Brother TC-211

Note that Pico Systems (my company) makes a resolver to quadrature converter board. See :
pico-systems.com/osc2.5/catalog/product_...ath=2&products_id=32
for more info.

There's no sense in replacing good servo motors with steppers. The larger the machine, the worse steppers perform.

Jon

Making a resolver converter is just silly, there are off-the-shelf solutions. Jon has mentioned the Pico interface, and I have two machines using the Mesa 7i49 card. Both are fully integrated with LinuxCNC.
In fact, on my lathe I took an encoder off of one servo and fitted a resolver. I like resolvers.

I'm thinking I might still try open loop steppers. The TC211 is quite a small machine I might get away with it. Cost is a factor. I don't want to spend $1000 on it. This machine cost $50, I don't think it is worth investing in it as I already spent $1000 on another CNC machine which is almost working. This Brother came as a chassis with motors and seemed a better project than converting a manual mill or buying a desktop engraver. I previously bought another bigger mill, also BT30, with drivers, tools, spares, manuals, controller and a full Bosch Rexroth control system which seemed a more cost effective and viable way to get started in CNC than investing 1000s in the Brother.

Someone on youtube has a Grisly Mill converted to CNC using open loop stepper motors, and ball screws, which gave me the idea to restart this project with a low end $250 refit. It would be very useful to have this nice small Brother mill with hand controls on it as a manual mill and ideally DRO type functionality, as I don't have any mill at all, and really need something for small projects that don't require CNC. I was wondering if I could add some digital scales to the axes and use that to provide a closed loop output.

As the machine has no drives or any electronics, it does seem appealing to design and build a motor driver, resolver, etc, rather than spend say $5K on a nice easy life solution, off the shelf controllers, cards, etc. Especially as I will probably blow up a few, and will want multiple machines. Perhaps this is how projects lose track, never get finished, and end up being sold for $50?

JohnW wrote: As the machine has no drives or any electronics, it does seem appealing to design and build a motor driver, resolver, etc, rather than spend say $5K on a nice easy life solution, off the shelf controllers, cards, etc. Especially as I will probably blow up a few, and will want multiple machines. Perhaps this is how projects lose track, never get finished, and end up being sold for $50?

Have a look as STMBL if you are prepared to build your own drives.
github.com/rene-dev/stmbl/wiki/conf

Resolver-feedback is handled by default, and it integrates very neatly with LinuxCNC.

Are the servo motors already mounted on the machine? Replacing them with steppers + stepper drives will cost more than a couple hundred $. A 3-axis PWM system from Pico Systems, with brushless motor servo amps and the resolver converters will cost $1150. That will be all you need to get the 3 axes running. Not sure what you have for a spindle motor, but you may need some kind of VFD to run that.

Ah, with our PWM system, you will have a DRO function automatically. Just hit E-stop, and you can crank the motors and use the screen readout as a DRO.

Having designed several servo amplifiers, I can't recommend it unless you are a real electronics guru, there are many pitfalls, and you will end up popping a lot of power transistors and gate driver chips.

Jon

Some really useful options there andypugh and jmelson thanks. All the motors came with the TC-211 but for some reason had been removed, the same for the spindle motor, and tool changer motor. Some good options there to mull over, thanks.

The original motors will have been carefully chosen through a time consuming engineering process by someone who knew exactly what they were doing.

I think it makes sense to keep them.

JohnW wrote: Some really useful options there andypugh and jmelson thanks. All the motors came with the TC-211 but for some reason had been removed, the same for the spindle motor, and tool changer motor. Some good options there to mull over, thanks.

Removed, but you still have them, or removed and you DO NOT have them? makes a big difference!

Jon

JohnW wrote: I bought one of these TC211's with the good intention of building a servo motor resolver interface. However, my partner wants to buy a crappy desk top CNC as I have taken so long now. I am thinking there are some NEMA 34, 3 axis stepper motor kits on ebay with parallel port control.

OK, I looked up some pictures of the TC211, and you are totally NUTS! That machine is WAY too big for steppers!
The X and Y might just handle it, but the entire Z axis is on vertical ways.. I don't know what it weighs, but it has to be a LOT!
You need a SERIOUS servo motor on that axis, at least.

Also note the TC211 is a TAPPING center, not a milling machine. So, the spindle is not up to the kind of side loads that are seen in heavier milling operations.

Jon

I still have the motors. They need a good clean but turn smoothly (ie bearings are OK at least). X and Y are 100w 3.25kg/cm servo motors, Z is 200w 6.5kg/cm according to the original sales brochures for the machine. One thing I have noticed is that the ball spindle pitch on the machine seems more coarse that I would have expected. It all looks standard, and I wondered how they manage to meet the original precision spec of 0.01mm. What sort of angular positioning accuracy are the original (Toshiba?) resolvers likely to achieve? Yes, the Z axis is quite heavy! It has the original a 1.5KW servo spindle motor on it. I was thinking of a counter weight if I converted the machine to manual only.

With regard to side loads, I was more concerned with the actual vertical ways not being rigid enough for milling, or getting damaged from side loads. From pictures on the web the spindle tube appears about 6 or 7 inches long, with 4 ball bearing races, two at each end... The spec says the spindle motor is a 1.5KW Servo motor. Is it a servo because for the tapping operations, you need to synchronise the exact number of rotations with plunge depth for thread cutting?