[captainmerzlak]

ok, so I'm completely new to metalworking i bought a cnc/mill off a guy a few months ago. everything has gone pretty good so far accept that the x axis had about 20tho of backlash in it. today it went up to 40tho so i ripped the machine apart to find out what was going on. i think i found the problem but i have no idea where or what to order to fix it. here are some pictures i took. any help would be great.
thanks

the mill is a harbor freight mill i think.


when i pulled the table, this is what i found. is this a ballnut?

,

it looks like set screws held these together at one time. not anymore...




this is all pulled apart.



these last 2 pictures are all i have to identify the cnc kit.




does anyone know where i can order what i think is the ballnut? should i replace the other while i have it apart? anything else i should replace while its apart? maybe replace the rails that take up the play on the axis?

[handlewanker]

No messing about....get a new ball nut and ball screw, rolled will be OK.....a ground type will be too expensive....... otherwise without any mechanical knowledge you'll be chasing your tail trying to work with probably worn out stuff.

It appears from the first photo that the assembly you have is a double ball nut type.....this is OK if you are doing super accurate and heavy milling and need the absolute backlash free capability that double ball nuts are designed to give, but for every day work a single rolled screw with a nut will still last a long time.

Measure the pitch of the screw....( the distance between the grooves from one groove to the next one) and the diam........a 1605 ball screw has a diam of 16mm and a pitch of 5mm, and a 2005.....do the sums etc.

A new ball screw/nut assembly......VERY IMPORTANT.....don't let the plastic tube insert in the nut that keeps the balls from dropping out get taken out before you roll it onto the ball screw.....the screw should push the inset out as it enters the nut......if the ball nut is already on the screw....DON'T TAKE IT OFF.

Usually.....and I could be wrong.......the new nut has a flange to screw it against the ball nut housing......photo of a ball nut attached if I can find one......the housing is a simple block of iron with a hole in the middle for the nut and some holes in the top and face for the fixing screws.

The housing gets bolted underneath the mill table and the nut is retained in the housing with the screws in the flange face.

Not knowing the exact design of your mill, I'd say that without anyone side by side to guide you .......(and it would be great if the photos were a bit bigger and in JPEG format) and providing the existing ball screw/nut layout is the same or similar as the one you want to replace it with, then it's just a bolt off/on affair.

Any time you get second hand equipment you need to determine the condition of all the moving parts.

BTW, if you do go to buy a screw make sure it's machined on both ends the same as the existing one.....very important.
The photo is an unmachined one.
Ian.

[captainmerzlak]

No messing about....get a new ball nut and ball screw, rolled will be OK.....a ground type will be too expensive....... otherwise without any mechanical knowledge you'll be chasing your tail trying to work with probably worn out stuff.

It appears from the first photo that the assembly you have is a double ball nut type.....this is OK if you are doing super accurate and heavy milling and need the absolute backlash free capability that double ball nuts are designed to give, but for every day work a single rolled screw with a nut will still last a long time.

Measure the pitch of the screw....( the distance between the grooves from one groove to the next one) and the diam........a 1605 ball screw has a diam of 16mm and a pitch of 5mm, and a 2005.....do the sums etc.

A new ball screw/nut assembly......VERY IMPORTANT.....don't let the plastic tube insert in the nut that keeps the balls from dropping out get taken out before you roll it onto the ball screw.....the screw should push the inset out as it enters the nut......if the ball nut is already on the screw....DON'T TAKE IT OFF.

Usually.....and I could be wrong.......the new nut has a flange to screw it against the ball nut housing......photo of a ball nut attached if I can find one......the housing is a simple block of iron with a hole in the middle for the nut and some holes in the top and face for the fixing screws.

The housing gets bolted underneath the mill table and the nut is retained in the housing with the screws in the flange face.

Not knowing the exact design of your mill, I'd say that without anyone side by side to guide you .......(and it would be great if the photos were a bit bigger and in JPEG format) and providing the existing ball screw/nut layout is the same or similar as the one you want to replace it with, then it's just a bolt off/on affair.

Any time you get second hand equipment you need to determine the condition of all the moving parts.

BTW, if you do go to buy a screw make sure it's machined on both ends the same as the existing one.....very important.
The photo is an unmachined one.
Ian.

Looks like 5mm pitch. I'm not sure of where to measure the diameter but one of them was close to 16mm. So I'm guessing this is a 1605?
Thanks for the in depth answer, it was very helpful. Here are some pics of measurements.

[Wiggles84]

Looking at your pictures, I'd say that almost all of the back lash is coming from the failed connection between the ball nut and the ball nut mount.

To me it looks like that kit uses a flange less ball nut, then they used the set screw holes in the nut for the ballscrew wiper (white plastic piece ) to attach the nut to the mount.

You should be able to put in a new set of hole into the mount in a different orientation and be back up and running.


Andrew

[captainmerzlak]

Looking at your pictures, I'd say that almost all of the back lash is coming from the failed connection between the ball nut and the ball nut mount.

To me it looks like that kit uses a flange less ball nut, then they used the set screw holes in the nut for the ballscrew wiper (white plastic piece ) to attach the nut to the mount.

You should be able to put in a new set of hole into the mount in a different orientation and be back up and running.


Andrew

Thanks for the advice. I'm going to order a new one, but in the meantime I'm going to take your advice to get up and running(If I don't loose any of these balls first)

[SCzEngrgGroup]

What you have is a standard 1605 single-nut screw, which was VERY badly mounted. You'll have to buy a new screw and nut, then machine the ends to match the old one (some vendors will do the machining for you, based on a drawing you provide, at extra cost). When you replace it, re-design how the nut is mounted to the machine, or the new one won't last long either. Those two tiny screws were doomed to fail from the start.

Regards,
Ray L.

[handlewanker]

Hi.....if this isn't a standard mounting procedure, could it be a DIY attempt to have a double ball nut?

If the 2 existing nuts drifted apart......how?......perhaps the screw itself is still OK and only needs another nut bolted on.... flange to flange.... with a spacer to make it good to go again........a hard rubber or plastic spacer would probably be better than a solid steel one as it would allow a bit of resilience without making the nuts too tight.

It would be impossible to just bolt the second nut hard against the first nut flange as the pitch may not allow the bolt holes to line up when the two flanges come together......either too far apart or part of a pitch out.
Ian.

[G59]

If the 2 existing nuts drifted apart......how?

It's not a double nut.

[arizonavideo]

The ball nut mounting idea might be OK if you used 4 screw over the two that they did.

Drilling into the ball nut will require a carbide drill bit. The flange needs to be a bit longer as the failure mode looks to be that the wall was too thin.

If you have a lathe you could deepen the pocket on the ball nut and the mounting block and two fresh bolts might last for a while.