# Making A Backlash Take Up Gadget, Help



## davidh (Jan 26, 2016)

i have almost completed my cnc frame and cannot figure out how to make a anti backlash thing for the ball shaft and ball nuts i have.   i have thought of different configuration but in my head none of them will work.  this is the nut and shaft i have, the nut has a really weird thread and i made the nuts to attach those to the proper items, if i remember correct its 7/8"-16 thread or some weird thing.   please help, give me an idea or two so i can complete this gantry and get on with the rest of the project. . . . . I'm running out of saturdays, so to speak.


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## JimDawson (Jan 26, 2016)

Is this a double or single nut system?  With a single ball nut, you are at the mercy of the ball clearance.  There is no way to preload it.  The only way to do it is to install bigger balls.  Many times these will have 0.123 balls in them, and you can preload them by using 0.125 balls.


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## Holescreek (Jan 26, 2016)

I used two ball nuts with bellview washers between them to provide spring preload.


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## hermetic (Jan 27, 2016)

I think you mean Belville washers, there is also one made which is a flat spring of about two or three coils. I think the conical belvilles will be a bit stiff for this application, sorry about the huge pic!


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## Holescreek (Jan 27, 2016)

Yeah, however it's spelled they did the trick.  It's been too long for memory to be precise but I know there is more than one washer sandwiched inside the couplers to get the calculated preload.


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## RJSakowski (Jan 27, 2016)

Stacking Belville's so they are opposing (crowns in opposition) will decrease the spring constant.  Two opposing will give 1/2 the spring constant, 3 opposing will give 1/3, etc.  Stacking in series, on the other hand will double the spring constant for two, triple for three, etc.


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## Baithog (Jan 27, 2016)

there are 4 major ways to solve the ball screw backlash issue.

The easiest and most costly is to just buy better screws.
You could also fit the nut to the screw by changing the ball size. That makes your low cost screw into a precision one. Balls of various sizes are available on ebay, as well as other tool suppliers. You would need a micrometer that can read tenths, but the procedure should be doable by anyone that can fab a machine. You have nuts with external ball returns. They are easier to do than the cheap screws currently on ebay. Instructions are on the internet if you look for them. A video of doing my style nut is at 




The third is second most popular and is described above. Belville washers require some engineering smarts. A screw adjusted cage is maybe easier to shoot it from the hip.
The most popular, IMHO, is to deal with the backlash in the machine controller. Both Mach and LinuxCNC have that capability.
I use acme screws with anti-backlash nuts on my small machine, but you are already down the ball screw route.


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