Geared Peristaltic Quick-Fit Pump Extruder experiments

Even before my universal paste extruder, I have had it on my list to re-investigate the peristaltic pump at some point.

This was one of the last things I started for my 30 days of creation back in June #30DOC.

Many peristaltic pumps are already on Thingiverse, but none of them really jumped out at me, so I decided to design a geared version of the peristaltic pump for use on my Quick-fit X carriage.


My main aim for this project is to be able to pump and therefore extrude and print with cements, plasters, clays and super saturated sugar solutions, but small steps, first I need to get it working.

I was very aware that the tube is a really critical factor in any peristaltic pump, it can make or break a perfectly good design.

I had seen some designs that used quite inflexible plastic tubes and Motor's directly driving the pump mechanism, all leading to low performance and high torque requirements, that looked like a bad idea to me, so I decided from the outset to use Silicone tube and a herringbone gear set along with 4 bearings in an attempt to reduce pulsing of the pumped material to a very minimum.

My first prototype used a 6mm silicon tube with 4mm internal dimension, it was not as soft as I wanted, but was all that was available from my local aquarium shop.

The design went well but had one major flaw, it was almost impossible to assemble! I could not get the set of bearings in place while the tube was already inserted, and feeding in the tube afterwards was very tricky. 

Around this time I managed to get hold of some other silicone tubes from a model shop, these are normally used as fuel connections in RC models and aircraft.


The pink one was exactly what I was looking for, was soft, but with quite a think wall.

I revised the design dimensions to accommodate the new pink tube and split the top to make assembly possible - this has a lever on top so you can feed in the tube after the bearings are in place, then screw it together.

The second prototype assembled easily and to my surprise actually worked quite well.


It had one flaw, the lever wants to spring out, so the horizontal screw on the left hand side allows the tube to bulge out, it needs vertical pressure on the left hand side, the same as I did on the right.

Problem area for the V2 design.

In the video I'm holding the left hand side down, every now and again it pushes up releasing pressure on the tube, so the pump stops working. That's easily fixed in the next revision V3 below - 

Now you can assemble the pump easily and insert the tube when the gear and bearings are all fitted, then screw down the top clamp.

The tube is retained and fixed in place with this clamp, it uses a 4mm outer (2mm inner) PTFE tube as the nozzle.

Next steps are to attach a motor and work out the esteps then try to print something with some different materials!

I decided to release it now in the early development stages as I have a lot of things going on at the moment and may not be able to do much more on this until after the summer.

And as I type this, I'm exactly at this point with the development, so if you want to join me and maybe even beat me to getting it all working, head over to Thingiverse for the files to print one out and let me know how you get on!
And just to remind you it 's another thing designed to fit on my Quick-fit X-carriage.

Still lots of things yet to resolve with different materials and also if they are going to need to be under pressure to work at the viscosity you need to print out something?

Exciting? I think so, I have visions of a cement printer.... and maybe an unlimited supply of garden gnomes :)

Thanks for reading.

Rich.

P.S. - I also just started up a dedicated website for richrap.com - still early days but it'll grow over time, let me know what you would like to see on it! And I'm not going to stop blogging on here, just do more and more hopefully.

High power hot-end for fast printing - dual resistor & easier thermistor

This is the first of a few new hot-end designs I have been testing, I mounted it to my new ‘Bling’ machine for some speed and temperature testing, it’s performing well, here is how I made it - 

I decided to try a new shape for the heater block, normally you want a low profile block with a short hot-zone, but I specifically wanted to try a triangular shaped block for a number of reasons / goals - 

• I wanted to mount 2 x Resistor heating elements in the block so a wide base made this easy.
• I wanted to try a longer heating zone to see how fast I could extrude.
• Triangle gives smaller mass at the top, hopefully to reduce oozing due to the longer heating-zone.
• I wanted to be able to easily wrap the block in PTFE sheet, a triangle gives a easy to wrap shape and is insulated at the top with two thickness of PTFE.
• For the future I want to be able to extrude fast @ 300 degrees C with less than a 4 degrees C temperature drop while printing solid layers.

Next I REALLY wanted to switch away from using the tiny dipped thermistors the size of pixi-dust with ultra thin connecting wires, they are such a pain to use and don’t really have many plus points apart from the low thermal mass/quick response. I now only use a ‘normal’ Axial style. I can fully recommend doing this, it’s 1000 x easier to build and much less fragile, I also think I get much better temperature reading stability, response time is fine.

HONEYWELL S&C / FENWALL  135-104LAG-J01 Link Here - 

Thermistor Type:NTC; Resistance:100kohm; Thermistor Tolerance:± 10%; Beta Value (K):3974K; Operating Temperature Range:-60°C to +300°C;

You can buy them from Farnell -  only £0.25p

I have used 2 x 10ohm Vitreous enamel resistors in parallel; this gives approximately a 5ohm load where you would normally use a single 6.8ohm resistor.

The resistors are either side of the nozzle, giving nice constant heating.

The axial thermistor is slightly above the resistors and is just touching the side of the nozzle barrel, this placement gives me a quite constant 3 degrees C lower reading than the inside of the nozzle throughout the temperature range, which is fine.

Wrap the thermistor body and legs in Kapton to insulate.

Use Aluminum foil or tape around the Resistor body, it should be a good tight fit in the block. 

All in place and secured with Fire cement.

The part make-up looks like this. (Ignore the PTFE washers; I didn’t use these in the end).

I also wrapped the heating block in a strip of 0.5mm PTFE sheet.

Still using PEEK in this design, I expect to remove this part in the next version.

All wired up using high temperature heat-shrink and silicon coated wires.

And assembled.

I added a small heatsink, but I doubt this is really required.

The PEEK block is only luke-warm to the touch even after 4+ hours of printing – Note I am using a small 40mm directional fan aimed at the PTFE.

I will do some more tests to see if I can switch off this fan and still keep a cool cold-end.

My Fan-duct for Greg's Linear bearing X Carriage is on Thingiverse here.

It’s printed just over 2Kg of material so far at ~160mm/Sec and it’s performing well; I’m really happy with it. All of the multicoloured Faberdashery printing in my previous blog update was done with this setup along with some ABS parts and build sheets.

I have not yet found an upper speed limit as I need to do more testing, but it manages to print PLA at 180mm/sec with only a 2 degrees C drop in temperature when doing whole build-plates of full infill layers.

I will be testing ABS more extensively with it over the next week and seeing how fast I can get it working with different materials.

My main observation now is that you do need to run this style of hot-end at a minimum of 80mm/sec, and I need a 1.5mm extruder reverse to make sure oozing is not a problem. At speeds lower than 60mm/sec it’s better to use a smaller heating zone/block.

Next time I will still use a triangular block but make it slightly smaller overall and a little shorter.

Thanks for looking, I would be really interested in any comments or opinions on high-speed printing and hot-ends designed for speed and also high (290+ temperature) - you'll see why in a future post....

Rich.

DIY non stick hot end and temperature calibration

PLA is sticky, it seems to stick to almost everything including Aluminium blocks and hot-ends, in an attempt to limit mess on my extruders I'm using a PTFE cooking liner cut to size. 

This stuff is great, it's thin, very low cost (£1 / sheet) handles 260 Degrees C temperature and cuts easily.

You could use Silicon cooking sheet, but that tends to be thicker and rips, this stuff seems to work very well.

Cut out to wrap around the heater block.

Hold it all in place with a twist of copper wire (not Kapton tape as PLA and ABS sticks to that)

I'm using a Thermocouple down the inside of the heater barrel.

And even though my thermistor is perfectly calibrated it's location on the heater block reads higher than the actual temperature inside the heating barrel. To be expected, but something to remember especially using PLA.

To get a constant 195 Degrees C inside I need to run my heater block and thermistor control loop at 210 degrees C.

It's always worth trying to check and calibrate your set-up so you can know what temperature you are actually extruding at.

I will be connecting the Bowden cable and trying to print something later tonight, so hopefully I'll have some more updates tomorrow.

Rich

Hot-end for 1.75mm Filament (Push-fit Bowden)

My new push-fit 1.75mm Hot end is finished, it's based on similar designs like Adrian's new micro hot-end -

Here is how I made it -

I am a big fan of using off-the-shelf parts where possible in Reprapping, so using Pneumatic Push-fit connectors was an obvious choice for attaching the PTFE (bowden) tube to my extruder assembly.

The other standard part I always try to use is the metal rail mounts shown above. They work well as a clamp and  are low cost (£2 / $3) and easy to modify.

This 8mm mount above is manually tapped so I can screw in the Push-fit (1/8")

I'm using a simple Aluminium R/A piece to mount to my Repstrap, you could use something different to mount to Mendel, Prusa or Rapman machines.

10mm PEEK rod and block, 1.75mm Hot-end with 0.35mm Nozzle.

Turn down both ends of the PEEK rod (one 7.2mm and the other 8mm).

Then with a 4mm drill bore the barrel - the PEEK will expand and shrink so the hole will be undersized, but that's good.

Cut a length of 4mm (outer) PTFE tube.

Then you need to push the PTFE tube into the PEEK barrel, this is hard so taper the tube end with a pencil sharpener and force it in, you may need some PTFE spray to help this process.

Cut down the tube but make sure to allow both ends of the tube to compress slightly, one in the push-fit end and the other in the hot-end, you can tighten down the push-fit after it's all at temperature as the PTFE tube will elongate with temperature, you don't want any leaks.

Drill your PEEK block so it has the same spacing as the rail mount.

Drill your chosen mounting bracket.

Assemble with 55mm M4 bolts, washers and nuts, you can use a Nyloc nut at the top, it should not get hot enough to melt them.

You will need to tighten everything after it gets up to temperature for the first time, the PEEK will bend.

The other end of the PTFE tube is connected via a push-fit on the Extruder, so the 1.75mm filament can be driven down the tube to the hot-end.

I hope to have some examples of it running soon, I now have the last remaining Pololu stepper drivers, so I can start to wire-up the ScrewBall strap and get back to 3D printing (another 3D printer) !

Rich.