Y AXES MALFUNCTION

[tdoz]

Hello everyone,

I use a 4 axes machine and recently I am having trouble with my Y axis.

I have attached :
1. Photos of how I locate Y zero and Z zero,
2. Photos of where I set the coordinates for the two axes to zero,
3. RhinoCam simulation of a simple test job,
4. G code for the simple job,
5. A picture comparing the codes for the top cut and bottom cut. Please observe that the A0 and A180 portions of the codes are perfect mirror images.
6. A picture of the end result.

It wasn’t having alignment problems like this before. I just don’t know what happened.

Your suggestions will be highly appreciated. Thank you.

Tdoz

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[tdoz]

Sorry guys.

I did not exactly specify the problem.

When I cut a path from the top halfway into the material and I rotate the material 180 degrees to cut the same path from the bottom, the two cuts do not align. There is some gap/distortions caused by non alignment of the Y axis no matter how many times I locate the Y zero.

Thanks.

Tdoz

[Jim Dawson]

Is the end dimension of the first cut correct? I'm wondering if the Y axis is losing position on the first cut.

[tdoz]

Jim,

Thank you for your reply.

I will check the dimensions by cutting a fresh measured sample and get back to you.

Best regards.

[tdoz]

Jim,

First, do you approve of the way I locate Y zero and Z zero as shown in the attached photo? If not can you recommend a better method because the little I know about CNC is all self taught.

While I got a better result this time I am very concerned that I have my cut slanted. I have drawn an exaggeration model to each attached photos as the photos alone do not present a clear view of what is happening.

The Y axis is gradually losing position as it moves down on X.

Please help.

Best regards.

[Jim Dawson]

Your zero location technique should be fine. It's just a starting point and the cuts will be relative to that position, worst case would everything would be offset from the desired location if zero was not in the correct location. But that would not affect the relationship between the X and Y axis which should run at perfect (theoretically) right angles to each other with the Z axis perfectly perpendicular to the X/Y plane. These relationships are (should be) built into the machine.


So the questions are: Do your X & Y run at right angles to each other? Is your 4th axis fixture lined up with one of the axes?

I can't really tell from your pictures what your setup looks like, need a little wider view to have a better understanding of your overall setup. My best guess at this point is that your fixture is not in line with an axis.

[tdoz]

Jim,

I have attached a wider photo.

Best regards, sir.

[Jim Dawson]

Wow! That's quite a machine, I've never seen one like it. Looks very well built. The picture is very helpful.

Let's assume that your machine is squared up properly and is mechanically OK. You should be able to check this by making a right angle cut and checking it with a square.

In order to get the tool paths to match on your part, everything must be machined square to start with. Since you are locating on the back side of the part, it also must be machined square, as must the backstop or fixture. The the part must seat in the fixture exactly the same way when turned over.

My best guess is that your part is not exactly square to start with. Even when working on metal working tools and locating very carefully it is very difficult to get tool paths to match like you are trying to do. If the part could be cut in one setup the result would be what you are looking for.

I hope this helps.

[tdoz]

Jim,

You don't know how much I appreciate your reply.

Thank you, sir, for complementing my machine. It is servo driven with ball screw on Z and Y axis, HSD spindle and it weighs 2 tons.

But all that gets me nowhere.

What I can add is that I have had it for a year and everything was perfect until 2 weeks ago.

When you say "part" do you mean the object I am trying to produce or do you mean part of the machine itself? Because I have been flipping models 180 degrees without any trouble.

Could the solution be in re-configuring/re-calibrating the machine?

Regards, please.

- - - Updated - - -

Jim,

You don't know how much I appreciate your reply.

Thank you, sir, for complementing my machine. It is servo driven with ball screw on Z and Y axis, HSD spindle and it weighs 2 tons.

But all that gets me nowhere.

What I can add is that I have had it for a year and everything was perfect until 2 weeks ago.

When you say "part" do you mean the object I am trying to produce or do you mean part of the machine itself? Because I have been flipping models 180 degrees without any trouble.

Could the solution be in re-configuring/re-calibrating the machine?

Best regards, as always.

[Jim Dawson]

By ''part'' I mean the object you are trying to produce. I didn't realize you had previously been able to do this and the problems just started recently. In that case it could be a mechanical or electrical problem. This would be the kind of error I would expect to see with an encoder losing position. Could be a bad encoder, or a mechanical issue with whatever drives the encoder.

I had a similar problem on my milling machine, the Y axis would drift on multiple cuts. Turned out the encoder drive belt was bad and was slipping so the axis was losing a very small amount of position on each pass.

Maybe a good test would be to cut a square, maybe about 4x4 inches, and step down about 0.025'' per pass. That way you would be able to see if the axis is drifting over a number of passes.

[tdoz]

Yeah! I can do that!

[tdoz]

Jim,

I didn’t do a 4x4 inch test. I did a 4x37 inch with the 37inch on the suspect axis. Attached are photos of the outcome.
It was smooth and crisp. The only error is a 0.19 degree off square. I don’t know if that is the drift you are looking for.

The manufacturer insists that the wood placement is not in the center. I have refused to believe them but unless you have a new suggestion I intend to do something extreme to see if they are correct.

Best regards.

[Jim Dawson]

That workpiece is nearly perfect. I think that pretty much eliminates my thoughts. Looks like a slight alignment problem in the X/Y axis but that's not what is causing the original problem.

The only other thing I can think of is to do the same test again, but rather than a straight line, put some curves in it and see what happens. It is possible that the coupling or pulleys could be loose between the motor and the lead screw. You might mark it with a sharpy and see if anything is moving there.

The test you have in mind might would be in order also.

[tdoz]

Jim,

This is my extreme centering of stock.

Measure the diameter of the recess at the center of the 4 jaw chuck (95 mm).

Clamp stock in place and turn the stock slightly smaller (94.5 mm) than the above diameter at about 4 inches from the head stock and tail stock ends.

Cut the stock loose.

Insert the turned end into the recess in the center of the 4 jaw chuck at both the head and the tail stock.

I will be happy to know if anyone can advise me of a better way to center stock.

Run your usual test of milling the stock halfway from the top, rotate the stock 180 degrees and mill the bottom to meet the top milling.

Same bad result which I have sent to the manufacturers.

They are thinking about it.

See attached pictures. I will love to show videos but somehow I can’t upload to cnczone.

Best regards

[Jim Dawson]

Are the chuck spindle centerlines in line with each other? I don't know how they would get out of alignment, but I'm running out of ideas here.

For videos, I upload to YouTube, then link in the post.

[tdoz]

Jim, please.

If you are running out of ideas, people like me should secure accommodation on death row in a prison in Texas.

Anyway, the chuck center lines are not in line (please see attached photos). Because the span between them could be up to 7 feet I don't think 1/8th or 3/16 gap will create all these problems. Do you?

This case file is still open and I am itching to get back to work.

Best regards, sir.

[Jim Dawson]

Don't jump off of a tall building just yet

Your second picture tells a big story. You have a spindle alignment problem. That amount of error is huge and would explain the offset in your cuts. Having said that, I have no idea how to do the alignment on your machine. I'm guessing there is a method of doing that, adjusting screws or something. It could be that the entire rotary axis of the machine is out of alignment with the rest of the machine. Some testing with a dial indicator is in order. I would start with the bed rails for the rotary axis, and work from there.

[tdoz]

Hello Jim.

I sent this reply two days ago and I can't see it again.

Anyway, the tailstock seats on four linear bearing blocks (please see the attached photos). While trying, unsuccessfully, to adjust the allen bolts I ended up removing the tailstock off the rails. I found one of the forward blocks is damaged and has lost all the linear balls on one side. So there is adequate room for the cutting lines to shift.

I have contacted the manufacturers for a replacement and I hope that should solve the problem.

Best regards, sir.


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