EMC - bad dimensions

[Smooth90]

I am running a very basic setup with my fireball v90 but a slight problem has hit me and I'm entirely convinced that it is because of emc.

I have a powerful stepper setup with a 40v power supply. The machine also has anti backlash nuts.

My problem is that my machine is consistently cutting things to smaller dimensions than they should be.

Here is my G code

( Made using CamBam - http://www.cambam.co.uk ) (

That code SHOULD* make a 1x1 square with two holding tabs, and .52 inches deep (two .26in passes). However no matter how many times I look at the g code and verify it the machine never cuts it correctly. I have made about 10 (1x1 squares) and every single one of them measures .975 x .990 inches. No matter what I do I cannot get 1.000 x 1.000 which is what I want and the code says.

The machine is practically brand new (2 months) and has had very little work through it. Although I have had a few nasty collisions with the bit/step blocks. The bit snapped every time and didn't hurt the machine. Other than that it is new. I looked into backlash being the problem but these cuts are too consistent and too large for that to be the case (plus I have anti backlash nuts).

Meshcam seems to do better than Cambam and gets closer to the dimensions think 1.000 x 1.010. The only reason for this is that meshcam is for 3d and does lots of little moves to accomplish the same square rather than long stretches like cambam does (faster) (2.5d). Meshcam takes 3 - 4 times longer to cut the square than cambam does.

This makes me think that emc is having an error somewhere inside it where it is not timing something correctly resulting in bad dimensions.


So what could be wrong with emc that is causing it to do this??

ANY help would be greatly appreciated I am in a bind here and have no idea what to do/try!!!

[wendtmk]

Incorrect tool offset? Incorrect tool diameter? Are you sure the scale for each axis in your ini file is set correctly? Could be a number of things.

Mark

[lerman]

Who configured EMC for you?
Did the system ever work?
If yes, when happened immediately before it stopped working.

Some possibilities:
1 -- If it never worked, look at the timing of the signals to the stepper. (That's why the who configured question is important.)

2 -- Check that the "anti-backlash" nuts aren't too tight. That could cause the stepper to miss steps.

3 -- Try decreasing the feed by a large amount. A factor of five or ten would make for a good test. If it works then, it is probably a mechanical problem.

Talk to the people on the emc-users irc channel.

Ken

[Smooth90]

1. I used the step config menu and followed the instructions they had on their website.

FireBall V90 EMC2 Step Conf

My latency test comes out to around 10,000 - 12,000 ns at the absolute max.

I am going to go play around with the step time and space settings to see if they have any effect on the issue.

If did in fact work a little while ago I have a video on youtube that proves it.

YouTube - Fireball CNC V90 Lexan Milling
The coins fit perfectly and the square measured exactly 3.000 x 3.000 inches when it was complete.

2. I will remove the lead screws on the x/y axis and completely reassemble the anti backlash nuts. Clean them out to as I think that some mdf dust may have gotten in them.

3. Once I have finished the above I will try to heavily reduce the feedrate and see where that gets me.

Thanks for the reply's!

Will post back in a few hours with results.

[MrWild]

If you have two different dimensions for a square pocket, chances are you have developed lash. If EMC worked, there is no way that I know of that it would start causing problems. About the only place EMC might give a hiccup of this nature is if the steps per inch were changed some how in the step config file. Open your config file and see.

[Smooth90]

So I just finished tearing down the X, Y, and Z axis. Everything was cleaned, inspected, and reassembled. The backlash nuts look fine. I compared the X axis nut to the Y axis nut and couldn't tell the difference. They were dirty and had mdf dust inside them as I had thought and now they are clean. The only real problem/issue I noticed was that the x axis nut block underneath the machine was a bit loose. I fixed that and its perfect now.

The machine runs great on all axis's now and has very smooth motion.

Once I connected it all up I ran another 1x1 block test with some .35in thick LDPE plastic. I chose to use slow feed rates this time.

The first test I did was at 25 ipm.

The block came out to be.

X axis - > .994 in

Y axis - > .990 in

Then I cut a second block at an even lower feedrate 10ipm.

X axis - > .994 in

Y axis - > .995 in

After cleaning out everything it seems to be working better but remember I also heavily reduced the feedrate. I don't think it is lash at this point because lash that is .005 - .010 inches is pretty bad especially at such low speeds. On top of that its practically a new machine, with anti backlash nuts again very unlikely that I've developed such bad lash.


There is also more evidence that I've thought of which disproves it being a hardware malfunction. The machine obviously cut the piece in the video perfectly....now it can't do that.....why???? Well the only thing that happened which was stressing to the hardware between now and then was a bit snapping off. This bit snapped while it was being pushed by the X AXIS. So if that movement/snap damaged anything it would be the X axis and the Y axis would have been completely left alone. However we not only see incorrect dimensions on both axis but there is greater slop on the Y axis the axis that was not subjected to high stresses.


At this point I am thinking that the settings from probotix need to be tweaked or that my computer is the issue. I am running on a laptop and have read that power saving features can interfere with emc trying to use the parallel port.

Two more things to try

Tweak the settings

EMC on a desktop


Will post back soon when I have tried these things.

[ninefinger]

Did you check the couplers for the screws to the stepper? If a set screw is a bit loose on a flat it can present itself as backlash. Ask me how I know.

Mike

[MrWild]

You got rid of .015 and .020 in lash. If it had been the fault of EMC there would have been NO change from your efforts. What you have here is a "Carburetor problem." What's that? Well, a carb problem is where you don't know how one works so any problem a motor has, you are sure has to be in that blasted carburetor. I know this sounds like a simplistic answer, but after seeing it time and again (the mind set) I can only make one suggestion to you. Buy yourself a copy of Mach. You aren't going to be happy until you do, and will just keep blaming EMC. Heck even after Mach forces you to tune the last of the lash out of your system you will still tell folks how EMC let you down.

Once you have Mach installed, try running your square pocket in the other direction. I predict interesting results. Don't bother trying this with EMC as the results you get, will cement your conviction it is a EMC problem for sure. What to expect with Mach running in the opposite direction is a larger pocket. Say 1.015 x 1.020.

Don't assume a crash in just one direction only screws up your machine in a single axis. It sounds like the Z has a problem as the lash seems to be equal for X and Y. It sounds like the Z axis slide has gotten loose, the acme nuts or thrust bearings are loose, or the spindle has gotten loose. By using the lash compensation in Mach you will be able to dial all of your problems away and then can trash EMC for all that listen. Of course I'd tighten up all slides/screws and check the spindle for looseness before I blamed EMC, but the lash compensation in Mach will let you not worry about machine looseness.

It's time to buy a new carburetor for your motor because until you do, you won't look for the real problem elsewhere.

[Smooth90]

I had never made flats on the motors so I went ahead and did that today then set the screws on the flats. Right now they are perfect well connected and secured no way there is any movement.

So I did another 2 tests after this and found that at 10ipm I got very close to perfect. It was .996 x .998.

I am probably just going to switch to mach 3 now (trial version) and see how it runs. If I can compensate for the lash and get down to +- .001 inches it will be fine.

Thanks for the input!

Will post back after I've tried mach 3.

[ninefinger]

Originally Posted by Smooth90 The only real problem/issue I noticed was that the x axis nut block underneath the machine was a bit loose. I fixed that and its perfect now. I don't think it is lash at this point because lash that is .005 - .010 inches is pretty bad especially at such low speeds. On top of that its practically a new machine, with anti backlash nuts again very unlikely that I've developed such bad lash. There is also more evidence that I've thought of which disproves it being a hardware malfunction. The machine obviously cut the piece in the video perfectly....now it can't do that.....why????

You found one mechanical problem and it solved a bunch of your missing travel (ie not software), .005 to 0.010 lash is not that much for a machine with acme screws and anti-backlash nuts to develop. The machine hasn't been static since that video - it wasn't you making the video was it? If not then I'm guessing the machine was purchased and shipped from one place to another.

Sounds like you need to do a bunch more investigating of the mechanical aspects of the machine before chasing software gremlins.

Start by measuring backlash - not a cut. As Mr Wild pointed out a cut can have other variables at play that can affect the cut ( sloppy z axis travel, undersize cutter, loose spindle bearings...) Use an indicator to measure the backlash.
Other sources of "backlash" - the bearings supporting the screw - can the screw move back and forth at all?
Being a stepper machine it can loose steps too. That is why there are recommendations to slow it way down. IF its loosing steps going slower will usually help. If its loosing steps then you need to look for why - is there binding in the travel? Are the nuts too tight? Are the slides clean? etc.

[Smooth90]

I went and ordered a pci card adapter so that I can use one of my beefier computers with mach 3.

I also ordered a dial test indicator w/stand that is accurate to .0005" this way I can test to see if runout is the problem whether it is in the collet, collet nut, bit, or spindle bearing I will find it.

If runout is not the the issue then I will have mach 3 to compensate for backlash and if that works then backlash would have been the problem from the beginning.

Now I just have to wait to get the stuff but the problem should be resolved.

[MrWild]

Well, no... The problem itself will be masked, but not resolved. Still, if it makes you parts that pass inspection at the end of the day, then that's good enough. Be careful about lash compensation in Mach. You can use it to such an extent the entire machine becomes sloppy. The indicator is a tool you should have already. It'd have pinpointed the problems without the need of a Mach Motion purchase.