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Author Topic: Creeping Y position. Anyone know something else I can try?  (Read 10661 times)

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Offline Hood

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Re: Creeping Y position. Anyone know something else I can try?
« Reply #10 on: August 06, 2008, 05:27:47 PM »
What is the pitch of the belt/pulleys? Or if you can tell me how far it travels with 1 turn of the motor?

Hood
Re: Creeping Y position. Anyone know something else I can try?
« Reply #11 on: August 06, 2008, 05:37:35 PM »
Pitch is 0.375(L)

Thanks

Dave
Saltspring
Re: Creeping Y position. Anyone know something else I can try?
« Reply #12 on: August 06, 2008, 05:42:06 PM »
Correction on the reduction - I have three stages:

10 teeth to 24 teeth
10 teeth to 36 teeth
10 teeth to 24 teeth

Then the long belts that drive the gantry

Sorry about that.

Dave
Saltspring

Offline zarzul

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Re: Creeping Y position. Anyone know something else I can try?
« Reply #13 on: August 06, 2008, 05:45:20 PM »
Dave,

Maybe a little more detail on what you are calling creep,  if you start at Y0 and go somewhere Y+ then come back to Y0, and it is not in the exact same start point, that could be just simple backlash.

If you go from Y0 to Y+ then back to Y0, and do that 20 times and it comes out .016 X 20 off from Y0 would mean something different.    If exactly .016 X 20 off you have excellent repeatability and it is probably something to do with pulse triggering. 

If it is more random it could be binding causing you to miss steps only in one direction (going Y-) or noise on your system causing false stepping in the Y+ direction. 

Arnie
Re: Creeping Y position. Anyone know something else I can try?
« Reply #14 on: August 06, 2008, 05:56:43 PM »
Hi Arnie,

It's your second paragraph - it is very repeatable. If I run the test program 20 time, Y+ is out by 0.16 X 20. If I run the program 100 times, it's out 0.16 X 100. In each case, , the DRO is reporting Y0. I'm not saying that there is NO backlash, but it's not noticable.

Thanks

Dave
Saltspring

Offline Hood

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Re: Creeping Y position. Anyone know something else I can try?
« Reply #15 on: August 06, 2008, 06:10:43 PM »
Dave
 afraid I dont really follow on the reduction, is this all on one axis or is it three different axis?
Do you have a pic of your setup that you could attach to clear things in my mind


Hood
Re: Creeping Y position. Anyone know something else I can try?
« Reply #16 on: August 06, 2008, 06:49:05 PM »
Hi Hood,

Sorry - my explanation is lacking badly. I've attached a photo of the speed reducer. Please excuse how it all looks - I had no faith in the beginning that I could do this, so I built it out of MDF and ACME screws..., to prove out the concept. It worked, but showed up the weak points, so now I'm converting it to 1/4" aluminum and belts. I'm an ex-millwright, and metal makes a whole lot more sense to me.

Yes, there are three axles for each speed reducer, the final one being the shaft that drives the X axis belt on either side of the table. Each axle runs on sealed bearings, First one is tensioned by sliding the motor mount, second one is tension with the idler wheel, third one is tensioned by sliding the Reductioon assembly. The long drive belts are tensioned with sliders too (see lower left). The Y axis is reduced in exactly the same manner.

Hope this helps.

Thanks again for your time.

Dave
Saltspring Island.

Offline Hood

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Re: Creeping Y position. Anyone know something else I can try?
« Reply #17 on: August 06, 2008, 07:02:39 PM »
That is brilliant :)
Its late here and my brain isnt working too well at this time of night so working out how far it will move with one rev is beyond me. I will look again in the morning and things will be clearer.
 Presuming the white belt is clamped to the table bearings?

Hood
Re: Creeping Y position. Anyone know something else I can try?
« Reply #18 on: August 06, 2008, 07:56:07 PM »
Well, thank you for that kind word but around here it's known more as the "Rube Goldberg" approach than it is "brilliant". As in..., "if you can go expensive, go rustic!" :-) However, if you liked that one, here are a few more views.

I've already converted the Z Axis to aluminum, and it still uses an ACME screw. I think I'll leave that as it is..

The next picture is of the Y-Axis Reduce (short axis). It's the same as the X-Axis Reducer (long Axis), except that the final driver pulley is behind the reducer frame.

Next is the where the long drive belt mounts to the gantry. The reason that it is so far away from the table, is because I decided to widen the gantry when I make it out of aluminum, to give me 26 inches of cutting width. At that time, the belts will be attached directly to the gantry, without the outboard mount.

The table is stationary, because I wanted to be able to cwork on twelve foot boards. According to my plan (I've never done it), I should be able to make four feet of carvings, move the board along the X Axis,  re-register it, then carve the next section. Theoretically, there is no limit to the length of board I can carve, other than the length of the wood I can find.

As I said, it's pretty crude at this stage - I'd never seen a CNC machine before I built this one, so there are many things that I'll do differently on the next iteration.

Thanks again fro your help, Hood - I look forward to seeing what you come up with tomorrow.

Thanks to everyone else, as well.

Dave
Saltspring Island



Offline Chip

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Re: Creeping Y position. Anyone know something else I can try?
« Reply #19 on: August 06, 2008, 11:09:21 PM »
Hi, Dave

Looks to me you have 5 stages 10 to 36, (36 to 10), 10 to 24, (24 to 10), 10 to 24, The first 4 cancle each other out.

Stepper 1 turn = 2000 * 3.6 / 3.6 * 2.4 / 2.4 * 2.4 = 4800 Steps Per. Inch, So you only have a 2.4 ratio at the end.

If both axises have the same ratio then 4800 steps per is the number.

You really need to change the ratio around to get the step count up

You Will\Can get DRO not quite showing the full move on the display with under 10,000 Steps Per Value.

Is your error on the DRO or Actual measured loss at the cutter.?

Your pins should remain as you have them , Only addressing the Low Actives and Pulse width settings in my post.

Some drives are sensitive to "Step Dir pulses",  "All" the  Step & Dir "Low Actives" need to be in the same State ether (X or Checked).

If you need to "Revers" an Axis direction, It should be done in "Homes & Limits" (Reversed coll- um).

Missed the drive type "Gecko's", Pulse width Of 2 or 3 should be Fine.(This adjustment just gives your drives more time to see Mach's Pulses).

Thanks, Chip