CNC Rotary Modifications and Portrait Sculpt

I've been further experimenting with the rotary axis on my router this week. The first goal was to produce a small head sculpture. The idea was to make a wood version of this sculpt I'd previously 3D printed. This is the result:

 

Milling a New Block - A Small Test

I started with a small block of Poplar, roughly 4" x 4" x 6". Poplar is really nice - huge trees so it's easy to get large, clear chunks of wood. I can get 16/4 (4" thick in the rough) near where I live. Poplar has a pleasing, subtle grain pattern. It's downside is the color (often a slight greenish cast with lighter sapwood). Staining can be used to make this more uniform and pleasing but applied to the raw wood it tends to be very blotchy. So sealing before staining is required.

Tools

The tools I used get divided into roughing (taking off large amounts of wood), finishing (taking the form from rough to smooth), and detail (drawing in fine detail). Roughing are at the top, finishing in the middle, and detail at the bottom. The lowest tool is an extender giving the tools a greater reach.

Roughing happens with tools called end mills. These tool cut on the side of the tool as well as the end. They have sharp corners.

Finishing happens with ball end tools. These cut a curved bottom trough. Lowering the step over of each successive cuts makes the surface smoother and smoother.

These are the end mills I use:

Large Roughing: 1/2" 4 Flute Extra Long High Speed Steel End Mill

Medium Roughing: 3/8" 4 Flute Extra Long High Speed Steel End Mill

Fine Finishing: 1/8" 4 Flute Long Ball End Mill

Pencil: 1/16" 3 Flute Ball Nose End Mill

I also use this extender: Tool Holder Extension

Stock Preparation

The block was jointed on two perpendicular faces to make one reference corner where all the measurements could be taken from. 

For the chuck of the head stock to grip the block you need a square chunk of material. These is easily done by gluing on small plywood blocks to the ends of the block. 

Roughing

Here are some photos of the cutting process - roughing passes on all four sides. This is done with a 3/8" bit. Depth is 1/4", step over is 1/4". I left 0.1" of stock above the finished surface on the roughing passes.

The final side doesn't have much wood left!

Finishing 

The next step is smoothing passes over each side. Because of limited length of the flutes on the cutters and tool reach it is programmed to only go so deep (and thus so far laterally on each side). I used a 1/8" ball end mill.

Continuing to rotate to each side the final form becomes clearer:

That tool is tapered 1 degree. Even that small amount is problematic in this application. I'll use straight tool next time.

Detail - Pencil Toolpath

The final pass, in this case done on just the face side, was a Pencil Toolpath. It automatically finds the crevices in the form and follows them. Here's the mesh surface in green with the tool path in cyan and the lead-ins and traverses in yellow.

Here's the sculpt without the pencil cut yet - you can see the lack of definition in the eyes, nose and mouth:

I cut it a few times, quickly adjusting the Z0.0 point, with each pass going 0.01" deeper, until I got it looking the way I wanted:

Also of note is the extra material around the neck. This can't be easily reached using the depth I had set so it has to be removed by hand with carving tools. Some has been carved away already on one side.

Trimming and Carving

The sculpt has to be cut free of the support material at the top and bottom. The bottom is really useful for clamping in a vise so that's the last thing to go. First step is to band saw off the top support leaving enough to carve down to the hair: 

To clean up the neck and hair doesn't require many tools. A V gouge, a U Gouge and a variety of flatter and wider gouges. 

Here's the clean up in progress:

Finishing

After some detail sanding using tools like those shown below I applied two coats of satin polyurethane.

A Larger Test

This next attempt was 10" long, 6.5" thick and 7.75" wide laminated from two pieces of 16/4 Basswood. Same 3D model just scaled up.

For the roughing of this block I used the 3/8" four-flute upshear endmill. I started with a step-down of 3/8" and a step-over of 1/4". That's very reasonable if the block was fixed to the table! Let's see how it went shall we?!

As before I glued on 2"x 2" plywood blocks to grip the stock:

Clamped in the head stock chuck it's ready to go.

It started fine but during a helix lead-in the upward pull of the endmill was too much for the rotary motor to hold - the block twisted and the bit gouged it. It was a high speed steel bit (which can handle more deflection than solid carbide) so no tool breakage. And the slash was into material that'd be removed anyway. So no harm done. Disappointing though ... the helix cut that caused it to give way wasn't even all the way towards the edge of the block. Hmmm...

I changed the roughing settings to a 1/4" step-down and 1/8" step-over. I also halved the plunge angle of the entry helix. This is a lot more gentle (and a lot slower!)

With that change the cutting went okay. This block is Basswood. Woodworkers know this cuts beautifully with gouges - a real pleasure. As you can see it's pretty fuzzy when cut on the endgrain with router cutters.

Here's the result after some quick sanding. It would need more to really refine it but I'm going to simply use this test to show my students the difference between roughing and finishing. Also the difference in surface quality between milling side grain and end grain.

Another problem with this large block... tool reach. In particular the length of the cutting edge of the 1/8" ball-end mill I was using. It has a 1" cutting length and a 3" overall length. Not adequate for the back of the head.

The tool extender shown in the image above can certainly help in some cases. But it's about 1" wide at the chuck. This width can be a problem when trying to reach down to near vertical surfaces to mill.

I have some tapered tools but there's an issue with the taper affecting the shape beyond the cutting tip.

More Holding Power

Sooooooo... I think the holding power of the motor that came with the rotary kit was quite disappointing! I decided to replace it. The one that came with the rotary kit has a holding torque of 3.5N/m. The one I replaced it with has 6.8N/m - nearly twice as much. Here's a picture comparing the two (new one installed, old above it). The new one is longer and heavier and much better made. It uses 7 amps rather than 4.8 so I had to change the DIP switches on the motor controller in the electronics cabinet.

The existing timing pulley worked fine on the new motor shaft. I just had to remove the key from the shaft before sliding it on and securing the set screws.

So far this feel much more solid. But more milling is required to really know.

Areas for Improvement

I want to have deeper holding blocks. 0.7" Baltic Birch plywood is not thick enough. The tools come too close to the head stock chuck. I had no collisions but it is nerve wracking. I'd also like to devise a way to re-register the block in the machine if I need to take it out for any reason.

I attended a workshop on Audoesk Fusion 360 software. I was impressed by the toolpath programming options available. I've been using Mastercam for years. But there's a lot to like about Fusion - and it's MUCH cheaper. I'm very interested in some of its toolpath options for quick roughing. They helix plunge the tool in much deeper and take repeated shallow, circular cuts. This is better than the parallel cuts I used because they engage more of the tool length. For finishing they have some nice toolpaths to deal with the change from mostly horizontal to mostly vertical surfaces. This is a problem with the parallel approach I used.

So that's where I'm headed next.

Read More

CNC Router Rotary Axis

This post documents adding a rotary axis to my CNC Router Parts router.

My router was a 3-axis machine. Adding a 4th rotary axis allows considerably more flexibility as the part to be machined can be rotated to expose different faces for cutting. I'd previously done some 4-axis router work at Stamps School of Art & Design - here's that post. I really wanted to add this capability to my router.

After exploring a few options - most of which were very expensive - I chose to go with an inexpensive kit from China. It was only $358 including shipping. I'd have to figure out how to get it hooked in to the electronics then build my own mount.

Rotary Axis Hardware

I ordered it and it shipped from Hong Kong the next day. It was ordered on Thursday June 30th and arrived in Michigan, USA on Tuesday July 5th. Not bad!

It includes a tail stock, a self-centering 4 jaw chuck, a Nema 34 stepper motor, and a 4:1 ratio belt drive. It includes both inside and outside jaws.

Electronics Hookup

To connect it to my setup I had to solder on a 4 pin XLR male connector.

Then using one of CNC Router Parts standard cables I could plug directly into my controller:

I had to set the dip switches in the electronics cabinet to match the 4.8 amps of the motor (the other motors I'm using are 7 amps). Then set the steps per revolution in Mach3 and it was ready to run.

Under Table Mount

I went through several iterations when designing how to mount the motor/chuck and tailstock. The requirements were:

• It had to be always hooked up - never removed from the machine. I wanted to be able to use it without much hassle. 
• It had to be moved out of the way when I wanted to 3-axis route using the entire 4'x4' bed. 
• It had to be rigid when locked in place. 
• And it obviously had to support a variety of part sizes including wide ones. 

I messed around with a lot of ideas. One was cantilevering the parts from one of the horizontal rails in the frame. But I thought this would be too much torque on the frame - the motor/chuck weighs 19 pounds.

In the end I decided to make it out of aluminum extrusions. I  choose components from 80 / 20 Inc. They have quite a few parts including sliding ones. And a great CAD library of their parts. So I could fully 3D model the design.

This is the final design, as seen from below the table. The existing frame is light blue. The new components are gray. The handles shown lock movable parts of the assembly.

Here's a front view of the frame in the lowered, beneath the table position, so 3-axis routing can happen over the full table:

Here's the frame raised up, slid up those verticals, ready to route. The center line of the axis is right at the top of the table. That's the lowest reach of the spindle:

Here's the tail stock moved forward for a smaller part. It slides along on the horizontal rail:

This configuration allows for a part that's 22" long and 14" in diameter.

After having 80/20 review the design they gave me a quote. The parts arrived at my house in just under two weeks.

Assembly

The parts were easy and enjoyable to put together. The linear bearings as 80/20 refers to them work quite well. Things slide smoothly and lock solidly,

Loosen the four corner yellow handles and you can lower the entire assembly beneath the table.

In the up position the centerline of the axis is right at the top of the frame which is close to the lower limit of the reach of the tool.

Chuck Setup

The 4th axis has a four jaw self-centering chuck which has to be assembled in a particular sequence. If this isn't followed the jaws will not all line up correctly. This process is outlined below:

Identify the numbered jaws and the numbered slots. The jaws are labelled on their side. The slot numbers are stamped into the back face of the slot (you'll need a flashlight to see them).

• Using the key, turn the scroll observing the number one slot until the outermost end of the scroll appears. You should see the edge of the thread just appearing to enter the slot. 
• Next turn it back a little just enough to allow the #1 jaw to enter the slot. 
• Then push the jaw down as far as it will go (which isn't very far). 
• Next, using the key turn the scroll so that it engages the first tooth of the jaw and starts to pull it inwards. You can give it a light tug to make sure it's engaged. 
• Rotate the chuck until the next slot is up then turn the scroll until the start of the thread appears in the next slot. 

Repeat the above with the #2 jaw and continue with jaws 3 and 4. This procedure ensures that all the jaws are synchronized with the scroll. Here you can see them coming together properly, and aligned with the point of the tail stock:

Alignment / Calibration

The rotary axis needs to be exactly aligned with the Y axis of the router. X needs to be zeroed over that axis. And the Z height needs to be zeroed on the centerline.

I bought an aluminum cylinder to use as a calibration tool. It was very straight and uniform in diameter (1.875").

As carefully as I could I marked the centerline, and used a punch to create a starter dent in the end.

Then I drilled a small hole which will accept the tail stock point.

This bar then gets chucked up between the centers. I put a dowel pin in the spindle and carefully jogged the axis to look for variations using a feeler gage. One end of the horizontal rail can be moved to level things out.

I had to tweak the tailstock location a teeeeeny bit in X to get it aligned. But this is really about as good as I can get it without a probing routine which touches off at multiple points on the bar and compensates for any axial deviation in software. If I can locate a Mach3 probing routine I'd certainly like to try it.

Toolpath Programming

There are several possibilities for how to program the cutting. A powerful, but very simple method is to simply rotate the part to a new face, then 3-axis mill it from that position.

I'm using my standard 3-axis router profile. I manually rotate the chuck using the MDI interface of Mach3. I just type in G90 G0 A90.0 and it rotates to an absolute rotation of 90 degrees. Then I run the toolpath from the side. Doing G90 G0 A-90.0 and it rotates to the other side. You can also rotate in a relative manner using code like G91 G0 A10. It's really easy, and of course keeps the simple 3-axis toolpath programming.

An alternative is to rotate the part as it is cutting much like a slow speed lathe.

Summary

I'm excited to finally have this running. First work will be some portrait sculptures much larger than I've been able to do in the past.

Here's a link to an early test of the system.

Read More

CNC Router Rotary Axis

This post documents adding a rotary axis to my CNC Router Parts router.

My router was a 3-axis machine. Adding a 4th rotary axis allows considerably more flexibility as the part to be machined can be rotated to expose different faces for cutting. I'd previously done some 4-axis router work at Stamps School of Art & Design - here's that post. I really wanted to add this capability to my router.

After exploring a few options - most of which were very expensive - I chose to go with an inexpensive kit from China. It was only $358 including shipping. I'd have to figure out how to get it hooked in to the electronics then build my own mount.

Rotary Axis Hardware

I ordered it and it shipped from Hong Kong the next day. It was ordered on Thursday June 30th and arrived in Michigan, USA on Tuesday July 5th. Not bad!

It includes a tail stock, a self-centering 4 jaw chuck, a Nema 34 stepper motor, and a 4:1 ratio belt drive. It includes both inside and outside jaws.

Electronics Hookup

To connect it to my setup I had to solder on a 4 pin XLR male connector.

Then using one of CNC Router Parts standard cables I could plug directly into my controller:

I had to set the dip switches in the electronics cabinet to match the 4.8 amps of the motor (the other motors I'm using are 7 amps). Then set the steps per revolution in Mach3 and it was ready to run.

Under Table Mount

I went through several iterations when designing how to mount the motor/chuck and tailstock. The requirements were:

• It had to be always hooked up - never removed from the machine. I wanted to be able to use it without much hassle. 
• It had to be moved out of the way when I wanted to 3-axis route using the entire 4'x4' bed. 
• It had to be rigid when locked in place. 
• And it obviously had to support a variety of part sizes including wide ones. 

I messed around with a lot of ideas. One was cantilevering the parts from one of the horizontal rails in the frame. But I thought this would be too much torque on the frame - the motor/chuck weighs 19 pounds.

In the end I decided to make it out of aluminum extrusions. I  choose components from 80 / 20 Inc. They have quite a few parts including sliding ones. And a great CAD library of their parts. So I could fully 3D model the design.

This is the final design, as seen from below the table. The existing frame is light blue. The new components are gray. The handles shown lock movable parts of the assembly.

Here's a front view of the frame in the lowered, beneath the table position, so 3-axis routing can happen over the full table:

Here's the frame raised up, slid up those verticals, ready to route. The center line of the axis is right at the top of the table. That's the lowest reach of the spindle:

Here's the tail stock moved forward for a smaller part. It slides along on the horizontal rail:

This configuration allows for a part that's 22" long and 14" in diameter.

After having 80/20 review the design they gave me a quote. The parts arrived at my house in just under two weeks.

Assembly

The parts were easy and enjoyable to put together. The linear bearings as 80/20 refers to them work quite well. Things slide smoothly and lock solidly,

Loosen the four corner yellow handles and you can lower the entire assembly beneath the table.

In the up position the centerline of the axis is right at the top of the frame which is close to the lower limit of the reach of the tool.

Chuck Setup

The 4th axis has a four jaw self-centering chuck which has to be assembled in a particular sequence. If this isn't followed the jaws will not all line up correctly. This process is outlined below:

Identify the numbered jaws and the numbered slots. The jaws are labelled on their side. The slot numbers are stamped into the back face of the slot (you'll need a flashlight to see them).

• Using the key, turn the scroll observing the number one slot until the outermost end of the scroll appears. You should see the edge of the thread just appearing to enter the slot. 
• Next turn it back a little just enough to allow the #1 jaw to enter the slot. 
• Then push the jaw down as far as it will go (which isn't very far). 
• Next, using the key turn the scroll so that it engages the first tooth of the jaw and starts to pull it inwards. You can give it a light tug to make sure it's engaged. 
• Rotate the chuck until the next slot is up then turn the scroll until the start of the thread appears in the next slot. 

Repeat the above with the #2 jaw and continue with jaws 3 and 4. This procedure ensures that all the jaws are synchronized with the scroll. Here you can see them coming together properly, and aligned with the point of the tail stock:

Alignment / Calibration

The rotary axis needs to be exactly aligned with the Y axis of the router. X needs to be zeroed over that axis. And the Z height needs to be zeroed on the centerline.

I bought an aluminum cylinder to use as a calibration tool. It was very straight and uniform in diameter (1.875").

As carefully as I could I marked the centerline, and used a punch to create a starter dent in the end.

Then I drilled a small hole which will accept the tail stock point.

This bar then gets chucked up between the centers. I put a dowel pin in the spindle and carefully jogged the axis to look for variations using a feeler gage. One end of the horizontal rail can be moved to level things out.

I had to tweak the tailstock location a teeeeeny bit in X to get it aligned. But this is really about as good as I can get it without a probing routine which touches off at multiple points on the bar and compensates for any axial deviation in software. If I can locate a Mach3 probing routine I'd certainly like to try it.

Toolpath Programming

There are several possibilities for how to program the cutting. A powerful, but very simple method is to simply rotate the part to a new face, then 3-axis mill it from that position.

I'm using my standard 3-axis router profile. I manually rotate the chuck using the MDI interface of Mach3. I just type in G90 G0 A90.0 and it rotates to an absolute rotation of 90 degrees. Then I run the toolpath from the side. Doing G90 G0 A-90.0 and it rotates to the other side. It's really easy, and of course keeps the simple 3-axis toolpath programming.

An alternative is to rotate the part as it is cutting much like a slow speed lathe.

Summary

I'm excited to finally have this running. First work will be some portrait sculptures much larger than I've been able to do in the past.

Read More