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Jun 23, 2019, 07:52 PM
treefinder
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Watched your last vid. Do you have a router speed control for your vacuum? Sounded like you turned it on high (to set the piece) then backed off to hold. Sounds a lot better than the regular speed!
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Jun 23, 2019, 10:17 PM
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Quote:
Originally Posted by springer
Should have read back through the thread. I was thinking 1500mm/min was what you were using. I can for sure slow down the traverse speed. Depending on direction, it sounded like it was working pretty hard pushing through. I will try a thousand then less and see how she idoes. I'm using a 2s lipo, but a 1500kv emax 2812 motor, so definitely getting different speeds than a 3S 2822. About 3/4 throttle it seems to smooth out in free run (not in the foam) mode, so I have been cutting at that speed. I have a tach sensor, but last time I tried to use it on an actual prop, it picked up the florescent lights instead of the prop. Not sure I can give you good rpm nunbers. I suppose the proof is in the running, have to just try more variations.

On the flattening, I have some half inch 4'x8' foamular board that I think I will use, as it is really flat, maybe think about some grooves for vac table function. I am following your guidance with crown down work piece, but the MPF seconds sheets I am using have lots of waves and MPF is less rigid than dtf with paper on (which I assume your were cutting?) Increasing retract distance seems to work ok for now. I need to scrounge some pipe or bar stock for the sides, though in absence of suction.

I will have to ponder the z axis registration. How far out of the nozzle does your needle extend full down? If you register zero at work piece surface and needle full down, how far into the foam do you typically run? I am thinking that the deeper it goes the more side loading it gets? Right now mine extends ~15mm from tip and I set the guide about 5mm above the work surface. 10mm into foam or two thicknesses. Sound right?

It occurs to me that your zeroing sets you up nicely for partial or score cuts!

Gotta say, though that this machine is pretty cool concept. Plaudits to you and the others who came up with it!
The projection of the needle from the guide really only determines the max depth of cut you can get. To fab a needle I usually just put an overly long needle at top of stroke and snip it off even with the tip of the guide. I then unmount it, point it on the side of a grinder, and then remount. That gives me about a stroke-length worth of needle projection... and max depth of cut.

Touching the material surface with the running cutter, I'm setting the exact lowest point in the stroke at material surface. From there, "material thickness plus a couple of mm" will work for any thickness of material up to max DOC. For partial/score/marking cuts, make the DOC whatever percentage of material thickness you want to use... 10%, 50%, etc. (without the couple mm additional).

Don't worry about the side-loading ... if you set a feed-rate appropriate to the cutter speed, it all works out.

I'm sure you're running pretty high cutter RPMs if you've been getting decent cuts at 1500 mm/min. With 2s and 1500kv motor, you're getting 10k - 11krpm at full-throttle (7.4v * 1500kv)... and nearly that, at 3/4 throttle. ESC's are very non-linear... you probably pass through 6k-8krpm at 1/4 - 1/3 throttle. With MPF, maybe that's okay. As long as your cutter seems to be running smoothly and relatively stress-free, and you're getting decent cuts, you may be able to cut fine at those rates. I would be interested to know the actual RPMs you're seeing... as I say, I've never cut any MPF.

-- David
Jun 23, 2019, 10:33 PM
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Quote:
Originally Posted by springer
Watched your last vid. Do you have a router speed control for your vacuum? Sounded like you turned it on high (to set the piece) then backed off to hold. Sounds a lot better than the regular speed!
Yeah, that entire video was just to demonstrate the steps I go through to start a cut. It can all be accomplished in less than a minute, if you've premarked the servo tester dial with the cutter speed... you can skip all the laser tach stuff. And I do indeed have a router speed control on the shop-vac. I found that there's enough vacuum -- even at the lowest speed setting -- to securely hold the several sheets I've cut... and with the small "kerf" of the needle cutter I think it'll work fine for most cut jobs. If not, you can always crank it up a bit. It might not be a bad idea to turn it on with the MAX setting to "set" it (as I did in the video), smooth it with a wipe of the hand, and then turn it down to MIN. It is indeed far less noisy, running at reduced speed.

-- David
Last edited by dkj4linux; Jun 23, 2019 at 10:39 PM.
Jun 24, 2019, 10:11 AM
treefinder
springer's Avatar
Looks like a stop at Harbor Freigbt for me. I don't have one of those controllers, but once I have one, expect I will find any number of uses besides the vac system! I will try using the HK "tach" and see what I can get from it and let you know.
Jun 25, 2019, 03:46 PM
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When last I left off, FoamRipper had gotten a new laser. To continue, here are my latest adventures in air-assist…

Still a fan of “pawpawpaw85″‘s air-assist shroud I’ve used several times, I’ve discovered one I think I like a bit more… “danwar”‘s “Laser Air Assist Shroud” (https://www.thingiverse.com/thing:2626593). I’ve replaced the radial fan, however, with a small printed adapter that allows connection of some vinyl tubing (3/8″ ID x 1/2″ OD) from the big box store. At the other end, I’ve connected a fairly nice, relatively quiet, air pump… powered by an inexpensive router speed control, for adjusting the flow of air from nozzle.

A crude test over the range of the speed control, showing the air flow from MIN to MAX…

Playing with air-assist.... for 2.5 watt diode laser (0 min 56 sec)


Here’s the air pump, router speed control, and vinyl tubing connected through another printed adapter…

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Shroud with printed adapter and vinyl tubing…

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Mounted on the FoamRipper’s laser housing…

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Top-view…

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and “shades of gray” test run.

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Later.

— David
Jun 25, 2019, 06:07 PM
treefinder
springer's Avatar
Interesting, does that blow the smoke away?
I finished a full kit. Took 21 minutes with the feed at 2000 mm/min. Unfortunately neither of my "tachs" worked on the flywheel for rpm measurements. Have to check FBs for one. The mig nozzle got hot. Too hot to touch, though the wire didn't feel hot. Maybe it dissipates heat better? Also the Z stepper got hot too, while x and y steppers were cold. The Z is a different unit than the other three. It moves nowhere near as much as the others. I wonder if the vibration is messing up it's holding position, forcing it to continually micro adjust? I also am using the original 12V, 2.5A power supply for steppers and control board. Maybe need more capacity?
I also have a small X axis registration issue. I attribute that to belt tension (lack of) I will tighten that next time. Other than 3 parts where beginning didn't match ending by 1/16" all went well, though. Well enough o should build the kit!
Jun 25, 2019, 07:22 PM
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Quote:
Originally Posted by springer
Interesting, does that blow the smoke away?
I finished a full kit. Took 21 minutes with the feed at 2000 mm/min. Unfortunately neither of my "tachs" worked on the flywheel for rpm measurements. Have to check FBs for one. The mig nozzle got hot. Too hot to touch, though the wire didn't feel hot. Maybe it dissipates heat better? Also the Z stepper got hot too, while x and y steppers were cold. The Z is a different unit than the other three. It moves nowhere near as much as the others. I wonder if the vibration is messing up it's holding position, forcing it to continually micro adjust? I also am using the original 12V, 2.5A power supply for steppers and control board. Maybe need more capacity?
I also have a small X axis registration issue. I attribute that to belt tension (lack of) I will tighten that next time. Other than 3 parts where beginning didn't match ending by 1/16" all went well, though. Well enough o should build the kit!
Springer,

Air-assist clears smoke, suppresses flames, helps remove embers/debris in the kerf, and enables a "hotter", faster cut.

Sorry about the tach problems... this is the tach I use -- https://www.amazon.com/AGPtek%C2%AE-...4AZVAWHTDWH5MV

You're cutting awfully fast. It may be part of the reason for "registrations issues" and start and end points not meeting up properly.

Another thing, remember the drive ratios for X/Y are different from Z... and Z has to make many more steps to move the same distance; i.e. it works harder when it is working. It also has to pull completely out of the material before a move and, at the speeds you're cutting, it may be seeing a lot of side forces.

Another thing to check is the reference voltage on the little A4988 driver modules. For those modules, IIRC the Vref is supposed to be 0.4v - 0.5v for 1 amp steppers. I'd at least check the Z driver and if it's significantly higher than that, it's probably the reason for the motor running hot. Turning the little pot on the module CCW should lower the Vref (and motor current) and keep the motor cooler. It's a really fiddly adjustment and the Vref is actually measured on the pot (where the screwdriver adjustment is) so be careful... it's easy to slip and short stuff out. Here's a page that might help...

https://www.reprap.org/wiki/Pololu_stepper_driver_board

Regarding the Mig-tip heating, here's what I wrote for a guy over on the FliteTest forum recently...

================
I believe Jason's explanation of what is going with the pre-guides here is entirely correct. Further, I believe the Mig welding tip, which is our "main guide", with its relatively large thermal mass and its proximity to the needle point and the material being cut, is likely going to be the culprit with most heat-related foam-cutting issues.

In my thinking and experience -- without pre-guides of some sort -- the flexing needle enters the Mig-welding tip, bends as it can within the bore, and then exits the tip... all with considerable friction and the resultant buildup of heat. If it gets hot enough -- and it will, if something isn't done to control it -- some heat is transferred to the business end of the needle and the foam it contacts, and the localized heating will eventually result in melted foam coating the needle, and eventually being drawn up into the tip. Only bad things result... and the cutter and cut quality suffer.

The pre-guides are simply an attempt to move the flexing needle's points of constraint out of the Mig-tip (the main guide) to a point ABOVE it. In constraining the needle's motion to as near straight-line, up-and-down as possible BEFORE it enters the main guide... we hopefully reduce the friction, and generation of heat, to manageable levels.

So, effective pre-guides have at least two points of constraint... an entry at the top and an exit at the bottom. The bearings on Jason's cutter are arranged such that the two upper-most bearings serve as entry constraint and the lower-most bearings, the exit constraint. On my oil-saturated wooden pre-guides, I have upper and lower wooden "plates" (or stacks of plates) with a very small aperture (hole), separated by the thickness of the plastic cutter body platform... and providing the points of constraint. In addition, I most often fill the area between the upper and lower guides with packed cotton, which is saturated with light machine oil, and helps lubricate and stabilize any erratic motion of the needle.

Alternatively, you could simply do away with the pre-guides and direct a flow of air at the Mig-welding tip, sufficient to keep it cool... similar to the part-cooling fan on a 3d printer. Fins are sometimes added to the tip as well... to increase the surface area. Another possibility is to use a main guide that doesn't have the thermal mass the Mig-tip does. The sports-ball inflation needles used on early cutter seemed to stay cooler far better... but it isn't as robust and long-lasting. Another thought I've kicked around -- but not yet tried -- is using the wooden stack idea to build a non-metallic main guide. And, there is at least one person I know of that has used a teflon/nylon/? tip to surprisingly good effect... but I suspect it -- and possibly the wooden-stack -- won't be as robust and long lasting as the Mig-tip.

So, which is better? Since this is all seat-of-the-pants engineering... you decide. Thankfully, the cutter is such a simple and inexpensive mechanism, trial and error methods to sneak up on something that works for you is not out of the question; i.e. YMMV.

Have fun. That is, after all, what DIY is all about... isn't it?

===============================

I assume you're referring to a plane as a "full kit"? I'd love to see it but please don't abandon getting your CNC tuned up and running. It's so much more fun when your cut jobs run to completion and yield clean, accurate, cuts.

Later.

-- David
Jun 26, 2019, 06:58 AM
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Now that I think of it you could probably use the air-assist scheme I used for the laser... and direct the air-flow at the Mig-tip guide. It's maybe equally easy to run small, flexible tubing to the needle-cutter and clip it on with a small printed part... as it is to mount a fan, hook it up to power, and figure out how to direct it at the guide. Wouldn't need a lavish pre-guide scheme if you can keep the guide sufficiently cool...
Jun 26, 2019, 07:39 AM
treefinder
springer's Avatar
Great price on the tach, just ordered one!
On this last test, I reduced the feed speed from 1500 to 1000. It that still too fast? What feed do you typically run now? I played with different needle speeds, and could tell a small difference in sound between half and full throttle (less at full) which I interpreted to side loads being less at higher rpm. I still don't have a feel for how fast is too fast. Movement seems smooth, cuts are smooth and straight.

Interesting thoughts on the Z axis motor. I will try and check the Vref. It is certainly possible that the board (being an eleksmaker board on an eleksmaker machine) is preset for the steppers that came with the original unit (even though the board is 3 axis and not the original board). The Z stepper is an adafruit unit I bought when I was gonna make a machine from scratch. It may want a different Vref. I was more concerned that the power supply was inadequate for the full setup with added stepper, but everything seems to move ok, and only the Z stepper gets hot. So I guess 2.5 maps is adequate for now.

It's funny (in a "great minds" way) I just read through the more recent pages of the flite test thread and the post you showed with interest! I have a 2" pancake fan I got for the Anet A8 but haven't used yet. That might be a solution. Also been thinking about a series of aluminum disks with punched center holes to make a flanged hole and press fit onto weld tip for cooling fins. Fun how one project leads to another! Interestingly, so far while the tip gets hot, I haven't noticed any melted foam messing up the needle or tip. But then yesterday was the first continuous run for a full sheet.

Appreciate your guidance!
Jun 26, 2019, 09:44 AM
treefinder
springer's Avatar
Well, a browse back through the thread found this: " So, the general idea is to get relatively smooth operation at the speed required to achieve decent cuts in the material of choice... generally 6000-8000 rpm, at 600-800 mm/min feed rate, for DTFB; i.e. 10-15 perforations per mm yields decent cuts."

I suppose if I paid more attention, I would have started with 600 mm/min instead of the 1500 that I actually did! So my last run was still a good bit faster feed than you use, will have to try it at the more sedate feed and see how it runs! (have to go through another plane and separate parts, getting bored at making parts for the OSR!) I will say that the cut edge of each piece was smooth and straight even at the 1500 feed only a tiny bit of "fuzz" on bottom edge corner.

On another aspect of the side loading/heating, etc, I wonder if shortening the stroke would have a good effect on heating? Haven't really looked at the flywheel to see if there is room to move the bearing, etc toward the motor shaft, but I find my stroke penetrates three layers if I have the guide tip set around 5mm off top of work surface. Have you done any work on changing stroke?

viewed the video on last page again (avoiding going out to split wood, too hot!). It looks to me like you have your tip about 10mm off the top work surface when cutting. Is that a good distance? I was thinking lower is better, but maybe not so....
Last edited by springer; Jun 26, 2019 at 09:50 AM.
Jun 26, 2019, 06:22 PM
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Quote:
Originally Posted by springer
Well, a browse back through the thread found this: " So, the general idea is to get relatively smooth operation at the speed required to achieve decent cuts in the material of choice... generally 6000-8000 rpm, at 600-800 mm/min feed rate, for DTFB; i.e. 10-15 perforations per mm yields decent cuts."

I suppose if I paid more attention, I would have started with 600 mm/min instead of the 1500 that I actually did! So my last run was still a good bit faster feed than you use, will have to try it at the more sedate feed and see how it runs! (have to go through another plane and separate parts, getting bored at making parts for the OSR!) I will say that the cut edge of each piece was smooth and straight even at the 1500 feed only a tiny bit of "fuzz" on bottom edge corner.

On another aspect of the side loading/heating, etc, I wonder if shortening the stroke would have a good effect on heating? Haven't really looked at the flywheel to see if there is room to move the bearing, etc toward the motor shaft, but I find my stroke penetrates three layers if I have the guide tip set around 5mm off top of work surface. Have you done any work on changing stroke?

viewed the video on last page again (avoiding going out to split wood, too hot!). It looks to me like you have your tip about 10mm off the top work surface when cutting. Is that a good distance? I was thinking lower is better, but maybe not so....
Until you really have a handle on the actual rpm's your cutter is running at, there's no way to determine what feed rate is too fast/slow... other than trial and error, as you are doing now. The tach will help immensely... as soon as you can get the actual rpm's, you'll know the exact feed rate that will give the proper perforation/mm to give good cuts.

To get a clean cut, the perforations must overlap slightly... and through experience, I've found 10-15 perforations/mm to work nicely for DTFB. For MPF, I don't know... it could be more or less, but based on your cuts being "smooth and straight" you may be fine. If too few perforations/mm (too fast feedrate or too slow cutter speed) you will lack enough overlap to get clean cuts... if too many, you're dwelling in an area longer than necessary. taking longer to complete the job, and running risk of localized heating issues. So, finding that range of acceptable perforations/mm (and acceptable cut quality) for the material you are cutting is kind of... the goal. Running the SLOWEST cutter speed at a given feedrate to get quality cuts is better than running too fast. Wear and tear on the cutter mechanics is reduced -- as is the buildup of friction-heat in the Mig-tip guide -- and this should give the most stress-free and longest-lasting operation from the cutter. If your cutter sounds "angry" or "scary" in operation... you're probably just running too high rpms for balanced operation.

Length of the stroke determines the absolute MAX thickness of material it is possible to cut... and the thickness of the material you want to cut, with allowed clearances above and below, will determine the MIN stroke you want. Regardless of length however, a complete stroke takes exactly one revolution of the motor. Most of my cutters have had 12mm - 14mm strokes... but the slip-on flywheel has slightly more because of the motor and flywheel geometries. I think balance issues will generally be magnified with longer strokes but the slip-on flywheel seems to run more smoothly and is much easier to balance than my prior versions... so we may get away with it. I would keep the needle length on the short side however... too long and it will magnify the results of too large side-forces from too high feed rate (it takes slightly longer to clear the cut and you'll see it dragging in the cut...), harmonics, etc. I suspect my needle was too long in whatever video you were watching (I'm not really doing serious cutting... it's mostly test cuts...) but if you're getting clean through cuts and the guide is consistently 10mm above the surface of the material, that's probably a good reason to snip off another 5mm or so off the needle, as long as you're holding the sheet being cut flat and firm.

-- David
Jun 26, 2019, 09:11 PM
treefinder
springer's Avatar
The tach should come by the 2nd or so. Guess I will get serious then. I will look at the needle length again. It disappears into the guide on up stroke already, so I assume shortening won't be an issue with that. I will get some good measurements.
Last edited by springer; Jun 27, 2019 at 01:20 PM.
Jul 01, 2019, 08:48 PM
treefinder
springer's Avatar
Well, this has been an interesting week in the adventure with my needle cutter! Lots of learning!
1. While waiting for the tach to arrive, I played with Grbl settings to see if speed and acceleration could help with heating, etc. I reduced Zmax feed to 350 from 500 where I had it. That still sounded smooth, didn't seem to affect the heating up of the Z stepper, tho. Also reduced acceleration to 1500mm/sec^2 from 5000. Maybe need to further slow that down. X and Y accel is at 400.
2. I looked at the stepper driver Vref settings. X and Y were .58v and they stayed cold during all testing. Z Vref was .66v, so I reduced it to .55, similar to the others. subsequent tests showed no reduction in heating. I further reduced it to .3v. Still gets hot not quite as hot as at .66, so I guess maybe there is something else I am missing. I am using a power supply that puts out 2.5A max, so perhaps that is involved somehow?
3. I got a router speed control at HF, and set up a vac table with a small shop vac. Since I need 1.5" to get the foam to the needler, I scrounged some Foamular and made three layers with slots. I learned to my chagrin that the slots are too wide. small parts fall into them and some while being cut. Need to rethink that. Part of the rethinking was to lower the Z axis mechanism by 2" by reprinting the base. While trying to print another kit, I discovered that my length available is only 45", because the Z axis and needler takes 5+ inches off the Y axis available. I think I may reprint a base that turns the Z 90 degrees in PV and have the needler on the side, like yours. Live and learn.
4. I learned a lot about how to use and not to use the wafer plugin. It works fine if you have everything just right, but is intolerant to small errors in planes and line proximity. The universal Grbl sender is working fine for me. Free and just enough features to be useful.
5. Tach came today, and I found that about half throttle is 9000rpm. The last cuts were made with motor at that speed, and XY feed at 800mm/min. It sounded good as long as I wasn't running over a slot in the spoiler board! Cuts are smooth and straight. Midweek I broke another needle, same place at the eye. I noticed in some pix, that yours looks like nut is not snugged tight. I have been tightening the nut (thinking bearing will allow smooth movement). This third needle, I didn't tighten the nut, just snug, so it can pivot. I printed a full sheet 47x20" with no issues, so perhaps I have it mostly down.
Jul 01, 2019, 11:50 PM
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Quote:
Originally Posted by springer
Well, this has been an interesting week in the adventure with my needle cutter! Lots of learning!
1. While waiting for the tach to arrive, I played with Grbl settings to see if speed and acceleration could help with heating, etc. I reduced Zmax feed to 350 from 500 where I had it. That still sounded smooth, didn't seem to affect the heating up of the Z stepper, tho. Also reduced acceleration to 1500mm/sec^2 from 5000. Maybe need to further slow that down. X and Y accel is at 400.
2. I looked at the stepper driver Vref settings. X and Y were .58v and they stayed cold during all testing. Z Vref was .66v, so I reduced it to .55, similar to the others. subsequent tests showed no reduction in heating. I further reduced it to .3v. Still gets hot not quite as hot as at .66, so I guess maybe there is something else I am missing. I am using a power supply that puts out 2.5A max, so perhaps that is involved somehow?
3. I got a router speed control at HF, and set up a vac table with a small shop vac. Since I need 1.5" to get the foam to the needler, I scrounged some Foamular and made three layers with slots. I learned to my chagrin that the slots are too wide. small parts fall into them and some while being cut. Need to rethink that. Part of the rethinking was to lower the Z axis mechanism by 2" by reprinting the base. While trying to print another kit, I discovered that my length available is only 45", because the Z axis and needler takes 5+ inches off the Y axis available. I think I may reprint a base that turns the Z 90 degrees in PV and have the needler on the side, like yours. Live and learn.
4. I learned a lot about how to use and not to use the wafer plugin. It works fine if you have everything just right, but is intolerant to small errors in planes and line proximity. The universal Grbl sender is working fine for me. Free and just enough features to be useful.
5. Tach came today, and I found that about half throttle is 9000rpm. The last cuts were made with motor at that speed, and XY feed at 800mm/min. It sounded good as long as I wasn't running over a slot in the spoiler board! Cuts are smooth and straight. Midweek I broke another needle, same place at the eye. I noticed in some pix, that yours looks like nut is not snugged tight. I have been tightening the nut (thinking bearing will allow smooth movement). This third needle, I didn't tighten the nut, just snug, so it can pivot. I printed a full sheet 47x20" with no issues, so perhaps I have it mostly down.
You need to add a "holes" top layer to your vacuum setup... just use another piece of DTFB with 1/4" holes at the intersections of the slots (why'd you make the slots so large?). Refer back at my video of a job setup. My total stack is FOUR layers high,... counting the piece being cut. The bottom 3 layers are the vacuum pad; i.e. two "slotted" layers and a removable "holes" layer (it'll eventually get chewed up and need to be replaced)... and then the workpiece goes on top. Nothing falls through the 1/4" holes... and vacuum is maintained. This video -- turn down the sound! -- shows me lining up the two loose sheets... the removable/replaceable "holes" top sheet of the vacuum pad itself and then the workpiece...

DTFB vacuum pad -- first test (2 min 17 sec)


I'd leave those Vrefs at about 0.5 volts... those sound about right IIRC, Remember that Z has to make a lot more steps to move a distance than X and Y. Your GT2 belts have 2mm between teeth and your pulley has 16 (20?) teeth, so you move 32mm (40mm) in X and Y with EACH REVOLUTION of the motors. Your Z axis, on the other hand, moves only the pitch distance of one thread of the leadscrew in one revolution... just a millimeter or two. So, given the same number of steps to make the motors turn one revolution... X and Y moves maybe 30X as far as Z does in one revolution of the drive motor. Depending on how active and high the Z axis movement during a cut job... the Z-axis motor might actually work harder and get warmer than the others. If you can touch it and comfortably keep your hand on it -- it's not uncomfortably hot -- you're probably okay.

I doubt the GRBL settings are going to affect much during operation other than set steps/mm and max rates and limits... that you may never approach during a cut job. I'd stick with the defaults (they're reasonable) for most things, like acceleration and jerk... until I had good reason to change them. The actual feed rates and other operational parameters you set up for the job WHEN YOU ARE DOING THE CAM will have a far greater effect... run to run. 9000 rpm and 800 mm/min doesn't sound bad (though it is faster than most folks run because we're now able to get higher cutter rpms with the new flywheel)... but recognize that the stepper motors work harder -- and heat up the faster -- the more you push them. And their efficiency and torque drop off with rpm. I don't think you're really pushing them beyond limits here... but, remember, you don't get something for nuthin'; i.e. something, somewhere, is gonna have to "pedal faster" and "sweat" and work harder to get the extra speed.

A 2.5 amp power supply is a pretty wimpy... I'd change it out for a 5-6 amp model and put that nagging suspicion to rest. And I don't need to crunch/squeeze the needle loops simply because I'm using a nyloc nut to lock it on and am not too worried about it backing off.

Nuff for now... it's getting late.

-- David
Last edited by dkj4linux; Jul 02, 2019 at 07:20 AM.
Jul 02, 2019, 09:08 AM
treefinder
springer's Avatar
"(why'd you make the slots so large?)" Yeah, why did I make them so large?
I think somewhere in the recesses of my brain I thought "bigger is better". In reality, not so much!

I was looking at the height of the stack after finishing the sheet yesterday, and I still have around 3/4" gap from X axis gantry/trolley and the pink foam. So I can use a scrap MPF sheet as the "holes" layer without any more fuss. I think I will cut up the pink slot scrap and glue it in the intersection between X and Y slots, more support and no closing up of air paths. All this just because I built the Z axis unit a couple inches higher than i should have. "The iterative process "! So, how did you poke the holes in the "holes board"?

On the steppers, i understand the difference between the belt vs screw drives more clearly since i started playing with feeds, acceleration, etc. The thing that seems weird to me, though is the Z stepper moves faster and more revolutions when it moves, but nearly all the time it just holds a position while the other three steppers move continuously. So does it get hot holding position? As it is, it is not too hot to hold my hand on it, so I will just see how long it survives. It is different than the other three motors, and not the one that came with the Z mechanism. I swapped it in because it was a couple ounces lighter than the original. I read somewhere that the accelerations in the Grbl version I got defaulted to laser speeds (hich accel) and mechanical setups accelerations should be lower. I can tell no difference, but lower accelerations should be lower stress, I would think.

Forgot to mention that tightening up the X belt took the slight offset out that I was getting when cut returned to start point. So another lesson learned.

I salvaged an AT computer power supply for a hot wire power supply a while ago, suppose I should try it and see what happens. Although I can't see any obvious issues with the 2.5 amp one. Even the 2000mm/min motion between cuts is smooth and continuous.

On the needle tightening, my original thinking was tight nut, so it wouldn't introduce slop or come loose. But like you, I have a nylock nut, so coming loose isn't a real issue, and I suspect that even though the bearing allows stress free rotation, the tight nut may have introduced other stresses, like in motor shaft direction? So, as I said, this time the nut is just a bit loose so loop has more freedom to float. We'll see....

Fun to learn new stuff! I think I will sharpen a piece of tubing and go poke some holes in a sheet of MPF!
Last edited by springer; Jul 02, 2019 at 09:16 AM.


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