Saturday, August 27, 2016

New Profile Linear Rails for CNC Router

CNC Router Parts, the company which makes the parts kit for my router, came out with a new version of the system. The most significant change was using profiled linear rails and bearings. These happen to be the same bearing type used on the Onsrud routers at the Taubman College FABLab I'm used to using. So I decided to give these a try and ordered an upgrade kit. The parts shipped about one and a half weeks after ordering.


The first step was to strip the router down to the frame. It started here:

The current rail system looks like this. The rails are easiest to see at the top of the picture - hardened steel rails held at a 45 degree angle by brackets.

It was easy to disassemble and I was able to leave all the electronics intact except for simply disconnecting the motors. I removed the spoilboard and took the opportunity to re-tune the frame: making sure everything was square, level and aligned flat.

To be replaced are the hardened steel rails, the carriages for gantry, and the entire Z-axis assembly. I'll be reusing some of the plates as reinforcement for the frame and base. But I now have a LOT of spare parts!


With the frame cleared the new system could be installed. The rails are polished steel. They are fastened to the extrusions with T-nuts every few inches:

The linear bearings slide along the rails and are attached to other parts with four screws. The black plastic plate in the middle of the bearing keeps the ball bearings in place until the unit is slid onto the rail.  There is a grease fitting on one end and they periodically need to be re-filled.

The new rails get aligned parallel to the top using the provided fixture which keeps them 10mm from the top of the extrusion:

Once the rails are installed the new gantry supports are put in place. These are about 50% thicker than those they replace. This design seems more refined than what was there before. Attached to these supports are the two bearings which grip the rails.

New vertical extrusions are attached to the gantry supports.

The horizontal member of the gantry is now supported on 1" thick aluminum plates. These are secured through the plate into the end of the vertical extrusion. Then the gantry is secured from below, and using a face plate from behind. This system feels a lot more secure than what was used before. 

There are new linear rails on the gantry for the Y axis travel. 

Four linear bearings are attached to a plate which supports the Z axis. There's no detectable play in it whatsoever. There's a new Z axis assembly. It is better in that the motor no longer moves up and down. Instead just he plate the spindle is attached to moves. This means you don't need a cable carrier now. The Z axis assembly is on the table still to be installed.

Here's the Z axis and spindle installed:

I removed the spoilboard to check if the Y axis (across the front of the machine) was perfectly parallel to the front rail. If not I'd adjust the proximity sensors at the back to further tune the square. Things are looking good!

Final Tuning

With everything up and running it was time to check how accurate things are. The first step was to check for runout on the spindle. I put a 1/4" endmill in the spindle and ran it at 8,000 RPM. Then I moved a dial gage onto an area of the shank with no flutes to see if the needle moves. No motion I can see in the needle.

Next is to bore some holes into a sheet of melamine to test for square. If it's not square you can compensate by adjusting the number of steps per inch in the motor setup. I reset both X and Y to 2038 steps. Then milled a pattern of 3/8" holes which measure outside to outside at 8" square.

The holes are milled to 0.379". The dowel pins are 0.374". It's a tight fit. It measures 8.000" exactly in both directions. So far so good.

Next to check the diagonals. They each measure 11.159". Nice!


This new rail system has a much more solid feel. There is no play at all in any axis of motion. It's also much simpler to put together. This is a real step forward for their kits. I see they also improved the frame (no more corner brackets which can slip). And a much better cross brace setup for the base. CNCRouterParts is really moving things forward.

Wednesday, May 25, 2016

Slip Casting Update

This post is an update to my earlier post on slip casting 3D printed forms. It contains some of the new designs I'm working on and some pictures of the earlier finished pieces.

I've gotten some of the first pieces glazed and fired. The 3D print is on the left. The first glazed/fired sample is on the right. They shrink (about 11-12%) during the first firing. The top gets sanded flat making them smaller still.


The first step after firing is to rinse them off. The first firing leaves some residue and you want a clean surface for the glaze to adhere well.

The next stage is to put some wax on the bottom of the pieces so they don't get any glaze there which would stick them to the kiln shelf:

I've come to learn that it's better to put a "foot" on the form. In this way you can glaze all the way to the bottom of the visible form - the foot will hold it up keeping the glaze off the kiln shelf.

I really wanted to experiment with the glazing. At the Ann Arbor Art Center, this is how the glazes are stored - 5 gallon buckets with a brush to stir them up. The solids settle out and need to be mixed back in - it takes a few minutes for some that haven't been used in a while:

The vases get dipped using tongs. The vase in the rear has two dips which overlap. So there will be three different colors. The vase in the front is a solid color from a single dip. Once the glaze has dried it's easy to smooth out the bumps and drips you see. You can also fill in the areas where the tongs hit by just rubbing adjacent glaze into the holes.

Waxing, dipping, brushing, drizzling...

Here are some of the finished pieces:

New Designs

I've also been working on some new designs. The first ones are simple two part molds. This one is shown in the 3D printer at Taubman College Fab Lab.

Here's the printer (on the right):

This is going to be a mug. Quite large in anticipation of the shrinking.

Molds in progress... starting to add the clay to support the form. Note the extra clay around the lip of the cup. This allows the slip cast form to be higher than the final part. It can then be sanded down flat to get it to touch the points at the top of the design. That's necessary because the slip cast form is often uneven at the very top. This also seals the cup against the cottle board so no plaster can flow in.

Fully embedded in the clay. Need to seal the vertical edges and it's ready to pour.

First half done - very crisp detail:

Here's the first one just out of the mold. After it hardens a bit I need to fix the seams, sand the top edge down, and clean it up.

Here are a few of the originals and the new forms ready to bisque fire. I've found a card scraper is really good at shaving the dry clay into a flat plane - perfect for cleaning up the seams:

Here are three after glazing:

Here's another design - about 7.5" tall. It was printed at Shapeways. The Shapeways PLA prints are a little crisper than the ABS prints at Taubman. I actually prefer the ABS plastic for slip casting though. They are harder and clean up easier.

I added a foot after printing (a scrap piece of cherry glued on). Doing this after the printing is better because the print won't require support material at the bottom - the foot would require a large cantilever of the form outside the foot:

This one needs a three part mold. Here are the set-up for the three mold parts and the result:

So the form is buried more than half way - keeping about 120 degrees of the form exposed to the plaster:

Next another third of the form is blocked off. This is ready to pour:

Set up for the final pour which completes it:

The three resulting parts:

Some more pieces getting fixed up for bisque firing - the three piece mold ones take a fair amount of work:

And after bisque firing:

Belle Kogan Slip Cast Forms

I went to a small exhibition at the University of Michigan of the slip casting work of industrial designer Belle Kogan (1902-2000). Here are some pictures of the work. These pieces are from the collection of Bernard and Barbara Banet of Ann Arbor, Michigan.

I love the geometric aspect to some of these pieces, in particular her Prismatique line. These are all two or three piece molds. I find these pieces very inspiring.
Vase, 1962

Vase, 1962

Compote, 1962

Compote, 1962

Vase, 1938

Pitcher Vase, 1938

Vases, 1938

 Gladiolus Vase, 1952

Double Vase, 1953

I was so fond of Belle's work I had to pick one up for myself - off eBay. They are plentiful and cheap as they were mass produced.