Our Laguna Swift CNC’s rotary attachment uses the A-axis to control its rotation. Internally the RichAuto B58E handheld controller has a setting for the maximum speed limits (Max Spd Limits) for the X, Y, Z and A axes.
Previously the A-axis was set to 5000 degrees/minute which is about 14 RPM. This was too slow for some VCarve uses (see Practical Implications for VCarve Users below)
Today I changed this setting to 18000 degrees/minute or 50 RPM to improve performance of doing roughing rotary cuts which had been limited by the previous setting.
Practical Implications for VCarve Users
When creating a rotary toolpath in VCarve, you specify the tool feed rate in inches per minute (IPM) just as you would for a flat job.
However, when using a wrapped rotary job, VCarve maps the Y-axis to the rotary A-axis. The CNC controller must then convert the requested feed rate into A-axis motion measured in degrees per minute.
As a result, the maximum A-axis speed configured in the controller can limit the feed rates that VCarve is able to achieve.
Example: 18" Long × 2.5" Diameter Rotary Blank
Suppose you are machining a spindle blank that is:
Length = 18"
Diameter = 2.5"
The circumference of the stock is:
Circumference = π × 2.5
= 7.854"
In a wrapped rotary job, the VCarve job dimensions become:
X = 18.000"
Y = 7.854"
The X dimension represents the length of the spindle.
The Y dimension represents one complete revolution around the stock.
Example Roughing Feed Rate
Suppose a roughing toolpath is configured in VCarve with:
Feed Rate = 150 IPM
To achieve 150 IPM at the surface of a 2.5" diameter workpiece, the controller must rotate the A-axis at:
A-axis speed =
(150 × 360) / (π × 2.5)
A-axis speed = 6,875 deg/min
Original Controller Configuration
The original RichAuto A-axis speed limit was:
5000 deg/min
However, the roughing toolpath requires:
6875 deg/min
Since:
6875 > 5000
the controller cannot achieve the programmed feed rate.
Even though VCarve requests:
150 IPM
the machine is physically limited by the A-axis maximum speed setting.
The actual maximum feed rate becomes:
Maximum IPM =
(5000 × π × 2.5) / 360
Maximum IPM = 109 IPM
Therefore a roughing toolpath programmed at:
150 IPM
would actually be limited to approximately:
109 IPM
at the surface of the stock.
Updated Controller Configuration
Suppose the A-axis maximum speed is increased to:
18000 deg/min
The same roughing toolpath still requires:
6875 deg/min
but now:
6875 < 18000
Therefore the machine can achieve the full programmed feed rate.
The VCarve user can enter:
150 IPM
and the machine will actually cut at approximately:
150 IPM
on the surface of the stock.
Common Rotary Feed Rates
The following table shows the A-axis speed required to achieve common feed rates on 2.5" diameter stock.
| Desired Feed (IPM) | Required A-Axis Speed (deg/min) |
|---|---|
| 50 | 2,292 |
| 75 | 3,438 |
| 100 | 4,584 |
| 109 | 4,997 |
| 125 | 5,730 |
| 150 | 6,875 |
| 200 | 9,167 |
| 250 | 11,459 |
| 300 | 13,751 |
| 350 | 16,043 |
| 393 | 18,015 |
Notice that approximately:
393 IPM requires 18,000 deg/min
which is the proposed A-axis maximum speed.
Maximum Achievable Feed Rates
The maximum surface feed rate depends on both the stock diameter and the controller’s A-axis speed limit.
Original 5,000 deg/min Limit
| Stock Diameter | Maximum Surface Feed Rate |
|---|---|
| 1.5" | 65 IPM |
| 2.0" | 87 IPM |
| 2.5" | 109 IPM |
Updated 18,000 deg/min Limit
| Stock Diameter | Maximum Surface Feed Rate |
|---|---|
| 1.5" | 236 IPM |
| 2.0" | 314 IPM |
| 2.5" | 393 IPM |
Summary
The original controller configuration limited the A-axis to:
5000 deg/min
On the machine’s largest practical stock diameter of approximately:
2.5"
this limited the maximum achievable feed rate to:
109 IPM
As a result, a typical roughing feed rate of:
150 IPM
could never be achieved, regardless of the value entered into VCarve.
Increasing the A-axis speed limit to:
18000 deg/min
raises the maximum achievable feed rate on 2.5" stock to approximately:
393 IPM
This allows common roughing and finishing feed rates to be achieved without the controller becoming the limiting factor.
For a VCarve user, the practical result is simple:
- With a 5,000 deg/min A-axis limit, many rotary toolpaths are feed-rate limited by the controller.
- With an 18,000 deg/min A-axis limit, normal rotary feed rates are achievable.
- A 150 IPM roughing cut on 2.5" stock is impossible with a 5,000 deg/min limit, but easily achievable with an 18,000 deg/min limit.
- The feed rate entered into VCarve more closely matches the actual feed rate at the surface of the workpiece.