Constructing Janus, by Dirk

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Re: Constructing Janus, by Dirk

Postby bdring » Sat Sep 03, 2011 8:37 pm

I had a similar problem once and found that the last mirror needed to rotated a bit. If you must shim, you can also shim just the mirror holder.
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Re: New Belts installed and start of alignment

Postby BenJackson » Sun Sep 04, 2011 1:33 am

dirktheeng wrote:However the beam is not reflected strait up and down when it comes off the last mirror. I am not sure why at this point. However, I suspect that my entire gantry is out of level. That is, it is the top is rotated to the rear if the axis of rotation is colinear with the travel axis of the y axis. That is going to be a little bit hard to adjust as there isn't any adjustment in that direction. I am thinking about shimming the rear bearing on the cart up a little bit.


Two factors prevented my final mirror from pointing straight down:

1. The biggest effect was due to the entire final mirror/lens assembly being rotated in its assembly. The assembly actually comes apart (the two halves unscrew) and by rotating it you can swing the final laser spot through a huge angle.

2. My gantry was also twisted: The end plates were square to each other (as a result of assembling on a flat surface as recommended) but the 2040 beam was tipped forward so that the carriage angled down toward the front. I actually fixed that first before realizing (1) and now I think you could cancel that error with adjustments of (1).
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Laser Head Mirror way out of square

Postby dirktheeng » Sun Sep 04, 2011 4:40 pm

Gents,

I will try to rotate the mirror like you said and see if I can get the beam to be more square to the table. I hope my gantry isn't twisted down the length.

Here's a pic showing how bad it is right now:

DSCN4155.JPG
bad alignment
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Re: Constructing Janus, by Dirk

Postby bdring » Sun Sep 04, 2011 5:07 pm

I think you would see that much of an angle in the gantry. Place that square on the gantry carriage for a visual reference. Could the mirror in the holder be off?
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Re: Constructing Janus, by Dirk

Postby BenJackson » Sun Sep 04, 2011 5:44 pm

Just remove the lens retaining ring and then unscrew the entire lens holder from the bottom of the plate. When you loosen that the entire final mirror will be free to rotate and you can easily fix that aim. I think I had to use soft-jaw pliers to get it apart but it's definitely just threaded. I had originally assumed a pre-aligned press-fit but when I hit an even worse slant problem than yours I realized it must come apart.

After pre-aiming with a red laser I only made about a 1/16th turn on one thumbscrew and the CO2 laser was all set. I never had any trouble like hitting the inside of the air assist. I don't know that I would have gotten everything nearly so well aligned without being able to see the problems (especially the one Dirk is illustrating).
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pre-alignment is done

Postby dirktheeng » Sun Sep 04, 2011 7:29 pm

All,

I completed the first round of alignment. The last lense housing did need to be turned as Ben and Bart were suggesting. That took care of the misalignment and got it into the vertical plane that contains the axis of travel in the y direction. It was still somewhat off in the other direction after I got it turned, so I shimmed up one side with 2 pieces of note card stock. I cut them out in a U shape to fit around the screw housing. Seemed to work pretty well. It's pretty good now.

Also, I found that my gantry is not noticably warped (if at all). I set up my laser line to be aligned with the cart travel at a sligt angle tilting forward. Then I moved the cart to put the laser spot on top of the line right in the middle. I moved it from one end to the other and it stayed right in the middle. This isn't a really accurate way to test this, but it does show that if there is anything there, it isn't bad.

Here's a pic showing the aligned laser head on the cart.

DSCN4157.JPG
aligned lense housing


you can see the shim on the right side.
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Ready for final alignment

Postby dirktheeng » Sun Sep 04, 2011 10:46 pm

All,

Janus is ready for the final alignment. I decided to put the skins on to reduce the risk of an accident and to stiffen up the frame. I moved it out into the middle of the room and got all the screws in. One tip you can use to get the screws in the vertical posts is to use a bent piece of a small zip tie to support the bottom of the assembly nut as you put the screw in. It slides in the small gap between the frame and pannel and you can pull it out easily once the screw gets started. I got the screws tight all along the top and then moved the whole thing into the place where I wanted it to be for final position. I re-leveled the the frame with my laser level (I love that thing) to be sure everything was flat again and then tigthened down all the screws on the pannels to lock it in place. The whole frame is noticably stiffer now. The only skin I have left to put on is the top rear skin and I want to make the holes for the hinges into slots so I can take it off easily.

Oh yea, when I put the laser tube in place of the red laser, I loostened only 1 screw on each holder and put the tube in place, made the connections, and tigthened it up with the same screw I loostened before. Hopefully this will have retained the alignment with the red laser, but we will see.

I put the door in place so I could make sure I didn't have clearance issues with the beam and also to hold the switch down so I can manually fire the laser from the front pannel.

Now I have to cut out some targets so I can finish the alignment. I wanted to use hot glue to tack them in place, but I think I can manage with tape as I forgot to get a hot glue gun this week after work.

Here's a pic of the laser in all it's glory:

DSCN4158.JPG
Laser ready for final alignment


I will probably do the alignment tomorrow as I want to have a nice dinner with my wife and maybe watch a movie together. She has to work at the hospital tomorrow so I won't see her on my day off and I'll have plenty of time to work tomorrow.

I only have a few things left to do:

1) put the dore pannel in
2) size the table up and put it in place
3) make the window pannel thing for the vent
4) install the fan and ducting
5) cut stuff!
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Disappointed with the LOUD air pump

Postby dirktheeng » Sun Sep 04, 2011 11:11 pm

All,

I ordered one of those 45 LPM air pumps. I got it in the mail this week and man is that thing loud. It is by FAR the loudest part of this rig. I re-examined the air flow needs and calculated that a flow rate of only 0.36 lpm will give a nozzle velocity of 150 ft/min. I am seriously considering buying a small, quiet fish tank pump. If all we need is enough flow to protect the lens from any smoke, this will more than do it. I will probably try to find one that will give a flow rate around 5LPM. Reducing this flow rate will also probably help keep the lens from rattlign loose.

Does anybody want to buy this pump off of me? I paid about $45 for it and would sell it for that.
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Re: Disappointed with the LOUD air pump

Postby twehr » Sun Sep 04, 2011 11:20 pm

dirktheeng wrote:All,

... If all we need is enough flow to protect the lens from any smoke, this will more than do it. ...


Air also helps clear the kerf when cutting acrylic, so you will want more volume than you calculated for. Air on acrylic lets you cut cleaner and faster.
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Re: Disappointed with the LOUD air pump

Postby dirktheeng » Mon Sep 05, 2011 12:10 am

twehr wrote:
dirktheeng wrote:All,

... If all we need is enough flow to protect the lens from any smoke, this will more than do it. ...


Air also helps clear the kerf when cutting acrylic, so you will want more volume than you calculated for. Air on acrylic lets you cut cleaner and faster.



maybe I'll wait to make a decision until I see it cut, but it is pretty loud. I could put it in a foam lined box with some air flow to help keep it cool.
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