Magnate Barley Twist Bit

[SteveNelson46]

Has anyone had any success with the 2" Magnate barley twist bit (7552)?. I downloaded the bit profile from Magnate to create the bit and set it up with what I think is the correct parameters (2" spacing, .5" DOC) and it looks good in the preview but the actual cut comes out with a flat space on the tops of the spirals. I think that I have cut at least 10 or more trials in scrap wood using different depths and spacing but nothing seem to work. If I cut it as raster it comes out perfect. I used the spiral wrap gadget to create the vectors with 2" spacing (width of the bit) between the spirals.

[Rcnewcomb]

but the actual cut comes out with a flat space on the tops of the spirals

Can you post a photo of the actual results?

[SteveNelson46]

but the actual cut comes out with a flat space on the tops of the spirals

Can you post a photo of the actual results?

I will as soon as I can cut another one. I threw the trials away and the trash man already picked them up.

The flat spots are on the high arcs where the two paths come together. This would normally indicate that the spacing is incorrect but the bit is 2" wide so the spacing needs to be the same. If I make the vectors closer together the results will be a high ridge where the bit paths come together to form the high round over. If I set the bit depth deeper the cut will show as too deep everywhere. I know my z-zero is set spot on (set to rotational axis) because other projects have turned out okay. I even tried setting the z-zero to the top of the material but got the same results. The blank is exactly 3" round. I turned it on my lathe with a Vega duplicator with a depth stop locked to make a straight even final passes.

[TReischl]

Hmmm. Tossing a few extra variables in there by turning it on your lathe and then mounting it on the 4th axis.

Howzabout just turn it to size on the rotary and give it a go?

Just a thought.

[SteveNelson46]

Okay, here is what it cuts like. If I set the DOC slightly deeper it helps the flat spots but clearly shows the outline of the cut as too deep.

Ted, I tried that on other projects. It works but rounding on the lathe with a duplicator is about 20 times faster and smoother.

I don't have a lot of experience with profile cuts and bit shapes but I'm starting to think it has something to do with the bit geometry or machine setup. Especially since it looks good in the preview.

[mtylerfl]

Steve,

Did you measure the Bit itself to confirm the dimensions? The photo of the carve appears there is a mis-match between the Profile and the actual bit dimensions. Long-shot guess, on my part.

Reading your posts, it seems you’ve tried everything else (cut deeper, reduce vector spacing).

[SteveNelson46]

Steve,

Did you measure the Bit itself to confirm the dimensions? The photo of the carve appears there is a mis-match between the Profile and the actual bit dimensions. Long-shot guess, on my part.

Reading your posts, it seems you’ve tried everything else (cut deeper, reduce vector spacing).

I downloaded the bit profiles PDF from Magnate. They are DXF drawings with the full bit shape. Now that I think about it, sometimes dxf shapes are not always as they seem. I've also heard reports about Magnate bits are not always as precise as they claim to be.

[Rcnewcomb]

sometimes dxf shapes are not always as they seem

The manufacturer may have a broader tolerance range, i.e. +/- 5% to 10%

My guess is that you will need to tweek the form tool geometry.

[SteveNelson46]

This is a pic of the actual bit.

[TReischl]

Another thought. . .

Do you set the spacing (2 inches) as measured along the axis?

The reason I ask that is that it looks to me like the spiral tool paths are too far apart.

In the gadget are you setting the spacing using:

Not really sure which one should be used? Just on my first cup of coffee this morning.

And I hear you about turning the diameter on a lathe to be much faster.

[SteveNelson46]

Another thought. . .

Do you set the spacing (2 inches) as measured along the axis?

The reason I ask that is that it looks to me like the spiral tool paths are too far apart.

In the gadget are you setting the spacing using:

Capture.JPG

Not really sure which one should be used? Just on my first cup of coffee this morning.

And I hear you about turning the diameter on a lathe to be much faster.

Ted,

Yes! I set the spacing for 2". That's what the width of the bit measures. I'm going to lower the bit to the spoilboard and check the actual depth of cut in a few minutes. After my first cup of caffeine (tea) this morning also.

[kp91]

I have only done barley twists on a manual ornamental mill, using several of the Magnate bits. You might want to look at the manual cutting instructions and see if there is some insight that might help.

https://lwmcnc.com/cnc-mills/past-model ... echniques/

[mtylerfl]

Hi Steve,

Try one more experiment, if you’re up for it, that is.

Start with a turned blank of 2” diameter (instead of 3”). Then run the barley twist with your Magnate bit.

[SteveNelson46]

Hi Steve,

Try one more experiment, if you’re up for it, that is.

Start with a turned blank of 2” diameter (instead of 3”). Then run the barley twist with your Magnate bit.

Thanks Michael. I've sent the files, example pics, and a description of the problem to Vectric support. Just waiting for a reply.

My guess is that the "Spiral Pitch" option should be used but I just don't know how it is implemented in the software or how to calculate it. I'm doing the research now.

[Rcnewcomb]

Steve,
Just to keep you company I've ordered two different sized barley twist bits from Magnate and I'll run some rotary tests myself. I hope to have some good samples for the October Users Group in Denver.