How Fast Can We Spin A Titanium Skateboard Wheel? 

What would you guys suggest on how to get our RPMs higher? Our next three strategies are to try lighter materials (magnesium or carbon fiber), hollowed out wheels, and finally smaller diameter wheels. At this point those seem to be our only bottle necks, anything we’re over looking?

If you're asking if it would produce a sonic boom, that's a no. A spinning object doesn't produce the kind of compression force needed for a boom. A sonic boom is produced when air is compressed at a faster rate than it can expand itself. The wheel would have to be moving, not spinning. Since the wheel is a uniform shape, there's nowhere along the wheel for air to accumulate and compress. As far as producing a different pitch or tone, though... That's beyond me. I'm not familiar with that part of physics

Try making a magnesium wheel but press fit a titanium sleeve around the outer diameter to give it more strength. Should hit crazy high RPMs as magnesium is significantly lighter than even aluminum.

Take it from a guy who mass machines titanium on the regular, whatever speed you think you should be running at, halve it. Most machinists who are unfamiliar with the material go way too fast and destory any cutting edge you once had. Bi-metal band saw blades will cut it but have to be sharp and run slow, 300 series stainless slow. Cutting it on the lathe, use carbide and go a hair slower than stainless steel speeds.

Jet engine engineer here. First, fun to see the resin wheel break into thirds, that's exactly how a disk would be expected to "burst" as it's called at my company. You can see the damage that little thing did to your machine. Imagine what would happen if a 200lb chunk of nickel broke up like that. Second, do NOT hollow out the inside. Material closest to the rotation axis is actually what is doing all the work to hold the disk together. It's also the most efficient material in terms of added strength/weight. Third, while I don't know the dimensions of your wheel, the outer diameter might already be breaking the sound barrier. A 60mm wheel would have to spin to 109k RPM for the outer edge to reach the sound barrier. As others have stated, due to the smooth outer surface, there really isn't anything to generate a shockwave and make an audible sound. This is outside my lane, but I question your speed estimation methodology. How do you know the frequency you are picking up is the once-per-rev tone and not something like the passing frequency of the bearing balls

This is the type of unhinged video that got me hooked on youtube back in its early days.

I'm an engineer. The limiting factor on wheel RPM is parasitic drag from air resistance and bearing friction; not the weight of the material. If you had low enough friction, the outer surface would achieve the same velocity as the jet. The best way to achieve lower air drag is to polish the surface of the wheel, and place the whole contraption in a somewhat airtight cylindrical container, so a rotating mass of air can form around it, instead of accelerating the stationary air in the room. But by far the biggest improvement could be had by removing the grease from the bearing. After all you only need it to work once.

Should have just drawn a white line on the wheel

First, use a silver or white line for contrast to get the Tachometer to work. Also, the titanium wheel would most likely have a different resonant frequency especially since you changed the bearings. Bearings are usually the noise maker anyway and since you upgraded them the frequencies almost certainly wouldn’t correspond to the same RPMS. You very likely exceeded the RPMs of the aluminum wheel with this experiment. Keep it up, i love this stuff, it’s why i like engineering!

The trick to ti on the band saw... 1 flood coolant, 2 brand new Lennox blade! 3 turn the band speed as low as it goes, I don't care if the Internet gave you a different speed. If it's a variable speed, turn the adjuster till the band stops moving then turn it up till it barely works. If it's a multi speed, put a vfd controller on the motor to slow it down. I've been able to turn induction motors down to 15 hz which is 1/4 speed. It might even go down to 10hz. As for the lathe, If it's a fairly heavy lathe you can take pretty heavy cuts. If you have lots of cooling like a CNC you may even be able to go a reasonable RPM. Ti likes CNC lathes. Continuous cuts are good. Thick chips are good. Prefer a feed/rev relationship over higher rpm. Thin chips are bad, high rpm is generally bad unless you have the cooling capacity. For a manual lathe use power feed and if you want to be safe use a very low rpm. Always use new sharp tools. For a milling machine, well if it's CNC use climbing cuts and a fixed feed rate, no slowing down for corners. Use healthy oversteps. A thin chips will harden the work and break the cutter faster than an abrupt 90 corner with a heavier volumetric load will. If you are manually milling, you may be able to face it. But good luck profiling it. It hates conventional cuts and heat. But climbing cuts heavy enough to punch through the work hardened surface will likely draw the work into the cutter. You can try locking the gibs and letting the leadscrew pull through the friction. But a CNC with ball nuts is just a more reliable way to work with it.

0:10 I laughed way too hard and I have no idea why lmao

Bearing will affect the sound/harmonics. Can’t use the previous frequency. Next time don’t anodize it so there is more contrast for the meter!!

This whole channel feels like a post-apocalyptic Waterjet Channel where a lone survivor stumbles upon the location and partial ruins of the Waterjet Channel and started making videos to keep from going insane.

This is the first video of yours that I've watched and while waterjet videos don't exactly peak my interest the comedy/editing will keep me watching haha, keep it up

11:00 you know it’s crazy when your water starts sparking

The peak frequency of the fundamental tone on the Titanium sample reached a maximum of 953Hz (on my spectrogram). That equates to 57,180 RPM. I'd throw out your tachometer, and ignore any previous readings. Working out new speeds based upon the previous rpm measured with it will be giving falsely high results for everything. They can pick up false signals (harmonics) and give you twice the speed or more. Here's my measurements: *Resin + Titanium Shavings:* 429 Hz * 60 = 25,740 RPM *Copper:* 332 Hz * 60 = 19,920 RPM *Titanium:* 953 Hz * 60 = 57,180 RPM

Since the titanium isn't gonna get gouged out as much, to maximize the speed you are gonna want to have it hit the wheel further out so the water stream is hitting at an angle closer to tangent of the surface of the wheel.

You could possibly increase the max speed at the outer diameter by creating a tophat shaped wheel. Point the waterjet at the smaller diameter section and the larger half may move faster than the water from the jet just like higher gearing in a car. It will however be harder to spin.

1:51 "I turned my camera too late but this is just what happened: uyumymiprr khhh"

I like your sense of humor. Makes me feel at home.

Here's an idea to get the tachometer to read. You guys electrocuted it so it turned blue, well dip half of it In the solution so it becomes a different colour than the other half. I don't know how the tachometer exactly works, but it's how I think it does, it should be able to give a reading. And it won't rub off like the sharpie did.(I have no idea if it will actually work but it's an idea)

Legend has it the wheel spins faster than Sonic

Where did the original guys go?

"Uhhhhh, I know! I'll just leave it on the ground!" Sent me to space, MY SIDES

I'm glad you guys decided to take the frequency of the sound.... Over just drawing a white line on the wheel, or a "tracking dot " from a 3D scanner. But you know it worked

my guess would be the tachometer functions on contrast to generate a differential pulse wave, then just spits out pulses per second to pulses per minute to get RPM, the blue anodization may have hindered the contrast (red laser), so maybe try a white spray paint and the sharpie black line, a wider black line may be beneficial because at higher RPM the contrast would produce a fainter pulse signal for a thin one with respect to the sensors sample rate.

Im sure the harmonics would be completely different between the materials and bearings used. The pitch used between them for estimates can't be reliable

If you're gonna keep bumping up the RPMs, you'll need a better measuring method. Get a very small disc magnet, drill a hole in the side of your wheel (not the circumference, it'll get thrown off, just the side, as close to the bearing as you can to avoid imbalance), JB weld it in, balance it, and then use a read head pulled out of an old tape deck, hooked to an oscilliscope, to measure the speed of the wheel. An optical tachometer just isn't gonna keep up at these speeds, although you may have better results spray painting it black, and then adding a retro-reflective white strip.

"oh I know! I'll just put it on the ground." I spat me drink at that gold right there

RIP Dr Pepper who made the ultimate sacrifice for this video

It's not a waterjet channel video without a taste test. Good job.

Haven't seen Strongbad in a hot minute

FYI, when you're cutting titanium, prevent the shavings from catching fire. The fumes can be quite dangerous to inhale and can burn extremely bright.

3:10 the forbidden flashlight

Make sure it's perfectly balanced, I could tell just from the hand spin it was off balance since it ended up swinging back and forth around the heavy side. The imbalance is going to cause the bearings to wear unevenly and cause more friction. Use a hobby propeller balancer to get it as close as possible to perfect. I would also suggest rounding off the corners and trying to shoot for a flattened sphere shape to avoid air turbulence. Good luck!

Try using a fan to clear the water mist Also, thread a reflective bolt into the side so you can get an accurate tachometer reading.

you could cut out a little tab/wing on the side of the wheel that will receive air resistance instead of water, possibly allowing you to test the sound barrier idea

You have few things you need to work out with yourself but other than that you are somewhat entertaining to a guy who never smiles. Take that as a compliment...

7:16 "just leave it on the ground" just froze my brain

Ok that was really cool

Next time use Liquid Paper. A black Sharpie over a dark surface won't work.

"How do we measure that?" With white tape or paint. Damn. Also, SURELY you can set up a safe system to read the RPMs without having to run up to it after it's already slowed down a bit. Danger isn't entertaining regarding these types of tests...at least not to me.

Was not expecting a flashback to my childhood 1 minute into a water jet channel video

Have you spun nickel metal yet? Would also be cool to see the titanium wheel lightened up and see if you can increase that spead. Maybe Nurle the outside too for extra friction with the water and media. Awesome video, now i need to convince my company to let me try some experiments 😂

I broke the titanium rods in my back😅

I think fully precision machining the wheel is gonna end up being a needed step to really optimize it, that oughta get some interesting results! And I wonder if machining a groove in a resin wheel and then encasing wire might be cool? That’d be a fun comparison to this wire one! Ye could even try making a batch with different material wire, maybe?

10:11 If you had the world's first 100% energy transfer device; which would technically be breaking the rules of thermodynamics simply by the small distance.

The jet could be more tangential to the wheel, because of the bigger size of the wheel. Also, the bigger the wheel, the slower the"water speed" will make it spin. Made me remember the first Mini with their small wheels and short life tires. Thank you for the content!

The Cheat is to the Limit, cmon fhqwhgads .

Check out the fitting of bearings on good downhill longboard wheels. Bearings are always a super tight fit. Also taking advantage of how durable titanium is, you should hollow it out a bit. Like a titanium whiffle ball. I think the groove it cut in those resin wheels really affected how it was spinning.

It accounts as ALL OF IT. -certified googler here.

The double let’s grove tonight caught my ass so off guard 😂😂

11:23 someone in the comments could probably calculate the RPM based on the sound pitch or something

nice job 😁

11:10 sound frequency was roughly 1000hz, so approximately 60,000 rpm (very roughly). So the assuming the wheel's got a diameter of around 3 inches, edge would be moving at ((1000*60*60*(3/12/5280)*3.14) which is around 530 miles an hour on the rim. Seems close to your result, of course who knows how accurate the camera's recording or my measurement are lol.

There is no way i would have stood close enough to get the laser reading. That looks terrifying.

I didn’t like how few cuts i had on my hands so i decided to change that😂 genius!

7:17 nice pun with the earth/ground wire!

I'm not a smart person, butt I love to think - that I'm a smart person. Add new batteries to the tach, (Taco) a shield for the tachometer's sensor's 'view' (+ a small, adjoining fan?) and a groove into the wheel's side for better 'traction' between the water jet and wheel. Whatever the tach 'looks at' needs to be exaggerated. BONUS! (I hope this helps)>>>Aim the jet at a smaller circumference of the wheel. HF!

Juggling the hot titanium fresh off the lathe is too relatable

5:28 Interesting fact: In high-power rocketry they mix titanium sponge into some of the solid fuel motors and the result is a beautiful shower of sparks from the rocket as it blasts off into the sky.

20 mph is not the speed limit it is the frequency of your barrier 13:43

You want to make it go really really fast using the same wheel and setup? Put the wheel on a slight tilt so that the water jet can it the side of the wheel. Then accelerate the wheel to the maximum (until frequency stops climbing) like you do here, but then move the water jet head to the side of the wheel starting from the outter diameter, and moving slowly in the direction of the center. The closer to the center the faster (RPM) the wheel will go, because the water speed is constant so is the surface speed wherever the water hits the wheel, and in a smaller diameter that means higher RPM. Just remember moving the jet slowly because the inner it goes the more rotational inertia it has to overcome in order to accelerate the wheel. To mesure the RPM you can paint a white stripe in the wheel, or paint the side white and put a black stripe.

I hope there is a part 2 to this video where you try different kinds of lead or metals. This was top 3 of videos you have ever done in my opinion. I want to see 2 bullets fuse now and hope you get it done. Good Luck and God Bless

Those laser tachometers usually come with a few little reflective stick on tape markers for such cases like this

The little sayings complete with original video clips are killing me😂❤

0:57 strong bad fqhwgahds reference???!! as a former homestar runner addict you got me good

Blasting a block of magnesium with a water jet sounds like a fun and safe Idea.

No amount of money would make me get my hands that close to a screeching titanium cylinder.

Fascinating. I'm not a skater (73) and it's 3:45 am. Watched the whole video in the middle of the night. LOL

when you used the titanium shavings as a moustache, i subbed

From someone that used to be a cnc machinist that worked with Titanium we used coolant / lubricant in all aspects , Ban saw had coolant/lube , As did the lathe and Mill and even then sometimes the machine would still catch fire if the coolant/ lube level was not paid attention to over the runs. Yes Titanium burns hot and it even requires a special extinguisher to put it out.

Only way to get higher rpm with the same setup: move wheel so the water is tangent and centered on the outermost part of the wheel

The next time, please do the hardest metal in the world, Tungsten

Mill it to relieve weight, machine sections of super fine grooves to catch the water, machine the rest of the surface with divots to reduce drag.

have you calculated the water speed to know if with this pressure it even possible to acheave soun barrier

Yes, the drag on the wheel exponentially increases, the faster it spins. I would not rely on the tone of a wheel of a different material to estimate the speed of the Ti wheel. Measure it optically. If you have to, use an oscilloscope to probe the IR photodiode on your chinesium harbor freight tachometer, then count the frequency with the oscilloscope. Adjusting the position of the wheel vs the stream might help you in two ways 1. Optimizing the momentum transfer from the water to the wheel by 1a. Getting as close to tangent as possible without 1b. Reducing the amount & duration of water contacting the wheel before flying off 2. Reducing the friction on the bearings by reducing the downward force from the stream (the closer to the center of the wheel = more radial force & friction on the bearing and the less torque/ tangential momentum transfer to the wheel). Probably the best thing you could do to make this experiment easier is scuff a stripe on the wheel to reflect, sharpie the rest black. Setup your chinesium tach on a chinesium tripod, tap into your chinesium tach photodiode, connect an oscilloscope, monitor from a safe distance. Then start playing with your... Position of the jet. Then you're set. Bet.

Strongbad reference =subscribed. Way back in the archives of the interwebs.

Great entertainment. I can tell you have working around this shop forever as your ability to cover all ideas or theorys with tests along with funny spats makes this very fun to watch! Great job!

There is a fine line between genius and insanity, good luck with your travels

Safety guy: "I can build a boom for the tachometer" "Naw it's good I'll take the grenade for science!"

I'd much rather watch *you* wrestle with that stuff. Thanks for the work so we could watch this.

As Colin Chapman once said "If you want to go faster.... just add lightness" thats your answer right there my boy. Now go get that sound barrier broken, im intrigued as to what will happen.

everybody gangsta till the wheel starts spinning so fast it starts sounding like a freaking jet engine

6:37 Drugs are a hell of a drug.

I must say, i love the little monty python easter eggs too, im a long time fan of monty python and i have huge respect for anyone that appreciates that epic british humour, its the funniest shit out there in my opinion and requires a certain kind of humour and whit to enjoy 😊 this channel is gold

Assist with air and paint it black with a white or silver mark to measure RPM . Get fingernail polish that matches the silver tape that was supplied with the tachometer. The air will serve two assisting properties. The motion and lower the pressure due to that Bernoulli thing.. You could also use an air bearing for reduced friction. Make a steel spool that fits the profile of the titanium and pump air out of the center of the spool. Replace any grease the bearing might have with WD-40. Good Luck

Thx for not using the lord's name in vain! :D

I was not ready for the strongbad clip hahaha

We want to see a Nokia 3310 casted in resin.

I think this is like your 5,000th video where your rpm reader cant read it. I'd suggest actually cutting a line into the side wall, or getting a different reader. Even if it does read, the sound of the wheel has slowed down by half by the time it works.

6:22 A-10 Be like:

Thank you for the Strong Bad reference.

Yes it would count as breaking the sound barrier because the outside surface of the wheel is indeed traveling, maybe in circles but it is traveling through space at a certain speed.

The energy in that 80k RPM titanium spinning wheel is off the chart. Enough to kill people behind body armour.

Magnetic mish metal girt is made this way. the wheel is cooled with liquid/gaseous nitrogen, and then a thin stream of molten metal is poured onto it. At the appropriate speed and mixtures, magnetic powder is formed. General Electric patented this process, decades ago. Used for many other similar manufacturing techniques.

I came for the science, I stayed for the humor😂

Now does anybody else realize that the wheel was spinning so fast that the water didn’t even touch the wheel before it got flung to the side

The Homestar Runner reference was pretty epic.

12am: i should probably go to bed now 2am: Well well well, lets see what happens when you spin a titanium wheel at supersonic speeds!