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RC Keith CNC Hot Wire build log

thenated0g

Drinker of coffee, Maker of things
Mentor
#25
Got a lot done this weekend. Towers are fully assembled and i just have to make a spot for them on my workbench and get the motors wired to the controller
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Here they are with the distance between the wire attachment point on the towers exactly at 30". It requires about 53" wide of space.
IMG_20180603_183740.jpg IMG_20180603_184057.jpg
Starting to wire up the controller
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thenated0g

Drinker of coffee, Maker of things
Mentor
#26
Did all the wiring over the past couple days and got into the Linuxcnc setup configuration program this morning. Having a couple issues getting motors spinning but they are "thunking" so i know they are connected. Only spent about 10 minutes on the issue so im sure its just something simple like the limit switches be reversed or forgetting to turn the estop off.

Still considering how i want to accomplish getting heat to the wire. The 3 options in my mind are to use a power supply (server PS in pic below) with a dimmer switch, lipo charger with a hot wire function (allows control of voltage and amps, or purchasing an adjustable power supply ($25-50).

IMG_20180606_214503.jpg
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Also i wanted to post some more about the geometry of the table and how you can "trick" your software into cutting more sweep in a wing than you think you can.

As i discussed above in an earlier post, I originally wanted to make a wide table, maybe around 50" cutting area. But i had to adjust the width of the table to accommodate the sweep i wanted to cut. Have the tables closer together reduces the the distance of travel on the horizontal axis to achieve that cut.

In the pictures below, the black shape represents the wing i want to cut, the lines extending out represent the position the wire needs to get to to cut, red is the cutting table, and green is an imaginary shape.
In this picture you can see that with a 60" wide table you cannot get the cut you need, the towers cannot travel far enough
2018-06-05 (1).png

Because of that i was going to change my table width/wire length to 30". You can see that this allows the towers to get in position.
2018-06-05 (3).png

What if instead we could rotate the wing on the cutting area and line up the trailing edge with the hot wire, what would that do? This is the exact same wing but lining it up with the trailing edge. You can see that now it allows for a much wider bed.
2018-06-05.png

In this tutorial i am trying to use all free software, so this problem may not be an issue in other payed software. In the free software you cannot "place" the wing down on the bed and position it like you can in a 3d printer slicer, like cura. It just assumes that the square block of foam is directly in "front", squared up to the front of the cutting area and centered. So what we need to do to accomplish this "rotation" of the foam is to trick the software by "hiding" the wing we want inside an imaginary shape we are going to have the software cut out for us. We will position our foam in that area in such a way to get the shape we want.

Keith will have a video out soon explaining this concept and i will post it below, but i had a few questions when i posted this on IG so figured i would document what i could now.

What we want to do is rotate the wing so that the trailing edge is parallel to the wire (bottom of the table is home). Than we need to measure a box around that shape (green box). What we want from that is vertical and horizontal dimensions. The vertical up and down length will be the wing ROOT Chord we enter in the software. The Horizontal length along the wire is our wingspan. The right dimension up to where the leading edge crosses it is our new tip Chord. Now you could either cut the foam to shape of our desired wing ahead of time or you could trace the shape of the wing on a block of foam and cut the faces manually after the gcode runs.
2018-06-05 (2).png

Its kind of a strange concept, hope i explained it ok. Like i said, i will post Keiths video once he has it out.
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#27

I was having some issues getting the motors to spin up. When you setup the axis there is a button to "test" the motors and spin them. But it wouldnt spin. But as soon as i would close that test box they would "thunk". If you have a 3d printer its similar to the motors being disabled so you can move them around manually. So i knew i had it connected. Turns out i made it more difficult than it needed to be. I had manually setup the inputs in the software. These are the options that tell linuxcnc what is connected to the 25 pins of the printer cable. Unknow to me there are presets for known controllers. So i selected tb6560 4 axis and bam...i had one of the pins set wrong. Motors spinning!

After that i had a few more issues related to using a new CAM software. I didnt know that the ESTOP is automatically enabled when the software turn son, I hadnt plugged in my Home/limit switches but had enabled them in software, and i had no idea how to "place" the towers in position. I think its called a soft start. So basically the gcode was telling the motors they had to go into negative space past the limits of the table. Once i figured out how to move the towers forward AND tell linuxcnc i had done so (soft start) it ran the cuts. Really beautiful sound after wanting to build this literally for 2 years.

IMG_20180607_215229.jpg

In the picture below you can see the trailing edges of the wing in blue and green. They are behind the limit of the table by 10mm. Thats the -10.0 in red. It was telling me the problem i just didnt know what i was looking at. Now i can clearly see them sticking outside the red box indicator of my cutting area.
IMG_20180607_220155.jpg

This weekend i am going to work on getting the home and limit switches working so i can use that to automatically reference HOME and get into position for cutting. Also will get the lead screws installed so i can see some towers moving.

This morning i started modding my dell server power supply to give me power for whatever i use to heat the nichrome wire.
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#28
Wow! What a great build! Your documentation of your progress is great too. Thanks for sharing this with the community.
Do you still use the NCGen? I personally know the guy who wrote it. He is the same guy who sells the Foam Casualty CNCs. I use the NCGen for all my designs. I am using a slightly altered version of LinuxCNC Axis on my machine. It works great, versatile, and has a nice GUI. It is easy to get into the ini files and change things as needed. Even add your own buttons that perform various functions like a cutoff or turn on/off the hotwire for testing.

I don't know, is LinuxCNC Axis the same as just LinuxCNC?
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#30
One thing i have come to realize is that cnc hot cutting is much like 3d printing or any other hobby. You are never going to get the perfect settings or beable to just take someone else's settings and they are perfect. You have to come to understand your machine. That happens by experience, which means using it a lot. And in this case, going thru a lot of foam practicing over and over. You should see the pile of wing cores on my work bench. Heres the very first thing i cut out. Way too hot or not enough speed. Lots of variables to change and test.
IMG_20180608_203052.jpg

Some guys online suggest going very slow and low power. Some guys say crank it up and go fast so that the wire is never touching. Im still playing with these settings but do have able to cut nice things. I tried going the slow/low route first. I think i will try the other way soon and crank up the heat. Some places online say you want it almost dragging the foam and you should have very fine hairs left behind on a good cut.
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At first i was using a 6s battery thinking i needed a ton of power. But at the moment i am using a 12v pc power supply. 95mm a minute is my cutting speed and about 13watts of power.
IMG_20180610_211558.jpg

Did some wire management this weekend as well. I need to come up with a different solution to hold the foam in place, but this is working for now. I got a piece of foam that was above and below the limits of the bottom and back corner of the cutting area and cut myself a "flat" area (to the axis at least) for the foam to sit.
IMG_20180610_132209.jpg

I have been having a couple issues here and there which i will discuss later, but right now i can load in a shape and cut it. Getting it perfect will be something that just happens as i continue using it. Also i have heard from several sources that using a denser higher quality foam makes getting good cuts a lot easier. Im sure as soon as i get some epp or other foam i will be back to testing cuts and finding a good speed/heat again.
 
#31
First, I admit that I am unfamiliar with this software. So my question is does the software automatically keep the wire aligned as it cuts the tip and root of a tapered cord? When using a hand controlled bow that was always a point of issue. If you previously discussed this I apologize for missing it.
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#32
First, I admit that I am unfamiliar with this software. So my question is does the software automatically keep the wire aligned as it cuts the tip and root of a tapered cord? When using a hand controlled bow that was always a point of issue. If you previously discussed this I apologize for missing it.
In the webpage software you describe the shape of the wing that you want. You give it the root airfoil and the tip airfoil dat files. It figures out the positions of the two towers to get the wire in place to trace that shape in the foam.

you cut out your piece of foam with the span exactly as you put it above and the chord of the foam should be a little bit bigger than the deepest cut). I usually plan this out ahead of time in inkscape or fusion 360 to figure out a piece of foam that will fit the cuts.

The NC cutting file the website or design software gives you is telling the towers how to get in position to make those cuts. I will put some pics below to show you the end product i currently have from testing. Really nice leading edge, flat leading edge and the trailing edge just gets paper thin before disappearing.

Not sure if im answering your question. Ask me anything you want, its not bothering me. I am still troubleshooting and experimenting. Trying different wires. When doing manual cuts i was using 90lb fishing steel. For this setup i tried nichrome 24g. I have some Rene 41 28g on order. There are lots of different opinions online. Go really slow with low heat, go really fast with high heat. The wire should be almost dragging, the wire shouldnt be touching the foam at all......

Last night i was doing a pretty extreme sweep, this meant that one tower got really far from the other. The distance between towers when they are "homed" and parellel is about 39.75 inches. When one tower all the way forward the distance is about 50". That means the springs have to beable to keep tension at 39.75 but beable to streatch 11 more inches. I found out quickly that my springs are NOT meant to streatch like that lol. Machine ground to a halt. Heating wires popped of the wire from so much stretch and the wire cooled pulling all my foam forward. lol.

Hitting ACE today for some more springs.

I have only had a 3d printer for about 2 or 3 months and i find the two very similar. You have to play around with the settings and learn the machine. Even part to part you will probably have different settings you go to. I was thinking that depending on the sweep angle i am cutting i may have a selection of springs with different tension or stretch that i switch out.
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PsyBorg

Fly Angry
Mentor
#33
That cut looks as good as any production cuts I have seem maybe even more smooth already. Just the super thin trailing edges are like flashing from injection molding so I imagine some post cut cleanup is expected like anything else foam / plastics.

I would say what ever settings you used for that particular cut were spot on.
 

thenated0g

Drinker of coffee, Maker of things
Mentor
#34
Yeah you usually would trim the back and remove the control surface area to be replace with something more rigid. Maybe even put a wooden TE spar in.
 
#35
In the webpage software you describe the shape of the wing that you want. You give it the root airfoil and the tip airfoil dat files. It figures out the positions of the two towers to get the wire in place to trace that shape in the foam.

you cut out your piece of foam with the span exactly as you put it above and the chord of the foam should be a little bit bigger than the deepest cut). I usually plan this out ahead of time in inkscape or fusion 360 to figure out a piece of foam that will fit the cuts.

The NC cutting file the website or design software gives you is telling the towers how to get in position to make those cuts. I will put some pics below to show you the end product i currently have from testing. Really nice leading edge, flat leading edge and the trailing edge just gets paper thin before disappearing.

Not sure if im answering your question. Ask me anything you want, its not bothering me. I am still troubleshooting and experimenting. Trying different wires. When doing manual cuts i was using 90lb fishing steel. For this setup i tried nichrome 24g. I have some Rene 41 28g on order. There are lots of different opinions online. Go really slow with low heat, go really fast with high heat. The wire should be almost dragging, the wire shouldnt be touching the foam at all......

Last night i was doing a pretty extreme sweep, this meant that one tower got really far from the other. The distance between towers when they are "homed" and parellel is about 39.75 inches. When one tower all the way forward the distance is about 50". That means the springs have to beable to keep tension at 39.75 but beable to streatch 11 more inches. I found out quickly that my springs are NOT meant to streatch like that lol. Machine ground to a halt. Heating wires popped of the wire from so much stretch and the wire cooled pulling all my foam forward. lol.

Hitting ACE today for some more springs.

I have only had a 3d printer for about 2 or 3 months and i find the two very similar. You have to play around with the settings and learn the machine. Even part to part you will probably have different settings you go to. I was thinking that depending on the sweep angle i am cutting i may have a selection of springs with different tension or stretch that i switch out.
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thenated0g

Drinker of coffee, Maker of things
Mentor
#39
Shifting gears and going to a different gcode/cutting file design software.

Over the past couple weeks i have been slowly dialing in the speed and heat i want for this xps/Homedepot foam. I have finally settled on Rene 41 28.5g wire. It is amazingly small and strong. Kerf so small its almost like doing a razer blade cut on the fast side (root). I guess because it is so small, the mass, that even putting what would normally be too much heat thru it, it just doesnt radiate as much heat out into the foam, or not as far. Pretty happy with it. I think i got about 10 feet for $6 or so dollars from Jacobs online. Shipped super quick.
At the time of posting this i am using 100mm a minute speed and around 11 watts of power, around 11.96v i think.

Here is an example of how nicely its cutting as of 6/16/2018
http://instagr.am/p/BkErSGrlnha/
But, since i have been testing on scraps, i have never had a reason to try cutting out a left and a right side. This weekend i was attempting my first project and ran into problems with the mirrored side. Long story short, there is something not quite right with the web page cutting program. One side not only cuts a different speed, but the geometry is drastically different as show below.
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Linuxcnc display window is fine, but it comes out really strange. It should be cutting out both roots on one side and both tips on the other, which it is, but as shown they are way different.

So as I wait for the web page to get fixed Keith suggested i try out Jedicut. Its also a free product, but is a windows program, not a webpage. It will do cutting files and CAM, but i will be using it to output a gdcode file since i have linuxcnc working already. While they do have an english version to download, the error messages are still in the french language, so some googling is required lol

Also as a side bonus when googling issues with it you pretty quickly get into some light saber battle results :)

I will post as get more into this program.

https://www.jedicut.com/en/

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Balu

Moderator
Staff member
Admin
Moderator
#40
I do like the pulley idea. In fact you could probably use a sensor to adjust the speed of the foam "feeder" or the heat by measuring if the wire gets pulled too much...