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Re: Possible Crooked Flange Bearing?

Posted: Fri Feb 07, 2014 5:39 pm
by chomdh
Thanks MeanderBolt. It looked to me like the standard height nut on the underside would interfere with the z axis makerslide due to the shim plate not being tall enough. Did you have any issues with that fitment?

Also, can anyone please describe their assembly method for the threaded rod + bearing+ motor assembly and any tricks they used to get the rod running as true as possible (without wobble).

I put the thin lower nut on the rod, inserted the rod through the bearing bore, installed an M8 washer and standard (thick) M8 nut from my assortment of fasteners on the top side of the bearing, then tightened the two nuts. The rod still wobbles at this point due to the bearing's internal clearance from what I've gathered. Then I attached the flexible coupler. Again, I still had a good bit of wobble when I rotated the rod. Then I threaded the standoffs into the stepper motor and tightened the couple to the motor shaft. Does that sound like the best way to get a wobble-free z axis rod? Should the rod rotate without wobble with only the nuts + washers installed? It would be nice to know this before adding the coupler and motor.

That was actually the second time I assembled the Z axis. Before using the M8 washer and standard thick M8 nut on the top side of the bearing, I used the 2 thin M8 nuts included with the kit. I think there was actually less wobble that 1st time I assembled the Z axis. Adding the washer and new nut didn't seem to help. Maybe I just need to take it apart again and try another nut & washer - with a thick one on the lower location of the rod.

Thanks.

Re: Possible Crooked Flange Bearing?

Posted: Sat Feb 08, 2014 6:29 pm
by will1384
I fixed my problem, the M8 threaded rod is not 8mm, its like 7.8 + or -, and when you tighten down the flexible coupler with an 8mm hole it will be off center with something smaller than 8mm, so I measured and out 22 centimeters of Teflon tape and cut with scissors, them carefully wrapped it onto the end of the M8 threaded rod, making sure its even and unwrinkled, and now its almost perfect, have a look:

https://picasaweb.google.com/1113484813 ... 7653411826

I still see a slight wobble, and I wonder if slightly more Teflon tape would remove it, but I worry that by trying to fix it I my make it worse LOL.

I also tried Aluminum Foil Tape, I cut one piece to 2-1/2cm x 1cm and that was almost exactly all the way around, but one piece was not enough, and two pieces was to much.

Re: Possible Crooked Flange Bearing?

Posted: Sat Feb 08, 2014 7:55 pm
by MeanderBolt
Ok, before you spend a lot of time on nuts, verify that this is not a bent rod by rolling it on a known flat surface. The MDF sent with your Shapeoko should work perfectly for this. Rule this out first. If this is happy, then proceed.

I would say, being that there is a shown history of wobble with the provided nuts, if you have a wobble problem, do not spend a lot of time torturing yourself, just go to the store and spend the $1.50 and get some good nuts and washers. Stop trying to fix something that might not be able to be fixed, and worse, something that could cause a potential problem later if you are able to force it to work now. Just my $.02.
More, WillAdams, if you read this, can you make a note on the wiki about the possibility of the goofy nuts? This would be a great help to future worried people.
chomdh wrote:Also, can anyone please describe their assembly method for the threaded rod + bearing+ motor assembly and any tricks they used to get the rod running as true as possible (without wobble).
Sure.
How I did my Z head assembly...
I assembled it with the *stepper already attached to the flange bearing plates > shim, and into the MakerSlide. I slid the flexible coupler all the way up to the stepper (I kept it loose enough to just barely hold it's place wherever it was situated). I put the new M8 nut on the M8 Rod and turned it down so the length put it through the bearing, with enough length 1. to add the top nut, 2. have enough length to securely attach the flexible collar, and enough space between the rod and the coupler to get the wrench in to tighten the bolt. In reality, all these things are possible if you are able to just barely get the wrench in and out, so that was my standard measurement. Does that make sense?

So, I would then insert the rod with pre-measured distance through the bearing. As it is coming through, put the top washer and nut over the bearing and thread the rod into it. I usually just turned the rod from below the bearing to pull the top nut down as it was easier in the limited space than trying to twist the top nut over and over. So the top washer and nut is on and down to the bearing. Tighten it down withe the 2 wrenches going in opposite directions. Once this it tight, lay it flat and on it's back and look for wobble. If it still has silly wobble, then you need to go back and figure out what is wrong. If you got new nuts, this should not be an issue.

*I am sure that there are many ways to skin this cat, but I found that the easiest way to finally get the z-stepper stack together was to put the standoffs into the stepper. I needed to use 2 M3 washers per standoff as the screws on the standoff were too long. Once you have these in place and tight, you then have somewhere for the screws (that hold the bearing plate sandwich together) to go. I always got my washers on my M3 and M5 screws before starting the next section. So get the 3 M3 screws with washers attached ready, put them through the bottom plate, add the nylon spacers to the screws. Get the spring on the bearing, put it through the hole in the top plate and sandwich this down over the lower plate and screws. While trying with all your might to keep this goofy thing together get one screw into one of the standoffs. If you can get a couple turns on the screw, wrestle the others into their holes as well. Then tighten each one. I usually did a light tighten across all of them then went back for a deeper tightening. Once that is together then you can take the 2 M5 screws and go the other direction and through the shim, and into the Makerslide. Note that you will probably need to readjust the distance from the back of the neck once the z sled gets attached and raised up a ways, so don't tighten too much at this point (thinking of the stepper as the head, the shim as neck and Makerslide as back)(weird I know, but it worked for me) 8-) .

The instructions are a little vague here and they do not show this process with the stepper involved. This got me very confused as there did not seem to be a logical order to this step. I keep joking that if felt like a chicken >< egg sort of scenario. WillAdams rightly said some steps nearly take a third hand.
chomdh wrote:Did you have any issues with that fitment?
No. Once I did the above, it all worked very well. There are screws going in from the bottom of the plate anyway. Once the Z sled is attached and is in travel, it should not be an issue. If it is, it would only be a millimeter or so at most. More than likely you will not be raising the sled up that high anyhow.

Re: Possible Crooked Flange Bearing?

Posted: Sat Feb 08, 2014 9:49 pm
by will1384
will1384 wrote:I fixed my problem, the M8 threaded rod is not 8mm, its like 7.8 + or -, and when you tighten down the flexible coupler with an 8mm hole it will be off center with something smaller than 8mm, so I measured and out 22 centimeters of Teflon tape and cut with scissors, them carefully wrapped it onto the end of the M8 threaded rod, making sure its even and unwrinkled, and now its almost perfect, have a look:

https://picasaweb.google.com/1113484813 ... 7653411826

I still see a slight wobble, and I wonder if slightly more Teflon tape would remove it, but I worry that by trying to fix it I my make it worse LOL.

I also tried Aluminum Foil Tape, I cut one piece to 2-1/2cm x 1cm and that was almost exactly all the way around, but one piece was not enough, and two pieces was to much.
I went and tried to cut some wood clamps, and when under load the Teflon tape slipped, so now I have to rethink my strategy :( I am going to try again with the Teflon tape, and tighten it down a little more.

What I need is a 8mm threaded rod with the last half inch or maybe centimeter unthreaded.

Re: Possible Crooked Flange Bearing?

Posted: Sun Feb 09, 2014 12:47 am
by gmfoster
Re guarding your Teflon tape.. I have never had luck with tape for this kind of fix,

I had a similar situation with some 1/4 inch couplers and solved it by cutting a section out of a coke can. Rolled it around the 1/4 screw and and then cut it where there was a small slit. This worked out really well and you can cut coke cans here with scissors. Not sure it would work in your case. I am currently trying to make bushings so I van get by with my 4 mm shaft motors.

Re: Possible Crooked Flange Bearing?

Posted: Sun Feb 09, 2014 3:04 am
by will1384
gmfoster wrote:Re guarding your Teflon tape.. I have never had luck with tape for this kind of fix,

I had a similar situation with some 1/4 inch couplers and solved it by cutting a section out of a coke can. Rolled it around the 1/4 screw and and then cut it where there was a small slit. This worked out really well and you can cut coke cans here with scissors. Not sure it would work in your case. I am currently trying to make bushings so I van get by with my 4 mm shaft motors.
Thanks for the idea.

I tried the nuts and washers fix, I got 100 of each, and could never find a combination that would work, I tried a different coupler with the same results, I tried aluminum foil tape and electrical tape, I tried Drill Bit Stop Collars in place of nuts, nothing is working.

On my last CNC router I had the same problem, I resorted to using a rubber hose as a coupler, I hope I don't have to do that again.