Lathe conversion from stock to CNC

More
20 Jul 2012 07:13 #22234 by Soundreflections
I have read somewhere that one can get higher accuracy for threading with dual encoders and, of cource a 1 PPR homing pulse. I would run one disc, with 2 sensors, perhaps LEDs to make sure they are out of phase.
I have to admit the cost is looking a bit daunting! If I read the specs correctly, the Pico can drive 4 motors (with amps), take 4 encoders for the steppers 16 inputs and 8 outputs? Can I use some digital inputs for the spindle encoder, or is it better to use 2 axis encoder inputs?
I am happy to have various cards, or one card, depending on flexibility and cost.
Regards
Peet

Please Log in or Create an account to join the conversation.

More
20 Jul 2012 11:01 #22238 by BigJohnT
Yes, a normal encoder has two signals that are out of phase with each other and an index pulse once per revolution. A differential encoder is what is usually used and they have 6 signal lines A, A~, B, B~, Z, Z~ with Z being the index line. Thread quality will depend on the whole package not just the encoder.

John

Please Log in or Create an account to join the conversation.

More
20 Jul 2012 12:43 #22240 by andypugh
Soundreflections wrote:

I have read somewhere that one can get higher accuracy for threading with dual encoders and, of cource a 1 PPR homing pulse. I would run one disc, with 2 sensors, perhaps LEDs to make sure they are out of phase.

In that case then you just need one set of encoder inputs. All LinuxCNC "encoder" modules have three inputs, Phase A, Phase B and the Index.
If your disc has about 100 slots then you can use a parallel port for all IO.
if you go up to 1000 slots then you need a dedicated IO board such as the Pico or Mesa. Now that we know you are only talking about one encoder, the 7i76 looks like a good choice again.

My lathe has 100 slots, threading works nicely.

if you want to get started for minimal outlay one of the very cheap eBay kits might suit: (comes with a spare motor)
www.ebay.co.uk/itm/3-Axis-TB6560-Driver-...NC-Kit-/251095203360
Or, slightly higher quality and more modular and only 2 axis
www.ebay.co.uk/itm/Cnc-2-Axis-Lathe-Cont...3-EMC2-/320946904472
That second set is a lot like the drivers I am using, except better and higher current. I don't think you would go far wrong with that.

Please Log in or Create an account to join the conversation.

More
20 Jul 2012 18:07 #22243 by Soundreflections
Hi,
Thanks for the replies. I have now got a pulley for my motor and I have today bought a belt that actually fits the new setup. I need to gte down to programming my VFD to actually give me some torque where I need it, as I currently not start my lathe in its highest gearing.

Andy, you are tempting me sorely with your findings. I am especially looking at the second finding you posted, as it has stronger motors than the first and is still cheaper than what I think I can buy the various parts for. I cannot tell whether it includes a spindle encoder interface or not, I certainly do not think it would include motor encoder interfaces, but I am sure I can add those at a later stage if I want to maintain manual with DRO.
I take it you are quite sure I will get this setup running on Linux CNC?

Thanks and regards
Peet

Please Log in or Create an account to join the conversation.

More
21 Jul 2012 16:18 #22273 by Soundreflections
I have now spent the day cleaning my entire moving assembly (temporarily gone blank for the term), every gear, thread... Now I finally have a very smooth working lathe, I cleaned the grease I had before put on the ways off, using only machine oil as a lubricant. I realise I have used grease on all the other slides, which I realise is probably not the best, which is why I was advised against it (belatedly) at projectsinmetal, where I first started posting about my lathe.
Now of course I cannot think of something to make!
Regards
Peet

Please Log in or Create an account to join the conversation.

More
21 Jul 2012 17:39 #22284 by BigJohnT
Way Oil is the proper lubricant for machine ways. I use Mobil Vactra Oil #2 Way Oil for all my machine ways.

You could make me some oil cups for my Samson lathe LOL.

John

Please Log in or Create an account to join the conversation.

More
24 Jul 2012 10:18 #22379 by Soundreflections
Thanks John, I will see if I can get way oil. Sounds like I need to ask your advise on all the lubricants to use.

I would be interested in the oil cups, something practical to do! (LOL) Would then have helped if I was on CNC.

Ended up making this, though I still need to finish the ends.

Cheers for now.
Peet
Attachments:

Please Log in or Create an account to join the conversation.

More
27 Jul 2012 06:45 #22506 by Soundreflections
I may have found a cheaper source of motors, waiting for their response. In the mean time I am considering wiring limit and home switches, so a few questions / thoughts on that.
Firstly having a home and origin points are confusing me a bit, is the home switch the home position and the origin a virtual point where the tool will start / end?
Would I be heading in the right direction if I am thinking of a home / origin where the Z axis would be backed out (Max soft + limit), the X axis at about the point where the tool holder about aligns with the jaws? My thinking is that would put the tool closest to a probable starting point, clearing max diameter for easier work on chuck / with tailstock.
Can one have a switch on the tailstock, as the carriage has limited movement if the tailstock is close, especially if the work piece is quite short?
I am thinking of fitting switches / sensors so long, maybe get the PC mounted... whilst I prep to get motors and drives.
I may try to source a diagram of a breakout one can build, maybe a PIC interface. My one PIC demo board has a quite capable PIC, with USB interface (I think)
Thanks
Peet

Please Log in or Create an account to join the conversation.

More
27 Jul 2012 07:29 #22507 by Soundreflections
Any comments on motors? I am thinking of getting a www.interinar.com/public_docs/23KM-K723-23V.pdf for the X axis and www.interinar.com/public_docs/23KM-K102-P1V.pdf for Z, though I have not had to deal with motor / load / voltages before, so am a bit in the dark here. I suppose if the motor is too weak one gears it down? Just have a slower machine?

Also can one take something like a "gaming" joystick and assign the various buttons, hat switch... to various functions, or is a dedicated, switch based input better?

Thanks
Peet

Please Log in or Create an account to join the conversation.

More
27 Jul 2012 10:42 #22510 by andypugh
Soundreflections wrote:

Any comments on motors? I am thinking of getting a www.interinar.com/public_docs/23KM-K723-23V.pdf for the X axis and www.interinar.com/public_docs/23KM-K102-P1V.pdf for Z, though I have not had to deal with motor / load / voltages before, so am a bit in the dark here. I suppose if the motor is too weak one gears it down? Just have a slower machine?

I think you might be confusing X and Z. Z is generally the axis parallel to the spindle, so on a lathe the Z is the longitudinal feed and X is the cross-slide.
On my lathe the Z motor is rated 3.5Nm and the X is 2.5Nm. I am not actually sure that those ratings were accurate, though.

Also can one take something like a "gaming" joystick and assign the various buttons, hat switch... to various functions

Gamepads work fine, I am happy with mine.
wiki.linuxcnc.org/cgi-bin/wiki.pl?Simple_Remote_Pendant

Please Log in or Create an account to join the conversation.

Moderators: piasdom
Time to create page: 0.183 seconds
Powered by Kunena Forum