Introduction: Micro Lathe Upgrade
If you peruse this type of thing, you have probably seen a number and variety of small "mini" (more like Micro) lathes and machine tools for sale on eBay and websites like Banggood. They are sold under brand names such as Raitool, The One Tool or Zhouyu. They basically all use the same headstock and motor but some versions are built mostly from aluminum (cross slides and handwheels) while others go the injection molded plastic route. I bought an aluminum version, seen above, from an eBay vendor for ~$100.
The first two short comings you notice is that they are wildly under powered and that there is very little usable swing. Other than that, the construction is not that bad. You won't be boring out engine blocks with these, but with a couple of mods, you can make a passable little hobbyist metal lathe.
In this Instructable I will lead you thru upgrading the spindle motor and building some risers for the headstock, tailstock and toolholder. Most of the mods are 3D printed in ABS. Two parts will be required from eBay, Amazon, Banggood, Aliexpress or an equivalent site (Google "3420 DC Motor"):
The "3420" or "marshmallow" motors run anywhere from $14 to $25 depending on the deal you can get. They are permanent magnet with ball bearings and are quite nice torquey motors. They come in 12V or 24V, with typical ratings of 12V-3000RPM and 24V-6000RPM.
For some other parts that will fit this lathe:
Step 1: Step 1: the Pitiful Motor
When you remove the belt cover (one Philips head screw) you will see the two pulleys that make up the headstock belt drive train. The top, tiny pulley is press fit to a tiny (toy) motor mounted in a plastic enclosure above the headstock. The motor enclosure is mounted to the headstock and the headstock to the lathe bed with an interesting two piece screw wedge (more on this later). When you disassemble the motor mount enclosure (3 screws), you will end up with the motor shown to the right in the second photo. We are going to replace that small fry with the motor to its left: a motor known on eBay and Banggood as a Marshmallow motor or a 3420 motor. This is a hefty and powerful (30W!) DC brush, ball-bearing motor. For $14-$25, it is quite the bargain!
So how do we use this motor on the lathe headstock? I have attached an STL file of a part I designed using OnShape. I printed this at 100% infill, flat side down with ABS on a Qidi printer. It took a little over two hours on my printer.
Note that the screws used to attach this mount to the headstock are the same as are used to attach the bearing cover plate: wood or sheet metal screws. (See the illustration above.) I used 2 inch long, flat head #6 screws. Remove the four original screws and attach the motor mount as shown. I used a little candle wax on the screw threads before I screwed them in, to help with the thread forming and to prevent galling. Alternately, you could (carefully!) tap the holes in the back side of the headstock to be 6-32 and use 6-32 flat head machine screws. The wax lubricated wood or sheet metal screws work just fine.
In my experience these motors run cool for extended periods of time, so no worries that the ABS mount will soften.
NOTE: I HAVE ADDED TWO REGENS OF THE MOTOR MOUNT STL BECAUSE THERE HAVE BEEN PROBLEMS THAT SOME READERS HAVE ENCOUNTERED IN LOADING THE ORIGINAL FILE INTO THEIR SLICERS. ONE IS LABELLED MM AND THE OTHER IS LABELED INCH.
Step 2: Step 2: Add the New Motor to the Mount
Mount the pulley on the motor shaft. Use the existing hole thru the shaft to locate the set screw in the pulley. Tighten both set screws in the pulley.
The motor attaches to the mount using the two M4 x 0.7 screws that stick out from the motor face. These are nearly an 8-32 thread but not quite. I did have an M4 tap so I just retapped some 8-32 stainless nuts to metric.
But if you do not have small size metric taps, you will need to find the M4 nuts. #6 or #8 washers can be used to thermally insulate the motor from the mount. Both Lowes and Home Depot carry M4 nuts in their metric hardware drawers.
Slip the motor screws into the M4 size hole and slot on the mount. Add another washer and nut to the other side of both screws.
And the mount was designed so that the original lathe belt is still used! Note that the mount was designed for adjustable tensioning of the belt. Finger tension the motor and then tighten the nuts on the M4 screws. Amazon carries a replacement belt:
One other thing you may want to try, which should help reduce motor vibration would be to use rubber washers between the motor and the mount. So far this has not been a major problem on my lathe as the combination of the ABS mount and the Z031 gear belt run decently smooth.
Step 3: Step 3: Making the Offset Blocks
A 24mm tall offset block was designed in OnShape to be printed and provide a boost for both the headstock and tailstock. Attached is the STL you can print. Make a copy in your slicer program so that you can print two at once. Again, I used ABS at 100% infill. Two of these take six plus hours to print.
Note these blocks clamp on both sides with the existing wedge clamp. Extra wedge clamps are available from Banggood:
Another approach may be just to purchase a riser block:
An addition you may want to add to the offset headstock is another side clamping plate so the headstock is clamped from both sides. Here is one from Aliexpress:
Step 4: Step 4. Building Wedges
Attaching the offset blocks to both the headstock and tailstock require one more wedge clamp than we have. Again Onshape was used for the initial design. I believe the screws I used were 6-32 by 2 inch long with a standard nut (I used brass.) As mentioned in the previous section you can also just purchase these wedges at Banggood for a reasonable cost.
Step 5: Step 5: Prepping the Motor
Get out your soldering iron and desolder the cable from the original motor. We will solder this to the new motor.
So take the cable off the old motor. Put some heatshrink tubing (1/8 inch diameter) on the motor cable to use to insulate after we solder the wires on. Solder the wires from the 3420 motor to the wires to the original connector. There were not any markers on the connector wire to orient the the motor red and black wires to. At this stage, plug in the motor to the power supply and make sure the spindle on the headstock turns in the proper direction. If it doesn't, unsolder and reverse the wires.
The power supply that came with my lathe seems adequate to drive the new motor.
There is an adjustable power supply upgrade that is inexpensive and allows you to run the lathe motor at different speeds.
Of course, like the motor, you will have to swap the connector from the original power supply to the new adjustable power. The instructions above should suffice for this also.
Step 6: Step 6: Mount the Lathe
Any lathe is pretty useless without stability to use it. If your lathe came with a mounting board and you can figure out the mounting scheme, by all means use it.
I found that by mounting my lathe to a plastic cutting board (Walmart, Sam's Club, Target) and then clamping the cutting board to whatever desk or table I was working at, you could actually do useful things. Note that based on the thickness of the cutting board you purchase, you will need to adjust your mounting screw length. I used flathead screws and countersunk the bottom of the cutting board. I also used these:
For the mounting to the bottom of the lathe bed.
One of the side benefits of using a cutting board is that it makes it easy to pick up the lathe to brush it off into a garbage can for clean up.
Step 7: Step 7: Add an Adjustable Tool Post
One of the last things is to add an adjustable quick change tool post (QCTP) to the lathe. These are available pretty cheap, I got mine for less than $30 with a boring bar. Here are some examples:
To mount the QCTP on the microlathe, I used a 5/16 hex head bolt and nut to mount it to the cross slide. (I do not have the lathe with me at the moment to check dimensions. So perhaps wait for the next revision in two weeks...) I ended up grinding the head of the bolt to match the tapered groove of the cross slide. Again, I will post photos the next time I am where the lathe is. You will need to make a riser block to put under the QCTP to get the tool to the right level versus the spindle center. As you can see from the photos I cut some 0.25 thick aluminum to the rough outline of the QCTP base and drilled a 5/16 hole thru the center. This part could probably be 3D printed but the aluminum adds some nice stability.
There are some other things you may want, including a drill chuck for the tailstock:
I will try to add to this as I have more time, filling in some of the gaps and making new accessories. Things like indexing heads, using calipers as digital travel indicators or improvements to the accuracy. One of things I did run across was this CNC version... just adding the photo as food for thought.
Of course, you could just buy a used Unimat or Sherline or Taig or even a 7 inch Chinese minilathe. But if you already have one of these Zhouyu machines, a better motor, some risers and a QCTP will really allow you to turn parts from brass, aluminum, engineering plastics, wood, etc. And sometimes all you need is a micro lathe.