Things like this, give me a smile when I’m reading something because it feels personal. It’s a joke, it’s something that came to your mind at that moment (or at the moment you were posting) but that’s the stuff that most people would probably remove from a book and that I would enjoy reading.
I would tell my wife “Look, Lotaxi works in an environment that’s as loud as ” and she would look at me like the weirdo I am… but I find it funny and interesting haha.
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I don’t often find something to talk about, but when I do you can’t shut me up. Overcommunication shouldn’t be hard.
I’m glad you think so! My original prototype is still a daily carry for me, and the last time I heard from the only other person who has one it’s one of his, too. I’m super excited to see what more people think.
I’m kinda figuring that out, yeah. Just doing my best to make the wait less excruciating. I’ve been paid deposit money, so I’m trying to make the wait have some value as well.
I’m finding that out, yeah. I’ve moved past a lot of the difficulty with learning how to program the parts with my new CAM system, and I’ve gotten enough experience with most of the tooling I need, so at this point it’s just having the machinery run. I’m using the lathe more consistently for my side gig here than I do for my day job. I’m apparently shaking some things loose that need some fixing.
Hit a snag, letting you know. The encoder that gives the controller feedback on how fast the spindle is turning went out while I was cutting a yoyo last Friday. On the machining side, that means that I don’t have a way to get a consistent chip load on anything I cut that has a changing diameter as I move along the shape profile. On the product side, it means I don’t have a good way to get a clean surface on anything I cut. I can still use the machine and cut stuff, but I’m not expecting particularly good results until I get the part replaced.
It’s a much less involved repair than the spindle rebuild, so that’s a plus. Essentially as soon as I have the replacement part in hand it should be as easy as bolting it on and plugging it in. I’ve already started the process of sourcing a replacement, though according to both of the companies I’m asking they are apparently made to order and the manufacturing lead time is between 1 and 3 weeks. As soon as I have my boss’ go ahead, that’ll get ordered.
I’ll do a writeup of why the encoder failure is a pretty big deal tonight after my wife goes to bed. Should shed some light on the mechanics of surface finish and tool wear, might be interesting to some people.
In the meantime, in the interest of doing what I can to hit the end of April deadline for earlies, I’ll try and cut a unit or two in constant linear feed mode (instead of constant feed/rev mode) and see how that goes. I’m not expecting it to be all that great, and the attempt might end up killing a couple inserts. I’ll report back when I have a chance to test.
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So. Feeds and Speeds. One of the more interesting basic topics in machining.
Machining obviously takes force. You’re bending a small piece of the surface up until it breaks. The part that comes off the workpiece is called a “chip.” there’s a few different ways they can form:
Controlling this uses some interesting geometry in your cutter that can be material, movement, feature, or surface dependent. It gets more than a little complicated, so we can deal with that later. In any case, the action of shearing or breaking a chip of material off the stock creates a LOT of friction, which means a lot of heat. There are typically two ways to control that: Slow down the rate of cutting or reduce the necessary force. Reducing force breaks down further into changing geometry or taking a shallower cut. Geometry changes mean new tooling, which can be rather expensive, and shallower cutting will likely just kill your tools quicker in exchange for a short term positive result. In the worse case, shallower cutting means you’re not cutting enough material to cool the cutter. Most cutters rely on the material itself to absorb much of that friction heat, so if you don’t take a deep enough cut you’ll burn the cutter just by virtue of rubbing against the workpiece without cutting enough of it. At a basic level, the easiest way to do things is to keep the cutting surface happy by balancing the rate of speed as the material passes over it while cutting enough material to keep the cutter happy.
And so we get to the concept of surface speed. Think of a circle. It’s got a circumference, right? Well in the machining world we look at the rate of that circumference’s travel past the cutting point of the tool in a period of time. For me, that’s feet per minute. So I measure the speed of machining in Surface Feet per Minute, or SFM.
There’s a slight complication to that, though. A constant RPM isn’t gonna do much for you. Except for very specific processes like drilling or turning a cylindrical shaft, the diameter at which you’re cutting is gonna change, and the circumference with it. In order to create a constant surface speed, then, you’ve gotta change the rate or rotation to match the new diameter. The smaller the diameter, the faster the rotation needs to be to keep the rate the surface passes the cutter constant. The term in machining is a Constant Surface Speed (CSS) mode of rotation. The machine calculates the proper rate of rotation for a given cutting diameter and varies the RPM accordingly. You lose the battle at some point because you can’t spin up to infinity and the center of rotation technically doesn’t move, but you do what you can and the speed only goes down anyway.
The second piece to this is the rate the cutter moves. There’s 2 ways to approach that as well: feed per time and advancement per revolution. Feed per minute is what it says in the tin: pick a distance for the cutter to travel in a unit of time, and it does. In my case inches/minute or IPM. I’ve got one machine that measures movement in inches per hour, but wire EDM is a completely different animal. Anyway, feed/time isn’t really used in turning if it can be helped because the speed of the work is gonna change due to the CSS mode explained above. The annoyance is that your finish is going to change. Take the following picture:
Notice how the machine lines (typically called the “scallop”) left behind by the cutter get further apart and more pronounced as they approach the outer diameter of the workpiece. That’s there because CSS dictated that the rotation should slow as the cutter approached the larger diameter, but the feed rate didn’t slow down.
The image above is a quick overview of how a scallop develops based on feed and tool geometry. Pay attention to how the cusp forms relative to the leftward motion of the tool nose. Think about how that might change if the movement of the tool sped up or slowed down over time. Now look at the photo of the actual machined item again. Where the center is seeing 4000RPM, the edges of the workpiece might only be seeing 1000RPM. If the cutter is moving at a static 7IPM, then for every rotation of the workpiece near the center the cutter is moving 0.0017in. Near the outside diameter, though, it’s moving .007in. That’s a massive difference in the surface finish and quality that you can see very plainly. It’s very important, then, to get a consistent rate of movement across the workpiece, specifically in relation to the RPM of the spindle.
The solution to that is to make the cutter move a static distance per rotation of the workpiece. Let the feed speed up or slow down to match the momentary RPM of the spindle. That’s dictated as feed per revolution, or feed/rev.
The above systems are what are very commonly referred to as “speeds and feeds.” Rate or surface speed of rotation, feed rate of tool.
Now we finally get to why the encoder is a big deal. It’s essentially like the speedometer in your car. It’s actively measuring the true speed of the spindle to make adjustments to the movement of the tool. The machine’s controller can tell the spindle to rotate at 3000RPM, but how does it really know how fast it’s moving? It looks for feedback from the encoder. When the thing failed, I was making a facing cut on a piece of stock. It froze pretty much all feed/rev movement because as far as the machine is concerned the spindle is always spinning at 0RPM even if it’s actually putting out 95dB at 4000RPM. It knocks out consistent surface finishes entirely, but worse than that it means that I’m limited to feed/min. You can try to counter some of the effects of this by keeping your target speed reasonable, but your feed not being tied to rotation is an issue. At small diameters where the rate of rotation would want to be moving toward infinity the surface speed might be fine for the feed rate. Go to the boundary of where the spindle can keep up, though, and you’ll start to quickly overwhelm the cutter because you won’t be cutting enough material to keep things cool. You’ll eventually hit your happy place as the machine slows down, but without being able to track the speed with feed you’ll then run into the issue I showed above with the finish getting much more coarse as you approach your maximum diameter.
Where this relates specifically to the Queen Bee is that I’m using titanium. Titanium SUUUUUUUUUUUUCKS at conducting heat. Where most materials like steel, aluminum, brass, copper, etc will readily accept heat, titanium rejects it.
This means that instead of keeping itself cool by getting rid of the friction heat in the chip, you’ll just dump that heat into your tool. Hot things get soft, soft tools can’t cut and just get deformed and destroy themselves against the workpiece. This gets magnified by the fact that titanium likes to work harden. If you’re not cutting enough of it, you’ll just make the surface super hard. Increasing hardness means increasing friction, increasing friction means creating more heat. It’s an incredibly vicious cycle, and that property is why so many people consider titanium to be a nightmare to work with. Now apply that to what I mentioned above with the cutting action you can expect in a feed/min situation using CSS rotation. It’ll be a problem pretty quick.
I think that my roughing paths will be fine because they don’t care about the tools quality too much as long as they don’t shatter (heavy feeds, allowable imprecise movement, just getting rid of the bulk of the material while leaving enough to take some finish passes), but not being able to use feed/rev will be hell on my finishing tools, which are much more delicate.
We’ll see how this goes. New encoder is going to take a minimum of 2 weeks to get here, so I might still have time to get a few good units made by the end of the month. Here’s hoping.
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Fascinating.
This is not related but it made me wonder why didn’t LPs have a different pitch as the stylus gets closer to the center. Found a thread that explains it (if you’re interested)
Come to think, I’ve seen the effect shown on the third picture in some metal pieces and I always thought it was an artistic decission. I mean, like the manufacturer said “I want a spiral and the closer it is to the center, the shorter the distance between the lines” xD
Titanium does sound nitpicky. Like… you have to really plan and calculate everything ahead of time because you have to do as much as you can in the first try. Not much room for a “I’ll fix it later”
I imagine it’s possible, but it’s quite inefficient.
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Possibly an artifact of a manual movement machine, too. But yeah that’s what causes it!
It’s more that you need to understand how things behave and what your end result needs to be. Compared to a lot of other materials there’s a lot more to consider, though, for sure.
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The encoder is finally ordered. Took a bit of convincing to get my boss to admit we couldn’t just fix the one we have.
Turns out potted LED’s with an unknown wavelength are a little difficult to source, let alone reach >_>
Now to wait for them to build it. Yaaaaaay 
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Official info from the manufacturer states 85dBA at 1m from the head stock at 1.6m from the floor. So we’re still considerably louder than we should be, but it’s not quite as extreme as previously thought.
On a related note, it looks like we’ll be paying for expedition of the spindle rebuild when we get to that stage. I’m really hoping we are slow enough to send it out that the new encoder gets here and I have a couple weeks to use the lathe before we pull the spindle cartridge. I’ll be driving it to a shop in LA and it’ll take at least another 2 weeks to get it back. If the spindle has any real damage done to it by the last couple years’ vibration, then it’ll need to be sent for chrome plating and grinding before the rebuild and balance can happen, which only makes things worse from a time perspective.
There are 4 bearings that need to be replaced. Three at the front, the right side of this image, and the one toward the left, almost in the middle of the image. It’s the three toward the right that are in the rebuild area. I’ll need to replace the one on the left too, but the machine doesn’t need to go anywhere for that.
Plenty of pieces to the spindle, in any case. I’m really happy I don’t need to be the one to do the job >_>
Before the spindle leaves our shop for the rebuild, my top priority at this point is to cut 15-20 units at the very least so I can get them out to the people who are waiting on early units. That’ll leave me with a couple extra for finish tests, too.
In other news, I’m using this break I’ve found myself in to try and work on my packaging. I’d like it to be made of not-cardboard and not-plastic. I’ve got a buddy with a CNC router who I’ll hire to cut some material, and I have a good idea of what I want it to be. Preferably wood, and I’m shooting to invoke honeycomb with a hexagonal structure and I’ll try and incorporate wax of some kind. If things smell subtly of honey and maybe a flower like lavender when you open the box, that’d be super cool too. For a finished product, I was playing with the idea of tying the scent to the colorway.
I figure this delay should at least improve the result you guys receive, so if I can manage to get some prototype boxes made before the Queens are ready then I’ll ship the early units in them to see how they travel.
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The box ideas sound amazing!!! 
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I’m no good with proper rendering, and I can’t model drippy wax in SolidWorks, but this is the initial model idea.
Idea is to seal them with bottling wax and then include a pull-strip to cut the seam and allow the lid to be lifted away.
Gonna see about using walnut because I love the color. I don’t want to use veneers on something cheaper, but it’s also kind of a shame to cover up something as nice as walnut with a bunch of wax.
I’m not a woodworker, though. Any other ideas out there on what kind of wood might look nice?
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