Wednesday, September 18, 2013

Wind wave sculpture

I'm working with friend on a wind-powered kinetic sculpture. This is a half-scale model out of wood to verify the mechanics.



And here's a road test with the sail attached. I'm calling out engine RPM to estimate speed because the speedometer is not very accurate at low speeds. 1900 rpm equals somewhere between 9 & 10 mph.





This test provided great information about how it behaves in the wind. We're going to try less offset on the crankarm and reduce the amount of travel in the rods. Oh, and make it stronger, too.

Saturday, July 20, 2013

Router lathe – upgrades and wood sign



Router lathe – upgrades and wood sign.

Here's a wood sign I made for a friend's woodworking shop, Artsubstrates. This is the first time I've wrapped a 3D shape around the rotary axis. It worked better than expected.

 

(note: from here on is going to be pretty dull for anyone not building a cnc machine. ...and maybe for those who do, as well.)
I generated the text using "FEngrave" a great piece of software for generating gcode for signs. It does one thing and does it very well. Highly recommended. Then I used CNCWrapper , another wonderful piece of software, to take the output from FEngrave and wrap it around the rotary axis. There was a little hand editing since I had FEngrave configured incorrectly so it generated G2 and G3 (curve) commands*, and CNCWrapper can't convert them. (Not FEngrave's or CNCWrapper's fault -- purely user error and those commands are not compatible with a rotary axis)
*it turns out FEngrave has a setting to turn off curves. ....if I'd just been paying attention. "Settings > General Settings > Enable Arc Fitting"-- uncheck. Thanks Scott!

Recent upgrades:

Some upgrades were required to convert from arduino 2 axis control to 3 axis CNC. Added was new z  axis assembly with stepper motor and controller, new belts and pulleys on the rotary axis to increase the gear ratio, and limit switches on the linear axes.


New Z axis assembly with motor.
The new Z axis assembly has 3/8" aluminum plate for the base and the carriage platform, 5/8" O1 tool steel rods for rails and UHMW bearings to slide on. I made another UHMW nut and used the acme threaded rod left over from the X axis. I'll have to re-think the UHMW bearing though -- they slide really smoothly by themselves but take a lot of adjustment to get the carriage to slide without binding with all 4 attached.

Limit switches on Z axis
Motor and switch wiring

Showing the limit switches and motor wiring on the Z axis. I used ethernet cable and jacks for the limit switches, and heavier 22g wire for the motor.



New rotary axis belts
 The big automobile timing belt and diy pulley were replaced two XL timing belts and pulleys. increases the motor/ axis ratio from the previous 4:1 to 16:1. This provides a lot more holding power against the router and gives smoother rotary axis travel and much finer resolution. With the old belt, there was more backlash that I liked and at larger diameters, one step on the motor translated into as much as .003" of travel. With the new belts and gear reduction, resolution at large diameters is still very fine and I see less chatter during heavy cuts.

The current belts are neoprene with polyester fibers, which do stretch a little and is more noticeable with the double gear reduction. I purchased new belts with kevlar fibers that have very little stretch, but haven't installed them yet.

All this is because these 285 oz/in motors are OK for the two linear axis, but a bit puny for the rotary axis. A motor upgrade on the rotary axis may be in order, but would require a bigger power supply and new controller as well -- not in the current budget.
 




Wiring to the electronics enclosure. 5 pin XLR connectors with 22g stranded cable for the motors and ethernet cable and jacks for the limit switches and e-stop button. There's a vented cover for this enclosure, but after an overheating incident where the cooling fan lost power and the controllers started making real funny noises and smelling bad, I don't have the courage to close it up yet. I'm thinking of putting in a temperature monitor, but that may be overkill.



Sunday, May 5, 2013

Router lathe -- converted to CNC


A lot has happened on the router lathe and this posting is way overdue. It's gained a nice new 3rd axis carriage driven by a stepper motor, adding programmable z-axis (depth of cut) control,  and has been converted from arduino control to full CNC, controlled by a PC running Mach3. Here's a video of the first major part cut on the machine since the rebuild.


The conversion to a CNC controller opens up huge potential. The arduino was great for spirals, but it took a lot of code to generate them. I found I could do in 3 0r 4 lines of g code what took 100+ lines of arduino code.  I could have installed Grbl and continued using the arduino as the CNC controller, but I like the feedback graphical programs like Mach3 and EMC2 provide. Although I do have an idea for a little internal thread-cutting machine that Grbl might be perfect for.

Cutting the square profile proved to be a bit of a challenge. Unfortunately, on this machine there's no way to move the cutter relative to the center line of the part (bad planning!), so cutting a flat is a little more complicated. After a calling up some forgotten math and doing some sloppy Excel scripting, I was able to make a spreadsheet to generate code to control depth of cut / rotation ratio that generates a flat surface as the part rotates. Then, rotating the part by increments between each cut to produce the spiral was a matter of learning how to use parameters and subroutines in g code to create loops

Here's the Excel function to make the square:  
=((Offset/COS(angle))+(tool_radius/COS(angle)))-tool_radius
...where offset is the distance from the center of the part to the flat surface you want to generate, angle is the angle relative to the axis of the cutter and tool_radius is... well tool radius. I have a spreadsheet that does all the math and generates g code for different angles and offsets. I'd be happy to share if anyone's interested, but I don't want to post it in its current unfinished state.

Saturday, March 23, 2013

Tripod head adapter


This is an adapter for a ball-head tripod for use with a spotting scope. A ball head works great for a camera, but not so great with a spotting scope -- it's tough to aim a scope when you loosen the ball and everything gets all floppy. This adapter adds a vertical plane tilt mechanism to the top of the ball head. Just lock the ball tight and use the tripod's pan (rotation) and this adapter for the vertical.This setup allows me to have both options -- a pan/tilt for the scope and a ball head for a camera, without carrying a bunch of gear. Plus, the pan mechanism that came with the tripod on the ball head is amazingly smooth, so I get to use that with both heads.

It has an Arca type dovetail quick-release plate on the bottom that attaches to the ball head on the tripod, and a clamp on top to attach to the scope.




The center pivot block is solid acetal plastic, or Delrin and the rest is aluminum. The acetal against aluminum provides a silky smooth motion.

Tilt adapter breakdown



















The clamp and plates are compatible with the tripod hardware. The springs fit into holes on either side of the screw and parallel to it to keep the clamp open when not tightened.

Arca type clamp


The plate on the left goes on the bottom and is relieved to fit a locking pin in the tripod head's clamp. The one on the right fits on the scope and attaches to the top.

arca type mounting plates



It works great. Smooth tilt, easy to use. I can pop the whole scope / adapter assembly off and use the ball head with a camera.

Tilt adapter with scope mounted


And here's the tripod with the scope and top assembly removed, and a camera on the ball head. It works very well and only takes a few seconds to switch.

Adapter removed, camera mounted


When I started I figured I could find some standard dimensions for Arca Swiss type dovetail quick-release clamp and plate. I didn't have much luck, so I'll share what I came up with. These are what I used, but I had to tweak the clamp side a bit to make it fit. They should be a good starting point, but use them at your own risk. I have no idea if the Promaster tripod they were based on is a standard size.

Arca type dovetail quick release plate dimensions
I used a couple of 3/32" drills to measure the dovetails (actually .094" dia)


Arca type dovetail quick release clamp dimensions
The clamp side dovetail needed to be cut more than shown here to fit the plate.





Thursday, September 20, 2012

Mobius carvings




I've been salvaging old douglas fir beams from building demolitions for carving. Douglas fir takes on this wonderful texture when it gets old: it becomes more consistent, less difference in hardness between the rings, and it's easier to carve across the grain than new fir. With a sharp chisel, you can make big, bold cuts. Very satisfying. These two mobius carvings were early projects from reclaimed fir.


First attempt -- about 6" 



It was a bit tough to visualize how the surfaces wrapped around the shape, so I started with models. First, I made a donut from modeling clay, drew the corners as they wrapped around the shape, and then scraped a flat plane between the lines. Next, I built a series of models in Sketchup -- a bit laborious, but it helped a lot to see what needed to be done.



To make the small mobius, I started with a donut with a round cross-section, traced the corners as they wrapped around the part and carved a flat surface between the lines, being careful to measure the flats  radially. The larger one was harder: I made it in two halves, doweled together. The majority of the shaping was performed on each half separately, then the finish work was done with the part glued together.

Monday, August 6, 2012

Corner table from reclaimed fir

A friend gave me some old fir boards torn out of her attic. They were getting in the way where I stacked them in the shop, so I decided to mill them down before storing them. But once I started cutting, I got a little carried away and made a table top to go with the spindle I made in the last post.

quarter-round table. front view

The top is a 24" radius quarter round, with the leg centered roughly in the table top.


quarter-round table. top view


The curved front apron was made of several thin pieces of stock laminated around a curved fixture and glued.

table apron


The tripod base with the legs attached by dovetails. The front two legs are at right angles to each other and the rear leg is much shorter. One major mistake was the thin dovetail web between the front legs, that ended up being a weak point I struggled with later.

table legs

It was interesting to build a traditional piece like this. Spindle-turned work always seems to lead in that direction, and in this case, it forced me review some basic skills. It was a good time for that review -- I made a couple of mistakes that could have been avoided if I was a bit more in practice. It was a pretty quick job, and a lot of fun. And it replaces a really ugly folding table in the corner of my living room.

Wednesday, July 4, 2012

Router lathe: making real parts




cutting flutes on a big spindle (5" dia, 22" long)

 First "real" parts -- the big bolt was fun, but just a test, and a bit of a joke. This is the first "real" part -- a base for a round table (I think). I turned the spindle by hand on the manual wood lathe, and modified the thread code to cut a series of flutes. It worked pretty well, in spite of a couple of errors in the code:

1. I intended to climb cut (feed with the cutter so the bit pulls with the direction of travel. Makes a cleaner cut across grain). This code runs the cutter against the direction of travel (conventional cut), which is more prone to splitting when cutting across the grain.

2. I rotate the part by one degree between the forward and reverse cut in order to make a slightly wider cut. But I didn't account for that when spinning between flutes, so each cut advances one degree around the spindle. I actually like the way it looks, so I didn't fix it, but it was a (happy) mistake.


< New lead screw  CNC conversion >