# Laser engraving lathe



## BrianM (Aug 18, 2012)

Since I'm rather limited on the amount of available funding for my multitude of hobbies, I decided to combine a few...electronics, programming, and pen making.

I'm working on a DIY laser engraving "lathe".
This will be a small "lathe" (I'm estimating 18"x18" foot print) that the pen mandrel and blank is mounted on with the laser mounted on a carriage above it.  The rotation of the pen and the movement of the laser will be computer controlled.

I've been collecting parts for a while and finally this evening I was able to test fire the laser.

Prior to this test I was worried that the laser wouldn't be powerful enough to burn an image in a reasonable time. This test proved that I should instead be worried about the laser being too powerful.

Testing on a Turkish Walnut

I still have a lot of work to do. I have to build the mechanical parts and write the software to control laser lathe. 

If anyone is interested I can post a build log during construction and testing.

-Brian


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## Simplex (Aug 18, 2012)

That's pretty cool!  I'll look forward to seeing it when it's complete.  Id be interested in the build log too.  Keep us posted on how things go.


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## alamocdc (Aug 18, 2012)

Dang, Brian, I think I saw the laser actually burn through the blank at one point. Or was I just seeing things?


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## BrianM (Aug 18, 2012)

alamocdc said:


> Dang, Brian, I think I saw the laser actually burn through the blank at one point. Or was I just seeing things?




I'm fairly sure it was a trick of the camera.  The laser is so bright that the reflections off the smoke make the light bounce around everywhere.


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## Jgrden (Aug 18, 2012)

Yes. interested.


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## leestoresund (Aug 18, 2012)

You're gonna have to have a steadier hand to get any business.


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## BrianM (Aug 18, 2012)

leestoresund said:


> You're gonna have to have a steadier hand to get any business.



LOL. 
I know. Even with a steady hand my writing is not something you could call good.


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## Rich L (Aug 19, 2012)

That's a pretty cool start. What are you going to do about managing power and spot size? Pulsing, ND filters, optics ... ??

Cheers,
Rich


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## skiprat (Aug 19, 2012)

Rich L said:


> That's a pretty cool start. What are you going to do about managing power and spot size? Pulsing, ND filters, optics ... ??
> 
> Cheers,
> Rich


 
Party pooper!!!:biggrin:

Brian, good luck with your endeavour. Keep us posted please!!:wink:


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## Donovan (Aug 19, 2012)

Hi Brian I cant see youtube where I am. Web filtering  What laser did you use. I am in the process to build a 4 access CNC mill and I want to add a laser to it just for the same jobs

Cheers


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## Ligget (Aug 19, 2012)

Keep going Brian, I would love to see your finished creation! :good:


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## BrianM (Aug 19, 2012)

Rich L said:


> That's a pretty cool start. What are you going to do about managing power and spot size? Pulsing, ND filters, optics ... ??
> 
> Cheers,
> Rich



The output power will be controlled by the PC using PWM. The laser module has a manual focus lens, so it will essentially be fixed focus during operation. Spot size will probably be around 0.5mm or so.




Donovan said:


> Hi Brian I cant see youtube where I am. Web filtering  What laser did you use. I am in the process to build a 4 access CNC mill and I want to add a laser to it just for the same jobs
> 
> Cheers



The laser is a Nichia NDB7875 445nm 9mm Laser Diode. Purchased it off ebay.
Most of the available high power blue lasers have been pulled from DLP Projectors.  A good resource is Laser Pointer Forums


I'll update this thread as the build progresses. I'm currently working on building the driver circuit for the laser.


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## BrianM (Aug 19, 2012)

Thought I would post a magnified view (30x) of the results. 
Picture was taken by holding my phone camera up to the microscope eyepiece.

The center dot was a very quick pulse. It was a fast as I could press and release a pushbutton switch. Probably between 1/4 and 1/2 second.
The width of the mark is around 0.5mm and the depth of the mark is about 0.7mm.

The more I play with this thing, the more I want to get it finished so I can engrave some pens.


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## btboone (Aug 19, 2012)

Definitely invest in some good laser glasses that are made for that wavelength.  The wavelength is such that your eye lens can focus it into a small spot and perminently damage your retina.  I got some from Newport Corporation that have an optical density of 10 for my wavelength.  The optical density is a measure of how much light of a specific wavelength is attenuated.  It's a logarithmic scale where each number represents 10 times the previous numbers blocking ability. You want an optical density of 7 or better if you can.  Eyesight is nothing to play around with.

With a proper lens setup, it is possible to get a much finer spot size than that.  That wavelength should be capable of going to around 20 microns or so.  That's way less than a hair!


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## btboone (Aug 19, 2012)

I'm working on a somewhat similar project.  I couldn't find what I was looking for, so decided to assemble my own system.  I'm using a Sherline rotary axis and will have a machine table do the XY motion under the laser head, which is fixed to the Z column.  I will be using g-code to drive it and will have an auto focusing head.  I scaled the rotary axis to 3.6", so it thinks of it as a standard Y axis instead of a rotary.  This means I draw my artwork in CAD then stretch it until it's exactly 3.6" in the rotary direction.  This eliminates the error in diameter calculations that would otherwise have to be used to get the proper circumference and number of steps per revolution.  I've used that type of setup on a tabletop mill with good results.

I'm making a full enclosure so the infrared light can't escape.  It is near infrared, so very dangerous to the eyes.  I will be using high pressure nitrogen as an assist gas, so I'll need to be able to turn that on and off in the g-code as well as control the laser and capacitive sensing system.  My big parts should arrive in a couple weeks, so I'm excited as you are waiting on the good stuff.


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## Rich L (Aug 20, 2012)

BrianM said:


> Rich L said:
> 
> 
> > That's a pretty cool start. What are you going to do about managing power and spot size? Pulsing, ND filters, optics ... ??
> ...



Cool. A suggestion  (like Bruce says) -  if you have room to insert a small (not too small) beam expansion/refocusing optic then you would have better power density on target. You may need a spatial filter to make that work well with that laser. Your PWM scheme would then have increased dynamic range and you'd get better graphic resolution in your engraving.

Actually that would be hot!  

Cheers,
Rich


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## sbell111 (Aug 20, 2012)

I have no clue about all the technical stuff that has been discussed, but keep going.  I am fascinated.


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## skiprat (Aug 20, 2012)

sbell111 said:


> I have no clue about all the technical stuff that has been discussed, but keep going. I am fascinated.


 
LOL, :biggrin:I'm glad I'm not the only one that thought some of these guys were talking a different langauge:biggrin:.


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## Rich L (Aug 20, 2012)

skiprat said:


> sbell111 said:
> 
> 
> > I have no clue about all the technical stuff that has been discussed, but keep going. I am fascinated.
> ...



You guys make me laugh, too!

Cheers,
Rich


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## btboone (Aug 20, 2012)

My credit card's a bit toasty right now.  I ordered my laser head today.


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## skiprat (Aug 20, 2012)

btboone said:


> My credit card's a bit toasty right now. I ordered my laser head today.


 
Quit complaining Bruce !!!  I'd have to sell my wife, kids, cats and house just to get any of the toys you have:biggrin:


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## btboone (Aug 20, 2012)

It will be fun.  A lot of stuff should arrive in a week or two.


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## BrianM (Aug 20, 2012)

btboone said:


> Definitely invest in some good laser glasses that are made for that wavelength.  .....
> 
> With a proper lens setup, it is possible to get a much finer spot size than that.  That wavelength should be capable of going to around 20 microns or so.  That's way less than a hair!



I've got a fairly decent pair of safety glasses. I've read too many accounts of people burning holes in their retinas.  I don't want to become another statistic.


I played around a bit more and managed to get the burned dot down to 0.4mm.  I'm sure I can get it smaller, but with the laser in a very crude mount and the pen blank being hand held I doubt I can get better resolution until I have it mounted to a frame where I can control the laser to work-piece distance a bit better. 

I also have to consider the accuracy of my mechanism used to move the pen and laser.  I have to make sure the laser dot is wide enough to not leave a large space between scan lines.


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## NewLondon88 (Aug 20, 2012)

BrianM said:


> I played around a bit more and managed to get the burned dot down to 0.4mm.  I'm sure I can get it smaller, but with the laser in a very crude mount and the pen blank being hand held I doubt I can get better resolution until I have it mounted to a frame where I can control the laser to work-piece distance a bit better.
> 
> I also have to consider the accuracy of my mechanism used to move the pen and laser.  I have to make sure the laser dot is wide enough to not leave a large space between scan lines.



good concerns, but just be aware that a .5mm spot size gives you
an effective resolution of 50dpi. Not good at all. at .4mm you're up
to around 66dpi. You're going to need to get in the 200dpi and above
range for effective resolution, otherwise it will look ragged.

But as others have mentioned, the way to do that is with optics. Lenses
can focus your beam tighter which not only increases the resolution, it
also increases the power density. More power in a smaller spot means
you can move faster and be more productive.

Don't worry about the spot size being too small. Most lasers compensate
by making multiple passes in tiny increments. That's why lasers might 
have a setting of 1000dpi, but a spot size of 0.005" (200dpi) it will
move the media 1/1000 of an inch at a time and the beam paths will
overlap.


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## btboone (Aug 20, 2012)

NewLondon88 said:


> BrianM said:
> 
> 
> > Don't worry about the spot size being too small.
> ...


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## BrianM (Aug 20, 2012)

I guess I will be working on reducing the spot size.
It looks like I have a bit of lens research to do.


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## btboone (Aug 20, 2012)

What the fiber lasers do is use a collimator to pull the beam to a large parallel beam then another to do the fine focus.  The first planoconvex lens has the flat side to the source and the second lens has the flat side toward the focus.


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## frank123 (Aug 20, 2012)

Advice for those playing with lasers:

Never stare into the beam with your remaining good eye.


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## NewLondon88 (Aug 20, 2012)

other good advice:

this is not a toy.
This is NOT a toy! 

THIS IS NOT A TOY!!!! 

(hee hee... it's a toy!) :wink:


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## Rich L (Aug 20, 2012)

Here's a good link to get started with the thought process

Focusing and Collimating

You're not likely going to get a 20µm spot spending simple money on optics but if you can get even close to 100µm you've done a superb job. One thing seriously in your favor is you're not trying to move the spot around.

The lens system is simple and one you can build yourself - what you'll likely be fighting is the aberration that comes out of your OEM diode assembly. The only way you'll get around that is through using a spatial filter.

Good luck!

Cheers,
Rich


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## BrianM (Aug 21, 2012)

Thanks for the link. I'm off to do some reading.


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