Cutting foam sheets... with a needle!

[dkj4linux]

Looks great! I really want to try doing some of those style of cuts at some point....

I finally got my drag knife on Friday and tried to do a bit of playing with my CNC over the weekend. But mostly had frustration...then caught some kind of food poisoning or flu and spent Saturday evening and Sunday feeling miserable

Friday I designed and printed a mount for my new drag knife. Took 5 revisions to get something usable...and I'm still not very happy with it. It's similar to the design allted shared but is designed to work with the hicwic quick change mount. Problem is there's no good way to print it without support which I'm not happy about. I could make it work as a two piece print but that bugs me too. What I have now is usable but not really nice enough I'm ready to share it yet.

Before the illness hit on Saturday I finally added a few threaded inserts to my CNC table so I can bolt stuff down. My plan was to bolt down my old 2'x2' base to use as a waste board, and machine a 12"x12" pocket in it to drop a mirror tile into which I would cut vinyl on. By machining the pocket I figured it would result in a flat surface that's even with the toolhead to make up for the fact that I still haven't got around to fully final leveling all four corners.

Well, that didn't go great. Thankfully I decided to test cut in some pink foam first. First cut came out almost twice as deep as I expected. It seems something is wrong with my Z axis and I'm getting almost double the depth I'm setting. So for second test cut I just halved my z but I need to look into just what's wrong there. Could be my z steps are wrong but I'm not sure how or why since I'm using the threaded rod/stepper drivers/settings specified by allted....just need to do some digging and see what's going on.

With my depth halved in estlcam I was able to make a nice cut in the foam and my mirror tile fits perfectly. I then put my dial indicator on (I made a quick change mount for it when I first built the machine) and found that there was still way more variation in high across the glass than I expected.) It's not horrible...about 15 thousands from the lowest to highest...but still not what I had been hoping for

I tried doing a few sample cuts on some vinyl with it but the vicious1 site was down so I couldn't find the suggested settings and then I started throwing up...so no further progress

I also still think there's something off about my machine since I expanded it. The center section just doesn't "look right" like it's not square anymore. Not sure if one or more of my pieces of conduit isn't straight or what. It was all really nice and square as a 2' machine and the printed parts haven't changed so I really suspect it's the new longer conduit pieces. But if I'm going to take it apart to replace those I want to do the new plastic parts too. So need to start printing I guess

It's fine for the needle cutter where z accuracy isn't a big deal....but for all the other things I want to do with the machine....I really need to figure out what's going on.

I hope you are feeling better now, Jason. I, too, am just getting over a week of illness (stomach bug and dehydration with a lot of flu-like symptoms)... laid me low starting on Thursday, week before Thanksgiving, and had it all that weekend and into early week. Finally went to the doctor (daughter thankfully "nagged" me into it...) on Monday and had improved enough to enjoy Thanksgiving with the kids. Thankfully they all came to me so I didn't have to traval.

Amazing the parallel universes we are running in... I, too, recently ordered and received a drag knife from Ryan but haven't done anything with it yet. Made a mount similar to Ryan's and adapted it for hicwic's quick-change mount... did it in two pieces, though, after the first -- with all the support -- didn't turn out worth a flip. I also have a large Donek drag knife that I got a couple of years ago but haven't done anything with yet.

I really think leveling your machine would be preferable to milling out a parallel suface... it's really not that difficult IMHO. I hate the noise of a dremel or router and frankly I never felt the MPCNC was rigid enough in the larger size to attempt such a thing. I've leveled mine with that simple little adjustable guage and it seems close enough for everything I've ever done... haven't put a dial indicator on it yet though.

I would highly recommend getting all those upgraded plastic parts printed and installed... it feels far more sturdy and square than my old one(s). My new 2'x2' laser machine has the upgraded parts and attached wooden base and sits on a thick piece of tempered glass... I plan to start playing with the drag knife on that machine when I get the time.

I've printed yet another set of Z-axis parts... SIL want's a camera slide to play with and I think the Z-axis and lead-screw assembly can be modified to get us something to play with. Using a 36" piece of 5/16" all-thread so should see about 30"-34" of travel when all is said and done.

Hope you get your machine straightened out and running right. I know I feel "lost" when one of my machines goes on the fritz... -- David

 

[jhitesma]

Amazing the parallel universes we are running in... I, too, recently ordered and received a drag knife from Ryan but haven't done anything with it yet. Made a mount similar to Ryan's and adapted it for hicwic's quick-change mount... did it in two pieces, though, after the first -- with all the support -- didn't turn out worth a flip. I also have a large Donek drag knife that I got a couple of years ago but haven't done anything with yet.

Just to clarify I got my drag knife from banggood, couldn't pass up $9 for the holder and 15 blades. But it's a slightly different size/shape than the one Ryan sells so his holder wasn't well suited. I was able to get my design to print well with support - but only by printing it in...ugh...ABS Support on ABS removes easily...anything else and I tend to damage parts removing support because of the better bonding. Thankfully I did that makergeeks monthly subscription deal and the first box came with a roll of ugly army green ABS. (I'm also using it to print the openrc truggy since that seems decently suited to ABS for most parts and like it would look decent in army green.) I'll probably revise my design to a two part print though so it's easier to reproduce before I share it.

I really think leveling your machine would be preferable to milling out a parallel suface... it's really not that difficult IMHO. I hate the noise of a dremel or router and frankly I never felt the MPCNC was rigid enough in the larger size to attempt such a thing. I've leveled mine with that simple little adjustable guage and it seems close enough for everything I've ever done... haven't put a dial indicator on it yet though.

To be fair I did level it...just haven't gone though and really fine tuned the level like I did on the 2' version where I got super critical and spent a few hours getting it within 1mm at all corners. On that setup right on the baseboard I saw about half the variation I see in my milled pocket - most of which I figured was just the particle board itself not being perfectly flat

Main reason I haven't done it on the big setup is access. It's a tight fit in my shop and getting to the back corner means having to move the whole table. And there's now stuff stored under it so that means moving all of that stuff first which makes it even harder to get around in there. But it's not going to get any easier so I need to just suck it up and do it.

The dial indicator was mostly just out of curiosity - but is a handy testing tool.

Even with the corners perfectly leveled I plan on using a milled pocket for glass to cut vinyl on. Given how little knife is used and how little z travel it just seems like having the flattest most parallel work surface possible is pretty important there. Plus the knife holder Ryan sells seems a little nicer than mine - I note his has a rounded surface where the knife sticks out while mine is flat. So his is probably a bit more forgiving with setup while mine wants to snag on the vinyl if you set it too tight against the surface.

I would highly recommend getting all those upgraded plastic parts printed and installed... it feels far more sturdy and square than my old one(s). My new 2'x2' laser machine has the upgraded parts and attached wooden base and sits on a thick piece of tempered glass... I plan to start playing with the drag knife on that machine when I get the time.

I'm really tempted to build up a second machine because I really liked the 2'x2' size better for everything except the needle cutter. But I'd put the new parts on the big machine first since it needs the most help with sturdiness, then use the current parts on a 2' machine until I print another set of new parts. But if I put in the time/effort to print new parts I'm really leaning towards replacing the conduit with 1" stainless on the big setup as well.

Either way weather has finally cooled off officially (two weeks ago it was still A/C weather, one week ago we were sleeping with the windows open, now we're considering turning on the heat!) so I'm getting ready to restock on filament. But going to give the Maker Geek monthly box one more go for December and get past Christmas before I want to spend much money. I've not been overly impressed with MG's PLA so far. Their ABS is nice for ABS (less smell than others I've used - but still warps without an enclosed build chamber), and their PETG I love...but their PLA just doesn't play nice for me. When it works it works great...but it randomly just clogs or jams in my extruder and I haven't had that problem with any other PLA or filaments from other suppliers. The roll of PLA in this months box seemed to be working well, but sure enough after the first few parts it started having issues for me like every other roll of PLA I've had from them Looked at getting some more hatchbox...but the price has gone up and is about the same as Atomic now, and I'd rather support a US based MFG like Atomic than China/Hatchbox. In fact with the discount code Atomic gives out in the reprap community his stuff is now a buck or so cheaper than most Hatchbox colors. And the filament I've had from him is spectacular.

I've printed yet another set of Z-axis parts... SIL want's a camera slide to play with and I think the Z-axis and lead-screw assembly can be modified to get us something to play with. Using a 36" piece of 5/16" all-thread so should see about 30"-34" of travel when all is said and done.

Hope you get your machine straightened out and running right. I know I feel "lost" when one of my machines goes on the fritz... -- David

Well it's still working well for the needle cutter, I just haven't done much needle cutting since I haven't had time to finish my vac table and all my foam refuses to sit flat and I'm too easily distracted to move weights around while it cuts I just want to get it working better for light milling and vinyl cutting now.

I'm curious to see what you do with the camera slide. I've been playing with a few setups to get some motion into time lapse videos.

Real quick and dirty test to see how the speed of a microwave turntable motor would do, just had the camera stuck on one of my kids toys running against a 2x4 so it's a bit jerky:

I was thinking about using two of the X/Y carriers one two pieces of conduit to make a track. I really want to do some kind of curved track...but that's a far bigger issue to tackle

I also still really want to try designing a delta printer based around MPCNC concepts...just far too many projects and never enough time!

 

[RAGII]

Quick question regarding the laser setup. Is it necessary to have a housing, or can you use the heat sink for attaching to the MPCNC? I do not have access to a 3D printer so my mounts are all made of wood and attach via the generic mount that was included with the MPCNC printed kit I purchased.

 

[dkj4linux]

Quick question regarding the laser setup. Is it necessary to have a housing, or can you use the heat sink for attaching to the MPCNC? I do not have access to a 3D printer so my mounts are all made of wood and attach via the generic mount that was included with the MPCNC printed kit I purchased.

I thought someone else might jump in to answer the question... I'm hardly an authority on the subject. I see no reason you can't use the laser without a housing though I can think of a couple of reasons that make sense to me to have one. The "spurious" light is more readily contained and the nozzle helps concentrate the fan exhaust to clear the smoke and help control any flame. And, IMO it just looks "cool" to print it in a color that lights up when the laser fires... -- David

 

[dkj4linux]

...
I'm curious to see what you do with the camera slide. I've been playing with a few setups to get some motion into time lapse videos.

Real quick and dirty test to see how the speed of a microwave turntable motor would do, just had the camera stuck on one of my kids toys running against a 2x4 so it's a bit jerky:

I was thinking about using two of the X/Y carriers one two pieces of conduit to make a track. I really want to do some kind of curved track...but that's a far bigger issue to tackle

I also still really want to try designing a delta printer based around MPCNC concepts...just far too many projects and never enough time!

Jason,

I set up the camera slide first with a lead-screw... it was much too loud and too slow (for me to play with...)

So I whipped up a couple of motor and ider mounts using the C-Z-lower from MPCNC -- to keep the conduit spacing -- and printed a couple of C-XYZ and C-spacers for the trolley. It's now belt-driven and has 32" or so of travel... I powered the stepper with an Arduino Uno and spare A4988 driver I had.

I'm mostly following the camera slider tutorials on Brainy-bits (https://brainy-bits.com/tutorials/)... I've not yet implemented the rotation-axis and used the A4988 instead of the EasyDriver module he uses. Using full-stepping at the moment. -- David

 

[jhitesma]

Camera slider looks great! Since I haven't actually printed the new Z parts yet I wasn't picturing things the way you have it working - that's way nicer than what I thought you were going to do

There was a guy in the folger IRC channel who was building a PT head for his slider to do really fancy timelapses of prints. He was even syncing it with marlin so the print head would always be in the right place when a shot fired. Even just a slider makes for some very nice time lapse but adding a pan/tilt option can really make them super impressive.

I may have to look at doing something like yours...that looks much more elegant than what I had been thinking about tackling at some point!

 

[dkj4linux]

More camera slider progress...

First, please understand that I am NOT a photographer and really don't know squat about photo equipment or how it's used. But here's where I am now with the camera slider... patterned completely after the one presented in the following tutorial

https://brainy-bits.com/tutorials/dual-axis-camera-slider-using-joystick-in-and-out/

I don't know whether this slider is functionally what anyone would want in a camera slider, but Yvan at Brainy-Bits undoubtably knows more about the subject than I do so I'm trusting his judgement completely. Besides it's a fun build and not all that difficult... though I haven't yet gotten his software to work properly (the interrupt isn't working). I'm sure one of you will be able to whip it into shape in a heartbeat

Anyway I was stricken by the similarity to the MPCNC's assembly (though he hid most of his mechanical bits in a box...) -- and since I already had a couple of parts already printed up -- I set about trying to functionally duplicate his slider. I first used the MPCNC's basic Z-axis lead-screw idea but quickly bored of the noise and lack of zip... so whipped up a motor mount and idler that kept the MPCNC Z-axis conduit spacing and switched it over to belt-drive. So, here it is in all it's glory, so far... my not-quite-yet-finished MostlyPrintedCameraSlider (MPCS?)

Yvan's rotation axis on the trolley reminded me of the Greg's Wade extruder gear set...



But it needed to be a lot bigger...



Found a cute little turntable (http://www.thingiverse.com/thing:1061970) that used a skate bearing as I envisioned... but needed teeth around it so it could be driven...



Then found an OpenSCAD parametric herringbone gear generator (http://www.thingiverse.com/thing:6544) that was almost perfect size in it's near-default configuration... the motor drive gear has a problem when printing but it's functional as is, I think...



A little work in Tinkercad to lighten up the big gear and house the skate bearing (similar to the little turntable)...



And, viola! A turntable on a linear axis...



As I said, I don't have the software part working yet but I'm sure it's fixable. I can run the previous tutorial sketch just fine... this adds an interrupt routine, triggered when the joystick switch is clicked, to capture the current position of the two axis, as setpoints. I want to get this running pretty much as designed by Yvan first. Then I hope to try controlling it with an IR remote (played enough with that already to trap codes and execute instructions)... so I can also hopefully help grandson switch over to IR remote control of the robot he's playing with.

I'm having fun playing with this... though my plate is pretty full at the moment. What say ye? Anyone interested... other than Jason? -- David

 

[GremlinRC]

Hi David, that looks great. To be honest the camera slider is not really my thing but the mechanism behind a linear actuator is exactly me cup of tea. This and the latest FT episode on 3d printed planes really has my attention. Can I ask you guys a question about 3d printing? I assume I can use my existing ballscrew CNC machine as a base for 3D printing? From what I gather from the little research I have done is that I'd need a hotend and extruder mechanism and a hot plate to keep the material from cooling too quickly. Is there else any other major component needed? Also is there a sort of standard kit that you guys are using. I see the prusa i3 seems to be the machine of choice. I know very little about this so any advice is appreciated.

Cheers

Dave

 

[dkj4linux]

Hi David, that looks great. To be honest the camera slider is not really my thing but the mechanism behind a linear actuator is exactly me cup of tea. This and the latest FT episode on 3d printed planes really has my attention. Can I ask you guys a question about 3d printing? I assume I can use my existing ballscrew CNC machine as a base for 3D printing? From what I gather from the little research I have done is that I'd need a hotend and extruder mechanism and a hot plate to keep the material from cooling too quickly. Is there else any other major component needed? Also is there a sort of standard kit that you guys are using. I see the prusa i3 seems to be the machine of choice. I know very little about this so any advice is appreciated.

Cheers

Dave

Thanks, Dave. I feel pretty much the same way about the camera slider but, as I said, it's a fun build and not too difficult... a nice Arduino-controlled playtoy. Gives me an opportunity to play with micro-stepping, acceleration, etc.

I'm hoping Jason and some of the others will jump in here regarding your 3d printer questions. They understand all the settings and different filaments far better than I... I don't play around too much with mine as long as I'm getting parts that work for my projects.

That said, I have built, and been totally happy with, two FolgerTech 2020 all-aluminum Prusa I3 machines... they are "kits" (actually just all the bits and pieces needed to build a 3d-printer) and mine are completely stock. Jason has the same FolgerTech 2020 Prusa I3 that he's reasonably happy with but he's upgraded it substantially IIRC and says there are better deals out there now... he'll have to tell you which ones and why he feels that way. The FolgerTech 2020 has it's own lengthy thread right here in the FT forum... and Jason has been a major contributor.

-- David

 

[GremlinRC]

That said, I have built, and been totally happy with, two FolgerTech 2020 all-aluminum Prusa I3 machines...

Thanks David.

Having snooped around a bit more, I've come to the conclusion that I'll proably be as well off just buying one of those kits like yours in the new year. Problem is with 2 CNC machines a milling machine and a lathe, I'm running out of space in my 13' x 10' workshop! Saying that a 3D printer can stay indoors, my wife wont complain (too much) if I set one up in the spare room!

My drag knife arrived so I have plenty to be playing with. First job will be to make a cutting table that will sit on the CNC bed and can be levelled perfectly. It doesn't need to be very big. I'm thinking of a piece of glass sheet bonded to a piece of 3/4 ply Place some sarin wrap on the CNC bed top it with some bondo squish the ply/glass on top and get it perfectly level, leave the bondo to set. Then I mark the position on the bed so I can remove and replace it in the same spot every time and I should have a nice level cutting table ofr the drag knife.

Jason have you managed to make any progress?

Cheers

Dave.

 

[jhitesma]

Jason have you managed to make any progress?

Been fighting with a multirotor that suddenly doesn't want to fly the past week (long story...but it originally was running a "Flying F4" flight controller I built out of my old MW based controllers sensors and a STM32 F4 Discovery board...but a year ago when dRonin forked from TauLabs we discovered some major issues with the Discovery F4 and decided to drop support for the Flying F4. Quad had been flying at that point and one of the developers of dRonin sent me a sparky board to replace my Flying F4...I found some bugs with Sparky's support getting that setup...which were fixed. But then never actually got the Sparky mounted and tried to fly it until about a week ago. Finally got it in and tried to fly and the quad wouldn't get off the ground. Motors would randomly cut out. I suspected it was vibration issues since this is an older bigger quad with lower frequency vibrations than the newer 250 quads everyone flies anymore. Swapped the board for an Omnibus F4 I had been sent to test and couldn't get DSM to work on it Finally got DSM working tonight and got quad to fly again...but it's still doing goofy things at random so it seems I've still got a vibration issue and the Omnibus F4 is just slightly less sensitive to them than the Sparky was and the old MPU-6050 on my Flying F4 setup was the least sensitive and the vibes weren't an issue for it at all.

Anyway...that's been sucking all my time. Then today we hosted our annual mini gingerbread house build. This is something my mom started back in the early 80's when I was a kid. We make "gingerbread" houses out of graham crackers. My daughter invited some friends over and we wound up with 6 kids between 5 and 8 - who ate more candy than they stuck on their houses...then got to play in the yard. Well, after warning them not to go in my shop 5 minutes later I look outside and of course my shop door is open Gave them a good talking to and locked the door. Came out to eat my dinner in the shop (late dinner, daughter already in bed so shop is the least disruptive place for me to eat) and found that one of the kids had shoved a stick into the lock on my shop and it broke off in there If they had just ASKED I would have gladly given them a tour of the shop...but no they had to jam my lock with a stick. And of course my lock picks are in the shop. Thankfully I still had a pushrod small enough to get in there in the back room.

Well, the pushrod cleared the lock out enough I could get the door open...but then couldn't get my key out. So I got to take the lock apart. I rekeyed these locks myself when we moved in here 9 years ago so no big deal. But...I made the mistake of trying to take it apart while eating my dinner. Forgot one little trick to this deadbolt and sent all the pins and springs flying...right into my dinner

Thankfully at this point my luck turned, I was able to find ALL of the pins and springs without biting or swallowing any. And more remarkably without really trying managed to get them all back into the right positions first try!

So...with all that out of the way I'm getting ready to try the drag knife again...but thought I'd check the forum first

I'll check in tomorrow with any success or failure updates

As for 3D printing. A 3D printer is really just a small CNC machine with an extruder on it. And you can get an aluminum Mk8 extruder for $15 shipped on ebay ( at least to the US...not sure about Ireland may be a bit more or less due to shipping.) and then just need a Nema 14 motor to strap to it and a way to drive it. But...that said CNC machines tend to have different stepper driver setups and firmware (or are driver by a computer with Mach or something instead of with a dedicated controller) so adapting one to do 3D printing is probably more hassle than it's worth. But fully possible just like how the MPCNC can be used for 3D printing (but is built more like a 3D printer than a traditional CNC as far as wiring and steppers/control circuits.)

I like the Folger 2020 i3 and it's a pretty good deal for the price. It's not without it's faults though. The instructions it comes with are pretty poor...and the default firmware Folger provides is pretty out of date. It can all work..but takes some knowledge of how the things should go together and work. If you've got the money the latest official Prusa i3 is a heck of a machine and is getting 3D printer of the year awards left and right. There are a few other i3 clones that are a bit cheaper than the Folger and a bit nicer in some ways. Having the Z steppers on the top for the Folger isn't ideal, but there isn't a good way to move them to the bottom with the 2020 frame. Some of the others also come with better hot ends and include inductive sensors for auto bed leveling now at the same or lower price as the Folger. But...on the other hand they're mostly Chinese made kits or pre-assembled setups so quality can vary wildly from one to the next.

The Folger kit is "made" in the US from Chinese parts so quality can also vary wildly. It's not at all uncommon to get some bad parts with it. But Folgers tech support is really good about replacing them. Not a big deal here in the US - but if you have to ship parts across an ocean...might not be the best option for you. My kit had a bad LCD adapter board and a bad hot end thermister. I've heard of at least 6 other people who had hot end thermister issues out of the box as well - it's just not a very robust design (the wires are crimped in a brass ferule that fairly commonly breaks through the insulation and shorts it out or breaks one of the leads.) I originally got replacement thermisters off amazon to fix mine (first few days I just kept re-soldering the broken leg every 2-3 prints while I waited on Amazon) and then swapped to a e3d v6 all metal hot end because I wanted to print higher temp materials. I love the e3d...but it wouldn't work with the all metal extruder I had swapped for the original injection molded plastic one that came with the folger...and the injection molded one didn't work as well as I'd like - it worked...but didn't put enough pressure on the idler for the filament so I had some issues with slippage. The metal extruder I swapped to had an adjustable spring so I could turn up the tension on the idler and that improved my consistence and print quality big time. But since the metal extruder wouldn't work with the v6 I had to switch to a different printed extruder...and it's ok...better than the stock folger one and works very well with TPU since the filament is well constrained after the drive wheel...but the idler design isn't as nice as it isn't quite as good as the metal mk8 extruder I had been running...despite the nicer hot end. I've printed a geared wades extruder that should give me the best of all worlds...but have had it sitting here for 6 months and can't bring myself to install it because I can't figure out a good way to mount my inductive sensor on it and what I have now works "well enough".

Having the 3D printer inside isn't bad...as long as you don't print ABS. (Nylon isn't great to print without ventilation either...it doesn't smell bad but the fumes aren't healthy.) If you're only going to print PLA, PETG and TPU then inside is probably no big deal. They aren't that loud (other than the 30mm fan on the e3d...that thing is crazy loud...I finally swapped mine last week for a noctura 40mm fan which is basically silent and am loving how quiet the printer is again!)

Ok...time to go try a few more cuts with this drag knife

 

[jhitesma]

Well, got the drag knife working...but still not dialed in 100%

These are small ~1" tall K's (my daughters initial) I did as a quick first test. The one on the right I accidentally broke while peeling it off the backing...I just wasn't being very careful.


You can see one I haven't peeled off yet on the right if you look carefully, I think it came out the best of the 3 I did.


In that last photo you can see on the one in the middle that I had my cutting depth a bit too deep still as it started to go through the backing in a few spots. I'm not entirely sure why the corners are getting a little mangled...could just be the detail is too small for this knife...or it could be the face of the knife not being 100% smooth snagging on it - I want to try polishing the face of the knife a bit more still to see if it helps.

Getting the depth and pressure setup right is tricky. These were all cut at the same knife depth - just slightly different how much pressure I used. So I'm surprised that one cut through the backing as that should be the knife depth more than pressure that controls how deep it cuts. Overall I'm thinking the super cheap blade holder is my big problem and I should have spent a few dollars more on a nicer holder.

Basically the best results I got so far were with the blade sticking out just a tiny bit - I actually have to look through my magnifier to even see it sticking out. And lowering my z until I can just barely see the "springs" on the mount start to deflect. If I lower it to where they definitely deflect - then it cuts through the backing. If I lower it to where I can't detect any flex on them then it doesn't cut through the vinyl. But right where it just barely starts to deflect seems to work "just right". I'm using 0.2mm for the depth of cut as vicious suggests...but with my z being goofy I'm probably actually getting 0.4mm. I'm also using 'engrave' in estlcam instead of doing an inside or outside cut like vicious did and I didn't have any problems with the cut connecting without any 'lead in' like he used.

Probably won't be able to get out to my shop again until Wednesday or Thursday...but going to try polishing the face and cutting something bigger to see how that goes next.

 

[dkj4linux]

Well, got the drag knife working...but still not dialed in 100%
...

I'm not entirely sure why the corners are getting a little mangled...could just be the detail is too small for this knife...or it could be the face of the knife not being 100% smooth snagging on it - I want to try polishing the face of the knife a bit more still to see if it helps.
...
Probably won't be able to get out to my shop again until Wednesday or Thursday...but going to try polishing the face and cutting something bigger to see how that goes next.

Jason,

Getting clean, accurate, corners and accurately-sized pieces with a drag knife is almost impossible without "corner/offset compensation" of some sort... unless the offset is very small and the material very thin [which, hopefully most of the time, is gonna be true and/or "good enough" (negligible?)]. But it's the blade offset and angle that are responsible for the lifting/tearing/stretching/rounding (the "nicks") at all the sharp corners you're seeing.

You may know all this already... but for those that don't: Think of the toolhead "center" (that follows the toolpath) being immediately above the FRONT wheel of a bicycle... while the knife tip is trailing along, immediately over the BACK wheel; i.e. the "offset". The BACK wheel always tracks *inside* the FRONT wheel on sharp turns and arcs; i.e. rounding over sharp corners and cutting slightly under-sized arcs and circles. The only way to get accurate corners and properly size arcs/circles is to have the BACK wheel actually follow the toolpath at corners and on arcs; i.e. drive slightly past the corner, until the the BACK wheel is at the corner, and then pivoting/swiveling around the BACK wheel, swinging the FRONT wheel around in an arc (with radius equal to the offset) until it aligns with the toolpath exiting the corner. The compensated toolpath (as much as is shown) should then look something like this...


I have a Donek drag knife I bought a couple of years ago but have never used... it's uses a utility knife blade and is for thick materials. The relatively large offset and blade angle practically REQUIRE compensation for the resulting cuts to be at all clean and accurate. The Donek folks show a way to post-process the gcode (using an Excel spreadsheet macro) to add "corner compensation" and have a video or two that explains the problem and process nicely. -- David

 

[jhitesma]

Makes perfect sense David, and a big part of why I was always wary of drag knifes in general. I also figured that estlcam isn't ideal for generating the gcode for a drag knife but haven't really looked into other options yet. It's such a tiny tiny blade it probably doesn't take much offset, I'm guessing .3-.5mm is all since the blade itself is barely 1mm wide by my eyeball.

I suspect on things where the smallest detail is bigger than that it's not even noticeable. Which is why I wanted to try something bigger next. But might be worth looking into a post-processor or a better CAM option for the knife.

 

[GremlinRC]

Makes perfect sense David, and a big part of why I was always wary of drag knifes in general. I also figured that estlcam isn't ideal for generating the gcode for a drag knife but haven't really looked into other options yet. It's such a tiny tiny blade it probably doesn't take much offset, I'm guessing .3-.5mm is all since the blade itself is barely 1mm wide by my eyeball.

I suspect on things where the smallest detail is bigger than that it's not even noticeable. Which is why I wanted to try something bigger next. But might be worth looking into a post-processor or a better CAM option for the knife.

Very interesting results Jason, couple of thoughts. Is it possible that the knife is going too fast around the corners and dragging before the blade has had a chance to rotate? The second thing is if you use 'Exact Stop' mode that might help since the machine would have to slow/accelerate at each node of the toolpath. I agree, I have the exact same dragknife in front of me and I just measured the offset as 0.5mm (The blade is 1mm, the shaft is 2mm and the tip is at the edge of the blade)

Of course David as absolutely right about offsetting but I don't think offsetting should end if with ragged corners. I would imagine it would result in the cut not exactly following the toolpath in those corners.

 

[dkj4linux]

Very interesting results Jason, couple of thoughts. Is it possible that the knife is going too fast around the corners and dragging before the blade has had a chance to rotate? The second thing is if you use 'Exact Stop' mode that might help since the machine would have to slow/accelerate at each node of the toolpath. I agree, I have the exact same dragknife in front of me and I just measured the offset as 0.5mm (The blade is 1mm, the shaft is 2mm and the tip is at the edge of the blade)

Of course David as absolutely right about offsetting but I don't think offsetting should end if with ragged corners. I would imagine it would result in the cut not exactly following the toolpath in those corners.

The slight rounding is from the blade offset (tracking inside the corner) and the nicking/lifting/mangling in the corner from the blade angle... cutting edge at top of material leads the cutting edge at bottom; i.e. blade cutting edge not perpendicular to material while pivoting/rotating. Stab butter with butter knife and twist... -- David

 

[GremlinRC]

Stab butter with butter knife and twist... -- David

Yes!! I see that now. Brilliant analogy!

Jason I got three different blade angles with my holder, which one did you use?

 

[jhitesma]

I got the three different angles as well. It's my understanding that the bigger the angle the thicker the material the blade can be used on. This page has a graphic showing the difference between 45 and 60:

http://www.uscutter.com/Roland-Replacement-Blade-Pack-3-60-degree-and-3-45-degree-blades

I'm using the 60 right now, for not reason other than it was what I grabbed first. I couldn't really eyeball the different angles very well and tried to pick the 45 but guessed wrong

Though that's probably working in my favor since it means less of the blade is sticking into the material.

I'm probably going to try cutting our company logo next, it's all curves so should be fairly easy without having to "fix" the corners. I did find the stuff from donek that David mentioned here: http://donektools.com/free-cnc-router-software/links-2/ It's in inches though and I work in metric so would require a bit more mental gymnastics than I was up for last night not that I had any time to actually get to my machine anyway....I really want to build a second smaller machine again that I can use inside for drag knife, laser, pens, and other things that aren't loud and/or don't need the big work area.

I peeled out that last K I cut and it was really nice. The "stencil" part left behind looks almost perfect, and the corners were just barely mangled on the K...my daughter still liked it Pretty sure on something bigger it would hardly be noticeable and the gcode processing script would fix it right up (though I see estlcam9 has support for dragknife's but it sounds like it's in the firmware he makes...now that he's starting to support the RAMPS/Mega with his firmware I'm tempted to give it a try.)

 

[GremlinRC]

I use CamBam and I found a python script which will add corner offsets for any given polyline.



However in every poly there seems to be a strange corner with the offset going the wrong way. Maybe that's where you need to set your startpoint. More experimenting needed.



Jason, any chance of a photo of your knife mount?

Cheers

Dave.

 

[GremlinRC]

Sohere's what I came up with from bits lying about the place. The collar is half a shaft coupler which I bored out on the lathe so its a smooth sliding fit over the knife holder, there is no lateral movement inside the collar. I rubbed a little wd40 on the shaft to assist the slide. The spring is easily removable for changing blades. You can see the spring is retained inside a recess at the top so it won't go anywhere. The pressure required to push the holder up is quite lite but it springs back without catching or binding.



So now to mount it up and give it a spin.

Cheers

Dave.