Matt Makes

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Gears and OpenSCAD

I spent part of yesterday playing with OpenSCAD and trying to make gears. I hit a few major issues in doing this, and one of them is that in reality, I know very little about gears and the vocabulary associated with them. I mean, what is a “circular pitch” or a “diametric pitch”? Why wouldn’t my gears mesh together nicely after I’d spent hours making them fit the design? After all this nonsense I thought I’d put together a little primer, just so if I’ve forgotten the next time I come around to this, I can refer back here.

The Anatomy of a Gear

Gear Diameters

Gear Diameters

There are 2 diameters (and hence 2 radii) that can be referred to in terms of gears. The internal diameter is the diameter of the circle that aligns with the base of the teeth. The external diameter is the diameter of the circle that hits the top of the teeth. With these there are also the relevant internal and external circles. Confusingly the outer circle is called the “addendum circle” and the inner circle is the “root circle”

Circles of Gears

Circles of Gears

Ok, now lets talk about pitch. It’s not that black sticky stuff you seal a roof with, but in this case it’s the point or plane which interacts with the next gear or rack. The pitch circle can be taken as being the addendum circle, if you had a 2d gear. In a 3d system you would have a pitch cylinder of the external diameter of the gear and depth of the thinnest gear. Still with me? Good.

The “circular pitch” of a gear is the circumference of the pitch circle divided by the number of teeth. There is also a diametric pitch, which is the diameter of the pitch circle divided by the number of teeth. For your gears to mesh properly, they have to have the same circular pitch or the same diametric pitch. By mesh, I mean that they won’t jump teeth or slip as the gears rotate.

With all of that, you’ve got the basis of the terminology to use the MCAD gears library. However, I found a better library was this public domain involute parametrized gear library. It’s a bit easier to use and produces nicer gear (IMHO).

Right! Thats your lot. Diagrams and all this time.

“Gold” Buddha

I’m always looking at new ways of finishing 3D prints and as I walked past a local charity shop recently I noticed a gold leaf coated picture frame. It was quite old and the leaf was rubbing off in places. but it started me wondering if you could apply gold leaf to a 3d print.

Yoda Buddha Print

Yoda Buddha Print

I started reading around and a few people had similar ideas, so the process of doing it started running around in my head. First we’d need a 3D model to work with. A browse of thingiverse brought me to this, specifically the Yoda Buddha model. Slice it and print it and we have a model to work with!

Unfortunately as the model was printing, the filament got tangled about half way up his belly (you can just see the line where it failed) and his ears didn’t print very well, but as they say in film and TV, we can fix that in post.

Before we fill and resculpt the flaws we need to go around and just have a quick sand of any loose fibres or droopy bits. Just take a file and work around slowly and methodically to remove these.

Sorting these flaws is a bit time consuming, but I tend to do it with car body filler. It’s a two part resin mix that has the consistency of a paste and is very easy to sand when it’s dry. I’ll cover the work surface with aluminium foil, and then make up a small foil tray to mix the filler in. Mix up the filler following the destructions and then apply carefully (but quickly) to the gaps. With the ears I applied a blob, let it set a little bit while I worked elsewhere, then came back with a sculpting tool and re-sculpted it back to the desired shape.

Let that dry overnight and then we have to deal with those accursed print lines. A touch of sanding in some places get’s rid of the nastier bits and then we can coat the model with XTC-3D. Now we get onto the interesting bit, applying the gold leaf to the model.

If I’m honest, I had no idea how to do do this, so I went onto YouTube and watched half a dozen videos on applying gold leaf. They all agreed that you should apply the glue, let it set for a while and then apply the gold leaf. Leave that to dry and then rub it all over with a soft cloth. The question I had was what glue do you use for gold leaf? It turns out there is something called “Gold Leaf Size” which is actually a glue. Silly name for an adhesive.

I ended up doing this in two passes. Some of the areas on the buddha are really hard to get too and I ended up wasting a lot of gold leaf. The end result? Well, see for yourself :)

 

Gold Yoda Buddha

TCT Show 2015

The big 3D printing show in the UK is the TCT show, which fell on September the 30th and October the 1st this year. Being on the look out for some new filaments to play with and for upgrade ideas for my Prusa, I thought it would be a good idea to go along. Conveniently another member of TVRRUG was heading to Birmingham to have a look around at the same time, so lift sharing always makes life easier!

Once we’d arrived at the NEC and registered we started by heading over to the RepRap Zone to find RepRapPro and have a chat about the Fisher Delta. David had been having a few bed leveling issues on his Fisher and wanted to pick the brains of the guys on their stand. It turns out that they have had some reports of the acrylic build plates being slightly bowed, and after an explanation of how the 4 point leveling works, explained some ways that they’re looking at mitigating it in the future. Quite an interesting technical chat on how the Duet firmware does leveling.

RepRapPro Fisher Deltas

RepRapPro Fisher Deltas

One really interesting thing we noticed wandering around the show was just how many stands had Fishers on them. They seem to be becoming an incredibly popular printer very quickly, which isn’t surprising with the price point they’re at.

Looking around the RepRap Zone I was made quite jealous of the giant kossel on display by Think3dPrint3d. It’s quite tempting to slowly build one of these over time. The aluminum extrusion and the stepper motors is probably the most expensive thing these days.

At this point we went and had a look at a few of the stereo-lithography printer manufacturers. Specifically looking at the different resins that are available on the market these days and the new printers that are popping up.

Stereo Lithography Printer

Stereo Lithography Printer

The all seem to be moving into the same general form factor now. An acrylic or something top, with a glass dish at the bottom to receive the resin, then the light source underneath. Some of the higher end machines had wipers, or the ability to do a wiping motion with the print between layers.

The resins seem to be moving quite quickly now that the machine are becoming more and more accessible to people. One resin that we saw produced flexible prints, which opened up a whole swath of possibilities that the resin printers had been missing before. Another resin worked with visible light, instead of UV, allowing the company to produce a printer using standard LCD type display. They where also talking of having a printer in R&D that was based on a 42″ TV as the display. The resin itself was only about £30 a litre as well. Starting to become on par with the cost of regular filament.

The next thing on the tour of filaments was a company showing off the various metal filled filaments they had on offer. These metal filled filaments produce a really lovely result once they been cleaned up, sanded and buffed out and it was interesting to see the proliferation of new PLA and something type filaments around the show.

 

Now onto what was the most exciting thing for me I think, the Strooder. I vaguely remember this being announced months and months ago and being very skeptical of it. They where at the show with a working production model and a few demo models showing it running, as well as an array of prints done on newly made and recycled filaments. Before I go any further, I should probably explain what the Strooder is. It’s a machine that takes either pellets or ground down prints in the back, and melts it down into new filament which is pumped out the front.

The Strooder

The Strooder

Will this little machine change the world? Probably not. However, a kilo of PLA pellets comes in at around £6.99 and to that you add just 1% by weight of colourant and you can have any colour filament you want. It also opens up the doors to mixing different types of plastics together to get different properties from what’s available on the consumer market.

The prints they had on display from recycled filament weren’t of an astounding quality, but they where good enough, and if you where just prototyping and cycling through something for a mechanical fit, the economics certainly make sense.

The machine comes in around £250 +VAT and they’re hoping to ship January/February 2016. Definitely one I’ll be keeping an eye on.

The rest of the show was more of the same really. I came away with a fair few samples of filament to play with on the Fisher and a few new sources for filament too. It was quite an interesting day out, and I can see myself going again next year!

RepRapPro Fisher Delta 3D Printer

Delta Mechanism

Delta Mechanism

RepRapPro recently announced a new, low cost delta type 3d printer they where bringing to market. The Fisher is a small, mostly acrylic and printed PLA delta printer that is designed to print in PLA. When preorders where available they where £199+VAT which was remarkably cheap. They’ve since gone up to £249+VAT.

Delta printers differ from regular 3d printers in that they have a print head that is suspended on a set of rods, which in turn are connected via ball joints to a carriage that just moves up and down. By moving each of the carriages up and down in different patterns the head is made to move inside the plane of the printer. A regular 3D printer has an X,Y and Z carriage which only moves in it’s own dimension. As with anything, each method has its pro’s and con’s, but I have to admit, the delta style is both more compact, and a little more impressive looking.

What you get in the box is a complete set of parts to make the Fisher. The acrylic parts are all laser cut, and the plastic components are all 3d printed. The printed parts are printed very well, needing very little, if any, fettling to make them dimensionally correct. Most of the fettling I had to do was just trimming off that last 0.5mm of brim on the outside of some holes, and tidying up a couple of strings. The instructions are still beta and you sometimes have to make a bit of a logical leap to interpret the text to the picture, but overall the build itself is quite simple. I’d like to cover a couple of places in the instructions that I struggled with though.

Starting out with the frame itself, the only place I messed up here was identifying which way around the bottom plate went. The instructions just give you a picture and tell you to ensure it’s in that orientation without many textual pointers. The thing that should be pointed out is that there are a pair of small (3mm) holes on one edge of the acrylic sheet and these should go on the side with the plate that has the electronics holes (not one of the logos). It’s a bit of a bugger to move stuff around at the end of the process if you miss this! I probably wasted half an hour or so correcting this little mistake. I would also leave the endstops until towards the end of the build. It’s a lot easier to understand where they go once you’ve got the frame together. Just make sure that there is one for every pillar.

Constructed Fisher Frame

The frame constructed

With the effector, make sure you read the instructions twice (at least!) before you put it together. The pictures on the docs aren’t amazing for this step.

For the hotend, the main thing to take in account is that when it says use a 2.5mm drill bit to ream out the PTFE tube, USE A 2.5mm BIT! 2.3mm isn’t big enough unfortunately. I wasted about 3 or 4 hours trying to understand why the hotend wasn’t extruding with this. Very, very aggravating! Goes to highlight the point of reading the instructions thoroughly though.

When you’re making up the arms to hang the effector assembly, I would leave the nylocks a little loose so you can get them over the balls easily. DON’T PUT TOO MUCH PRESSURE ON THE ACRYLIC WHEN YOU ATTACH THESE! I broke 2 sets of arms this way, luckily I was in a fully equipped/stocked Hackspace and had access to a laser cutter and acrylic to replace them! This is why Open Source hardware is awesome :)

Once you’ve got to the stage where you’re trying to home the machine, I would trim a bit of the loose bit of the belts off. I found that it occasionally interfered with the carriages reaching the ends.

So after putting it together, what’s it like to work with? Well, it can be run a lot quicker than my TVRRUG Round 2 machine. I’m very uncertain about the Bowden mechanism, but since this is my first one, I’m hoping that will pass. It certainly makes sense to keep the heavy extruder mechanism off the dangling head. The filament feed is a bit of a fiddle to get in with the top on. I might actually design a little thing that goes inside it that encourages the filament into the hole, rather than it being just a small hole in the middle of a bigger hole.

The software on the duet is quite comprehensive. I especially like the way it gives you information on the 3 different ways it estimates print time (by file progression, filament usage and layer time). The facility to write and upload new macros is quite useful as well, though the only one I’ve written so far was to raise the Z 0 point a touch as it was a bit low for my tastes. Uploading gcode files over the web interface is also very easy. Given time I think the main thing I’d improve here is to lay out the jog controls in the same way that pronterface does so it’s a bit more understandable from first view. The current layout works, but makes me think too much.

Complete First Print

Complete First Print

In terms of slicing, RepRapPro provide an ini file for Slic3r which seems to work really well. The print quality that comes out of it is good as you can see in the image. The BuildTak bed surface really works remarkably well! I’ve found the best way to remove objects from this is with a palette knife that’s had the edges ground down to wiggle under the print.

It’s quite a nice little printer, all in all. I think the only real changes I would make is to add a bottom acrylic plate to keep the electronics hidden and to change the filament inlet to be some kind of cone or equivalent to help guide the filament into the hole. Now we just need to see how it copes over a few months of heavy printing!

XTC-3D 3D Print Smoothing Resin

Recently after getting the 3D printing bug again, I’ve been looking at methods of smoothing PLA prints. With ABS you can use Acetone Vapour Smoothing to smooth out your prints, but with PLA the chemicals to do this are a lot more noxious.

Malcolm, over at the TVRRUG had recently purchased some XTC-3D to test, so it seemed an opportune moment to try it out. XTC-3D is a 2 part resin that you coat a printed object in. As it dries it pulls itself together smoothing out the layers in the 3D print, or so the blurb says!  To test this we took a few printed objects of varying qualities and applied the resin as per the instructions (2:1 of parts A:B). We mixed it up in a plastic container and then spread it over the prints using some foam brushes. It was then left to dry over night.

Before:

 

During:

After:

The resin has made a significant difference, especially on the cat model. On some of the train pieces it glooped into corners so might have been put on too thick. On the red piece it was put on too thin in some places, but a second coating might resolve this. The next experiment will be painting on top of these to see how they come out!

Quiet couple of weeks

A dead tree I quite fancy painting.

A dead tree I quite fancy painting.

I’ve been a bit lax in putting up any additional blog posts or videos recently, this is down to a few personal reasons. However, at the moment I am working on improving my RepRap and investigating methods of finishing prints to remove the layer lines as far as possible. I’m hoping to do a short video on that in the next week comparing sanding and using a commercial resin kit.

I’ve also got a comparison between cura and slic3r in the works. The difference between these has really amazed me, so I think it’s worth taking some time to review the two! I’ve also started documenting the temperature settings I’ve been using for various filaments in my RepRap 3D printer, which can be found here. More on the 3d printing front to come shortly.

I’ve also added painting a picture of this dead tree to my to do list. I don’t know why but it really appeals to me.

 

Kitchen Shelves

I’d been considering getting some shelves for my kitchen for a little while. My pile of onions, garlic and potatoes had been annoying me for some time and a way to tidy it up would be awesome. I look around at some commercially available shelves, but never really found anything that would fit the gap. I’d been looking for a little challenge to do some joinery and push myself a little with my woodworking, and thought this would be a good project.

I made a few mistakes along the way,mostly to do with cutting my rebates too thin and not centering the work pieces correctly on the radial arm saw, but the end result was quite pleasing.