Sunday, July 22, 2012

Turk's Head print...

The Turk's Head print came out so nicely I thought I'd give it a little space of it's own. It might even make a novel Scout woggle, but you might want to use the version without a base and take on the challenge of a supported print!

I printed it in PLA at .3mm layer height with a .45mm width and 20% infill. It was set to a perimeter speed of 30mm/sec and left to chug away while I walked the dog.

What I have observed when printing in black PLA is that the final finish can change from gloss to matt depending on whether you have a cooling fan on it or not, but also depending on the print temperature. This item has more of a matt finish. I dropped the print temperature down from 185Deg C to 183Deg C as I observed the initial few layers looking a bit 'soft' and shiny. On my current config there is a bit of downward air flow from the x-carriage mounted fan and this seems to serve well as a work cooling fan as the print head moves about.

While the print resolution could be considered quite coarse by current standards, there is forgiveness of the surface finish as you eye seems to be tricked into thinking it is a woven cord or rope type material. It's a nice object to print. I'll probably reprint it once I get some white PLA. Would probably look better in white.

Y-carriage changes...

I've recently changed the number of linear bearings (LM8UUs) under my y-carriage, reducing the count from four to three. While my y-carriage was running smoothly enough I could detect slight binding on either end of the travel and I couldn't get rid of it no matter how much tweaking I did to the positions of the four bearing mounts. My suspicion was down to slight irregularities or even minor bows in the rods. I'm sure precision ground rods would be a better solution, but I figured moving to a tripod bearing arrangement was worth a go.



I drilled new mounting holes in the middle of the left side and moved one bearing bracket to the middle-left position. I kept two bearings to the side closest to the belt to minimise any turning motion the belt might introduce with less alignment constraint on one side. The base plate looks like a piece of Swiss Cheese at this stage with various experimental reworks, but you should be able to make out the new bearing mount positions in the photo above. A smaller change I've also made is the reversal of the y-belt at the idler end (far side), to give a smoother belt surface contact with the far idler bearing(s).

With the most firm supports for the heated bed and top plate now in a triangular shape I felt the next step was to reduce the spring loaded adjustable supports to three also. I've always felt that levelling the print bed would be a lot easier with three points of adjustment rather than four, and this was an ideal opportunity to explore that design. You can see a new hole in the centre left edge of base plate to take the spring loaded levelling bolt.

Manual movement of the y-carriage was much smoother through the entire travel length, a full 200mm distance. My only final compromise was to not completely tighten the bolts on the left bearing bracket, allowing it some minor horizontal play. I think it may be best to replace that 'smooth' rod eventually as it seems to have some imperfections.

Levelling the print bed:
Levelling the bed was a dawdle! Now with only three adjustment points it took no time at all to get it level. I started on the right hand side where there are two adjustment screws, positioned the print head to the right and manually moved the y-carriage back and forth adjusting the right screws until the bed was level. I then moved the print head manually left and right, adjusting the left bed adjuster until the bed was completely level. I did this first pass levelling visually with the print head about 5mm from the bed. I lowered the print head and repeated the process to fine-tune the levelling.

Print bed levelling was made even easier with these 'trapped nut' thumb wheels, visible in photo above.


Conclusion: In the case of y-carriage bearings and print bed levelling, three points of contact is as good if not better than four. The only proviso is that you have a sufficiently ridgid print bed plate, so that it doesn't droop in the unsupported corners.


The movement of the y-axis feels, and even sounds smoother with only three bearings. It may be a better compromise solutions if you are using rolled stainless smooth rods as against precision ground rods.


My current config:
To show the new y-carriage in action, and to give a general overview of my current configuration here's a short video clip. It's printing the Turks Head from Thingiverse.

It's still a Mendel Prusa layout, with my wooden Vertexes(?) and z-motor mounts remaining on from my original fully wooden construction. I've a mix-up of x-ends but plan to upgrade those shortly. I've a Greg's Wade Reloaded extruder and a j-head IV 3mm hot-end with a .5mm nozzle. I've a 'four resistor' heated bed which is thermistor controlled but the temperature manually set via a pot.

Thanks for viewing. Now I'm back to printing! :)



Tuesday, July 17, 2012

60mm fan holder for Gen6 cooling...

Quick Post: It's good to keep the electronics cool. I salvaged a lovely quiet 60mm fan recently so I printed off a holder from thingiverse for it (http://www.thingiverse.com/thing:13469). I modified the base plate of the holder so it clipped on to the printers threaded rods. See photos...
There was a bit of stray airflow on to my printed bed, so I slotted a clear plastic lid behind the board to stop unmanaged airflow to the bed. I'll also need to fit a fan-guard to the fan. I'm happy to leave it as an open sided arrangement for now.
Here's a view of the reverse side. I simply took the base plate from thingiverse into Sketchup, added a tab at  the top, rounded the corners and repositioned the push-on rod mountings.

Cooool! :-)

Sunday, July 15, 2012

More extruder talk...

There's such a variety of RepRap part designs out there that you really have to match them up carefully if you plan to upgrade any individual aspect of your printer. You can 'pick 'n' mix' but as I've learned you should think it through and double check everything before starting in to an upgrade. Here are some examples of the minor issues I bumped into when I bought a new extruder hot-end, the J-Head IV-B.
The j-head has a 16mm diameter insulator (the black PEEK cylinder). You have to find some way to mount the insulator to the extruder body. There are many options. There are various mounting plates available to fit the notch, and then bolt the plate under the extruder, but the top of the insulator must still insert into the extruder. My existing extruder only had a 12mm hole in it's base, so I had to print a new extruder. I had a look around and decided I'd try this extruder (Jonas Kuehling's version of Greg's Wade extruder). Jonas has a variant with a 16mm hole in the base, and holes to bolt across the insulator notch.

By the way, RichRap also supports the lower end of the j-head with a modified bracket. You can review that here: http://richrap.blogspot.ie/2012/03/mendelmax-quick-fit-x-and-quick-fit.html (scroll way down in his post to the Extruder section.)

So I had to print a new extruder. To save effort (so I thought!) I'd transfer the hobbed bolt and recently printed herringbone gears from the extruder I was removing, but I soon found more complications. The combination of Triffid_Hunter's Herringbone Gears, my hobbed bolt and Jonas' extruder just wouldn't line up. The hobbed notch wouldn't align with the filament guide hole and there was not enough travel for the motor to close the small gear fully against the large gear! I should have just reassembled the old extruder at that point and printed Jonas' gear set that did match, but no, nothing like a challenge! :) A second printer would be handy!

I reversed the hobbed bold and put the nut and a lock-nut on the large gear side allowing adjustment and perfect alignment of the hobbed bolt to the filament. I fitted a spring on the other side to keep some tension on the bolt. Between the filament in the notch and the meshing herringbone gears there is actually little incentive for the hobbed bolt to drift horizontally anyway. Here's a photo or two of the current hobbed bolt arrangement! It's been running like this for a few weeks without issue.

Securing the hot-end insulator: The insulator pushes into the extruder base and a common way of securing it seems to be with two M3 bolts through the holes in the extruder and across the notch in the insulator. You may have to pre-drill, glancing the insulator notch to get those bolts to fit. I'm not familiar with the mechanical properties of PEEK. It feels extremely hard and tough. I figured a 3mm drill meeting it at an acute angle would just bend away into the plastic so I took an alternative approach to securing it. I made a simple pin from coat-hanger wire, rounded the tops with a small file and pushed it in with a small clamp (photo below).


It's a tight fit and hold the insulter amazing well. There's no movement in the hot-end. I'm printing for weeks with this securing method and the hot-end/insulator remains securely attached.

I added a little bit of PVC tube to the pin to gently secure the wires rising from the hot-end. The pin can be removed with a wire hook and a firm pull.

Oh... the poorly meshing gears due to mismatch of gears and extruder... I elongated the motor mounting slots with a round needle file and motor now travels close enough for the gears to mesh perfectly. Not idle, but it works!

BTW - here's a photo of all the components that went in to the new extruder.


General comment on extruders: Once you have your printer running smoothly, there is little enough call for the quick-release mechanism on the idler-bearing, and indeed if you've clogged up the hobbed bolt badly the best way to clean it is to remove the bolt. Also, some have felt the need, including me, that a top filament guide is necessary in the design, leading to the return of a top guide.
This brings me to the argument that Nophead presents for the Wade's style extruder. If you use a spring in conjunction with a regular nut on the hobbed bolt then the nut won't loosen, but can easily be removed if you need to inspect or clear the hobbing. Also, if you have got your idler spring tension just right, the last thing you want to be doing is backing the bolts off to remove the idler. If you aren't removing the idler, then four securing bolts makes little odds over two bolts and a hinge, and in some ways makes for a more evenly pressured idler.


I printed it out (photo above) and will fit it out and try it at some point. (I've thickened the base so I can fit a larger gear and have it clear the x-carriage. An interesting side-effect of thickening the base is it gives even more robust support to the 16mm diam insulator, but I would caution that you need significant active cooling on the hot-end insulator if you are going to mount it directly in to a PLA extruder. Another clever touch to Nophead's variant is a circular recess at the inner most end of the 16mm hole. This allows the insulator to seat perfectly into the extruder base without any clean-up of the hole. (You'd have to be there to appreciate that detail fully! :) )

Since I'm on 'extruders' I'd also like to highlight this set of RepRap design reworks by the guys at EckerTech, which includes an interesting take on the extruder. Their extruder design features, hinged idler with no hinge bolt, a single compression bolt on the idler with no spring (good argument for using a washer presented), and a motor that rotates about one mounting point to adjust rather than sliding! Nice work, and they mention in their forum that they plan to publish their designs once they are finished tidying them up. Nice work.

As always, thanks for viewing. Comments and questions welcome!
Regards,
NumberSix







Sunday, July 8, 2012

PVA coated print bed experiment

There was a recent suggestion on the forum from Enlightx that a coating of diluted PVA (50:50), painted on to the print bed would aid adhesion of the printed object, preventing warping or even breakaway. The suggestion was echoed and tried by Rich on his blog. I gave it a go, diluting to a ratio of 1:8. At this point I've been using it for over a week, printing each evening. Here's some feedback on the experiment.


It brushes on easily and dries to a foggy finish. I left it overnight, then put it back on the printer. You could probably paint it directly while on your printer and dry it with your heated bed.

I printed my first few pieces to this newly coated surface with what I now think was too low a layer height, causing it to bond too well to the surface. As the week went on I got more brave and raised the first layer height until it was just a light touch to the surface. Here's a short video that shows how well the printed piece adheres to the newly coated surface.  Even when cold I had to apply some significant force to remove the piece.

You can see the fogged mirror surface in this photo below, and an object that printed without budging. I printed many objects for the week, large and small, and there was no warping what so ever.

The underside shows no ill effects from the PVA (photo below). The first layer infill seems to loop slightly short of the perimeter in the photo. It looks fine in solid layers further up the print. I may have set the first layer too high in this case, preventing the first layer squeezing out to the perimeter.


Conclusion: The dilute PVA coating has a positive effect on print bonding to the print bed. I'd recommend starting with a more dilute solution, perhaps 1:20, and add more coats if that doesn't improve bonding.

If you have been in the habit of running a very low first layer then you can certainly back that off. Too low a first layer will result in the piece being very difficult to remove from the print bed (as in my short video).

Be careful when tugging pieces from the glass as the glass could crack rather than the piece give way.

The shadow of previously printed pieces remains in the PVA coating. It will be interesting to see if this impacts on the finish surface of subsequent prints.

Finally, it will be interesting to see if the adhesion benefit will diminish significantly over time. If it does then it seems that a fresh coat of dilute PVA would be cheap and easy to re-apply.

Thanks for viewing!
NumberSix

Monday, July 2, 2012

The Hot-end...

The majority of extruder hot-ends on the market at the moment come as kits of varying degrees. There's a certain amount of assembly you have to do yourself, but this is changing rapidly, and not too soon I think.

(J-Head IV-b shown above.)

It comes with a resistor and thermistor but they are not fitted. Fitting them is 'fun' the first few times, but after a while becomes a bit tedious. I can see the expanding market moving to some level of pre-assembly, as I can see the broader user population more willing to pay a premium for pre-assembled units and less interested in this doing this it themselves. Even for the enthusiast the process of gathering the heat resistant wiring and appropriate connectors is a bit of a chore and added cost. Another reason I'd favour pre assembly is the 'quality assurance' and consistency that would come from pre-assembled hot-end, which might include some level of thermal bedding-in and testing of the resistor/thermistor. These steps would certainly be worth the little extra, as well as the time saved.

[ J-Head heater block and integrated nozzle shown in picture. The advantage of this design is it's an all-in-one unit and can't leak. You have no worries about tightening on nozzles or loose fitting heater blocks needing lock nuts. the disadvantage is you can't just easily swap out the nozzle to change to a different orifice size. ]

There are many instructional sequences showing the assembly of the hot-end but I thought the process and sequence I've adopted might be worth sharing. I always like to insulate the heater block and have some photos showing that process also below.

Tip: I remove the pin from a small pop-rivet, snip it's head off, and use it as a joiner. I don't solder this joint as solder may melt. I use a PTFE lined, braided wire sleeve on the resistor. I salvaged the wire from an old iron. It's designed for high temperatures!

The resistor that comes with the J-head is 5.6 ohms. With a 12v supply, I've found this gives a very nice heating time and seems well able to keep the block hot in comparison to the 6.8 ohm resistor, also popular in the market. The 5.6 ohm resistor also has a more cylindrical shape and is a snug fit to the brass block. The other resistors (6.8 ohm, Green in colour) I've bough were slightly lozenge in shape and not a good fit. 

This photos shows wires attached either side of the resistor. The choice of colours has no significance.

The tiny little 100k glass thermistor needs it's wires kept apart. I've tried the ptfe sleeve idea on one of the wires, but I've found this bulky. The extension wires are soldered and the joints head-shrinked. Be sure to scrape the wires bare first. They are slightly coated.

What I've found as a better way to keep the thermistor wires apart is to sandwich them between some high-temperature tape (above photo).

The thermistor is inserted into the hole in the brass block and the wires wrapped around the corner of the block, curved around more so than bent at a sharp angle. The tape holds it somewhat, but the addition of the other insulation jacket will hold it in place very well. I don't bother with any fire cement or silicone. It's a personal preference. Also note all joints are heat-shrink wrapped at this stage. The resistor gets removed one last time to fit the insulation jacket.

I use a very light sheet of ptfe to warp the brass heater-block. The material is rated to 280Deg C, and is commonly used as baking tray or oven liner. Wrapping the heater block in this material is more an art form than a science. You may be able to make out the folds and cuts I make in the sheet from the photos.

Once I'm happy that everything is fitting nicely I tape everything down with kapton tape.

And there it is, snug as a bug!

This jacket keeps the heat in allowing faster heat times, and means less work for the resistor to maintain a given temperature. It also protects the heat-block from the negative effects of stray fan air currents. Finally it reduces radiating heat from the heat-block to the newly printed job below it.

One final step is to cut out the holes for the resistor after the jacket is fitted. Mind your fingers!

With the hole cut out, I used a bar through the hole, and small wrench on the insulator notch to tighten home the head into the insulator. It's hard to describe how tight this should be. It's a 'good hand tight'. It came pre-assembled, so I actually marked the joint with a dab of Tippex before taking it apart. I reassembled until the two white marks realigned!

I've more extruder related photos to post but out of time for now. Thanks for viewing!
NumberSix

Sunday, July 1, 2012

New extruder assembly...

One thing lead to another recently, and before I knew it I was half way to building a new extruder! I had been printing very consistently with an experimental hot-end hitched to a Greg's Hinged drive, but that was a .35mm nozzle and printing was slooooow! The max layer height being the limiting factor. Quality was excellent though as was evident in the Herringbone Gear Set print.

I bought a new hot-end, the J-Head IV-B (4b), printed a new extruder 'cold-end', the Greg's Wade Reloaded version.
(photo of reverse view. You decide which is the back/front!)

There's lots more to be said; detail on why I chose what I did and detail on the assembly process. I'm a fan of insulating the heater block as the keen observers will spot. I've a lot more photos and descriptions to post, but for now I just wanted to get the blogging back under way!

Thanks for viewing!
NumberSix