Month: June 2017

Building A Boring Head

A Carriage Stop For The Lathe

I havent been completely idle on builds like TinyMill.

Ive just needed more tools.

One thing Ive been wanting for quite some time is a boring head for my mill. And when I was re-designing the x-y stage for TinyMill, I realized that I actually needed one. So Im going to build one, because Im crazy. Ill be following another one of Deans builds.

One thing that I considered in my decision to build this was cost. And because I dont just happen to have large diameter pieces of steel lying around, that could be pretty high. And then, when looking at metals, I noticed that for some reason, fine grain cast iron was cheaper than steel. And after a lengthy discussion on the HMEM forums, I reached the conclusion that cast iron would be alright.

So this is where I am now.

 

I have a 1 foot length of 1 3/4 cast iron, and some new hacksaw blades. Hopefully theyll ease the process of cutting this monster.

And now, if youll excuse me, I have a date with a bench vise and a hacksaw.

Building A Boring Head Part 2

Building A Boring Head

 

And so it begins.

 

I cut off a couple 1.25 lengths of the cast iron bar, and faced the ends to make them pretty. The big thing about this cast iron bar is that it isnt round. So although the ends of the bar are flat now, they arent necessarily perpendicular to the length, or even parallel with each other.

 

I popped one in the 4-jaw chuck, and faced the end again. I now have an end thats flat and straight as long as its in the same setup. I then turned down a section to 1.395, as called for in the prints.  That section is now actually round and perpendicular to the faced end. This end of the workpiece is now a datum, a reference that I know and can work off of for my next operations.

 

This end of the stock gets threaded 3/4 16. So I started by drilling out to the largest diameter I have, which is 1/2.

 

And I then bored it out to 0.7031, which is the required diameter for putting in 3/4 16 threads. Since the bore was done in the same setup as the facing and turning, the bore is concentric with the outside diameter.

And now I face a conundrum. I dont have a 3/4 16 tap. And I dont have an internal threading tool. I have some broken cutters I could grind into one, but theyre all carbide, which my aluminum oxide grinding wheel just cant handle. So Im stalled until either I buy one or think up how to make one. Stay tuned.

An Aside Making Counterbores

TinyMill Part 6

Over the course of designing some more parts for TinyMill, I realized that I needed to counterbore some holes. I could easily fake it with an end mill or drill bit, but one of my design goals was to not have any kludges. I could buy a counterbore, but thats $30 for a set that I might use one of every (not) so often. Or I could buy some drill rod and make my own. Guess which option I chose.

Before I start, I need to give credit where its due. I first learned that I could make counterbores on the HMEM forums, and then learned how to from Deans excellent page. Seriously. Dean did a really good job of walking through how to make a counterbore. So Im not going to make a tutorial. These are just a few selected photos of the process, and some notes. So lets begin.

 

This is a length of 3/8 O-1 Drill rod. A 36 length cost me about $3 (shipped!) from Enco. Its about 5 long. The counterbore Im making is for a M4 SHCS, so it has to be turned down to 8.25mm.

 

A sharp carbide cutter works wonders on tool steel. I got to about 0.0005 over my final diameter, then brought it down with some 220 and 600 grit sandpaper (with oil) on a parallel to keep everything nice and flat.

 

Repeat that for the pilot and you have a nice cutter blank.

 

Lacking any method of indexing, I had to make a fixture for cutting the flutes. It would have been nice to use a piece of hex stock (to get a 6-flute cutter), but I didnt have any. So a piece of 7/8 square 12L14 was pressed into service. It was drilled for the cutter, and had a set screw added in the top.

I didnt take any pictures of milling the flutes. Thats a lie. The milling fixture was just so in the way of the light that none of them were any good at all.

On Deans page, he mills the reliefs for the ends of the flutes. I had just indicated my vise in square, and didnt really feel like canting it off at an angle, so I did all the reliefs (very, very carefully) with a fine file. It worked well.

 

A final shot, of the heat treating. It went fairly well, although pure propane lacks a bit in the heat department and my flame was a bit on the small side of what I would have liked. A quench in motor oil and then a quick tempering brought the hardness to somewhere around 50 rockwell. Plenty good.

So now I know how to make  counterbores. Its pretty good, and I have to make a couple more, but now Im a bit addicted. Uh-oh.

Making Coasters

Inspiration

A while ago I found out about Evil Mad Scientist Labs font coasters. I thought it would be lots of fun to make my own, and so I began scanning for fonts and material. I decided that Times New Roman was too drab, and settled on something more exciting Webdings. I had been putting this project off until I found a roll of cork in the basement, and then I had no excuse. What follows is an attempt at documenting the process of making a font coaster on a CNC router.

The Photos

Here are the photos. The coaster is a ) (right-parenthesis) in Wingdings.

 

This is how it looks in EMC.

 

The machine over a piece of 1/4 cork. I just tacked it down with blue tape, because Im too lazy to do anything else.

 

The initial plunge. Im using a 1/8 end mill from Drill Bit City.

 

Cork cuts like a dream. Smooth edges, and I can cut pretty deep. I was using depth passes of 0.08, but really could have done 0.12 (or deeper) if I wanted.

 

The dust is pretty fine and hard to clean up, so a vacuum is a must. I really need to make a vacuum mount so I dont have to hold it myself.

 

Engraving the inner ring.

 

Cutting out the final shape.

 

The finished coaster. Its about 3.25 in diameter. I accidentally cut the inner ring 10 times deeper than I meant to. It should be 0.014 deep instead of 0.14 deep, but at least it shows up well in this photo.

Thats really it for coasters, as I make more designs Ill put up more photos.

Introducing The Odd-End

Quantum ORD Bot

 

Ive been printing a lot lately with a couple of extruders. On my ORD bot, I use a MakerBot MK7, and on my cupcake, I use a MakerGear stepper plastruder. And what Ive come to realize is that I dont really like either of them. Or rather, I really like some elements of each, but not really the whole package for either.

The MK7 is very compact, and I really like that, especially for a smaller printer like the ORD bot. And the hot-end is uniquely short. It is about 20mm shorter than the MakerGear. That being said, the drive sucks. The filament idler is a piece of delrin that is held pressed into the filament using not a spring, but the flex of the drive housing. Theres a lot of stress there, and no adjustment. It is also driven directly off of a NEMA 17 stepper motor. That would be great if it needed to turn at high speeds, and it does mean thet theres no gearbox to take up space. But it doesnt turn at high speeds, and to get the needed torque It sucks down about 1.6A. That means the motor gets really toasty (so theres a heat sink to cool it, which takes up space), and the driver gets so hot that I have to fan-cool it or it goes into thermal shutdown. Not good.

The MakerGear, on the other hand, uses a geared stepper. It has awesome torque, even with the driver turned almost all the way down (so the driver and motor are always cool to the touch). The only problem is that the gearbox takes up a lot of space and weight. But the filament drive uses a proper ball bearing driven by springs, and the drive gear is accessible so you can clean it without dismantling the extruder. My only real kvetch is that the hot-end is long (and unlike the MK7, not all-metal).

So I have two extruders, and in the end, I dont really like either of them. Frankly, I cant find one I really do like, but thats just because Im very picky. But I have tools, so Im not allowed to complain. I need to design my own extruder. I started with the hot-end. I wanted something like the MK7, but lower friction. The MK7 has a relatively high-friction thermal barrier, which is also made of the somewhat thermally conductive stainless steel. I dont plan on extruding any crazy polymers (such as ploycarbonate yet), so I shouldnt ever need to go above 280ºC. This means that I can use a plastic thermal barrier. Stainless is alright (an order of magnitude less conductivity than brass), but something like PTFE or PEEK (an order of magnitude less than stainless) is even better. PTFE also has crazy low friction. But its not strong, so I can take a page from MakerGear and make a hybrid insulator. I came up with a PEEK shell and a PTFE liner. The PEEK provides structure, and the PTFE provides low friction.

The heater block was fairly simple. I took a block, and added a threaded hole for attaching the nozzle and thermal barrier. I used a power resistor for a heating element, since theyre cheap and easily available. And just for kicks, I threw in a divot to stick a thermistor in. I spent a while trying to decide if I wanted a thermocouple or a thermistor. Thermocouples are good to 1600ºC (not necessary) and need no calibration (nice). But theyre incredibly noise sensitive.  have one on the MK7 extruder, and even with tons of filtering cant get all the noise off the signal. So I decided on a thermistor, which is pretty much noise-proof (nice), and cheap (even better).

And so the last component is the nozzle. I have no engineering background, and so I dont really have any way to quantify the design of something like a nozzle. So I went on intuition and drew out something that just looked right. But now enough blathering, its time to make this beast.

 

Heres how the thermal barrier came out. I single-point cut the M8 threads on the lathe because I didnt have a die, drilled it out to 4mm, and slipped in a bit of PTFE tubing. That was pretty easy.

 

The heater block was another easy one. It has two holes, and was a nice quick job on the mill.

 

This was the hard one. I turned the nozzle out of hex bar. The threads were cut on the lathe again, but the nozzle hole was drilled on the mill. I just cant make the lathe go fast enough to use a 0.4mm bit.

 

And here it is assembled, with a US penny for scale. I assembled it, cemented in a resistor, and fired it up. I dont have a drive for it yet, so I just pushed filament through by hand. It went through easily, so thats a success. And it came out 22mm shorter than a MakerGear hot-end, so thats a success. I guess now I have to build a drive for it and really put it through its paces. Or make a bunch more. Or both.

What The Hell Has Been Going On Here?

Motor Controllers Autopsy And Analysis

I mean really, its been four months. Thats not cool. Which means now I get to try to sum up a whole lot of things in as few words as possible. This should be interesting.

ChipiKart

I did finish it.

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See? It even ended up looking somewhat presentable with the Mercedes 300SL body on it. I ended up using 120A Kelly controllers on it, as the hacked jasontrollers just werent cutting it. I regret nothing. Proper controllers are a thing of beauty.

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With it being a racing power wheel and all, I raced it. The crowds really enjoyed that something with really tiny wheels could go so fast. Unfortunately, I started hitting some serious problems.

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During qualifying at Kansas City Maker Faire, my right motor committed suicide. On hard acceleration out of the first corner, the shaft twisted so hard that it snapped itself off inside the motor. I disconnected it and raced on one-wheel drive, which was disappointing. With both motors, I had qualified third overall against some much larger and more powerful cars. Chipikart had some potential.

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Unfortunately, realizing that potential was not meant to be. During the races at Detroit Maker Faire, the body was completely destroyed and both of my sensor boards were severely damaged. No good. But I brought it out to New York and raced there anyway. And there, Chipikart met its ultimate demise when the rear and was completely run over by a larger car. Both motors were internally shorting, and the sensors were gone. Chipikart was no more.

But it was a lot of fun, and a learned a lot along the way,  so its not really a loss. I got some fantastic batteries and controllers to re-use in the future. I found out that by putting 3600W to each rear wheel, I can wear down a set of colsons to the hard plastic core in just under 25 minutes. And I think I set a couple power wheels drift records. But most of all, I built a chibikart for $435, which is almost exactly 1/3 the cost of the original. And thats pretty cool. Now that Im not racing, Im going to finally finish putting together all the drawings. Probably.

 Real Cars

I bought one.

SONY DSC

Its a 1987 BMW 535i, and it has quite a colorful past. Im not going to dwell on it too long, since you can read about it here. I document some of the more entertaining repairs here. You should check it out.

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Oh, and I autocross it. Because its loud, slow, entertaining, and also because body roll.

Design

Ill leave you with a taste of things to come now that I have time to write about them.

ImagewC

This is a limited-slip differential, sized to fit in a power wheel. Its 3.25 in diameter, 3 wide, and weighs 2.5lb. More on this soon, because Im away from tools for the next few months and so all I have is CAD. This is going to get interesting.

Playing With Motors Sensors!

 

I mentioned before that I had gotten a sensor board from Charles. I had one board, which I intend to mount on TinyBike. However, I also want to put them on chipikart, which has two motors. Clearly, more sensors are needed, so I ordered some boards from my favorite purple board fab.

And two weeks later, they arrived! Solder party time!

A short time later, sensors! My three boards next to the MIT original®. Now to print some mounts and then Wait a minute. I dont have motors yet.