Need advise for high precision cnc

[k-linkz]

Hi guys,

i see some advice for building an high precision milling CNC looking for something +/- 5 or 1.5 micron precision.

from my understanding it should be a close loop.

so here is what i was thinking:

- LinuxCNC for operation

- MESA breakoutboard or Kflop with kanalog extension (then i change the LinuxCNC for windows and use Kmotion instead)

- AC Servo motor

- encoder i was thinking : https://www.aliexpress.com/item/Free...iABEgI7fPD_BwE

a linear encoder

i'm block at the AC servo drive. I've look at the gecko drive. but it seem to me (and do correct me if i'm wrong) that the close loop stop at the drive part. didn't see an encoder output to plug into the breakout board.

didn't want to use step motor as i'm worry it may skip steps.

ball screw ? open to suggestion. most likely something from aliexpress or ebay knowing myself

cnc size is about 2 meters X 2 meters X 1 meter (size is not set in stone, can be readjusted if needed)


what do you guys think.

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[awerby]

If you really need to hold 1.5 micron (plus or minus approximately 0.0000590551") accuracy over 2 meters, I doubt that any ebay/aliexpress ball screws are going to work for you. In fact, that's something that even the most expensive ball screws will have trouble achieving. I don't want to dampen your enthusiasm for building a machine, but starting with more realistic tolerances will make it a lot easier to accomplish without costing you a large fortune. Here's a link to a ball screw manufacturer's resources page: https://dynatect.com/resources/ball-...ign-resources/ Their top grade precision-ground screws (DIN/JIS C1 grade) are specified as accurate to 5 microns over 300 mm. You might call them and ask what it would cost for a screw that would meet your specifications - if it's even possible. Since even a small variation in temperature will throw measurements off by more than that, the ball screws would require internal cooling, and the whole assembly would need to be operated in a climate-controlled environment. Are you sure you really need that much accuracy? Most people here are ecstatic if their machines can hold +/- .0005" overall; if you want more than that you have to be willing to pay for it.

[k-linkz]

If you really need to hold 1.5 micron (plus or minus approximately 0.0000590551") accuracy over 2 meters, I doubt that any ebay/aliexpress ball screws are going to work for you. In fact, that's something that even the most expensive ball screws will have trouble achieving. I don't want to dampen your enthusiasm for building a machine, but starting with more realistic tolerances will make it a lot easier to accomplish without costing you a large fortune. Here's a link to a ball screw manufacturer's resources page: https://dynatect.com/resources/ball-...ign-resources/ Their top grade precision-ground screws (DIN/JIS C1 grade) are specified as accurate to 5 microns over 300 mm. You might call them and ask what it would cost for a screw that would meet your specifications - if it's even possible. Since even a small variation in temperature will throw measurements off by more than that, the ball screws would require internal cooling, and the whole assembly would need to be operated in a climate-controlled environment. Are you sure you really need that much accuracy? Most people here are ecstatic if their machines can hold +/- .0005" overall; if you want more than that you have to be willing to pay for it.

thanks for the reply and the link i'll have a look.
i can drop the accuracy over to 1 meter. 1 X 1 X 1.

yes climate-control environment - no problem for that- with humidity control and negative pressure if needed.

i agree, " if you want more than that you have to be willing to pay for it" but the question is who do i pay ?

i'm trying create a blue print of how much it's going to cost me so when i go at the bank and mortgage the house i have an idea about how much i want/need.

[bostosh]

Get a Quote, Pay these guys, no problem, get parts.
Precision Manufacturing at Moore Tool: Precision Machining Technology, Precision Tools

Anyone here ever done precision work under .0002 ?

[Jim Dawson]

With those specifications you have moved well out of the hobby class machine into a high precision full on industrial machine. Forget about Gecko, Kmotion, Mesa, and Chinese ball screws. You will need industrial hardware.

First start with a good used 6030 Fadal just to get a solid platform, work envelope, motors, and drives to work with.

Pour a low expansion concrete isolation base for the machine to sit on.

Rebuild the ball screws as needed to get zero backlash.

Rebuild ways as needed.

Install temperature controls in the building to keep the environment at a constant 18°C

Then rip out the controls.

Install 0.5 um resolution linear encoders on all axes.

Install a 4080 Galil motion controller to run the system, and yes, close the loop at the controller.

Calibrate the system using a laser infromenter.

Now you have a chance at actually holding the the specification that you want.


What you are proposing is going to be very expensive. I have two machines in my shop that will hold <+/- 0.01mm consistently, but they also each have about $10,000 in controls upgrades and that's just the hardware cost. Both have a work envelope of about 32x12.5 inches. Your work envelope requirement adds an order of magnitude of difficulty in holding your specs.

[Jim Dawson]

Anyone here ever done precision work under .0002 ?

Yes, but it normally requires temperature control and precision grinding equipment.

I'm happy if my DRO reads +/- 0.0001, without regard what the cutter is actually doing.

[k-linkz]

With those specifications you have moved well out of the hobby class machine into a high precision full on industrial machine. Forget about Gecko, Kmotion, Mesa, and Chinese ball screws. You will need industrial hardware.

First start with a good used 6030 Fadal just to get a solid platform, work envelope, motors, and drives to work with.

Pour a low expansion concrete isolation base for the machine to sit on.

Rebuild the ball screws as needed to get zero backlash.

Rebuild ways as needed.

Install temperature controls in the building to keep the environment at a constant 18°C

Then rip out the controls.

Install 0.5 um resolution linear encoders on all axes.

Install a 4080 Galil motion controller to run the system, and yes, close the loop at the controller.

Calibrate the system using a laser infromenter.

Now you have a chance at actually holding the the specification that you want.


What you are proposing is going to be very expensive. I have two machines in my shop that will hold <+/- 0.01mm consistently, but they also each have about $10,000 in controls upgrades and that's just the hardware cost. Both have a work envelope of about 32x12.5 inches. Your work envelope requirement adds an order of magnitude of difficulty in holding your specs.

Thank Jim, this is about what i was looking for. I'm more use to Fanuc hardware then Fadal, but they can't be that different. I'll give Galil a try, never used them but heard the name many time over in this forum.

is Galil the only motion control that does high accuracy at this level ? just curious.

thanks everyone much appreciate the help

[Jim Dawson]

Fanuc is fine. I have Fanuc AC servos on my lathe, and am perfectly satisfied with them so far. The old (1989) OT controller leaves something to be desired. I'll upgrade it one of these days.

Galil is the least cost and easiest to learn to program of the industrial motion controllers. I have been using them for about 20 years. There are several others; Delta Tau, Siemens, Allen Bradley, Rexroth, Mitsubishi, and several others. Also no proprietary programming software to buy, Notepad or any text editor will do. Their software is free also.

Since I didn't scare you off with what this project involves, I'll be happy to offer any advice requested. I have have built 3 crazy accurate machines, one tested at +/- 0 microns on one part we had checked on a high end CMM. The jury is still out on the 4th machine.