How to change an STL hole size without scaling the part

Example: a 6 mm hole becomes 8 mm

Suppose a bracket has two 6 mm through-holes, 40 mm apart, and an outside length of 60 mm. You want both holes to become 8 mm while keeping their centers and the outside shape fixed. This is an illustrative design brief, not a measurement from a customer part.

Scaling everything by 8 ÷ 6, or about 1.333, would also turn the 40 mm spacing into about 53.33 mm and the 60 mm length into 80 mm. That changes the fit. Remove material around each hole while leaving unrelated geometry alone.

1. Confirm units, centers, and the real requirement

Keep the original file. Confirm its units against a known measurement, then locate each hole axis in your editing software. Decide whether the change is diameter, center spacing, depth, or a counterbore; each is a different operation.

The MeshRebuild checker can show overall bounding-box dimensions and mesh diagnostics. It does not measure hole diameters or center spacing and does not edit the STL. Use it as a preliminary check, then use CAD measurements or supplied references for the feature that matters.

2. For one enlargement, try a mesh cut in Fusion

Insert the STL with the intended units. Create a separate cylindrical cutting body at the confirmed hole center, with an 8 mm diameter in this example. Extend it through the entire plate. Keep a copy of the target so you can compare the result.

Fusion's Mesh Combine command operates on mesh bodies. If your cutter is a solid, use Mesh > Create > Tessellate to make a mesh copy; choose refinement appropriate to the required geometry. Then use Mesh > Modify > Combine, select the bracket as Target Body and the cylinder mesh as Tool Body, and choose Cut. Preview the change and preserve the tools if useful.

Repeat for the other hole. This does not add a native Hole feature to the imported design. Check the resulting circular approximation and remaining wall thickness; the cylinder's nominal diameter alone does not prove the exported mesh is suitable.

3. Use solid editing when the geometry supports it

If you already have the original CAD or a suitable solid, prefer that source. Fusion's Hole tool can use exact placement, diameter, and depth settings on a solid body. A native hole or its driving sketch can then expose the dimension you need to change.

Converting STL to a solid is another possible route, but inspect the result first. Fusion's Faceted method preserves individual mesh faces, while Prismatic uses face groups to infer features. A ring of flat faces is not automatically one editable cylindrical face. Test the intended cut before investing in a full conversion workflow.

A smaller hole or new spacing needs a different plan

Subtracting another cylinder cannot make an existing opening smaller. You need to restore material and create the new opening, or reconstruct the surrounding feature. Moving a hole similarly leaves its old position to fill. Check both operations together so you do not keep an unintended slot or hidden internal geometry.

For several revisions, a simple rebuilt plate with constrained hole centers and named diameters can be easier to maintain. Request those controls explicitly, especially when mounting spacing must change independently of the outside length.

4. Reopen the export and check what stayed fixed

Export a separate revised file and reopen it. Verify the new hole size in suitable measurement software, the 40 mm center spacing, and the 60 mm outside length from the example. Inspect the cut in section and check the mesh again. A successful operation alone does not establish fit with the mating part.

If conversion or Boolean operations remain unreliable, describe the modification in a project review: which hole changes, its target size, the dimensions that stay fixed, and the CAD application you use. That gives a rebuild a concrete purpose and a clear acceptance check.