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How difficult is your z-axis lead screw to turn?

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Re: How difficult is your z-axis lead screw to turn?

Postby Ken » Wed Oct 26, 2011 12:50 am

On that Anti-Backlash Nut, I noticed that it's two parts
pressing against each other by the push of the spring,
and I could press them together with my fingers to
compress the spring. With the spring compressed I found
the lead screw easy to turn while inserting it into the
Anti-Backlash Nut and easier to turn from that time on.
Also during the easier insertion, I could feel and see
for sure that I wasn't cross-threading and hurting anything.
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Re: How difficult is your z-axis lead screw to turn?

Postby Mr Ron » Sat Nov 26, 2011 10:11 pm

You must realize that an anti-backlash nut has to have a near zero clearance with the screw in order for it to work with zero backlash. Plastic is used so it will wear enough and conform to the threads contours. Aside from the ball screw type, there are three materials that are used for anti-backlash nuts; the before mentioned plastic, a bronze and a steel nut. The latter two cost much more because they have to be machined to close tolerances. They also cause the screw to wear. A plastic nut won't wear the screw, but it will loosen up over time and require replacement. The plastic ones also don't take the loads the metallic ones can.
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Re: How difficult is your z-axis lead screw to turn?

Postby Awesomeness » Sat Nov 26, 2011 11:50 pm

Mr Ron wrote:You must realize that an anti-backlash nut has to have a near zero clearance with the screw in order for it to work with zero backlash.


Not usually: That would be true if you were trying to call a single solid nut an anti-backlash device, but most "anti-backlash nuts" are two nuts that are spring loaded apart, as the previous post described. They essentially work like a controlled version of using two nuts as a jam-nut system. One side of the device is riding on the left side of its threads, with no slack (backlash), and the other side is riding on its right side threads, also with no slack - effectively giving no slack in either direction. (Take note that the spring has to be fairly strong, because if the CNC puts overpowers the spring, the anti-backlash properties become overriden.)

There are other variants of anti-backlash devices, such as long thread-plates, that are cut too small and are pressed into the screw from all sides. More than one way to skin a cat.
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Re: How difficult is your z-axis lead screw to turn?

Postby 1planeguy » Wed Dec 14, 2011 4:52 pm

I bought a pair of 1/2" snap rings and used them just like you did your homemade washers. The snap rings are available about anywhere (got mine from Home Depot) and are VERY thin...just another idea.



Rye wrote:I may have stumbled on one of the reasons the Z axis lead screw is hard to turn.

I am building a BlackToe 4.1 and after installing the leadscrew into the Z axis assembly -- with bearings, collar and coupler installed --, I noticed that the screw would turn easily for about 180 degrees and then hang up and become quite difficult to turn. After some looking around I found that both the top coupler and the lower collar were rubbing on the outer race of the bearing. I cut out a pair of thrust washers to fit between the coupler/bearing and the collar bearing. They were .5" ID and just unde.75" OD so that they did not rub on the outer race. Now the screw turn easily.

I cut the prototype washers out of poly and then out of melamine (formica) by clamping the material in the drill press, drilling a .5' hole for the ID followed by a .75" hole saw to cut the OD. The melamine washers will probably work for a while until I can find something better. I have attached a photo of the washer assembly which shows the initial white poly washers. Poly is way to soft..

I have contacted Diego on this but so far they havent come up with a resolution. I am hoping that they will find a good washer from Boker's and mail a pair to each of us who have the problem.
ThrustWasher.jpg
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Re: How difficult is your z-axis lead screw to turn?

Postby mkfn4071 » Thu Dec 22, 2011 4:54 am

I am having the same problem and after screwing it up and down by hand for about 20 min i managed to get it go down but still doesnt go up

here is a video of it

http://www.youtube.com/watch?v=oV2ew08bbpI

and is it supposed to go this slow?
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Re: How difficult is your z-axis lead screw to turn?

Postby Awesomeness » Thu Dec 22, 2011 3:54 pm

That is a bit slow.

You shouldn't really ever have any trouble with it going down. I suspect something else is causing excessive resistance. Make sure you haven't tightened the z-axis tower bearings so tight that they don't turn, for example. Also, put some dry wax teflon spray on the screw (you can get it at Lowe's/Home Depot/etc.).
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Re: How difficult is your z-axis lead screw to turn?

Postby mkfn4071 » Thu Dec 22, 2011 10:53 pm

ya i over looked the pins on the drivers the smaller motors for z and y were all set to 0 so its all good now.

and i used powered grafite it works very well... its at homedepot in the key making area
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Re: How difficult is your z-axis lead screw to turn?

Postby hkstaub2 » Mon Jan 28, 2013 12:43 am

FYI.(and I guess you know this) Just by pure dumb luck I googled the part and found if you get the spring by your finger tips and pull up the thing moves like butter.
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Re: How difficult is your z-axis lead screw to turn?

Postby denmark219 » Mon Nov 18, 2013 10:22 pm

Rye I had the exact same issue and was actually causing my Z axis to stall. What I did was drop the collet a bit so that now my stepping motor deals with the brunt of the weight. I'm not sure this is a great fix because I don't think the motor is designed to handle this kind of lateral load. Parallel load? whatever. It's working fine for now and I'm back up and running. Now if I could just get my machine to self zero itself. That would be sweet!
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Re: How difficult is your z-axis lead screw to turn?

Postby Awesomeness » Tue Dec 03, 2013 6:04 pm

denmark219 wrote:...this kind of lateral load. Parallel load? whatever.


"Axial load" is the term you're looking for. :D

I'm not sure what axial load the motors are rated for, but you should be ok.
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