[Mhiran]

Hello!
NEWBIE ALERT!
I was just wondering, what the exact difference is between a normal 1/2 inch leadscrew nut and an anti-backlash nut. My understanding so far, is that it will lead to in-accuracies, but how much? I can live with upto 2/16ths of an inch tolerance, so would I need to use a anti - backlash nuts?

Also, would I be able to improvise these fancy nuts?
I have seen on some sites that a slit is cut into a normal nut or something like that?!
Thanks
Mhiran

[anoel]

2/16? that an an eighth of an inch... That's huge... The eye can detect tolerance variations without much trouble down to a 1/100 of an inch, (particularly when inspecting a circle, a trained eye can scrutinize even better.) When you have backlash you end up with oval circles and non square squares, with gouges. your parts won't line up, 3D carvings turn out like blobs and have gouges. Backlash and rigidity are the enemies of CNC... The more you eliminate them the better.

I's not difficult at all to make an antibacklash nut from Delrin or UHMW. So why comprimise. Several of us here have done it with great success.

Regular brass or bronze nuts can be used to a fair degree by using two of them in contention or compression. But there is still some axial play in them that may or may not prove to provide some problems with vibration and or noise.

[Mhiran]

Hmmm, I have read about these Delrin nuts, but, if anybody has a pic of one of these nuts I would be grateful.

When making a nut of out of Delrin, would I only need to tap it, using a tap made out of my leadscrew? Is that all?

Where can I find Delrin? I'm guessing a plastics supplier...

[kong]

There is some delrin going on ebay at the mo, over here, not long left on that one though. It is a fair price, if you hunt around you won't find it cheaper. As for the nut, you may not think you need anti-backlash now, but when you become profficient with your machine, you will kick yourself. There is a useful thread about the taps here and for pictures of an easy deign, check out Balsamans nuts! Post number 119 on that page. Hope it helps.

[Mhiran]

Bought some Delrin just a second ago . Now, I already have a 1/2 inch tap... I was wondering if that would be ok for the ol' Anti-Backlash nut?

Also what actually makes a nut made out of Delrin, an anti-backlash one, and one just made out of brass, just a backlash one?

Thanks
Mhiran

[kong]

If you look at the Balsaman link I posted, you can see the slit in the nut. So if you bung in a couple of screws, the two halves get pulled together, squeezing (only very gently) the two halves of the thread together, removing the "play" from between the nut and the leadscrew. Don't mean to sound dumb, but the tap needs to be an Acme thread, you don't state what type the 1/2" tap you have is!

[Mhiran]

It is an acme thread!

Hmmm, I'm not sure that I understand.
The Balsaman post doesnt look like its made out of Delrin...?

[kong]

No its not, it was a bronze type material I think. If you read through the thread though, he says somewhere he had some problems with that nut, due to its hardness. The delrin will provide you with less friction, will be easier to tap/cut and on a hobby/home machine, will last just as long as bronze. When you mailed me, I said I would be using bronze, this is because the new machine will be much faster than the old stepper driven one, so bronze will last longer. That machine currently has nuts made from Tufnol - a hard plastic similar to delrin, and they are running fine. Just use a nice anti-backlash design, and get cutting!

[Mhiran]

Hmmm,
So all i need to make the nut is to tap it?
Then fix this to the gantry?

[kong]

Doh! This will give you a regular nut. If you are happy with that, then go with it. The backlash will be someting like 0.2 - 0.4mm, but may increase with usage. If you put the slit down the middle, then add a screw across the slit, you can tighten it up to remove the backlash as the two halves come together. I hope you understand the difference between the two types of nut you can make. I guess you could just do what you said for now, then slit the nut later on as the backlash becomes critical. Personally, I would slit the nut now to create the anti-backlash nut.

[Mhiran]

Ohhhh! I see now!
So you basically compress the nut to the leadscrew?

Kong don't you have msn or something like that?

[Mhiran]

Like this?

[kong]

That will work, although it would be better if the slit were......jeez, difficult to explain.....image you made two nuts, then screwed them both onto the acme rod. Now image they are tight together, well thats where the slit should go. Down the middle, between the two nuts. Then, when you tighten the little connecting screws, it pulls the two nuts together tighter. Sorry for that lame attempt, but I hope you get the idea.

[Mhiran]

Hmmm!
Like this?

[Mhiran]

I think I have sorted it now. Like this?

[creative_mind]

How about this? I've never built one, but...

[Mhiran]

Damn you!
LOL, ok, my 3D was good for an MS Paint attempt.
Basically, are you telling me that is how you do it? Do you know that, that will work?
Thanks
Mhiran

[kong]

Yep, woodys got it, thats what I was trying to explain! Nice one.
The slit not going all the way through keeps the two halves together, and when you put the screw in that little hole, you can pull the two halves tighter together, squeezing the threads and reducing the backlash.

[Mhiran]

I get it!
LOL
Finally!
So I can shove one screw down the middle through both halves and tighten it.
I guess I can't tighten it too much

[anoel]

Honestly I'd go with 2 separate nuts. One that attaches to the axis and another that attaches to the original via two screws tighten up those two screws to pull the nuts together and eliminate the backlash. Much like the one that Mhiran posted last.

Woody, I'd suspect a chance for binding in your nut since it would bend the nut in the axial direction.