One-Week Build

General discussion of laser machines

X axis movement

Postby twehr » Mon Mar 28, 2011 9:33 pm

Problem solved. That behavior was during an initial test before final routing of wires. When I disconnected, routed, and reconnected the wires, it was working fine. The only thing I can think of is the first connections had a single strand of wire shorting someplace. But you have to admid, it was pretty cool - self-reversing edge detection. :mrgreen:

FYI - limits were not yet connected. I was controlling only with the arrow keys. Mach 3 DRO showed constant movement in only one direction, depending on which direction i started with, even after reveraing. The drives are 5042's from light object, just like some that kelling tech sells (the all just self brand generic drives).

I am on to the gantry movement now. Works well for the most part. There seems to be a lot of audible vibration in the y axis that is not present in the x axis. X is smoth and quiet. Y is pretty loud. I'll hit that again in the morning.

Once the movement is all good, it is on to the laser itself and optics. I would love to think this is going to all be wrapped up in the next couple of says, but suspect it will be later in the week.
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Re: One-Week Build

Postby bdring » Mon Mar 28, 2011 10:30 pm

Crazy Motors: I had a similar experience once where a pin backed out in a connector, so three out of four wires were connected. It tended to run in the direction of least resistance, but roughly and with no power. Be careful though. That can destroy many motor drivers.

The Y axis is definitely audibly noisier than the X. I think the frame is amplifying the normal noise of the stepper. I tried to mitigate it a little by adding long slots to the bracket.

Stepper are notoriously noisy. Many people have written software to play music with them. Makerbot even sells a cork gasket for that. It looks like that could be easily laser cut. Thingaverse has files for them.

ybrkt.JPG
ybrkt.JPG (10.75 KiB) Viewed 14478 times
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Day 5 - the one we want to forget

Postby twehr » Wed Mar 30, 2011 12:17 am

Today was one of those where for any step forward, you were forced to take at least two back.

The focus this morning was to finish up the y axis noise issues.

[movie - very noise y-axis at 100mm/sec]


First I made sure that everything on the frame was tight and not introducing rattle from the motor vibrations. That helped a bit, but not nearly enough.

Taking a clue from Bart's post, I made a cork gasket. Ended up making two and sandwiching the y motor mount. Probably overkill, but I think it helped quite a bit. The gasket sandwich is shown in the next video. You will also see/hear the final solution - changing speed. The primary cause of the vibration was the speed that I was testing at - 100mm/sec. Appears that is the perfect speed that matches the natural frequency of the frame. Faster or slower and there is a huge difference in the sound level. Watch the video and witness it for yourself.

[movie - quieter at 300mm/sec]


All sounds good, right? Successful day, right? Well, let's not get carried away.

Seeing the Y axis running at 300mm/sec (actually had it up to 500mm/sec and it worked find), I decided to see what the X axis could do. After all, it has less mass so it should really scream, right? Well, it should have. But, the x axis is limited to about 125mm/sec. Obviously, that is not going to work and something has to be wrong. What was wrong was that the laser head carriage was putting too much drag on the motor and can't handle the speed.

Why is it inducing drag? Drag is certainly a function of the tightness of the rollers on the v-rails. I already had it as loose as it could be, just barely taking any slop out of the carriage. But I was always setting it in the center of the run. And indeed, in the center of the rail, all works great. But on both ends (left more than right), there is a lot more drag. Adjusting for proper fit on the ends, leaves a lot of slop in the middle. Only thing that can cause that is misalignment of the two v-rails. Very close inspection shows a slight gap on the ends between the v-rails and the gantry extrusion. Both rails were flat on the rail on one surface, but not the other. I was inspecting with a mirror and will post pics when I get it torn apart to put in the replacement. The cause was probably inconsistent pressure on all parts of the rail at time of gluing. The gantry is pretty long, and holding the length of the rails is not easy (at least for me).

I had a piece of 2040 that could be cut to size, but I still needed the v-rails. Ordered from McMaster Carr today to be overnighted for delivery tomorrow. Will have to cut the rails and glue them tomorrow, then replace the bad piece on Thursday, after the new one has had a chance to sit for 24 hours. At that point, I will also try to remove the old rails, just to see if it is possible in case someone else ever needs to salvage a bad glue-up.

The remainder of today was spent getting the extrusion cut to size and playing with the electronics, installing tube mounts, and the like. I installed and ran the wiring for a motor for the z-axis. Later I need to get another sprocket, belt, and controller. But those will be easy to install when I am ready. Nothing very big, as we still have to be able to tear down the gantry and rebuild it before I can go ahead with the remaining optics and the laser itself. Tomorrow, before the new v-rail arrives, I will probably go ahead and mount and wire the DSP controller. Wanted to wait till everything else was done for this, but the mechanical setback means I'll be pushed for time on Thursday and Friday.

It was a frustrating day, for sure. But going ahead without everything working correctly at each step is not smart. I would rather give up some time now and be happy when I am done, rather than be disappointed later.
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Re: One-Week Build

Postby r691175002 » Wed Mar 30, 2011 12:43 am

I did the same to my x-axis but I managed to catch it before the glue had completely set. I jammed the rails against the extrusion by tightening clamps around the ends and applying a bunch of pressure.

Depending on what glue you used you might be able to save it.
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Re: One-Week Build

Postby bdring » Wed Mar 30, 2011 1:30 am

That's a shame about the v rail gluing. Getting those parallel is very important. I used to use epoxy, but I was always nervous about the thickness of the glue and that was only going to be a mil or two different. I like the superglue because you can actually feel the rail register on the extrusion. Maybe something got behind the rail. Do a no glue test fit first next time to make sure everything is right.

This is why I want to get a custom extrusion. A perfect fit at about $3 a foot.
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Re: One-Week Build

Postby LeonS » Wed Mar 30, 2011 1:42 am

Ok. You got my attention. I am going down to mic my rails. Yikes :o
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Re: One-Week Build

Postby LeonS » Wed Mar 30, 2011 1:58 am

My X rail varies by 0.21 mm from the middle to the ends. My left Y rail seems to be at about .3 mm wider than the middle of the rails. I hope that is close enough.

I suspect I was paying more attention to the middle of the rails when I was squeezing them after applying the glue.

Tim, how much variance did you have in your X rail?

- Leon
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Re: One-Week Build

Postby twehr » Wed Mar 30, 2011 2:06 am

I did not want to remove the current rail until I get the new one built. However, I can measure what I've got first thing in the morning and post that.
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Measurements

Postby twehr » Wed Mar 30, 2011 1:30 pm

I measured the width on the X v-rails this morning. Here is what I found.

V-rail Measurements.png


The big question is: How much deviation is acceptable? Not an easy question to answer.

The measurements and corresponding performance on the y axis would indicate that up to .008" (.203 mm) should be OK. Obviously, the .011" (.279 mm) and .013" (.330 mm) I am getting on the X axis is not. If I were to try to set a standard, based on what I am seeing, I would say something in the neighborhood of .0078" (.200 mm) should be the max deviation. It would certainly be useful if Bart and others, once they get to that point, would measure and report on performance.

All in all, I am convinced that Bart's extruded rails are the way to go. Bart - I'll be happy to buy the first set and put them in this machine to test.

Visually, however, the gap is barely noticeable. I tried to get shots in a mirror, but it just was not clear enough, so I will wait for that till I get it out of the machine. From what I could see, it appears that it is only one rail that has a problem - the front rail - the longer one. I am tempted to go ahead and pull it and see if it can be salvaged before I build the new one. We'll see.
Last edited by twehr on Wed Mar 30, 2011 1:36 pm, edited 1 time in total.
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Re: One-Week Build

Postby twehr » Wed Mar 30, 2011 1:35 pm

LeonS wrote:My X rail varies by 0.21 mm from the middle to the ends. My left Y rail seems to be at about .3 mm wider than the middle of the rails. I hope that is close enough.

I suspect I was paying more attention to the middle of the rails when I was squeezing them after applying the glue.

Tim, how much variance did you have in your X rail?

- Leon


Leon. Be sure to see my last post. I suspect you may be able to live with the X rail, but the Y is pretty close to the deviation that is causing my problems. That being said, I am pretty anal about the speeds the machine is capable of. I hate limitations. Engraving needs a wide range (especially on the upper end) of speeds to handle different materials. Cutting, on the other hand, needs finer control at the button end. Yours may be perfect for cutting.

It may also be that, since the y is driven from both ends (albeit with a single motor) that the .3 mm will not limit your y speed as much as it did my x speed.
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