Wednesday, January 10, 2018
Emma loves doing crafts, and tape if a tool she use a lot. I always want to make a cute tape holder for her.
I prototyped with some plywood first, and tweaked some design, like the slot width and dpeth.
The more I looked at it, the more it looked like a naughty unicorn whale. So I added the corn with brass rod
Thursday, January 4, 2018
I got this very nice Alder slab from a friend. They cut down a dead tree about 2 years ago, and I got a 2 inch slab about 24 inch wide and 5 feet long. The slab is pretty stable didn't move much over the year.
I rip it in the middle first. the slab is not totally flat, about 1/4 off from end to end. I don't want to joint it, I want to keep the thickness, and I don't need the surface to be totally flat. So I hand planed it, until it is mostly flat, I didn't take out all the saw marks I think it is pretty nice to have those rustic characters.
To mount it floating on the wall, cut out a 2x1.5 rabbit to take a mounting strip. I connect the mounting strip and the shelf with 1/2 EMT pipe on the first piece. This is from the idea of my lumber rack, since I don't have a drill bit that is perfect size for the pipe, 11/16 is a bit too small, and 3/4 is bit too big. I use 11/16 to drill the hole and tilt the bit to enlarge the hole. The pipe is about 5 inches long. The mounting strip is fixed to the studs with three 5 inch long bolts.
Tuesday, January 2, 2018
pantorouter is very cool machine, but I find the template is difficult to adjust. And since I want to try different things, that means I need to make a lot of different template every time.
Ever since I build my CNC machine, I wanted to convert the pantorouter to CNC one. But since the pantorouter, material wise, didn't cost much, it makes sense to make a new one for the CNC version.
I spend some time drawing up the CAD model, and tweaking the design. I decided to make it out of metal, mostly from t-slot aluminum. They are strong, easy to cut and versatile to mount.
The design is a mix of CRP's linear rail and Pantorouter. Since I have a CNC, and some of the parts needs to be custom made anyway, I want to make most parts myself. Here're highlights of the design:
- the linear rail is roller skate bearing on cold rolled steel.
- all axis will use ACME screw and nuts, that means the I need to take out the back lash. My big CNC use have ACME screw/nut setup on the Z axis, and because the whole Z assembly always push down on the nut, back lash was never a problem. But on this machine, some axis are horizontal, so take out back lash is a must.
- due Y stepper setup. It would be easier to synchronize and since the whole gantry is going to push weight a lot, have two stepper drive it means I can use the same motor.
I've never cut aluminum thicker than 1/4 before, so the work table needs to be improved. my existing table use 1/4 t-track screwed down on 3/4 MDF with #6 screw. It can't take too much hold down power, the #6 screw is easily pulled out. So I replaced the table with 3x1 aluminum t-track extrusions.
And before cutting metal piece, I cut them out on plywood, to make sure the geometry works. Mahcining out some of the piece is complicated, the bearing block, for example, need 7 tool changes and remount the piece once. On the initial prototypes, there were obvious backlashes. After tightening the belt one X and Y, it dropped to 3-5 thou, which is acceptable.
As I don't have much experience cutting metal, I tested the cutting parameter on some scrap piece, starting with 1/10 of the amount I used to cut wood, and gradually increase, until I'm satisfied with the quality and speed. The final parameters are:
- DOC: 0.05 inch
- speed: 15 IPM
- spindle speed: 12000 RPM
Some of the deep holes, 2 inch deep, are drilled, not milled, since I don't have bit with that long flute. My spindle is high speed spindle, not much torque on low RPM, so I have to drill with at least 8000 RPM, that generates a lot of heat. I sprayed the cutting area with WD40 every couple seconds to keep it lubricated and cool. It worked out ok.
Even though you see it in CAD model that everything should fit together, but when you put everthing together the first time, and they fit perfectly, it still surprise you.
The machine is bigger than I imaged, and pretty heavy. To help the assembly, I get a cheap harbor freight lifting table, and modified it to a height adjustable assembly table. I made a torsion box top and added a foot operate table lowering lever.
On my first CNC, I used Gecko G540 for drivers, it works great, but it's not the most cost effective way. For this build I want to try 4 stepper driver + PP break out board. The first stepper driver I tried is some implementation based on TB6600. On paper it should have at least 2.5A continues peak power output, but in reality, it's less than 1.5A, and the idle current is only 30%. This means the holding power is only 30%. Worse yet, 3 out of 5 driver died within the first 2 hour of testing. Then I read some post and did some research, and purchased DM542T. It was much better, the driver stayed cool, and almost silent operation, adjustable current. It was actually better than the G540. Wiring it up was straightforward, and since I had some experience with linuxCNC, setting it up takes no time. For the enclosure of all electronics, I up-cycled some old power supply box.
I want to put the machine on the cart for my pantorouter, including monitor and keyboard. So I made a monitor stand for it. It rotates about a metal pipe, which is fixed to the side of the cart.
The machine does look much bigger than it's little brother.
Here's first cut on a custom mortise and tenon.
Some design improvement:
- The spindle is mounted on the aluminum extrusion directly, this is to reduce the distance between the rail and the center of the spindle, so there's less deflection and save some vertical space.
- All major 90 degree joint have aluminum brace, especially the Y pillar and the base. I use two 12x12x1/4 aluminum to add strength.
- I have 4 set screw to puch against the thrust bearing to create pre-load, this take out any back lashes from the thrust bearing.
- I use 3x3 beam for the X axis, this provided extra stiffness for the X-Z assembly
Emma loves doing crafts, and tape if a tool she use a lot. I always want to make a cute tape holder for her. I prototyped with some ...
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