Hello Guest it is September 16, 2019, 07:13:11 AM

Author Topic: worm gear cad design  (Read 15924 times)

0 Members and 1 Guest are viewing this topic.

Re: worm gear cad design
« Reply #20 on: December 24, 2013, 04:50:02 PM »
What a great explanation thank you i did the settings as above and i try to run the program as above
Step 1:

G0 G21 G49 G40.1 G17 G80 G50 G90 G98
and it says error in this line is there something wrong with this line of codes maybe error  on a setting
man im toubling you lots God bless you!!!!!! ;)
Re: worm gear cad design
« Reply #21 on: December 24, 2013, 04:50:55 PM »
What a great explanation thank you i did the settings as above and i try to run the program as above
Step 1:

G0 G21 G49 G40.1 G17 G80 G50 G90 G98
and it says error in this line is there something wrong with this line of codes maybe error  on a setting
man im toubling you lots God bless you!!!!!!
Re: worm gear cad design
« Reply #22 on: December 24, 2013, 09:40:33 PM »
khaled:

I rewrote this on my machine, and it loads with NO fault.
The post I sent for you to try, would not load on my machine either. Do not know why?
However, this loaded fine:



(27 Pitch 2-Start Thread)
G0 G21 G49 G40.1 G17 G80 G50 G90 G98 

G0 Z20.0
G0 X0.0 Y0.0 A0.0
M03 S1000
G1 Z-1.0 F10 M7
G1 X162.0 A2160.0 F500
G0 Z20.0
G0 X0.0 A0.0 M9
M30

If this gives trouble, retype the program on your computer by hand. If you copy/pasted the first
program, perhaps there were some Windows/Word letters that cannot be seen. I am using a brand new
computer with Win7, and there are some bugs to work out maybe. I specifically made sure this was saved
in plain text format. That is the only thing I can think of.

John

Re: worm gear cad design
« Reply #23 on: December 25, 2013, 01:08:18 PM »
Good afternoon
thankx yeh i checked it could of been alphabet that i used also and now it works with this new Gcodes
could you please advise on the Rotary table settings on the method for 'steps per'
rotary pulley 40 teeth
the motor pulley 20 teeth
how would i calculate the steps per ; velocity and motor tuning?
Re: worm gear cad design
« Reply #24 on: December 25, 2013, 02:14:46 PM »
Khaled:

What is the rotary table gear ratio ratio?
What are the steps per revolution of the motor driving rotary table?

John
Re: worm gear cad design
« Reply #25 on: December 25, 2013, 02:43:59 PM »
The rotary ratio is 40 to 1
motor steps 200 per revolution.
Re: worm gear cad design
« Reply #26 on: December 25, 2013, 05:15:53 PM »

The rotary ratio is 40 to 1
motor steps 200 per revolution.
Re: worm gear cad design
« Reply #27 on: December 25, 2013, 06:29:16 PM »
Khaled:

If the rotary table ratio is 40:1, that means 40 turns of the input shaft of rotary table = 1 rotary table revolution, or 360 degrees.

1 turn of the rotary table equals 360 degrees / 40 = 9 degrees per 1 input shaft rotation.  

This seems like a very large movement for a rotary table. Most rotary tables over 150mm diameter (about 6 inch) are 90:1 ratio, and rotary tables in the 100mm diameter (4 inch table diameter) are usually 72:1.

Please recheck if the table ratio is 40:1

Such a ratio is a very poor use for a CNC machine.

If that is true, then the timing belt reduction of 2:1 = 400 motor steps for 1 Table input shaft rotation.

The equation to calculate STEPS PER is:
Motor steps per revolution (200) * ratio of timing belt drive (2) * ratio of Rotary table (40)  = Total number pulses to go 360 degrees = 16000
Divide this number (16000) by 360 degrees = STEPS PER 1 degree = 44.44444

You cannot have a fractional STEPS PER except if it is an even fraction equal to micro-steps, like 1/2, 1/4, 1/8 micro-steps, then a fraction like .5, .25, .125 will equate to a whole number when factored with the multiplier of 2,4,8 in the final calculation.

If the larger pulley is a multiple of 9, then the STEPS PER will be a whole number for your 40:1 table ratio.

20:45 = 50 STEPS PER
20:54 = 60
20:63 = 70
20:72 = 80

400 motor steps / 9 degrees per table shaft rotation = 44.44444 steps for 1 degree table rotation.

The STEPS PER must be a whole number, and not some fraction unless it was 44.5 or 44.25, and in that case micro-stepping of 1/2 or 1/4 would work. These two examples would work because if micro-stepping 1/2, and using 44.5, the STEPS PER = 89, and micro-stepping 1/4, STEPS PER = 177.

If you use a 20 tooth pulley on the motor, the other pulley must be a factor of 9; 45, 54, 63 etc. to get a whole number for STEPS PER.

John
Re: worm gear cad design
« Reply #28 on: December 26, 2013, 01:17:26 PM »
 ;)HI John
Thankx again for the explanation yes i have a 40:1 universal table maybe its old but i do have a VERTEX HV10 254 diameter which is 90:1 but it has a backlash which im not sure how to minimise! its mounted shaft to shaft so would the calculation 200* 90 =18000/ 360 = 50 steps per is this correct?
but my problem is this rotary table has backlash is there a way to minimise it on the table itself. i know its done on mach3 settings for backlash but dont see on the rotary table.
THANKX

Re: worm gear cad design
« Reply #29 on: December 26, 2013, 03:54:18 PM »
Khaled:

The 254mm table, 90:1 ratio is a much better choice. However I  would still use a reduction from stepping motor to worm screw of table. Since the table worm shaft is much higher from the base, a 60t pulley or even an 80T woulld be better. If you used 20t to 80t timing belt reduction, the steps per would be exactly 200. This would make 1 turn of the motor = 1 degree of rotation. This will have much better torque, and the motor will be operating in its better range. The the cutting action will not be fast anyhow, as a 10mm ball cutter at full depth in the finish pass cannot be pushed fast at all. It also will require a quite LOW spindle RPM, as a great deal of cutter surface is in contact; it must be a slow, steady cutting action with coolant. So, the greater reduction all works for the positive.

As far as backlash, there is usually a means of adjusting the worm screw to ring gear to account for general wear. In addition to getting less backlash, if you put some kind of slight drag on the table with a friction material like a piece of leather, it will stay tight against one side of the ring gear; and the cutting force is a constant load in one direction only. You are not making a cut in a forward/reverse situation, like an X/Y axis anyhow. If you get it apart, you will probably find it needs lubrication if it has sat for a long time. The backlash will not be a problem if all things are setup correct. In rotary axis machining, having everything rigid is very important.

Testing the cutting action with a standard cutter of smaller diameter as I suggested, you can test how the cutting action works best by programming the cut from left to right, and then try cutting from right to left X axis motion. One direction may prove better due to the cutter forces, and backlash. When starting the cut, you can also do an MDI, moving the table and X axis backwards from the start position about 10mm, and then back to the start point, and all backlash will be out of both the X axis, and the rotary table. You can get all the correct settings, feedrate, best cutting direction on a test blank.

Once your mechanical motor setup is done, spend time getting the A axis motor tuning working smooth. There are some good trial and error tutorials in the forum how to get the best performance with stepping motors. The Velocity and Accel settings for the Rotory table will be quite a bit higher than the X or Y axis settings. Just keep increasing the numbers, and listen to the motor sound, and smoothness. It will eventually stall, or sound really bad. Back off the settings about 10 or 15%. You will get a feel after testing, what works best. It is all a trial and error unless you have the high-end drivers that have computerized analysis feedback.

John