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Author Topic: CNC Lathe conversion with threading  (Read 4444 times)

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CNC Lathe conversion with threading
« on: April 23, 2016, 01:08:11 PM »
Hi hello everyone,
I have decided to convert a small Chinese bench top lathe to cnc 210 mm Swing by 400 mm cts, brush less DC motor. Could anyone help me decide on what Bob i need and any other control card info so the lathe will produce what i want.
My big worry is screw cutting, looking at the forum it seems that it is a bit hit and miss with results if you are new to it.

Help required to decide on items below.
What control boards to use, index pulse problems, which version of mach3 Turn to use.
Maybe you can see why i am looking for help before i start rather than diving straight in.

Required Functions:
2 axis , X and Z
Spindle control, start/stop/ speed control.
Threading Control.
USB pc connection.

My Mach3 experience, i have done a basic 3 axis mill and a router, both working fine. I used the AKZ250 (Leafboy77) Board for these machines but i have been told that this board will not support index pulse for threading.
So i need help from members please so can get this project up and running without to much pain.

I look forward to any info that will point me in the right right direction,
Thanks a bunch.

Cheryl

Offline RICH

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Re: CNC Lathe conversion with threading
« Reply #1 on: April 23, 2016, 02:02:51 PM »
Cheryl,

Have a look at the write up called "Threading On The Lathe- MACH3 Turn".
Don't know if it's still included in a MAch3 software download but you will find the latest in Memeber's Doc's. It cover's a lot about threading.

I am currently using V.062 along with a PP and all seems to work well so far,BUT,
must use at least a version greater than 3.043.33 and probably 3.042.38 would be  better.

I use a Hall's Affect sensor, but an index wheel will work fine for the index for PP.

Note if your lathe has a "wimpy" motor then your threading may be limited in size
even when using some of the other cutting methods. The ability to do good threading will only
be as good as your total lathe "system" which also includes physical setup. Your pc should provide a good pulse, not much variation from Kernal speed ( the closer and more consistant the better ) as actual DRO rpm should not vary by much...say 1-2 rpm. The threading cycle provides for motor slowdown, but frankly, it's not the way to go.

If you don't use a PP then an external motion controller is need that supports threading.
Not up and the latest greatest so research before you buy. Post back for suggested boards.

Now since your just starting your project, strongly suggest, that the heart of your lathe,
namely the axis screws should not be junk and do it so there is no backlash.

Threading is not hit or miss if you do it right the first time and know before you go!

Seems someone has told me that before, :D
And I never listened ;)
Slow learners we Lithvac's  ::)


RICH
   
Re: CNC Lathe conversion with threading
« Reply #2 on: April 24, 2016, 11:27:26 AM »
Thanks for your reply.
Just printed off the Threading on a lathe doc. read later today.
Excuse my ignorance what is PP?

I have done most of the mechanical work ball screws installed.
Limit/home switches installed

Starting to build the controller enclosure so this is where it gets interesting.
I was thinking of using cnc4pc index pulse card C3 to get the pulse with a slotted disc.
How many slots, a single or multiple.

Z axis 16 mm x 5 mm ball screw with 2 x thrust bearings
X axis 12 mm x 4 mm ball screw with 2 x thrust bearings
Cannot detect any backlash.
Motor is 600 watt brush less Dc 0-300 Vdc

What Breakout board could you advise, i would like to use USB to keep it as my Bench Mill and Router.

In Mach3, should the Plugin Turndiags-Turn-Diags-1.00.1 be switched on?

Thanks for your advice and help.
Best wishes,
Cheryl

Offline RICH

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Re: CNC Lathe conversion with threading
« Reply #3 on: April 24, 2016, 07:05:49 PM »
Cheryl,

PP is  Parallel Port.

You only use one slot. Can make a disc from a CD disc...cut slot...paint it black.

Not up on the latest greatest breakout boards. I have no need for one here.
Others will chime in for sure and make suggestions.

No, DO NOT use any turn diagnostics plugs in's as they were used for testing a long time ago.

RICH

Offline Hood

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Re: CNC Lathe conversion with threading
« Reply #4 on: April 26, 2016, 03:14:04 AM »
The Ethernet SmoothStepper would likely be my choice for a small lathe.
Hood
Re: CNC Lathe conversion with threading
« Reply #5 on: May 03, 2016, 04:06:10 AM »
Thank you all for your assistance.
If i use a Ethernet smooth stepper,
 
Firstly, what would i use to generate the index pulse, my thought was to use the C3 card from CPC4PC.

Second my lathe has an on board pot which i assume would need to be replaced by one controlled by other means all the add on cards that i have seen output 0-10 Vdc the pot on my lathe uses 0-5  Vdc.

How can i overcome these issues?

Hope i can get some answers.

Best wishes,
Cheryl

Offline Hood

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Re: CNC Lathe conversion with threading
« Reply #6 on: May 03, 2016, 07:28:14 AM »
You can use anything for the Index that will cause 1 pulse per rev.
I used to use a slotted disc with an opto switch, nice and cheap and worked well, only the disc, opto and a resistor required, under £10.

If you are happy with manual control of the spindle there is no need to change, or you could keep using the pot for speed and if wished you could have relays switch Fwd/Rev/Off.

Hood
Re: CNC Lathe conversion with threading
« Reply #7 on: May 04, 2016, 04:28:28 AM »
Hi Hood,

Thanks for the reply.
For your info i am doing a Tech course based on cnc machine control and my husband and i thought the best way to learn is for me to build some and use them. I have a bench top mill and router which i converted, so i have gained some experience.

For the lathe i am converting i want screw cutting.

I was going to use cnc4pc, C3 board for index pulse, i have one left over from when i converted my bench top mill. Would this be suitable with ETSS.

I want to use full spindle control i have a dual relay board.

I think my biggest problem is what i cant get my head around is how to control spindle speed, the control board that comes within the lathe works on 0-5 Vdc for the Pot.

How can i use the 5 Vdc reference voltage with ETSS to give speed control or will i need another board from somewhere to do this?

Best wishes,
Cheryl

Offline Hood

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Re: CNC Lathe conversion with threading
« Reply #8 on: May 04, 2016, 04:55:18 AM »
For your information, srewcutting will work fine with manual spindle control, all it requires is an Index pulse so that Mach can see what the spindle RPM is and the pulse also acts as a trigger for starting the threading pass at the correct point.

Yes the C3 should work fine if you already have one.

Regarding speed control then I am not certain what is available as I use servos on my machines.
  I think possibly the PMDX 107 works with 0-5v but I also seem to recall it requires you use the associated breakout board, probably the PMDX 126 which the ESS will fit directly onto. You will find info at www.pmdx.com

I am not sure what is available from CNC4PC but they may also have spindle control boards that are capable of 0-5v, you would need to have a look at their site of email Arturo to see. I think they also have breakout boards which are designed for the ESS to fit onto.

Peter Homann also does spindle control boards but again unsure of what is available, check out www.homanndesigns.com

Hood
Re: CNC Lathe conversion with threading
« Reply #9 on: May 08, 2016, 08:49:03 PM »
Cnc4pc have one. I can look up the number later. I have one on my lathe that has a DC spindle motor. It used a 0-5v signal instead of the usual 0-10v. Work good.
Don