Design Guidelines for Composite, Wood and Plastic

Specifications, tips, and best practices for designing your CNC machined composite, plastic, and wood materials.
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Table of Contents

Best File Formats for CNC Machine Routing

Files Accepted by Our Instant Quote System:

Adobe Illustrator.ai
AutoCAD.dxf, .step, .stp
Fusion360.dxf, .step, .stp
SolidWorks.dxf, .step, .stp

For CNC routing, we accept 2D vector files in the following formats: DXF (Preferred), AI (Adobe Illustrator), EPS, and DWG.

We also accept 3D files in the STEP and STP formats.

If you design your parts in non-CAD software (Adobe Illustrator, Inkscape, CorelDraw) please send us the original (native) .ai or .eps file. We’ll take care of the conversion on our end.

Please note that we cannot accept or process STL (mesh) files or raster-type (JPEG, TIFF, PNG, BMP) files. 

Stuck with only a raster file (JPEG, GIF, PNG)?

We have tutorials to help you convert your art to vector in Adobe Illustrator and Inkscape.

Tooling Diameter and Radius

For composite materials, we use a CNC, chip-subtractive method (2-dimensional CNC flatbed machining) to cut your parts. We’ll use a 0.125″ bit, so allow for a radius of .063” on all internal geometry and minimum hole size of .125”.

Simple, 2-Dimensional, Perpendicular Cuts

  • No V-groves
  • No Threads
  • No 3D Contours
  • No Partial Depth Cuts
  • No Double-Sided Cuts
  • No Counter Bores

Minimum and Maximum Part Sizes

For composite materials, we are limiting the minimum and maximum part sizes in order to provide you with the quickest and most efficient CNC machining possible.

Minimum part size:

  • 1” x 2”

Maximum part size:

  • 44” x 23” (Delrin) 
  • 44” x 30” (ABS, ACM, HDPE, MDF, Plywood, and UHMW)


Overall size limitations for cutting by material can also be found in our part sizing chart

CNC Router Tabs

All parts machined using the CNC router will have small fixturing tabs leftover on the edges. We use these tabs to ensure your parts remain in place and secure during the manufacturing process.

Tabs will be approximately .1875″ wide, and the depth will be equal to half of your chosen material thickness. These tabs can be easily sanded down and will not affect your final design in any way. 

Check out our information on using fixture tabs in CNC machining if you have further questions.

Internal Geometry Considerations

Inside angles (acute angles) will have a slight radius due to the use of a round cutting tool. The radius will be .063″ due to the tool’s .125″ diameter.

Outside corners are unaffected, but tooling limitations make it impractical for us to produce perfectly square or sharp inside corners.

Material Removal and Design Density Considerations

Parts with large amounts of material removal may be impractical for us to produce. Grills, grates, and perforated patterns are not recommended and may be rejected.

We recommend no more than 50% material removed from a given part. The more material that you remove, the greater the risk that your part will move during the cutting process and become damaged.

Using Dogbone Fillets for Square Corners

If you have been designing in CAD for any length of time, you will be familiar with standard fillets. You may be less familiar with another type of fillet commonly used with CNC milling: The “Dogbone” fillet.

A standard fillet is used to reduce the sharpness of corners. You can modify corners with either a chamfer or curve.

The solution: Dogbone fillets!

However, for materials that are CNC machined, the inner corners can never be sharper than the diameter of the cutting tool. This is because the tooling is round, and it’s not possible to get perfectly square corners on interior geometry. Instead, these corners will be slightly rounded inwards (approximately .063″ radius). This can cause problems when joining parts, as a part with square edges might not fit in a hole or slot with rounded corners.

Ready, set go!

Now that you have the knowledge you are ready to start designing your parts for the CNC mill. Questions? Email us anytime: support@sendcutsend.com

Pre-flight Checklist

Materials available for CNC Routing

Start your first SendCutSend project today!

Upload your CAD design or use our parts builder and get a free instant quote on your custom laser cut parts, all delivered to your door in a matter of days.

No CAD File? No Problem! Send your sketch or template to our Design Services team.

View More Guidelines

We proudly use hardware by PEM

Flush stud, M8 x 1.25, .472" Zinc plus Clear Chromate

Thread SizeM8 x 1.25
Hole size in sheet (+0.003/-.0.000).315″
Minimum sheet thickness0.94″
Maximum sheet thickness.347″
Fastener materialSteel
Minimum distance hole C/L to edge0.378″
When determining the distance between two or more fasteners, you can calculate the distance by the formula, C/L to edge + 1/2 the diameter of the second mounting hole..535″
Recommended panel materialSteel/Aluminum
Coating typeZinc
Aluminum material ranges (5052, 6061, 7075)0.100″-0.250″
Steel material ranges (CRS, HRPO, HR)0.104″-0.250″

Get an Instant Quote for Waterjet Cutting

We proudly use hardware by PEM

Flush Standoff, 4-40, .250" Zinc plus Clear Chromate

Thread Size4-40 x .250″
Hole size in sheet (+0.003/-.0.000).168″
Minimum sheet thickness0.040″
Maximum sheet thickness.125″
Fastener materialSteel
Minimum distance hole C/L to edge0.230″
When determining the distance between two or more fasteners, you can calculate the distance by the formula, C/L to edge + 1/2 the diameter of the second mounting hole..314″
Recommended panel materialSteel/Aluminum
Coating typeZinc
Aluminum material ranges (5052, 6061, 7075)0.040″-0.125″
Steel material ranges (CRS, HRPO, HR)0.048″-0.119″