Need help with Calculations

[BeerFizz]

Hi,

Just finished the Y axis of my mini mill conversion.

The clamp in the pics is just holding the Gauge steady.

Here are some pics:

[BeerFizz]

Configuration:

Harbor Freight Mini Mill.

pre loaded ball screws from:
http://homeshopcnc.com/page2.html

Ball nut mount from:
http://www.kdntool.com/userfiles/ybnm_1.jpg

thrust bearings set up as a "fixed mount" from:
http://www.vxb.com/Merchant2/merchan...NGULAR_CONTACT

Pulleys and belt from:
SDP/SI
used the 3mm(GT) series which are suppose to have less backlash.

Hitachi motor with 500 line per rev encoder.

Geckos

Bob Campbell breakout board.

MACH III

[BeerFizz]

OK,

Just got this put together and I ran some tests to see how accurate this setup would be and I'm a little disappointed.

The distance traveled appears to be a Little less then I think it should be, however, when I tell it to return to zero, it comes back to the exact spot.

Please check the following calculations and let me know if they look good to you.

Thanks
Phil

[cp8071]

Probably easier to use the number of teeth on each pulley as the ratio rather than the diameters. Try that and re-run your numbers.

CP

[BeerFizz]

Easier, but more accurate?? I'll try it and see.

[BeerFizz]

Difference between teeth and pitch:

[BeerFizz]

So which is the right way to make the calculations?

Use pitch or use teeth?

[ViperTX]

Well which one gives you the correct distance?

[sendkeys]

Do it right in the middle only talking about .00005 inch(+- little) , ball screw will have 10 times more error than that. That's if by the looks of it that's a .003 error rolled screw middle will come out to .000025 error one way or the other.

remember to add in a error of one graduation per revolution on the indicator.

[cp8071]

How far off are you? If we knew your counts to try for an inch, and the actual distance travelled, then we could help with where the error lays.

You say 500 lines per revolution, but 512 would be the next normal value. That would give you 28912.94 counts per inch. So the error introduced by your wrong counts per inch would make 1" actually 0.97656" ... is this what you're seeing?

CP

[BeerFizz]

Thanks for all the responses.

I think there are 3 things at play here.

1. I'm a little over anxious :-)

2. I have not tuned the geckos yet. I was waiting until I had everything put together, so that it was not far off the final weight/power requirements. because of the lack of tuning, the geckos are not "snapping" to the final position like the should. (I think). Over the weekend, I'll tune them and see how it works.

3. I think I'm expecting too much. At least for now.

All in all, it doesn't seem to bad.

[motomitch1]

So which is the right way to make the calculations?

Use pitch or use teeth?

teeth