Machining

Moving Up, Z-Axis Comes to Life

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My 3D prints wouldn’t be very 3D if I didn’t get some z-axis control so I dove into the most complicated fabrication this project had (not that it’s all that complicated). First up I started turning some diameters on my leadscrew. It’s an 11/32″-10, 3 start leadscrew (I think) that I picked up for free as a sample. The Shapeoko style ACME screw probably would have worked just as well, but despite my overblown budget for tools, I am trying to make this printer for cheap.

Lead Screw

First step, I made some shims of aluminum foil, folded four layers thick, to act as a bit of a cushion between the lathe chuck jaws and the leadscrew. I previously tested the hardness of the leadscrew by scratching it with a steel file so I knew it was soft enough to cut. Without making some actual soft-jaws for the chuck (which you really should have a 4-jaw chuck for anyway) I figured the aluminum foil might help a bit.

Using a carbide bit, I turned the 8mm diameters for the 608 skate bearings to slide on and the 1/4″ diameter for a retaining nut. The 8mm diameter was just slightly smaller than the original leadscrew OD, but there seems to be enough of a step to retain the bearing. After I pulled the leadscrew off I cleaned up the ends of the threads by the end of the 8mm diameter so the leadnut would slide on nice without cutting into it. (The plastic leadnut can’t take too much rough play.)

Next I used a 1/4″-28 threading die to put some threads on one end of the leadscrew. I clamped the leadscrew back in the lathe to hold it steady. It was a bit tricky to get things started, because the material is still fairly hard. After the threads were cut as far as they could go, I turned on the lathe and used a Dremel cutoff wheel to add an undercut at the end of the threads by hand. (I didn’t have a small grooving tool made up.)

Bearing Plates

Next up was the bearing plates. I started with some aluminum plate and cut them to rough length on the bandsaw.

The first piece that was cut had a nice square end to start, but the second had two bandsaw-cut ends. I cleaned up one edge in the mill, then I thought I would stack both the upper and lower plates and clamp them and mill them at the same time. This was NOT a good idea, likely because I was being lazy and didn’t try to give the pieces a nice matching machined edge in the clamping direction; relying on the stock width. The longer one ended up sliding around while I was milling so I fell back to just clamping one at a time and measuring. You can see in the first picture below that I’m lifting my small vise off the table using some parallels turned on their sides and using a third, taller one to adjust for square.

Since both plates would be needing a nice 22mm hole for the bearing and I didn’t have a 22mm reamer or the appropriate drill sizes I knew I would be breaking out my rotary table. This meant I was going to be spending some setup time and I wanted to get both plates done in one go. I modified the bottom plate design from what I originally had so it was exactly the same (minus holes for mounting the motor). I clamped both plates (now of equal length) in the vise again and used a small army of drill bits and reamers to get all the other holes machined. I also tapped some holes for the #8-32 screws I was using to retain the bearings and milled the slots.

After the initial machining everything was done except for the 22mm bearing hole. You can see that on the lower bearing plate (right) I didn’t drill the side holes completely for the motor mount. I didn’t need these holes in the bottom plate (though I left the top one anyway), and my vise parallels were right below the bottom plate in those areas so I couldn’t drill through anyway.

Now it was set up the rotary table. It took a few tries to figure out what I was doing, but finally I got it. I used a MT2 taper in the center of the rotary table and carefully moved the mill table so that the taper lined up with an empty endmill holder in the mill head. This got me close enough to indicate off. and finish the job. Luckily I had a dial test indicator holder that fit in that same endmill holder (3/8″). I pulled out the MT2 taper from the rotary table and put the indicator in, adjusting the mill table as needed.

Now that the rotary table was centered on the mill head the next step was to center the work on the rotary table. I realized that I should not have tried to open up the bearing hole as large as possible before putting it on the rotary table. This center hole was too large for me to use my center-finder now so I ended up just putting in the reamer I last used to open that hole. This got things centered pretty well, then I had to indicate off the surface again. To prevent the two plates from separating I put some screws through the conveniently placed tapped holes.

They came out nice and shinny:

Leadnut Bracket

I used my paper template method to layout hole locations on the leadnut bracket as well. Here I needed to layout holes in more than one plane. I found out that a Tap-Ease stick did a pretty good job at sticking the templates down. The waxy stuff would hold the paper to the aluminum, but still allow me to slide it and adjust it to the right spot if needed.

I just used a hand drill and bench vise for the two M5 holes. I learned from my mistake this time and made sure I kept the large hole hole on the other side…small…before I started milling it on my rotary table. This allowed me to use a center in the punched mark. Before clamping I used a few small vise parallels under the aluminum angle’s overhang to space it up from the vise a bit. This isn’t an awfully rigid way to clamp the part for this milling operation, but chatter didn’t matter much for this hole. It just had to be reasonably close to the diameter of the leadnut.

Here’s the final bracket. I messed up the first time I tried to make it because I drilled the two M5 holes as clearance holes instead of tapped. While trying to assemble the z-axis I couldn’t figure out how I planned to fit the M5 nuts in place. That was because I didn’t. Oh well, the second time through was much faster and I hadn’t taken apart my milling setup yet.

Next I needed to trim down the lead nut so it wouldn’t interfere with the x-axis motor. The disk sander made quick work of it. I started freehand then to get the angle right I mounted the leadnut to the bracket and used the edge of the bracket as a visual guide.

The assembly starts by attaching the top bearing plate to the z-axis MakerSlide and putting the leadscrew with bearing and coupling in place. (The leadnut isn’t trimmed yet because I forgot the first time I assembled it.) The motor attaches through some standoffs with M3x40 screws. The leadnut bracket is installed on the XZ shuttle and the z-axis assembly drops in from above.

Here’s the z-axis assembled:

I checked the flexibility again and wasn’t happy with things. It also seemed like the z MakerSlide was at a bit of an angle. Looking at the bottom of the XZ shuttle I noticed that the v-wheels were a bit too closely spaced. This is due to the shim washers being thinner than the bearing on the top side. I pulled things appart and replaced five of the shim washers with a bearing. The bearing was actually cheaper than the same size spacer from McMaster-Carr, and it was on hand.

I’m still not confident that both v-wheels are in the right places, but it feels better than it was. Next I checked the square of the z-axis. I wasn’t happy here either. It looked like the top of the extrusion was tipped a bit to the back of the machine. (toward the right of the image) I ended up disassembling the y-axis carriages enough to loosen up the screws that held the x-axis extrusion tight. Then I shifted the screws within their clearance to straighten up the z-axis.

I also checked the x-axis MakerSlide for perpendicularity to the base of the y-axis carriages.

Design Hardening: Brackets

After re-assembling things, I was about to start checking the height setup of the upper frame in preparation of really doing some printing. I noticed a missed opportunity with the z-adjust brackets. I should have made them longer so they could also pick up the bottom of the y-axis MakerSlide extrusions and help keep the frame rigid. So I made them. I did have to sneak a bit of extra thought here too. Since the brackets would be mounting to the top surface of the MakerSlide they had to avoid the v-rail feature. This meant that the screws had to be offset a bit instead of centered in the bracket as before.
I also added some extra brackets to the lower frame and moved the double L brackets that hold the legs to the top frame from the front to below the x-axis extrusion.
Here’s a shot of the machine as it is.
Next it was time to give things a real test. I zip tied a pen to the z-axis and got ready to write a message. My less-than-optimal work process was to:
  1. Create a drawing in SolidWorks and export it as a dxf file.
  2. Import the dxf into a SolidWorks part file sketch.
  3. Use HSMWorks to create toolpaths for the 2D contouring operation.
  4. Export G-Code from HSMWorks.
  5. Use a Python script correct the G-Code for use with my firmware.
  6. Load the G-Code into PrintRun (Pronterface).
  7. Print!
You can download all the files shown in the video below on my Box.com folder here.

[youtube https://www.youtube.com/watch?v=VKxtmuk3qOg]

X-Axis: Bigger Stronger Faster

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I had trouble with my XZ Carriage flexing a bit too much for my liking. Before I tried extreme measures of adding a second piece of MakerSlide and another set of wheels, I figured I’d try some Open Rail first. I sponsored the Kickstarter project so I had some samples laying around. I cut two strips of this to the same size as my x-axis MakerSlide extrusion and bolted them on.

That’s a ton of T-nuts and M5 screw. I had to carefully line up all the T-nuts first then hold the Open Rail in place while I put in the screws. If I bumped it and shifted a T-nut away from a screw hold before I put a screw in, I would have to pull everything apart and start over. Luckily this didn’t happen.

I actually had more trouble with trying to use washers as spacers when reassembling my XZ carriage. I helped hold a stack together with a bit of tape. This worked pretty well. Also worth noting is that the orientation of these flat washers matter. These washers are stamped and have one rounded edge and one more sharp edge. The washers also curve just slightly away from the rounded edge. If you stack them so that they are all pointing in the same direction they have a smaller stack height than if you alternate them. I alternated my washers and that got me within about half a mm of where I wanted them.

You can see the alternating washers in the spacer set closest to the camera below. After struggling with that for about 3 minutes you can see my improved assembly method on the far one. You can also see the extra set of V-wheels for the new V-rail.

This modification did add quite a lot of stiffness to the XZ carriage. The z-axis does not flex nearly as much. Now the weak point seems to be a combination of two things:

  1. The carriage plate closest to the z-axis bends in the middle away from the screws. This is bending within the carriage plate itself. Modifications such as these reinforcing blocks shown about halfway down on this forum topic should also help me. (But I will have trouble trying to fit things around my Z Leadscrew.
  2. The z-axis V-wheel bearings are shifting on their races in the same way the x-axis ones did. I’m going to live with this problem for now. Things may improve when the leadscrew is installed.

The architecture for the x-axis on my machine didn’t lend itself to having the same style belt clamps as the x-axis did. I originally wanted to run the belts close to the extrusion as shown in the picture above. I tried putting some eye-bolts on the Y Carriage plate, but this would end up stealing over an inch of my usable x-axis travel on each side. The yellow cable tie shown was an attempt to make a larger radius for the belt to push it closer to the x-axis extrusion.

Next I thought of having some bracket that would push the eye bolt down from the top. This would make it much closer to the carriage plate, but it would be complicated and would not be as friendly to adjust. Also shown here is another attempt at increasing the wrap radius using some home electrical wire (single copper conductor).  I didn’t like this either.

I even tried making something out of Steel Tec parts, but this was a mess.

Next I started playing around with putting the eye bolts on the motor carriage plate instead. I had to route the belt upside down now, around some extra idler pulleys installed on the top corners of the X motor carriage plate. Although the time I put into machining the other idler pulleys so they would fit between the V-wheels would now be a waste (yes, btw, I machined those pulleys) and this setup doesn’t look quite as nice, I think this will be my best option.

I went back to CAD and some sketch paper and figured out what my bracket would have to look like. I needed to make the eye bolt a bit higher than the belt horizon because I needed room for the lock nut over top of the Y motor. If I made the bolt in line with the horizon, then the threads would be just above the motor and I couldn’t tighten it there. I thought about tapping the bracket, but that would mean I would have to remove the belt to turn the bolt and tighten it or else twist the belt. I printed a template and fabbed it up. Apparently I was paying too much attention to the vertical dimensions because my eye bolt mounting hole needed some post-design shifting in the horizontal to get it to line up with the belt. A rat tail file helped me out.

With both brackets completed I used some pieces of Steel Tec to make belt clamps. Those are #8 screws and nuts. This all turned out pretty well.

Ok, I wasn’t going to mention machining these idlers I didn’t end up using, but there are some interesting points. I did some sketching and found out that I could still fit a 9mm idler between my V-wheels when I doubled my rails. These little salvaged idlers are a machined tube with a 5x5x16mm bearing pressed in them. I knew I needed only enough room for 2 shim washers on either side of the bearing and I needed to make sure I machined it symmetrically. So, I put the two washers on the bearing and measured the depth to the outer edge. Then, on my lathe I faced the bearing end until I got to this depth.

Aloris BXA Quick Change on Smithy Granite

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First off: Quick info for anyone wanting to put an Aloris BXA toolpost holder on your Smithy Granite 1324 as quickly as possible with acceptable results should buy:
  • Aloris BXA holder (used, from eBay $230)
  • Smithy’s Chicago Bolt (new, $3.50)
  • Bronze Sleeve Bushing 1/2 x 5/8 x 1-1/8″
  • Flat Washer 9/16″
  • Aluminum or other thin foil for shimming

Here’s a look at all the parts needed.

I needed to make a slight detour from the 3D desktop fabrication project to put my lathe back together. Many months ago I bought an Aloris BXA quick change toolpost holder with some accessories on eBay for cheap. I needed to modify my lathe’s compound top slide to accept the larger bolt required for the larger toolpost holder.

After pulling the compound apart, I decided that I didn’t feel like trying to press out the existing shaft, then try to machine a  larger replacement and press it in, all while having a crippled lathe. So, I took the easy route and bought Smithy’s “Chicago Bolt” for $3.50 and figured out how to make it work.

This bolt diameter was still too small for the Aloris holder, but I bought a 1/2 x 5/8 x 1-1/8 bronze bushing to bridge the gap. Seeing as the original compond’s bolt was metric and the Aloris’ bore was English, I had to shim the shaft with some aluminum foil to get a tight fit. I also had to buy a 9/16″ flat washer to go under the Chicago Bolt at the top of the toolpost holder.

I re-assembled my compound (having taken it apart only to see if I wanted to replace the bolt, which I didn’t) and put everything back on my lathe. Quick and easy, the toolpost holder was on the compound. The bolt doesn’t supply the same clamping force as the massive 1/2″ Aloris one would, but I think on the whole things are better now. Maybe later I’ll modify the compound top slide, but for now I have a much easier way to adjust my cutting tools and swap between them.

It did seem to work pretty well for cutting. The height had plenty of adjustment both up and down. Even if it’s not as solid as it would be on a toolroom lathe, it’s certainly more solid than the original Smithy toolpost holder. And, this American-made steel was cheaper than a Chinese knock-off that I could buy new.