CNC Services Northwest

Centroid CNC control sales, service, training and support

Frequently Asked Questions

Centroid Retrofits

A: Yes, but it might not be worth the time, effort and expense.

Before you can install a CNC control on a manual mill, you will need to:

1. Replace the X and Y leadscrews with precision ground ballscrews
2. Install servo motor mounts on X and Y, and obtain suitable pulleys and belts
3. Install limit switches on X and Y
4. Install a quill drive kit for the Z axis, with integral servo motor mount and limit switches

You will end up with a very versatile machine: one which can be run as a full 3-axis CNC; a semi-manual 2-axis CNC; or a manual mill with DRO position display.

However, if your objective is just to have a good CNC mill, you may well save time and money by purchasing a good used CNC knee mill, such as a Bridgeport Boss, a Shizuoka AN-S or ST-N, or a Supermax YCM-40, and retrofitting it. These machines often sell on eBay for $1,500 to $3,000 in good mechanical condition but with outdated and unreliable controls.

Q: How much does it cost to retrofit my older CNC mill or lathe?

A: That depends on a lot of factors. My customers have spent everywhere from $8,000 to $50,000 for control retrofits.

Basic Centroid 3-axis DC Servo CNC retrofit controls start at around $9,700 for an M39S with a hand pendant, and a little under $11,000 for an M400S with its complete console.

If your machine is fairly basic (a 3-axis mill or 2-axis lathe, without an automatic tool changer or any especially arcane gadgetry you want to keep), then you can probably do the bulk of the installation yourself. However, even with these machines you would do well to hire me for one or two days of professional help for the final setup, testing, and training in programming and operation.

If the machine has an automatic tool changer or other specialized devices that need to be integrated, then you will probably want to hire additional professional help with the wiring and PLC programming.

If you are busy and would rather spend your time designing and machining parts, rather than tinkering with controls, then you can hire me to do the entire installation. Depending on the machine, control, and your location, this will usually take from four days to two weeks, and cost between $2,000 and $5,000. Large and complex retrofits, such as the Giddings & Lewis and Pratt & Whitney machines shown in my retrofit gallery typically take three to four weeks on site.

Various options are available as add-ons to a basic control package, to simplify installation, power larger machines, and provide a little more professional finish. These include:

1. M Function Pre-wire ($725): Factory-installed reversing contactors for the spindle motor; contactor for flood coolant pump; and pre-connected cables for mist coolant, auto lube, limit switches and spindle high/low range switch.
2. S Function Pre-wire ($499): Same as the M Function Pre-wire above, except that a pre-connected cable for a variable frequency spindle drive (inverter) is provided instead of reversing contactors.
3. High Power Upgrade ($850): Larger transformer, allowing the entire control to operate on 208V, 230V, or 460V power. Absent this upgrade, the control system runs on 120V single-phase power, but switches higher-voltage three-phase power for the spindle and coolant (requiring two separate power service connections).
4. MS Connectors on Servo Motors ($161 per axis): This option provides circular metal mil-spec pin connectors on the servo motors and cables. The standard motors and cables are direct-wired through a strain relief, with internal plug connections.
5. 40 in-lb motor upgrade ($290 per axis): Upgrade from the standard DC servos, which provide 29 in-lb continuous stall torque, to motors with 40 in-lb continuous stall torque.
6. 40 in-lb brake motor upgrade ($325): Same as above, but motor also has an integral holding brake that clamps the shaft when power is removed. These are useful for unbalanced axes then would otherwise fall when power is removed (e.g. a knee mill which drives the knee as the Z axis instead of the quill, or the Z axis on many router tables).
7. Sealtite conduit on motor cables ($75 per axis, plus requires MS connectors above): Provides liquidtight flexible conduit on motor cables, for additional protection against physical damage.

All this generally applies to DC servo controls. For larger machines (generally those with 10HP or larger spindle motors) you will probably want an AC servo control instead. These start at $3K to $4K more than the DC servo controls.

Q: What is the difference between an M39 and an M400?

A: The M39 uses a conventional PC keyboard and monitor, which you supply, and a handheld pendant for the jog panel.

The M39 includes a support arm and tray. You can use whatever keyboard and monitor you like, from a surplus CRT to a modern LCD.

The M39 computer is in the upper part of the electrical cabinet, usually on the side or back of the machine.

The M39 is somewhat less expensive, and so appeals to the home market. Also, with its walkaround pendant, it is a good choice for large-format router tables.

The M400 includes an industrial console, with the LCD display, keyboard, and jog panel built in.

The M400 computer is inside the console, making access to the USB ports somewhat more convenient.

Q: Do I need to buy the hand pendant with an M39?

A: No, but I highly recommend it.

The control software provides a "keyboard jog panel", so you can use PC keyboard controls for machine jogging, spindle control, coolant control, etc..

If you omit the pendant and use keyboard jogging, you must supply and wire in an appropriate Emergency Stop pushbutton.

Q: Should I pay extra for one of the pre-wire options?

A: Probably.

If you are proficient with electrical controls, and know where to buy contactors, starters, and shielded multi-conductor cable, then you can save several hundred dollars by sourcing these parts and installing them yourself.

If you just want a control that you can install quickly and easily, then it is well worth your while to purchase either the M-function or S-function prewire.

Q: Should I pay extra for the high-power upgrade option?

A: Perhaps.

For small knee mills using 29 in-lb motors, you do not need to extra power that this option provides. However, the option does give you a cleaner installation, in that there is only one power service connection (to 208-240 VAC power).

If you require 40 in-lb motors, or need to run on 480 VAC service, then you need the high-power upgrade.

Q: Can I save money by reusing my old servo drives and motors?

A: Probably not. The Centroid control is designed to use its own servo drives, via a proprietary fiber optic interface.

Centroid's OPTIC1 unit is available for interfacing to third-party servo drives, provided those drives can operate in a torque mode (not velocity mode), using a +/- 10VDC analog reference.

For lower-power drives (anything comparable to the 29 in-lb or 40 in-lb DC servos, or the 1kW AC servos), it makes more sense to use Centroid drives than to try to interface to third-party drives.

For higher-power systems, especially those using well-proven late model torque mode drives like the Yaskawa Sigma series, it definitely makes sense to use the OPTIC1 interface and keep the existing drives and motors.

Q: Okay, but what about using my Boss DC servo motors with the Centroid drive?

A: If you are doing your own installation, and you have the inclination and ability to adapt the old motor cables or make new motor cables, then it may make sense. If you are hiring me to do the installation, you will spend more on the additional labor to adapt to the old motors than you would spend on new motors.

Note that if you do keep the old motors, you may need to install new position encoders. Early Boss servo systems often used 250-line (1000-count) encoders. For optimum performance you should use at least 1000-line (4000-count) encoders. Centroid motors come standard with 2000-line (8000-count) encoders.

Also, some older motors will have TTL (single-ended) encoders. You need encoders with a differential line driver output (they should have 8 wires).

Copyright © 2008 Marc Leonard
Last updated 07-Oct-2008 MBL