Smooth Arc Function

David Lewis

David Lewis

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Last year I bought a 3-axis DRO to go with a new BP clone, and I was excited to find out about the smooth arc function, however I cannot get it to work. I assume there are parameters I do not understand, but I'm a smart guy and I am at a loss. For reference, it is a DRO Pros 3M, Z on the knee (I also have an independent quill scale).

For reference, I have the origin set to the rear left corner of the work. The flycutter has a 73mm cutter radius.

I want to cut a convex 329mm radius arc which is centered at X120mm/Z-329mm. I will be hand feeding in Y, and I felt that the flycutter would be a better option than an end mill, for the radius of the insert and for the fewer passes I'll have to take. I would also consider turning the work to cut Y/Z instead of X/Z, and then I'd be able to use the X-axis power feed. I think the programming would work the same either way.

The cut I want to make is similar to the sharpie mark on the front face of the work. Can anyone help me figure this out?

IMG_0492.JPG
 
Flycutters, like end mills, only cut a plane surface, unless they are inclined or tilted out of parallel with travel. Then they cut a more ore less concave surface. In your case, you should just treat this as a 73mm end mill. It will take many passes to profile out a convex radius as you have laid out on the part. Whether there really is an advantage over a ball nose end mill, I have my reservations. I am not familiar with your DRO, but it may indeed have a profile function that will help you.
 
Thanks for the reply, Tony. The point of the flycutter is that I'll be taking light passes anyway and simultaneously removing all the excess material at the same time. A twofer! But that isn't really part of my question, so maybe I could have phrased it better.

I'll be treating the flycutter as a 73mm end mill, for sure. That part's clear.

Part of my problem is that the function asks for a starting point and an ending point, but the ending point is completely irrelevant and would require a lot of math to figure out, so I decided to fool it into ending at 180 degrees after starting at 90 degrees (the vertical sharpie line in the photo). I'd just stop machining when I reached the end of the material. Is this approach flawed?

Does anyone here have any experience with XZ smooth arc function on a DRO? It seems like an incredibly useful tool that is not self-explanatory how to use. There aren't even any videos on YouTube on the subject. I'm going to make one when I figure it out! I already have a channel, but it's just a bunch of short videos of chips flying. If you want to see the Suburban Tool flycutter in slo-mo, that's the place to go to see it!

For reference, I'll know I've programmed the function properly when the tip of my tool is touching the surface of the work at Z-zero directly above the axis of the arc, which happens to be X+120mm. No amount of futzing with the settings seems to put the tool in that position.
 
Hi David,

I don't have any experience with the smoothing function on a DRO but have manually cut arcs like you are trying to do. Does the DRO ask for the cutter diameter and corner radii? If not my guess would be that the DRO assumes you are using a ballnose endmill and will put the center of the spindle/flycutter on the vertical line you have drawn on the stock so a ballnose endmill would be tangent to the arc you are trying to cut.

Kevin
 
If this is a true arc (segment of a circle) then I wonder if you couldn't start at the top, and of course, as you move out in Y and down in Z (provided the part is oriented that way) , you could just stop wherever the part edge is. I don't know the DRO, but I am beginning to wonder whether it can comp both for the radius of the insert plus the flycutter swing, as Kevin mentions. I would hazard a guess it would be more for use with a ballnose end mill.

Maybe someone with that feature on their DRO will come up with some tips.
 
Not familiar with the function, but I would think you would need a start and ending points for the arc to be calculated.
 
I think I may have partially figured this out, but DRO PROS is going to call me later this morning with a walk through. Maybe once I figure this out I'll post a tutorial!
 
The two biggest takeaways from my conversation with Todd at DRO PROS are:

1) Smooth Arc geometry is always measured from ABS, NOT incremental!
2) XYZ-zero is the trailing edge of the cutter (which does the cutting!)! Essentially, the axis of the spindle is irrelevant.

I still plan to keep my ABS origin on the top left corner of the fixed jaw of my vise, and use offsets to determine the coordinates to enter, but I cannot rely on INC for Smooth Arc function.

I'll probably follow up with a tutorial or some kind of example of this working.
 
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