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 . . . → Read More: 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!

In this article, we will describe a small departure from the original plans in the use of a different strategy for the ball-bearing trucks that are used to roll the axes back and forth along their linear rails.  These trucks, like many other homebrew CNC trucks, are made of skateboard bearings bolted to the outside of aluminum right angle stock, which is available in any local big-box hardware store and can be cut and drilled with simple tools.  It’s a sturdy setup that gives a nice smooth motion.

Our beef with the original trucks is that they used undersized . . . → Read More: JRGO Style Trucks for the CNC Router]]>

This is the second article on a small CNC router build – go here for the first article to see where it all starts.

In this article, we will describe a small departure from the original plans in the use of a different strategy for the ball-bearing trucks that are used to roll the axes back and forth along their linear rails.  These trucks, like many other homebrew CNC trucks, are made of skateboard bearings bolted to the outside of aluminum right angle stock, which is available in any local big-box hardware store and can be cut and drilled with simple tools.  It’s a sturdy setup that gives a nice smooth motion.

Our beef with the original trucks is that they used undersized screws and oversized holes to hold the skateboard bearings.  This was done, presumably, to offer some adjustability as well as to allow the bearings to be mounted directly in line with each other.  That’s cool and all, but since there will always be some dead space between the inner bearing race (which is 5/16″) and the screw (which isn’t), it seems like one good whack to any of the axes could push the bearings off their alignment and leave the truck rattling a bit loose.  Even in the case of no impact, the axes will be loaded with the cutting force and seem like they could drift over time if the friction of the washer were the only thing holding the bearing race in place.

So, we decided to use JRGO-style trucks with offset bearings and full 5/16″ hardware.  This gives a sturdy setup with good tolerances with a minimal amount of work.  The biggest challenge was to determine the proper spacing to be used.  Since the 5/16″ bolt heads take up over half of the width of the inside of the aluminum angle, they cannot be mounted directly in line with each other and must be offset a bit to get the bolt heads to fit.  This seems like it should be no big deal, especially since the offset between the bearings is a fraction of the distance between the two bearings on one side.  For all intents and purposes, the bearings should be very resistant to twisting and torquing even with their slight offset.

Drill Template

We won’t say the actual lengths of aluminum angle used in the project, but for each of them the drill template is the same.  For the outsides (bearing closest to end), we drilled 5/8″ from the end and 9/16″ from the outer edge of the aluminum stock.  For the insides, it was 1 1/8″ from end and again 9/16″ from the outer edge.  This may seem confusing, but is really quite easy – measure one side (say the outside bearing), flip and use the same measurement on the opposite end.  Then turn the angle stock around and do the “inside” measurement.  Flip around again and mark the other inside point and you are done.  All our measurements and marking was done by hand using an adjustable combination square – an invaluable tool for this project.  These distances can be modified a bit, but these are the distances that will protect the bearing in case one of the axes crashes against the end of travel – the aluminum angle will hit before the bearing does.

The holes we will drill are 5/16″, and will need a small pilot hole first.  As with anytime you’re drilling aluminum, first punch a divot at your intended drill point with a nail or something to keep the drill bit from wandering.  Drill a small pilot hole, and then  swap to the 5/16″ drill bit and drill the final hole.  You should be able to fit the 5/16″ x 1″ hex bolts with relative ease.  But we’re not there yet – remove those bolts and get your router out, it’s time for some danger!

Drill Template

Figure 1 – Drill Template for our Variety of JRGO-Style Trucks

Bolt Mounting Slots

We’ll still need to mount these babies flush to a piece of wood, and the Solsylva method of filing and drilling right at the peak of the angle seems tricky.  Additionally, we’re going to use 5/16″ x 2″ hex bolts for a heavy duty mount so we will want to countersink the entire 1/2″ hex bolt head right into the angle aluminum itself.  And, we’re lazy…  So we took the easy way out and used a router with a 1/2″ bit (and a simple homemade jig) to mill a small channel right in the peak of the alumimum angle.  You do have a router, right?  You’re building a CNC router, aren’t you?  So go buy one if you don’t already have one!

The routered notches for the hex bolt heads are visible in the pic below.  This may look like a tricky cut, but is actually dead simple if you have some spare bits of wood that you can make a jig out of.  What you want to do is make a wooden channel about 1 3/8″ wide that the aluminum angle slides into, peak up.  Don’t use measurements, press fit it by hand to make sure the aluminum is held TIGHTLY!  Two strips of 1×2 nailed to a 2×4 worked great, and in our case came out perfectly flush with the peak of the aluminum angle when shimmed with a couple of washers.  At the end of the wooden channel, you’ll nail another piece of wood to act as a backstop to keep the aluminum from sliding any further.  One last chunk of 2×4 right outside of that to act as an alignment stop for the router, and you’re ready to go.

The idea is that you stuff a piece of aluminum angle down your wooden channel until it hits the 1×2 endstop.  Then, the router can slide laterally across the aluminum angle to mill out the groove, while being held tightly to the taller 2×4 chunk endstop.  This will cut a groove that is always the same distance (1 3/8″ to beginning of slot) from the end of the aluminum stock.  Stick in a piece of aluminum, mill a slot.  Pull out and stick in other end, mill other slot.  Easy as pie!  Chock up your router so the bit is sticking down about 3/16″ and with a slow sideways swipe your 1/2″ bit will route the perfect groove to hold the head of the hex bolt.  The points of the hex bolt will stick out sideways over the sides and give a nice strong surface to hold onto.

The router will mill mostly through solid aluminum, but will break through a small (1/16″) slot to the inside.  We’ll still need to use a drill to zip a 5/16″ hole in the slots for the bolt to fit down into.  Then you’re good to go.  For the first one, start shallow on the router depth and increase gradually while using a hex bolt head to see how deep flush is for your particular bolt.

We apologize that there are no pictures of the jig that was used to cut these slots, but rest assured it’s very simple.  Our target was to place the outer edge of the slot at about 1 3/8″ from the end so it would not interfere with the bolts holding.  Ours came out a little closer to the end than that, but still works fine.

A few assembled units.

Figure 2 – Completed Modified JRGO Trucks.  Note the Router-Milled Mounting Slots in the Angle’s Peak

Asm

The assembly is quite easy as well.  Stick a 5/16″ x 1″ hex bolt through each of the four mounting holes and put a nut on.  Then a washer, a 608ZZ skate bearing, a second washer, and a final nut.  Look to the picture above for a visual assembly example.  Since there is not enough clearance for locknuts, use threadlocker, superglue, or Derpina’s nail polish on both the first and second nuts to make sure they will not rotate loose.  And please, make sure the threadlocker on that first nut is dry before continuing assembly – Mike!@   In total, the hardware that you will need for these trucks is

• 6 pieces of Aluminum Angle Stock, cut to the proper sizes – About $5 for a 3′ length
• 24x 608ZZ Skate Bearings – About $20 for 50 or so from eBay, with shipping
• 24x 5/16″ x 1″ Hex Head Bolts – About $5
• 48x 5/16″ Hex Nuts – Another $6 for 100x
• 48x 5/16 Flat Washers – Another $6 for 50x
• 12x 5/16″ x 2″ Hex Bolts (for mounting the trucks to their respective wooden frames) – ??  Another couple bucks, probably.

Here’s a pic of the trucks sturdily mounted to the Y-axis table.  The flush-mounted hex bolt is clearly visible residing in the slots milled in the peak.  Perfect fit!

Trucks in place.

Figure 3 – Bottom of the Y-Table Showing the Trucks and Mounting Bolts

Please note that since you are messing around with the mounting hole spacing, you’ll need to measure and modify the hole spacing for the truck mounting holes.  And the mounting holes you drill will need to be 5/16″, of course.

The mounting is very sturdy – for the Y table shown above, a single washer and a single locknut are used to hold the trucks in place.  When mounting, don’t tighten too tightly initially.  FIRST make sure that the trucks are actually parallel to the edge of their mounting block, THEN tighten – the aluminum angle will dig grooves into the soft pine and lock their position in place for all eternity.  You want it to be right.

Until next time – good luck!