Today I tried to work some things out on the machine. But I am not sure if the spacer will work...
If you get 2 nuts on a bolt with a washer in between the nuts, the nuts will still lock up!
What is going on here?
Change the size of the washer. As I said before, the spacing washer/shim size is critical. It may only need to be 0.05mm thick, hence the use of brass shim as it is as thin as paper. Maybe try a bit of old beer can metal in there instead of the washer?
I was just testing it and the washer is 2mm? Surely thats big enough!
Big enough? It's waaaaaay too big! This process is about finding a shim/washer that is small enough. You to start with something 0.1mm thick.
I know it is too big, I was just testing the theory. It doesnt seem to work with that? Are you saying that if I use a thinner shim the nuts on the thread will not lock up?
Yep. On the inside of the nuts, there is a thread that you have cut. This thread runs in the thread on the leadscrew, happy so far?! It is the tightness between one "tooth" in the nut, against one "tooth" on the leadscrew thread that you are trying to adjust.
So have a guess at the distance between these two parts, and that's the thickness of the shim that will be too big. I guess the distance will be something like 0.2mm, depending on how well you tapped your nuts.
Therefore, any shim THICKER than this distance will cause the nuts to lock. It may seem pointless at the moment trying to close such a small gap, but as you use your machine, the nuts will wear, and this gap will become bigger, leading to inaccuracies. So, have a beer, think about it some more, then cut up the can and try using a piece in between your nuts. You may need a couple of pieces to stop the nuts locking, you may need less, I don't know. But if you now understand the principal, you will work the rest out. Of course, you could go with one nut for now, but that would be an easy exit after all the time you have put in!
OK, I had 2 beers LOL.
Used the can to cut some spacers, but when I shoved them onto the leadscrew, the nut moves but very roughly...
I don't see the point really I agree, hmmm. I'm not sure now!
AH! But you now have movement! This is perfect, you get the idea now, and it is working, albeit roughly. So you now need to find a smaller spacer. If you are using two pieces of beer can, just use one. If not, you have two choices. You can either splash out and buy the proper brass shim from RS, from the link I provided earlier, or (better solution), you wait until your machine has been running for a week or so, which the give the nuts time to wear a little, then the spacers you have now will be perfect. The only problems you're gonna encounter is how to get to those dam nuts to adjust them once you've finnished your machine!
It is sort of working. If I tighten it up more(to the max), (with the spacer) it stops working and just locks.
Ok then, try adding another spacer, then tighten it.
These nuts keep on locking. Ive tried 1 spacer to 8 spacers...
Just a quick thought, you are using the two screws to tighten the nuts together, not turning them? If you turn the nuts, they will always lock. I'm sure you know what I mean, but check back to Anoels picture, you see the two screws? You do have those in place don't you?!
Of course!Im not that thick! lol.
Sorry, just checking! For now then, I would leave out the spacers, just screw the two nuts together, and use it. As you notice backlash developing with use of your machine, you can add the shims.
Hmm, what I have been doing, is tightening the nuts together, until they are approx 1 thread away and then they will easily turn. I then have been tightening the screws, with the spacer in between the 2 nuts. This was the correct way right?
I think that I will invest in some of the brass material as I have put quite a lot of effort into these nuts now.
Last edited by Mhiran; 08-28-2003 at 09:45 AM.
How long do plastic nuts made this way last?
I was playing at the hardware store, the other day...found some bell washers which provided some "spring" between two nuts. I also played with a neoprene washer, for the same purpose.Hmm, what I have been doing, is tightening the nuts together, until they are approx 1 thread away and then they will easily turn. I then have been tightening the screws, with the spacer in between the 2 nuts. This was the correct way right?
Wouldn't it be possible to use some standard nuts, of whatever thread type, and just crank them down tighter, till these "squishy" spacers gave the right spacing between them? There'd be a little bit of spring, too, to help adjust for the inconsistencies in thread spacing, if you used cheaper lead screws.
It seemed to work pretty well on the allthread at the store...of course, I didn't have a dial indicator with me! ;-)
-- Chuck Knight
The problem you will get trying to use bell washers is that they can (and will) "give" under varying loads. The two nut technique gives you true rigidity while the bell washers don't. Your goal is to have tight positioning regardless of the load your nut/screw combination might encounter.
FYI - bell washers are often used on nuts in everyday applications to help make sure they don't back off due to vibration and such. In these applications, if the nut were to back off just a little, the bell washer would take up the slack and insure that there is still pressure between a nut and the surface it is suppose to be pressing against. If the bell washer weren't there, the system would be loose the very moment nut moved at all. This technique is really nice when used in high vibration applications where the nut has to be taken on and off on a regular basis.
Steve
I wonder if Mhiran ever got the anti-backlash nut working?
It sounded as though he was locking the two nuts together with a spacer in between. Of course, it will always lock up if you do that. The nuts are not jammed together, but are locked against mutual rotation, at such a seperation that prevents undue binding on the screw, yet eliminates most of the backlash.
First you get good, then you get fast. Then grouchiness sets in.
(Note: The opinions expressed in this post are my own and are not necessarily those of CNCzone and its management)
I don't know about Mhiran but tread did help me.
Posting Permissions
Reply with Quote