Questions Before Starting a Build

General discussion of laser machines

Questions Before Starting a Build

Postby r691175002 » Wed Dec 15, 2010 8:55 pm

Hi,
I've always wanted a laser cutter but worthwhile models have always been beyond my budget. The open source laser looks fairly easy to build (especially with the kits) and is far more capable than the super-low end Chinese models.

I've been going through most of the material on the build to get a good idea of how things work before I start buying parts and had a few questions.

I'm not completely sure what is required on the electronics end of the laser cutter. From what I've seen the two options are the DSP and Retina controller. The Retina seems to have an advantage on the software end and looks higher quality but I have no idea how easy it is to integrate with the build since a lot of its configuration is preset.
The DSP controller has the nifty control panel and is much cheaper but I don't want to be left behind on the software front since both controllers are a major investment.

Has anyone successfully tried a retina controller with a diy laser cutter? How difficult would it be to set it up?

I'm also fairly confused in terms of stepper drivers since there are so many options. Would this work? http://www.lightobject.com/New-version- ... -P274.aspx


In the new smaller build, there is talk about gluing the V-rail instead of drilling holes. That would save a fair deal of work so is that also a valid option on the larger model? Also, I haven't been able to find the exact part number of the V-rail.


I plan on printing off the bill of materials and all the drawings and working out exactly what I need so I'll probably have more questions later. If I can get this going I will try to do a comprehensive build log from the very start because a good step by step instructions would probably encourage more people to try this and if I mess up people can tell me right away.

Thanks,
Ryan
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Re: Questions Before Starting a Build

Postby bdring » Wed Dec 15, 2010 10:01 pm

I have had bad luck with any TB6560 based board. The motors are very noisy and jittery. It may be just me. I may have an especially noisy parallel port or something, but most other boards work fine. I do like to adjust the step rate sometimes and the Geckos do not allow that.

I have used the Retina Engrave controller with my DIY machine. It produces engravings better than I ever expected when I started this project. With that said, I have not used the DSP controller and lasersafe1 is pretty happy with his.

By the way, I get a kick out of the term DSP. That was a way to impress someone 15-20 years ago. It is like saying CD quality. It does not impress like it used to. You can get 8 bit micros with DSP for more than 10 years now. The XMOS has of course DSP instructions on it, but you probably would not use them for this application...sorry...rant over.

Gluing v rails. I did it with my buildlog bot and it worked fine, but that was over a smaller length. I am counting on it working for the new laser, but it has yet to be tested. I used JB Weld the first time, but I plan to try a much thinner fast setting glue this time. The rail is very easy to register on the edge, but you need to make sure the glue is consistently thick. A thinner glue might be easier. The load is trying to keep the rails on so the glue strength is not the issue. Get the rails from McMaster.
Bart
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Re: Questions Before Starting a Build

Postby r691175002 » Thu Dec 16, 2010 12:48 am

The biggest thing preventing me from building a laser cutter in the past has been the electronics. I'm alright with the mechanical stuff but the sheer number of variations when it comes to all the software and electronics (and the cost) always scared me away. A long time ago I built a toy diode laser cutter using an arduino and that is the extent of my knowledge.


If the cheaper drivers aren't worthwhile, how about mixing the retina and gecko?
You mentioned that they are compatible as long as the pinouts get double checked here: viewtopic.php?f=22&t=316&p=1703&hilit=gecko#p1701

That just leaves two more questions in terms of compatibility, I assume that the machine has 1000Steps/inch since you have a retina working. The last requirement is that the rest of the electronics is compatible with the 3.3v signals from the retina. Are the laser power supplies also compatible? I will likely get the model from lightobjects.com however it looks like identical power supplies are available on ebay for way less.
Your stepper motor drivers and laser power supply must be able to work from 3.3V CMOS signals at 2mA. Most standalone stepper motor drivers with opto-isolators require 5v at 25mA. In these cases, you will need a build or purchase a 3rd party breakout board with driver buffer chips. We provide no support on parts or interfacing to parts we don't sell, including 3rd party laser power supplies and stepper motor drivers.



Unfortunately I haven't had a computer with a parallel port in years :/
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Re: Questions Before Starting a Build

Postby bdring » Thu Dec 16, 2010 2:55 am

Sorry about the slow reply, but I wanted to check some things out first. Most of the time my laser is middle of some odd experiment or total tear down. I reinstalled my Gecko G540 and Retina engrave controller to verify things.

The Retina engrave controller runs my Gecko G540 and laser enable fine. Actually, many parallel ports, including mine are 3.3V. You do need to get the steps to 1000 dpi. You can do this by adjusting the pulleys. An easy way for the 10 microstep Gecko to do it would be to use a 200 step/rev stepper and a 25 tooth pulley. With my stock setup you would need a 4 microstep controller.

Whoever you buy the tube and power supply from tell them you are from buildlog.net.
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Re: Questions Before Starting a Build

Postby r691175002 » Thu Dec 16, 2010 7:53 am

Switching to 1.8 degree stepper motors and 25 tooth pulleys seems like the simplest way of getting the 1000 steps/inch.

Kelling seems to have the perfect motor here: http://kelinginc.com/index.php?main_pag ... c316255ba9

I'm no expert at electronics but the specs seem similar aside from the 1.8deg/step. Switching to the larger pulleys should be no problem since the belt will only be 1.5mm further out and I can just stick a washer under the clamping screw or something. I'll probably run the motors off 36 or 48V to make up for the larger pulleys.

I noticed that the retina only supports 2 axes. Can I just run the z axis wires off the a 555 timer somewhere and make my own jog buttons? I also noticed that the gecko and retina have specific input/output pins. I assume the limit switches can be run through the gecko but the laser signal has to go straight from the retina to the power supply?


Thanks for all your help so far, I'm getting more and more confident I can pull this off. I'll be sure to let them know I am from buildlog when I start placing orders.
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Re: Questions Before Starting a Build

Postby bdring » Thu Dec 16, 2010 1:09 pm

That motor will work fine. The motor voltage/current should not really be affected. The speed of the the actual mechanisms is not changing, just the resolution. The NEMA 17s are more than fast enough but they can get hot if you overdrive them. The G540 seems to run them cooler than other drives. I would stick with 24V.

When I run the Retina I just manually move the Z axis by either pulling the belt along or using a nut driver on the top of one of the lead screws. I rarely have to move the Z more than a few tenths. You could also just use a DC motor.

You run the laser enable signal straight to the laser power supply. Avoid running through any optos, etc which can affect the timing. I have a basic schematic at the bottom of the drawings page.

I would go straight to the Retina with a the limits too. I think the Gecko might output 5V.
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Re: Questions Before Starting a Build

Postby bdring » Thu Dec 16, 2010 3:17 pm

Just for fun, I might try that light object board driven straight from the Retina Engrave controller. I happen to have one. That will put the issue to rest.
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Re: Questions Before Starting a Build

Postby bdring » Fri Dec 17, 2010 1:54 am

I tested the Retina Engrave Controller with the LightObject stepper driver, and it worked fine. The stepper enable even worked. I did not try a real engrave, just a test of the steppers. I would need a custom cable to breakout the laser enable pin.

The signal must be a lot cleaner than my parallel port, because I get poor results from my parallel port.

DSCN0569.JPG
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Re: Questions Before Starting a Build

Postby r691175002 » Fri Dec 17, 2010 2:37 am

I'll probably go with the gecko just because if I ever upgrade the build or cannibalize parts down the road it will be more useful. The mach 3 support means that I will be able to toss on a dremel and do some really light work (perhaps circuit boards) or play with 3d printing like you've been doing.

This is going to seem like a silly question but does the retina controller have a male or female connector? The only pictures I can find of any of the electronics don't show the connector.

I'm trying to run through every step of the build in my mind because I'm in Canada and I want to get everything in as few shipments as possible.

One thing I have going for myself is that I have a mini lathe and mill so I can make anything super weird. Even better, since the gecko has easily swappable connectors I might be able to borrow it for some cnc experimentation on the other machines later.
Last edited by r691175002 on Fri Dec 17, 2010 3:22 am, edited 2 times in total.
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Re: Questions Before Starting a Build

Postby bdring » Fri Dec 17, 2010 3:16 am

If cost is not the main criteria, then the Gecko is the way to go.

The Retina has a female connector...like a PC.

The nice thing about the Gecko is the way the current is set. If you put the resistor in the stepper motor connector, Moving it around is quick because there is less to reset.
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