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Old 12-20-2014, 08:50 PM   #91
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I can understand the problem with backlash, the more bits, belts and joins you have could be a problem. I'm still in the process of trying to understand all the controls needed, drivers etc and how they work.

Paul.


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Old 12-21-2014, 05:19 AM   #92
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I just upgraded from 24v DC to 48v DC. It's improved my rapid speed to a reliable 30 in sec. I don't think it should have any affect on holding torque or cutting speeds, the latter being more a matter of material and depth of cut.

I don't think the timing belts on my machine introduce much if any backlash. My mill has about .003" backlash on each axis and some, if not all of that may be the ball screws.


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Old 12-22-2014, 11:03 AM   #93
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30 inch a sec ?? you sure about that

good with the volt change. when i did mine the norm was to take the rated volts of the stepper and times it by 20 to 25 and that was it.

3tho backlash not bad for a home build. i have a bit of backlash in mine, seems to be coming from the fixed end bearings. not much point in getting rid of it as the deflection in the column is more than the backlash.
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Old 12-22-2014, 04:47 PM   #94
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30 inch a sec ?? you sure about that
Guess I meant 30" a minute!
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Old 03-06-2015, 08:24 AM   #95
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Hello!
Here is my version of rong fu 30 cnc. Z-axis is made also with ballscrew. I have solidworks 3d files of z-axis, if somebody wants them, I can upload these to download area.
Attached Thumbnails
rf30a.jpg   rf30b.jpg   rf30 3d.jpg  

Last edited by Pertsa; 03-06-2015 at 08:55 AM.
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Old 03-07-2015, 01:05 AM   #96
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If you had meant 30"/sec, I would have said you're Rong Fu. 😃
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Old 05-07-2015, 08:27 PM   #97
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Quote:
Originally Posted by Pertsa View Post
Hello!
Here is my version of rong fu 30 cnc. Z-axis is made also with ballscrew. I have solidworks 3d files of z-axis, if somebody wants them, I can upload these to download area.
Can anyone enlighten me on how the Ballscrew is held and driven. I just can't make it out, ?
Maybe Pertsa you can post or send the drawings as you have suggested. I would be very grateful.
Chuck, I,m sorry to stomp all over your article,maybe my post can be moved ?
You did a great job of your conversion and thanks again for your help. I think I'm in favour of the Z axis under ballscrew control.
Regards
George
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Old 05-13-2015, 05:02 AM   #98
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Can anyone enlighten me on how the Ballscrew is held and driven. I just can't make it out, ?
Maybe Pertsa you can post or send the drawings as you have suggested. I would be very grateful.
Chuck, I,m sorry to stomp all over your article,maybe my post can be moved ?
You did a great job of your conversion and thanks again for your help. I think I'm in favour of the Z axis under ballscrew control.
Regards
George
George, there is no problem with other people posting related topics in this thread. More information and questions are always welcome.

First, on the Z-Axis, I too felt that a ball driven Z-Axis would be better and most other folks have the same opinion. However, Using the existing Z-Axis feed was so much simpler to install and, so far, at least, it has worked flawlessly, even in when cutting harder materials like steel. The weight of the spindle assembly is substantial, probably 15 pounds or more, and I've never had a cutter bounce or lift, even with pretty aggressive cuts.

The ball screws I bought from China had no finished ends. I turned the ends down to half inch diameter shoulder with a carbide cutting tool. The ballscrew is hardened, but carbide will cut it with slow feeds. You can also use a toolpost grinder to take it to final fit and finish if necessary... I didn't.

I then made a 17mm round shank to fit inside the existing X and Y table end bearings. Each shank had socket with a grub screw to fasten on to the ends of the ballscrew. The socket end of the shank has a larger outside diameter to accommodate the socket.

If you are attaching the motor directly to the ball screw, you can buy shaft couplers that will connect two different diameters. These usually are 3 pieces with a rubber center so they will tolerate slight misalignment.

Hope this helps and don't hesitate to fire off more questions...

Chuck

Last edited by cfellows; 05-13-2015 at 05:04 AM.
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Old 05-13-2015, 02:53 PM   #99
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Thanks Chuck,
I value your input.
My reason to go to the Ballscrew Z axis is that I have lost major steps with the arrangement like yours. I broke a couple of cutters and that was on aluminium where the axis lost it's place and drove down through the material!!!! My set cut depth was only .25mm at the time and the tool plunged down about 6 - 8mm deep. I'm not sure if my accel values are correct with regard to the tool retracting. That's when I can here the stepper make a zip sound. I don't think my belt is slipping
Is there anything more that I can tell you to help you help me what is going wrong

Regards

George
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Old 05-13-2015, 05:26 PM   #100
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Quote:
Originally Posted by Len-Tikular View Post
Thanks Chuck,
I value your input.
My reason to go to the Ballscrew Z axis is that I have lost major steps with the arrangement like yours. I broke a couple of cutters and that was on aluminium where the axis lost it's place and drove down through the material!!!! My set cut depth was only .25mm at the time and the tool plunged down about 6 - 8mm deep. I'm not sure if my accel values are correct with regard to the tool retracting. That's when I can here the stepper make a zip sound. I don't think my belt is slipping
Is there anything more that I can tell you to help you help me what is going wrong

Regards

George
A couple of things come to mind, and please pardon me if I'm stating the obvious. Just trying to cover all the bases.

First, of course, would be to check if the downfeed clamp is loosened. I know, it sounds silly, but I frequently tighten my clamp to make the spindle assembly more rigid during level cutting then forget to loosen it when the Z-axis needs to move.

The second would be the speed setting on the rapid movement of the Z-axis. If you are using Mach3, you can set the maximum rate of speed in the config/motor tuning menu option. I have 425oz in nema 23 steppers with an inductance of 24 milli-henrys so, while they have a lot of low end torque, they won't spin very fast. The gearing on my Z-Axis is such that it takes 48000 steps per inch of travel. It seems to run consistently in both directions without skipping steps at about 15 inches per minute but I have it set to 10 with acceleration set to 1 in per sec per sec. I keep it set really low since Z-Axis speed isn't really important to me.

I don't know how familiar you are with Mach3, but you can hold down the shift key while you press FN and Down Arrow or Up Arrow to do a rapid movement of the Z-Axis. I set my speed by setting the speed at about 50 inches per minute and run the Z-Axis up and down several times using the computer keyboard. If it skips steps, I drop the speed down another 5 in per minute and try again. I repeat this until it moves smoothly without ever skipping. Then I usually drop it down a few steps until I get the best sound from the stepper.

Hope this helps.

Chuck


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