Some doubts and problem with picking and placing components

[mrandt]

Have you tuned the current setting for the motors on TinyG board? Maybe your steppers are "missing" steps / stalling?

This might be the result of mechanical problems, i.e. too much resistance.

My suggestion: Remove belts and make sure all wheels run smoothly across the whole range of movement. You might also run into problems if your Y-maker slides (left and right) are not exactly paralell - in this case movement will require more force near one end.

Also the two extrusions that make up the X-slides (gantry) must be well aligned - usually the screws have a little bit of play in the steel plate holes.

Common approach:
1. mark the face of the eccentric spacer closest to the hole (thinnest wall) - you should have done that during construction if you followed Juha's instructions

2. turn all spacers so that the markers face AWAY from the maker slide rail (so minimum tension of the wheel aggainst the rail)

3. all wheels should have a tiny bit of play aggainst rail now - it should be possible to turn each wheel without moving the plate along the makerslide
-> if the fit is still too tight, you can try to lossen, adjust and fasten again the fixed wheels opposite the eccentric wheel
-> if still not OK, you might need to remove the wheels and file the mounting holes slightly larger - suggest to do that on the fixed wheel, not the eccentric one

4. make sure all wheels run smoothly across the whole range of each makerslide
-> if that is not the case, check rails are parallel
-> on X-axis (gantry) try to loosen, adjust and fasten again the steel plates left and right

5. if everything is fine up to this point, start tightening the V-wheels by slowly turning eccentric spacers. The wheels should just be tight enough so it becomes difficult to turn them without moving the plate along the rail. Also check fixed wheels opposite of eccentric ones.

6. As a rule of thumb, tighten the eccentric spacers one after another diagonally - i.e. front left, rear right, rear left, front right etc. and make sure to keep coming back and check again the ones you already fixed

7. check movement of both X and Y axes along whole range again - should run smoothly with very little force needed. A bit of silicone spray on the rails does not hurt and will ruther reduce wear on the wheels - just don't use any oil based lubricant as it will stick like glue, attract dust and kill the plastic wheels

8. Attach belts again. The belts don't have to be very tight and are IMHO not a common source of error. They contain glass fibre (or something similar) so they cannot be stretched. The teeth in the pulleys will make sure that the belt advance / retract per revolution is constant. So just make sure they are tight enough that the pulley won't skip teeth of the belt and that they are straight (don't hang loose in the middle).

9. Adjust motor currents as described by Juha in the instructions - make sure they don't stall or skip steps.

10. Disable slack compensation and squareness correction in software for the start and try if you can reliably achieve positional accuracy - i.e. camera / needle return to the same physical point for a given coordinate after moving around for a bit.

11. If you can't move machine to same location, try to go slower (lower acceleration and speed settings).

For the A-axis things are more complicates. I would also remove belt, loosen the screws and try to align the tube perfectly orhogonal to the table. Two right angles help with this task - once it is orthogonal, fix the screws again and adjust as necessary. Then attach belt and spring again and do not overtighten belt.

Good luck and don't get frustrated - you will get there eventually

[RMM]

Thank you for the detailed writeup. The advise and inspiration are greatly appreciated. I will try again and report back.

[JuKu]

Thank you from me also! This will go on the main site as well.

Couple more:
The range of "good" belt tightness is big. You don't want to stress the machine; if the mechanics start to bend, they are too tight. No one is going to have the belt so loose that the belt would jump teeth, you are looking for smoothness. Think of pulling a car starting with a loose or tight rope.

When you adjust Y axis belts, try to get them about same tightness. Do this with pulleys loose from the axis and even out the tension by moving the machine manually back and forth before tightening the pulleys. Do this with the gantry in the middle of the beam. You might need to move the machine a little to get access to the pulley set screws when retightening them. If so, move it from the middle of the beam so that the gantry is not twisted by this.

Look for anything loose: Idlers and idler posts, pulleys and couplers, wheel mounts, beam mounts.

[android]

* If the bearings have excessive slack (like the >1mm seen above) they are faulty and I'll replace them.

bearings??? are you mentioning about GT2-36 pulley?????if it is I have a spare one in hand. I will try with it.

Also, your needle nominal offset values look a bit odd. They are much larger than in a standard machine - you have modified the camera or the needle mount, I suppose? This is fine, of course, but the odd thing is that they are so even.

I kind of modified my down camera holder(designed it in a 3D printer). It is now closer to needle than original machine.

but the odd thing is that they are so even

???????????????????????

Yes, there is a 1mm difference, on purpose. The idea is that optimally, the calibration is done at the level the needle is when placing parts. We are not doing the calibration for each component. The accuracy is most critical on small parts, and I'm guessing 1mm for average small part height.

So, should I set up camera location at PCB level or at the height needle calibration occurs( 1mm less that PCB level)???

edit
oh.... LHFC8 bearing

[android]

@juha
should i set the up camera location at the height machine does needle calibration(1mm less that PCB level) or at PCB level.
It'd be great if you or anyone can post some screen shots of the needle position when setting "up camera" location and after "needle to cam"
One another thing I noted is that after "needle to cam">> needle down and raise needle 1mm(height at which Needle calibration occurs) , tip is at the exact centre.

This is fine, of course, but the odd thing is that they are so even.

I'm not much of an English guy and I didn't understand what you meant here!!!!!!!!!!

[JuKu]

Your images show needle nominal offset as 99.00mm and 62.50mm. If you follow the instructions (http://www.liteplacer.com/setting-camera-locations/), I think it is unlikely to end up precisely 1mm and 0.5mm off. It is possible, of course; the values just looked odd and potentially, hint of where the problem might be.

[android]

Okay,
What about photos??? can you post some, please

And where should I set the up cam location, 1mm above PCB level or at the PCB level??