50w Tube replacement

[Roger Lueck]

>> I swear they mounted the original tube before assembling the cabinet. There is no freakin way you can get to the back screws on the rings. Not with any screwdriver I know of anyhow. I managed to get them loose enough and got the front two off so I was able to twist the upper ring off and over the old tube and back over the new one. Not a good scenario. I think I will look at designing up a different tube mount ring and 3D print it before I replace this tube again. <<


You are correct the back screws on my Chinese laser are a PITA also. The intent is to replace the mounts when I replace the tube in the next couple months when the current one dies.
Could you post a photo of your tube mounts, I'd like to see what you design to facilitate ease of removal/installation as well as the ability to adjust the tube alignment and height.

[Mike Audleman]

>> I swear they mounted the original tube before assembling the cabinet. There is no freakin way you can get to the back screws on the rings. Not with any screwdriver I know of anyhow. I managed to get them loose enough and got the front two off so I was able to twist the upper ring off and over the old tube and back over the new one. Not a good scenario. I think I will look at designing up a different tube mount ring and 3D print it before I replace this tube again. <<


You are correct the back screws on my Chinese laser are a PITA also. The intent is to replace the mounts when I replace the tube in the next couple months when the current one dies.
Could you post a photo of your tube mounts, I'd like to see what you design to facilitate ease of removal/installation as well as the ability to adjust the tube alignment and height.

I am working on a new mount design right now. Just beginning the process. Is your rear area 106mm deep and 131mm tall. The top overhang is 35mm and the bottom lip sticks up 13mm.

I put up some photos of the rear tube area here:
http://www.ipernity.com/doc/wolfie/album/973282

[Dave Sheldrake]

800mm is a 38 watt,

850-860mm is a 40 watt

1,050mm is a 50 watt

1,220mm is a 60 watt

Running an 800mm at over 14mA will kill it very quickly

On the ebay page it says 800mm, 850mm and 1,000mm all on the same advert

[Mike Audleman]

800mm is a 38 watt,

850-860mm is a 40 watt

1,050mm is a 50 watt

1,220mm is a 60 watt

Running an 800mm at over 14mA will kill it very quickly

On the ebay page it says 800mm, 850mm and 1,000mm all on the same advert

Once again the cat supplies very useful info!

The tube I pulled out (not knowing for sure where to measure) is 32-1/4" end to end measured from the outside of the glass at each end. That comes to 819mm. The pins (anode and cathode) are almost exactly 30". There really isn't a measurement thats obvious that is 31-1/2" (roughly).

Thing that I can't find marked on the 50w PSU is the output voltage and I don't have a HV DVM to measure it. Knowing the amps doesn't tell me the power consumed without the voltage. Suppose I could solder up a 100:1 resistor network and measure the voltage across that and get a rough idea. Then I could back convert to mA for 38w, 40w and 50w given what the PSU is supplying.

An ammeter is next on the mods list after I get this tube mount finished. Given the "ground" name I see on wiring diagrams, this is DC. I have a few old analog ammeters. Need to dig through the bin and find one with the right mA range. Hopefully a 0-50 which would suit the box if I upgrade the tube to a 60w at some point.

Is the "ground" off the tube actually a ground? I mean is it actually tied to the chassis ground or is it floating?

My instinct is to put the ammeter in the ground line as it has less voltage potential. Do you know if the KV from the HV lead would appear on the ground lead if the connection between the PSU and the ammeter should be severed/broken? If so, then I will have to insulate the rear of the ammeter case against KV potential. The wire used in this machine for the ground lead does not appear to be insulated against KV potential and looks like standard 400-600v hookup wire. Half thinking I should replace it with KV rated wire if the ground is floating.

[Dave Sheldrake]

the return wire is fine at the guage it is

The tube is a base 40 watt at that length, voltage between a 35 watt and a 60 watt is only 1 KV difference so no biggy, current though is important, drop an analog meter into the return line, make sure you don't go over 14-15mA MAX though Mike. You can reduce current either on a Pot through a small hole in the PSU (some models) or on an internal Pot inside the PSU (on others)

Those machines from Keuhi are well known for having the current pumped up to get 50 watts from a 40 watt tube, it tends to burn them out pretty quickly

0-50 mA will cover all tubes up to 280 watts

[Mike Audleman]

I hope you post photos of how you mount your laser tube as I will be replacing mine in the next couple months. You are correct, the screws in the back are a PITA,

Design Goals:

1. Fit my machine and tube
2. Solidly support tube
3. Can be installed without modifying the machine
4. Can be installed without being an octopus
5. Tube easily installed and removed
6. Easy to adjust tube position at any time
7. Use mostly common materials (preferably what I have on hand)
8. Easy to reproduce
9. Can be adapted for additional tube sizes (upgrades later)

Here is the design I came up with:


I rendered it out with various colors of glass material so its easy to see the different pieces and how they will go together. I will be printing mine from PETG all one color.

I am still tinkering with the fiddly bits but I have tested a preview print of the outer frame and the inner holder. The outer frame fits perfectly in my laser tube compartment. The tube holder is a little tighter than I want so I am re-printing it. Luckily I didn't dispose of the old tube so I have it to easily test the fixture with

I looked at several designs already out there and took clues from them to come up with my design.

The first was this one:
http://www.thingiverse.com/thing:420853

I liked the adjustment ability. Obviously he did get it mounted but I haven't a clue how. The C faces in and on my machine, the mounting tray is threaded so the screws must be put in from the top. I wasn't totally excited about the wireties either. From this design, I kept the outer/inner frame concept and the idea of the knobs.

The other item I took cues from was at about 20:30 into this video:
https://www.youtube.com/watch?v=NVzCMIq8dlc

I haven't laser cut any acrylic as yet (well, not successfully) so I am sticking to what I know. 3D printing. But I liked the compression ring he made with the 3 pieces of tubing. So my inner ring design incorporates that concept.

The result:

The outer frame can be installed in my machine from the rear and fits nicely. And, if you want to fidget you CAN install it with the tube in place. It does fit around a tube thats currently held in place with the stock brackets. Not easy. Can be done. Not a requirement of the design but more of a "hey, that works" option.

Once the outer bracket is screwed down every other operation can be easily completed. The tube can be put into the frame easily because the front of the square support goes on last so its an open C until the door is in place. The rings are loosely attached to the tube prior to putting it in the frames. Then you can access the bottom screw to tighten it once in the frame.

The door goes on last once the tube is in and is attached to the frame with a couple hex head cap M4's.

The hangar screws are standard M4 cap screws. There will be M4 nuts against the tube ring to lock the screws. Adjustment knobs contain a M4 nut. I used M4 heat set inserts in most areas. See the pattern Everything M4. That means you only need one allen wrench and a small open end wrench (or crescent or needlenose) for the locking nuts.

I beveled the bottom rear corner of the outer frame so your ground wire can be captive behind it if you wish. I am not sure if I will captive my ground wire there or not.

The designed parts will nest and print in a single run on my printer (though I have been printing each individually during the testing). I haven't tried but I bet I could get two on the plate if I tried hard enough.

[Mike Audleman]

So here is the first full print:


Being Easter, not sure I will have time to do much more with it today. Will get the heatsets installed and collect the other hardware I need for a final in-cabinet assembly test. Assuming that goes well, I should be able to get a WIP thing published to thingiverse sometime this week.

If anyone has any thoughts on changes speak up.

[Roger Lueck]

Mike,

Attached is a sketch of the dimensions for the laser tube compartment on my machine. It appears the space on my machine is very similar to yours, probably made by the same Chinese manufacturer, just different colored paint and name.

RogerBitmap in Laser Tube Mounting Bracket Bit Map.jpg

[Mike Audleman]

Mike,

Attached is a sketch of the dimensions for the laser tube compartment on my machine. It appears the space on my machine is very similar to yours, probably made by the same Chinese manufacturer, just different colored paint and name.

RogerBitmap in Laser Tube Mounting Bracket Bit Map.jpg

It appears like your compartment is much deeper than mine. I only did rough measurements with a MM ruler but I am pretty sure I wasn't off by 20mm. I will prep the compartment dimension test STL tonight and attach it here for you to download and print. Right now it doesn't have marks on it for either front lip or top overhang but I wll add those to it. Then you can quick print it and set it in your compartment to see how yours relates to mine. Yours being bigger is better If your measurements are right, and mine are too, yours is about 20mm deeper. If that is indeed the case, the mount will fit yours very easily.

[Mike Audleman]

Here is the work area template I made that fits comfortably in my compartment. I have marked the upper open area and the lower lip

Work Area Wolfie.zip

[Mike Audleman]

I got the heatsets installed on both brackets tonight. Unfortunately, I am out of longer M4 screws so I will have to hit the hardware store for some more before I can complete the assembly and swap out the old tube supports with these.

In any event, the first test fit went pretty well. The tubing I had selected was too stiff for my liking and the local science store didn't have the right diameter silicone and the latex tubing they had was too squishy and I felt it didn't support the tube rigidly enough.

But they had some gray 14" x 4" x 1/4" sticky back foam pad and strips of that seems to be a good fit. Holds the tube well without a lot of pressure so it should allow for any heat expansion and should make a nice vibration dampener. $1.50 well spent.








The tube clamp is screwed down to the tube and will hold it fairly firmly without undue pressure on the glass The outer frame is not (lack of long M4 screws). But in position, everything looks spot on for alignment and fit.

The tube is fairly well aligned as it sits now so the position once the new supports are put in place should be about where it is now. But I want to look into Russ's methods on tube alignment and these adjustable fittings should make that an easy task to properly square the tube up with the gantry.

[Mike Audleman]

I got to the hardware store. I wanted M4x30 all thread but they didn't have any. Longest they had was M4x25. But I think its just long enough. Barely.
Here is my assembled tube:


This photo album shows the assembly steps:
http://www.ipernity.com/doc/wolfie/album/974382


All in all, it took be a bit over an hour to assemble everything. Would have taken less time if I had collected all my tools in one place, had finished putting the clips on the annode and cathode wires (so they are easily removable) and wasn't taking photos during the assembly And, it would have taken even less time had I remembered to attach the hoses and bleed all the air out of the tube before mounting it (nudge nudge wink wink). I had to remove the tube, bleed it, and re-insert it. To remove the tube, you only have to take the top hangar screw out of the ring and remove the two door screws on each bracket. The tube will then come out in one piece easily.

As you can see, I decided to run the ground wire inside the outer frame so its a very easy task to lift the tube out as a whole without undoing the connections in the event bubbles do form later.

[John Lifer]

Nice. So are your brass inserts closed bottom? I see a nut on top of the insert, guessing locking into position. You are not going to be tweeking on this thing often, but if the insert is open to the tube, be mindful!!!!!!! that nut could loosen over time and you would have a bad issue. Otherwise things look good. Minor adjustments can be done to get perfect.

[Mike Audleman]

Nice. So are your brass inserts closed bottom? I see a nut on top of the insert, guessing locking into position. You are not going to be tweeking on this thing often, but if the insert is open to the tube, be mindful!!!!!!! that nut could loosen over time and you would have a bad issue. Otherwise things look good. Minor adjustments can be done to get perfect.

They are open. Frankly I wasn't aware there were closed inserts

And yes, the nut locks the screw to the ring so it can't turn as you adjust the thumb wheels. After adjusting the tube, you then lock it with the 2nd thumb wheel. So both the wheel AND the nut would have to work loose in the same direction (out) and work loose sufficiently enough for the screw to also work loose in the completely opposite direction (in) to allow the screw to get to the tube. Frankly I don't see that happening . But if thats a worry, I think a dab of removable LocTite (blue or purple) on the screw before running the nut down against the ring will take care of it.

Before I post the STL, I will be closing the screw hole on the inside. Right now the hole goes through into the inner tube area of the ring as I wasn't sure yet whether I was going to put a nut in from the inside or one on the outside or put the brass insert in from the inside or the outside so it was easier just to blow the hole all the way thorough on the prototype. After I close that, you would have to screw the screw through the plastic before it actually reached the tube.

Also, the inner diameter of the mount ring is 55mm. The tube is 50mm. So thats another 2.5mm clearance you would have to drive the screw before it could impact the tube.

Could you drive the screw in and shatter the tube? Yea, if it were long enough. M4x25 aren't long enough to reach the tube, not positive about M4x30 but I don't think so. I would have to get into the mesh app and measure from the outside of the frame to the tube surface and see what the shortest screw would be to reach the tube. But I am guessing that if you got the smarts to be able to print the parts on a complicated 3D printer with really HOT parts, dismantle your laser cutter without killing yourself on the HV, install the new mounts, mount the tube and ultimately align it correctly, I presumed you got the smarts not to screw a 6" long piece of all thread into your glass tube

I presumed a certain level of intelligence given the tool its designed to fit. I was going on the assumption that the type of person using this was not the type of person they printed "Open Here" on the top of cereal boxes for. Its not idiot proof. But, I didn't design it for idiots.


After I make some last minute tweaks to the design I will get the STL up on Thingiverse. I needed to enlarge the holes in the base of the outer frame as the mount screws they used on the original brackets were larger than I thought they were (M5 or M6, haven't measured them yet). And close the holes in the tube ring. Other than that, I think the design came out quite well.

I aligned the beam last night. I put 4 pips in a piece of poster board with the gantry moved to the 4 extreme corners and the pips are quite tiny and the "tape method" says its aligned well with the hot spots at the extremes overlapping such that I can't tell how much they are off, if at all.

I just got an idea . I will have to test it this weekend if I can acquire something from work here.

[John Lifer]

I'm not worried about it that much, You wouldn't do that! But ME on the other hand? 10pm, hurrying to get another tube up and running? Yep, hole right thru it. And the screw could be 10mm short and I'd still find a way to screw it up!!!!!
It sounds like you are putting the mount out for others to use, just close the hole on your 3D part and all is good! (yeah, you could find closed inserts, but not nearly as easy as thru threaded). And I thought it was a multi method of locking the screw.

Good job. It is different from what I've seen made up and actually works better. You have easy directional changes in both directions. And doing this way forces you to align better. ( at least in my opinion, you just can't drop onto a fixed base and bolt down as I did with mine and I DO have slight angled cut in the Y direction which makes me believe that the tube is not in same plane as the moving rail. I can't adjust the head on my machine, it has to be the tube. And I'm lazy)