Laser cutter questions. How to set focus?

[Adrian Page]

I'm still shopping for a laser. How do you set the focus on a Chinese laser cutter if you don't have an up/down motorized table? The laser I like wants $500 more for the up/down table and I think I can just block up the rotary fixture with a simple jig I could put in place of the knife bars. I just don't know how the focus is set. Does my plan have any merit? I would pony up the 500 bucks but I don't even know if I will ever engrave a cylinder. I need the laser to cut balsa and ply R/C airplane parts. I thought it might be nice to be able to engrave on a cylinder at some point but I have no projects in mind at this point.

Adrian

[David Somers]

Morning Adrian!

The way you asked your question makes me think you are mixing things up in what you are asking. I will start off by talking about the table and if I missed your point just say so.

The lens on a laser is fixed. The system does not focus like a camera might by adjusting that lens. Instead, to focus you raise and lower your object until the surface to be engraved or cut is at the correct distance from the lens. Unless I am mistaken, even though the table on the machine you are considering may not have a motor to raise and lower the object it will still have a crank system to raise and lower the table. Same idea, just a different mechanical system to do the job.

BTW. A rotary device is focused on in the same way as a flat object. You can focus on the object held in the rotary by raising and lowering the table with a manual crank system or a motorized system.

Dave

[Ross Moshinsky]

Don't buy a laser without a motorized table. I don't even know why the Chinese offer it as an option.

[Adrian Page]

Don't buy a laser without a motorized table. I don't even know why the Chinese offer it as an option.

Why?

Adrian

[Ross Moshinsky]

Why?

Adrian

Because the table moves up and down to focus based on your material. Why do you want to make your life difficult for $500?

What if one day you need to work with 5 different materials? You're either stuck manually moving the table 5 times or moving the lens up and down which is typically not considered the best idea.

[Adrian Page]

Because the table moves up and down to focus based on your material. Why do you want to make your life difficult for $500?

What if one day you need to work with 5 different materials? You're either stuck manually moving the table 5 times or moving the lens up and down which is typically not considered the best idea.

Ross,

My original question indicates that I do not have any idea how a laser is focused.The question itself, "How do you set the focus on a Chinese laser cutter if you don't have an up/down motorized table?" was a clue to this. I was not trying make to my life difficult for $500. I was trying to find out how a laser machine is focused.

So you can move the lens up and down to focus?

Adrian

[Dave Sheldrake]

The big flatbeds all have fixed tables and the lens holder is moved, it's a royal pain in the rear too (until I added torsion tubes to do it)

cheers

Dave

[Adrian Page]

So... is this one adjustable?

288785

Adrian

[Adrian Page]

This one says it's adjustable. It looks simple enough. Am I missing something here?288786 My main mission for the laser will be to cut between 1/4" and 1/16" balsa.

Adrian

[Dave Sheldrake]

Yup, you can slide them up and down to get your focal point but it's a pain to do it and get it accurate (although using slip gauges can work quite well under the nozzle) The chinese systems that use threads aren't usually cut very accurately so that adjustment system often leads to miss alignment :(

cheers

Dave

[Adrian Page]

Thanks Dave! I can turn a height gauge on my lathe easily enough. I don't anticipate changing it very often. It's just good to know there is a simple method to do so. Did you make a custom setup of some sort to do this? "torsion tubes"? If it really bugs me I can fab up a movable table for a lot less that $500. You have to bear in mind that I love to tinker with things. If I had time I would build my own machine. There is no doubt that I will modify whatever machine I end up with. It will merely be a starting point.

Adrian

[Scott Shepherd]

Adrian, was it you that built that plane out of coroplast a few years back? The real, flying, actual plane out of coroplast?

[Adrian Page]

No Steve... that was Bob Stevens in Florida. (SignManiac on 101)

Adrian

[Scott Shepherd]

Ahh, that's right.

I can't wait to see what you do with the laser. I cut wing struts (my name for them) for a guy that makes real planes, but it's on our CNC router because they are too large for our laser. I got a repeat order for them today. Once you get going, you'll be making all kinds of stuff.

[Adrian Page]

I hope I get to make lots of interesting stuff Steve. The KS is at $11,600 now. I think I might get a bigger laser!

Adrian

[Adrian Page]

Ever laser cut HDU Steve?

Adrian

[Scott Shepherd]

Ever laser cut HDU Steve?

Adrian

I haven't cut it, but I have engraved it. It does pretty well!

[Adrian Page]

I'm thinking I might be able to make signs out of it. ;)

Adrian

[Sotos Patistas]

Adrian,

FWIW, I'm following your endeavor closely. Years ago I was looking for a nice Gee Bee kit and came upon your designs. In actually, your Newbee is more my speed as I had a fondness for smaller, tamer flying planes. About that time, I got my own laser and pretty much stopped buying kits, and just cut my own designs, though nothing as sophisticated as your designs. I stopped flying and kitting a few years ago, but not before designing a nice flying and reasonably well received 40 size 3D profile plane whose selling point was that the builder had absolutely no cutting to do. Every part was laser cut, and the parts interlocked and self aligned so well that no plans were needed for the build. I have more time these days and feel the itch to start building again. I have a bipe in mind that may be first on the list.
Once you get your laser, you'll see lots of opportunities to put it to use. I'll be continuing to follow your progress with interest.

Sotos

[Adrian Page]

Hi Sotos! So you cut airplane kits with a laser? What do you think of the RECI Z2 for cutting our balsa and plywood parts? Will I be happy or wish I had more power? Anything else you can tell me that would help me get the best combination of parts for my laser would be great.

Adrian

[Sotos Patistas]

Adrian,

I cut kits with a 35 watt RF fired laser, so I would think the 80 - 90 watts I see the Z2 listed at should give you plenty of power. With only 35 watts, cutting 1/4" balsa was at times a challenge. Going too slow left the edges unacceptably charred, going too fast and the cut didn't go all the way through. I don't think you'll have that problem with the Z2. The density of the balsa I was getting varied so much, that I ended up having to weigh each plank, and adjusting the speed accordingly. Cuts were always done at 100% power.
With my laser, a LaserPro Explorer, the stock 2 1/2" focal length lense was adequate. As you've likely learned at this point, the beam as it exits the focal lense is somewhat hourglass shaped, so with 1/4" balsa, in order to avoid cuts that were "angled", it was sometimes helpful to focus just a bit below the surface of the wood. The "throat" of the hourglass is deeper with a longer focal length lense, however, the focal "spot" is also bigger, and a little weaker. I tried a 4" lense once, but with only 35 watts at hand, I didn't have the power to get through 1/4" balsa. It's an option you might consider with your Z2 however. If you do, you may end up needing to adjust your drawings for the bigger spot, something I never did with the 2 1/2" lense. Also, my personal opinion is that you not overlook the usefulness of being able to engrave. I think there are lots of kits being cut with less than 80 watts.

I hope this info helps, and hopfully I didn't cloud the issue for you. Lastly, if you still have doubts about your choice of power, what you might consider is making a request of the members of the Sawmill community to cut some sample parts for you. Hopefully, someone with a similar laser to the one you are considering will volunteer. Send them the balsa stock and CAD files and ask that they cut the parts and either take photos for you, or send the parts back. I'm sure we have some Canadian folks here as that would ease the shipping hassle, though not certain any of them are Reci owners. I received similar assistance once when I was having issues by having another member with a like powered laser cut the parts I was having trouble with and it was a great help. As I gather you've noticed, there are some very helpful folks here.
If I can offer any additional info you might find helpful, please don't hesitate to ask. BTW, the Kickstarter venture is a great idea!
Lastly, here are a few of pics of the fast build I put out several years ago. What can I say, I like to build, but I'm always in a hurry. :)288880288881288882288883288884

[Scott Shepherd]

Here are some parts I cut on our router.

288894

[Adrian Page]

Thank you Sotos for that lengthy thread! Very helpful. The 35 watt laser looks like it cut thin balsa very well.

Adrian

[Sotos Patistas]

Adrian,

Happy to share what I've learned. FWIW, the balsa shown in my pics of the rudder and hor stab/elevator is all 1/4". Also, with my 35 watt machine, 1/8" lite ply is no problem, however aircraft ply doesn't cut well at all due to the glue used. It can be lasered, but chars much more than lite or birch ply.

Steve,

I take it those are the full scale aircraft parts you mentioned earlier and that it is aircraft ply. May I ask, how thick it is and was it cut in one pass? Also, I don't see any tabs. Was a vacuum system of some sort used? thanks.

Sotos

[Scott Shepherd]

Steve,

I take it those are the full scale aircraft parts you mentioned earlier and that it is aircraft ply. May I ask, how thick it is and was it cut in one pass? Also, I don't see any tabs. Was a vacuum system of some sort used? thanks.

Sotos

Sotos, yes, they were full scale. No tabs, vacuum table used, it was 1/4" thick and done in 1 pass.

[Lucy Lee]

If without motorized up&down. the laser head, can be adjustable about 3cm or so ,so if you want thick materials, needs motorized up&down ,

[Adrian Page]

I think various arrangements could be devised to achieve the equivalent of an up down table function for occasional use.

Adrian

[Adrian Page]

Somebody once said,"How do you focus a laser without a motorized table?" Then somebody else offered a disparaging anecdote about horses and water...

Adrian

[Mike Null]

And a number of others offered that buying a machine without a motorized table would be a mistake. If I'm reading correctly you have over $11,000 to spend. Whatever you buy ought to have a motorized table for that price. And, yes, i understand that you can build a table--but why?

[Dave Sheldrake]

I'm of the school, better to have it and not need it than not have it and need it.

It does make on the fly adjustment easy (my up down is wired to buttons on the faceplate not via the PAD) other than the flatbeds that don't have the option I wouldn't buy a machine without motorised rise and fall.

cheers

Dave

[Ross Moshinsky]

And a number of others offered that buying a machine without a motorized table would be a mistake. If I'm reading correctly you have over $11,000 to spend. Whatever you buy ought to have a motorized table for that price. And, yes, i understand that you can build a table--but why?


I'm of the school, better to have it and not need it than not have it and need it.

It does make on the fly adjustment easy (my up down is wired to buttons on the faceplate not via the PAD) other than the flatbeds that don't have the option I wouldn't buy a machine without motorised rise and fall.

cheers

Dave

Exactly. It's like buying a car without power windows and door locks. It's not even an option on most cars and most people wouldn't consider living without them.

[Adrian Page]

And a number of others offered that buying a machine without a motorized table would be a mistake. If I'm reading correctly you have over $11,000 to spend. Whatever you buy ought to have a motorized table for that price. And, yes, i understand that you can build a table--but why?

After kickstarter takes out it's fees and the money is converted to US funds I will have about $9800 to purchase a laser and enough materials to assemble and ship out about 80 model airplane kits. The machine I am looking at costs $500 more with a motorized table. As I understand it, I do not need a motorized table to cut the kits. I can see it would be more convenient but I am using other people's money in effect. I am being cautious with the money.

I may well end up buying the machine with the powered table but it won't be because someone said I should, or made a "clever" comment... it will be because I learned as much as I could about my options and made an informed decision.

From an engineering standpoint I find it bizarre that one would choose to move a 4 foot by 3 foot table accurately when one could move a 1/2 ounce piece of glass instead. There must be some reason that is not readily apparent as they all seem to go with the moving table. Is it really that difficult to adjust the length of the tube?

Grateful for all the information,
Adrian

[Scott Shepherd]

From an engineering standpoint I find it bizarre that one would choose to move a 4 foot by 3 foot table accurately when one could move a 1/2 ounce piece of glass instead. There must be some reason that is not readily apparent as they all seem to go with the moving table. Is it really that difficult to adjust the length of the tube?

Grateful for all the information,
Adrian

I haven't used or seen a Chinese machine without a motorized table, so I'm only speculating on the reasoning here, but my guess is that, in general, you don't want to move/mess with the optics. Once they are perfectly aligned, you want to leave it that way, which is why I'd think the tables move up and down, not touching the optics path. Moving the head up and down might be moving the optics (not sure, haven't seen how they work, but not sure how you'd move the head down or up without moving the optics path, would be something less than desirable as a general rule. It's not the "end of the world" type stuff, but my guess is that it just introduces one more thing into the equation that causes the possibly for something to go wrong in the path of the optics, alignment wise.

That's purely a guess.

[Matt McCoy]

Have you seen this?
288939

[Dave Sheldrake]

Have you seen this?
288939

I have indeed Matt and it does make me giggle everytime :)


Is it really that difficult to adjust the length of the tube?

With any degree of accuracy yes it does Adi, it also leads to wear on the lens holder body and the above mentioned optical miss-alignment.

cheers

Dave

[Adrian Page]

Thanks Dave. If little effort is put into the head I can see it being a pain to adjust. I suppose just the act of loosening the clamp or whatever holds the lens tube could jiggle something out of alignment on a lightly built machine.

What was the torque tube business you mentioned earlier?

Adrian

[Bill George]

So the table has a hand crank instead of a motor? How often is he going to change the adjustment cutting balsa wood for kits? Later on he could add a motor if needed.

[Mike Null]

Bill

I believe the table is fixed. There is about 3 cm adjustment in the lens as I read Lucy Lee's post.

[David Somers]

Oooooh A completely fixed Table? Yucko!

Adrian. This is my personal opinion. But if Mike is correctly reading Lucy don't do the fixed table. You are spending a lot of money for a system that will have lost a lot of flexibility for you. And all for $500? And I daresay you will have reduced its resale value in the future should you choose to bail out of airplane making and flip burgers or something else equally lucrative.

Dave

[Bill George]

I did not know what model or brand he was buying. Lucy works for GWeike is that what he is buying?

[Adrian Page]

Check this out: http://www.bodorcnc.com/products/Laser-Engraving-Cutting-Machines/1122.html It automatically follows the contour of a part. Pretty nifty.288963

[Scott Shepherd]

Adrian, don't forget you'll be using this for a lot of sign related products once you get going, so it might not be as little movement between jobs as you think. You might be cutting 1/4" plywood, then 1/2" acrylic letters, then 1/8" acrylic, etc. Our table moves up and down all throughout the day.

Just something to think about.

[Adrian Page]

Yeah... looks like I should go for the moving table. I didn't realize that the adjustment in the head was no good. Thanks for the input.

Adrian

[Dave Sheldrake]

http://www.thorlabs.co.uk/newgrouppage9.cfm?objectgroup_id=4109

The zoom housing Adi, I have them fitted to my flatbeds to cope with moves for the fixed bed.

cheers

Dave

[Michael Hunter]

I attended a demo of a Chinese machine.
Trying out a variety of materials, focusing the laser by moving the lens up and down (with the help of a small acrylic spacer) looked pretty slick - UNTIL the whole lens assembly fell apart in the guy's hand!

[Adrian Page]

I attended a demo of a Chinese machine.
Trying out a variety of materials, focusing the laser by moving the lens up and down (with the help of a small acrylic spacer) looked pretty slick - UNTIL the whole lens assembly fell apart in the guy's hand!

That must have been embarrassing for the poor fellow! Was he able to repair it?

Adrian

[Kev Williams]

I haven't used or seen a Chinese machine without a motorized table, so I'm only speculating on the reasoning here, but my guess is that, in general, you don't want to move/mess with the optics. Once they are perfectly aligned, you want to leave it that way, which is why I'd think the tables move up and down, not touching the optics path. Moving the head up and down might be moving the optics (not sure, haven't seen how they work, but not sure how you'd move the head down or up without moving the optics path, would be something less than desirable as a general rule. It's not the "end of the world" type stuff, but my guess is that it just introduces one more thing into the equation that causes the possibly for something to go wrong in the path of the optics, alignment wise.

That's purely a guess.

When I bought my Triumph, it was largely an experiment, so I went as cheap as possible, which meant no motorized table. I have run into focus issues, strictly based on the height of the material. Like, the max thickness material I can engrave with the supplied lens barrel is about 3/4". If I'm doing something thicker I remove the table and put in a wood table that settles in about 4" lower. As it is I'm shimming up what I'm engraving to get it within focus range. The supplied lens barrel is about 3" long, and the barrel has about 3/4" of useable travel, and I've found no significant difference in where the beam hits the lens or ends up on the work regardless of where the barrel is clamped. At this moment Triumph is making me some longer barrels to about 8" long, and I'll be shortening an original length barrel. With these, I should have 5" of useable focus travel overall, and be able to accommodate 1-1/2" thick material on the main table.

I don't forsee any issues. I assume there will be some beam offset when using the longer tubes, but every job has to be aligned properly anyway so it shouldn't matter much.

[Adrian Page]

Thanks for posting that Kev. I find it interesting that you're not ordering a movable table after living without one.

Adrian

[Kev Williams]

Thanks for posting that Kev. I find it interesting that you're not ordering a movable table after living without one.

Adrian
Not that big a deal for me. My run-of-the-mill stuff is flat SS and aluminum panels, and a little wood. I also do a little acrylic cutting. For anything else, I just McGuiver something up as needed! ;)

But my next machine will have a moving table!

[David Somers]

Kev,

Thinking ahead for Adrian. Do you think the lack of a moving table will affect the resale value of your machine?

Dave

[Adrian Page]

Dunno. Resale value of a Chinese laser appears to be roughly twice whatever it costs FOB China.

Adrian

[Mike Null]

You will be very lucky to get half your purchase price if you use it for a year. Less if you use it for more than a year. Remember, David is talking about a "used" machine price.

That fixed table will be a show stopper for most people.

[Adrian Page]

I'm going to order the machine with a moving table.

Adrian

[Adrian Page]

Well... I ordered the machine with a fixed table. It has arrived and I'm learning to use it. I have been cutting 1/8" to 1" material and focusing it with the plastic spacer provided and the lens tube. It takes 2 or 3 seconds to focus. I don't think it will cut much more than an inch thick material but I'm good for 1.25" with the tube that came with the machine.

Adrian

[Julian Harrison]

I'm still shopping for a laser. How do you set the focus on a Chinese laser cutter if you don't have an up/down motorized table? The laser I like wants $500 more for the up/down table and I think I can just block up the rotary fixture with a simple jig I could put in place of the knife bars. I just don't know how the focus is set. Does my plan have any merit? I would pony up the 500 bucks but I don't even know if I will ever engrave a cylinder. I need the laser to cut balsa and ply R/C airplane parts. I thought it might be nice to be able to engrave on a cylinder at some point but I have no projects in mind at this point.

Adrian

Saw this as opposed to banking material. Thought was a nice tool. Rather than buy one you can lay one out online just search create angle online. I will try and make a PDF after I get the mm set up with the angle. I am thinking 0-30mm might be ideal.

326775

[David Somers]

Julian,

Not trying to nit pick you, but unless I am misreading your graphic insert, that ruler is actually measuring the distance from the bottom of the lens tube, the cone", to the material, not the distance from the lens to the material. The lens is much higher up in the tube. It would be misleading to refer to that as the "focal length" if I am viewing that correctly? It is still quite useful, just not measuring the actual focal length as the graphic states.

Dave

[Adrian Page]

Saw this as opposed to banking material. Thought was a nice tool. Rather than buy one you can lay one out online just search create angle online. I will try and make a PDF after I get the mm set up with the angle. I am thinking 0-30mm might be ideal.

326775

I think I would be more inclined(see what I did there?) to make one on my laser cutter. BTW after living with the laser for a while I am glad I bought the fixed table. Setting the focus is extremely easy and quick on the Bodor. You place a gauge under the head, loosen the collar, the head drops down onto the gauge and you tighten the collar. Easy. I have had zero issues with it throwing off the focus.

The fixed table has a nice cone shaped sheet metal intake duct the size of the table so It sucks out fumes very well. With the moving table you don't get that.

Adrian

[Keith Winter]

David the lens is at a fixed point just above the cone in my machine. So yes you can vary how far the lens insert goes into the lens head, but the focal distance is always the same because the lens is not changing in it's placement relative to the object you are cutting. The only distance that is changing is in relation to the distance to the mirror above directing the beam down onto the lens. So if 6 mm is your focal distance that would never change no matter what since the lens remains the same distance from the object you are cutting. So the tool would be nice to have for sure :)

[David Somers]

Morning Keith!

I think we may be saying the same thing? Like you my lens is higher up in the tube, but it is always a fixed distance from the tip of the cone to the lens. And like you, my tube slides in and out of the tube that is attached to the mirror block. The distance from my lens to the mirror may change, but the distance from the lens to the tip of the cone is fixed. I was just pointing out that the tool is measuring the distance from the material to the bottom of the tube's cone. It isnt measuring the distance from the material to the lens itself which would be the focal length. If I took my lens with a 2 inch focal length and took that literally and made a spacer 2 inches high and used that to set the distance between the material and the tip of my cone I would find my focus was way off. I was just trying to point out a term that might be confusing to newbies not clear yet on that whole lens structure. Does that make more sense?

Dave

[Keith Winter]

I see now what you're saying. You're correct sir!

[Glen Monaghan]

The markings on the sloped "ruler" _could_ be made to indicate height of lens rather than height of cone tip. If, for instance, the lens was 1" above the cone tip, the bottom of the ruler would start at 1 rather than 0, the mark 0.75" higher would be labeled 1.75 instead of 0.75, etc. Then, as long as the lens always mounts at the same place, you wouldn't have to change focus tools (the ruler) when you changed lenses, you'd just position the tip of the cone at the appropriate marking for the installed lens' focal length (2.0 for a 2" lens, 1.5 for a 1.5" lens, etc.)