New Design Ideas - Looking for Feedback

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New Design Ideas - Looking for Feedback

Postby mikegrundvig » Mon Oct 31, 2011 3:24 am

Hi all; I'm working on a design for my laser cutter and am looking for feedback on the design. I'm going with a range of at least 4' by 2' which makes me think the "gantry-mount tube" is the right way to go. With a large working area, I don't want to have the alignment problem with flying optics. To that end, I'm making everything sturdy and solid. I'm using linear rails for the X and Y axis - I don't have the motor mounts and such figured out yet. I'll get those figured out as I move along.

I'm thinking something like this for the mirror mounts.
mirror-mount.JPG

I've designed a pair of grooves into the top and bottom plates to ensure that they align perpendicular to the gantry. Then I've cut channels at 45 degrees to ensure the mirrors are aligned to each other. I plan on drilling a hole in the gantry 8020 to let the beam pass through.

Here is a pic of the tube mounts:
laser-tube-mount.JPG

Notice how they wrap around the 8020, this will ensure the tube is aligned accurately and consistently. This combined with the mirror mount design should cause the mirrors and the beam to be consistently aligned.

Here is just a quick picture of the frame as it stands. Lots more to add to it but I figured I'd include this still.
full-frame.JPG


I'd love any feedback and advice. Thanks!

-Mike
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Re: New Design Ideas - Looking for Feedback

Postby bdring » Mon Oct 31, 2011 12:35 pm

The tube does not need to be perfectly aligned, just stable. The distance between the tube and the first mirror and second mirror is static, you just need the second mirror to be adjustable.
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Re: New Design Ideas - Looking for Feedback

Postby BenJackson » Mon Oct 31, 2011 5:50 pm

I think you should allow for the cooling tubing in your harness. It needs to be well supported so it doesn't break off the glass nipple it is attached to.

Also I think that the water outlet tube (which is the front of mine, based on some diagram I found) should have the tubing exit on the top so that bubbles are more readily forced out.
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Re: New Design Ideas - Looking for Feedback

Postby bdring » Mon Oct 31, 2011 6:25 pm

You might want to consider some safety covers as well, since you will often have your hands in the area of high voltage. Interlocks cannot always be 100% trusted. You should also try to keep the electrodes as far from metal as possible. I would use 2 inches of clearance and maybe double that for creepage as a guideline
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Re: New Design Ideas - Looking for Feedback

Postby mikegrundvig » Wed Nov 02, 2011 3:23 am

Thanks for the great advice and feedback!

The tube does not need to be perfectly aligned, just stable. The distance between the tube and the first mirror and second mirror is static, you just need the second mirror to be adjustable.
Yeah, I've got it this way mostly so I can create a single mount design and it works for both sides. It's just to avoid having to create one and mirror it and machine them separately if they were asymmetrical. Lazy, I know :)

I think you should allow for the cooling tubing in your harness. It needs to be well supported so it doesn't break off the glass nipple it is attached to.
Great idea, I've added a pair of .38" holes in the tube mount that can be used for this purpose.

Also I think that the water outlet tube (which is the front of mine, based on some diagram I found) should have the tubing exit on the top so that bubbles are more readily forced out.
and
You should also try to keep the electrodes as far from metal as possible. I would use 2 inches of clearance and maybe double that for creepage as a guideline
Not sure these can both be done with my current design. I figure I'll rotate the tube to move the electrodes as far as possible from metal. The mounting rings are easy enough to move as it is but it will be a juggling match to go between the two requirements.

So here are two new pictures showing where things are at now. The mirror mount has been changed a lot. There was no reason to support sliding diagonally (no idea what I was thinking at the time) so this design allows only for sliding the mirrors in-and-out (perpendicular to the gantry). Their angle is enforced with slots cut in the holder and a pair of 1/8" dowel pins on the top and bottom. In practice, this works very well for maintaining the angle. This will also support different sized tubes with nothing but a small adjustment in the future. I'm likely going to tweak the tube mounts slightly to contain a place for the HV wiring as well and to support larger diameter tubes directly.
Attachments
tube-mount-detail.JPG
mirror-mount-v2.JPG
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Re: New Design Ideas - Looking for Feedback

Postby TLHarrell » Wed Nov 02, 2011 3:31 pm

A couple of those parts look like they'll be a challenge to fabricate. The ones with the holes drilled in the ends...
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Re: New Design Ideas - Looking for Feedback

Postby mikegrundvig » Thu Nov 03, 2011 3:40 am

A couple of those parts look like they'll be a challenge to fabricate. The ones with the holes drilled in the ends...
Nah, it's not too bad. The trick is to align the vise accurately to the machine and touch it off so then when you drop parts in, their edge is already known. I use a laser edge finder and it's good to a few thousandths pretty easily and that's more than good enough for something like this.

To keep things super strong and rigid, I've designed a 90 degree angle brace to secure the most critical 8020 joints - specifically the 1530 pieces that make up the "box" in the center of the rig. It has the odd setup so it can be used for a joint in either direction.
90-degree-brace.JPG


I had, what I think, is a good idea for a coolant tank when going through the 8020 catalog. Apparently, 8020 is rated to >100 PSI so you can run fluids or gasses through it. I've designed this "cap" that will hold a gasket and plug the 1530 ends. One inch of 1530 gives you a volume of slightly more than 0.75 cubic inches. That means that the four stationary pieces of 1530 I have currently will give me a total volume of a touch less than 2/3rds of a gallon of coolant. Additionally, this volume is going to be a superb heat sink as it's part of the frame itself. I will augment the rest of the volume I need with a good quality PC radiator system. I figure with the frame tank as well as a storage/radiator combo I'll probably be looking at something on the order of 1 1/2 gallons of coolant at a minimum. Far less then the 5 gallon bucket many of you use but also a far more effective heat exchange so I think it should be enough. It will be easy enough to add in another tank if I need more volume. I also plan on plumbing in some temperature gauges just to be extra safe. The groove in the first picture shows where I would add some gasket material to seal things off nicely.
gasket-bracket-rear.JPG
gasket-bracket-front.JPG


Anyways, as always, feedback is appreciated!

-Mike
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Re: New Design Ideas - Looking for Feedback

Postby TLHarrell » Thu Nov 03, 2011 4:58 pm

So, basically your design will require fabrication of parts on a CNC mill.... that puts it out of my reach to fabricate. But maybe it'll spark some ideas for my unit when I get to designing.

I'm not sure adding a coolant reservoir in the gantry is the way to go. You still will need to plumb the supply and return lines to the tube through a cable carrier on the Y axis. It will add another +/-6 lbs to the gantry. And it adds another set of fittings to buy, install, test and maintain. Up to you, but personally I like to keep things simpler.

Might be more interesting to plumb it for air and use it as another means of air assist.
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Re: New Design Ideas - Looking for Feedback

Postby r691175002 » Thu Nov 03, 2011 5:28 pm

Initially I thought plumbing the coolant through extrusion was brilliant, but after some consideration I would be careful since thermal expansion over lengths of 4'+ will start to become a serious problem if the water hits 10-15 celcius above ambient.

I suspect that if the water is symmetrical on both sides of the frame (so that you avoid twisting/bending the frame out of parallel) it won't be a problem.

What size laser are you planning? If you run water through the extrusion you will not need a radiator. I cool my 40W tube with about a gallon of water in a bucket with a lid (no radiator) and it isn't a problem.

I have no idea how your design will perform but be careful regarding rigidity. Cutting a square at 60IPM+ will have insane accelerations and swinging a tube around like that will flex the extrusion.
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Re: New Design Ideas - Looking for Feedback

Postby BenJackson » Thu Nov 03, 2011 7:43 pm

I wonder if you could just loop it through the gantry and rely on the gantry as the heatsink.
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