Motors Minimum RPM ( wrt rigid tapping )

Just curious, I also custom wrote Rigid Tapping for my control, Camsoft. At the heart of this control is a Galil card and they have an electronic gearing option. The idea was to slave the Z travel movement to the spindle encoder. Once running correctly it has never broken a tap, MAN is it fast.

What is your approach?
 
Karl_T said:
Just curious, I also custom wrote Rigid Tapping for my control, Camsoft. At the heart of this control is a Galil card and they have an electronic gearing option. The idea was to slave the Z travel movement to the spindle encoder. Once running correctly it has never broken a tap, MAN is it fast.

What is your approach?
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My control board is the Centroid Acorn. At least using their “intercom” conversational code generator it should be able to take advantage of the spindle encoder to slave the Z to the spindle speed. However my goal is to use Fusion 360 to create my Cam code. Before my first attempt last night I wasn’t aware that Fusion *might* not create the appropriate code “automagically” to tell Centroids control to sync the z travel to the spindle. I made one change to Centroids setup parameters but i’m not yet sure if it was effective. ( I was using an oversized bit , possibly too oversized because the threads were non existent after the tapping process ) just by eye , I have some doubt however that true syncing is occurring, yet. )) It occurred to me after testing last night I could try looking at the g code created by Centroids intercom conversational to compare it to the g-code created by Fusion to see if I can dechiper if the Slave command is being sent at all, or if it is using the wrong terms. I’ve got no experience to work from so if you have any ideas on where to look i’d appreciate it. I am posting to the centroid acorn forum so there might be some more info coming shortly to help understand this better. Also, i’m not sure if I need to further adjust my VFD so less delays need to occur as there might be some boundaries that need to be met with regard to slaving in a open loop scenario ( open loop being stepper motors for the x,y and z ) . I have no idea, yet what decell and accel time *2* is. It got late so I stopped working on it. More progress today , I hope.

Edit / Note : (I ended up not using the compression /tension head due to not having the correct ER collet size for the tap. Instead I just chucked the tap up for true rigid tapping. No broken taps yet, due to the oversized holes ;-)

Thanks for asking !

Jake
 
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The correct Post Processor should take care of all that, are Centroid not working on a Post Processor for Fusion 360?
Conversational programming is of little use for complex 3D parts so you'd think Centroid would like their customers to have access to some competent CAD/CAM, the product remains an "interesting toy" without.
 
magicniner said:
The correct Post Processor should take care of all that, are Centroid not working on a Post Processor for Fusion 360?
Conversational programming is of little use for complex 3D parts so you'd think Centroid would like their customers to have access to some competent CAD/CAM, the product remains an "interesting toy" without.
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Fusion360 has a post process output labeled Centroid which is what I used. However I watched a video last night of a guy explaining rigid tapping that appeared to know his stuff his own Fanuc vertical mill wouldn’t work initially to sync the Z to the spindle , so he had to make custom changes to his g code to enable slaving. From the author of this video, it appears this might be a common issue, large or small.
The Acorn has certainly done a great job compared to my previous control solutions. So we’ll see, obviously i’m Not experienced enough to say what’s at fault yet, or if even it’s not working yet. Until I use the correct bit for the tap i’m not going to start judging what’s going on. Sadly I need a 2.5mm bit for a 3mm tap. Something that I don’t have. Lol and nothing I have comes close. So it’s either under or over sized. I chose over sized, to avoid the fate of too many broken taps while I sort this out.

Jake
 
That's a perfect description of a Post Processor that isn't fully compatible with the controller.
Sadly that's not at all unusual, custom Post Processors typically cost a lot of money to have written, insignificant when set beside a new Haas VMC and CAD/CAM suite but for a hardware company to aim a product at the hobby market and not provide a good post processor for at least one common budget CAM system is, at least, very disappointing.
 
magicniner said:
That's a perfect description of a Post Processor that isn't fully compatible with the controller.
Sadly that's not at all unusual, custom Post Processors typically cost a lot of money to have written, insignificant when set beside a new Haas VMC and CAD/CAM suite but for a hardware company to aim a product at the hobby market and not provide a good post processor for at least one common budget CAM system is, at least, very disappointing.
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It’s early yet to say one way or the other. I’ll post back here if indeed Fusion360 is creating the appropriate code for the Acorn to do rigid tapping ( outside it’s own intercon ). It’s the first time anyone has posted such an issue so I kind of doubt it’s more than me just needing to set it up properly. Thanks for the heads up that this could be something that isn’t addressed properly.

Jake
 
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magicniner said:
Floating tap holder with clutch, not a cheap option though :D
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You do not need a clutch per se, given a functioning Z axis it will tap at the correct lead yet will not know the radial spindle position without the 4th axis control, a floating tap holder allows tapping without a spindle control by taking the rotational spindle position out of the program.

Picture this, 1/4"-20 TPI tap into the part using a .050" per revolution Z feedrate then the spindle stops at the bottom of the hole, it now reverses rotation direction 120 Degrees out of phase from where it stopped because there is no spindle position control, this will leave a broken tap in the part.. A floating holder will allow for any spindle position error.
 
The motor spec sheet says the speed range is 1000-1. That would of course be with a compatible vector VFD, but it suggests the motor is optimized for low speed operation. Lets suppose the the max speed is 240 hz = 7200 rpm. Then 1/000 of that is 7.2 rpm. It would be worthwhile getting full specs on the motor and maybe talking to a rep. What's the lowest speed for "constant torque, etc. Does the motor have winding thermostats or other overheat warning provisions. Possibly you might reconsider your belt ratios.
 
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