Archive for November, 2014

160-000

The plasma table CNC build has officially gone into fabrication phase. I have sacrificed multiple, sleepless, nights coming up with a game plan and determining the best sequence to build the table in. I have opted not to use any existing plans but instead engineer the table my way. I have a “big picture” in mind however all the details that are required to ensure the concept will be completed are yet to be determined.

Most tables are typically started by building the main frame. Since there are so many unknowns as far as gantry sizes and, more importantly, X,Y,Z travel dimensions I decided I am going to start from the center of the universe. In this case I am going to build the entire table around the tip of the plasma torch. This would mean I begin with my Z axis.

Since part of the construction of the Z-axis involves its ability to move along the X-axis I needed to come up with a linear movement system. X and Y axis linear movement methods are obviously nothing new. There are multiple systems that a proven to work well. My favorite has always been the Dualvee Bearing design coupled with the Vee rails. It takes care of both the radial and axial movements all in one shot and it does it in a fairly compact set up.

Since the whole point of fabricating the CNC is to actual “fabricate” I wanted to avoid purchasing as many components as possible and instead build the items. Coming up with a simple linear motion system that I had the skills, and equipment, to build was tough. I didn’t want to clutter up the sliders with aluminum plates housing 8 bearings each just to keep things smooth and straight.

After much thought I took some inspiration from the Vee bearing design and opted to build my own version but without the Vee. My version would incorporate a radius bearing that would ride along a 4140 alloy rod. If the design works it will control the radial and axial loads just like a Vee bearing does.

Weight of the table is a huge factor and this will become evident why later on in the build. So after a bit of experimenting I came up with a system to accurately machine radius bearings out of aluminum. Aluminum is not exactly the first choice for bearing material however in my case the loads are not massive plus the ability to anodize aluminum will certainly add a layer of hardness. The following outlines the first steps in building the CNC table by starting with the axis bearings.

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People often ask for the plans of some of the things I build. I figured I would start by posting the intricate CAD drawings of the bearing assemblies. Here is all the information for the world to see.

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Here are the bearings in various stages of production. They are all machined from 2″ 6061 round bar. The outer finished dimensions are .750″ wide with a 1.975″ diameter.

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The blank is hogged out with a 1″ drill bit on the lathe.

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Next it gets bored out down to the .001″ to accept the press fit bearing.

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A custom fabricated arbor was required in order to perform the external machining using both the lathe and the milling machine. Here is the steel arbor I built to secure the aluminum blanks.

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The outside diameter gets lathed down to 1.975″ before it gets moved over to the milling machine.

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The rotary table was set up vertically and the blank gets secured in order to allow a .125″ deep cut using a .675″ endmill.

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This is the final machined bearing housing before it goes into finishing stage.

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All the bearing housing then got a 2 stage polishing in order to smooth things up.

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Here is the set of 8 ready to move on to the anodizing phase.

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In order to remove all of the cutting oil and polishing compounds the housings recieve a soaking in a heated solution of SP degreaser.

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After getting a good scrubbing in hot soapy water the units get rigged for hanging in the sulphuric acid anodizing bath.

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Everything gets hung and electrically connected ready for a 2 hour soaking.

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The power supply gets connected to the bearing housings and 4.50 amps at 15 volts is dialed in for 120 minutes.

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These are what the housings look like after they are anodized. The shiney, polished, aluminum turns to a dull light grey color.

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All the housings then recieve a dip in the heated orange dye tank. To keep the color consistant they are all timed for an 8 minute bath.

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Here are the housings fresh out of the dye tank.

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Time to press the bearings in. In order not to damage the finish on the housings I machined a couple of bushings that I used to keep the housing, and bearing, straight and protected while they get mated using the vise.

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Finished product. I will be curious to know how well the anodized surfaces will stand up to wear and tear. Having them colored orange will make it easy to determine the extent of wear they are suffering from.