Preventing the X-car from derailing

[fleinbach]

I believe everyone has experienced this before. The X-car derails after something happened that wasn't supposed to. It looks something like this………


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And you know the steps you will have to go through putting it back. First you have to disengage both X motors. Then you have to pick up the X-car and put it back on the rails. This is easiest with two people. All of this does not take an extremely long time to do but it is a nuisance. Well this week I finally found time to make my modification that I believe will alleviate this problem. I wanted a solution that would not prohibit the X-car from rising up in the air when it strikes something, putting unnecessary strain on the spindle motor.

My solution was to add stop blocks to the inside edge of the X-car. These blocks ride approximately 1/32 to 1/16th inch along the X-rail acting as a guide rail when the X-car jumps off the X-rail. They will not prohibit the Xcar from bouncing up, but they will stop any side motion thus allowing the V roller bearings to fall back onto the Xrail. And they will do this without putting any additional strain on the spindle motor.

It should work something like this……..



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[gerald_d]

Good idea!

How about adding a proxy switch that rides the x-car and looks at the rail - if the rail gets too far away it stops the motors.

[paco]

That's two VERY GREAT IDEAS!

[fleinbach]

Thanks Gerald,and Paco

That sounds like a good idea but under certain circumstances it might not work. Such as if you are jogging and hit something you're not supposed to the momentum could be sufficient to jump the rail even if the motors stopped. Also this fix is much less expensive. I used four pieces of quarter-inch aluminum 1" x 3" I had laying around. I had to mill them using the ShopBot about 1/16th of an inch to get the proper clearance. They did not have to be as long as is shown in the picture but it did allow for the top edge to lock its position using only one bolt for attachment. I used a 1/4-20 machine screw and threaded the aluminum block.


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[billp]

Frank,
What about using a piece of HDPE, or Delrin instead? This way even in the worst case scenario you wouldn't take a chance of marring the blue powder coating on the outside of the rails? By the way, this is a VERY good idea you have....
P.S. Since I don't always have the luxury of a second set of hands I have found that a 4 x 4 used as a "lever arm" works very easily to lift the Y carraige back onto the X rails...

[gerald_d]

Bill, it is tempting to make Delrin blocks over the rails and dispense with the rollers altogether.......

Frank, I didn't mean a switch to replace your idea, but in addition to your idea.

As I said somewhere else, we have probably jumped the y-car about 20 times in 4.5 years, but have never jumped an x-car. Probably because we don't have "hold-down" rollers for the y-car, so that lifts first. It must take a serious mistake to lift that huge gantry!

[fleinbach]

Thanks Bill, I meant to mention that there are several other materials that could be used since they are simply spacer blocks.

Believe it or not, I can actually put the carriage back on the rails by myself by releasing only the front motor spring. This is probably not the best thing to do since it does put some strain in places that it shouldn't.

First I release the spring. Then I moved the Y-carriage all the way to the back. Next is a bit tricky, I pick the side closest to me up just enough to clear the rail, I can then pick up the right side enough to get one wheel on the track. I am right-handed. Then I pick up the other side to get the second rear wheel on. After that the front just drops in place.

There are several reasons I have had the Xcar jumped the track. Some were user operator errors, others were maintenance issues and some were software related. At one point a few months ago it was jumping the track for no apparent reason about twice a week. When I was standing there watching it jog at 30 inches per second, totally clear of all obstructions, it just jumped off the rail. I researched and found that the rear X-motor pinion gear was loose. I surmise that after moving down the table the gear twisted one-way and locked enough to return about half way before it slipped in the other direction creating an isometric force that caused it to jump off the track.

[billp]

Hmmmm,
Maybe at one of this year's Camps we can solicit videos of " carraige jumping events". Something like the belt sander drag races in California...It could put a whole new meaning on the term "ramps"...
For those of you who have not stood at one end of an Alpha machine and had the operator launch the carraige at you running near full warp speed, it is VERY impressive....

[gerald_d]

Power tool drag races (http://www.teamkiss.com/powertool/powertooldragrace.html)

[larryk (Unregistered Guest)]

I tell ya , I been looking alot in to linear guides.This is one reason! but I would like to see if any one has try it ? It would make it so muck stiffer!

[gerald_d]

When things go wrong, something's got to give - what your choice of "give" point larryk?