting an experienced professional will give you peace of mind.
The below tips will explain how to create optimal engineering drawings that properly communicate your real requirements as well as save you money and time.
First tip: Only dimension the measurable and critical features
All dimensional call-outs will require inspection. But you can just ensure that a dimension that will be measurable by hand-techniques, such as pin gauges, micrometers as well as calipers.
Usually measurable:
- Outside parallel dimensions
- Inside parallel dimensions
- The depth
- The hole or bore diameter
Not measurable with hand tools:
- The hole center to the edge distance
- The hole center to the center distance
- The dimension of the reference geometry
- The distance between the surfaces that are not parallel
- The radius between the surfaces
Second tip: Communicate the hole tapping requirements with depth and thread size
The thread depth is difficult to measure with precision; thus, the depth call-out is usually treated as a minimum.
Third tip: Try consolidating the call-outs when several same features are present on the view
Dimension just 1 feature and name the dimension as “#X placeholder”, so this means that the feature will exist in that view a “X Number” times.
Fourth tip: Communicate the assembly intent of the fundamental features
If the whole assembly is actually being machined, provide an instruction or assembly drawing. If you will be installing an external hardware, provide the part number so the expert can identify it.
Fifth tip: Whenever a hardware installation is needed, provide the part number on the drawing
Just noting down “press-fit M4 dowel” does not provide a machine shop dowel material information or length. If the machine shop cannot identify the part, they cannot purchase it.
Sixth tip: Leave out the optional operation call-outs
When secondary operations are optional, such as anodizing and polishing, and are definitely not critical, it is actually best to request a quote for those add-ons in a separate way, so that you will know the additional required cost and delivery time. Many professionals do not think that these optional operations are worth the additional cost and lead time until in the prototyping is almost finished.
Likewise, if you are not sure of the material you need to use or you are trying some alternate materials, leave material out so it does not cause confusion when producing.
Seventh tip: Do not over-tolerance or over-dimension the designs
Usually, only certain features on a part are truly needed to its function, therefore you really want the machinist to be paying extra attention to those features. When you are over-dimensioning, the truly necessary requirements can be lost in the noise, so you should assign only tolerances to critical features. Likewise, over-dimensioning will drive up the cost of your prototype.