Hi Don,
Mach does monitor the index while in G95 but it isn’t all that dependable and can only cope with a fairly small change in speed. When it starts a G95 move it first monitors the spindle speed and takes an average over a number of counts. It then works out the feed rate and starts moving. Once it is moving it monitors the spindle speed and adjusts a feed rate override to compensate for any changes.
When used for turning I never got reliable threads even with a machine that had a very stable spindle. I have never tried it for milling. If you have a compression type tap holder it should be close enough. I wouldn’t trust it for rigid tapping. I know of one manufacurer that runs a servo motor for the spindle. When you switch to tapping mode their breakout board connects the spindle to the A axis step/direction outputs then does tapping as coordinated Z-A moves. This works very well for rigid tapping.
Les
On 23/06/2014 03:15, Don@Campbell-Gemstones.com (Don@Campbell-Gemstones.com) [sheetcam] wrote:
Brian, I read a lot of weird stuff today about G95 and Mach3. All the way from best thing since sliced bread to worst idea yet.  One thing popped out that caught my attention. It was a comment that once the move had started, it no longer monitored the index, but fed at the speed that was detected when the move started. If I’m remembering that post correctly, it states it is the same for the mill and turn. That would say that if your spindle got sluggish going into a tap or thread cycle, it may well overfeed as the feed was set as soon as the z move started, even though the tap or tool wasn’t in the work yet.
This has been an interesting problem.Â
I was already to test it on some aluminum when I realized I hadn’t made a lock for the reverse arm yet. I’ll probably get that finished tomorrow and the try to tap some holes.
Don
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Posted by: Les Newell <les.newell@fastmail.co.uk>
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