Need Help!- RF45 mill/drill clone 4axis - help in cutting through mind boggling options

[nick mulder]

Hello all,

I own a ZX45 mill/drill (chinese clone of the RF45) - I also have a 6" rotary table for it ...

My plan is to convert it to CNC then build things with it that will in turn themselves use the same servos to operate - robots/gadgets of sorts, running my own/other control systems (i.e. not CNC/gcode)...

Problem is there seems to be a mind boggling amount of consideration involved

Things I have tentatively decided upon:

• 4 axes (Although having a rotary table may make a 4th axis redundant in many cases, I see the need for 4 axes in my other projects)

• Servos instead of steppers (my projects may require both closed loop and the extra power that I've learned servos lend themselves to)

• EMC2 (simply as I want to get into linux)

Some quick questions off the top of my head:

• are the ebay/chinese CNC kits any good ?

• is my ZX45 ok out of the box or will it need ballscrews and/or other mods?

• what are the hidden costs that I don't know about yet ?

• I live in 240/50Hz land - any consideration there ?

I guess in a more general sense I'm asking is is there a kind of checklist for effectively converting a CNC mill/drill like the ZX45 ?

thanks in advance for any info...

[Valen]

We converted ours,
we used ballscrews from ebay.

http://wiki.linuxcnc.org/cgi-bin/emc...akeAndRussells
400W direct drive motors, we used linear scales, but normal rotary scales are probably the best bet.

Needed some minor surgery with an angle grinder to fit ballnuts in some places.

If your interested we might think about doing some kind of kit, shipping "over the ditch" isn't too bad.

[nick mulder]

Cool - its good to see one going

thanks for that ...

Direct drive huh - interesting - the head is really 100Kg ? Wow ... Are you running off the crank at the rear column or somehow accessing the rack/shaft (?) that the normal Z wheel would run ?

The rear crank certainly feels like its lifting 100Kg ! (friction mostly)

Linear scales ? are they like linear encoders ? So you get the info from the piece itself, after the backlash - is that the idea ? You're kinda moving the problem from the piece to the motor system ?

Belleville washers - like spring washers, but constant force around the diameter ? So you do have ballscrews, just not expensive ones, or ?

If you have any links to the ballscrew suppliers that'd be interesting as would a drawing of the ballnuts and washers ...

Thanks again ! - very interesting

[Valen]

we replaced the z axis screw with a ballscrew, we also replaced the mounting for the nut as the whole thing is held on with one floppy bolt.

the linear encoders we use are .001mm resolution
http://en.wikipedia.org/wiki/Linear_encoder
the idea is to measure the movement of the actual part

however any backlash in the system means the motor moves building up speed and the control loop doesn't know about it, so it overshoots.

hence the double ballnut + spring system.

yes we are using inexpensive ballscrews and the accurate scales to compensate.

we are going to add encoders to the motors because with stick/slip we are seeing effects like backlash that are causing issues paticularly with the Z axis tuning.

we got them of ebay linearmotionbearings2008 is the seller

[nick mulder]

hmmm - off topic maybe but so if you had both linear encoders on the bed/workpiece and rotary encoders on the drive you then have all the info you need for the system to acount for backlash... Slow slow start until the linear encoder kicks in a count or so, then away you go ?

But I guess the backlash will be nearish the same every time so its prob just a parameter that the system is programmed with (?) 'blind' so to speak, but armed with the foreknowedge of previous operators experience/measurement ??

Talking out of my bum perhaps I'm yet to use a system.

Do you have any photos of the ballscrews and how they were installed ? What sizes did you end up with ? Also the motors you have, do you have access to a spec sheet or model/part # ?

Thanks much mate so far !