1mm off when cutting

it's my first post here so - Hello everyone!

I would like to ask you if you could help me with wrong size after cutting. I spent whole weekend trying to figure out what's going on there and I've decided to look into internet and ask here also.
My problem is that machine is always 1mm missing both in X and Y direction when cutting. With the same adjustments on cnc controller (estlcam) and with the same miling bit (3mm diameter) I did several tests:
- cnc program for 50*50mm square result was 49*49mm
- cnc program for 100*100mm square result was 99*99 mm
- cnc program for a plywood tray handle like in the picture below has a final dimensions 99mm (where should be 100), 24mm (where should be 25), 319 (where should be 320) and so on.
uchwyt.jpg

Finally I did the tray handle with good dimensions by cheating on machine by preparing .nc program with 4mm diameter bit (but real diameter ounted in the spindle was 3mm). But it's not a solution....

The software (both for .nc files preparation and for control of cnc and program execution) is ESTLCAM. Microstepping X/Y/Z are 1600/1600/800. Distance per revolution are 59,94mm/59,88mm/8mm. In jog mode when I put "X100" the machine is going exactly 100,00mm in straight line, when I put go "X1200" the result is 1200,00mm. In Y axis is the same, not matter if travel is small like 100mm or long like 1200mm, so everything seems to be allright with "distance per revolution" and microstepping.

When the machine is executing some .NC program, altought it's written correctly, the results are always 1mm to small on X and Y. It's not up to resulution of the steps (distance per revolution), because in jog mode everything is fine

I've just found few posts on some forums in the internet like "My OX CNC is always cut 1mm to much in xy", but unfortunately there is no any solution or just a comment how someone who had asked figured out finally what was going on..
I've taken note of that those question were up to big size OX (like 1000 or 1500mm size) and double belt solution....... so maybe this is a key: not really smooth movement because of "tight" assembly of Xtreme Solid Wheels on double belt + decceleration before corner when .nc program executing + 85% of intertia for X and Y motor set in ESTLCAM = reason of lost dimension(losts steps). When trying to measure travels in jog mode "X100" means go straight 100mm - so there is no corner, so different decceleration way and value.. Maybe. I don't know. It's just my idea right now.


Have anybody heard about this problem and solution? Thanks in advance!!



My machine is built with
- 1500mm*1500mm v-slot profiles,
- double belt (GT2-3m timming belt, pitch 3mm, 6mm width) & ACME rod 8mm pitch
- Nema23 178.5oz/inch on each axis + 20 teeth pulleys
- V-solid wheels
- Arduino Uno R3 (original one, not a clone) + 4*TB6600 set to 1/8
- all wires with shielding:
- from Arduino to TB6600 (step and dir) grounded on TB's GND pin
- from nema23 to TB6600 (A+,A-,B+,B-) grounded on TB's GND

 

This printscreen it's from Designspark

 

exactly. I did several test.

Because I supossed that maybe there was some issue with "Part" (for outside shape) and "Hole" (for inside shape) option I also tried cut by engraving mode - I put the deep of engraving equal to board thickness. I used proper strategy of toolpath for inside and outside contour. Result was also bad - 1mm missing.
After that I prepared g-code by myself in notepad and the result was the same - 1mm missing both X and Y....

 

Forgive me, I hadn't enough time to give some feedback to you. I checked that lower belt (i'm running dual belt system) and it's not well attached to the v-rail's slot. When the carragies with pulleys were moving along the X or Y axis then there was something like wave in the bottom belt, don't know how to describe it better. Anyway bottom belt was not attached in every place and sometimes it was going up like a wave when carragie was moving, sometimes was flat and seemd to be attached, but wasnt. It was also the reason of the resistantce in movement of X and Y. I'm not still sure about if it is the reason of 1mm off in every cut, but seems to be. I agree with @Christian James that running .nc programs can unmask some problems and despite of good results in jog mode there are some problems with program execution. When any of carriages it's not able to move smoothly then during .nc programs execution the decceleration distance and percentage factor of inertia when turining on the corners have a lot in common with lack of milimeters in milling parts.

Within today I will re-assembly belts and test.
I will let you know final results.

Regards

 

@Gary Caruso did you see it ? It's made with 0.13mm adhesive from 3M.

When i was assemblying dual-belt for a first time I did use VHB acrylic foam tape from 3M which was 0.6mm thick. The result was that the surface of upper belt that has contact with pulleys was not so hidden in the v-slot, was a little bit to high. I suppouse that tape thickness may be depend on belt model or producer, maybe.
Yesterday I removed lower belt, quickly and without any problem because the belt wasn't well attached to the v-slot. Something bad happend with VHB tape. I assembled once again the carragies but with single belt and seems to be much smoother and lighter to move on. Today I'm going to make some test.
Seems that dual-belt was my problem, but still not so sure. I will let you know later.

@CNCMD Previously machine's set-up was with dvr8825 stepstick and grbl shield. I was doing then only some engraving things and other stuff which didn't require accuracy. I did a precise milling only once with some problems also, but I finally did. I was considering this dificulty of not getting precise part like fault of lack of amperage for Nema23. So I can sum it up and say: no, machine never was too accurate

 

@Rob Taylor I've just finished milling of mentioned by you square doughnut. Outter square was 70x70mm. Inner was 20x20mm. .NC file prepared in ESTLCAM and next machinned with ESTLCAM Controller. The results was 69x69 and almost 21x21mm. I did it in PCV 5mm thickness, depth 2mm by one pass.

Before I started milling I double checked v-wheels&eccentric nuts, also the tensions of belts. I also put a two long rullers and checked in JOG mode if machine is always getting desired point. X100 was exactly 100,00mm, X1300 was 1.300,00mm. Same for Y. Evrthing was allright.

Next I started to do milling manualy: I was typing ccordinates one by one. diam. 3mm end mill.
F1000, S10000
AZ-1
X73
Y73
X-73
Y-73
AZ-2
and so on, up to the AZ-5,1

The result was........... 69x69!!!!!!!!!

I was suprised, moreover I had checked milling gauge of 3mm diam. end mill few days ago when problem had occured for a first time and width of the milled line was exactly 3,00 mm. I've checked it once again now by milling deep (about 2-3mm) line on my baseboard and another line on PCV and the width was 3,00mm, exactly like diameter of end mill.

I did also some tests with DOC 0,5mm in PCV (so it was 10 pases for 5mm thick pcv). By .nc program or "manualy", with high speed like 2m/min and slowly 0,5m/min.. results were the same .....69x69.

I do not understand anything now what's going on....

Tomorrow I will probably try with another CAM and controller...... but from the other side i'm not convinced that it could solve my problem when JOG mode is very accurate, milling kerf exactly fits the diameter of end mill.

I wish that solution for this problem was so simple...

Best regards

 

Can the spindle and the bit wobbling cause that deviation of dimension, when gauge exactly fits end mill diameter?

 

@CNCMD my values are:

Nema23 (200steps/rev) + GT2-3M (3mm pitch) + 20teeth pulleys

- Microstepping set on TB6600: 1/8
- Steps per revolution (in ESTLCAM controller) X/Y/Z: 1600 / 1600 / 800
- Distance per revolution (in ESTLCAM controller) X / Y / Z: 59,94 / 60,06 / 60,00 - values set by making different travels (100mm, 500mm, 1200mm) - and they match always in jog mode, for X10 or X1200 machine goes exactly where I want to.
- Max feedrate: 9 000 mm/min
- Acceleration distance: 10 mm (tried also different)
- Intertia: 75% (already tried with values from 0 to 99%)

But to be honest I do not understand what's wrong with my steps adjustment...

@jeffmorris endmill 3mm is set up in Estlcam as 3mm diameter endmill. I tried also with 2mm diameter endmill which was set up as 2mm in Estlcam Tool List. The result was the same. 1mm off.

There is no backlash on Z-axis. Spindle mouting is PLA printed with 100% infill, attached to V-slot Z axis profile with bolts. The spindle is attached to PLA mouting by pipe hose clamp hoops. It's robust

 

When I said robust I was thinking about spindle mouting made of PLA. There is no flexion on it. I would never say that cnc router made of aluminium profiles is a robust structure
Just a while ago I've done some test with the square doughnut one again (70x70 outter, 20x20 inner), but I set up in Estlcam the diameter of the endmill with value of 3,5mm - so I've cheated machine a little bit. Real diameter of bit was 3,00 mm. Milled line on the baseboard had a width of 3,00mm. Next I've launched program.
The results are: 70x70 and about 20,4 x 20,4.. something more than 20mm). I'm going crazy

 

OK, so look. I put 60,00 both for X and Y. I cut a 2x2 square, than measure and calculate new distance per revolution value. I put the new value and after programming controller I start milling. 2inch x 2inch square is exactly 2,00 inch x 2,00 inch. OK, but then I would like to cut 5x5" square (without any changes in the set up of controller like) and after milling I'm receiving 5,5 x 5,5. In jog mode when I say X58,2 (2") then the travelled distance is 58,20mm. When I put X100 then machine goes +/- 104 mm. Your solution it's not a key. I tried it few days ago because I was considering for a while my new set up with TB6600 like something different, unregular, where more important is distance per revolution value measurment during milling than in jog mode, but no. It's not working like this.
Last two thing to check now: another controller like grbl panel (or something else? appreciate your recomendiations) and spidle (from electrical side).

I'm going for a short vacation tomorrow so I will not have a chance to play with OX next days, but I promise to go back here and give you all the response what is the reason.

Thank you
Regards