Vibration Senstivity`

qa

#1

Can you talk a little about how sensitive the GF will be to external vibrations?

For instance…my GF will be housed in a building that is about 130 years old. The floors are “uneven,” think 2 inch differences in the relevant room. Think shims. Think about floors that have more give than newer buildings.

For instance…on another thread where I asked about this someone else was talking about how the GF will be in a building that is 150+ years old which vibrates when a large truck goes by.

How sensitive will the GF be to these things? Will I have to top toe around when I am using it?


Are self made vibrations an issue?
#2

Just put it on a foam rubber isolation mat. They are pretty inexpensive (or just get foot pads for it). We all used to have these under our dot-matrix printers to prevent the reverse of the printer shaking the room…

[edited: typo]


#3

I believe another thread said there is an air inlet on the bottom so you might want to do isolation with plywood on top to be sure not to restrict the cooling air flow?


#4

So the individual feet pads would leave the bottom open (actually more open than sitting on the table)


#6

Stepper motors are very hard to fight with when they are active. And Dan said there is a double belt system, so that should also be pretty rock solid.

Your primary concern with vibration will almost certainly be the material you placed in the forge moving around. Get a few strong rare earth magnets and you should be set.


#7

That’s a good point about fixing materials. There have been a few mentions in the forum, especially in regard to having a magnetic cookie tray for fixing things in place. A couple of other laser discussion groups have showed various jigs and clamps to assist in this aspect. Hadn’t thought about any vibration during the running of the machine displacing the material.


#8

Material movement is a pretty large factor in deciding on order of cuts as well. Always engrave before you cut, since if you have a warped piece of material, once you cut something free it may drop a distance.

The air assist can also cause flimsy materials to shift around. When I tried cutting a cotton shirt, it curled back over itself a little bit.

Closed lid will keep you from my major problem… touching the material yourself on accident and moving it mid-cut.


#9

I have been planning to put the Forge on a wheeled cart. But this thread got me thinking about problems with that. Since the laser tube is on the moving crossarm, I imagine it has considerable mass, and if the mechanism starts and stops rapidly, the reaction forces produced might cause the whole cart to move. That might cause issues with shifting the material being cut. Or worse, it might interfere with the ability of the mechanism to position the laser beam accurately. I know that when working with servo motors, it is important to anchor them in a very specific way to avoid instabilities in the positioning feedback loop. Dan, is this an issue I should be concerned with?


#10

I’m not sure the laser is on a moving arm. CO2 lasers seem to increase in length as power increases and 40W seems to be about 30 inches. The width of the glowforge is only 38 inches, and the bed is centered so if the laser moved it would give you and approximate 4 inch working width.

Also from a cooling view I really don’t think you want the complexity of a laser moving around.

From the videos it looks like a set up with a few enclosed mirrors and a focusing lens with some great ideas to track material distance, scan invisible(probably printed with UV reactive ink) barcodes, and align the cut on the moving “head”. On the head I suspect there is a low power laser diode that can be used for the distance tracking.


#11

@ihermit2

But the position of the laser is largely irrelevant to my question. The moving carriage has mass regardless of whether it carries the laser.


#12

I plan on placing mine on a rough built table of framing lumber and plywood I made several years ago. Because of the room geometry where it will reside, and if I want to use the pass through slot, it may need to move to different places in the room. Therefore, I will be placing locking casters on the table legs this weekend. Between the locking casters and the decent mass/solidity of the table, I’m not concerned about it. Of course I’m using a table I built and not a rolling computer stand or similar. But either way, I’ve seen Dan say he wants an accuracy of .001", and you’re not going to get that if the servo motors are generating enough momentum to be rocking the case. I expect their early prototypes would have pointed out any problems in how they managed ramping their motors.


#14

I hadn’t considered the stopping force for the entire gantry (and yes, @ihermit2, the whole laser tube moves. Dan said they have a custom tube which is shorter than normal for the wattage. The tube moving means that it will be considerably harder to modify this laser with a stronger tube, a common first modification on other cheap laser systems).

This is not a 3D printer. Those machines move rapidly in a direction, lurch to a sudden stop, then move rapidly in a new direction. This is done in quick succession, and when doing fill on a narrow segment, can seriously vibrate a frame.

The laser though, when doing fill does a full horizontal line at a time. So the gantry only moves after a line has been completed, and only moves a very tiny (kerf width) distance. The distance is so minor that speed isn’t really needed, so I doubt it is used.

When doing non-fill, the laser is moving along programmed arcs and straight lines. I suppose someone could do a short zig-zag along the horizontal, and that could lead to some vibration issues akin to a 3D printer. But such a cut seems highly impractical, so I doubt it will come up often.


#15

yeah I totally see that now after reviewing the open house highlights http://www.youtube.com/watch?v=w7CghG_6NS4

not sure how I missed the big tube shifting front to back before.


#16

When I bought my 3D printer I was surprised about how violent the shaking of the machine was. My main concern was that it would shake itself apart, but it was also obnoxios to listen to and I worried about the effect it was having on print quality. So I looked around for a solution and found these vibration pads for washing machines.

http://m.lowes.com/pd/Kellett-Shake-Away-Vibration-Pad-(Black)/1078011?http://m.lowes.com/pd/Kellett-Shake-Away-Vibration-Pad-(Black)/1078011=

My printer still moves, but its now a gentle swaying and the noise is much better. I can’t really tell if it had much impact on print quality (I never tried to do a comparison test.)

If I have concerns about the shaking of the glow forge I will pick up another pack and forget about it. I’m hoping the glow forge is more solid like my shapeoko 3 cnc machine and won’t require the pads.


#17

We’re using steppers, not servos, so you have less risk of control loop oscillations. (I was kind of bummed about this because I like PID controllers, but Mark showed me the logic early on and he was right).


#18

I also found this