Category: 3D Printing

D-Bot – 3D printer upgrades

About 2 years ago I built the D-Bot  which is a core-xy style 3d printer. What this means is I have a printer with a relatively large build volume of roughly 300mm^3 and a fairly rigid mechanical structure.  My efforts on this design can be seen starting at: http://bronkalla.com/blog/2017/03/12/new-3d-printer-project/

To the basic printer design, I made a number of modifications (of course). Te major changes included a high performance extruder – Micron EME Cobra all metal extruder with thermocouple sensor as well as a 24v power supply to hit the high temperatures I needed for printing Nylon and other high temp plastics.

The printer control is based on the open source Marlin software (which is incredible)  and  Rumba controller board.  The Marlin software is highly configurable and supports many dozens of printer configurations, controller boards and commercial printer. However, this configurability comes at a cost (learning curve) for the infrequent user.

This configuration (D-Bot) also  did not come without aggravations. The dual z stepper drivers for the vertical motion, are prone to getting out of sync when powered down (one side lower than the other). This was aided by the habit of the cats walking across the printer when I was not around, as well as the default power down of the stepper drivers between prints. So for every print session, I would need to re-level the printer bed across the X axis (left to right as you face it) a few times. In addition, the original microswitch based home sensor was not that accurate.  So after levelling, I would need pfutz with the zero position to get the first layer of the print to come out at the right thickness.  The microswitch was replaced with an optical sensor last year, but it was still on only one side.

This worked for 2 years and then I said no more, there has to be some upgrades I can do to make this easier, more repeatable and reliable.  That turned into a part time project over the winter and now is working very nicely. Upgrades included:

  1. Printing igus iGlidur 180 Y carriage slider bearings to replace the v-roller wheels.   This lead to better print quality. The igus filament required printing at 250C so this was one of the uses of the high temperature print head (in addition to nylon). The X axis will need to wait, as a future project.
  2. Moving from  Marlin 1.0.9 to 1.1.9 (latest and reportedly final version) of the software that drives the printer.  This meant carefully handling all of the changes to the software, recompiling and uploading the software multiple times to get the printer back in working order with no other (physical) changes.
  3.  Adding a second Z-axis (vertical) home sensor so that each of the Z stepper drivers would have their own independent home sensor and after homing the printer the bed would be basically level.  This required some adjustment of the parts in Sketchup (not easy with STL models) and then some Marlin configuration changes to make it work.   The homing of the printer is now SO much better. Not just the dual z sensors, but the Marlin homing logic is much better and doing it properly (back off and fast seek in and then back off again with slow in to get final zero).
  4. Adding a BL-Touch for automatic bed leveling sensing.  The mounting bracket for the BL-touch was based on using the new bottom Y carriage bracket for the igus slider bearings.  Getting the BL-Touch to work was the most infuriating  part of the project. The documentation of the theory of operation of the BL Touch is spotty and this is coupled with contradicting info for configuring it in Marlin on the web as well as scant info on doing it with my 3d printer controller board.   So yesterday’s snow  storm gave me the quiet break to sit down and systematically dig into how to do this. In the end, it worked (and I ended up with a spare BL-Touch).

So now I have a radically improved 3D printer and it is ready for more projects.

Crib – Mattress frame

The mattress needs to be height adjustable. With this design there are 3 heights available. High, low and floor.

The frame is made of 3/4×3/4 ” 14 gauge steel tubing. It is sized to fit about 3/4″ inside of the wood frame.

The frame is supported at the corners, however the screw and nut locations would collide with the sides. So I used buried nuts welded into the end rail pieces prior to assembly. To do  this the holes are drilled (#7) and tapped (1/4-20 ) 3/4″ from each end. A sacrificial bolt is inserted and a nut is placed on it finger tight. The nuts are then welded in place. I used a MIG welder.  However the day was windy and my skills rusty after the long winter so they are not the prettiest of welds.  (so feel free to pick on my weld quality)

I have often used this technique for buried fasteners when bolting through relatively thin stock like this or for beds where the nut plates are buried in the wood legs.

The holes for the webbing were then drilled in the  sides. It is much easier to do this while the frame is still in pieces. I always make a list of the hole distances prior to marking and drilling. This is easy in a spreadsheet and minimizes the chances for an error half way through and the piece ending up looking like swiss cheese.  I will use #8 x1/2″ hex head self tapping sheet metal screws. The holes are 9/64″ or #28 drill.

The frame was then welded up, welds ground flush, flap disk sanded (120 grit) primed and painted.

The webbing is 2″ light polypropylene webbing. I ordered a 150 foot roll and used most of it.

The webbing ends are folded over and secured with the screw and washer. If you have restrung an old aluminum lawn chair, you know the drill.

When securing the second end the triangle tip should hang over the side by about 1/2″.  Now you start the screw through the webbing. Next you use a nut driver or impact driver and hex bit to lever the screw over after catching the tip in the hole. This adds just the right tension. Use hex head screws, I can’t imagine how frustrating this would be with just a straight screwdriver.  The long straps are tighter than the sides and installed first as I did not want to bow in the sides

The frame is hung from these small pieces. They make the hole spacing forgiving and provide access to the screws that are otherwise hidden mostly by the frame. 1/4″ long spacers are placed between the straps and frame. These were made on the 3D printer, although you could also pay the price at the hardware store.

Now ready for delivery. Gap around the mattress is one finger thickness – just about perfect.

3D Printing Nylon

One of my goals when building the printer was to be able to print nylon and other high temp materials.

For the trike, I wanted to print some parts for the chain idlers in nylon. So I ordered some Taulman Bridge nylon filament in Black.  This is supposed to be one of the easier nylon variants to print.  Going into this I knew that getting the nylon to stick to the build plate can be tricky and it absorbs moisture from the air which will cause printing problems.

The filament arrived, but it  was repackaged, not on the original Taulman spool and keeper as shown on the Taulman website or on Amazon. It was vac bagged with no silica gel which was suspicious. I started printing at 255C with 60c bed temp on hairspray. Lots of popping noises (like Rice Krispies) and peeled up like a potato chip on the 3rd layer.

Next, I tried Elmer’s wood worker’s glue. I had some left from past woodworking projects and it was getting thick. So I thought it was worth a try after seeing the PVA recommendation on the Taulman website. This sticks incredibly well!!! Actually hard to remove if you put the glue on too thick. Still lots of popping, puffs of steam and rough textured surface. increasing the temp to 265C helped only slightly. After the first night’s attempt I had placed it in a cat litter bucket with silica gel to try to dry t out. I had a few glossy areas (must have been down by the silica gel. So I had a clue I was on the right track despite a poor overall print.

You only need a very thin coat of glue. If it is too thick, it peels off with the part. I was easily doing 6 parts per coating.  Probably could do more if the location was not exactly the same each time.

The next day, I baked the spool at 220F on convect for 5 hours . This made a huge difference. Now printing nicely with a glossy finish and no popping. The spool look a bit potato chippish however. It warped due to the heat.
I am using a Hbot with Micron cobra extruder (all metal) and high flow 0.5mm nozzle. Printing @60mm/sec. I have not tried faster with the dry filament yet. Basically I am able to print at the same speed as PLA or ASA.

The parts are side plates for chain idlers for my recumbent racing trike project. They are 80mm in diameter. On the left is the “wet” version, right was made after drying the filament in the oven .

Drying the filament made a huge improvement in the print quality. Without the drying I would have rated this filament a failure.

During testing of the idler concept the strength and durability of the nylon became evident. The chain was not restrained and kept bouncing off the idler gear, deforming the nylon flanges. The same tests with PLA shattered.

Next for the printer will be new bearings for the print head carriage. A spool of iglidur180 has arrived. I will be moving from the bearing wheels to low friction fixed sliders

I also need to leave a note on the printer as to which filament was left in the head at the end of a session.  I have taken to cutting the filament off at the the top of the print head and letting it cool. This avoids the jams I had been having by pulling the filament out and leaving globs of filament in the feed tube. However the range of temps I am printing with is now quite large (nylon @ 255C down to PLA at 170C). So tonight I was tring to feed in the PLA for some frame tube end caps and had to remember to crank up the temp to clean out the nylon and purge, lowering the temp as the nylon was all fed out.

Recumbent trike – idlers and longer ride

The trike is now mostly done, but the drive train was giving me grief. The idlers were not working out and I replace the rear cassette due to skipping.  The previous owner of the components had beat the bike more than I initially thought with damage to the cassette and outer crank chain ring , both of which had to be replaced.  Maybe there was a good reason he cracked his Trek carbon fiber frame?

After having problems with:

  • Metal pulleys as idlers . These were garden tractor style A size v-belt pulleys form Northern Tools. There were metal shavings everywhere and the chain would pop off.
  • Hybrid pulleys. I used sprockets from the old gear cluster and 3D printed nylon sides and spacer to center them over the ball bearings. They held together, but after 5 miles were wobbling badly and the low gears were skipping. The chain would rock off the sprockets, ride on the sides or pop off all together. The nylon withstood a huge amount of force and merely deformed without breaking. However with a 9/32″ wide bearing, there was too much lateral force.
  • Hybrid pulleys versions 2&3. I used PLA for the test models. However, it blew apart under stress in less than 3 miles.  There were problems with geometry and the bearing to sprocket interface.   I was not thrilled with the thought of making new parts out of aluminum to withstand the stress and support 2 bearings per pulley. Nylon flexed too much and I would have needed to bake the spool again due to the humidity. to drive off the absorbed moisture prior to printing.

I then again turned to Google. This lead to Terra Cycle idler pulleys. http://t-cycle.com/idlers-chain-management-c-41/idlers-c-41_9/sport-power-idler-p-134.html They were highly recommended on the AZ website and elsewhere.   I ordered a couple of these and one of thier 28″ chain tubes as an upgrade from the garden hose.  With the research, I also decided to redo the chain tube supports and let the sprockets and chain tube slide freely on the shaft rather than being held side to side in a fixed location.   The resulting setup is seen below.  I used 1/16″ x 3/4″ aluminum stock and bent it to match the chain tube. This was easier to make and the integral chain retention is a huge benefit.

You can also see above, that when the old front idler shattered, the chain was then rubbing on the underside of the handlebars.

With these installed, I dressed for cycling (cycle shorts, not my regular cargo shorts) so as not to appear to be flashing the passersby. The padding of the cycling shorts was not necessary but the snug fit was.  I then did an intermediate length “shake down” ride. Just shy of 20 miles and nothing fell off or bound up. I still need to do some derailleur adjustment (some skipping under hard stress) and front brake fiddling (some squeaking/ rubbing of he disks) and front wheel toe-in adjustment as well as tying down the right front brake cable which is rubbing my calf.

However, it rode very well overall. It was comfortable and fun. There were plenty of interested looks on the bike trail, as you might expect.  Max speed was 26 MPH and average was 12.  Still below my road bike, but I hope with a bit more tuning and remembering to top off the tires, I should break even.  My back, wrists and hands felt much better than on the road bike. Conversely, my shoulders and biceps were a bit stretched as my hands are below and behind my back due to the reach for the handlebars. Legs were pretty good, but my shins are a bit sore tonight.  I expect that there will be some “human break in” for the new riding position.

 

3D printer Improvements – Bed leveling and Thermocouple Amp

3 point bed leveling was needed. I really should have done this from the beginning. 4 point is way too hard to do and results in warped plates. 3 point gives nice control and no warping problems. The right side of the heated bed has the single screw.

I now have it set up with 3 “glass cutting board” build plates. One is plain glass for PLA, a second has blue painters tape for PETG, a third has a layer of PEI attached for other filament types.  The cheap glass cutting boards are working out great for build plates:  Premium Tempered Glass Cutting Board Bundle 4 Pack – 11.75″ x 15.75″
by Clever Chef Link: http://a.co/goO8N7c

Next I tackled switching over to the thermocouple temperature sensor for the print head. The amplifiers finally came from China.

The thermocouples have a major advantage over thermistors for high temperature sensing as they can go to much higher temperatures. These will be needed for printing Nylon, Polycarbonate and other materials. The amplifier is very simple see: http://reprap.org/wiki/ExtThermoCouple_1.0

What is not mentioned anywhere is that when you configure for the thermocouple amp for the Rumba board you must connect it to a different input pin! I had to dig through the .h header files and then the schematic to finally figure this out. Otherwise the system was saying hte temp was 398 degrees C at ambient air temp due to the open circuit. In the photo below, the lonely yellow wire is the output from the thermocouple amp. 

All of the other temperature inputs are on the left edge of the board, neatly arranged.

After I had it connected and reading the correct ambient temp, about 22C, it was time to run some tests to tune the heater control circuit. The heater control is done by a PID control loop. Most of my control loop theory and Laplace transforms are long forgotten. So I decided to use the PD auto tuning of the Marlin firmware.  There were a few initial runs, but now I need to get serious. Here is one of the first attempts at running with the thermocouple. The output is very noisy and the temperature control oscillates will not settle down

The results when running the auto calibration were not great. Part of the problem was excessive noise on the temperature sensor lines. I had to move the amplifier up near the print head to make it be usable. There is still more noise on the temperature feedback than I would like, but it is running with reasonable stability.  I ended up using the recommendation for the PID settings form Micron EME that makes the print head I am using.  Here is a print head heat plot made while printing a cover for the enclosure for the Rumba controller board that I am using.

I am now printing PETG with some reliability, but I still have some problems with the filament stripping and jamming at the drive gear. One other problem was the PETG filament had absorbed moisture over the last month, leading to lots of tiny bubbles in the extrusion. I “baked” the  filament for 24 hours at 100 degrees (bread proof setting on my oven) and this cured most of the bubbles by driving off the moisture. The filament will now be stored in a plastic box with silica gel to absorb the moisture.

Here is a shot of the top cover of the Rumba board case being printed.  Teal says the printer sounds like an old school video game while doing the fan openings.

 

Additional links:

http://reprap.org/wiki/RUMBA

3D Printing parts for the Printer
At this point the printer isl making more parts for itself. Teal (my wife) compared it to Frankenstein adding his own parts after he had an arm attached.

One of the first part sets was to make a case and mount for the display. The case turned out quite well, but the design of the bracket to mount it to the frame was unusable. So I will be searching for another or designing one myself.

The advantages of being able to walk away and let the printer just run and return to a safe state are huge. With the print head on the CNC router, I had to keep checking on the progress and shut it down at the end as the software could not control the print head heater . Now not only is it running and shutting down properly I get messages on my phone confirming the status. With Repetier host https://www.repetier.com/, you can add an app to your phone, Repetier Informer, and get notifications of start, stop, faults and progress (among others). So today as I was again multitasking,getting the spring gardening done and wandering about the yard, I was getting notifications so I could check up on the printing status while finishing the placement of 20 yards of wood chips and propagating many perennials. This was to gain more flower beds with perennial plantings and reduce lawn area and Buckthorn thickets. I was doing my Earth Day yard work.

Today the printer was making cable chain. I am not sure if this a good trade-off of time vs cost. Cable chain is used to make a nice flexible assembly to hold your wires / cables for moving devices. For the CNC router  I bought the cable chain from an eBay supplier in China. For the 3D printer, the printer itself is making the cable chain links but I have to do the part clean-up and fitting. The printing is not yet tuned in well enough to avoid a lot of hand work on these parts.

Spool holder to hold the filament spool while printing.: http://www.thingiverse.com/thing:1959643/#files.  This replaces the ugly aluminum rod seen earlier in the photos and removes obstructions. This is a very nice and simple, functionally designed part. “Frankenstein printer” did well on making this appendage.

Cable chain. This supports the wires going to print head in a neater manner than the spiral wrap. I am using the part designs from: http://www.thingiverse.com/thing:611593/#files . I wanted cable chain that would be open on top so I do not have to re-run the wires in the frame with the need to then disconnect re-connect everything for the print head. We will see how this turns out. The notches look like they will need some fiting for the snake shaped cable retainers (cable ties bay do instead). Cable chain parts are slow to print . A set of 16 links takes about 5 hours. Then there is some tedious hand work to clean up the parts and make them fit together well. I think 2 sets of 16 links, plus the end parts should suffice for the print head cable chain. Here is the first set of links fitted together, roughly straight and as a U.

3D Printer is Running!

The printer is now running It is roughly assembled (as you can see) and now it is time for fine tuning and making parts for itself. I love it when a tool is at the state where it can help finish its own build or rebuild making parts. Cases for the boards, cable retainers, cable covers, cable chains, proper spool support are all on the short list.

There has been a bit of additional grey hair added getting here:

The Rambo control board will not connect at all via USB3. It must be a USB 2 connection . This is the case for both the Arduino downloads and Repetier control software. I did not pay attention when I originally programmed the board and then subsequently rearranged the USB ports…

Along the way the first Rambo board stopped communicating via USB. Many tries to get this going, re-download drivers, try to re-flash the USB chip but to no avail. I ended up returning the first one (still barely within the 30 day amazon return period) and got another. So far so good. I was able to get it programmed and it is running well so far.

As mentioned previously the thermocouple adapter wont work with the 12864 display. So I have jammed a thermistor on top of the heater block as I don’t want to pull out the thermocouple temporarily and risk damaging it and the thermistor is working OK for now. It is still off by about 15 degrees, too hot, and the temperature control overshoots. However the adapters are on their way.

The new nozzles form Micron finally came. It takes almost 4 weeks from Israel with normal shipping. I am currently using the high flow 0.5mm nozzle.

Fan for the print head heater must be directly connected to 12v. Not fan 0 or 1 . It needs to be always on. Not doing this lead to new and novel ways to jam the filament.

It pays to double check the tooth count on the gears. The first test cube was well undersized and over-extruded. The steps per mm settings are now corrected.

12v power supply was just not enough to get the print head up to temp. I needed to switch to 24v.

Still need to find a better way to adhere the cork to the bottom of the heated print bed.

The plain glass rectangular cutting boards form Amazon are working well as build plates. So far printing the PLA to the clean glass with no additives. Clean with denatured alcohol.  On the old setup I was getting to decent adhesion with blue tape wiped with lacquer thinner.

Some of the issues were self inflicted as I was time splitting between house / yard projects, this and several other things. At times I hit my multi-tasking limits.

So now I am adjusting settings and printing parts. First successful test cube is below.

Snot string was due to still having the print head too hot due to poor contact with the thermistor.

Finished test cube. Size is now dead on.  This was with 0.35mm layer height, 60mm/s internal speed 30mm/s perimeters.

Now starting printer parts. Here is the back of the case for the display being printed.

 

The Repetier control software is great. It is much better than truing to control the printer directly via the twisty-turny knob on the  display.  Overall, I am rally impressed with the open source software (Marlin and Repetier) of this project.

Completed back panel for the display:

 

3D printer progress – assembly and test

At this point the frame is largely assembled. The carriages are mounted, the heated bed is installed and things actually move (at least manually).

I used a MK2A 300x300mmaluminum heatbed and had to move the motor motor and leadscrew mounts. The motors need to move out from the back as well. This is a good thing as otherwise the motor move would interfere with the 3×3 triangles. Flipping them over fixes that issue. However the smaller top 3×1 brackets do need to get trimmed for clearance. This was a quick trip to the band saw. .

The first piece to get moving is the bed elevation. The critical part of the motor alignment is at the bottom end. Need to get the motors under the drive screws. Sight along the frame to see that the screws are parallel to the legs in both directions and then tighten them down. The safety stops in the firmware need to be over-ridden as normally you can’t move the  axes to a negative position. In this case, negative is UP . So in Configuration.h make the changes as shown below to get the over-ride for testing and the homing directions:

// ENDSTOP SETTINGS:
// Sets direction of endstops when homing; 1=MAX, -1=MIN
#define X_HOME_DIR -1 // left
#define Y_HOME_DIR 1 // rear
#define Z_HOME_DIR -1 //top

You need to comment out the block below. It prevents the use of the max direction endstops. It took a while to find as I was troubleshooting why X&Z would home nicely but Y would not do any homing movement at all.

// Disable max endstops for compatibility with endstop checking routine
//#if defined(COREXY) && !defined(DISABLE_MAX_ENDSTOPS)
//#define DISABLE_MAX_ENDSTOPS
//#endif

#define min_software_endstops false // If true, axis won’t move to coordinates less than HOME_POS. — allow for testing
#define max_software_endstops false // If true, axis won’t move to coordinates greater than the defined lengths below.

This will allow moving the bed upwards under manual control.

I also made the initial settings for the stepper calibration. I am using 32 step microstepping (rather than the more typical 16), 8mm pitch threaded rod and a Micron EME cobra extruder. So the step calibration at this point looks like:

#define DEFAULT_AXIS_STEPS_PER_UNIT   {200,200,812,1168*2} // 32 microstep 16 tooth gears, 8mm acme rod & micron extruder

Belt installation was straightforward, but make sure to place a screwdriver blade behind the nuts for the clamp bars before inserting the screws. It is far to easy to push the nuts back and have them fall out as you attempt to clamp the belt to the carriage.

Currently all 3 axes are moving, and homing. Calibration still needs to be checked.

I was also configuring the temperature sensors to get the thermistor for the heated bed to work and get ready for print head testing. I am also running a thermocouple for the print head. I want to run thermocouples for the print head to use high temp plastics such as Nylon. The low output signal from a thermocouple requires an additional amplifier or special A to D convertor.  I had purchased the Max6675 thermocouple digital adapter. However, it turns out it is not compatible with having a 128×64 display!!! There are shared conflicting pins. NUTS!. Now I have to order some AD597 adapter analog boards (and wait for them to come form China, as I could not find any stocked in the US).

When I started the project I downloaded the Marlin software directly. I would have been better off starting with the package on the d-bot page (or at least using the configuration.h file). It was in a line by line comparison that I found the Y axis homing culprit. http://www.thingiverse.com/thing:1001065/#files   and select d_bot_marlin.zip

D-Bot 3D printer frame assembly

The printer frame is built out of V-slot linear rail http://openbuildspartstore.com/v-slot-linear-rail/. This is similar to the 80/20 and Bosch rails I have used on the CNC router but with one crucial difference: the slots are V shaped a the top. This allows rollers to run in the grooves to provide the motion without having to add linear rails like I used on the CNC router. This is far lower cost, but also lower precision. However, the test prints I am seeing from a friends unit look great.

The precision of the cuts is critical to rigidity and squareness of the printer. You should use a non-ferrous metal blade  in either a chop saw or radial arm saw. I use a Bosch PRO1080NF 10-Inch 80 Tooth TCG (triple chip grind). This has served me well for several years.  When using the radial arm saw as I did be careful to prevent over-feeding. The stop system on my saw makes for nice repeatable cuts.

Once cut, the ends of a number of the rails must be tapped for M5 screws. The extrusions already have proper sized holes but this is still tedious if using a regular plug tap. This is is where a “gun” tap or “spiral point” tap which is designed for through hole power tapping comes in very handy. I started using these for the 100’s of tapped holes on the CNC router. I used plenty of cutting fluid and a hand drill with the tap chucked lightly to tap the holes. Practice first and have some spare taps on hand prior to doing this on the v-rail. Snapped taps are darn near impossible to remove from aluminum.