Question: I'm trying to cut grooves into this handle shown in the image below. I need them cut along the red line.

[![enter image description here](https://i.stack.imgur.com/dVTuW.png)](https://i.stack.imgur.com/dVTuW.png)

I want them to be look like the grooves marked by red in this image below:

[![enter image description here](https://i.stack.imgur.com/z4kUW.jpg)](https://i.stack.imgur.com/z4kUW.jpg)

How would I got about cutting even grooves into the the mesh along the red line in the first image? I'll provide the mesh in a file.
[![](https://blend-exchange.giantcowfilms.com/embedImage.png?bid=3592)](https://blend-exchange.giantcowfilms.com/b/3592/)

Answer: 
I would start over completely and create the topology in 2D first, in all quads, tracing the reference image.

[![Mesh topology example](https://i.stack.imgur.com/MxMTv.jpg)](https://i.stack.imgur.com/MxMTv.jpg)

(Sorry for the two-billion pixel screen shots. You can thank retina display.)

Anyway, if you make topology like this you can get the curves you're hoping to achieve without cutting.

Consider this a starting point, and also just an example of one possible way you could do it.

Note the tightly-spaced holding loops around the curves that add sharpness. These also serve as a buffer between those curves and the 5-poles in some spots:

[![A 5-pole buffered by a holding loop](https://i.stack.imgur.com/48Yf9.png)](https://i.stack.imgur.com/48Yf9.png)

*Above: A 5-pole (marked in red) buffered by a holding loop (green).*

As you've probably noticed, more closely-spaced holding loops create sharper edges.

[![Holding loop spacing determines edge sharpness](https://i.stack.imgur.com/Rs2nc.png)](https://i.stack.imgur.com/Rs2nc.png)

*Above: A more widely-spaced loop (green) will create softer edges, while a more tightly-spaced loop (orange) will create sharper edges.*

Topology is a broad topic, but it's just about collecting different techniques, and adjusting how you think about shapes. It's half art form and half math. Stick with it.
This can be done using the [Knife Project tool](https://docs.blender.org/manual/en/dev/modeling/meshes/editing/subdividing/knife_subdivide.html).

In your specific case:

1. Create a curve object that follows the shape of the curve you want to cut [![enter image description here](https://i.stack.imgur.com/tD04Z.png)](https://i.stack.imgur.com/tD04Z.png)
2. Select both the curve object and the object you want to cut (note that the curve object should be selected first)
3. Jump into edit mode and click `Knife Project` on the left panel under Mesh Tools[![enter image description here](https://i.stack.imgur.com/P5fBm.png)](https://i.stack.imgur.com/P5fBm.png)