The KTM Conundrum
Why is PETG so Hard?
Turns out it isn’t really, except for me.
The Design in pristine 3D Land
Recently, S, a colleague and friend, asked me to help him with a little problem.
His Austrian beast (KTM 450) has an annoying habit of pitching him off its back and in the process bruising its clutch cover. Some shielding is obviously required but what exactly?
Whilst pondering this, during what must have been a post lockdown alcohol binge, S asks me: “You have a 3D Printer, Right? Could you help me with a little project?”. To this, with all due arrogance and bluster, I reply: “Yes, I do. I can make anything you need”. As you can now imagine, this is where the problems started.
It started off well enough, S arrives one Saturday afternoon with his beast beating the earth, and the eardrums, into submission. Since this well engineered monster is made in Austria (Austrian engineering is like German Engineering, just better), there couldn’t possibly be anything wrong with it, could there? Well, the massive impact crater, suggests otherwise.
It turns out that when the earth no longer feels like being beaten into submission, and beats back, the brake pedal smashes into the clutch cover in a manner approximating a minor car crash. As such, the pedal leaves the earlier mentioned impact crater.
Since ablative armor and kinetic shields are some 300 years away, a simpler solution is needed.
This simpler solution, we decided, would take the form of a clutch cover protector made from PETG (Polyethylene Teraphthalate - Glycol, try and say that 5 times fast). PETG has great thermal properties and, by all accounts, prints rather well on a 3D printer. The moral of the story, don’t trust the internet. Trust YouTube instead, at least you can see the crazy for yourself.
Anyway, I digress.
Since we are “Engineers”, the Vernier (Supersized, for extra accuracy, YESSS!!!!!) immediately makes an appearance and all relevant measurements are made by, sort of, measuring and making “Engineered” guesses.
The “Engineered” guesses are duly translated into CAD using Fusion 360, producing the model you see at the beginning of this post, resplendent in the 3D World of White and Grey. Since this is way too depressing, especially after a good few months of Lockdown and the world falling down around us, I decided to break out the “Good” Plastic for the prototype.
S was kicked out the door, with a promise of prototype the following morning, the trusty FlashForge Adventurer 3 Loaded up with AMS MambaWire Baidu Blue Satin PLA was given a fresh new model to munch on and off I go to bed.
Next morning, the prototype, seen here, was waiting waiting patiently, looking all pretty in blue.
After a stiff coffee, S is informed of the masterpiece awaiting his inspection and I move onto other things. A few hours later, an aural assault accompanies S’s arrival on the scene.
The prototype is strapped to the Austrian Beast and a few things become immediately apparent:
The Austrians are challenging the Germans in the Great Clearance War (a BD would struggle to get in there),
The Austrians can’t seem to use uniform spacing on anything,
The Austrians haven’t worked out how to defy the laws of Physics yet, despite all reports to the contrary.
Heat, clearance and bolt spacings are all a problem requiring “innovative” solutions.
Meet back later to see how this all turns out…………
----- A Few Days Later -----
Now that I had recovered from my initial shock at the Austrian Engineers having the same issues as every other engineer on Planet earth, and probably a few other planets as well, it was time to figure out what to do about these issues.
Firstly, and only Firstly because it is the easiest, is the heat issue. Since we don't have the equipment to measure the exact temperature of the area around the clutch cover we have to make one of those annoying “Engineering” guesses again. Only this time it is more like an Educated guess. Since you can actually ride the bike and not spontaneously combust, suggests the temperatures, in the area, stay below 100°C. Therefore, our initial guess of using PETG (Bottle plastic according to M) will work, PLA not so much.
This means RCWD PETG (Rental Car White Depression PETG) and not awe inspiring Baidu blue. I could feel the weight of collective disappointment resting on my shoulders, then I stood up and he fell over. So all problems solved, right? Wrong, the Revenge of the Si…., apologies, Austrian “Engineers” was close at hand.
One of those earlier “Engineering" Guesses was, when 6 mounting bolts are used and they are in what appears to be a hexagonal arrangement then the centre spacing will be the same. Well, someone never told the Austrians this. KTM seems to like 5 bolts to be evenly spaced and then 6th to be offset by 5.72°. Extra credit for precision, not 5.7 or 5.75, exactly 5.72°.
The solution involved nearly 4 hours of SFS (Swearing, Fiddling and Swearing some more) until I discovered the ability to switch off one of the features to be generated in the circular pattern tool used to generate all the holes. This enabled the 6th hole to be redrawn and placed in exactly the right position to satisfy the Engineering Gods. All was right with the world as all issues had been solved.
Nothing snaps you out of Clarkson-esk smug face like an overlooked booby trap left by the Sit……, sorry, Austrian “Engineers”.
Turns out, the clutch cover develops a severe incontinence problem when not bolted down tight enough to make diamond from pencils.
Therefore, the initial plan of using the protector to clamp the bottom 3 points of the cover wasn't going to work. A stand off, of some description, would be required.
Unfortunately, due to the Austrians treating clearances like an extreme sport, there was literally no space available for a standoff. So what to do?
The answer arrived, like The Flash in Batman vs Superman, very conveniently. Longer bolts, with a nut about halfway, would be threaded through the protector and then the nut would become the Diamond manufacturer and the protector would semi float on the shank of the bolt. Clearance issue solved, or so I thought.
It was at this point, the not so common, common sense showed up. This annoying fact of life pointed out that you need space for the nut and the spanner to tighten it. So out came the miniature chain saw, in the form of the Fusion 360 extrusion tool, and 5mm was hacked off the bottom of the mounting tabs to provide said space.
What was left is what is seen at the start of this post, including the requisite Logo, for completeness/Vanity.
Now comes the easy bit right?
Well, in a word, NO!!!!!!!
It seems I offended the 3D printing gods in the effort to appease the engineering gods.
The resultant part has no obvious printing orientation. Overhangs and cantilever abound and the only way to deal with this is supports. Indeed I used these on the prototype so I am not sure why the printing gods took offense, but oh boy were they upset.
9 failed prints (this is a 14+hr print BTW), 3 nozzle cleanings, 2 extruder disassembles and a bed releveling (because the gods are particularly vindictive) later, PETG flows properly.
Now we get to see if we can get this right.
SuperPrinting Sunday it is.
------ Breaking News ------
So SuperPrinting Sunday went quite well, I guess.
The Protector print finally finished, which is good, in sort of the same way the Imperial Japanese Navy thought the outcome of the Battle of the Coral sea was “Good". Unfortunately, my “Battle of Midway" is about to begin.
The problem I am facing is terrible print quality, under-extrusion and welded supports.
The welded supports are understandable. I was forced to kill off retraction completely. Any sort of retraction caused a nozzle blockage.
I suspect the issue lies with the Teflon liner of the Hotend. The adventurer, for all its good points, doesn't run an all metal hot end. This means a Teflon tube backs up the nozzle. Since Teflon is an excellent insulator and not directly heated, as soon as you retract filament, the molten end is pulled into the tube. It is at this point where it solidifies and conforms to the tube’s dimensions. The Bowden extruder simply doesn't have the power, or control, to reliably dislodge this and a semi-blockage occurs.
Dropping the retraction to 0mm helps with this but results in under extrusion overall as travel movement related stringing robs the nozzle of primed plastic, which the extruder never refills properly.
An all metal hotend may go some way to resolving this issue, except, one doesn't exist for the Adventurer 3.
Unlike the IJN, I think I might need to admit defeat after my “Battle of Midway”.
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