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Cutting foam sheets... with a needle!

jhitesma

Some guy in the desert
Mentor
Oh, and the grey spots...yeah...too much oil. It doesn't take much and is easy to add more than needed. It should dry up fairly quickly though and then the spots will go away. When I have that happen usually it stops spotting after just a few minutes. Once I added the guide bearings to my cutter I found the oil didn't really give any benefit but I still do it out of habit. But if you need the oil to keep the temps under control it's probably a sign that you're still running too high of an RPM if you're using a proven cutter design. (If it's not a proven design then it may be too short or benefit from some form of guiding to help the needle have less friction in the welding tip.) Or you may have too high of a feed rate...but that seems to be the least common situation. I can run a high enough feed rate I see the needle deflecting but still don't get heat built up as long as the RPM's are within the safe range.

I don't even use 7.5mm cutting depth. I use 6mm for a full cut and 2.5mm for score lines and .75mm for marking cuts or paper peel lines where I just want to go through the top paper and not the foam.

The vacuum table does help a lot with keeping foam flat and consistent due to the way foam sheets just aren't very flat to begin with. I couldn't get away with the 0.75mm marking cuts until I switched to the vacuum table - they were always either deeper than I wanted or missed the paper entirely. I used to just put the foam down "crown down" so the high part was facing down in the center...and then some pins on the outside corners to flatten it out. And on particularly bad pieces of foam sometimes pins along the edges if it was still curling up with the corners pinned down. I used a sheet of 1/2" pink insulation foam as the spoil board so it would be larger than the foam and I'd have room to pin things down well.
 
Awesome insight into my current situation. Any chance you have pictures of your vacuum table setup? I'd like to try to make one as well. I suspect my temp issues were the result of me being ignorant and just bending my current needle back to "strait" after it popped off the bearing and was pulled around the foam before I could kill the cnc. I've switched to a new needle which seems to have made a really big difference. I'm inclined to think my motor speed isn't fast enough since my cuts at 7.5mm depth and 8mm/second resulted in a dotted line on the backside of the foamboard. Didn't take much to just run the Exacto knife over it to separate everything but I know it could be better so just going to be patient one more day till the optical tack gets here. I also have plans to set up my cnc to use the control board to manage the ESC at some point. I guess my question for you is regarding the modifications to the firmware, will that need to be reflashed if I were to switch the cnc over to cutting wood at some other point?

Edit: I wonder if my cutting depth is affected by the way I sharpen my needles? I've been putting a pretty deep taper on them, it probably goes up the needle a good mm or so. This is what the back of my foam board looks like
MVIMG_20200902_141152.jpg
 
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Yet another update on my journey, I've been too impatient to wait for the optical tachometer so I just tried to do some slower testing but twice now I've had the need sheer off where it wraps around the bearing. I managed to get a really clean bend with no sharp edges so I'm surprised to see it breaking there but suspect its the result of still being too fast on the motor RPM's... I'll know more on that front tomorrow. I'd like to see if anyone else can shed some light on the break given the included pictures. I looked a little closer and saw that the screw holding the bearing on the flywheel appears to be angled out from the center ever so slightly not sure if it's gotten hot and caused the PLA to get soft or what but I'll be printing one or two extra flywheels now that I'm realizing its got issues.
MVIMG_20200902_163344.jpg MVIMG_20200902_163323.jpg MVIMG_20200902_163243.jpg
 

jhitesma

Some guy in the desert
Mentor
Cutting depth it's important to get your zero right - which it's important to have your work flat :) Make sure the needle is fully extended when setting your zero - it's easy to bump it and then you wind up cutting deeper than you thought.

Setting up marlin to enable a servo output doesn't affect use as a normal CNC. It's just there when you need it. As long as you don't send the gcode commands to enable and set the servo it doesn't do anything. If you search this thread for my posts with 'servo' in them you should find details on how I set it up.

Same for the vacuum table, I've posted photos and I think even a link to an OnShape project for cutting it. It's just 3 sheets of foam board. One with horizontal strips cut out, one with vertical, and one with holes where the strips intersect. I cut all three out with the needle cutter then glued them together. Then I cut some openings in the side to fit a vacuum plenum that I think @rockyboy shared previously. Again - search on our posts with 'vacuum' and you should be able to find it.
 
Cutting depth it's important to get your zero right - which it's important to have your work flat :) Make sure the needle is fully extended when setting your zero - it's easy to bump it and then you wind up cutting deeper than you thought.

Setting up marlin to enable a servo output doesn't affect use as a normal CNC. It's just there when you need it. As long as you don't send the gcode commands to enable and set the servo it doesn't do anything. If you search this thread for my posts with 'servo' in them you should find details on how I set it up.

Same for the vacuum table, I've posted photos and I think even a link to an OnShape project for cutting it. It's just 3 sheets of foam board. One with horizontal strips cut out, one with vertical, and one with holes where the strips intersect. I cut all three out with the needle cutter then glued them together. Then I cut some openings in the side to fit a vacuum plenum that I think @rockyboy shared previously. Again - search on our posts with 'vacuum' and you should be able to find it.
ahh yeah, I have seen that!! I was more curious if that's how you went about it :) I'll make that my next project. Also, I didn't realize till today that is actually possible to search within a thread so I'll be doing a lot more of that and less posting since I know you guys have all answered these questions many times over. Either way thanks so very much for the guidance and advice.
 
Being computer nerd, I've gone down the OpenJSCAD route for the design of some components for my machine. OpenJSCAD is the Javascript version of OpenSCAD. As I was writing the code for different elements, I realised I was repeating myself so it was time to put it into a generic function. Here is a function called "plate" that accepts a list of holes to be drilled, with x/y coordinates and a diameter. It creates a 'plate' that has all those holes in it. Then you can just download the STL and print. An additional feature is the ability to create a counter-sunk/recess or a pillar at the site of the hole.

It seems like a common operation that others building CNC machines would find useful, so I'm sharing here.

JavaScript:
// title      : Drilled plate for needle cutter
// author     : Graham Agnew
// license    : MIT License
// revision   : 0.001
// file       : plate.jscad
function ccircle(r) {
    return circle({r:r,center:true});
}
// drillList is an array of arrays. Sub-arrays should have three or five elements.
// The elements are the drilled hole x, y, diameter and optionally a
// recess depth and its diameter. If the recess depth is negative then it's a pillar.
function plate(args) {
    const DEFAULT_THICKNESS = 3;
    let thickness = args.thickness || DEFAULT_THICKNESS;
    let drillList = args.drillList || [];
    let h = [];
    // Create the hull for the plate
    for (let i = 0; i < drillList.length; i++) {
        h.push(ccircle(drillList[i][2]/2 + thickness).
                        translate([drillList[i][0], drillList[i][1]]));
    }
    let p = hull(h).extrude({offset:[0,0,thickness]});
    // Add the drilled holes
    for (let i = 0; i < drillList.length; i++) {
        let recess = drillList[i][3] || 0;
        if (recess > 0) {
            p = difference(p, cylinder({r:drillList[i][4]/2, h:recess}).
                    translate([drillList[i][0], drillList[i][1],thickness-recess]));
        }
        if (recess < 0) {
            p = union(p, cylinder({r:drillList[i][4]/2, h:-recess}).
                    translate([drillList[i][0], drillList[i][1],thickness]));
        }
        p = difference(p, cylinder({r:drillList[i][2]/2, h:thickness-recess}).
                        translate([drillList[i][0], drillList[i][1]]));
    }
    return p;
}

function main () {
    let wp = 80; // width of plate
    let hr = 20; // height of rail
    let dw = 25; // diameter of wheel
    let db = 5; // diameter of bolt
    let m3 = 3;
    let de = 7; // diameter of eccentric nut
    let tp = 3; // thickness of plate
                // also used as the thickness of the plate beyond the hull
  
    let mm = 31; // motor mount spacing for NEMA 17

  return plate({drillList: [
        [-wp/2,dw/2,db], [wp/2,dw/2,db], [0,-(dw/2+hr),db]
        ,[-mm/2,0,3,-13,10],[mm/2,0,3,-13,10],[-mm/2,mm,3,-13,10],[mm/2,mm,3,-13,10],[0,mm/2,25]
        ,[-mm/2,-mm/2,db],[mm/2,-mm/2,db]
      ]});
}
The code above can be pasted into OpenJSCAD.org, and then modified to your liking and the STL downloaded for printing. The sample here looks like this:

1599338263104.png
 
A cautionary tale: when I built my needle cutter/CNC machine, I got 6 ft lengths of extrusion and cut them down to allow for the X axis and Z axis mechanisms. All was well until I added the needler to the mix. The additional couple of inches added meant I couldn't cut a full 48" sheet of MPF . I rearranged templates and files to shorten them for a while. But then I wanted to cut a 33" Blu baby and couldn't get it to fit 24x45" sheet. Finally got the idea to extend the 1" foamular spoiler board past the fwd end of the frame. No vacuum holes in it, but the sheet still lays nice and flat. A bit rube goldberg, but it works!

The moral? Make sure you are positive of your extrusion needs before you cut them!
 

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dkj4linux

Well-known member
Okay… today was laser day.

Remember the “20W” laser I “zapped” with static a while ago? I ordered a new controller off Ebay that looked as though it should work.

I set up the “zapped” laser module for retest… to confirm what I was seeing before setting it aside.


Sure enough it was acting the same way… Grbl gcodes M3S0, M3S10, M3S100, M3S500, M3S1000, M3S0 seems to be working… but the laser output was pitifully weak. So I removed the old laser controller board and installed the new. Fully expecting to see the laser at full power again… I was disappointed the see that the new one acted exactly as the old one did. So, now I know the laser diode itself is what suffered the static damage. Oh, well.

Here are a few photos of the board replacement. The test set up with just the laser power and PWM outputs hooked up (not seen is the Pi 3B+ and CNC.js I’m using to control things)…

20200909_154313.jpg


The replacement laser controller board in the middle…
20200909_154720.jpg


Old controller and fan disconnected from board…
20200909_160744.jpg


The old controller board (bottom) and new (top)…
20200909_160831.jpg


The new controller board has been installed and powered up…
20200909_164108.jpg


As noted, the new board acted exactly as the old one… it recognized gcodes, but the output was pitifully weak. So, one mystery “solved” (that is, I know what’s wrong with it)… and on to the next.

I received a second Neje 6W laser module this past week, finally catching up with @geodave… <nah-nah-na-nah-nah!> ;) And, though I had ordered and received the 5v to 3.3v level converter boards as well, I still questioned the need for them. So I revisited all the Neje laser module webpages I could find once more, seeing time and again the 3.3v - 12V PWM claim on the modulation input… and since I had a working lashup sitting there on my “bench” I decided the heck with it. So I unpackaged one on the Neje modules and hooked up the power pins to +12V and GND… and the PWM pin to the same +5V PWM I use with all my other lasers. And, voila! A working laser.

Time will tell, of course, but I’m pretty sure the Neje laser modules PWM input is relatively “bulletproof”… in the least, handling +5V PWM okay. This pretty much sets my mind at ease and, providing these work as well as hoped, it’ll be nice to have a line on a relatively inexpensive, and reasonably powerful, diode laser module. Thanks, Mike (@dart1280) on the V1Engineering site, for providing a link to these laser modules!

– David
 

dkj4linux

Well-known member
So you have experience with 2.5, 6 and 20 watt lasers. What are the pros and cons/capabilities?
Hey, Mike. Actually, no... I don't. The 20W unit really was only ~5.5W and the Neje 6W unit seems to be more like 2W-2.5W, at best.

Remember the muscle car horsepower "wars" from the 60's... with everybody fudging the numbers and claiming more horsepower than their competitor? It's kinda like that with lasers now... they're actually quoting the *input* operating power... not the actual laser output power. The Neje 6000 runs on 12V at about 0.5 amp... wait for it, 6W! And the 20W unit did, in fact, have significantly greater power... until I blew it up with static. But the largest single diode lasers are about 5.5W, as I understand it... and guess what? Operates on 12V at a little less than 2A... or, 20W! Wow! :rolleyes:

I really would have liked to play some more with the 20W unit but I don't really feel "led" at this point to pay $100+ for a new one. So, I'll muddle around with these lesser ones for a while and see what gives.

-- David
 

dkj4linux

Well-known member
Oh. to answer your question... the Banggood/Eleksmaker 2.5W and 3.5W lasers I have are, I think, actually rated more properly. I find, however, that I seem to be able to do as well with the 2.5W as the 3.5W... I think because of a smaller spot size for the 2.5W unit. I simply cannot get the 3.5W unit focused as tightly as the 2.5W one... and it's better IMO to have 2.5W concentrated on a unit area than 3.5W spread over 2-4 times that area.
 
Ha! Not Led..... interesting on the ratings. That sounds like what I was reading back when banggood started proliferating laser modules. Higher ratings, but they all worked about same. So what's the difference, efficiency? We get scammed by higher input power, for less efficient unit? Is this some natural barrier, or are "real" uses just not needing more power? Like dollar tree foam properties are defined by the gazillion used for posterboard and garage sale signs, not the hundreds of sheets used for model planes.
 

dkj4linux

Well-known member
Ha! Not Led..... interesting on the ratings. That sounds like what I was reading back when banggood started proliferating laser modules. Higher ratings, but they all worked about same. So what's the difference, efficiency? We get scammed by higher input power, for less efficient unit? Is this some natural barrier, or are "real" uses just not needing more power? Like dollar tree foam properties are defined by the gazillion used for posterboard and garage sale signs, not the hundreds of sheets used for model planes.
Talking through my hat, I'm pretty sure it's the size and shape the chunk of laser material and the fact that the "beam" is not really round/circular, but more rectangular... if you defocus the beam a bit I think it's pretty easy to see. I also think I remember reading that the most powerful single laser diode currently made is only about 5.5W... and gets physically larger -- and with a larger spot size -- the more powerful it is. So, though a higher powered laser puts out more total energy than a lesser powered one... its energy is spread over a larger area and not really that much more effective, if any, than a lower powered one...

I'm pretty sure this is what I was seeing when I first tested a Banggood 3.5W laser and found it a bit disappointing that it didn't seem any more powerful than my 2.5W unit...
 
All,

Thurmond "Tritium" Moore informed me that several FliteTest "residents" ("RAM", "Bricks", "Tritium", etc.) had discovered my CNC-driven foam cutter... I found their posts in the "$150 Laser Cutter" thread. After snooping around a bit more, it appears there is interest in an economical alternative to lasers, modified plotters, sewing machines, etc. for cutting foam sheets.

Basically my foam cutter is a very fast reciprocating needle -- like a sewing machine -- mounted on your CNC machine. Set in a feed rate that yields 10-15 strokes/mm and you can cleanly cut DTF (paper on), blue-cor fanfold foam, etc. Pin a sheet of foam board onto the bed of your CNC, load in the plane's gcode, set the origin, and start the machine. Twenty minutes or so later you have a sheet of parts that are accurately cut, easily punched out, and hot-glued together. Score cuts are no problem.

The foam cutter itself can be built and easily adapted to your CNC machine for less than $20 worth of parts (less if you're a scrounger) and a little bit of your time. If you are interested in building one for yourself, I'm more than happy to monitor this thread, answer questions, and further interact here but rather than repeat *everything* I'll also provide (in a following post) links to other threads/sites that deal with the active design/development of this foam cutter and Ryan "Allted" Zellars' fantastic Mostly Printed CNC... and provides you with all the information you need to build and adapt one to your needs. -- David "dkj4linux" Johnson

All,

Thurmond "Tritium" Moore informed me that several FliteTest "residents" ("RAM", "Bricks", "Tritium", etc.) had discovered my CNC-driven foam cutter... I found their posts in the "$150 Laser Cutter" thread. After snooping around a bit more, it appears there is interest in an economical alternative to lasers, modified plotters, sewing machines, etc. for cutting foam sheets.

Basically my foam cutter is a very fast reciprocating needle -- like a sewing machine -- mounted on your CNC machine. Set in a feed rate that yields 10-15 strokes/mm and you can cleanly cut DTF (paper on), blue-cor fanfold foam, etc. Pin a sheet of foam board onto the bed of your CNC, load in the plane's gcode, set the origin, and start the machine. Twenty minutes or so later you have a sheet of parts that are accurately cut, easily punched out, and hot-glued together. Score cuts are no problem.

The foam cutter itself can be built and easily adapted to your CNC machine for less than $20 worth of parts (less if you're a scrounger) and a little bit of your time. If you are interested in building one for yourself, I'm more than happy to monitor this thread, answer questions, and further interact here but rather than repeat *everything* I'll also provide (in a following post) links to other threads/sites that deal with the active design/development of this foam cutter and Ryan "Allted" Zellars' fantastic Mostly Printed CNC... and provides you with all the information you need to build and adapt one to your needs. -- David "dkj4linux" Johnson

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