Project: Converting a milling machine to a CNC machine.

[Spawn]

I can already imagine people thinking “what has this to do with Electronics”. 
Maybe not so much, I could go on a CNC forum and post it there but lately a lot people are joining us here on EEVBlog forums with different background than only Electronics and also there is some Electronics involved with CNC machines like controllers and such.

I did work with milling machines but never with a CNC machine, so this is a fun project for me and I also will learn a lot if I build it myself, any advice and help form CNC gurus we got on the forum will be greatly appreciated.

If moderators or Dave think this doesn’t fit on this forum, please delete or lock the topic, no harm done

That being said, I mention earlier in some topics I got a Proxxon MF70 milling machine and wanted to convert to a CNC milling machine. It is a fairly small machine and fits nicely on my Electronics bench and it has its limits like not having big work area but still good enough for small things.

I was building a half wood, half Plexiglas box for my other equipment to keep things clean on my bench if I had to drill or saw something, but the milling machine fits there nicely too, probably I will add a top part to make it enclosure box but right now the shelf above is in the way because the milling machine is just little too high but I will find something for that :


Before we go further, I am trying to keep the costs low as possible so getting cheapest possible parts to make it work. I already have a Windows XP machine ready for this with Mach3 CNC on it.

I got the stepper motor mounts here, these are made for Nema 23 stepper motors, the reason I got this one is: I can’t make one myself because I don’t have access to a metal working shop as years ago. This one was cheap but also didn’t have rounded edges like most sets out there and that makes for me easy to mount the limit switches.  Also there is no need to change anything on my milling machine, even spindles will stay as they are, I only need to remove the little black handle on them.


I already ordered a 3 axis CNC controller with a Toshiba TB6560AHQ chip, this is very common controller and it supports stepper motors till 3A each axis:


I also ordered a 24V 15A switching power supply:


I am not sure if its worth mention but I will use switches below for limit switches, I will get two emergency stop buttons later on, one for the controller board to stop the program if things go wrong without cutting off its power and one for real emergency to cut off the power totally on the board and the PSU:


Here is the tricky part, at least for me. I didn’t figure out what stepper motor to get, it has to be a Nema23 but I am not sure what torque and size. The other thing I want it a double shafted stepper motor because I want to be able use the milling machine without CNC part for small projects but maybe someone can make this clear; does Mach3 lose any setting if I turn on the stepper motors manually?

After a lot reading around the motor below should be perfect fit power wise and it has double shaft. It is fairly heavy with 0.7kg on each stepper motor but the smaller ones don’t have the torque I need. It is a Nema23 57BYGH56-401B

Here some specs and photo of the motor:




So any of the CNC guru’s out there have some tips for me? Am I doing good so far or do I have to change something in my further plans?

[Radio Tech]

I am not a CNC guru bit have ran them at work when we made our own parts there.  From small milling CNC to the mighty Maseru that held hundreds of bits. From what I can see if your post you are on the right track.

Not sure what your projects are going to be, wood, aluminum or circuit boards?
If light wood and circuit boards then your motors should be around 180oz-in or so. With heavy metals you may want to go up to 300oz-in.  Guessing this due to the size of your machine.

I have a bench top milling machine that I am thinking about converting into a CNC. Been researching for a year now but have not done anything to get started.

[arekm]

Playing (as beginner) with exactly the same proxxon mf70 right now.  It's crap but cheap crap :-)

I'm using 1.25Nm motors (57H56-30008B). These are enough for such delicate machine.

Replacing Y plates will give you additional ~4cm:
http://0xfred.wordpress.com/2012/04/17/extending-the-mf70s-y-axis/
(note, there are two mf70 versions, so different plates for each, see comments in above url)

I'm using vacuum cleaner when milling and no "box" around mf70.

linuxcnc for driving and cambam for doing projects.

switches with short arm will be more precise (so you could use the same switches not only as limit switches but also as home+offset switches)

[KJDS]

That's an interesting board. not that I have any need to control a mill but my load pull set up has a misfunctioning, and non-pc controlled box to control the three stepper motors in it, so I'll buy one and have a play.

[GeoffS]

All looks OK to me except for that controller.
The tb6560 based boards as sold on eBay have a bad reputation for performance and reliability. See cnczone.com for more details.

[Spawn]

Thanks for the information guys

Not sure what your projects are going to be, wood, aluminum or circuit boards?

Radio Tech, I am planning to cut out porous PVC for front face work and do some letter engraving on front panels and time to time maybe letter engraving on aluminum but won’t cut aluminum with it, I am not thinking to do PCB work on it but I might try it to see how it goes.

That's an interesting board. not that I have any need to control a mill but my load pull set up has a misfunctioning, and non-pc controlled box to control the three stepper motors in it, so I'll buy one and have a play.

KJDS, this was the cheapest one I could find for 3 axis:
http://www.ebay.com/itm/221194934966
Here some interesting add-ons like a manual controller and a display:
http://www.ebay.com/itm/330887465697
http://www.ebay.com/itm/251232883889

Playing (as beginner) with exactly the same proxxon mf70 right now.  It's crap but cheap crap :-)

I'm using 1.25Nm motors (57H56-30008B). These are enough for such delicate machine.

Replacing Y plates will give you additional ~4cm:
http://0xfred.wordpress.com/2012/04/17/extending-the-mf70s-y-axis/
(note, there are two mf70 versions, so different plates for each, see comments in above url)

I'm using vacuum cleaner when milling and no "box" around mf70.

Ey! Not bad things about Proxxon, it is not crap! LOL just kidding 
I am in love with Proxxon you can call me Proxxon fan guy. After posting this here I went out and get a “second hand” Proxxon DSH scroll saw and it was just never used! On the local auction site pictures it was covered under the dust so I was thinking it was used but even the extra parts to make it work was not attached and where in sealed bag, so I got a new scroll saw for bargain! See photo below and you will understand how crazy I am about Proxxon’s

My new addition the to the family is right on the picture:



Sorry about going little off topic there, but when it comes to Proxxon I get excited. I know some people don’t like this X and Y axis (KT70) but if you know your equipment you can eliminate the play in there.

Arekm, thanks for that link, there is a CNC kit manufacturer which makes extended axis for both X and Y. I might do something later on but right now I am focusing on this CNC to get it work.
About the dust, I forgot to mention about the vacuum cleaner part, there will be fixed hoses to move around in the box for different machines, so I can attach a vacuum cleaner to the enclosure box external.

All looks OK to me except for that controller.
The tb6560 based boards as sold on eBay have a bad reputation for performance and reliability. See cnczone.com for more details.

Thanks for the heads up GeoffS, indeed I read a lot things about these boards, like switches for current settings not functioning and some people fry them because of the wrong settings and such, I wanted to give a shot for this price if it fails I am planning to get separate controller boards for each stepper motor and a control board.

[Gall]

This TB6560 CNC board is absolute crap. It has SEVERE errors in its design.



1. Its input is NOT really optically isolated! Yes, it has optocouplers, but both sides of these optocouplers are powered FROM THE SAME SOURCE.

2. Some revisions of these boards have collector and emitter of one of the optocouplers swapped. A stupid routing mistake.

3. The 12V power regulator works nearly at max load and overheats.

4. The power regulator is wired in such a way that 5V power is supplied after output power. The datasheet says that this may damage the IC.

5. The board has extra transistors in an attempt to lower the output current when idle. In fact this only causes glitches.

6. The output is really not diode protected: each second diode is missing. (Just 2 diodes per winding instead of 4).

7. The relay is wired without any protective diode. The inductive spike often damages the controlling transistor.

Do not rely on this board. Better return it.

[Gall]

http://www.ebay.com/itm/251232883889

This display tries to count steps by polling the inputs by a MCS-51 microcontroller. In fact it often misses steps when running at full speed.

I disassembled the board for parts and bought a Gecko instead. But there are cheaper alternatives. Many single channel TB6560 boards are good enough for a small stepper.

[Spawn]

Thanks Gall, there is no way I can return it because shipment costs from here would cost almost same as the board. Hell I didn’t even received it yet since I ordered yesterday and it is shipped. We can talk about the board when I receive it, I will take some high res pictures.
The one I showed there is a 4 axis one, I ordered a 3 axis board. In my research I read couple things about these boards but not detailed information as you did above so I need to check the model I get, thanks again.

[Alana]

There are 3,4,5 axis board of the same design. Had 4 and 5 axis versions for Rubik's cube solver and they are totally crap.
Next time I'm doing something with steppers its home made H-bridge from scratch.

[KJDS]

So if that board is crap, can someone recommend a pc driveable board that will run three small steppers that is good quality?

[FJV]

Maybe begin bij taking a look at the calculations stepper motor manufacturers use in their catalogues.

For instance Minebea:
http://www.eminebea.com/en/engineering_info/rotary/steppingmotor/pm_steppingmotor/cat-5/006.shtml



You may also want to look at cutting tool manufacturers for data on forces during cutting

[Gall]

So if that board is crap, can someone recommend a pc driveable board that will run three small steppers that is good quality?

Gecko G540 is the one of superb quality but quite expensive. It runs up to 4 four-wire steppers of NEMA23 size or smaller.

[DavidDLC]

Do your own, based on Microchip app:



David.

[Spawn]

How about these here guys?
http://www.ebay.com/itm/400454173192

Same kind a crap or is it better?

[peterthenovice]

looks decent for 200 bucks on a stick.

[Spawn]

Wow…
I just read 100+ pages on different forums and there is so many mixed information about this TB6560 most don’t recommend and some like it. The thing is most are using this board for higher voltage and have problems and around 24V there is not much complains, but there is also some easy fixes for smoother runs:  http://www.homediystuff.com/fixing-a-chinese-made-cnc-stepper-motor-driver-board-tb6560-chips/

[GeoffS]

How about these here guys?
http://www.ebay.com/itm/400454173192

Same kind a crap or is it better?

The separate motor controllers have one advantage in that when one dies, you replace only it. No information about the reliability of that one yet.
The breakout board doesn't list  optocouplers.
I don't know what your budget is but take a look at Automation Technologies in the US. The stuff they sell is reliable and well supported. I bought a 3D printer from them and had no issues with the goods supplied or sorting out some minor problems.

[GeoffS]

So if that board is crap, can someone recommend a pc driveable board that will run three small steppers that is good quality?

Gecko G540 is the one of superb quality but quite expensive. It runs up to 4 four-wire steppers of NEMA23 size or smaller.

for the Gecko G540. When the controller for one axis in my CNC router died, I went to a G540 with a higher voltage supply (48V vs 24V).
It was well worth the money.

[Spawn]

GeoffS, I have been reading a lot again since last night and Gecko’s are nice indeed but I think not worth for this machine because only the board cost almost same as the milling machine and this machine has really small work area so work piece / budget ratio is too high with a Gecko.

Meanwhile found something else which people recommend for a decent price too, they got two kits and this is the higher end one:
http://www.hobbycnc.com/products/hobbycnc-pro-chopper-driver-board-kits/

Right now I want to wait till I get this crappy board I bought and see what I can do with it, meanwhile I keep researching. So far I got most complete information what to do with a TB6560 board and it was posted on CNCzone after 55 pages reading in a topic there was someone who put all information together:
http://www.cnczone.com/forums/general_electronics_discussion/110986-how_i_fixed_my_chinese_tb6560_controller-55.html#post1218808
This shouldn’t be a problem for an electronics hobbyist.

I hope, I don’t sound stubborn guys, I really appreciate the input I got, but I got stuck with this board even before it was here    so I have to do my best with it before giving it up already. If I didn't get the warnings from you I wouldn’t be prepared for this, so thanks for that.

I still didn’t order the steppers yet, the one I mention before was 4 wires but hobbycnc pro board needs 6 or more wires, so I have to take that in consideration too. I am still in doubt about the shaft too, double shafted or not…

[GeoffS]

GeoffS, I have been reading a lot again since last night and Gecko’s are nice indeed but I think not worth for this machine because only the board cost almost same as the milling machine and this machine has really small work area so work piece / budget ratio is too high with a Gecko.

I agree, keep with the supplied controller for as long as it does the job. Read what you can on cnczone.com about the problems users have had with it and the cause which may help prolong its life.

Meanwhile found something else which people recommend for a decent price too, they got two kits and this is the higher end one:
http://www.hobbycnc.com/products/hobbycnc-pro-chopper-driver-board-kits/
/quote]

The hobbycnc kit has quite a good reputation and is well supported. Pricing is pretty good too.

Right now I want to wait till I get this crappy board I bought and see what I can do with it, meanwhile I keep researching. So far I got most complete information what to do with a TB6560 board and it was posted on CNCzone after 55 pages reading in a topic there was someone who put all information together:
http://www.cnczone.com/forums/general_electronics_discussion/110986-how_i_fixed_my_chinese_tb6560_controller-55.html#post1218808
This shouldn’t be a problem for an electronics hobbyist.

I hope, I don’t sound stubborn guys, I really appreciate the input I got, but I got stuck with this board even before it was here    so I have to do my best with it before giving it up already. If I didn't get the warnings from you I wouldn’t be prepared for this, so thanks for that.

I still didn’t order the steppers yet, the one I mention before was 4 wires but hobbycnc pro board needs 6 or more wires, so I have to take that in consideration too. I am still in doubt about the shaft too, double shafted or not…

Hobbycnc drivers are designed for unipolar motors which excludes the 4 wire bipolar type. Bipolar motors are generally more powerful for the size.
I'd say go with the bipolar motors, single shaft - the double shaft really has no advantage in your case.

[robrenz]

I don't think any stepper controller is going to keep track of position when you de-energize the motor and turn it by hand. So you might think about having three handwheels/encoders to also feed the driver boards for manual/jog mode where you would still have position readout on all three axes. That way you can focus on single shaft motors. You also may consider a timing belt reduction from the motors to the leadscrews instead of direct drive. This will allow improved resolution and torque at the sacrifice of top speed and smaller motors. Yes this route may cost more.

[Gall]

Ok. Since you already bought the TB6560 board, here is the recipe how to fix it.

Completely remove extra transistors controlling the output idle current. Let TB6560 work on its own.

Add one extra protection diode to each output.

Install a protection diode

Completely remove all optocouplers and short them. Then connect your own external optical isolator. Alternatively cut the traces on the board and provide isolated power to the input.

Remove 7812. Replace it with a DC-DC switch-mode module.

Add a relay to control the power on sequence.

The TB6560 is not so bad on its own. It is just incorrectly wired on these blue boards.

[Spawn]

I'd say go with the bipolar motors, single shaft - the double shaft really has no advantage in your case.

Yes that’s probably best thing to do GeoffS, the information is mixed up about the strength of the steppers all over the internet, in terms of torque people using a lot different steppers from 0.5Nm till 2Nm. I want a stepper around 200oz-in which is 1.4Nm and the stepper will be little bigger than I want.

I don't think any stepper controller is going to keep track of position when you de-energize the motor and turn it by hand. So you might think about having three handwheels/encoders to also feed the driver boards for manual/jog mode where you would still have position readout on all three axes.

I have been reading around again robrenz and most users are happy with controlling through Mach3 with the computer keyboard. If you have a wireless keyboard like me it will be even  better to control while you look at your work piece, needs some practice I think but that would be enough, there are manual controllers for the board I got but after modifications I have to make these won’t be reliable.

Ok. Since you already bought the TB6560 board, here is the recipe how to fix it.
The TB6560 is not so bad on its own. It is just incorrectly wired on these blue boards.

Indeed Gall,  the TB6560 is a good chip but people who put it together on this board have tried to cut the costs and board came out with a lot bugs, this is playing for years and they did some tiny fixes on the board but not the necessary ones, they should make better revisions by now and people would love to pay twice the price if those fixes where made.

Here are the fixes and checks I am considering:

• Some boards have shorted pin 25 at all TB6560 and these need to be checked.
• Need to check all dipswitches, some have been found not working
• Adding ground to each TB6560 through the heat sink
• Adding a diode over the spindle relay coil
• Removing 10K resistors for current save future which is not working and giving extra pulses
• Each 1000pF cap at pin 7 needs to be replaced with 330pF
• Removing opto’s and bypass them, to make sure use same power line for the PC and the PSU
• Adding 74HCL14 with a cap and resistors to clean the dirty step signals.
• Adding a bigger heat sink with external powered fan, so don’t need to worry about the 12v regulator
• Extra relay to turn on/off the spindle at 240V

All above information is coming from people at CNCZone and some from me so kudo’s to them, I didn’t write down the details why these changes have to be done those are already explained there. Some of the fixes are not necessary, I need to do some crucial ones even before powering up the board, and some people are even using this board for 2 years without any problem with small fixes so I need to check how the steppers act after each fix/mod.

About the output protection diodes Gall, I am reading so much last two days and I am not kidding when I say my eyes are even hurt by staring at screen, but I never seen anyone having problems with that, yes people mention that but there is no damage till now so far I could see, there are couple TB6560’s blown but that was because of the wrongly soldered pins and sometimes current setting dipswitches where not working.

The costs are relatively small, I can understand some mechanical people won’t like it since soldering and electronics is not their thing but for us lot here these are just easy fixes that’s why I decided to give it a go instead of getting another board. Bigger heat sink won’t cost me much but will help a lot for long runs.

[Spawn]

I am really bad in guessing sizes with surface mount components, I don’t have the board yet but I want to order some parts before I get it.

Can anyone tell me what type SMD capacitor this is? Maybe it is hard to see, if that’s the case I will wait till I get the board.


I think a 0603 but I am not 100% sure.