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Cutting foam sheets... with a needle!


Old and Bold RC PILOT
I cut the parts for the Edge the day after the plans were released. Fun build and it flies great. If I were to do it again I would re-enforce the motor box. after three flights mine is getting pretty spongy.... another reason why I'm looking at the water resistant stuff. I also added some sticks on the elevator.. one landing in tall grass and I wrinkled one side since the throws are so big and the leading edge hit the grass. View attachment 112785 View attachment 112784
There is a simple way to strengthen the FB (motor pod), without a major rebuild or similar and that is to paint it with PVA glue. Allow it to dry thoroughly and it stiffens the FB so much that it is like adding wooden bracing. Be careful though as the FB will become rather brittle as a result but it definitely will not be soft or spongy any longer!

have fun!
I decided to go ahead and craft a flywheel for the Emax CF2822 1200KV motor that I've been using on previous cutters... everything is a nice press-fit. I'm targeting 6000-8000 rpm since that is a common cutter speed for 600-900 mm/min feedrate or so. I also need to add a reflective strip to allow optical tach measurement of the speed and make some careful weight measurements of all the components to see just how close "pencil-whipping" the problem matches up with actual measurements and performance.





Alright... I'm chickenin' out. The relatively large diameter, relatively heavy, plastic flywheel gets pretty uncomfortable above a few thousand rpms... there's a lot of energy there. Symmetrically configured, but not perfectly balanced, there are resonances enough that cause the bench/table to shudder and vibrate... and I haven't even introduced any intentional imbalance yet. No way I'm comfortable trying for 6000 rpm... and I suspect it would be a nightmare to balance for most of us :eek:

So, I gave it some thought and recognized the needle cutter has always been a light load for these motors. So, I dropped all the exterior flange and pennies and decided to just do the "hub" section... keeping the embedded eccentric bearing and comfortably able to do the 6k - 8k rpm we'll need. The motor has plenty of power to drive the needle through the foam and apparently the motor bell and magnets is "flywheel" enough. So I'm going to take the easy way out for now... it's still a major departure from my previous flywheel assembly ;)




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Yeah, it'll need counterweight... no different from my previous flywheel. This is a first SWAG (scientific wild-a$$ guess) at a newer design... it will change. The extra bearing would get it closer, of course, but ultimately, I think it really comes down to how smoothly it runs with the the needle and guides installed. On my previous "flywheel", I had holes further out than the bearing location to put smaller counterweights opposite... this one I'm thinking of putting a radial hole (in the edge) to receive the threads of a long-ish screw with nuts/washers for counterweight, opposite the bearing position.
Bad penny! Bad, BAD, penny!

Did you know... pennies before 1982 were 3.11 grams (48 gn) and, after 1982, were the same exact dimensions but only 2.5 grams (38.6 gn)? And, wouldn't you know... I had randomly picked ONE pre-1982 penny out of my penny jar and all the rest were post-1982? No wonder that flywheel was so scary :eek:

Alright! With things now making more sense (cents?)... I still may not use it but the larger-diameter flywheel isn't really so scary when all the pennies are [nearly] the same weight. Easily got to 6000 rpm with just the basic, symmetric configuration... no eccectric stuff.

So, this morning, I've pulled out the Dubro prop-balancer that I had bought and never used... and got it assembled. I also located my small digital scale... and verified my pennies. I've also discovered that gravity still works... and now I'm off to see the wizard! :)
Well... so far, so good. The new slip-on flywheel (sized for Emax CF2822 1200kv motor) and a draft-quality cutter platform are shown in the following photos. It spins quite nicely up to full rpm with 7.4 volts and 0.9 amps... ~7300 rpm, ~6.5 watts, with needle installed. The overall cutter is more compact than my previous cutters and I've incorporated the standard MPCNC tool mount. I'm using laser-cut upper and lower needle guides, with a cotton-wad oiler (shown on gray cutter platform ) installed in the area between them. I'll try to get some actual cutting tests done in the next few days... :) -- David










For those following this build, here's installation of the cotton-wad oiler. It's easiest to put the needle in place prior to stuffing the cotton down into the cavity, around the needle. I usually pick up about 100 rpm at full throttle and drop the power consumption by about 0.2-0.3 watts over one without the oiler. Saturate the newly installed cotton with light machine oil and, after that, apply 2-3 drops to the needle where it enters the upper guide, every few sheets of foam. -- David







Its been a while since I've been able to get involved here, mostly due to life changes and I can see a lot of stuff has happened in the last year or so.

Jason, I'm deeply saddened at your tragic loss. I can't even imagine the pain you and your family must be going through. There's nothing anyone can say to make it any better. I just hope and pray that you and your family can find the strength in each other to see you through this. Time doesn't heal, but time does allow you to remember with a smile.

Deepest condolences,
An update...

Not unlike the old man who swerves unexpectedly on the highway... I've made a change of direction. I finally realized that -- with my new milling MPCNC and a new slip-on flywheel -- I also need a new foam-cutting machine. And, our own Mark ("moebeast") of FliteFest fame, had developed just the machine I need... a machine he calls Foam Ripper (https://www.thingiverse.com/thing:2520214). He also wrote up a great FT article describing it... https://www.flitetest.com/articles/another-cnc-foam-board-cutter.

Mark's machine began as a quest -- on the heels of his wildly successful MPCNC foam-cutting exploits at Flite Fest East 2017 -- to see how inexpensive a machine he could build. The resulting LowRider-inspired foam-cutting machine has fixed Y-axis rails and a Y-carriage with limited-range Z-lift and integrated needle cutter... and ultimately uses one less stepper motor, about half the number of bearings, and a quarter of the hardware, of the MPCNC. Here's his Foam Ripper machine in action...

So far, I've downloaded all the files, printed the major parts, and milled a couple of thin test plates for fit-check purposes. While the prints were accomplished without issue, I had scaling issues with the DXF file (X_Carriage_plate1.dxf) for 60mm wheels. I had to scale the DXF file up by 1.068 to get proper Nema 17 motor mount screw spacing (31mm) and 8mm hole diameters. I also had to center the narrow slot between the two wide slots in the upper portion of the plate to gain full range of Y-rail height adjustment. I then exported a new DXF file and imported it into Estlcam to generate the gcode for milling the plates.







My plan is to build the machine as Mark designed it... with the only deviation being a new needle cutter with slip-on flywheel to affix to the Z-axis "rails". Further, I want to keep the bed size "small-ish" -- just large enough for the vacuum bed, as seen in Mark's video.

More to come later... :)

-- David
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Some guy in the desert
I assume you've seen Ryan (Allted's) latest low rider design? Has me wondering how the needle cutter would do with it. Not sure if the needle cutter is heavy enough to work without lower wheels or not....Could try leaving the lower wheel off on the foam ripper and see how it does ;)

And thanks for the condolences everyone. We're just taking it day by day and trying to figure out what normal is now. Trying to stay positive and make sure I provide a great future for our daughter even if I have to do it myself now. Hobbies are definitely taking a bit of a back seat for at least a few months while I deal with the crazy amount of paperwork and lawyers that go along with something like this - but my daughter is showing more interest in my hobbies than before so who knows. Her girl scout troop is also looking to do some STEM related activities so I may be more involved in helping them with those soon too which will be nice for both of us.
It's great to hear from you, Jason. We are, of course, looking froward to having you back regularly... but please do it on YOUR timetable. I do remember the tremendous adjustment and amount of paperwork and procedure when I lost my wife 2-1/2 years ago. Thankfully, my daughter (grown) was there for me, to help me get things done and make some sense of all the yuck... I could not have done it without her.

Hang in there, Jason... we're still thinking and praying for you and your daughter. I'm glad she's taking an active interest in things and the STEM stuff sounds like it's right up your alley... and hers! :)

I'm familiar with the LowRider(s) and they certainly can do the job... my biggest hangup with it, however, is the larger, more expensive, SS tubing required. Mark's FoamRipper is IMO simpler, still uses 3/4" EMT, and is better suited to dedicated foam cutting and other light duty chores and a not-too-large work area. And, now that I can mill material (quite nicely, thank you!) on my recently-passed buddy's MPCNC rebuild -- hmm, maybe I ought to just name the machine "Henry" in his honor -- and have a new slip-on flywheel in development, I needed something "new" to play with and show off these new capabilities... and Mark's machine fits the bill nicely. And I'd love to see his creation get some more exposure... it's a really neat machine and far simpler/cheaper than any foam cutter system I've seen to date.

I hope to have an update later today... the build is really starting to take shape! -- David


Some guy in the desert
I'm familiar with the LowRider(s) and they certainly can do the job... my biggest hangup with it, however, is the larger, more expensive, SS tubing required. Mark's FoamRipper is IMO simpler, still uses 3/4" EMT, and is better suited to dedicated foam cutting and other light duty chores and a not-too-large work area.
Fully agreed. Was just thinking they're both kind of similar in that they ride on the table rather than being a self supporting machine. So was wondering if it may be possible to eliminate the lower wheel on the foam ripper as well to further simplify it and make it even cheaper.

I know Ryan said he was able to eliminate the lower wheels on the low rider because with proper feeds and speeds there's very little force in the Z direction. But...that's with a router/spindle. I just wonder if the needle would work like that or not...there's not a lot of force needed to puncture foam - but is it low enough that the lower wheels could be eliminated?
Alright! The promised update...

Last evening I spent about 2-1/2 hours riding herd on the milling of the two plates. I found, in my junkpile, an old broken, 18mm thick, particle-board panel from some crap piece of furniture long lost and forgotten. The tiny 1/8" single-flute endmill (from Ryan's shop) worked beautifully though I had to press off the little plastic depth collar to get enough bit showing to get through the panel. Milled at 10 mm/s and 5mm depth of cut and finish passes on all pockets... a slow procedure but quite accurate. I was thrilled...



So, this morning I started assembling one of the end plates. Mark's article leaves out a bit of detail, especially the spacers and bits to locate the wheels and idler bears, relative to each other... and the edge of the table. Took a few SWAG's at things and printed off things I thought it needed... and finally arrived at a freely rolling gantry on a 2' x 4' piece of plywood I had. Set it up on a short, roll-around, wire-shelf unit my wife had purchased somewhere along the way and I now have something I can walk around and touch/probe/prod/ponder what needs to be addressed next.
















Obviously, I need to make a lot of adjustments now... I wasn't expecting the belt to run so close to the table edge but that does appear to be the case with Mark's machine as well, judging from pictures in his article. i'll also probably change the plywood bed to MDF... I have a 4' x 4' piece over in the other house that I may cut a bit narrower. Mark used a 32" interior door... probably a better and lighter choice but I don't have one in my stash. I'd like to keep it on the smallish side but at least 6" more than the 24" width shown here... 30"-32" wide and 48" long should be just about perfect, large enough to comfortably place a DTFB sheet and vacuum hold-down setup, like Mark's. I did opt to merge the MPCNC tool mount with Mark's Z-slide setup so that any MPCNC tools could be mounted... as long as they fit between the rails. Mechanically, now, the basics are in place and I have something to play with. I'll belt it up and wire it as soon as I think it sound enough to proceed.

I don't know yet how necessary the lower wheel assembly is... but the plate DXF already had the slot and I had the wheels, bearings, and hardware to populate it. It shouldn't hurt anything so I'll go with it for now... I may just put a wing-nut on it and slip it up "close" to the bottom of the table edge, just for grins.

Anyway, there it is. Thanks, Mark, for sharing it with us. You hit your target dead-center IMHO... wanting to "see how inexpensive a machine [you] could build." I think this is really gonna be a neat machine... the simplest and least expensive foam cutter setup I've seen to date.

Great job, Mark!

-- David
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Well, Jason... you've got me thinking now. Uh-oh... :rolleyes:

Playing with belt position a bit ago and watching the gap between the endplate and edge of the table vary just a wee bit as I ran it back and forth by hand (motors aren't wired up yet!), it occurs to me that the edge of the table and the line of the taut belt may be the determining factors as to whether this thing runs straight or not. Under motor power, maybe it's more the belt(s)? Anyway, as I looked at it, I began to wonder...

If the bottom wheel *is* unnecessary (and it does indeed seem to be the case with the LR2)... then why not chop the entire bottom off the endplate and provide a simple clamped track/edge of some sort to guide the wheels/endplate across any flat surface? No table edge needed. Kind of a portable track-CNC system... belts and track, clamped across any flat surface. We could probably get away with it for foam-cutting and other light loads, I'll bet?

As Mark designed it, it's actually quite portable as is... think maybe he had that in mind for the next FliteFest event he attends? ;) A light-weight interior door on sawhorses, run not-too-heavy gantry into place on door, stretch belts semi-taut along door edge, and clamp belt ends in place... viola! Again... great job, Mark! I think I'll go with it as designed... for now ;)

Anyway, some more pictures...








-- David


Skill Collector
That's a great looking build David! I love the idea that it can run off a simple interior door for the torsion box with just an extra layer or two of DTFB for a spoiler board and simple clamps for the belts.

It really does become a portable setup that could be used at fly-ins, club meetings, science fairs, etc. unlike my Lowrider build which is on wheels and can move about the shop, but would need a dedicated trailer to transport.

Now I want to make another CNC machine :D
Well... now he's done it! Rockyboy has placed himself squarely on the list of usual suspects... and MUST shoulder the blame for this shocking (not really ;)) turn of events. He has shamed me -- shame, shame, I say! -- into taking the path of least resistance.



Lazy as I am, I decided It was actually easier to drive the 4 miles to Lowes and pick up a 32" x 80" interior door for $30... than it was to go 100 yards to the other house, wrassle a half-sheet of 3/4" MDF out of the house, drag out the circular saw, take half-a-day to set up the precisely parallel (to the factory edge) cut, exactly 32" away, and create all kinds of angst and fear of not doing it as accurately as "factory". Or, manhandle it up onto my small table saw... yada, yada...

A considerably larger work surface than planned, I guess I'll have to figure out how to live with it for a while... I do have one bedroom devoted to hobby storage and work area. Once I get it wired and running maybe I'll move it back there. I don't like the bedroom for my "base of operations" but the needle cutter is relatively clean and I don't mind letting it run unattended at times... especially if I can hear it.


Eventually, I may chop it off to 48" (or, possibly, 60") to make it a little more manageable but, realistically, I doubt I'll actually need the portability it offers. I'll leave that to Mark ("moebeast") and you younger guys... who are courageous, energetic, and ambitious enough to actually haul your machines to FliteFest or somesuch. So silly... ;)

BTW thanks for the kind words, Rockyboy! And, you're now just about committed to building another CNC machine... :eek:

-- David
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