Friday, January 28, 2011

A neat way to spackle

I'm working on painting our house, and I'm noticing that the previous owners left quite a few holes and dents in the walls. In other houses, I learned how to spackle walls that are basically flat, but these textured walls are new to me. I don't want to make too big of a flat area to cover up a small anchor hole, and re-texturing the walls afterwards seems like a less-than-elegant solution in my opinion. The trick, then, is to only apply spackle at the very spot where it is needed, avoiding the surrounding wall.

I came up with an idea that I hope will work. (I don't have the proof as of writing whether it does, but I'm hopeful.) I remember from my Walgreens days a syringe designed for oral and topical use. I couldn't find any for sale where I went tonight, but they had them behind the pharmacy counter for free, oddly enough. If this catches on, good luck finding them for free. I bet they'll always be on their website at the very least.
It's a simple enough idea, really. Dip the syringe into the spackle and suck it up. With the high viscosity of the spackle, you'll find that you have to continually move the syringe around because the surrounding spackle doesn't flow into the hole as quickly as you can suck it out. If you get air into the syringe, tap the handle to move the bubble to the tip, and squeeze slowly until a little spackle comes out.

Another little trick is how you actually apply the spackle. You need to be sure to wet the outside of the hole you're trying to plug. If you don't get a large wet edge, the spackle will probably fall out when it sets. (It would suck if that happened with a fresh coat of paint on it.)

Disclaimer: We hate our old wall colors. ;-)

Sanding with this method will be a little more time-consuming, but if you have an orbital sander, it's probably worth the trouble to avoid re-texturing and matching. I cheated and touched up with a finger a little bit to knock out some of that time. Even if I finish with a putty knife, I know that by starting with the syringe, the hole has spackle inside of it and not just near the surface. I hope this would add a bit more strength to it when it sets (assuming it's not too thick to completely set). I'm not looking to anchor shelving from it, but I do enjoy the comfort of overkill in household repairs.

Cleanup is a cinch if you don't wait too long.

Wednesday, January 26, 2011

First Run of the CNC

Last night I got my CNC running for the first time. Before I was able to draw pictures by holding a pen, but last night I was finally able to machine something with a usable tool.

I posted a short video on YouTube, but the boring uncut video is here in all its unglory. The example here is simply a 1" square milled with a 1/4" square-shoulder bit. It skipped a lot of steps in the Y direction, but the X direction came out within 0.010". (I brought it to work the next day and measured it with calibrated tooling there.)


The "mill" is a Harbor Freight drill with a keyless chuck. I probably paid $12 for it. It rides on two ball-bearing rails that once supported a minivan back seat and is controlled by a toothed belt drive from a large inkjet printer. The X-Y table was given to me by a former coworker; I'm told it was once in an engraver.

The stepper motors are driven by ULN2064 Darlington arrays which are powered from an old AT computer power supply. The ICs are mounted to the inside of an aluminum plate on a hobby project box. I strategically drilled holes in the box, the plate, and the power supply so the power supply fan would draw air through the box and cool the ICs attached to the heatsink/cover plate. The X-Y motors have resistor arrays totaling 8 ohms to limit the current on each of them, but I believe I'll soon short them to increase the current (and still be within the motor specs if I remember correctly).

The Darlington arrays are controlled directly from the parallel port of an old computer (given to me by a current coworker). There is no intermediate logic; I'm maxed out at the 4 outputs required for each motor, and I can't drive a bipolar motor with the current configuration.

Software has been doable, but it's soon going to be a bitch. I started from scratch in QuickBasic 7.1 (with OUT and INP statements to talk to the port). I eventually want to write something that will automate the conversion of an STL file (or something of the like) to a nearly optimal tool path. STL files aren't that difficult to read, after all.