Questions Before Starting a Build

General discussion of laser machines

Re: Questions Before Starting a Build

Postby r691175002 » Sun Dec 19, 2010 5:55 pm

I hate to ask you for even more after you've already tested so much for me, but I just realized that you could adjust the microstep resolution on Keling drivers from your build log. I checked the specifications and while Geckos 540 driver is not optoisolated, the Keling driver is.
It would be convenient if I could use the Keling drivers with the retina but it seems fairly probable that they wont work. The swap would also save me about 130$ since the drivers are cheaper and 25 tooth pulleys are only offered in aluminum.

Would a reasonably fast transistor be enough to bring the 3.3V to 5V or would it mush up the signal? At this point I'm pretty much on the fence between the two controllers since they both have advantages.
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Re: Questions Before Starting a Build

Postby bdring » Sun Dec 19, 2010 6:18 pm

I am in the process of testing. It may take a few days. It is not a ton of work, but the holidays have me running around a lot.

I think you could shift the voltage. I used this little do-dad for my XMOS testing and it worked fine. You might not need it though.

http://www.sparkfun.com/products/8745
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Re: Questions Before Starting a Build

Postby bdring » Mon Dec 20, 2010 2:46 am

The Retina engrave controller works for me with the KL 4020 stepper driver. I ran the test for about 5 minutes and did a simulated engrave. The motors were loose and not hooked up to the machine. The laser power supply was not connected to. At first I tried to use the keling breakout board but that did not work. The motors ran pretty smoothly with a slight resonance at one point in a slow ramp up, but the motors were not even bolted down. The resonance almost went away when I held them down.

Disclaimer: This is not an endorsement of this setup. I cannot guarantee this will work for you or damage the RE controller in the short or long term. Telling FSE "Bart said it is OK", does not mean anything to them.

Here is a picture of my setup. The RE controller is attached to a 25pin breakout board. The red and black clips supply 5V from a bench supply. This is required for the 4020s. I ran at various microstep settings and ran at 1.50amp. The motor power supply is 28V. The motors got only slightly warm.

4020_ra.jpg
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Re: Questions Before Starting a Build

Postby r691175002 » Mon Dec 20, 2010 3:21 am

Thanks for doing the test. My main concern is that the Keling drivers would just ignore the 3.3v signal but if motors are turning things should be okay. I'll try it with and without a voltage shifter and go with whatever works.

I've put together a list of what I need to buy and included it for anyone else who may be looking into doing the build. I'm not sure how hard I'll be hit by shipping but price wise it turned out pretty much as I expected. Once Christmas rolls by I'll start placing orders. I already have a few miscellaneous parts lying around so I'll see what I can salvage.

Considering the other laser cutters, the capabilities of your machine in terms of work area, tube power, build quality and electronics are incredible for the cost. Your smaller variant is shaping up to be even better in both price and ease of assembly as well.

I've calculated that I could ebay a 60W laser for around 300$ more but if this build works out I'll probably toss the extrusions in a year or two and rebuild the machine around a long life 80W tube and perhaps add a few inches of travel.

I've also been made aware that coated ZnSe windows will pass the CO2 beam but reflect a small (but visible) percentage of a laser in the visible spectrum. If I can get a window cheaply enough I'll try adding a 20mW green laser.
Last edited by r691175002 on Tue Dec 21, 2010 12:51 am, edited 1 time in total.
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Re: Questions Before Starting a Build

Postby r691175002 » Mon Dec 20, 2010 5:51 am

I've revised the price list a touch, throwing in some guesses for miscellaneous parts and bumping shipping (which informally includes any parts I've forgotten to include) up to 400$.

A general rule is that projects tend to cost significantly more than planned. Normally I go half again when making estimates but this is the first time I've done such a detailed list.

A final change I made was a fairly significant modification to the cover. I will be using 8 blind joints and 6 meters of their panel clamp rubber strip to embed 3mm acrylic in the cover. The change is about 20$ (Without the acrylic). I will also try to combine a green laser in with the CO2. I estimate that change to cost 50-80$ depending on what I can get the window for.

I am also strongly considering upgrading the Z table. The current material is 20 gauge aluminum sheet with hexagonal perforations. For 35$ more I can buy a 48x24" sheet of 1/4" aluminum honeycomb. Another 20$ upgrades that to 3/8" thick. Mostly a cosmetic upgrade but it will stay flatter and have less back reflection. I do plan on building a box under the Z-table for air intake and having something to put on top of the honeycomb because I intend to do a lot of paper cutting. I looked into thin steel sheet with 1/16" perforations but all of that stuff is really expensive so I'll probably end up drilling holes in some scrap.

I will be putting enough time and money into this project for a few cosmetic changes to be worthwhile (this is how my projects get expensive :/)

It appears that the retina and keling stepper drivers will play nice as long as I don't run any 5v inputs back into the retina. Shouldn't be a problem. I will probably cut the wires off a 12V wall-wart and drop some of it to 5V and 3.3V for the miscellaneous electrical requirements. I also have a few computer power supplies kicking around but they are all fairly large so I'll see what there is room for.

Image
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