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Radmot May 7, 2024 7:43:11 PM

How to prepare a technical drawing for CNC machining?

The ability to create a technical drawing is one of the fundamental skills of every engineer or person who has graduated from a vocational school or university in technical fields. The ability to create such a detailed view allows for a graphical representation of parts or entire systems (e.g., machines, with all dimensions tolerance described) in an easy-to-understand way, maintaining proportions and providing essential dimensions or angles.

This also makes it easier to understand how a specific mechanism should work, and how a particular part is situated in its context (e.g., what it interacts with, like a gear), but above all – it is meant to facilitate their production.

While graph paper, sharpened pencil, and other drafting tools still work well for traditional technical drawings (especially in the form of 'working sketches'), the rise in popularity of computer-aided design (CAD) systems has meant that most (if not all) projects are now transferred from paper to computers.

So how do you prepare such a technical drawing – whether traditional or in vector or 3D CAD file formats – for CNC machining to speed up the manufacturing process and reduce the risk of errors when transferring information to CNC machine controllers?

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What should a CNC technical drawing include?

A technical drawing, sent to a company operating on a machine park containing numerically controlled devices (CNC milling machines or lathes), is tasked with accurately describing the shape of the ordered part.

It is part of the project's technical documentation and is one of the key pieces of information that you need to provide to get a good CNC parts production quote.

How to prepare a project for CNC machining and what pieces of information such document should include: 

  • It should be prepared with due diligence and maintain maximum readability, e.g., views should not overlap each other, 
  • Contains all necessary information about dimensions (lengths, widths, depths, angles, radii, holes, threads, etc.), presented in the form of views with description; if needed – enriched with additional information,  
  • Describe all necessary recesses, thread pitches, etc.
  • If any area of ​​the drawing is illegible (e.g., requires a detailed description), it is worth creating a separate view describing it in a more readable scale,
  • Include isometric views of the ordered parts, at least one, preferably with a maintained scale that refers dimensionally to the part description,
  • Have a legend (e.g., 'all dimensions given in millimeters' od 'single letter x mean…'),
  • Specify the surface finish requirement (e.g., 'for further anodizing'), 
  • Include information about standard tolerance (e.g., 'below 0.1 mm'),
  • It is good to include on such a technical drawing sent with an order for CNC machining information about the desired material (e.g., 'aluminum 7075') or the standard for making this particular technical drawing (if you are accustomed to the design of the part, you can provide ISO standard from memory, just like desired surface roughness).

This list is relatively long but an experienced draftsman or engineer will automatically include each piece of this information on the drawing.

👉 If certain information is missing – a professional company dealing with CNC machining, such as RADMOT, will pay attention to this and ask for clarification. Do not hesitate and take advantage of our support.

Regardless of the format in which the technical drawing for CNC machining is delivered, such a document should be legible and made with due (preferably: maximum) diligence. This facilitates reading the technical drawing and at the same time allows you to avoid later problems with transferring information contained in it to CAD software or translating it into G-Code used in CNC machines.


In what format should the technical drawing be delivered?

The optimal format – both from the perspective of the client, as well as the estimating team or finally the team executing the order – is a 3D CAD file or one generated from this type of software, preferably in vector format (e.g., saved in the PDF).

It allows for quick transfer between computers and additionally gives immediate information to employees of a company dealing with CNC machining whether additional conversion pricing is necessary.

Additionally, it allows for the quick transfer of some data to CAD software and further – translation into G-Code, understandable for CNC devices.

Delivered files can be two-dimensional (2D) – although computer-aided design software allows generating three-dimensional files, these can be 2D renders, even without an isometric view.

Most designers and engineers who are graduates of technical fields (academic or vocational) are accustomed to quickly reading technical drawings and easily extracting all relevant information from them.

Although electronic versions of technical drawings (or rather: renders) are now standard, many clients still use classic formats - a scanned piece of paper with information about the project of the ordered part.

This is certainly a source of savings: not every company ordering CNC machining has CAD software, uses it for other purposes, or needs preliminary pricing of an object whose final technical documentation will be provided at the ordering stage.

Additionally, creating such a drawing is simpler – especially in simplified form – because it often does not require engaging people mainly dealing with CAD software to create it. Still, designers and engineers who are designing parts can prepare such a document.

However, it may be a source of additional costs at the production preparation stage - a handwritten technical drawing must be converted into an electronic form which can be time-consuming. Nevertheless - correctly given dimensions allow for speeding up this process and thus reducing the risk of error occurrence.


Why should a technical drawing be well-prepared?

The reason is simple: to minimize the risk of an error that could lead to the incorrect manufacturing of the ordered part. Often, just one incorrectly specified dimension can result in an entire batch of parts being suitable only for re-melting or further – costly – processing.

👉 Additionally, most professional companies involved in CNC machining services treat it as a crucial document for further work.

Although information about the part from the CAD file is easier to transfer to CNC machine controllers, specific data about dimensions or internal features from the technical drawing serve as a starting point for work and a reference during correctness verification.

This is extremely important, especially when working with large quantities of elements when one is incorrectly given value can impact the poor execution of the entire project, leading to necessary corrections and/or starting over.

At RADMOT we thoroughly check every technical drawing of a project – we verify whether all dimensions are legible and if it's possible to commence production of ordered parts based on this document. If any ambiguities arise at the stage of verifying such a document – we return to the client with a request for clarification.


One order, many benefits – this is how you collaborate with RADMOT

At RADMOT, we offer CNC milling services, CNC turning services, as well as a variety of additional services including washing, aluminum anodizing, laser marking, and assembly. We have over 80 modern machines at your disposal in our machine park, all from reputable manufacturers. Download the presentation and check on which machines we produce parts.

Contact us and tell us what you need. We have been providing CNC services for almost 40 years. Our quote is completely free. And if you have doubts about which technology will work best for you, our expert knowledge is at your service.


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