Jumping off rails

[GlenP]

I have read a post in the past about the gantry jumping off the rails. Does the new PRS model have the gantry fastened down or is it still held by gravity? Is this really any concern? I live in Canada and a cnc machine company is stating their machine is fastened down unlike the shopbot.

[Brady Watson]

Glen,
ShopBots don't simply 'jump off the rails'...the gantry can come off of the rails if there is an unmovable obstacle in it's way, just like everything else bound by the rules of physics. In 6yrs, mine has come off the rails exactly twice. One time it was because the machine outran me & my screwgun (in the middle of setting a square drive screw), which wedged itself under the gantry giving it no other place to go but up...and another with oddly shaped parts that were not held down properly, causing the material to get caught in the dust foot and rode it's way up a ramp caused by the material. BOTH cases, MY fault & a result of being impatient or not hitting the e-stop fast enough.

By 'coming off of the rails', the vee bearings just come off of the track. THE GANTRY DOES NOT WIND UP ON THE FLOOR!!! You just lift the gantry a 1/2" and pop it back on. The pinion gears attached to the motors keep the tool on the rails, but can safely break away in the event that you are the unmovable object.

-B

[harryball]

Mine has come off once as I was a newbie and it was my fault. I personally find it comforting knowing that if I make a mistake all that will happen is the gantry might lift off the rails instead of twisting and mangling metal.

Robert

[fleinbach]

Glenn,

The only time my Y-car has jumped off the rails was due to my error of jogging into material on the table because I forgot to lift the Z axis. I guess you could say I am a bit careless as I did this a few more times than Brady the first year I had my alpha. I also agree I would rather have the car jump off the rails then have something break. Each time I hit material it was with a ¼ inch bit and because the Y car was capable of jumping I never once even broke the bit.

Two years ago I made a modification that allows the Y car to lift off the rails with out de-railing. This gives me the best of both worlds. If something is struck the Y car is free to give way without breaking anything yet it stays right on the rails where it belongs. Oddly I can only remember one incident where I ran into something on the table since I made the modification. Maybe it made me more careful. LOL

You can see the modification here
http://www.talkshopbot.com/forum/show.cgi?tpc=28&post=25062#POST25062

[gabriel_mckeagney]

I had this issue with one of my operators. I discovered he was leaving large drawings in the file off the model space and sometimes the tool pathing was catching those vectors and they were getting written into the file. Then the gantry would go slam into the side unknowingly while we were running parts.
Once I realised this was the cause it stopped. My advice is not to keep a lot of vectors outside your model space, but break the job down into lots of small clean files.

Gabriel

[harryball]

The layering feature in VCPro4.0 solves this. I was having to keep 2 sets of roosting grooves for my bat houses... with layering just turn off what you don't want to see. You can even lock a layer, nothing is selectable, can't be toolpathed.

Robert

[srwtlc]

Due to the fact that the motors on a PRS are not tensioned by a spring/turnbuckle, but actually fastened solid, it's much less likely that the v-bearings will come off the track. I suppose that if you tried hard enough though.......