Z rail's eccentric nut keeps coming loose

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sawdust_tycoon
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Joined: Wed Feb 20, 2019 3:16 pm

Z rail's eccentric nut keeps coming loose

Post by sawdust_tycoon » Sat Mar 16, 2019 10:27 pm

I have been attempting some roughing with a 1/4" end bit on a rather large carve of MDF. On the last 3 attempts, after carving correctly for a while, the bit then travels beyond the board into negative X-axis territory (or once into extreme positive X-axis territory), where it should not be carving, ruining the piece. The erroneous travel is 6 to 8 inches from where the bit should be carving. I've checked my CAM using a simulator application and even manually inspected the G-Code. This problem is not the software. One obvious problem is that the lower eccentric nut on the Z plate has become loose and the lower wheel is no longer gripping the z rail. Each time, I re-tightened the eccentric nut (including the bolt), following the directions on Carbides website. I have 2 questions: (1) would it be a mistake to try to apply a tread-locking glue to threads of the bolt that couples with this eccentric nut, before rotating the nut for the appropriate cam tensioning? (2) Does anyone have any explanations as to why the X-axis movement suddenly becomes way off, as described. I can't understand why wobbly wheels on the Z rails causes the spindle to wander along the X axis.

WillAdams
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Re: Z rail's eccentric nut keeps coming loose

Post by WillAdams » Sun Mar 17, 2019 2:22 pm

1 - threadlock is the usual suggestion if a properly torqued nut and bolt won't hold --- please note for the eccentric nuts that once the nut/bolt are tensioned you have to turn the assembly in unison

2 - usually such issues are mechanical: https://wiki.shapeoko.com/index.php/FAQ#Mechanical
Shapeoko 3XL #0006 w/Makita RT0701 Router w/0.125″ and ¼″ Elaire precision collets
Nomad 883 Pro #596 (bamboo)

sawdust_tycoon
Posts: 3
Joined: Wed Feb 20, 2019 3:16 pm

Re: Z rail's eccentric nut keeps coming loose

Post by sawdust_tycoon » Wed Mar 27, 2019 8:10 pm

I read everything in Will's link to mechanical problems, and all parts in my machine seem to be properly installed, tensioned, cleaned, etc. I believe my Z-axis issue with the eccentric nut has been resolved by simply using blue, medium threadlock glue. However, on yet another attempt to carve a large bas-relief on my Shapeoko 3xxl (my third), the same problem destroyed my workpiece, namely the machine appears to have lost track of the X coordinates and began machining far to the right, about half on and half off the workpiece. As stated previously, I believe any software (CAM/G-code) problem has been properly ruled out. In hopes that someone may have experienced the same phenomena and found a solution, I a re-posting with more specific details about my situation.

1) the malfunction occurs during the rough cut stage, using G-Code produced by Meshcam. On my most recent attempt, I changed feeds and speeds to avoid the possibility that I was pushing the bit too fast. Specs on the most recent attempt: 1/4-inch sharp end bit, with 2 flutes 1 1/2-inches long (the entire length of the bit is around 3 inches); 70 inches per minute; stepover = .04 inches; depth per pass = 1/4 inch; 3D roughing rather than parallel; tolerance = .002 inches) In other words, the same problem occurred on various attempts with different feeds-speeds and different lines of G-Code cutting the same pattern.

2) here is where I suspect my problem originates: I am cutting standard MDF that is 17x25 inches x 1.5 inches thick. This thickness is attributable to 2 MDF boards (each 3/4 inches) being glued together with minimal wood glue, allowed to dry for at least 24 hours before any milling. Obviously, this roughing stage generates horrible quantities of very fine sawdust. Unfortunately, I have yet to get around to installing any dust sucking mechanism (such as the Suckit). Instead, to compensate I have been pausing the cutting about every 20 minutes and manually vacuuming the work area, giving special attention to the rails, wheels, and gears of all 3 axis, trying to reduce their exposure to the fine sawdust.

3) between my 2nd and 3rd failed attempts to cut this larger project, I successfully milled a 3/4-inch thick MDF workpiece with a different pattern without incident. It seems the machine is working fine, but can't handle the 1 1/2 inch deep project, even with the depth per pass set at just 1/4". During all three failures, the mishap occurred about an hour into the cutting, when the total cut depth was between 3/4 and 1 inch deep (i.e., during the third or fourth pass over the same path).

4) when I discovered that the bit had wandered off the workpiece yet again on my most recent try, I had no choice but to terminate the cut. My inspection of the machine revealed no loose wheels, wobbly parts, or other obvious issues.

My question: Does anyone know what is occurring to cause the machine to wander off the workpiece in the X axis direction? Too much sawdust? Wrong bit?

WillAdams
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Location: Pennsylvania --- south of the Turnpike, East of US-15
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Re: Z rail's eccentric nut keeps coming loose

Post by WillAdams » Sat Mar 30, 2019 1:22 pm

Usually it's a matter of getting the nuts properly tensioned --- once you get the eccentric nut tightened make sure that you turn it and the bolt in unison, and only clockwise (from the nut side) so as to not loosen it.

Some folks will use threadlock.
Shapeoko 3XL #0006 w/Makita RT0701 Router w/0.125″ and ¼″ Elaire precision collets
Nomad 883 Pro #596 (bamboo)

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