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G-Wizard Now Has V-Bit Feeds and Speeds for Engraving

Sep 20, 2011   //   by Bob Warfield   //   Beginner, Blog, CNC Router, Software, Techniques  //  No Comments

There have been a lot of requests to add V-Bit support to G-Wizard. A V-Bit is a special purpose bit intended for engraving. They come in all shapes and sizes, but usually they look something like this:


A V-Bit for Engraving…

They do a very nice job engraving, but feeds and speeds can be a bit tricky for a couple of reasons. First, that sharp point is a bit delicate and the geometry is not nearly as optimized for plowing through tons of material as a helical endmill. The good news is they’re best used with depths of cut of say 0.005 to 0.010″ (0.1 – 0.2 mm). That at least means that chip clearing should be easy and the cutting forces shouldn’t be too great.

That brings me to the second issue, which is that the “diameter” of your cutter is, well, not the diameter in the cut!

Because of that, G-Wizard needs to do compensation to figure the effective geometry just like it does for a ballnosed endmill. It turns out that since you’re only down in the cut 0.005-0.010″, you need to run a lot more rpms and treat things much differently, even though you may be running a 1/4″ shank tool. Here is a diagram showing the effective diameter for a 90 degree V-Bit with a 0.010″ depth of cut:

V-Bit Effective Diameter

The effective diameter in an 0.010″ depth of cut is only 0.020″!

To select a V-Bit in G-Wizard, treat it like an endmill. Choose either HSS or Carbide, depending on what material your V-Bit is made from. You’ll use the geometry menu to tell G-Wizard that this is a V-Bit and not an ordinary endmill:

G-Wizard Endmill Geometry Menu

Geometry menu for selecting ballnose or V-Bits…

Now it becomes obvious why we changed from using a checkbox for ballnoses in the last release!

Once you select a V-Bit from the geometry menu, G-Wizard does several things:

– It starts figuring out the effective diameter based on the angle of the V-Bit (30, 45, 60, or 90 are the commonly available tip angles) and the diameter. That will cause it to figure out the rpm and feedrate differently.

– Equally as important, it will dial back the feedrate quite a lot to account for the fact that the pointed tip is more delicate than a typical endmill. If you’re working with really nasty material (tough stainless or the like), you might consider using the gas pedal (Tortoise and Hare slider) to go a little more conservative.

That’s all there is to it!

BTW, 2linc is a great manufacturer for all things engraving and is one seller of V-Bits. There’s more there than engraving, but take a look for tips. I bring them up because one of the things they mention for CNC’ers is you can run a lot higher feedrates if you use one of their spring-loaded holders for your V-Bits. G-Wizard’s Feeds and Speeds for V-Bits assume a rigid holder, but you can double the feedrate if you have a spring-loaded holder. I assume the spring-loaded holder helps cushion the V-Bit’s delicate tip from undue shocks and lets it sort of find its own feedrate that works by backing off the depth if there is too much force involved. It also allows the engraving to follow a contour if you aren’t engraving a flat surface.

This new V-Bit feature is in G-Wizard Calculator Release 1.550 (the link is the Install Page). If you’re not a registered G-Wizard user and you’d like to try our free 30-day trial, check it out on this page.


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