CNC 8x12 8x14 Mini-Lathe X-Axis Prototype · Apr 4, 19:08

We’re nearing the home stretch on the 8x mini-lathe CNC conversion. In our previous articles, we showed the prototyping of the Z-axis and later tested it by hooking up a cordless drill to power the carriage.

We still need to make the motor spacers for the Z-axis, but that shouldn’t be too much of a task after this laborious X-axis motor plate. One of the reasons this plate took so long to make was because we decided to finally make a fixture plate. We also decided to get a bit fancy with the detail of the plate. There’s certainly little to no need for cut outs – weight savings isn’t important here.

After drawing up a quick 3D model of the plate and spacers using Autodesk Inventor (we also used Pro-Engineer and Solidwords for fun), we exported each STEP drawing into Mastercam and ran through numerous layouts and related toolpaths for drilling, contouring, and pocketing. This is where the fixture plate becomes invaluable. With a 4” wide plate and working within the constraints of the X2 mini-mill work envelope, we had to constantly re-index the workpiece to make specific operations.

Some time-saving tricks would have been to use “stand-offs” for the motor spacing, no cut-outs of the plate, and a saw to cut the slit for the bearing block hole.

We started with a piece of 4” wide 3/8” thick extruded aluminum bar. 1/2” would be fine too and probably preferred, but our stock was low, so in went the 3/8” bar. The first thing to do is to drill two (at least) 1/4” through holes for holding down the workpiece to the fixture plate:

Once mounted to the fixture plate (be sure to use expendable spacer blocks or you’ll dig into your nice plate!), a bunch of holes were pre-drilled – some for mounting, some in preparation for pocket cuts.

Next, it’s ornamental-cut time!

After making the cuts from that first position, we had to re-orient the workpiece for other cuts like this contour of an angled edge:

We even needed to flip the workpiece over for other contour cuts and the recessed countersunk pocket slots for the socket head cap screws:

The plate took over 5 re-positions.. an inevitable event when working with small work envelope machines. But in doing so you are forced to be creative!

We jumped ahead a bit. After boring out (actually, pocket cutting) the hole for the lathe’s x-axis bearing block housing, we test-fitted it.

After the edges were contoured (click here to view the video), we ended up with a plate sans motor bracket holes:

Now it’s time to pocket the countersunk recess slots so it’s off to the fixture plate we go:

Notice in the picture above that we again pre-drilled the holes. If our machine was more rigid, we may choose to skip this step. Even using centercutting end mills create some chatter and table movement when the end mill bites into the workpiece. This can cause sloppy pockets or other undesirable results.

Click on the following picture to see the pockets being machined (the quality of the videos in the remainder of the article are shot in 640×480 using a Sony CyberShot DSC-T3 with unlimited movie clip times as opposed to our Canon S210 Digital Elph which has a limited 15 second video time with only 320×240 resolution):

Once this was completed, we had one final step which was to bore and drill and tap a hole that when screwed down, tightens the bored hole clamp of the plate to the bearing block housing. This required that the vise be mounted on the fixture plate (another delay as we had to go and make new clamps to hold it down to the table. The hole drilling was uneventful save the additional clamping we had to use to prevent the top part of the clamp from wobbling about as we end milled and drilled.

With the plate out of the way, it was now time to remove the x-axis cross feed handle dial and measure it for the timing pulley that was to slip over it in its place. We chucked up a large enough timing pulley in the 8x and bored out the hole:

After the fit was ensured, we drilled and tapped two #6 holes in the pulley and created two corresponding recesses for the set screws to grip into for a positive lock. The pulley on the handle looks a little something like this:

With this out of the way, we now had to measure out the offset distance for the motor spacer blocks. We opted to make them out of solid billet instead of round rods – we think this looks better.

These were 1.5“x0.75” extrusions that were mounted to the fixture plate:

We probably could have fitted both on the plate to save some setup time, but since the depth of 1.5” required the use of a rather large (5/8” diameter) end mill, we wanted to have plenty of clearance for the lead ins and lead outs.

After 15 minutes of contouring at 0.040” DOC at 15-20IPM speeds and a spindle speed of 1500 or so, we ended up with this:

Here’s the pair:

Click on the picture below to see the video of the contours and chip break cycle cuts:

Now, with everything bolted, we found out that our preliminary dimensions were off a bit. This required that we use an idler “pulley” to take up some of the slack. This will get reworked so that the belt can be tensioned just with the slots. Take a look here with a NEMA 34 frame motor mounted:

The best part of all is to watch the cross slide move!

We again chucked a Sears Craftsman 19.2V cordless drill to the output shaft of the dual shaft Keling motor and had a go at moving the cross slide under power. Click on the picture to view the video:

That’s it for now. Our next and final article will show the CNC’d 8×12/14 mini-lathe running and making chips!

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