125 tcl conversion newbie

[30t000]

Hello everyone ,
I have wanted a small cnc lathe of my own for some years now . I use several at work and want to get my son in to this quite rewarding topic . I bought a 125 TCL last year but unfortunately it did not have the BBC to run it . I gave it to a friend of mine who has made his own breakout board for it and has got the lathe running in a very basic manner for me to setup as is needed .

My first question is about setting up the units for the X and Z axis . Apart from the board that has been added , the machine is bog standard . I think the leadscrew is 8mm dia with 3mm pitch . The pulley on the leadscrew is 20 teeth and 16 teeth on the motor pulley . So if I do the sums this comes to 0.4166 . I am assuming the motors are 200 step but I do not what the drivers are set up for . From here I get a bit lost . Can anyone help me with the next couple of steps please ?

Thank you for looking .

[Hood]

The way it works is you need to calculate the steps needed to move 1 unit ( in your case 1mm I presume?)
 So 200 steps to make the motor move one revolution
 20/16 = 1.25 turns of the motor to make the leadscrew move one revolution
 1/3 turns of leadscrew to move 1mm

so (200 x 1.25)/3 = 83.33333333333......... steps per mm.

If your drives have microstepping then you need to take that into account, for example if the microstepping is 8 then multiply that number by 8, if its 10 then multiply by 10.

If you set the steps per unit as 83.33333333333333333 and command a 10mm move and it moves 10mm then all is good, if it moves 5mm then your drives are half stepping so you need to double your steps per unit, if it moves 1mm then your drives have 10 microsteps so multiply the steps per unit by 10 etc etc.

3mm pitch seems a bit unusual, usually 5mm would be the norm but I have had ballscrews with 6mm pitch so it may well be 3mm.



Hood

[30t000]

Ruddy hell !!!! That was quick . Thank you very much for that , I will try it tomorrow when I get home from work . I will let you know how I got on . Triffick .

[30t000]

Well there you go .

Thanks for the input Hood . I tried the numbers you suggested but unfortunately they were not right for some reason . Probably on inspection at some point it will be the leadscrews I expect . I have not managed to get to them so that I can definitively say what they are . They were measured approximately and I thought that was good enough . Never mind .

The original settings were set to :- x 200,2500.2,500 1,and a 0 . Z was set to 200,1600,175,1 and a 0 .

Now the x steps is 200.133  and the Z is 199.9879 . These were derived by moving the axis 5mm , 10mm and 15mm at a time and reading off the measurement on the DTI . I then multiplied the steps by the amount of intended travel , and then divided the result by the actual distance travelled . This was done quite a few times until I got consistent results . I have a small amount of backlash in the system , but that out was taken prior to the measured move .

The only problem I have with the Z axis drive now is that at 50mm a minute feed , the motor seems to miss an awful lot of steps . Any other feedrate and I get damn good consistency . Any thoughts on this would be gratefully received .

I now need to make a toolplate for my TCL125 so that I can get to mount some tools and get cutting . HOORAH .



                                                   

[Hood]

Try increasing the Pulse width to 5 and see if that helps.
Hood

[30t000]

OK HOOD will do . I have not got a clue as far as these things go , soooooooooo what will increasing the pulse width do ? (in idiot terms if that's ok) .

[Hood]

It just makes the pulse wider which some drives require, especially older technology of which I think your drives will be.
Hood

[30t000]

I changed the pulse width without to much of a result I'm afraid .

Also on another subject , i think I have some backlash in my Z axis . I have put in the relevant amount and tried different % to get the backlash taken up before each move but without success . All that happens is the stepper starts to move , then slows and then catches up again . Any ideas ?

[Hood]

Never used the backlash comp but I think the normal is to have the speed  at 50% and the shuttle at 0.05

Hood