Saturday, August 27, 2016

New Profile Linear Rails for CNC Router

CNC Router Parts, the company which makes the parts kit for my router, came out with a new version of the system. The most significant change was using profiled linear rails and bearings. These happen to be the same bearing type used on the Onsrud routers at the Taubman College FABLab I'm used to using. So I decided to give these a try and ordered an upgrade kit. The parts shipped about one and a half weeks after ordering.

Disassembly

The first step was to strip the router down to the frame. It started here:

The current rail system looks like this. The rails are easiest to see at the top of the picture - hardened steel rails held at a 45 degree angle by brackets.

It was easy to disassemble and I was able to leave all the electronics intact except for simply disconnecting the motors. I removed the spoilboard and took the opportunity to re-tune the frame: making sure everything was square, level and aligned flat.

To be replaced are the hardened steel rails, the carriages for gantry, and the entire Z-axis assembly. I'll be reusing some of the plates as reinforcement for the frame and base. But I now have a LOT of spare parts!

Installation

With the frame cleared the new system could be installed. The rails are polished steel. They are fastened to the extrusions with T-nuts every few inches:

The linear bearings slide along the rails and are attached to other parts with four screws. The black plastic plate in the middle of the bearing keeps the ball bearings in place until the unit is slid onto the rail.  There is a grease fitting on one end and they periodically need to be re-filled.

The new rails get aligned parallel to the top using the provided fixture which keeps them 10mm from the top of the extrusion:

Once the rails are installed the new gantry supports are put in place. These are about 50% thicker than those they replace. This design seems more refined than what was there before. Attached to these supports are the two bearings which grip the rails.

New vertical extrusions are attached to the gantry supports.

The horizontal member of the gantry is now supported on 1" thick aluminum plates. These are secured through the plate into the end of the vertical extrusion. Then the gantry is secured from below, and using a face plate from behind. This system feels a lot more secure than what was used before. 

There are new linear rails on the gantry for the Y axis travel. 

Four linear bearings are attached to a plate which supports the Z axis. There's no detectable play in it whatsoever. There's a new Z axis assembly. It is better in that the motor no longer moves up and down. Instead just he plate the spindle is attached to moves. This means you don't need a cable carrier now. The Z axis assembly is on the table still to be installed.


Here's the Z axis and spindle installed:

I removed the spoilboard to check if the Y axis (across the front of the machine) was perfectly parallel to the front rail. If not I'd adjust the proximity sensors at the back to further tune the square. Things are looking good!

Final Tuning

With everything up and running it was time to check how accurate things are. The first step was to check for runout on the spindle. I put a 1/4" endmill in the spindle and ran it at 8,000 RPM. Then I moved a dial gage onto an area of the shank with no flutes to see if the needle moves. No motion I can see in the needle.

Next is to bore some holes into a sheet of melamine to test for square. If it's not square you can compensate by adjusting the number of steps per inch in the motor setup. I reset both X and Y to 2038 steps. Then milled a pattern of 3/8" holes which measure outside to outside at 8" square.

The holes are milled to 0.379". The dowel pins are 0.374". It's a tight fit. It measures 8.000" exactly in both directions. So far so good.

Next to check the diagonals. They each measure 11.159". Nice!
 


Lubrication

The bearings need to be lubricated every so often. I do so when I can see the bearings aren't laying down a small amount of grease when I jog the machine. As a reference, here's the video from CNC Router Parts on how to lubricate:


Summary

This new rail system has a much more solid feel. There is no play at all in any axis of motion. It's also much simpler to put together. This is a real step forward for their kits. I see they also improved the frame (no more corner brackets which can slip). And a much better cross brace setup for the base. CNCRouterParts is really moving things forward.

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