CNC Router Mod – Y Axis Crashbar

This article describes a quick and simple mod that can be made to the Solsylva 10×9 CNC Router to make the machine more durable against Axis crash.  This article is in the category CNC ROUTER, and is the next in the series of Beginnings of a CNC Build and JRGO Style Trucks for the CNC Router.

Today, we’re going to investigate and repair a minor annoyance in the Y-Axis.  At the extreme ends of travel, the roller bearings can make contact with the pipe straps used to hold the linear rails in place.  CRASH!  It’s not something you want to do, or usually intend to do, but axis crashes happen.  When they do, you really just want to minimize the possibility of damage to the machine.

Consider this: You load a gcode that has been scaled incorrectly, or forget to zero out your axes before clicking RUN.  The machine starts humming away happily, whirring over to it’s first point when WHAM!  It runs out of travel in one of the directions and runs the axis right into the side of the machine.  Ouch!  This situation is made worse by the fact that these initial movements are usually at very high speed (they call ‘em rapids for a reason) and therefore the force of the table and the inertia of it’s load is all directed to your poor bearing.  Double Ouch!!

This is not a great situation, as it will in the very least loosen and degrade your axis precision.  And at worst, dent or buckle the bearing race requiring you to tear down the machine and fix the bearing (oh, did you glue that table onto it’s axis?), or just live with a lumpy bearing that gives you one weird blip every inch and a half or so.

Here’s a closeup of the bearing touching the pipe strap.  And yes, even the stock trucks will do this, so it’s not a defect in the JRGO style trucks.  It’s mentioned in the assembly manual as something that might happen, but is essentially dismissed.  Maybe it isn’t that big of a deal, but to us it seems like something that should be addressed.

Fig 1 – Y Table at end of Travel, Showing Bearing Crash

You’re probably already thinking “Hey, why not just space those bearings back a bit to avoid crashing them?”  Which is a pretty good idea, except that in most cases there’s not a great deal of extra space left on this machine.  To add significant setback to the bearings would require setting back the mounting holes and everything else, and then your lateral torque resistance may suffer with such narrow mount spacing.

Another good idea would be to install some cool electronic endstops as is all the rage in the RepRap community.  Again, a great idea but one that adds cost and complexity – you need a controller that can properly interpret the endstop signals as well as to find some microswitches or something that operate reliably in the dusty, cruddy environment of CNC milling.

A cheap and easy alternative is to simply mount a little wooden bumper at the ends of the travel.  Then any crash is wood on wood and won’t affect the precision components of the axis – all you’ll end up with is just a cushy little dent in an ancillary piece of support.  No problem!

You dont’ want to make the bumper too thick, as it will remove distance from the total travel of that axis, but a quarter or eighth of an inch here or there isn’t going to break the bank.  The easiest way to do this is just to take a piece of the leftover 1×2 and cut it to 16″ long.  Actually, anything over about 6″ will work for the Y-Axis here, but a 16″ piece can span the entire length of the front plate and act as some additional support for keeping the main box square and tight.

Next, make a rip cut to chop that baby into two 1×1′s, and screw and glue one to each of the front and back plates, just under the rail supports.  You’ll probably also want to screw vertically into the rail supports to keep them held tight and avoid twisting from vertical loads.  Remember to use pilot holes, these thin boards will split easily!

Here’s a couple of pics to illustrate.  Please note that in the pictures, the bumper board is not yet screwed in.  Or sanded.  Or painted.

Fig 2 – A Tiny Little Bumper can Save your Trucks

That slight overhang is hidden by the actual overhang of the top of the rail supports.  If you don’t like it, then cut your bumper down to 15″.  Done deal.

Next we’ll take a closeup shot of the roller bearings, showing that they are NOT crashing.  Cool

Fig 3 – Roller Bearings No Longer Crash with Simple Bumper Installed

And that’s it for this short article.  We’ll probably install bumpers in the other axes as well, depending on their tendency to crash.  More to come later!

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