HP Plotter Take Apart and Analysis

A friend of mine found an old HP plotter from the mid 90’s on the side of the road. Knowing I was into electromechanical objects he asked if he should pick it up for me, and of course I said yes. We initially though about repairing it (its drive belt had desintigrated and it needed new ink), but realized that even after fixing it it would have little resale value.  We decided to take it apart and harvest it for parts, while along the way looking for interesting mechanisms and design features.

Printers are chock full of useful parts like motors, linear slides, encoders, and switches. In fact a very small crude CNC router could be made from the parts of two inkjet printers.

First impression based on getting it out of the car: this thing is heavy and built like a tank; the specification sheet says 95 lbs.

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Opening an access door reveals a few MB’s of RAM on standard SIMM cards.

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Removing more covers, and now we can see the linear encoder for plotter’s print head. This encoder sends position feedback to the plotter; once homed, the print head’s exact position along it’s travel is known. Barely perceptible scribed lines are in the lower clear portion. The black square in the center of the picture with white text is the read head.

 The silver looking strip is actually a stainless band that is pulled taught by a tensioner at the end. The considerable tension is needed as any sag in the encoder strip would lead to position errors of the print head and messed up prints.

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A view of the back, main control board on the left, power supply on the right.

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New Mold in Progress

I’ve been hard at work milling new molds, here’s a shot of the flycutter taking a finishing pass:

Sherline Mill Oiler Repair

While browsing the sherline website I stumble upon a page that describes a feature added to the CNC mills in 2010. It’s a series of passages in the saddle and an oil reservoir. This oiler system sends lubricant to the lead screws reducing wear. This is very important on a CNC machine as the axis moves much more and much faster than a manual mill ever would. Furthermore, the sherline uses a very simple 1/4-20 UNC threaded rod as the lead screw, which is much higher friction than the ball screw found on most CNC mills. I didn’t see this on my mill when I picked it up, but when I looked closer, what I though was a setscrew was actually the broken off remainder of the oil reservoir.

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The previous owner must have either over tightened it, or run into it with a mill. I used a screw extractor to remove the broken piece. It came out easily, it’s made of aluminum so the tool had no problem getting a good bite.

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I ordered the replacements through sherline, PN 50930 for the oiler body, and 50920 for the cap.

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Installation was as easy as screwing in the body.

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This was one of the easier repairs I’ve ever made, and a really pleasant discovery, as now I know that the mill is at most less than 4 years old.

The Apartment Workshop Series: Mini Mill

I’ve been thinking about getting my own mill for several years. I just like the idea of being able to shape metal. For the type of odd ball projects I like, I end up making a lot of my own parts, or customizing off the self ones. Having a mill allows me to do that easier and with much greater precision. I briefly looked at 3D printers, but parts produced on them have such low mechanical strength they really aren’t suited to my projects. Plus I like the idea supporting subtractive manufacturing (milling), as all anyone ever talks about is additive manufacturing (3d printing) these days.

Picking a mill can be a daunting task. There are so many factors to consider: price, working envelope, CNC or manual, construction, spindle type, etc. Being that I planned on operating this inside my living room, my options quickly narrowed. After much research I found several machines that fit the bill:

Little Machine Shop 3900 Solid Column mini mill

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Taig Micro Mill

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Sherline 2000/5400

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The taig and sherline are a closer match, as the LMS mill is more of a mini mill, while the others are more micro mills. The LMS mill was my favorite due to the much heavier construction, more powerful motor, and standard r8 spindle. However it is just slightly too large, on it’s own it is not that big, but when you factor in that it will need an enclosure (which is kind of a must have if you plane on running a mill inside your house) it just get’s too big.

Between the taig and sherline, I prefer the taig. It’s heavier steel construction make it much stiffer than the all aluminum sherline. Neither one will handle steel all that well, both can easily do plastic, but for aluminum the extra rigidity of the taig helps reduce chatter.

I was all set to buy a taig, but I came across a deal I could not pass up on craigslist. I got a sherline 2000 CNC ready mill, with steppers for less than 1/3rd the retail price. Whoever was using it last was cutting wood, as there are wood particles all over. It will need to be disassembled cleaned and lubed before use.

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It fits very nicely on my workbench, and even when an enclosure is added it should not hog too much of the work surface. It did not have a control box, so I’ll need to start looking at stepper drivers, power supplies, and machine control software. Looking forward to this!

The Apartment Workshop Series: Workbench

Due to a job change I no longer have access to the plethora of tools at my old job.  While there are some local hackerspaces, I really like having access to equipment whenever inspiration strikes, rather than having to wait unil the hackerspace is open (also working in your boxers on a Saturday morning). So I am setting up a small workshop in my apartment living room, were I plan to do everything from soldering to machining. This will be the first in a series of articles showing how I setup  and fill this space with various toys.

Every good work shop starts with a good workbench. My money-is-no-object bench would be a Lista cabinet with a maple butcher block top.

18733s3.tifUnfortunately these are disgustingly expensive when bought new and, unless you get lucky on craigslist or an auction, they are still expensive used. My goal is to replicate the Lista bench, but for an order of magnitude cheaper.

One of the first things you should do when designing a workbench is to think hard about what you will actually be using it for. A bench designed for SMT electrical work is a lot different than one for taking engines apart. I plan to use my bench for tool storage, some soldering/electronics, parts storage, machining (once I get a small mill and lathe), light assembly, and taking things apart. I took each of those tasks and figured out what requirements they would impose on my design.t

For tool storage (specifically, hand tools) the Lista cabinets are great as the many thin drawers allow for an enormous amount of storage in a small footprint. Lista cabinets are very similar to rolling tool carts found in garage shops (minus the caster wheels), so that’s where I started looking. I spent several hours researching rolling tool carts on garage journal and reached several conclusions. If you’ve got the money, tool truck boxes (snap on, matco, etc) are hard to beat. They offer the best construction, but at a hefty price tag. Surprisingly, Craftsman tool boxes were generally regarded as the worst quality, people described them as having thin gauge sheet metal, and really bad drawer slides. Also surprisingly, Harbor Freight tool boxes were said to be the best tool box for your money, decent quality, but still affordable.

I ended up getting Harbor Freight item#67831 and selling off the top box to recover some funds. Make sure you get the 26″ model, the brownish 30″ one is much lower quality.

With the tool storage figured out I started looking for a work surface. I like working on wood, as I can sand down and refinish it when it becomes too loaded up with crud (it also looks nice). I went looking for a low cost alternative for the maple top on the Lista bench, and found the Numerar series countertops from Ikea.

It isn’t as deep as I’d like (25″), but the construction (almost 1.5″ thick beech!) and price were spot on. I ended up getting the longer 96″ version, figuring I could always trim it down and use the extra as a lower shelf.

Next up were finding sturdy legs. I considered using wood 4×4 posts, but since this is in my living room and very visible, I wanted it to look a little nicer. I chose speed rail fittings and 1 1/4″ sch 40 aluminum pipe, as they are very strong, but gave it a slightly industrial look. I later found out that McMaster has a nice selection of pre made work bench legs, some with cut outs for electrical outlets.

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For medium sized parts storage I wanted to utilize the area under the work surface by hanging pull out drawers. Since I don’t have access to a cabinet shop to make custom drawers, I came up with my own solution. In my experience work bench drawers usually end up as a disorganized pile of random parts you don’t know what else to do with. Since the drawers are just one large space everything ends up mixing together.

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My solutions to this was bins with a divider grid system. These bins are dividable down to spaces 1″x1″, allowing for the creation of all sort of odd sides compartments. They also come in a variety of depths and colors, and are stackable.

The drawers slides ended up being one of the harder problems to solve. How do I hang these bins on the under side of the work surface? They have a large lip, and sloped sides so I couldn’t just attach off the self drawer slides. I considered building a self underneath that they could rest on, but interfacing with the speed rail was problematic. I really needed a bracket that the bins could slide on, supported by the lip that runs along the outside. If you know machine tools think of it like box ways. I initially thought about making my own from aluminum square tubing, but that would have been a lot of machining time to cut all the slots and holes (I needed to make about 8-10 slides).

I was browsing McMaster one day and found this aluminum extrusion that is normally used as trim around panels. It has the perfect shape to function as a slide, but still allow me to have a spot to screw it to the underside of the bench.

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With all the parts acquired I could start putting it all together. I first layer out the hole pattern for the leg fittings, insetting them slightly for appearance.

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3/16″ clearance hole for a 1/4″ lag bolt.

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The drawer slides came next, I drilled and counter sunk holes for  #8 wood screws. I had to counter sink them as the drawer would hit any fastener proud of the surface when pulled out.

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Aligning and spacing all the slides.

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Here’s the almost finished bench. I put on several coats of tung oil to act as a sealer, turning it a golden color. After this was taken I also added an additional leg in the center towards the front, as it needed a little more support mid-span.

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I ended up using the full length of the counter top material since it fit in the space and you can never have enough work surface.

If you’re curious here’s a few shots of the drawers filled with parts.

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First Part out of the Molder

I got access to a set of vintage molds from an actual mold-a-rama machine (the macaw) and put them on the machine. After two misfires the third one came out pretty good. A little incomplete on the wing tips. I need to setup multiple regulators on the air supply, that way I can run the injection piston at a higher pressure than the rest of the system, allowing me to fill the molds faster.

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Modern Dining Table Part 3: The Conclusion

Part 1 and Part 2 here.

This weekend I wrapped up my modern dining room table project by installing the legs. Rather than 4 individual legs, I chose two trapezoid shaped metal frames on each end.

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This table won’t have an apron, which gives rigidity to a table. Think of the point where the table attaches to the legs as a hinge. The further away from the hinge that the leg is supported the more rigid the connection, so apron = good, stretcher = better.

With a leg configuration like I have you’d normally need a stretcher between the legs to prevent the table from wobbling side to side.

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How to make a stable table. able.

To eliminate the need for a stretcher, the flanges where the top connects to the legs were made extra wide by adding a piece of 3/16″ angle to the steel tubing.  1/4″ lag bolts secure the legs to the top (pre-drill so you don’t split the wood!)

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I wanted some contrast between the legs and the warm natural look of the reclaimed wood table top. Rather than paint the legs I had them clear coated, allowing the welds and tube seams to show through.

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I need to put some felt pads under the legs to protect the floor, but other than that I’m going to call this one done.

Suppliers:

Wood table top: http://www.americanmaad.com/tables

Legs: http://www.etsy.com/shop/TRRTRY