Machsupport Forum

Mach Discussion => General Mach Discussion => Topic started by: N4NV on January 31, 2009, 08:14:56 PM

Title: MachTurn and tapping
Post by: N4NV on January 31, 2009, 08:14:56 PM

Now that I have my CHNC lathe working again I am excited about trying some new things.  I just got a Hardinge TT tap holder.  I think some call it a floating tap holder.  If the spindle is turning faster than the pitch of the tap, the tap pulls out of the holder and start rotating freely.  The tap can pull out about 3/8".  I am wondering if Mach can keep track of the spindle and z axis like single point tapping.  The problem I see arising is when the spindle changes direction, it may turn more than the pitch of the tap, pulling it beyond the 3/8" of travel, and depending on the time it takes to change direction, how can I know when to start the z axis move to back out the tap?

Thanks

Vince

Title: Re: MachTurn and tapping
Post by: Hood on February 01, 2009, 02:56:43 PM

All trial and error I think, hopefully not to much of the error part ;)
 In the future it is hoped the SmoothStepper will be able to sync an axis with the spindle but I think an encoder will be needed for that rather than just an Index pulse. How far iin the future I dont know as I dont think it will be a two minute job to code for that.
Hood

Title: Re: MachTurn and tapping
Post by: Graham Waterworth on February 01, 2009, 07:02:54 PM

Lathe tapping is done with a G32 that way it has pitch control and the floating unit is just to take up minor error in stop starts.

e.g.

G20 (METRIC)
(NORMAL SET UP LINES)

N1 T0101 M8(TAP M6*1 THREAD)
G00 X0 Z5. G97 S100 M3
G32 Z-15. F1.(MAY NEED AN M5 HERE)
Z5. M4
G00 X120. Z120 T0100
M1

Graham

Title: Re: MachTurn and tapping
Post by: N4NV on February 01, 2009, 07:34:44 PM

Quote from: Graham Waterworth on February 01, 2009, 07:02:54 PM

Lathe tapping is done with a G32 that way it has pitch control and the floating unit is just to take up minor error in stop starts.
e.g.
G20 (METRIC)
(NORMAL SET UP LINES)
N1 T0101 M8(TAP M6*1 THREAD)
G00 X0 Z5. G97 S100 M3
G32 Z-15. F1.(MAY NEED AN M5 HERE)
Z5. M4
G00 X120. Z120 T0100
M1
Graham

Ok, I looked up G32.  So if I understand it correctly, the floating unit will take up the distance from when the Z motions stops and the spindle stops as long as the spindle does not rotate more turns than the tap pitch in 3/8" (in my case)?  I can go straight from a M3 to M4 with my VFD.  I will have to give it a try.  With finer thread taps this should not be a problem. 

Thanks

Vince

Title: Re: MachTurn and tapping
Post by: N4NV on February 01, 2009, 07:45:34 PM

I just checked my lathe and any speed under 500 rpm my VFD can reverse direction in under 1 revolution so I guess I was getting worried about nothing.  Thanks again.

Vince