Sunday, November 20, 2016

Cherry tables

A couple of cherry side tables.

Finished tables

Specs:
Overall height: 28"
Top: 18" x 18"
Apron width: 14"
Apron height: 4"
Legs: 1.25" taper to .75"

The legs are mortised with 3/8" tenons and pinned with 1/4" dowels. 3/4" thick top, edged glued from 3 boards, hand planed and scraped flat. The bottom side of the top has 1/4" deep, by 2" long bevel, leaving a 1/2" thick edge. Finish is a seal coat of thinned shellac topped with  multiple coats of danish oil. The top surface was wet-sanded with 320 grit and oil to fill grain pores.

Some photos:

Pile of shavings from power and hand planing lumber
Many shavings


Clamped table bases



table bases showing dowels pinning mortises
Pinned mortises

Assembled bases and one table top


Attaching the table top
Attaching the top
















Lessons learned:
  • Biggest mistake: The dowels pinning the tenons are in the wrong location. They should be located closer to the edge of the leg to lock the tenon in effectively. It's not a huge concern because the glue joint has to fail before it's a problem.
  • Glue cleanup. I decided to try a different way to deal with glue squeeze-out. In the past, my approach has been to keep excess glue to a minimum and to allow any squeeze-out to partially cure then scrape it off. This time, I used a really wet rag and a spray bottle to clean up excess glue. Using a damp rag as recommended on the glue bottle embeds glue into the wood grain and can affect the finish, I had hoped that using lots of water to fully dilute the glue would wash it away without embedding into the wood grain. It worked, but not well -- lots of raised grain, discolored wood and  more sanding was required in the tough-to-sand joint between the leg and apron. Next time, I'll go back to the "let it dry and scrape" method.
  • I LOVE working with cherry. It's crisp and has great cross-grain strength so it responds to sharp cutting tools wonderfully. Hand planing and chisel work are an absolute joy.


Saturday, February 13, 2016

Lathe DRO Installation




Finally decided to add a DRO to the old South Bend Lathe. When looking for info on how to add digital scales to a '40s era lathe, I didn't find much, so I thought I'd share what I came up with. It hasn't seen much use, so it may evolve over time.

The X axis was fairly straightforward: there's room on the back of the lathe to hang the scale. The Y axis was more challenging: tight clearances on the carriage led to mounting the crossfeed scale behind the carriage. Fortunately, on this SB with the rear-mounted countershaft/motor assembly there was room behind the lathe. 

Cheap but decent digital scales


Aluminum angle bolted to the tapped holes for the taper
attachment I don't own.



1/8" aluminum  extension bolted to the crossfeed carriage. The side
of the crossfeed casting was milled flat and holes were tapped
in the cast iron.

X axis hanger clamped to the rear ways.

X axis scale attached to y axis aluminum angle

Sunday, June 21, 2015

New CNC

A new CNC has been taking shape in my shop over the last several months. It's a major rebuild of my previous router-lathe that adds another axis of movement and a lot more capability. I kept quiet about it until it was actually running because the design is a little unusual and I wasn't entirely sure if it was going to work -- I wanted to avoid having to say "that new machine I'm building? umm, never mind...".

It's still under construction, but far enough along that I can use it to make parts for itself.

Configured for flat work

Configured for 4th axis (lathe)
It's basically a standard 3-axis router built around an old 11" x 36" wood lathe. It has two configurations: a 3 axis router, or remove the table to access the lathe for 4th axis work. As with previous projects, most of the design work was done in Sketchup before and during construction.

Configured for rotary work on the lathe
With the table installed for flat work.


Here are the first cuts:

 




Rotary axis test.


The rotary axis (lathe) drive. 16:1 ratio -- kevlar belts.


Detail of the bearings on the gantry sides

Fabricated lathe bed and side rails


Sunday, August 17, 2014

New Bowls


Some hand-turned and CNC machined bowls.

Redwood burl. About 11"

12" cherry dyed black

5.5" mystery wood, dyed green



5.5" mystery wood, dyed black


Walnut spiral. 6.5", CNC


5" walnut, CNC


10" red cherry

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 another piece of software to take the output from FEngrave and wrap it around the rotary axis.

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.