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Darian S
09-20-2010, 04:51 AM
Hi, Looking for help please with spindle alignment as i think it is the cause of the following problem, Example: when cutting a circle (anyshape for that matter) with every pass im removing 4mm of material which leaves really noticebale lines in my work almost .5 to 1mm of a differance on each pass but only on the rear sides of my shapes the -x and -y so to speak?

I have tried differant cutters speeds and feeds and still the same (maybe less burrs some times)


Any ideas welcome, Thanks

See pics attached as they may explain it better than me, both pics are of the same part just differant sides.

doorknob
09-20-2010, 06:30 AM
This is just a guess, but the problem may be related to the reversal of the direction of motion of one of the axes - if so, then it might be due to uneven backlash or binding on one of the axes, perhaps also including missing one or more stepper steps as a result.

Darian S
09-21-2010, 05:57 AM
Hi Thanks for your advise, what do you mean by missing one or more stepper steps?.

Cheers

doorknob
09-21-2010, 10:32 AM
Your CNC router table probably has one stepper motor that moves it in the X direction and another stepper motor that moves it in the Y direction.

A stepper motor rotates the motor shaft a fraction of a turn (a "step") each time your computer sends a step command to it. Depending on the design of the motors and driver electronics used by the table, it may take anywhere from a couple hundred to a few thousand steps to rotate the motor shaft by one complete turn. Depending on the type of mechanical linkage between the motor shaft and the table, to move the table one inch may require ten or more complete turns of the motor shaft.

If there is any mechanical binding of the moving parts of the table, or too large a weight load to be moved compared with the power rating of the stepper motors, or if the motors are commanded to step more quickly than they are able to respond, then it is possible that the motor will sometimes "lose a step", that is, the motor will not be able to rotate by a step when it has been commanded to do so.

In such a situation, the computer will not know that the motor has lost one or more steps. Consequently, the actual location of the cutting tool on the workpiece will be different from the location where the computer thinks the tool is working, and the pattern cut into the workpiece will not be identical to the pattern that the computer commanded it to cut.

Darian S
09-21-2010, 07:43 PM
Hi Cheers for reply

I have two motors on my x axis as they are facing each other i have wired one the opposite to the other so they both drive in the same direction, i have looked futher into your advise and found that Mach3 will drive another slave axis (x)in my case do you suggest this is a better way to drive two motors? i guess it would be as then the both receive there on steps right?

More ideas welcome esp on how to set up a slave axis.

Thanks for your help

D

doorknob
09-21-2010, 08:02 PM
I do not have direct experience with Mach3 - perhaps someone who does can chime in here.

As for running both X-axis motors in parallel vs. using a "slave" axis drive, there's not much that I can suggest - if both motors are identical, then it should be OK to wire them up in parallel, as long as doing so does not exceed your driver electronics' current ratings. If you go to a "slave" axis drive configuration, then I expect that you will need to add a separate drive circuit for that motor.

Unless you are exceeding the X-axis driver's current rating, I'm not sure that I'd look to that as the most likely cause of your problems. Rather, I'd guess that backlash or misalignment of driving forces between the two X-axis drives, or binding in the X axis travel, or even a loose drive coupling might be a more fruitful thing to investigate, particularly in the region where reversal of the direction of motion takes place.

Having said that, I'm hardly an expert in these matters, and there are many more capable folks here who may be able to give you better advice...

ger21
09-21-2010, 08:03 PM
Do you have two motors on opposite ends of a single screw?

Darian S
09-21-2010, 08:12 PM
Hi

The two x motors are on ether side on the gantry, they both have there on stepper motor drivers, i have paralled the the feed to both of these units but reveresed the direction on one of them, i have since figured out how to make a slave axis of the X output in Mach3. I will reconfigure the machine toinght as post results thanks very much

D

Darian S
09-21-2010, 08:20 PM
Hi Also i might add that both stepper motors have there own small gear box so speak in order to get more tourqe i guess, on both sides of the machine is a linear rail that the gantry sits on this gets drive from a rack and pinion setup.

stk2008
09-21-2010, 08:22 PM
Hi am I reading this right you have two stepper motors on one on each end of a lead screw?.

If so is your machine that big you need two motors?.

You probably have one motor setup wrong or slipping?.
Got any pics of the machine?.

Thanks

Darian S
09-21-2010, 08:34 PM
Hi

Sorry if i havent made it very clear,

two motors drive the x axis
two linear rails down ether side of the machine
no lead srews but instead a rack drive (toothed rail) down ether side of the machibe.
The motors are on ether side of the gantry and a pinion from the gear box makes contact with the rack and thats how it moves.

The machine is 1200/2400 bed wise and x,y,z and i have a c10 breakout board driving the stepper motor controllers.

Will take pics and post
Cheers

Aryantes
09-21-2010, 11:28 PM
Make sure your table is perfectly perpendicular to your spindle.

I had this same issue and still do as I haven't found the perfect way to align my spindle.

I had chatter marks and chatter sounds but only on half of the circle.

The best thing to do would be to get a planing bit and surface your entire spoilboard if you think that the spindle is not aligned perfectly.

I haven't tried this yet but it should work for me but I am in the process of switching out a few parts.

jsheerin
09-22-2010, 02:37 PM
I would recommend driving each x motor controller from its own pins on the parallel port and using the slaving feature in mach. Some controllers (G540 for example) require more current than some parallel ports can put out. If you parallel two inputs, then you're drawing double the current from the parallel port which it might not like. When I had this type of problem, I had missed steps going in one direction, so I'd try this first.

I don't think from your picture it looks like your spindle is out of alignment. One way to test this quickly is to use a large diameter bit and make almost full width cuts back and forth in x, then in another area go back and forth in y. See if you can feel ridges between the cuts. If you can, your spindle is not aligned correctly to your machine. This is not something that's solved by surfacing your spoil board. You need to rotate the spindle slightly, possibly in two planes. I used some aluminum shims to do this on my router. To test this more precisely, use a dial test indicator on an extension bar mounted in your (unpowered) spindle. Put the dti towards +x and zero the reading. Now turn it 180 degrees to -x and see what the reading is. If it's still zero, it's aligned in that direction. If the reading is not the same (within whatever tolerance you want to hold), then adjust the alignment. Do the same in the y direction. If your spoilboard is soft, it can help to place a 123 block or some other type of gage block on top of the spoilboard and take readings off of that.

Darian S
09-23-2010, 06:32 AM
Hi Thanks very much for the replys, ill try these things over the weekend and post results

Cheers

D

mlabruyere
09-28-2010, 04:57 AM
I used some aluminum shims to do this on my router.

Where did you get the shims? Mine is off by .01" and it leaves rigdes....drives me crazy

jsheerin
09-28-2010, 11:12 AM
The grocery store. :> I took some aluminum foil and folded it up until I had the right thickness. It was a somewhat trial and error thing - shim, test, calculate new shim from results, fold up a new one, test, etc. but it only took a few tries to get the right thickness.

Phife
09-28-2010, 11:16 AM
Where did you get the shims? Mine is off by .01" and it leaves rigdes....drives me crazy

buy a set or two of feeler gauges, they make excellent shims and come in a large range of thicknesses to get the shimming just right.

dseitz
09-28-2010, 11:29 AM
Hello, I am sorry to bother you, but I am new to this site and can not figure out how to post a question. Any help is appreciated.
again sorry to bother you but this is the only way I know how to reach someone.
Thanks Dseitz

jsheerin
09-28-2010, 12:12 PM
Got the forum you want to post in, for example:
http://www.cnczone.com/forums/forumdisplay.php?f=48

There's a button that says 'new thread' on the left at the top and the bottom of the list of posts. Click that, from there it's pretty self explanatory - basically the same as what you just did.

mlabruyere
10-25-2010, 11:04 PM
The grocery store. :> I took some aluminum foil and folded it up until I had the right thickness. It was a somewhat trial and error thing - shim, test, calculate new shim from results, fold up a new one, test, etc. but it only took a few tries to get the right thickness.

Ha! That's what I ended up doing....took 3 sheets to get it aligned...worked great!