Welcome to the SeeMeCNC Community

I get to kick-off with the inaugural "build thread"! I'll use this thread to post my machine and mods I've made.

cheers,
Michael

Here is the 1st full print I made back on 3/8/2012:

[img]http://mhackney.zenfolio.com/img/s3/v39 ... 4228-4.jpg[/img]

It was a little ugly because I was experiencing a few problems:

1) I had not made the mods to the 3 Axis Board: removing the 2 diodes and jumping the opto isolators. That introduces skew and other funkiness.

2) I had the idler pulleys for the X and Y belts too tight so they would not rotate freely. That leads to "jumping" in the X or Y direction.

These were easy enough to fix.

cheers,
Michael

I keep an album of my machining and other exploits with lots of photos and comments. The album dedicated to my H-1 us located here: SeeMeCHC H-1 3D Printer.

Cheers,
Michael

Thats cool.
I am not seeing an image in the second post for some reason.

Not sure why Lee, I see it and it is coming from a public server. Sometimes firewalls filter images from posts. What do you see?

cheers,
Michael

FYI; I'm not seeing it either, just the word "image"

Thanks guys, I updated the link. The original was a tif image and I changed it to a jpg version. It is possible that some browsers may not show tifs? Let me know if you see it now. Make sure to do a page refresh to force it to reload.

cheers,
Michael

Yep.
I can see it now.

Ok, great! I'll have to remember to post JPGs. I don't know why that image was a tif format!

cheers,
Michael

I'm going to do this series of posts in near real time. I am working on a hotbed mod for my H-1. Initially controlled by a Velleman thermostat manually and then controlled from Mach via a Arduino.

I am using a time-honored technique for making heating elements - nichrome wire. This has a lot of benefits and very few negatives. It is inexpensive, nichrome was designed to be used as heating elements, you can tailor the properties of the heating element for your power supply and heat requirements, and you can tailor the size of the
heating element. I want to develop a system that can be used on virtually any sized 3D printer.

To get started, check out this cool NichromeCal calculator. I used it to determine the length and gauge of my element to achieve a temperature of about 225°F with a 12 v supply. I ended up with 120" of 16 gauge Nichrome. I ordered it from this site - good prices and fast shipping.

Then I designed the element layout itself. The bed on an H-1 is 7" wide x 7 1/2" long so I started there. I plan to have a piece of .1" aluminum as the top plate to even out the heating and for thermal mass. The lower plate will be 1/8" phenolic but I also have some other materials to play with that are better thermal insulators. I could also use a blanket of insulation between the heating bed and the H-1 bed. The top and bottom plates will be separated by 1/8" aluminum standoffs with the Nichrome element sandwiched between them. I came up with a simple "snake" design
for the wire. You can see it here along with the first few bends:

[img]http://mhackney.zenfolio.com/img/s11/v3 ... 7702-3.jpg[/img]

The wire bends easily. I used the Sharpie to wrap the wire around to get nice smooth bends. Here is the finished element bent to shape:

[img]http://mhackney.zenfolio.com/img/s3/v43 ... 7340-3.jpg[/img]

Then I snaked a braided fiberglass sleeve for electrical insulation - this is also a time-honored way of making Nichrome heaters:

[img]http://mhackney.zenfolio.com/img/s11/v31/p8201847-3.jpg[/img]

Now I am going to hook it up and give it a shot, but first I have to solder the Velleman kit!

cheers,
Michael

It's been 8 minutes now you should be done soldering the Velleman.

Had dinner first and just finished it!

tick tock tick tock....

Ok, here it is up and running.

[img]http://mhackney.zenfolio.com/img/s1/v20 ... 9133-3.jpg[/img]

The Velleman is stock so the temp won't go over about 90°F. I need to calculate the resistor to swap with R5. The aluminum plate is just some old tooling I had. I wanted to make sure the heater worked before cutting my good stuff! I'm ready to go now.

cheers,
Michael

Chris, for some reason PMs stopped working. I get a user not found error for you! Anyway, my nichrome resistance according to the calculations, 10' of 16 gauge is 2.595 ohms.

cheers,
Michael

What's your measured resistance though?

Measured is 2.7 ohms.


I replaced my R5 with 3 15K in series to give 45K thinking that would get me in the ball park. Turned down the Velleman pot to its lowest, turned on the power supply, and the Velleman led came on for a split second, the relay clicked off and that was that - it seems to be dead.

Michael

Hmm it should not have done that. I can take some measurements for you but it will have to wait til this evening.

No worries, that would be good.

I replaced the original R5 and still no glory. Need to do some testing.

Well, its not the IC - I swapped that out with the good one I have. I also tried to trace the circuit and could not find what's wrong.

I'm wondering if you popped a diode. I did accidentally when I was messing with mine.

RadioShack carries them:
1N4148

Chris, you were right, a diode was blown. In fact it was D2 and I blew it twice. It seems to be very sensitive to any jiggling of the power wires in the terminal blocks.

Anyway, I was able to try again. I still only get to about 90°F. So I swapped R5 with a resistor around 24K and was able to get to 140°F but don't know what the top end is. Here's a photo:
This has the 1/8" phenolic under and .1" aluminum plate on top (7" x 7 1/2" to fit the H-1 table). The nichrome gets very hot but the warm-up time was long. I need to do some calculations, I suspect I was shooting for a top end of 225°F in my calculations and with convection cooling I am probably going to wait all day to get there.

I'll report back.

cheers,
Michael

I will verify with pics if I did any resister changes and verify temps with my touch probe.

Ok, so here is what I currently have:

bed is 7" x 7.5" = 50.75 sq. in.

120" of 16 gauge nichrome wire at 12 volts. According to the NichromeCalc, this is too "cold" and off the bottom of the chart in terms of power. Total resistance is 2.595 Ω.

So, playing with the calculator by holding the gauge and volts fixed, I decreased the length of the wire to decrease the resistance and increase the temp. Here's one combination I came up with:

at 77.5" of wire, the temp is 460°F requiring 7 Amps and 85 Watts. The total resistance is 1.68 Ω.
This seems like a reasonable option so down to the shop to cut the wire.

cheers,
Michael

Ok, now I am making progress.

I cut the nichrome down to 77.5" and changed R5 on the Velleman bored to a 15KΩ resistor. Now, with the pot pegged on max I can reach almost 200°F with the stock Velleman thermistor (the blue "bug" that comes with the kit).
As you can see, I am drawing 7.12 Amps and the temp is 190°F. I was able to get to 198° before the thermostat starts cycling. The aluminum sheet is very evenly heated out to the edges. Once this is sealed up and insulated it should be a pretty nice hot bed.

I am curious for those of you that have the MakerBot hot bed, how hot does the bottom of it get? Is it hot enough to warp or melt the H-1 table?

cheers,
Michael