Tuesday, July 16, 2019

An Electrostatic Nanoparticle (?) Precipitator for UMMD

This is a project I started and then abandoned.  I recommend you don't do anything similar.  The idea was to capture particulate emissions from my printer using an electrostatic precipitator (ESP).  As the project progressed, I kept reading more and more scientific papers about the process and about the type of device I was using.  In the end, I came to the conclusion that an ESP that emits ozone is a very bad way to capture nanoparticles because the ozone will react with everything in the environment and may produce nastier stuff than it captures, including more nanoparticles!  I have added links to many of the papers I was reading at the end of the post. 

Please note- absence of odor is not a reliable indicator of the efficacy of a filter.  There are plenty of harmful things that you can inhale that have no odor.

What follows is stuff I was writing as I was working on the project:



In the last few years, there have been several research studies of the particulate and gas emissions from 3D printers (see the list below for some papers of interest), many suggesting unhealthy levels of both, especially if you print ABS, though at this time the long term health effects are unknown.

As a result, a lot of people are trying to make air filters that will capture the scary nanoparticles and volatile organic compounds (VOCs) produced by 3D printers.  Most go the route of using HEPA filters made for vacuum cleaners to capture particles and activated carbon filters to capture VOCs.

The one thing they all have in common is a lack of any objective measurements of the results.  Instruments that can count nanoparticles in the air are uncommon, expensive, and few people know how to use them well enough to get valid results.  So amateur attempts to mitigate 3D printer produced environmental air pollution is a guessing game at best.  And no, your nose is not an adequate instrument for testing, unless your only measure of success is elimination of odor.  Maybe your filter works, maybe it doesn't.  Maybe it captures the nanoparticles, or maybe it only captures the bigger particles that are currently assumed to be less harmful.

A different approach


I found a few research papers on air scrubbing systems that are used to remove nature's nanoparticles, commonly referred to a viruses, from the air in clean rooms and research facilities.  They use a combination of electrostatic precipitation (ESP) and "soft" (low energy) X-rays to electrically charge the particles and remove them from the air.  ESP's are commonly used to remove dust from the air in homes and commercial buildings, and to scrub particles from smoke stacks in industry.

In one paper, the author made comparative tests of the efficiency of electrostatic precipitation alone vs electrostatic precipitation plus soft x-rays.  He tested it at different voltages in the precipitator and found that above about 8kV, the ESP alone approached 100% efficiency at capturing the nanoparticles.  At lower voltages, the ESP alone wasn't so efficient and the soft x-rays, presumably because the tinier particles don't always get charged in the ESP, pushed the efficiency back up to 100%.

ESPs can be made very inexpensively.  Why would anyone want to go to the trouble of adding the soft x-rays, greatly increasing the expense of the system?  At the very high voltage where the ESP is 100% efficient at particle capture, there will be some corona discharge (sparks).  That corona does a couple things.  First, it appears that it manages to apply a charge to even the tiniest nanoparticles so they can be removed from the air, hence 100% efficiency at particle capture.  The other thing it does is produce ozone.

Ozone is triatomic oxygen and is reactive with many things in the environment including VOCs.  It also makes up a pretty large part of the brown haze in the air over cities on polluted days and isn't very healthy to breathe.  Ozone is commonly used to remove odors from homes that have had fires, gruesome criminal activity, and unfortunate accidents that result in bad smells caused by VOCs.

Oxygen prefers to be O2, not O3, so ozone happily gives up the extra oxygen atom to almost anything nearby that's willing to accept it.  That means ozone is unstable and and has a half-life of just a few minutes.  As temperature increases, the half-life decreases, so inside a heated 3D printer the ozone produced won't be around for long.  Hopefully, the extra oxygen will attach itself to VOCs, breaking them up, instead of attacking the rubber drive belts.

ESP construction


The image below shows the construction of the ESP used in one of the papers I've linked above and below.

Diagram of ESP with Soft Xray emitter used in this study.
It's just a metal tube with a wire running down the center, and has I/O for air flow.  Pretty simple.

How I built It


I chose to make a similar thing, but without the X-ray emitter.  I arranged a 40mm fan at the end of a piece of metal pipe (the collecting electrode) about 32 mm in diameter, and a thin wire down the center for the negative electrode.  I used a 12V to 20 kVDC converter, purchased for $10 via ebay, to provide the necessary electrical charge, and stole 12V from one of the DC-DC converters in the printer that I set up to do stuff like this.

I wanted the whole thing to be easy to clean, so I built it so that the pipe could easily be removed without having to do any major disassembly.

After a few failed and suboptimal attempts, I settled on a design printed in six parts.  There's a mounting bracket to hold the assembly on the printer's Z axis frame, an end cap, spring bar, a HV mount, a HV contact, and a fan mount.

The bracket has a ridge that fits into the frame t-slot and there's a single screw/t-nut to hold it in place.  It has slots for zip-ties that will hold the rest of the assembly in place.

The bracket screwed to the back of the Z axis frame and waiting for the rest of the assembly to be mounted.

The end cap fits on the top end of the pipe and holds the spring bar that puts tension on the central wire electrode.  The end cap and wire connection have to be removed to take the pipe out for cleaning.

This is the end cap and spring bar that is used to tension the central wire electrode.  The spring pulls on the wire and prevents is from touching the pipe.


The HV mount is a close fitting tube into which the pipe electrode slides, and also mounts the HV converter module.



The HV contact part fits over the pipe holder and the pipe and has a spring that makes contact with the pipe when it is inserted into the tube.

The HV contact has a spring inside that touches the pipe when it is inserted into the assembly.


Finally, the fan mount has the electrical connection for the central wire electrode, an air baffle that forces the air coming into the pipe to spin, and holds a 40 mm fan to blow air through the whole assembly.

This is the fan mount.  The blades force the air to spin as it flows through the pipe.  The negative electrode wire feeds through the hole in the center.
How do you mount a square fan on a round tube?  Fusion360 makes it easy using the loft function.  I drew the square-with-rounded-corners fan shape on one sketch and about 40mm above it, I drew a circle that would become the outer surface of the printed fan and tube mount.  Then I used the loft function in the "create" menu to connect the two as a solid, and finally, I used the shell function under the "modify" menu to hollow it out.  The resulting print varies smoothly from the square fan to the round pipe.  I used the same function to make the blade inside the fan mount that twists the air flow.

Here's the assembly set up for initial testing.  Left to right- 40mm fan, fan mount, HV contact, HV mount, end cap, spring spring bar.

There were a couple problems to deal with in this design.  I needed the pipe and tube to be easily removable for cleaning so I couldn't solder the HVDC wires to them.  Making the electrical connections foolproof and reliable was a bit of a challenge.  Also, I wanted it to be very easy to reinsert the pipe even if I couldn't see down inside the assembly because of its position in the printer.  That meant I had to design it to guide the pipe into the correct position to make electrical contact without effort.  I ended up with a spring as the electrical contact for the pipe.  It sits in a groove at the bottom of the pipe holder and when you push the pipe into it, the spring contacts the pipe that was sanded to bare metal.

The central wire electrode is just soldered to the HV lead coming from the converter module.  The end of the wire has a loop that hooks onto a spring at the far end of the pipe.  The spring is held in place by a printed plastic end cap and the removable spring bar.


Here's a look down the pipe with the HV converter running.  You can see the purple glow of the corona discharge along the central wire electrode.  It produces a little bit of fresh-smelling ozone that will hopefully break down VOCs from melting plastic in the printer.

Does it work?


I'll be printing ABS with it over the next few months and see if there's any ABS-stink while and after it runs.  I'll run a clean rag through the pipe to see what sort of particulate stuff it manages to pick up.  I don't have anything to count nanoparticles in the air, so this will be like everyone else's build-it-and-hope-it-works approach.


Relevant articles (some may be pay-walled):


Acute health effects of desktop 3D printing (fused deposition modeling) using acrylonitrile butadiene styrene and polylactic acid materials: An experimental exposure study in human volunteers


Characterization and Control of Nanoparticle Emission during 3D Printing

Ultrafine Particle Emissions From Desktop 3D Printers

Characterizing 3D Printing Emissions and Controls in an Office Environment

Destroy VOCs (Chemical Pollutants) at their Source | SanusAer Ozone Generators




Saturday, June 29, 2019

3D Printable Wago 221 Lever Nut Mounting Blocks

I like to use Wago 221 lever nuts in place of screw terminals and have started replacing screw terminals in my 3D printers with them.  To that end I designed a few printable mounting blocks to hold single and multiple lever nuts.

The Wagos come in 2, 3, and 5 wire parts (221-412, 221-413, and 221-415), handle 24-12 gauge wire, handle 32A up to 450V, and have multiple safety certifications (unlike the much cheaper Chinese made knock-offs).  Full specs are available here.  When I first got them I inserted some wires and then pulled at them and was unable to pull any of the wires out. They really hang on tightly to solid and stranded wires.  All the wires will connect together in each block.  The 5 wire blocks are great for making DC power distribution blocks in a 3D printer, as I did in UMMD.

I have printed the 2x2 and the 221-415 mounting blocks using ABS.  The other blocks are based on the same dimensions so they should work fine.  You insert the back end of the lever nut as far as it will go into the mounting block, then press down hard on the open end and it will snap into place.  They fit and hang on tightly so there's little danger of the lever nuts coming out of the blocks, and even if they do, the bare wires are entirely enclosed within the lever nuts, so nothing is going to short.

Here's the 1x5 mounting block with a 221-415 block installed.

Yes, they're pretty small.

Here's the 2x2 mounting block.  It uses 2 screws to mount on a flat surface or t-nuts to mount on t-slot.


Here are two vertical mounting blocks that hold 4 of the 221-412 lever nuts.  The one on the left has an 8 mm tang that prevents rotation in a t-slot (so you need to use bed-only support material when printing) and uses a single t-nut to hold it in place.  I used that one to make bed heater and thermistor connections in UMMD.  The one on the right is intended for mounting on a flat surface.
The CAD file is easy to edit for any combo of lever nuts you want to make.  You can DL the Fusion360 CAD file for the mounting blocks here.

Thursday, June 27, 2019

3D Printed White Board Marker and Eraser Holder

I used to use Expo white board markers.  They were just awful.  Even when new, the lines always looked faded and some colors of the ink were very difficult to erase from the board, even with the spray-on solvent.

I recently bought a 5 pack of Pilot BeGreen V Board Master markers.  OMG what a huge improvement!  The colors and lines are solid, and they all erase cleanly and easily using my old Expo eraser, a paper towel, or a rag.  The markers are refillable, but the refills cost more than buying new markers if you buy less than 12 of the same color at a time.  If you use a white board, get some!  And before you ask, no, I'm not being paid to say this.



I needed a shelf to hold the markers and an eraser (Expo!), so I spent 5 minutes in Fusion360 and designed a wall-mounted holder.

The holder prints upside down without any support material.  2 small screws or double sided tape will hold it on a wall or on your whiteboard.
 The CAD file is located here.

And here it is, in green ABS.
I may redesign it for use with suction cups...




Thursday, June 20, 2019

Replacing a B&L Microscope Lamp with an LED

I've recently been restoring some old microscopes for an organization called "Milwaukee Area Science Advocates" who have been gathering them from teacher's closets where they have been unused for a long time.  Many of them just need a cleaning to get them into usable condition, and a few need parts to be swapped.  Eventually the scopes will be used to promote science education by letting kids observe live microorganisms with them.

A couple of the scopes I've been working on are old Bausch & Lomb units with identical illuminators that slide into a bracket under the stage.  The illuminators are nothing fancy- just a 15W incandescent light bulb in a bakelite box with a blue tinted filter glass that probably absorbs IR and prevents the specimens on the slide from drying up.

One of the B&L microscopes with the funky illuminators.


The problem I ran into was that one of the two had a burned out light bulb.  I'm sure someone has a big stash of these bulbs somewhere, but not anywhere I could find, and even if I managed to find one, how much will it cost, and what's going to happen to the scope when the bulb burns out again?

The light bulb used in the substage illuminator.  15W 120V.
The substage illuminator opened up.  The blue glass blocks IR and helps keep specimens on the slide from drying out.

The light bulb base and switch.

I checked into adapting the E26 bulb socket to a candelabra (E12) bulb, but all the E12 bulbs and LEDs I could find were too long to fit into the enclosure.  After spending a while searching a few other possibilities, I decided I'd have to solve the problem myself, taking the easiest approach I could think of- I designed a printed part to screw into the light bulb socket in the bakelite enclosure, that holds an LED and a resistor, powered by a 6V wall wart, using the original power cord minus the AC plug.

I know from previous experience that a single, 5mm diameter, white, 20 mA LED easily throws enough light for a microscope, even at high magnification.  So I started working on the design for the light bulb replacement.  I quickly realized it would have to be done in two parts- one that screws into the E26 socket in the illuminator and the other that will hold the LED and allow it to be aligned with the optical path in the microscope.

The Base


The first thing I needed to do was duplicate the E26 light bulb base.  It's 26 mm diameter, but what are the specs for the threads?  A few minutes research revealed that E26 lamps have 7 threads per inch - that's 3.63 mm pitch - ugh!  I couldn't find a 7 tpi thread built in to Fusion360, so I created it by making a helix and subtracting it from a 26 mm diameter cylinder.

I needed to make electrical connections between the LED and the lamp socket, so I added a hole in the side of the base through which I could lay a wire in the threads.  The wire makes contact with the bulb base threads.  The other connection is made by looping a wire through the bar on the bottom of the base.  When the base is screwed into the socket, the wire will touch the center contact in the socket.  It probably won't get UL or TUV approval, but it works.

The base rendered in Fusion360.  The bar at the bottom holds the wire to make electrical contact with the lamp socket.


The LED Holder


The original bulb socket is mounted horizontally so the LED has to be turned 90 degrees off the axis of the base to point it up the optical axis of the microscope.  I couldn't predict exactly where it needed to be located, so I made the LED holder position adjustable to allow for alignment with the microscope optical axis.  The LED holder just friction fits into a hole in the base that allows it to slide in and out and rotate.  It grips tightly enough that it should stay aligned once set, though a drop of glue could be added to ensure stability.

Here are the two pieces used to make the LED holder.  The cylinder on the left fits into the hole in the base (middle).

Putting It All Together


I tested the 6V wall wart with the LED and resistors to get the current through the LED to about 20 mA.  I ended up using a 270 Ohm resistor.  If you try something like this you'll have to test it to see what value of resistor to use- unregulated wall-wart's voltages can be all over the place with a small load like a single LED.  I attached wires to the LED, fed them through the hole in the LED mount, and then attached them to the base to make electrical connections.

The LED in the base.  The wire will contact the threaded part of the lamp socket.  The bottom contact is also made by looping a wire around a plastic bar in the bottom of the base.

I cut the plug off the illuminator's power cord and wired the wall-wart to it, screwed in the LED mount and it lit up.  Then I put it into the microscope to make sure the light from the LED was aligned with the optical axis of the microscope.  The LED can be rotated and slid in and out of the base so it is easy to position it.

The illuminator with the LED replacing the incandescent lamp.  The blue glass is not really needed because there's no IR coming from the LED so it isn't going to heat up and dry out the specimen being viewed with the microscope.
That's it!  A pretty simple project making great use of a 3D printer.  The CAD file for the E26 to 5 mm LED adapter is located here.


Friday, June 7, 2019

Milwaukee MakerSpace on Fox6 TV local news broadcast

I spend my Tuesday evenings (and usually Sunday afternoons) at the Milwaukee MakerSpace. Channel 6 TV in Milwaukee recently took a tour of the Milwaukee MakerSpace.
Link to the broadcasts on the Fox6 web site.
And another page with more video.

If you're too lazy to click the links up there, here's video they shot of some of the things that go on at the MakerSpace:





You can see "The Spice Must Flow" sand table is in this video:




If you're in Milwaukee and you want to take a tour, we're open to the public on Tuesday nights at 7pm for meetings and tours.  The MakerSpace is located at 2555 S. Lenox St. in Bay View.



There are a lot of great restaurants in the area, but if you're hungry before or after a visit to the MakerSpace on a Tuesday night, Cafe Corazon (top left corner of the map, a few blocks from the MakerSpace) has great $2 tacos - I highly recommend the pork pibil!  It'll be the best 2 bucks you ever spent!

Tuesday, April 30, 2019

More Changes to UMMD's Z Axis

More Z Axis Updates

I "finished" UMMD about 1.5 years ago, but there have been quite a few changes to the machine over that time.  In particular, I have made a lot of changes to the Z axis and related parts that I will summarize in this post.

Pulleys and Belts


The original Z axis used 3 mm pitch steel core belts and 40 tooth pulleys.  I can't recall how I ended up using those parts- maybe I had them on-hand- but that combo led to an unfortunate 18 um/ustep in the Z axis.  After a few changes and some careful calculations, I ended up with 60 tooth 2mm pitch drive pulleys and belts, and now have glass core belts on the machine.  That gives a nice, round 20 um/ustep (at 16:1 ustepping).  The glass belts stretch about 3x as much as the steel core belts, but still not enough to matter.

One of the 60 tooth 2mm pitch drive pulleys.  The larger diameter of the pulley necessitated a redesign and fabrication of the Z axis top pulleys to keep the belts parallel to the linear guides.
The Z axis top pulley mounts had to be remade when I changed the drive pulley diameter to keep the belts parallel to the guide rails.  The original mounts had two carriage bolts to hold them in place and prevent the plate from rotating.  The new design has an antirotation tang that fits into the t-slot and uses a single carriage bolt to hold it in place.

The original pulley mounting bracket at the top of the Z axis used two carriage bolts to hold it in place and prevent it from rotating.  
This is one of the final top-of-the-Z-axis pulley mounts.  It was milled from a piece of 8mm thick tooling plate left over from the bed plate.  There's an anti rotation tang on the back side that fits into the t-slot.

Extruder Carriage

The extruder carriage has undergone more changes than any other part of the printer.  I used different extruders, different hot-ends, and different carriage designs.  The original carriage was made from a single piece of aluminum tubing with the extruder, motor, and hot-end all hanging below the X axis bearing block.  I thought that it looked too much like a pendulum, so I moved the extruder and motor above the bearing block leaving just the hot-end below.  I eventually settled on a two piece design that has the extruder and hot-end mounted on a metal plate with the belt clamps mounted on a smaller piece of tubing.  That allows the extruder and hot end to be removed without taking the belts out of the clamps or even relaxing the tension on the belts.  One thing about the design that has been a constant was the extraordinary length of the carriage.  This was necessary because of the way the bed was lifted on the Z axis.

Eventually, the very long extruder carriage started to bother me.  I can't really say that it was creating any problems in the prints, but it just didn't seem right.  Any minor wiggle in the X axis guide rail would be amplified by the long lever arm that the hot-end was mounted on, so I finally decided to do something about it.


Here's the extra long, almost final extruder mounting system that I wanted to shorten.  The extruder and motor are mounted just above the X axis bearing block and the hot-end is connected by a PTFE tube down below.  The length was needed so the hot end could reach the bed surface.


Bed Lifting Brackets and Z Axis Belt Clamps


If I was going to shorten the extruder carriage, the bed had to go up higher.  The easiest way to make that happen was to swap and flip over the bed lifting brackets that hold the bed assembly on the Z axis.  That raised the bed by about 50 mm, and moved the lever arm from the extruder carriage that whips around at high speed and acceleration, to the bed that only goes up and down a little.  Probably a good trade off.

The new positions of the bed lifting brackets.

While I was doing that, I changed the way that the Z axis belt clamps attach to the bed lifting brackets.  When I first built the machine, I didn't realize how hard it was going to be to release the Z axis belt clamps because of the dual layer PC panels that fit into the printer's frame (I'd have to remove a frame member to move a panel out of the way).  I also didn't anticipate the amount of experimenting I'd be doing with the Z axis.  Releasing the belt clamps from the brackets required a right angle screwdriver to get at the screws that were on the outside of the brackets, with very little room for my fingers to fit in the space.  I needed to flip the screws so that the heads were on the inside of the brackets instead of the outside.

The old way... my knuckles are up against the PC panel on the left.  There are four screws that I have to take out on each side of the Z axis.  The screws goes through a metal plate that holds the yellow belt clamp against the Z lifting bracket.

Much easier access to the Z axis belt clamp screws.  The tapped holes in the bracket were drilled  out to allow the screws to pass through the bracket and belt clamp and thread into a nut-plate on the opposite side of the belt clamp.

I drilled out the threaded holes in the brackets so that I could just push the screws through from the inside, and made two aluminum nut-plates with four tapped holes that the screws now thread into.  The belt clamps get trapped between the brackets and the metal plates just like before, only the screws are now easier to access.  It was so easy- I should have done it years ago!  Now if I want to remove the belt clamps I can just use a screwdriver from the inside of the brackets, under the bed support, where there is plenty of room to work and I can see exactly what I'm doing. Nice!  That will make future changes to the Z axis a lot easier.

Compare the two pictures above to see the differences in the bed lifting brackets.

This is one of two new nut-plates that clamp the Z axis belt clamps to the lifting brackets.  The material is 3 mm thick aluminum and the holes are threaded for 6-32 screws.

Z Axis Belt Clamp Redux


By now you've probably seen that I had a problem with the original belt clamp design that led to a failure of the steel core belts.  I redesigned the belt clamps based on a design I have used in SoM for about 6 years without any problems. 


The original clamp design worked like this.

And it failed like this!

New Z axis belt clamp design folds the belt back on itself to lock it in place.  The open side of the clamp (facing the camera in the photo) is closed with a rectangular aluminum nut plate that's held in place with 4 screws.


Extruder Carriage Modifications


Now that the bed lifted higher, I was able to cut the long, 5mm thick aluminum plate that mounts the extruder and hot-end on the carriage about 60mm shorter, allowing the hot-end to mount closer to the extruder.  The PTFE tube that connects the extruder to the hot end is also lot shorter than it was.  I feel better about it now.

The metal plate on the extruder carriage used to bump the X axis endstop, but that part of the plate was cut off (maybe I should have left part of it there to bump the switch).  I printed a new hot-end clamp that includes an extension that bumps the switch.

The old extruder carriage- the metal extension plate used to bump the X axis endstop, circled.


And here's the newly shortened extruder carriage.  There's not much room for bolting on a print cooling fan, but I rarely print PLA anyway.  The black hot-end clamp has a flag (to the right of the cooling fan) that bumps the X=0 switch.


This is the final extruder carriage design.  The extruder and hot-end mounting plate is 5 mm thick aluminum, and the belt clamp mounting tube is 1.5" x 2"x 1/8" aluminum tubing.  The belt clamps and hot-end clamp are printed ABS parts.  The plate holding the hot-end and extruder can be removed without taking off the belt clamps or releasing the belt tension.


Bed Heater


The 468MP adhesive holding the heater on the bottom of the bed plate started letting go several months ago, so I decided to peel the heater free and reattach it using high temperature silicone.  I made an attempt to remove the heater using the scraper I use to release prints from the bed, but it didn't work- the parts of the heater that were still stuck to the plate were really stuck to the plate.

I contacted Keenovo about it and they pointed me at this site for instructions on how to remove a heater from a plate and this site for instructions of preparing a plate to receive a heater that has 468MP adhesive.  Here's their manual on the heaters (which I had never seen before).

They recommend a few things I was previously unaware of, including sealing the edges of the heater with a bead of high temperature silicone, maybe to keep the adhesive from "drying out" and letting go?  Maybe I should seal the edges of the PEI sheet for the same reason...  They also recommend using a mechanical "sandwich" construction to ensure that the heater stays attached to the bed.

Per Keenovo's instructions, I heated the bed plate (to 100C) and used a scraper to release if from the bed.  I gouged the silicone in a couple spots, but fortunately didn't expose any of the heating wires.  Once I had the heater loose I looked at the underside.  The area that had come off the bed plate had been running very hot and singed the silicone on the underside of the heater.  I flexed the heater in the toasted area and it cracked, so I decided it wouldn't be safe to reuse it and ordered a new one without any adhesive.


The burnt bed heater.  The dark section cracked when I flexed the heater in that area, so I have ordered a new one without adhesive and I will cement it to the plate using high temperature silicone.
I mounted the new, adhesive-free heater on the bed plate using Permatex Red high temperature silicone purchased at a local auto parts store.

The TCO, previously mounted on the edge of the bed plate was moved to the heater and mounted using the same high temperature silicone that was used to mount the heater on the plate.  This was done so that if the heater comes off the plate, the TCO will stay with the heater and hopefully shut down the power before it starts a fire.

The new bed heater mounted on the plate using high temperature silicone.  The TCO is also attached using the same high temperature silicone inside the blob near the center of the heater.


Leveling Screw Block Redesign


Once I had the extruder remounted on the shorter plate and went to relevel the bed, I noticed that when I turned the roll screw, it was causing the bed to shift laterally.  That's shouldn't happen!  I found that the PTFE block holding the pitch screw was tilting/shifting in the t-slot.  The narrow PTFE block was held inside the t-slot by two small screws and they weren't holding fast so the block was wobbling in the slot.  I tried to tighten the screws and they stripped the holes in the PTFE.

Here's the original roll adjuster- the other two are about the same.  The PTFE block fits into the slot and is held in place by two small screws whose heads you can barely see in the bottom t-slot, behind the long roll adjustment screw.  It wasn't a very solid or reliable way to mount the PTFE blocks.

It was time to redesign the leveling screw blocks for more secure attachment to the support frame.  I was out of PTFE and the "local" plastics shop is about 40 miles away, and I just need a relatively small amount to use for this and future projects, so I did some shopping on ebay.  The first thing that struck me was how expensive PTFE is, or looks at first glance.

PTFE is a commodity, and you buy commodities by the price per weight.  The ebay listings usually have dimensions listed in inches, and PTFE has a density of 0.08 lbs/in^3, so I calculated the price/lb including the shipping cost when I compared the different listings.  It didn't really matter what the exact dimensions of the block were because I'm going to cut it up and mill it anyway.  I mostly use small blocks of the stuff, not large sheets, so I looked at bar/block listings at least 3/4" thick.

Here's a typical offering:

This one is a total of 13.125 in^3, which will weigh 1.05 lbs.  At a total cost of $23, that works out to about $22/lb. Ouch!


Here's an example of a pretty good deal:

These blocks of PTFE are 71.25 in^3 and have good dimensions to allow a lot of small parts to be made by cutting it up and milling.  71.25 in^3 will weigh 5.7 lbs.  I've probably used 1/10 that much PTFE in the last 10 years.  Total price is $36.80, which works out to $6.45/lb.  That seems like a pretty good price for PTFE.  
I ordered the block in the second photo.


The PTFE arrived in the mail- a literal brick!  I went to the makerspace and went to work on it.  In a couple hours I had three new PTFE blocks finished and ready to go.


The new PTFE leveling screw blocks.  You're looking at the bottom of the block on the left.  The tang just fits into the 8mm wide t-slot to prevent the block from rotating.

The bed support tee with new PTFE leveling screw blocks installed.  Each block is held in place with an M4 screw and t-nut.  The thickness of the blocks matches the length of the threaded part of the leveling screws- 13 mm.

One of the new leveling screw blocks.  The blocks are 30 x 24 x 13 mm.  So much neater than the original!



Here's the reference leveling screw with the new PTFE block in place.  I deliberately set the end of the PTFE block 5mm back from the edge of the t-slot so there would be more room for the spring.

The CAD file for the new design including the bed support and the bed plate itself is located here.

If you just want the CAD model of the sphere-head screws that are used for pitch and reference adjusters, here you go.

Electrical Connections

I had great results using Wago 221 lever nuts when I wired the controller, so I decided to use them to make the bed connections.  I designed and printed an ABS housing that is screwed to the support tee.  Another printed ABS part that fits tightly into the t-slot provides strain relief for the cable.  A Fusion360 file for this and other Wago mounts is here.

I used the Wago mount on the left to make connections to the bed heater and thermistor.  It has a tang that fits into the 8mm wide slot on the bed support tee.
I mounted the Wago bracket on the back side of the bed support tee, where the screw terminals had been.  That was a mistake.  It's hard to see it back there, hard to install and remove it.  I tried to move it to the front side where I could inspect it and release wires easily but, alas, I had cut the cables from the bed heater too short to reach the front side of the support tee.  I may turn the whole bed support assembly around so the electrical connections will be at the front side of the bed.  This is a mistake I won't repeat in my next printer...

Miscellaneous


I had to make a couple other small changes to accommodate the new configuration.  I printed new bottom-of-the-Z-axis bumpers to keep the bed assembly from going too far down (you can see one of them in the first photo at the top of this post).  Finally, I had to shorten some of the cables that run from the hot-end up to the extruder carriage cable.



Sunday, April 14, 2019

Floor Jack Pads: Pushing The Limits of 3D Printed Parts

My 12 year old Audi TT needs new shocks and I am preparing to do the work myself.  I've changed struts on two other cars, so I have most of the tools and a pretty good idea of what to expect.  Now I'm in the process of researching all the correct part numbers to order.

One tool that's been missing from my ever-growing collection is a floor jack.  I fixed that deficiency yesterday with a trip to Harbor Freight Tools where I bought a 3 ton, low profile, steel jack for $89.  I have no illusions about the quality, but it seems sturdily built (it weighs about 80 lbs) and should be fine for my infrequent uses like replacing the struts in my car and rotating the tires once in a while.

The jack did not come with any sort of pad on the saddle, and I don't want to try using it without one, so I did a little research.  Volkswagen Audi Group vehicles use a common lifting point "socket" that is best used with a jack pad that is made to fit.  I looked up commercial offerings and found some for about $8-10, made of polyurethane.  Polyurethane?  I can print that!

One of the jack pad makers was kind enough to provide dimensions:

Audi jack pad dimensions.

I modeled one of the pads in Fusion360 in about 30 seconds.  The commercial pad was only 69 mm in diameter but the saddle on my jack is 93 mm in diameter, so my model has a 90 mm diameter base.

My print used fluorescent green TPU- I won't have any trouble seeing it in the bottom of a drawer or toolbox.


UMMD has a 0.4 mm nozzle, so I used TPU filament in 0.24 mm layers, 0.5 mm line width, 6 perimeters, 8 top and bottom solid layers, and 40% triangular infill.  It used about 101g of filament and took about 5 hours to print at 40 mm/sec.  The print came out beautiful, and like all TPU prints, it's super tough.

Here's the jack with the naked saddle.  You need some sort of pad to protect the car!

Here's the jack with my custom 3D printed pad in the saddle.  The bump on top of the pad fits into the jacking receptacle on the car's frame.
Let's see if it's tough enough:


Well there you go!  TPU is one of the most amazing filaments you can get for a 3D printer!  It's easy to print (220C extruder, 45C bed, 30-40 mm/sec) and produces incredibly tough prints.

A view of the 40% triangular infill looking through the bottom of the Audi floor jack pad.

I used concentric infill for the bottom and top layers.  Other solid fill layers were set to rectilinear.  This nice Moire pattern appears in the bottom of the pad. The black smudge was acquired when I jacked up the car for the video.  Next time I'll take photos before I test a print under load.



Now I'll have to print a jack pad to fit my wife's car...

BMW jack pad dimensions.

BMW jack pad printing with 50% infill in fluorescent green TPU.


Done.



The Fusion360 models for Audi and BMW jack pads are here.