In detail: do-it-yourself ball screw repair from a real master for the site my.housecope.com.
When filling ball screws of any equipment, there is always the problem of counting the number of balls.
This time we managed to take a lot of pictures in detail. Therefore, everything did not fit in one article and I had to write the second part.
Nothing lasts forever. And foreign machines, after several years of work, become loose and require intervention. This time we will eliminate the backlash in the SPINNER PD ball screws.
This is a sequel. Beginning in the first and second parts.
I think that one of the distinguishing features of CNC lathes is the very frequent execution of the programmed threading operation. That is, threading is performed using cutters and the spindle revolutions are strictly coordinated with the coordinate movements. And this is where it is important to have correctly adjusted and serviceable ball screws.
The ball screw is dismantled from the machine. Further cleaning and disassembly must be carried out in a workshop. After flushing, the rolling surfaces of the ball screw nuts and the ball screw itself should be diagnosed, as well as look at the balls for chips.
Replace half nuts and balls if necessary. Moreover, the balls must be changed all at once. It is unacceptable to collect googles with balls from different batches of release.
Ball screw adjustment: by turning the half-nuts on ONE side, achieve a selection of the backlash in a pair (the nut should rotate smoothly by hand, but at the same time, slow down a little along the entire length of the shaft).
With spare parts available, the bulkhead can take up to three days to complete.
Maybe the title of the article will cause bewilderment to someone, but a new ball screw needs to be repaired before being installed on the machine.
Video (click to play).
The main problem of the new domestic ball screws is the quality of the bushings, more precisely, the place where the bushing and the inner groove of the half-nut mate (highlighted with an arrow in the photo).
clearances in the new ball screw half-nut
The fact is that the place of transition from the groove to the liner is untreated and has a small sill, through which the balls of the ball screw nuts cling and wedge when rolling.
There is only one repair method for such a new nut - using a hand-held miniature grinder with drill-type attachments (like a stamatolag), pour the transition from the groove into the insert. After that, jamming in the area of the inserted nut disappears.
The ball screw nut has two main types - this is a nut in which the backlash is selected by rearranging the half-nut on the tooth relative to the body and the nut in which the backlash is selected by grinding the distance half-rings.
Despite the seemingly different types of ball screw nuts, they have one common design link - this is the liner (in the figure it is called the return channel)
due to which the balls run from one nut stream to another. So, in the ball screw nut, it is the liner that is most often repaired. Why a liner? Because if you repair the brooks of nuts, then such an operation can be performed only on highly specialized equipment.
Well, well, that was a small digression - now about what exactly is being repaired in the liner.
The most common malfunction of the ball screw nut insert
- these are shells in streams along which balls roll. The reasons for the appearance of shells are the ingress of moisture into the nut, and, as a result, corrosion.
- the appearance of burrs on the receiving part of the streams. This can happen if the wrong number of balls has been placed in the ball screw nut and the balls simply roll onto each other.
How can these faults be repaired? The advice is this - a pneumatic drill and a grinding stone of approximately the following shape:
set of grinding attachments
Work should be done carefully. After leveling the defects, the place should be polished with zero-grade sandpaper.
Ball screw or Ballscrew- converts rotary motion into linear motion. Such a transfer has found its application in woodworking and metalworking machines, etc.
Structurally The ball screw consists of a screw and two half nuts.
The nut bodies and the screw itself are made of high quality alloy steel. Ball screws can be box-type and frameless.
Advantages of ball screws over screw gear:
High efficiency (up to 90%). High precision and rigidity of transmission.
Accurate movement is provided.
convenient adjustment of gaps.
Ball screw adjustment.
Depending on the version, the clearances can be adjusted in two different ways. As a rule, these are:
or grinding spacer half rings
or rearrangement of half nuts in the body per tooth
When adjusting the ball screws, it is important to understand that if the total backlash of the actuator in which the ball screws are used is 0.2 mm or more, the cause should be looked for in other places, and not in the ball screws.
My problem was solved like this (backlash along the x axis). Loose the nut. Tugged on it - dangles and rotates freely by inertia. Slightly tightened 2 screws (one is indicated by an arrow, the other is on the opposite side) and the problem was solved .. no backlash. Excitech 0609 machine.
I don’t think this is how you solved the problem. the task of these bolts is to lock the oil scraper ring (usually whales make it from white fluoroplastic-4). The correct solution to this problem is to replace the balls with slightly larger ones in order to provide preload, and where to get them. Post has been edited 3D-BiG: 11 August 2012 - 21:17
I don’t think this is how you solved the problem. the task of these bolts is to lock the oil scraper ring (usually whales make it from white fluoroplastic-4). The correct solution to this problem is to replace the balls with slightly larger ones in order to provide preload, and where to get them.
Then finally I don’t understand anything. where did the backlash come from ?? the machine is only a year old. But the backlash disappeared. Apparently not for long (( And here I was delighted. Anyway, thank you 3D-BIG.
The correct solution to this problem is to replace the balls with slightly larger ones in order to provide preload, and where to get them.
- carefully trying to screw the screw into the nut over the tray. If, at the same time, several balls have rolled out, then we put them back in their places and try this item from the beginning. - WELL, AT THE END ON THE FIFTH-SEVENTH ATTEMPT, IT WAS MANY TO TURN THE SCREW INTO THE NUT WITHOUT PUSHING OUT ANY BALL FROM ITS PLACE. - install the oil scraper rings in place and fix them with the screws mentioned above. - it remains to assemble the machine completely, test its operation and go to celebrate this event with a new dietary product: 60% water. - after being noted to try to see what glitters so familiarly in the corner, taking it out. Which will turn out to be a very familiar ball.
I'll put in my five kopecks. The new ball screw nut is assembled on an aluminum sleeve, which is fixed with two rubber rings put on it. The inner diameter of the sleeve sits on the sharpening of the screw under the thrust bearings (one ring is removed first) and the nut is quietly screwed onto the screw. But this is new! If there are no transport and installation bushings, then to facilitate the installation, I did the following: after the balls were “glued” into the nut on the lithium (whoever cycled, he knows how to assemble loose bearings without separators), a suitable piece of brass is taken (better, than copper - it springs better) foil and twists into a cylinder (1.5 - 2 turns) with a diameter slightly smaller than the inner hole of the nut with balls, and carefully, so as not to catch the balls, is inserted into the nut and released. Due to the spring properties, the cylinder unfolds and reliably holds the balls no worse than a standard sleeve. Now we put on the screwed end of the screw and calmly (at one time) screw the nut onto the screw.
PS: I have not yet understood about the groups of balls. It seems that there is only one of them in ball screws, in contrast to linear bearings. But maybe I don't know what, I have much less experience in disassembly-assemblies. Post has been edited by DEDAlex: 12 August 2012 - 01:16
- insert plastic / metal parts that are responsible for transferring balls from turn to turn, and at a minimum amount of lithol (if you overdo it, then in the next paragraph, due to the removal of excess, you will have to do several iterations) carefully arrange the balls along the turns in the nut in the nested places, keeping an equal number of balls in each group.
I thought the balls were being pushed in through these very holes (covered with red plastic pieces). And you write that first we insert plastic / metal parts, then carefully arrange the balls. So where to insert them (balls). I think I'll figure it out - I'll figure out what's what. I just don't want downtime because of the mess)
Yes, he was a fool. Then my first ball screw (ball screw, or a pair, if you like) came from China. Well, he was happy, twisted. And then I thought: what if you completely unscrew the nut? There must be some kind of protective system for the balls. Surely ...
In general, I unscrewed it. The balls, of course, crumbled. Miraculously collected it from the floor. Looked from all sides, figured: it's not so easy to assemble. Miraculously I counted all the balls, I didn't lose a single one.
By the way, this is how the ballnut looks like separately:
PTFE (most likely) bushings for protection from dirt:
Red inserts for ball grooves:
So, I had to surf the forums. People have suggested different ways, some say that it is impossible to reassemble the ball screw, but it is not!
First, let's clean the old grease and dirt off the parts.
I used either gasoline or white spirit, I don't remember.
Have you cleaned it up? Great, now we take a syringe and fill it with lithol or other viscous grease.
Now insert the red plugs into the nut. Our task is to fill all the tracks with lithol. Litol do not regret that in each circuit there is an equal amount of it. Let me remind you that in such a nut there are three circuits for balls. Who wants to get acquainted with the design of the nut - google for help.
In the previous photo, they seem to have run a little ahead ... In general, now we place the balls in the grooves very carefully with some magnetic thing (or vice versa, with non-magnetic tweezers - whoever is more comfortable). Each circuit must have the same number of balls. How many for a nut 1605 - I don't remember now, but you can count them on the spot.
This is how it looks now:
The balls are held securely in the lithium.
Now a tricky feint with the ears: fold the piece of paper and push it into the nut. Do it carefully so as not to move the balls. The paper is better thicker. If you have time, you can make papier-mâché (I did) or find a piece of pipe of the required diameter.
Well, now on the one hand (before you start, think about whether you are doing that side. No, I do not want to say that only one side is correct, just if the ends of the screw are different, then constructively you can get two different ball screws) carefully first we push it into a piece of paper, then push it in and start slowly screwing in the screw. Yes, along with a piece of paper:
Well, now you can insert the protective sleeves (they do not act as a transmission of movement, only protection) and fasten them with screws.
An overview of a specific product: a set of ball screws of the SFU1605-1000 type as elements of a CNC machine tool. The review will provide brief information on what a ball screw is and how to use it.
As a matter of fact, when trying to calculate and build an amateur CNC machine (milling cutter) on my own, I was faced with the fact that we either have expensive components for machines, or not quite what we need. Specifically, there was a problem with the acquisition of a lead screw or ball screw as transmission elements along the axes of the machine.
There are the following types of gears for CNC:
belt used together with gears mainly for lasers, since the laser has a light "head"
toothed... These are spur or helical gear racks and gears for moving along them.
lead screws there are T8 type (mainly used in 3D printers and other small-sized machines), TRR type, for example TRR12-3 with a POM nut (plastic).
ball screws - this is a screw and a nut to it. The nut has special bearings that move along a channel inside the nut.
As a rule, they are chosen taking into account the loading (mass of the portal / axis to be moved) and the influence of the backlash. In ball screws, the backlash is less due to bearings, they are considered more accurate and preferable, but at the same time they are quite expensive for homemade products.
Quote from Wiki: A helical gear is a mechanical gear that converts rotary motion into translational motion, or vice versa. In general, it consists of a screw and a nut. one of the main types: rolling ball screw (ball screw).
Ball screw (hereinafter referred to as the ball screw) is a more reliable analogue of the lead screw, but instead of a brass nut (or plastic as for screws of the TRR-12-3 type, as in my old project), there is a special nut with balls that mesh with the ball screw, choose all the backlash and at the same time reduce friction. For self-assembly of a CNC machine or 3D printer on a ball screw, you will need a ball screw, a nut to it, a coupling to the engine and outboard bearings.
Here's a small render from the internet. You can clearly see how the balls are distributed over the screw. Similar to T8, the ball screw has several threads.
To install the ball screws in the machine, you will need outboard bearings of the BK12 + BF12 (straight) or FK12 + FF12 (flanged) type, an elastic coupling 6.35 * 10mm for connecting to a NEMA23 motor on one side (6.35mm) and to the end of the ball screw on the other (10 mm) ).
Exterior view of the complete axle set: bearings BK12, BF12, circlip, nut for fixing the screw, nut holder SFU1605, coupling for the motor and the screw itself with nut.
Ball screw sizes for those who are going to purchase or design machine mechanics And separately for SFU1605 External view of the SFU1605 nut
External view of bearings BK12 + BF12 (left) and bearings with flange FK12 + FF12 (right). They differ in the way they are installed on the frame.
The ball screw nut is attached through a special adapter housing. Nut holder SFU1605, aluminum
For mounting on one axis (I have two per axis for Y), you will need:
1 x screw SFU1605-1000mm;
1 x BK12 bearing;
1 x BF12 bearing;
1 x Motor Coupling 6.35x10mm
1 x retaining ring
1 x nut.
Assembled it looks like this:
We attach it to the profile / frame of the machine through the holes in the bearing. For FK12 / FF12 bearings, everything is the same, only it must be fastened with a flange to the hole for the ball screw. The meaning does not change.
Now a little video explaining the principle of operation of ball screws. Pay attention to the movement of the balls (along the built-in channel inside the nut).
