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Author Topic: What Steps/ Units Settings for Z-axis (Quill) of CNC Retrofitted Radial Machine?  (Read 21073 times)

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Offline Hood

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If your native units are set to mm calculate your steps per mm, if you are in Imperial native then calculate your steps per to inch. It does not matter if your screw or rack is imperial and you are using metric native units or vice versa, all you do is convert.
 I have not read your zone thread yet and will go look now but what exactly is your problem? Is your Z not accurate with the calcs you have or is it you just dont see why it should be such a small number?
Hood

Offline khalid

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Hi Hood,
Thanks for helping me again;)... Both problems with the Z....a) 'Z' is not accurate b) The Motor runs very coarse... When I was calculating the Steps/Unit with The Dial Guage (10mm Range)..and I said the Z-axes Motor to go-down 7mm.. It goes down about 6.5mm with Jerks on the dial guage...

I have installed counterweight on the Quill and it is free to move with motor pully and i know i have no missed step..it moves like butter with 1200Oz-in Motors...

I want to run it fine and accurate.. I have tried many time to Move up and down but it goes up/down with sometime 0.5mm plus and sometime 0.6mm minus of actual moves...

I don't know whats wrong?

Offline RICH

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a) 'Z' is not accurate
Racks usually have a lot of backlash in them. I am refering to those on mills and drill presses. Counterwieght certainly helps remove some but still may not be linear / accurate over it's travel. You can probably find a "sweet spot" on it for some travel distance. On my mill there was a fine feed and that's where the stepper was attached for the Z. Some day will change it over to be ball screw driven. Using backlash compensation though works quite well.
I could be wrong, but, get  the steps per unit best you can and then see / map out the Z travel.

BTW, to get finer movement of the axis, you will need to increase the steps per unit. That best can be done via gearing and going to 10u steps instead of 1/2 stepping.
RICH

Offline khalid

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Hi RICH,
hanks for helping hands:)...I somewhere studied the higher microstep means loosing accuracy...However, I am seriously thinking of, to remove the pinion and externally drive the QUILL with Ball screw... The second option is to add worm-wheel  gear box upto 100:1 ratio!!!!..

As far as Backlash, I saw this machine was used two times after it purchase for a very short run...
Best Regards

Offline Hood

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Quite hard to tell from the pic but looks like a load of gearing in the head, presume for different feedrates, you may be able to alter the gearing to get it nearer 1:1 inside the head.

Hood

Offline khalid

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Hmm.. Excellent Hood:)... As far as I know, those gearings are for Automatic Feed and driven with Spindle Motor... If I enable it with Lever, i will no more use the Manual Feed.. It Means my Stepper will not work...However, nice idea and I didn't think on that earlier.. I will look into it and see how can i bring it to nearer to 1:1.. This will be great if i succeed...

Offline stirling

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Just to cover a couple of points FYI

to find the Pinion-Rack ratio or travel:
200 x 2 x 3 x Y= 12.344
Y=0.010286666666666666666666666666667  What does this means???
That is the pinion revs per mm. The inverse (97.213220998055735580038885294699) is mm per pinion rev - so your friend wasn't far out with his 4 inches.

...I somewhere studied the higher microstep means loosing accuracy...
Kind of but not quite. usteps though obviously finer resolution than full steps are not as accurate as full steps.Therefore they shouldn't be thpught of as making a system more accuarate. i.e. full steps may land within 5% of where they're meant to wheras usteps may land within 20% say, but this is non cumulative so it doesn't matter how many usteps you have it doesn't affect your step accuracy. For other reasons though there's no point in going above 10 usteps. Think of it as usteps give smoooooothness and gearing gives resolution, wheras alround quality gives accuracy.

Cheers

Ian

Offline khalid

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Hi Stirling Thanks.. and You are right about the Pinion movement figures.. Todays i checked by turning the Feed wheel...With One revolution (rough)  I am getting 120mm Rack movement it is almost 5inches.. and this is the reason I lost my Torque:(.. With 1200Oz-in Motor i am unable to drill a hole in Carbon steel..:(...

So installing Screw or worm-wheel will give me enough advantage to drill a hole in CS and SS material...
The same motors are installed on X/Y carriage and carries 220 lbs weight without loosing steps.. They are used in 1/2 steps mode with 5TPI lead screw and 3:1 reduction gears...

Regards

Offline stirling

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With One revolution (rough)  I am getting 120mm Rack movement it is almost 5inches.. and this is the reason I lost my Torque:(.. With 1200Oz-in Motor i am unable to drill a hole in Carbon steel..:(...
Well maybe.... but I wouldn't regard 1.6 inches per motor rev as out of order or anything like. That 1200 oz/in puppy should be unstoppable. I use 350oz/in steppers at about the same gearing as you and they'd push a bus  ;D

Cheers

Ian

Offline khalid

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Hi Ian..The Gearing for the Z-stepper Motor gives Torque:
1200 Oz-in Bipolar Mode, I am using it in Unipolar so Lets say I am getting 600Oz-in Torque straight away from the Motor..
Now , 600 x 3 =1800Oz-in torque at the Feed shaft.. So do you feel good at  this Torque for drilling hole in 30mm thick Carbon Steel Plate...
Following were my setting for Z-axis  Motors

Steps/Unit= 12.33   , Velocity=10mm/min  and Acceleration=5mm/min/min
200 steps, 1/2 step Mode, 3:1 Reduction Pully and further Rack/Pinion..

The Brand New HSS 2flute drill 7.8mm DORMER, Following were the Feed and speed
Spindle RPM= 900
Plunge feed= 41.072 mm/min
Engage feed =15.402 mm/min
Cut Feed =173 mm/min
and Rapid is used as Transfer Feed

The Motor when enabled, Can't be rotated with the help of Hand Force by forcing the big Pully... I don't know How you can Pull the bus with it?

Also, I have found that when backlash is enabled in Mach3, I can't increase my IPM!!!..If I set velocity says 200 the speed i am getting like i am getting 40.. Increasing The Velocity value in Mach3 motor tunning do not affect the speed of the system:(