This is very similar to the cables that was on my Dad's old drafting table that kept a parallel bar square to the table, but allowed it to move up and down the table smoothly. His used only one cable, and one spring to keep tension, but the same concept.
I purchased some 1/16 inch diameter wire, patio door pulleys, and now I have a rock solid gantry. I'm in process of building a Joe 4x4 hybrid, so the gantry is not visible, because it's not installed yet.
I had to zip the movie because of file size limitations.
You are in luck, I tossed this shell out because the bearing is a loose fit in it so after rummaging around in the rubbish tin, here it is. The shell is made from 30mm Bright Shaft as it is known in New Zealand. I made these 8mm wide and put my 90 degree V groove into it 2.5mm deep (5mm across the top). The shell has not been hardened. The bearing is made to be a press fit and is loctite into place for good measure. I include a picture of the bearing in place on the torsion box. There is only a 10mm gap to install the bearing so that the wires will not foul anything and not enough room to get my camera into. The bearings were put in place with 8mm rod and I installed 4 separate bearing to keep the wires running low. If I didn't have height problems I would have stacked 2 per threaded rod. To make sure the wires did not rub against each other where they cross, one pair of bearings were packed with a couple of washers which gives about 3mm clearance.
I mentioned in my first posting that i still had racking but only 0.5mm but I now find I am wrong. I have no racking now that I have properly tensioned up the wire. I could almost play a tune on it.
Peter
I'm glad it helped you Peter, I was sitting at work one day (I own a cabinet shop) and I was trying to figure out how to get rid of my racking issue caused by my wanting my drive screw to one side of the machine when I remembered building a entertainment cabinet with rather tall pocket doors, the picture I posted waaay back at the beginning of my post was from the instruction manual that came with the pocket door system and I recalled how it held the doors up so well without letting them droop or get out of sync. At that point I said "BINGO"! stopped by lowes, got some bits, went home and it took around an hour to make me a happy man!
Peter,
The v-groove shell is awesome. Very professional.
Well after a long discussion and still more research to do, I have been really thinking how rock solid is a Cable system on a cnc machine?
I know wyldesyde007 drives his gantry from the center so I'm sure this helps his machine quite a bit, I also know and remember when board drafting the parallel bar would get skewed when you applied force to one side opposite the other.
And if you study the cable system enough there really is nothing to lock the gantry side to the cables, so then the cable is free to move along the pulley's.
I am although convinced that this cable system helps tremendously with wyldesyde007's machine, and he has done an excellent job in executing it in his application but it may not be the best solution for everyones racking situation.
I wonder if you were to lock the gantry on one side and start the machine and apply motor torque while having a gage of some sort on the other side to measure the actual skew/rack in the gantry (the wider the gantry the greater the skew) and (also depends on your systems motor torque as to your results which will differ from machine to machine). I am curious as to the results because last night on my 4x4 machine I did test this out with the my belt system only to see if it is worth switching to an under the table type system.
I will posted the results in my thread as not to cloud this one up, but you may find it interesting or maybe not, its up to you.
Here is a link to my testing with my current belt system which used dual leadscrews, just for your information.
post #716
http://www.cnczone.com/forums/showth...721#post424721
Joe
Last edited by joecnc2006; 03-13-2008 at 05:56 PM.
Joe, I think you meant " drives his gantry from the side" you are correct in thinking if you locked down your machine on one side using a cable system that it would skew.On my rig it takes about 30lbs of force to get the gantry to twist and after removing the force the gantry goes right back to it's original position without any resyncing. This was never intended as a "milling metal parts precision fix" but rather a "get rid of a shaky gantry fix" although it does improve accuracy in my cuts (your results may vary)LOL.
I drive my 52" X axis from the middle and had trouble with racking. I picked up some 3/32" steel cable, pulleys and turnbuckles and did the following
The cable runs from 1 side of the gantry (the BLUE thing) #1 to #1 and from the #2 to #2. The 0's in the 4 corners are pulleys. I put turnbuckles on the back side of the gantry to tension the cables. Force pushing on 1 end of the gantry pulls the other end the opposite direction.
I think it cost me < $20 for it
Randy,
I did the same thing, same configuration. I'm still building my CNC, so don't know how well it will work, but I've got a good feeling.
Dave
Should work great for you.
I am in the process of rebuilding my X rails (modeled after the JGRO) no support and getting alot of sag spanning 52"... also trying a new design for Z. Then I will start my total new torsion box base build, wider spacing in both directions on the linear bearing for stability.
I checked out Lowes today , the local one does not arry that hardware . Iwill check out Home Depot this afternoon otherwise I will contact the maker if you have the manufacturers name ...regards mike hide
Here's the patio roller's I used.
I used pullies from garage door and work well and have a bearing installed.
The hardware I was referring to was to prevent pocket doors racking. If you consisder joes machine x axis in plan view, a cable attached to the frame lets say at the bottom left corner,runs over a pulley on the left hand side of the gantry then to a pulley on the right hand side of the gantry and then is attached to the right hand side of the frame [diagonally opposite corner].Another cable /pulley combination does the same on the other side.
One of the members used this arrangement to eliminate racking in the X axis .Apparently Lowes offered a manufacturers kit to prevent pocket doors racking and he used the kit to use on his machine . My local Lowes does not carry the kit so I would like to get the manufacturers name so I can order online ....regards mike hide
The accuride system is what I used as a model for my cabling system look here. http://www.accuridepocketdoor.com/
another design offered by KV uses a rack and pinion look here
http://www.rockler.com/product.cfm?p...=pocket%20door
Sorry,
I still don't get it. What moving knot?
Please explain
Thank you
smitjs