Toolpath help on bathymetric map

Hello All,

I am having trouble with the image below on how to do tool paths and which bit I should be using. It’s going to be a bathymetric map of the lakes in my area and each “layer” is 20’. It’s made up of about 60,000 lines and took a week to make. My capable computer is finally raising an eyebrow at these files.
Some of the lines below have very tight corners and I’d like them to be as accurate as possible.
Do I need to get a 1/16" or 1/32" down-cut flat bit or is there a way I can use my 1/32" ball nose bit and still have a flat bottomed ‘pocket’?
Also, I’m using vcarve and would appreciate any tips on how to make this as nice as possible.
Thanks in advance!

I’m interested in responses to this. I’d like to do relief maps as well.

You can make a flat-(enough)-bottomed pocket with any bit. But the number of passes is inversely proportional to the contact surface with the material at the desired depth of cut. A ball nose has a much smaller contact area with the material at the desired depth of cut, therefore it will require more passes to create a similar “flat” surface than a standard end mill.

I think your bigger concern may be the edges of the profile. If you want a sharp edge with no rounding, then a standard end mill is a must. A ball nose or tapered ball nose is going to leave material behind, simply due to the shape of the bit.


Instead of a side view of the cut, would I get sharper corners from a top-down view?
Sorry for the wording, it’s tough to explain properly.

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The only way to create sharp corners from a top-down view is with a V-bit. Otherwise, your corners will be limited to the radius of the bit, unless you are willing to settle on a “small-enough” bit radius.

A V-carve path (with V-bit) will automatically adjust the height of the bit as it carves to pull upward into those tight corners. You would probably want something like a 30° or even a 15° if you are wanting really fine detail. But it’s not clear how large you want to make this. A smaller angle will produce a more vertical profile wall, but it will never be perpendicular to the bottom.


I plan on doing a 31x47". Thank you for the response.

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I would recommend taking a small portion and doing some test runs on smaller material. It will both inform you and vet out problems before dedicating it to a large piece of material and the time to process it.

Iterating in small same scale parts can really help. In your case select what you think are problem spots and start with those.

Good luck and hope you post when you complete the project.


The above response is good advice and I would try using a .5 mm radius tapered ball nose bit for the best detail possible. However, the run time will be long. Test it and see how it works.


The hardest part about relief maps seems to be finding and converting the data. If you Google it you will find tutorials but almost every single one does it a different way and quite often uses out of date information that no longer works at all. (Lots of 404 Errors even on government sites) I’ve wasted a ton of time following directions only to find out part of the way through that the websites used don’t exist anymore or don’t have good data sets for places I’m interested in.

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That very likely is detailed enough for a carve at the size they mention (31x47"), particularly if they use a V-Carve tool path as opposed to a pocket tool path for each layer. This would minimize the corner radius which otherwise increases with depth of cut.

In any case, I fully agree they should run samples to determine what they like the best.

I used navionics to get lake depths, then screenshot and imported into sketchup where I used the freehand tool and carefully traced where I needed.


I had the same issue you can into - All the STRM (If I recall the name correctly) are no longer easily available on the government websites. I’ll have to dig up the link - but I did find a Map to STL website where you could plugin data and it generate an STL file.
But i’d really like to use the old way using the government data and a program called Big Topo.

I honestly should start a thread somewhere here and see what people are using now-days for topo.


Yeah, might be a good idea to have a thread somewhere dedicated to that type of project. Two of the options I found are Terrain2STL and Tangram Heightmapper

They seem good with a bit of tweaking to make a proper 3D Carve work. I think that sort of stepped Bathymetric style maps like this are really interesting too and seem a little more difficult to get right. Doesn’t have to be for lake/ocean depth either. Stepped mountainous terrain would look really cool too. I suppose you could just stop a full on 3D Carve in the roughing stage haha


Terrain2STL! That’s the one I was thinking of. I’ll have to try the other one out.

Still waiting for my machine to get here - but I’ve been fooling around a lot with trying to make a topo of my city here (Kingston, Into). I’ll see what I can come up with using that other one you mentioned.

Also man those water-body carvings are great too. Sure my dad would love one of the lake where our cabin is. Epoxy still freightens me a tad though.

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Here is what I’ve got so far. My lack of a down-cut 1/8" bit made for some tedious sanding. I ended up using a 1/8" upcut bit and got an acceptable outcome. this was my “practice”


Looks good. Is that one piece of wood or multiple pieces of wood laminated?

I did one piece of 3/4" ply and 0.1" deep pockets.