Design for Machining Toolkit

Tolerances represent dimensional accuracy of a part. It is the amount of acceptable variance in the dimension of a part. Typically, Protolabs will maintain a general machining tolerance of ±0.1 mm or better, however, our network partner can attain down to ±0.010 mm. The best thing about a standardised general tolerance of ±0.1 mm.. you don’t need to produce a 2D drawing, we can start manufacturing as soon as you have the 3D model.

Holes

In general, at Protolabs, most holes are interpolated with an end mill rather than drilled. Apart from allowing for greater flexibility in hole sizes but also offers better surface finishes than drilled holes. The same tool is also used for slots and pockets, which means a reduction in cycle time and part cost. The principle trade-off is that holes more than 6 diameters deep become challenging as they normally need specific drills, which may mean the part needs to be machined from both sides.

We take a more modern approach to thread making, rather than the traditional "taps" used to manually create a thread. We use a single point thread mill to helically cut the thread profile, this CNC process produces an accurate thread and one tool can be used to cut multiple threads that share the same pitch (number of threads per inch). UNC and UNF threads from #2 up to 1/2 inch M2 to M12 (metric) are possible within a single tool set. The full list is here.

Protolabs is capable of machining text, as long as space between characters and the stroke used to write is at least 0.5 mm
It is worth noting text should be:

• recessed not raised, 0.2 to 0.5 mm deep is normally sufficient, because it is quicker to remove material.
• fonts with radii, this includes arial, verdana, sans-serif or similar, because this suits circular tools.
• 20 point or larger, to ensure the text widths are greater than 0.5 mm.

Protolabs tool sets contain materials such as tungsten carbide, a super rigid material that offers maximum tool life and productivity with minimal deflection. But even the strongest tools deflect, as do metals and plastics that are machined.
Minimum feature thickness in the Protolabs factory is 0.5 to 1 mm and maximum single cut depth is 50 mm high and 1 mm wide, has a slenderness ratio of 50:1 - this can work in some materials, but 20:1 is a good general rule.*

As a part of the CNC machining process, sharp corners on a part will be radiused (rounded). This will be identified before the part is milled. In softer materials, tools are flat bottomed so only the tool diameter needs to be considered. In Harder metals it is typical for tools to have a tip radius too – this will leave a small radius in the bottom of pockets. **

We advise what percentage will be milled and what will remain un-milled, deviating from your original design. Dark blue areas are those where material will be left behind or indicates where features will not be formed. You can decide whether to modify your design or leave with the changes as they are.

Reasons for un-accessible material come in two categories:

• General design for CNC for example deep holes, galleries or internal features, deep threads, undercuts that can’t be reached, or tool access. These may be pushing the limits of any CNC process and might be candidates for 3D printing.
• Trade offs to manufacture quickly; holes deeper than x6 diameter, threads deeper than x3 diameter, undercuts that need special tools (t-cutters, woodruff cutters or Lollipop Cutters), large 5-axis parts or restricted tool access. This is because we stock a standardised toolset. We are always happy to offer advice, and have a huge range of CNC capabilities available via our digital network.

As part of your design analysis, you can easily highlight and assign holes which need threads, by simply clicking on your 3D model. 
We offer a selection of metric and inch (UNF, UNC) threads along with coil and key inserts, however, we do not install or supply inserts.
To make a hole eligible for threading it must be modelled at the pilot drill diameter. The software will detect eligible threads, enabling you to pick one-by-one or all of them in seconds.

Standard part tolerance at Protolabs is +/- 0.1 mm (or ISO-2768 medium). For features that are less than 1 mm, will be automatically highlighted as a thin wall geometry by the quoting system. You should keep in mind that we'll still allow it to be machined, so the machined part may differ slightly from your original design. Any thin walls below 0.5 mm risk breakage during machining, and flex or warp afterwards. Wherever possible, thickening them up is advised.

Maximum extents refers to the raw material and machining envelope. Depending on part geometry and fixturing/clamping requirements the maximum part size may be slightly smaller. For every upload we will analyse and provide feedback.

Find out the max extents for each, individual, material we stock at Protolabs.