CNC/DRO motor aligment ??

[bherr]

I have been trying for the past 2 days to get the motors aligned. Here's my problem:
1. Using Mach III I enter G01x-1F5>enter. The table travels to the X-1 location with the Jenix DRO reading 1.0070. I then hit X0 and the table returns to the X0 w/ Jenix reading .0000. good there! Now I tell the the table to move to the X1 location and it travels to 1.0200 and then back to X0 and the Jenix reads .0144. I've tried changing the motor steps per and the Blacklash settings but it seems if I get the -X good the +X is off. Or I get the +X good the -X is off.

I'm going to call Camtronics on Tuesday to see if Dan can offer some help, but if anyone knows how to fix this, please let me know.

Ben

[PoppaBear10]

It is not your motor tuning, you are experiencing backlash (even though you tried to adjust for it.

Goto Ball Screws if you can.

with acmes (that come with the shoptask), you can try and adjust out your backlash with the nuts on the end of the axis, (ecept the Z, there you can set your spring pull back pressure higher).

To get a true reading on your axis with acmes.. lets say you want to measure from 0 to -1.... start about at +0.25", then move to 0, then move to x-1, measure here... THEN continue to move in same direction to x-1.25, THEN reverse direction back to x-1, again measure you position, are you at x-1, if not not the amount, then step jog your axis to your dros reading x-1. Then go back to X0 note the the two distances of the original x0 to x-1, and the x-1 to x0 (the x-1 here may have to been adjusted).

But in any case the amount you get in the range of x0 to x-1 back to x0 will be the range that you want to tune your moters in.... any slop outside of that range (your backlash axis change of direction moves x0.25 and x-1.25 will show you the back lash amount of the mechanics of your axis. (NOTE: a few trouble spots to watch for on the shoptask, the little pulleys on the servos (or steppers), have tiny set screws that often allow them to slip a little on the shaft. I recommend redrilling a large hole and putting a big set screw in. (also on the X axis at the direction change lever watch that your bushing are all the way secure, the screw might move alittle here along its axis. The Y table watch the bushings on the turn handle end.

scott

[bherr]

poppabear10,

tried your approach?? Here's what I did:
1. X0 and marked the location with my dial meter and with a pcs of tape along the X axis and placed a mark at Xo.
2. ran the table out to X-1 and placed a mark on the tape and the dial indicator read.002 less than x-1 (DRO) read -1.0196.
3. ran the table to X+1 and placed mark on tape (DRO) read .9968.
4. ran table to X0, dial indicator read O (DRO) read -.0220.
All these reading were with a .002 backlash in Mach III
SECOND RUN:
1. Zero DRO
2. Ran to X-1 (DRO) .9978, X0 DRO at .0002, X+1 DR) at 1.0188,X0 at .0220
THIRD RUN:
1. Zero DRO
Ran to X-1 (DR0) at 1.0198, X) at .0220, X1 at .9968 & X0 at .0002

As you can see the numbers keep changing even though I haven't changes any motor steps or backlash. Any suggestions?????

Ben

[PoppaBear10]

suggestions, are the same, I probably was unable to articulate what I meant.

If you have Acme screws (assuming you do since you didnt say otherwize).
On the X axis at the right hand side, use the backlash nuts and tighten it up, to take out what you can.

Here's the thing, what I was trying to tell you above is this:

lets say starting a x0.25 move your axis from there to X0 (or just move it about 0.25 inches. Now where ever you are after the commanded x move 0.25 zero your dro. Then STILL moving in the same direction (moving in a negative direction), command a move from x0 to x-1. Note what the dro reading is (it may be even more accurate to set up your Caliper to varify the accuracy of your dro as well). Now go from where you axis stopped at x-1 a little further lets say another -0.25. don't worry about where this is on the dro, this is a turn around point. NOW move your axis Back the other way, moving from - to + by about 0.25 (these little moves make sure that all the slop/slack is out of the axis). Now REZERO your dro, now moving in the same "Back the opposite way", direction, command the move from x0 to x1 then measure your dro... The two measurements that you get one moving positive and one moving negative will be the real results of your motor tuning, if they are off (with the backlash minimized since you have started axis motion in the direction you wish to measure prior to measuring it), then do your calculations to get it going a true 1" (again moving in the direction you plan to move further in, prior to moving in that direction).

Once you get true 1" THEN do the back and fourth moves, i.e. but do them like this: move in a premove direciton first a short bit to take out lash, then send the axis from 0 to x1, THEN move from x1 back to 0!!! Record the dro, the amount that you are off at this point will be your (change direction), backlash, on the X axis on acme's it is about 0.006-0.011 per foot. with Ball Screws it is about 0.004/foot.

NOTE: the back lash compensation only works with staight liner moves, and then not real well. It has NO effect on CV/3D stuff.

I would highly recommend Servo's and Ball screw/nuts, also take a real, real close look at your gibs and the squareness of your table. Beware that you will have to put some work into the machine to get what you want. I can get NO measurable backlash in objects under 6" cubic envolope. BUT, when you goto larger objects, then you get about 0.004-0.005 per foot or so.

if you STILL get stuck, or what I am saying doesn't make sense, then send me a email to: poppabear@hughes.net and I will then send you my number and I can try to talk you through the issue.

Understand: the machine is NOT a bridge port, but given workpieces that fit into its working envolope the machine is not bad. I have never had a part (yet), that acually required less than 0.005" tolorance as of yet...

Poppa

[borrisl]

I had the same issues. "Sure would like the DRO to read EXACTLY what Mach says...." Worked myself up into a mess, until I upgraded to ball screws. Much better. Not perfect, but much better.

My next upgrade was double nut ball screws. Haven't had a chance to measure them, but I'm pretty sure it's going to be near perfect.

One thing I have learned: Shoptask is a HOBBY machine. If you want to get commercial accuracy you're going to have to work for it. Even then. It's not a production machine. I'm "planning" on using my 2 HIGHLY modified shoptask machines for producing prototypes and small production runs. After that it will be up to the big boys.

[P40Sortie]

I had a similar problem and I have Ball Screws. It was only with the X axis. I determined like PoppaBear10 said in his post that the timing pulley on the Stepper motor was coming loose. After I re-tightened it I had no more problems. However, on my Z-Axis the DRO was always one or two thousandths off. This was due to the DRO shaft being at a slight angle. I placed a washer to space it out more and it is accurate now. So you might want to recheck your X-Axis DRO shaft and make sure it is perfectly straight with no bends or off-angles.

Casey

[bherr]

I've finally determined that I'm going to have to go to ball screws. Shopmaster wants $799 and C&G research which states zero backlash wants $650 jsut for the X & Y axis and another $650 for the Z, which includes the whole gear box and motor. Seeing that I'm new to machining, where's the best place to get good quality Ball Screws for the Tri-power?????
Wanting for your inputs

[PoppaBear10]

well I guess that would depend on how much you want to spend in either time or money....

The ball screws/nuts that shoptask sells is from Nook industries, they are rolled screws precision about 0.004/ft. What you pay for from shoptask is there is a guy that "adapts", the screws to "plug and play" into your machine.
that is what you are paying the 800 for.

IF you can turn, and center drill acuratly the screws yourself you can save your self alot of money buy doing it your self. but remember the screws are HARD!!!

Nook also sells much higher accuracy screws....BUT, given the fact that unless you are able to PROFFESIONALLY scrap your ways, saddle, and get ALL the flex out of the mill quil arm on the shoptask, it would be doughtfull that you would get higher accuracy than the 0.004/foot anyway.

If you have the money, get the screws john sells for the machine, advantage is, if you get them and they are screwed up, you can return them for a replacement. IF you do your own screws and mess up, you buy a new screw and try again... If you have the talent and experience do it yourself, if not, buy Johns screws...

Scott