Hello Guest it is October 22, 2021, 11:05:09 AM

Author Topic: Matching Dros  (Read 6481 times)

0 Members and 1 Guest are viewing this topic.

Offline jimpinder

  •  1,232 1,232
  • Wakefield, West Yorks, UK
    • View Profile
Re: Matching Dros
« Reply #10 on: June 15, 2008, 11:39:55 PM »
This is exactly what I was saying (even with the correct numbers in). In actual fact there are not that many combinations of steps per inch.

Micro steps might change - depending on your cards ( some can do 1/2 steps right up to 1/16th steps) - motors seem to generally be 1.8degree these days - fixed at 200 steps per rev.

The difficulty might lie in the leadscrew. In Britain, although in theory we went metric many years ago, we never did, and all we have now, instead of one system, we have a metric/imperial mash. We have things that are sold as 8 feet by 4 feet in the building trade - and they turn out to be 2400 by 1200mm - i.e. short. I regulary buy 10mm bolts, the head on which should be 17 mill hex - the head turns out to be 5/8 inches.

I can see leadscrews in that sort of thing - marketed by some as 1/10 inch pitch, but being 2.5mm - it might not be as bad in America.

All I can say to Mr Cousins is - I hope you are following all this - it has certainly got a bit off the matching DRO's we started with. I think the pictorial by Rick spells out what I have been saying. Check your leadscrew with your manufacturer and see exactly what pitch it is if you are in doubt, and work from there.
Not me driving the engine - I'm better looking.

Offline Chip

  • *
  •  2,055 2,055
  • Gainesville Florida USA
    • View Profile
Re: Matching Dros
« Reply #11 on: June 16, 2008, 05:38:40 PM »

I'm sorry this has turned into a Mathmatical/Threory Class.

For Sure You Can Calibrate any Axis without knowing anything about the BallScrew Pitch or Reduction/Gearing.

Mach shows on it's DRO's to .0001 ackuracy, But in fact it retaines a .000000000000001 "15" dec. point's or so I Think, Precision Accuracy (The Remainder is "Applied" to the "Closest Step Per" Unit as setup in Motor Tuning.

In my last post I was trying to help you find out If you have Backlash Issues Also.


Using the 20,967 that's Giving you a 1 inch move.

Move the axis "pos" 1 inch "Pre-Load", (It takes backlash out, If there is any.

Then zero the indicator and your linear scale DRO, Move in the pos dir 1 inch.

Dose the indicator show a 1 inch move. ? _____________

Dose the linear scale "DRO" show a 1 inch move. ? _______________

Dose the Mach show a 1 inch move. ? ______________

Now move the other direction 1 inch.

Does the indicator move back to Zero, ? _________

Dose the linear scale "DRO" show a 1 inch move. ? __________

Dose the Mach show a 1 inch move. ? ________

If the indicator dosen't return to 0, The distance to go is "Backlash".

Thanks, Chip

Offline DAlgie

  •  314 314
    • View Profile
    • Algie Composite Aircraft
Re: Matching Dros
« Reply #12 on: June 16, 2008, 06:06:00 PM »
Hate to jump into this, but you might also check your table gibs out. Most smaller machines, and certainly the cheaper chinese machines use set screws for gib loads, these make up for a lot of manufacturing problems but aren't very rigid. My chinese lathe has the more rigid tapered gibs, BUT; they were very poorly fitted, had big clearance on one end while the other was tight, and weren't even STRAIGHT!, had some curvature to them. I had to surface grind the X axis one to the correct taper and to grind the bow out, then refit it. All this can make a table or crosslide walk around and if you have digital readout scales on one side this might account for your differences in readings and even backlash. Mount a dial indicator on the table side and grab it and load it by hand, you might be surprised to see one end move and the other be tight, etc.
Re: Matching Dros
« Reply #13 on: June 16, 2008, 08:20:18 PM »
Thanks for the advise guys.Chip i did what you said and everything came out great!!!THANKS.