I have some 2mm PTFE and can punch out the washers for you - (5 off 40 x 10, and 8 off 20 x 8). PM me your address and I'll send them out first class on monday if you still need them.. I used a slightly different combination but the ones listed above are what the drawings show. 1 off 40 x 10 on all motors and the idler and 2 off 20 x 8 on all but the z motor
Chris

Hi Chris,

That would be great. Sending Pm now.

i use washers made of plastic from a pet bottle. works like charm.
letme see if iam getting this right.
you are getting errors of 0.4mm on a 150mm travel? you have belt reducion? if not how many teeth you pinion have and module rack?
i have 24teeth on direct motor module 1 rack i think i have 0.3 mm error but i found that normal. do i have to spect more accuaricy?
maybe its a good idea to do a .tap normalised test file on mm and inches to compare machine errors. using most standard bits. like 6mm
btw i have a 6mm bit that is 5.96 mm

When I see your cutting pattern i think you have some clearance somewhere where you should not have. Especially the begin and ends from your lines are moving away.
Check your spring load. should be 12kg I checked my springload whith a bucket filled with 12 liter water. and measured the lenght of the spring.

when your machine is running (cutting) you can place your hand on the y cart and feel it. movements should be smooth.

power you motors on, and try to push the x, y and z slide by hand. if you can move them, it's not OK. should be solid as a rock.
1) check if the gears are fixed well
2) check spring load
3) check if your nuts for your motor mountings are not to tight. check this by removing the spring, you should be able to move the motor up and down
4) check the bolt which are used to "hang" there should not much clearance between hole and nut
5) check if you x slide and y cart are proper aligned in the guiding rail
6) check if you gear is nice in your rack, it's possible that the flange of the gear is touching something, so your gear is not properly in the rack
7) are your V bearings mount properly, or do you have clearance at the V bearing, check if the v-groove piece is fixed on the bearing.
8) is the same type rack and pinion used or did they mixed up metric / imperial

Teflon sheet can be easily cut with a heavy scissor. They don't need to be perfect round. drill a hole in the middle and ready (place the Teflon between two pieced of drilling to avoid that the teflon "run's" in the drill

Well an update. We have managed to get things a fair bit better.
We now do have it repeating cut lengths in both x and y to within +-0.1mm. Phew just about acceptable!

Fernando: I would certainly want and expect a better tollerance than 0.4mm from any CNC machine. We achieve pretty much +- 0.05 on our other machine. Before doing the test cuts we measured our tool 6.2mm rather than 6.35. This wa taken into account previously. What we ended up doing to get this right was we wrote a programm with a load of equal length cuts in each axis and took the average length of them all with a set of vernier calipers. Then knowing the steps per unit, pulse rate, pinion siz and pitch (20dp, 20T) etc we calculated back to what it needed to be. Just out of note the X was close to what the theory says but the Y was a bit off.
http://i245.photobucket.com/albums/g...104_154529.jpg
http://i245.photobucket.com/albums/g...104_154511.jpg
Still not quite got the z as accurate but I think with the rails as they are we are never going to get the same tollerance.

After much fetteling with the z plate, rollers, concentrics etc we do have the run out of cuts looking much better but we still are seeing it particularly on the plung in. On panel cutting it doens't really show up on square profiles but does a small amount at the plung point of circles.
http://i245.photobucket.com/albums/g...104_154615.jpg
http://i245.photobucket.com/albums/g...104_154622.jpg

The first couple of jobs are relatively simple cabinet work so I am just about happy enough to run them as it is. Last night I cut and attached some 18mm birch ply which
to day I am in the process of turning into our vacuum table.
http://i245.photobucket.com/albums/g...103_203943.jpg
This morning i skimmed the panel with a 2mm cut to level it off and at the moment (while i type now) it is cutting out the 6mm deep channels. All a bit labourious as the program for the rebated channels is 4 & 1/2 hours long and the surfacing was 2hours. One thing that was nice to see earlier and confirms the machine is not loosing steps is that even after surfacing the panel with a 1/4" end mill (yes I know, but we dont have any larger tools at hand) the machine went back to the home position I had set perfectly.
http://i245.photobucket.com/albums/g...104_144930.jpg
http://i245.photobucket.com/albums/g...104_152511.jpg
http://i245.photobucket.com/albums/g...104_152452.jpg
http://i245.photobucket.com/albums/g...104_154457.jpg

Hi Rik: The gears do seem quite well seated but I think I am still going to check the spring strength (i'll try your bucket and water test). We have some teflon washers coming thanks to the generosity of our fellow member cdev (Chris), hopefully this will help with the smoothness and rigidity of the motor mount action. We've been though and re-aligned/ straited our y rail and the Y car is now well seated all through its travel and the x already was, but of course the rails are quite inaccurate in the first place which will through things off a bit as it moves. One thing you mentioned may be worth a re-check one of the v-rollers on the Z slide did seem to have more lateral moevement (in X) than the rest, I may take this off and have another look at it to see if the v roler is propperly seated on the bearings.

Any way will keep hunting to try and track the last issues down.

ON a side note what vacuum pumps / motors are most mech mate users using?
We have a nice rotary vein Becker unit on our other machine but couldn't afford a new one of them. We did miss out on a nice Busch roary vein that went for penuts the other week but havent seen anything like it since for sensible money.

Anybody here using the shopbot style cabinet with multiple Lighthouse vacuum motors? Anybody know of good european equivalents (have looked and cant find lighthouse ove here).

SOSx,
What feeds and speeds are you using to carry out your test cuts?
Looking at the photos it maybe the bit flexing or the stepper motors not holding on the micro step.
To determin which problem mount the dial indicator on one axis and cut a straight line only with the other.
Anthony

your v wheels have bearing? there is any loose on the them? i did have problem with them becouse one loose wheel.

Hi there,

Many thank to Chris (cdev) for the teflon washers. It has definately improved both rigidity and action of the stepper mounting plates.

Antony were fairly certain were not loosing steps, tool bit returns to home bang on every time.

Still haven't had a chance to check the v wheel I was concerned about yet. Next thing on my list is stronger springs. Have looked at the specified spring and cant find anything identical with out having them custom made. Firstly does anybody know of any springs that are a direct fit in the uk or europe. Or the other option is I have found a possible substitute what do you all think of the T42480 on this page
http://www.assocspring.co.uk/p/16/ex...=#startcontent

It has a slightly higher maximum force about 16KG but this is when at maximum pull which is 20mm longer than I need.

What do you think?

I used these springs. http://www.strutsdirect.co.uk/compon...roducts_id/154
They come in at under 12 kg but by drilling a new hole about 20mm further out in line with the other holes but clear of the v rollers I get a bit more than 11kg force. The only thing to be careful of is to make sure that the stepper motors can take the the radial load. From memory, if the spring tension is around 12kg then the radial load on the motor shaft is around 20kg. I'm sure someone will correct me if I'm wrong.. This only applies to direct drive motors of course..

SOSx

Not in the least bit surprised the telflon washers improved the machine over using a steel washer.
How the original builder could seize up a joint that is supposed to move is beyond me :(.

Did you actually test your existing springs on the machine using the bucket method.
I wrote earlier they seemed a long way off the mark.
If you have a figure then it is always good to feed it back to the forum.
It shows the rest of the builders by how much they were out and gives others a chance to learn.

The table surfacing time you gave was too slow, way too slow.
I suspect even with a 6mm end mill to take 2 hours on a 4x4 you have not used the tool step over correctly.
There is no need to use a 10% stepover to surface a table - use 90%.
The operation removes very little material it is more like jogging than cutting, very little change of lost steps.
Smooth the motor acceleration on the x axis and wind up the speed - time is money you know :).

I also suggested that you lock the motors and wiggle the spindle.
You absolutely NEED to do this as your cut still indicates mechanical slop in the Z axis or a loose Y car pinion.

Regards
Ross

Update :mad:
 

Well time to back track a bit now.

It is not after the last calibration cutting distances accurately.
We thought we had it sorted with the method I described earlier.
We can get it to cut a specif distance with this method accurately and it will repeat that cut to within +-0.1mm but as soon as we do cuts of different lengths the measurments go out. They will repeat quite happily but they are still out and were talking 1-2mm here over a distance of 600mm.

We thought that it may be that our rack goes out of pitch or is not very accurate to it supposed pitch (or even if it might actually be mod 1.25 not 20dp), but today we have taken off both of the x racks and both meshed them together and measured them/counted the teeth and they are definitely dp20 and they mesh together nicely so it is not the rack. As Ive said before the error seems to be an incremental increase over distance which would suggest the settings for the steps per mm is not correct. But the theoretical calculations are out and every way of calibration that we have tried has not yielded success other than at a specif distance in both x and y axis.

We have still not been able to isolate the mechanical slop in the z slide although upon giving it a good tug you can feel it is there. one thing we thought might be cause of error is that the rack is not running perfectly strait along the bottom of the angle section it tapers in toward one end. In particular you can see this in the x rails as it is about 3-4mm difference from end to end of a 1700mm length. In the Y axis it is only maybe 1mm difference from end to end.

http://i1108.photobucket.com/albums/...0-31101053.jpg

Could this through out our steps per mm calculation by this much? Another option we have thought about is that as I've described our motor shafts are 12mm yet the pinions have a bore of 1/2inch. So we have them shimmed with drinks can sheet wrapped around. This seems to work quite well and definitely centers the pinion much better than the copper sheet shims that were in there before, but they do still leave the pinion with a slight wobbly rotation.

Surf cnc we did not actually measure the springs in the end with the water bucket method, but upon measuring there diameter 12mm and wire size of 1.4mm it is clear to see from looking at LOTS of spring specifications they are not able to produce 12kg of pull, maybe 6-7kg at best. But that has also raised another question our motors are only rated for 60N lateral load which is only 6.11Kg:( Are we going to kill them putting on the correct 12kg force springs (or 11Kg ones cdev recomended)? Maybe a gear reduction system for them is our only route there or larger geared steppers or a belt reduction. But to be honest at the moment I really wouldn't want to through any more money at it for things like that with out knowing they were going to sort our root problems out (which I don't think they will).

As for the surfacing of the vac bed I did a 2mm pass at 18000rpm, 3780mm/m and a step over over 75%.

To be honest this machine is really bugging us now, in many ways the little movement/slop on the z axis on entry and exit seems like the least of the machines issues at the moment seeing as we cant seem to find a way of getting to cut more than one specified distance correctly. Please dont take me as slating the Mech Mate design in any way, I actually think it is a very good design its just we've been unfortunate to buy one which unknown to us at the time implemented the design very poorly.

I really dont know what to try next?

What are your acceleration settings? Set them so slow that you can see and hear the accel and decel on every move, and try the calibrations again. You are still describing something that matches up with missed steps, which will vary with the length of the operation, but be somewhat consistent for a given length.

Try changing the computer, it may be not giving nice pulse train, if all mechanical issues have been checked turn to the electronics.
You can also check is there a nice 5V on the dir pin at the drives (as its harder to measure it on the step input)
Also you can try changing outputs for STEP/DIR , as I found on one computer that it would not output nice signal on only one output pin, PCI LPT port is another idea to try as its cheap.

I Dont know if Matt has seen the replies but if he does and can remember hopefully he'll put them up.
Brad surely if it was loosing steps it would'nt return to home correctly?

Hi Danilo-we have a smooth stepper board conected to a fairly decent spec all in one micro itx pc.
We have had that issue before with different computers on our other machine, but had pressumed the smooth stepper board would remove the possibily of this.

You are correct that losing steps would destroy repeatability on the return to a known location. So, if you have repeatability after cutting the inconsistent lengths, it's not lost steps. Of course, you could have repeatability of jogging, but loose steps under the cutting forces. If you have the repeatability under cutting conditions, but still have cuts of variable length, then we're either looking for a software issue, or a mechanical issue - we've exonerated the drivers and the motors.

This has got to be driving you guys bonkers. Wish we'd been able to nail it for you earlier.

Ok it's got to be annoying by now, however

1. Ignore any "motor spec" and just pull up the pinions to the "machine spec". Replace the motors with the right motors if or when they fail.

2. Calibrate over a long distance and accept the Mach 3 calibration then do a cut to ensure it agrees with the long calibration when cutting.
When in doubt calibrating over a long distance reasonably accurately beats calibrating over a short distance very accurately.

I would just like to confirm that you are using both the "Gear Steps Calculator" and then secondly the Mach3 axis calibration settings using the "Settings Tab" also labeled ALT F6.
The individual axis calibration routine is located directly above the Reset button.
If X axis needs different steps to the Y axis to be calibrated then so be it.

3. Your electronics laundry list seems pretty good quality.
Not much to be gained here but just kill the network when cutting, don't scroll the tool / table window around when cutting, run an AV scan, update windows... so the normal cautions should be fine.

4. The elephant in the room is the pinions and the racks.. Over the longer term consider some new pinions and have them correctly machined for your motor shafts.
The wobble has the effect of moving the gears slightly out of mesh twice on each rev.
The alignment of the rack to the pinion is also not perfect so as the pinion traverses along the rack it may not be fully engaged along the full 15mm width the rack.
So rather than a nice 100 percent seat you have both the pinion crawling out of square with the rack and the contact area changing as the pinion traverses along the rack.

Spraying the rack with cheap mat black paint will show you the contact area of the pinion on the rack after a few machine cycles to wear the paint off.

It is possible to pack the rack square to the pinion along its length using shims (the same drink cans as the pinion shims). If the rack is consistently out of square Gerald has even recommended bending the motor plate in the past.

Regards
Ross

Ever check for movement in the router, its mounting bracket & worn bearing ??

We'll back to it this morning. Once again thank you all for your input and support in trying to get his sorted. It is most definitely driving us up the wall a bit now as its just putting us further and further behind our work schedule and the idea was to free it up.

Brad- we do seem to have repeatability under cutting conditions. If we repeat a cut or program it will be the same roughly +-0.1mm, it will just be wrong?

Ross - As for motors/gearboxes I am just waiting to hear back from motion control now regarding prices for there planetary gear boxes and rotary encoders, as I think that more resolution and torque can only be a good thing and with rotary encoders we would know for certain if we loose any steps.

Also I am hoping that the planetary gear boxes can take a higher lateral load so be more capable of surviving the forces applied by correctly rated springs. Also we could use (for now) the 20T 1/2 inch pinions we have currently with out shims as we can get an output shaft of 1/2 inch not 12mm like we have now. I know it would be a bit under geared but I would sacrifice a bit of speed for resolution right now.

I can confirm we were using the gear steps calculator (and confirmed it in excel manually). We have also used the mach 3 axis calibration function. I think we have some black spray paint so will put some on tonight and have a look at the wear tomorrow.

You say kill the network when running? The wifi is disabled but the wired is left active, but we have never had any issues with this and our other machine?

As for calibration we started at 150mm using a small set of verniers then as we could get it accurately this way we then bought a dial gauge, borrowed some 0.0005mm accurate engineering slips and re worked using this method but i think that the tiny differences in the dial gauges angle in comparison the engineering slips face threw those test off. Again we could get it to repeat the one measurement accurately but as soon as we tried other measurements / cuts it would be off again? Then the last 4-5 days we borrowed a 1m long set of vernier calipers and re-did the calibrations using averaged cut lengths and this again would get it to repeat a 980mm cut or movement time and time again but as soon we cut a shorter length it was well out again?

Ken- We had a brand new 10mm thick alu mounting bracket machined and it seems pretty solid and the motor is firmly attached to it. I Think the slop is more in the Z car/slide i think?

While I've been typing this Ive just heard back from motion control and spoken to their head engineer. In case anybody was wondering on lateral forces on the shaft he has just done the calculations and for a pinion at the end of our motor shaft and with a 12kg spring load we are applying just under 20Kg force on the bearings and that they are quite comfortable much higher than this (he said more like 200kg before they break). For the gearboxes hey have given us a price of £170 (about $270) each for the encoders they are £70 each (about $110). Are these prices reasonable are htere cheaper/better options?

Why not re-build the Z-Spider? that should cost less than 170quid...

Some close-up pic of your Z-axis will help a lot. Namely The slide plate's V, the bearing assembly.

Hi Ken,

I'll take some pics of it in a bit.

Back to basics, are my assumptions correct here (from previous posts)

1. 1.8 degree 200 step per revolution stepper motors
2. 20 tooth module 1 pinions
3. 10 microstep setting on you MSD556 driver

My answer is 38.831 steps per mm ??

All that stuff about tuning things off was just to reduce other possible sources of error.
I'm a massive fan boy of reductionist problem solving.
I run my machine with the wireless on all the time.

So what gives with the steps, have I got something wrong.

Regards
Ross

8 microstep = 25.465 ?

Ross

I got 31.831 not 38.831

Another one with 8 microstep is ok.

Hi Ross - 1.8 degree 200 step per revolution indeed. But running on dp20 rack and pinions (20T indeed).

Oh yeah sorry, yes we are set to 10 micro steps on the MSD556 drive.

we made that by the maths to be 25.06337

Also thinking out loud...

The mechanical slop in the z axis may be from errors in the Z slide grinding.
It may be something as simple as being tight at one part of the z axis stroke and loose at another part of the stroke.

The check is to run the verniers over the width of the slide in several places to see if it has any significant variation in width.
Maybe tighten the V roller eccentrics while the Z slide is at the bottom of the stroke (where it does the majority of the cutting).

Ross

Typo, thanks viz

Ross

That does make sense. The rail grinding on the z slide is a little better than on on the x and y but still by no means exact. I had thought they were certainly contributing once again as we had tightened the concentric bushes as much as we could with the slide up.

When I see this cutting pattern, it's clearance some where. If you take your router in your hands, and you put some force on it, you must be able to move it.
put a magnet holder and a dial indicator to the different axis and figure out where you clearance is.
springs should be any problem to get, if you buy a longer spring, make it shorter. if you can not find the wright strength, mount 2, check my building log, I explain with pictures how to create the right spring. Yes I am spoiled, there's one street in the middle of Taipei with 4, yes 4 specialized sping shops, and a shop where I can buy teflon next door, but even across the supper marked in my naberhood is a shop run by 3 ladys were I can by the proper springs it's open to 22.00 in the evening.

that rail, I can see from 16.000 km away that's not straight at all
I was able to make a rail within 0.03 mm (not inch!) flatness. check my building log to see the measurement device I used.
When I should have this kind of cutting quality, I should not be able to sleep.:eek:

At the moment were just working out how to re-fix / re-drill the x racks and rail so that it sits both square to the rail from end to end and not tilted down its length. We actually just
tried shimming with a few washers on the outer edge to see if it corrected the slight tilt but it didn't seem to have much effect. The problem there is the bolts that hold it on actually go through the angle section right on the curved part of the angle and due to this have not been drilled strait (it looks like they were drilled from the bottom though).

Rik - in fairness Ive not been sleeping properly due to this b****y machine. And yes there is definatly some play in the z axis but we have been having a hard time tracking it down. As for the rails we know they are not good but at the same time they should not be causing errors in our calculation of steps per mm and this is my biggest concern right now. We can work on the slop but unless we can get it running different cut/travel distances correctly its absolutely no good to us replacing the rails.

We have ordered springs this morning so they should be here Monday or Tuesday. You are lucky to have supply shops like that locally. There are only a few specialist spring suppliers nationally over here. When I get a chance this evening i'll have perusal of your thread.

Keep up the good work.

OK try 31.831 steps per mm. Sorry about the typo adding to the chaos.
We use Gerald's gear steps calculator, it is an excel spreadsheet to calculate the steps per mm.
It is so powerful it can make dumb guys like me look smart :)

Ross

I think you've proven that you aren't loosing steps, so I wouldn't spend money on encoders - you can read more opinions on encoders in general here in the forum.

Try Ross' long calibration method, and see how that works out. He seems to be working on a good theory, which is that pinion wobble is making it impossible to get accurate measurements for calibration at short distances. A 3mm error over a 1m calibration set is a more accurate result that a .5mm error over 150mm calibration set.

Hi brad the last calculations / test measurements were over 980mm in both x and y as
our shorter measurements were not giving us good results on larger measurements even though they were less than +-0.1 repeatedly. So we moved to long measuments after borrowing some 1m long vernier calipers. We were able to get the machine repeatedly to cut the 980mm it to within +-0.1mm. so the results matched the program. So after running these test and setting it accordingly so that x and y correlate over this distance we decided to run a couple large panel test cuts of 600x600mm squares.
what we got was basically 601 in the x and 598 in y? It just doesn't make sense.

Apologies the numbers are wrong that I gave you for your DP20 rack and pinions.Went down the wrong path there not paying proper attention and specified the steps for module one rack and 20 tooth pinions.. but you already know this :o
Ross

No problem Ross. Yeah had twigged onto the mistake.

Mach 3 system has a variable that might affect that.
In the General Config page you will see:
Motion mode
(constant or exact)
Distance Mode
(absolute or incremental)

Try toggling into exact and absolute mode and try your cutting profile. Did you see a change from the original results?

Will try that tomorrow once we've got the racks back on properly. Once again its not proving to be an easy task. Thank sean