Update on the Never-Ending Printer Project

I installed the Y-axis screw drive in MegaMax using the old NEMA-23 stepper motor.  A couple really good things came from this:

1) I can now adjust the bed leveling screws from the underside of the bed using thumbwheels instead of a screw driver.  I know, I know, everyone else in the world has been able to do this from day 1…

Thumb screw for leveling print bed.   Screw is threaded into teflon block.

Thumb screw for leveling print bed. Screw is threaded into teflon block.

 

 

 

 

 

 

 

 

 

2) Unlike everyone else in the world, with fully supported linear guide rails, the print bed does not move in any direction but along the Y axis.  In the old scheme, with the end-supported round guide rails, the rails would flex and the bed would move up and down when applying pressure to it (sometimes even the screw driver pressure to adjust the bed leveling screws).  Now, if the bed moves at all in the vertical direction it’s because the bed plate (1/4″ aluminum) itself is flexing!

A couple bad things were also discovered:

1) The vibration and noise problem I was hoping to solve has not been solved.  It has been made worse, though the character of the noise is improved to musical tones instead of just harsh buzzing and rattling.

2) Several failed test prints at ever decreasing jerk, acceleration, and speed settings have demonstrated that the old motor simply doesn’t have enough torque to drive the screw reliably at reasonable printing speeds.

Shift occurred in Y-axis due to insufficient motor torque.

Shift occurred in Y-axis due to insufficient motor torque.

 

 

 

 

 

 

 

 

 

 

 

 

Further research into the first problem indicates that the vibration and noise are inherent in using steppers, and worse in MegaMax than in machines that use NEMA-17 motors because of the higher detent torque in the NEMA-23 size motors.  Detent torque is the little bump-bump you feel when you turn the motor shaft by hand.  The solution to the problem is to use a good driver for the motor and a higher voltage power supply.  The little A4988 chips in the Pololu drivers on the RAMPS board are very unintelligent- all they do is provide microstepping.  They work OK for NEMA-17 size motors because of the speeds and low detent torques in those motors.  When used with NEMA-23 motors the driver limitations become apparent – as they have in MegaMax- lots of noise and vibration.

Good stepper drivers are DSP based and automatically sense resonance and damp it electronically.  They use phase controlled sine wave currents to drive the motors smoothly.  Fortunately, DSP stepper drivers for NEMA-23 size motors are pretty cheap.   Here’s video of the DM542a driver pushing a NEMA-23 motor around.  I have ordered a DM542a driver.

The best power supply for stepper drivers is not a switcher, and running steppers from a switching supply will often result in a dead power supply.  I will be building a simple, unregulated transformer, rectifier, and filter cap supply to go with the new driver.

Next came the question of how to determine how much torque is needed to properly drive the Y-axis.  A bit of research took me here: Motor size calculator.  You just select the scheme for which you want to size the motor, enter the appropriate data, and it magically tells you how much torque you need to do the job.  When I ran the numbers on MegaMax, it told me that I need about 350 oz-in of torque (about double the torque of the motor I have).  I did a quick search and found a Chinese made (of course) 425 oz-in motor for $50.  Also on order…

The motor mount I am using is designed for a NEMA-34 size motor with which I use an adapter plate to allow the NEMA-23 motor to fit.  Since I’m buying a new motor anyway, why not just get a NEMA-34 motor?  It turns out that the best stepper for the job is generally the smallest motor that can provide the necessary torque.  A NEMA-34 motor could provide much more torque but the detent torque and rotor inertia would work against smooth and fast operation, and require a bigger power supply.

Back side of MegaMax showing motor mount, adapter plate, flexible coupler, and drive screw  in Y-axis.

Back side of MegaMax showing motor mount, adapter plate, flexible coupler, and drive screw in Y-axis.

 

 

 

 

 

 

 

 

 

 

 

The ATmega2560 and RAMPS boards will be replaced by a SmoothieBoard.  It has a much faster processor, much better connections for motors/external drivers, etc.  It currently lacks an easy way to add an LCD controller, so I may have to connect to a computer to start prints up (it has ethernet and a built in web server so it can be accessed from any computer on the network).  When a clean way to add an LCD controller becomes available, I’ll add it.  SmoothieBoard review

 

The never-ending 3D printer project

MegaMax has been and continues to be my main project for the last 2+ years.  I am currently working on some upgrades that will make him more Mega and even more Max.  The Y axis is being converted from belt drive to screw drive and the round guide rails are being replaced with linear guides and bearing blocks.  The X-axis will also get converted to linear guide and bearing block and change from 5mm pitch belt to 2 mm pitch belt drive.  I feel confident saying that once these modifications are complete the flaws/errors in prints will be due primarily to the nature of liquid plastic squirting through a nozzle, not positioning system errors.

I recently updated my web site with a sort of historical look at the project, including all the mistakes I’ve made along the way and the often failed attempts at correcting them.  Here is the page that shows how it all started, how it has ended up, and where it is going.  http://mark.rehorst.com/MegaMax_3D_Printer/index.html

Don’t ask me why I do this-  I have no choice.

MegaMax beginning

From this…

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

MegaMax present state...

To this…

Awesomeness in the Making – it’s the Holiday Make-A-Thon

holidayMakeathonBanner

Since 2010 Milwaukee Makerspace has partnered with Bucketworks to host a Holiday Make-A-Thon on the Friday following Thanksgiving. What do we do at the Make-A-Thon? We make things of course, but more importantly we make things for the holidays and help children of all ages make holiday items for gifts, decorations or donations.

Typically this event was held at Bucketworks. In 2013 Bucketworks was moving into their new space so the event was held at the Milwaukee Makerspace in Bayview.

The question for 2014 is “where are we going to hold the Holiday Make-A-Thon” or is it Make-A-Thons?

The answer is we can have multiple Make-A-Thons at different locations, hosted by different groups on the same day.

Please join us for the Holiday Make-A-Thon happening at the Milwaukee Makerspace and the Mini Make-A-Thon happening at UberDork Cafe on Friday November 28th, 2014 from 1:00pm to 6:00pm.

This event is competely free and we ask for donations to help cover the cost of materials.

Activities
Some of these are tentative and will rely on people to volunteer to make them happen!

  • Decorate a laser-cut ornament
  • Design a laser-cut ornament
  • Learn to solder a tie-pin
  • Design & 3D print a cookie cutter
  • Make a necklace / bracelet
  • Make a rose pin
  • Decorate your own gift wrapping paper
  • Fold a paper diamond ornament
  • Make a woodcut print

Refreshments
Want to bring something delicious to share? Please do!

  • Cookies
  • Pie
  • Leftovers!

A phone with a frickin’ laser!

My recent acquisition of a Meade ETX-90 telescope with computer go-to system for locating objects in the sky got me thinking that it would be nice to have a system to locate objects in the sky when you’re looking through binoculars or a telescope that doesn’t have a computer and motors to drive it.  To that end I came up with the idea of mounting a green laser pointer, commonly used by astronomy nutz to point out objects in the sky to noobs, on a cell phone or tablet running a program such as Google SkyMap or Skeye.

sky laser all parts

CAD rendering of the parts

After much thought and a few prototypes I came up with a system that allows a laser to mount on a phone and that assembly to mount on a tripod, a handle, or a telescope.  The tube that holds the laser has adjustment screws to allow the laser to be aligned with the SkyMap on the phone.  It also has to slots that fit over standard gun sight rails.  On one side I have a phone/tablet bracket that has a gunsight rail and slides into the laser tube, and the other side can be used for a rail that mounts on a tripod or a handle.  Extra rails can be mounted on telescope tubes.  I haven’t yet designed a binocular mount, but will soon.

 

IMG_0388

Parts printing on MegaMax

I printed the parts on MegaMax with Octave fluorescent red filament (that’s why the colors vary in the photos- the flash apparently excites the fluorescence in the picture with the handle).   All the parts fit VERY tightly together but I included screw holes for extra security.  The phone/tablet mounts on the bracket using velcro tape.  I think it may be better to print or buy a cheap case to fit the phone than screw it to the phone/tablet bracket.  I’ll be posting the design files to Thingiverse shortly.

IMG_0409

Phone and laser mounted on handle

IMG_0404

Phone and laser on a tripod

 

 

#TinkerOn, my friends… #TinkerOn

To celebrate the National Day of Making we’re proud to share these great videos we made with the folks at Liquid Wrench for their Tinkernation web site. Big thanks to Tom, Audrey, and Tiffany for being the voice of Milwaukee Makerspace, and to all the other members involved and our pals at Pumping Station: One in Chicago who run the Power Racing Series.

Warning: The videos range from fun to educational to a little ridiculous. Enjoy!

SnakeBite Extruder Works!

I repaired the Budaschnozzle hot-end over the weekend and bolted the SnakeBite extruder to it and then to MegaMax and tested it last night.  There’s plenty of tuning to do, but the first print looks promising:

 

Start of SnakeBite’s first print

 

More of SnakeBite’s first print

 

Not too pretty but it shows promise.

Not too pretty but it shows promise.

3D Printable Thermal Enclosure For 3D Printer

Well, OK, not the whole enclosure, just the parts that hold it together.

MegaMax can print big stuff but he’s had problems with large prints delaminating.  The answer seems to be enclosing the printer to keep the prints warm while printing.  I designed this box and 3D printable parts to hold it together so that I can take the box apart easily to work on MegaMax or move him to other locations and put it back together when I’m done.  The box is 38″ D x 28″ H x 32″ W.

box door open

 

 

 

 

 

 

 

 

 

 

box door closed

 

 

 

 

 

 

 

 

 

 

 

 

 

The box is made of 1″ PIR foam with corners suitably notched to accommodate the printed parts.  MegaMax has a 450 Watt heater in the printbed so the box gets super-toasty inside.  I suspect it gets a little too toasty but haven’t made any measurements yet.  I’ll soon be moving the electronics out of the box.  I didn’t do anything to seal the seams in the box because it doesn’t seem to be necessary.  I did tape the edges of some of the foam boards with clear packing tape to prevent damage.

Design and stl files are available at http://www.thingiverse.com/thing:269586

Snakebite Extruder Testing

rev7 extruder with hot-end

 

 

 

 

 

 

 

 

 

 

 

 

One of the biggest problems with FDM 3D printing is hot-end jamming.  There seem to be a lot of causes, most of which are not readily identifiable when a jam occurs.  One thing I have found is that after a hot-end jam I can usually grab the filament and manually push it and get it flowing through the hot-end again, though it is too late to save the failed print.  The most common means of driving the filament into the hot-end is to pinch the filament between a gear and a bearing and have a motor drive the gear, either directly (with 1.75mm filament) or via a gear reduction/torque multiplier arrangement (3mm filament).  When the hot end jams, the large force applied by the gear over the small area of the filament that is pinched between the gear and bearing usually chews a divot in the filament thus destroying the grip.

A couple weeks ago I started designing a 3mm filament extruder for 3D printing.  My hope is that this extruder will provide sufficient force on the filament to prevent hot-end jamming from ruining prints.  My design uses two counter-rotating 6-32 nuts twisting on the filament (like the way your hands twist in opposite directions when you give a “snakebite” to your friend) to drive it into the hot-end.  One is a normal, right-hand threaded nut, the other is left-hand threaded.  When the nuts turn in opposite directions, the torque that would try to twist the filament is cancelled while moving the filament forward and reverse without twisting.

The motor has to turn about 1.26 times to move 1mm of filament so there is a huge torque to axial force conversion.   The gear diameter is about 30mm.  That 1.26 rev moves the gear about 119mm at its perimeter.  That means there is about a 119:1 increase (ignoring losses in the gears, bearings, and nuts) in the force at the filament compared to the force at the gear.  That force is applied over a larger area of the filament than the usual pinch arrangement, so it is less likely (I hope!) to carve the filament and lose grip.  I tried stopping the filament by grabbing it with my fingers and holding as tightly as I could but it didn’t even slow down.

The firmware in the printer has to be tweaked so that it knows exactly how many steps of the motor are required to drive 1mm of filament.  The formula is:

32 rev/ 1 inch  X     1 inch /25.4 mm   X    200 steps/1 rev    X  16 microsteps/1 step   =  4031.496 microsteps/mm

For initial tests I just input 4031.5 using the rotary encoder on the LCD interface to the RAMPS board in MegaMax.

Here are the parts that I used:

Left hand threaded tap:  http://www.amazon.com/gp/product/B006YITGY8

5mm brass tubing:  http://www.ebay.com/itm/360828686174

5x16x5mm (625Z) bearings:  http://www.ebay.com/itm/321062568303

Plastic gears:  http://www.sciplus.com/p/PLASTIC-GEAR-SET-WITH-BUSHINGS_40234

I also used a NEMA-17 motor from a QU-BD extruder.

You can DL the STL files for the printed parts here:  http://www.thingiverse.com/thing:261037

Test printing will start in the next day or so and I will post another video showing success or failure.

Fingers crossed!