First I want to say this website has been a huge help learning this cnc plasma stuff. I just wish I would have found this before we bought a Burntable, and I think that may be my problem. I am using a Burntable with CandCNC Bladerunner dthc 2 system and ohmic sensor and a Hypertherm Powermax105. Software is Corel draw, Sheetcam and Mach 3. I am cutting 16ga steel with fine cut consumables and have tried using regular and low speed fine cut by the book. I found a post on this subject that Jim Colt posted about cutting a square check it then turn it 45* and do it again and doing this there was very little difference, the 45 was a little worse but over all they are both good. The problem seems to be on smaller stuff and art. I have checked and tightened all of the belts, and pinion gears and made sure there is no play in the gantry. It seems to be worse after I tightened everything. In mach the acceleration is set at 40 and the velocity is at 450 on x y and a axis. I am going to try to attach pictures and hope it works. In picture 3 it is showing a cut from the x axis and it looks good. Any suggestions will be appreciated.
something is definitely not right. I would double check everything to make sure it is tight and that there is no play at all in your gantry or torch. A couple other things to check is to see if you have a bent shaft on one of your drives. The wiggle appears to be consistent throughout the cut so I would suspect that something is either bent or wobbling as it moves.
Another thing to check is slat-wave. This is when your slats of your table move back and forth while you are cutting. Try to watch while the cut is being done to see if the slats are solid or if you can spot what is wiggling.
Is the cut only wiggling in one direction or on one axis? It is kinda hard to tell from the pictures. In one pic, it appears that it is wobbling in both the x and y axis....but in the other you state that it is only in the Y axis. If it is only one axis that is wobbling, that narrows the search down a lot.
I haven't seen or used a Burntable at all. But haven't heard much good about them. Hope it is not in the design of the table. Good luck and let us know what you find.
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As soon as I saw the pictures my immediate thoughts were mechanical freeplay, when I read the second line I saw a name familiar with problems posted here which sort of makes it very likely.
The main reason that your getting this on 16 gauge is the extra speed at which you have to travel. Also I have seen it posted here that Burntables doesn't support finecut use but as you have upgraded to CandCNC this should alleviate this problem.
To check for slat wiggle or movement as mentioned by Gamelord, place a glass of water on the sheet anywhere and watch to see if the water ripples. You can also use a stethoscope to listen to the movement and track where it's coming from.
I would guess that it's most likely rack to pinion meshing so have a real good look at that and when you think the spur gears are tight, undo them add some loctite and retighten them just a little more.
The only other time I have experience a wavy cut but nowhere near as severe as yours was when I had a damaged swirl ring. You say you are using finecuts, are you using the complete set of consumables as listed.
Murray
Thanks for the replies; I did have play in the torch and gantry actually a lot of play in the torch (cheap plastic torch holder) but I tightened everything up and it got worse. It does seem a lot worse on the gantry axis. Is it possible to have the pinion gear to tight in the rack? As far as the consumables everything is fine cut. I really feel that it is mechanical but was looking for suggestions. Maybe tomorrow I will loosen it back up a touch and see what happens. It was cutting ok (not great) before but as I said when I tightened it all up it got worse. I thought it should have been the other way around, get better when tightened .
Here are the things that will cause the severe waviness your pictures show:
- Mechanical backlash on the x and y axis. Loose gear mesh, loose or flimsy motor mounts, loose bearings etc.
-Slats moving...this usually only shows the waviness on one axis. Lay your hand gently on the plate while it is cutting...if plate is moving at all...then the slats need to be secured better.
-Z axis oscilation will do this. Put the height control in manual mode....if the problem goes away then you have some height control tuning to do.
-Motor and drive tuning. There are adjustable acceleration rates and gains....contact your machine builder for optimal settings. These usually require fine tuning based on the mass of each axis and your cut speed requirments.
Sometimes it is beneficial to mount a pen in the torch holder on a spring loaded device and trace parts on a piece of paper. This can help steer you to a particular axis....and on a few occasions I have seen the waviness disappear with a pen tracing, yet comes back with the torch on.....this, of course, would indicate an electrical noise issue which likely would require a call to the machine supplier.
I'm not really familiar with the Burntable first hand but I'm assuming it is a stepper drive system and as you say there are belts it is running reduction drives to the pinion gear meshing the rack with some sort of roller or bearing carrying the axis.
I have only really read bad reports on the brand and also was a couple on here talking of miss match and poor workmanship.
Do the pinions sit neatly in the rack?
Are the surfaces where the bearings/ rollers run straight, clean and smooth? you can check by stretching a piano wire or similar along the rail to make sure it's true in both directions.
Do the belts fit the gears properly?
Are the gears etc. machined the correct size for the shafts to ensure they are running true (not out off round) ie if a gear with a 1/4 inch (0.250 ") bore is installed on a 6 mm (0.2362 ")metric shaft and tightened on one side with a grub screw this will push the gear over or off center by 0.069 A metric belt on imperial gears can have the same effect.
Being steppers, with the power turned off you should be able to move both axis by hand quite smoothly and without huge resistance, you should also feel any lumpiness.
If you torch mount has any play in it at the fixing point, leverage factors will intensify this movement considerably at the cutting point ie if the end tip of your torch is 6 inches from your fixing point, every thou of movement at the mount becomes 6 thou at the cutting point.
So to give a long way of getting around to answering your question as to whether it can be "too tight", my answer would be yes if you don't have everything meshing and contacting 110% right. It's probably going to be a bit of a compromise in trial and error to fine tune it to be the best it can with what you have but looking at your pictures I thing you have a far way to go to get it to a stage that I would consider acceptable. I'd be spending a bit of time getting all the mechanicals fine tuned before trying to fire the torch, look, listen and measure.
Hope this helps and stick with it.
Murray
I tried the pen and paper thing that Jim suggested on this 8? star with the hole in the middle and it looked ok so I decided I would try to cut it with thc off and it looked ok then I tried it with thc on and this is what it looks like. Not perfect but a lot better than yesterday but I have not changed anything. I guess it don?t like working on Mondays.
Another test I tried to cut a name drawn in corel but it did not cut good so back to the drawing board with the pen and paper. I done the square then turned it 45* done it again and then I drew the name Donna which is about 5" long 1.5" high. looking at the squares it doesn't seem too bad but the name looks bad. Is that to small to try to cut?
OK that has told you quite a bit, more importantly it probably isn't as it really rules out the cutter, THC and electrical interference as these are not present in the pen test which brings you back to chasing the mechanical or motor tuning problem. You can now save burning up and wasting material and consumables and use ink and paper which is much cheaper.
Go back through the above and eliminate as many of these as possible until you find the cause or combination of causes.
Another thought, was the star you cut from a different size piece of material to your top pictures ? ie thickness and physical sheet size and location on the table while cutting. How did this piece compare in size and location to what you had your paper stuck to to do your pen tests?
Murray
The star was cut from the same sheet as the first pictures. I cut a couple from different areas on the sheet that were scrap and they both looked about the same. I done the name in a couple of different places with the same results. I found a bolt rubbing the inside of a pulley that I will fix tomorrow and hope that is the issue. This design is terrible. To adjust the alignment on the shaft you can?t get to the head of the bolt so the manual actually says to grab the THREADED end of the bolt with pliers and tighten the nut. I will make the repairs tomorrow and let you know. Thanks for the suggestions. Also the pen and paper is the trick thanks for the tip on that Jim.
That looks a lot like torch ocilation when the Z axis is TOO FAST and overshoots the target voltage setpoint. Try lowering the Z axis speed and accel by 50% then retest.
Or simply watch the torch cut and notice IF it is going up and down, up and down when cutting. Use proper Eye protection when veiwing the arc.
I went through everything fix the bolts that were rubbing the back of the pulley, checked for play in everything tried to get the belts aligned like they should be. All of the gears seemed to be meshed good and the pulleys are tight so I made another drawing of the same name with almost identical results. After checking again one of the gears had a very small amount of play so I tightened it and tried again and it got worse. Then I loosened it back up a touch and no difference. It seems like every time I try it it gets worse. I don?t think it is torch oscillation because when I do the pen and paper test the THC is off. Anybody got any other suggestions? I am at a total loss.
Seems like you are not hearing what is said.
Torch ocilations can be caused by the THC hunting to much.
The pen test does not move up and down because there is not signals from the THC to make it.
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To do a pen test that is used to compare the machines ability to stay on path, then make sure you are moving the pen at the same speed as the plasma torch would be cutting. At slower speeds you may see no waviness.
The pen test cannot test the height control....which only functions when the plasma arc is cutting. Oscilation in the height control (z axis) can be felt while cutting if you put you hand (carefully) on the torch during a cut. Z axis oscilation is a function of height control tuning, and it will cause severe waviness in a cut.
Me thinks distortion that bad from torch hunting would be immediately visible but its easy on a Bladerunner DTHCII to turn the THC off as it cuts. Did you replace the BT gantry single motor with the two 620's in the Bladerunner kit? The single motor they use is grossly underpowered for that gantry weight (over 100 lbs) What that does is effect your acceleration numbers. Poor acceleration begets rounded corners and bad turns. That being said, It looks to me like something mechanical. With the motors on and locked grab the gantry on each end and try to move it. Any slop will show up as movement . If you do get movment on either end then trace the drive trin back as you move it and see where the movement stops...the component before that is loose. Even a small amount can cause trouble. Check the torch holder by wiggling the bottom of the torch. Vibration in the torch can cause wiggly cuts but typically you see them when you change direction or a short distance. The pulleys and spur gear have to not wobble
If you did modify the table and mount two motors on the gantry (one one each end as we suggest) then make sure they are both tuned the same in MACH. Binding can cause some ugly cuts. Does it jog smoothly if you do both X and Y?
You are welcome to post on our Support Forum.
Your hand lightly on the torch can sense a lot of things. I sometimes will even close my eyes to focus on the sense of feeling. Even a hand on the gantry will show up poor motion.
Thanks for all of the help. I did change all of the motors and install the extra one on the gantry and I was totally surprised when I fired it up after the upgrade. There is a little movement in the plastic torch holder that I cant get out of it and I think that may be my problem. After all of the suggestions on here I have gone over everything and found a few issues, after correcting them it is a lot better but still has a little bit of wave in some of the cuts even with THC off. Unfortunately I think that is what we are stuck with until we can get real table to install this bladerunner kit (Best part of the table) on. I did find out don't always trust the drawing no matter how simple it is that will make you chase your tail. Thank you all for your help.
tcaudle wrote:Me thinks distortion that bad from torch hunting would be immediately visible but its easy on a Bladerunner DTHCII to turn the THC off as it cuts. Did you replace the BT gantry single motor with the two 620's in the Bladerunner kit? The single motor they use is grossly underpowered for that gantry weight (over 100 lbs) What that does is effect your acceleration numbers. Poor acceleration begets rounded corners and bad turns. That being said, It looks to me like something mechanical. With the motors on and locked grab the gantry on each end and try to move it. Any slop will show up as movement . If you do get movment on either end then trace the drive trin back as you move it and see where the movement stops...the component before that is loose. Even a small amount can cause trouble. Check the torch holder by wiggling the bottom of the torch. Vibration in the torch can cause wiggly cuts but typically you see them when you change direction or a short distance. The pulleys and spur gear have to not wobble
If you did modify the table and mount two motors on the gantry (one one each end as we suggest) then make sure they are both tuned the same in MACH. Binding can cause some ugly cuts. Does it jog smoothly if you do both X and Y?
You are welcome to post on our Support Forum.
Your hand lightly on the torch can sense a lot of things. I sometimes will even close my eyes to focus on the sense of feeling. Even a hand on the gantry will show up poor motion.
This is some good advise, along with all the rest in this post!!!!!!!!!!!!!
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