In short: A drawing for CNC machining must have a complete set of dimensions, tolerances where the part joins another, the material grade, the surface finish and the number of pieces. It is best to add a 3D model in a STEP file. Missing any of this means questions, a delayed quote or a part that does not fit.
Which dimensions and tolerances must be on the drawing?
The drawing must have all dimensions needed to make the part, and tolerances wherever the part works with another. A machine will make dimensions without tolerances in the usual range, but for bearing seats, shafts or mating surfaces it is worth stating the accuracy directly. A dimension that cannot be read, or that contradicts another one, stops the work, because someone has to ask.
Is a 3D model enough without a drawing?
A 3D model describes the shape but cannot replace a drawing, because it does not carry all the requirements. From a STEP file the machine reads the geometry, and from the drawing it learns about tolerances, fits, threads, roughness and finish. So it is best to send both: the 3D model for programming the machining and the drawing with the requirements.
What you can read from a 3D model (STEP) and from a drawing:
| 3D model (STEP) | Working drawing | |
|---|---|---|
| Shape and dimensions of the body | yes | yes |
| Tolerances and fits | no | yes |
| Threads and roughness | no | yes |
| Material and finish | no | yes |
| Data for programming the machining | yes | no |
What should I state about material and finish?
State the material grade, any heat treatment and the surface finish, for example a coating. The material decides the choice of tools and parameters, so “steel” is not enough, but the full grade designation is. If the part is to be hardened, painted or galvanised after machining, write it on the drawing, because it affects allowances and the order of operations.
How do I mark threads, holes and fits?
Mark threads with type, size and length, and holes with diameter, depth and whether they go through. Write fits, for example a shaft in a bushing, with a tolerance, because it decides whether the parts will work together. For holes for bearings and seals add the required surface roughness.
Does 5-axis machining change the requirements for the drawing?
Five-axis machining lets us machine a part from several sides in one setup, but it needs a good 3D model. The fewer the setups, the easier it is to keep the surfaces in position to each other, provided the model is accurate and complete. That is why for parts with a complex shape a 3D model in STEP format is as important as a drawing with tolerances.
Which drawing mistakes delay a quote and production?
What most often delays a quote and production:
- a missing material, tolerance or dimension,
- dimensions that contradict each other (two different dimensions of the same element mean someone has to decide which one applies),
- unreadable scans and photos of drawings,
- a missing number of pieces.
What if I have only a part and no drawing?
Then we first recreate the drawing from the part: we measure or scan it, build a 3D model and a working drawing, and then make the part. How this works step by step is described in our guide how to recreate a machine part that is no longer sold.
What should I send to get a CNC machining quote?
For a quote, send:
- the drawing and the 3D model (STEP),
- the material,
- the number of pieces,
- the required finish.
If you have only the part or photos with dimensions, send them and we will suggest how to prepare the documentation. We do the machining as part of 5-axis CNC machining, and we prepare drawings as part of CAD design services.
Frequently asked questions
Is a STEP file enough for CNC machining?
A STEP file is enough to read the shape, but without a drawing tolerances, fits, threads and finish are missing. It is best to send both.
What is more important on a drawing: dimensions or tolerances?
Both. Dimensions describe the shape and tolerances say how accurately it must be made. Tolerances matter most where the part works with another.
Do I have to state the material grade?
Yes. The material decides tools and machining parameters, as well as price and time, so the full grade designation shortens the quote.
What if I have only an old drawing or a photo?
We check the drawing against the part or photos and complete the missing dimensions. For complex parts it is safest to measure or scan the part itself.
Can I order the drawing and the machining in one place?
Yes. We prepare the documentation and make the part on a CNC machine, so the drawing does not travel between companies.
Do you have a drawing or a part to make?
Send the drawing, a 3D model or photos of the part with dimensions to biuro@omme.pl, or call: +48 570 471 653. We will assess the documentation and prepare a quote. See also our contact page.
