Smaller end mills

I notice when I use endmills to cut rectangles or squares in 1/2" acrylic there is a small radius at each corner that is more pronounced the greater diameter end mill.

I find myself using 1/8" end mills to cut out the shapes and having to square off the corners by hand with a file to precisely fit the objects that I’m fitting in the acrylic.

I tried looking up some 1/16" end mills but they don’t seem to be too widely available or seem to be more associated with 3d applications.

Is there a better way I can achieve a sharper right angle when making these cuts?

That’s just a fundamental limitation with geometry. As you note, the smaller the endmill, the less unwanted material to remove. There are some tricks you could play with V bits to remove some of the unwanted material, but there will always be some leftover.

It’s about the best you can do without changing the direction the endmill approached the workpiece, i.e. without another axis.


Yep, as Michael says, it’s a limitation of rotating tools.

There are cutters down at the 1-2mm size but at 1/2" thick you’re not likely to find any with that cutting length as they just won’t be strong enough, even if you did you’d have to step into the full cut in small increments to avoid breaking the cutter.

Is it safe to assume you don’t want to ‘dogbone’ the corners?

I’m not familiar with “dogbone” corners?

It’s where you add a little circle to the square corner to allow the cutter to clear the whole square, at the expense of some extra cutting.

Some people like them, others think they’re ugly, depending on your application they might be acceptable.

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This is precisely my problem; the outside corner (shaded in orange in the picture) is rounded when I need it to get it as square as possible. I’ve been filing that corner by hand and would like to find a way to eliminate that process

I didn’t know that was a link… the dog leg won’t work for me unfortunately…

thanks for the link!

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Use V carving to arrive at sharp (albeit angled vertically) corners?

That unfortunately won’t work in my application

you can get 2mm bits which are a nice balance between size and strength (I find that smaller bits snap easy)

there’s not too much you can do beyond that, round peg square hole kind of thing… especially if you can’t use a V bit.

that is, unless you’re willing to cut away a bit too much instead… then there are options obviously


What about a corner chisel?


I Don’t own one so don’t know, but does anyone else know if a laser can cut a sharper corner?

Yes, but there usually is a tiny tiny bit of radius to remove on parts cut with a laser, we are speaking of a laser kerf of up to 1mm.

I was just wondering the same thing. if anyone has used the jtech laser in conjunction with the shapeoko and able to align the two cuts perfectly or not

Corner chisel won’t work for 1/2" acrylic

This is an inherent problem with using round spinning tools: they can’t make interior sharp edges.

If you need to make squares, you need a different tool. For mills and lathes, there are rotary broaches. I don’t think these are compatible with Carbide 3D’s machines though

Aside from mills and lathes, there are regular broaches and more conventional tools like files.

Tiny endmills do exist but they’re very expensive, fragile and they require a spindle with crazy high concentricity.


Now there’s an interesting challenge for someone who knows what they are doing - is it possible to focus a laser beam to give less than a 1mm radius? Simplistically it must be possible as I can’t think what the limiting parameter might be other than the precision of the lenses being employed.

Do you have a recommended site for the 2mm bits?

No experience w/ lasers (to be frank, the safety implications and the need to filter/exhaust worry me to no end), but all the box generators which I have seen assume an essentially zero kerf, cutting directly along the line, and don’t adjust for the radius, assuming that the total cutting width of the laser (half off for each side of the line) will be equivalent to the glue line.

We have:

which I have found wonderfully useful — as noted, it’s far stronger than a 1/16" or 1/32" endmill, but sufficiently smaller than a 1/8" (3.175mm) endmill that it can cut far smaller details — I just wish we had an equivalent ball-nose.

3 Likes is what I use for 2mm bits… single flute (nice for plastics), down cut (nice for wood) and while you CAN snap them… they take a reasonable amount of abuse while not breaking the bank too much