[109jb]

I am working on a new machine and want to reduce backlash as much as possible without resorting to double ball nuts. I have some thompson ballscrew stock and nuts and intend to use oversize balls in them.For you guys that are using oversize balls, how are you determining how much oversize to use for the ball bearings? Is it a trial and error, a formula someone has devised, or other? Any help would be appreciated.

Thanks,

John B

[arizonavideo]

They are all different.

I have one extra Roton screw with re packed balls if you would like it. its long enough for the X axes.

[109jb]

I understand they are all different. I thought that maybe there was s rule of thumb like XXX backlash means getting balls that are XXX larger than what is currently installed to at least get close.

[Eldon_Joh]

the ball size will correspond to the correction: cosine of the contact angle.

[victorofga]

0.01-0.02 mm backlash will remain with single nut..
if you measure no more, then just leave as it is.. setting too tight wear out too early your screw..

[lcvette]

Is the double nut just not feasible to fit the application? Or just wanting to use what you have on hand? Hard to beat a double nut setup for dripping backlash.

As for repacking single nuts, it is so difficult to determine what will best fit and reduce backlash because some areas of the screw are just a little off and while a later ball repack works in some portions it would bind in others.

Trial and error would probably be the most accurate way to determine what will fit your particular screws.. Fortunately balls aren't crazy expensive. However for as little as double nuts cost from china direct unless there is a physical space constraint that wouldn't allow the use of a double nut, I think it would be hard to match the adjustability they allow. I personally prefer a spring loaded type because it helps eliminate the circle inconsistency in surface finish. I saw where zero backlash was accomplished this way a while back with a cheap c7 rolled screw bit it did require even more space to make work. So again the space limitations are certainly a real consideration.

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[victorofga]

icvette

that's mightbe the most important.. repacking isn't so simple as it looking... first try possible takes hour or more..
result wont be as expected..
what homebussiness can do, in my meaning a rolled screw pretty much sufficient.. ..
for 99 percent of works, the 0.015 mm backlash could be considered as no backlash..

it just need to see from practical side..


if something need to be so precise, then need to cut with wire edm, or need to grind..

[109jb]

lcvette - This is for a small XY table, so space is limited in the Y axis. Stock, the y-axis has 7.5" travel, which will reduce to about 7" with one ball nut. Double nuts would reduce the Y axis travel another 1.8". So double nuts on the Y-axis just aren't going to be an option. If I can get backlash down to less than 0.002" on this project I will be really happy. I have Thompson screws with double nuts on my G0704 so I do know the benefits of double nuts for backlash reduction..

victorofga - This is for a hobby machine and will see very infrequent use. Even if I put oversize balls in it I doubt that I would be able to wear them out in my lifetime.

Eldon_Joh - without knowing the designed contact angle, assuming one is really no better than guessing.

[Eldon_Joh]

Eldon_Joh - without knowing the designed contact angle, assuming one is really no better than guessing.

yeah, and i think i got that wrong on my second edit too.

you will have to draw out the triangles yourself and do some math that i haven't done since grade school.

you should be able to observe the contact angle with a microscope if your ballscrews are ground in the "Gothic arch" style, where the ball makes 4 points of contact at all times.

[lcvette]

icvette

that's mightbe the most important.. repacking isn't so simple as it looking... first try possible takes hour or more..
result wont be as expected..
what homebussiness can do, in my meaning a rolled screw pretty much sufficient.. ..
for 99 percent of works, the 0.015 mm backlash could be considered as no backlash..

it just need to see from practical side..


if something need to be so precise, then need to cut with wire edm, or need to grind..

Yes, but most single nuts only accomplish around .05mm as a general rule which is a far cry from .015mm which I would be very happy with.



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[lcvette]

lcvette - This is for a small XY table, so space is limited in the Y axis. Stock, the y-axis has 7.5" travel, which will reduce to about 7" with one ball nut. Double nuts would reduce the Y axis travel another 1.8". So double nuts on the Y-axis just aren't going to be an option. If I can get backlash down to less than 0.002" on this project I will be really happy. I have Thompson screws with double nuts on my G0704 so I do know the benefits of double nuts for backlash reduction..

victorofga - This is for a hobby machine and will see very infrequent use. Even if I put oversize balls in it I doubt that I would be able to wear them out in my lifetime.

Eldon_Joh - without knowing the designed contact angle, assuming one is really no better than guessing.

Good point, is there a way to open a hole and extend the ballscrew through it? On my base on the G0704, the nut travel through an opening so there was zero change in travel. Just a thought, I'm sure the xy table is pretty cramped. Being so small, you could use TBI ground screw with single nut in like a 12mm size, cost would be pretty cheap for Y as short as it is and it would get you down to under .001". Cost would be around $75 for screw and nut. Then if space was available a double nut on X would get backlash down near the ground screw.

I did this same thing on my mini Lathe because of cramped quarters on the X axis. Just a thought.

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[109jb]

icvette

that's mightbe the most important.. repacking isn't so simple as it looking... first try possible takes hour or more..
result wont be as expected..
what homebussiness can do, in my meaning a rolled screw pretty much sufficient.. ..
for 99 percent of works, the 0.015 mm backlash could be considered as no backlash..

it just need to see from practical side..


if something need to be so precise, then need to cut with wire edm, or need to grind..

You are making assumptions that that were not part of the question.

- You assume my screws already have less than 0.015 mm (0.0006 inches). I can assure you they do not and it is likely more like 0.004" (0.1 mm) based on my last machine build. The specs from the manufacturer only say that the screws will have less than 0.010" backlash (0.254 mm).
- I did not ask how much backlash is acceptable or "practical". Frankly, that is my decision not yours. You have made the assumption that because it is a hobby machine that it only needs the precision and backlash that you have determined. All I have said so far is that it is for a small XY table. I have not said what the purpose of it is. You cannot possibly determine what is necessary without knowing what the intended use is. In this case your assumptions are correct, but they were still misguided assumptions based on limited knowledge of the application.
- I did not ask if I could repack the ball nuts or how difficult it is to do. I have done it and know what it takes. It didn't take me an hour even the first time. Even if it does, so what isn't that my decision too.
- You assume that I intend to pack balls in so tight that they bind and wear the screw faster. Not my intention. I want lower backlash while retaining smooth operation which will not increase the wear rate. Even if it did cause accelerated wear, I'll never come close to wearing them out anyway.

If you have suggestions as to how to determine how much larger the balls can be then I welcome that input. Frankly though everything you have said is just saying "don't do it" which is not what was asked.

[109jb]

Good point, is there a way to open a hole and extend the ballscrew through it? On my base on the G0704, the nut travel through an opening so there was zero change in travel. Just a thought, I'm sure the xy table is pretty cramped. Being so small, you could use TBI ground screw with single nut in like a 12mm size, cost would be pretty cheap for Y as short as it is and it would get you down to under .001". Cost would be around $75 for screw and nut. Then if space was available a double nut on X would get backlash down near the ground screw.

I did this same thing on my mini Lathe because of cramped quarters on the X axis. Just a thought.

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I can't open a hole on this one because it would reduce material left to an unacceptable level.

I decided to use the ballscrews for a couple reasons. I have the table running with the stock acme screws but can only get 30 IPM. I know from experiments done with my G0704 that going from acme to ball screws can get about 5x speed increase. I don't need 5x, but 3x would be great. I would like at leasy 75 IPM rapids on this machine. Also, the stock screws have about 0.004" backlash. I already have the screw stock and ball nuts, so I plan to at least give them a try. You are right that I could double nut the X axis, but I figure that if going with increased size balls on the Y I might as well do it on the X too.

[AVRnj]

You are making assumptions that that were not part of the question.

- You assume my screws already have less than 0.015 mm (0.0006 inches). I can assure you they do not and it is likely more like 0.004" (0.1 mm) based on my last machine build. The specs from the manufacturer only say that the screws will have less than 0.010" backlash (0.254 mm).
- I did not ask how much backlash is acceptable or "practical". Frankly, that is my decision not yours. You have made the assumption that because it is a hobby machine that it only needs the precision and backlash that you have determined. All I have said so far is that it is for a small XY table. I have not said what the purpose of it is. You cannot possibly determine what is necessary without knowing what the intended use is. In this case your assumptions are correct, but they were still misguided assumptions based on limited knowledge of the application.
- I did not ask if I could repack the ball nuts or how difficult it is to do. I have done it and know what it takes. It didn't take me an hour even the first time. Even if it does, so what isn't that my decision too.
- You assume that I intend to pack balls in so tight that they bind and wear the screw faster. Not my intention. I want lower backlash while retaining smooth operation which will not increase the wear rate. Even if it did cause accelerated wear, I'll never come close to wearing them out anyway.

If you have suggestions as to how to determine how much larger the balls can be then I welcome that input. Frankly though everything you have said is just saying "don't do it" which is not what was asked.

.004 seems very high for ballscrews, are you sure that is in the ballscrews and not the combo of the ballscrews and AC or thrust bearings?

I have repacked a single ball nut with larger balls, and what I did was measure the existing balls, and ordered the next two larger sizes I could buy, they were cheap. I then tried each one, and only the one size up worked. The second size got in there, but there was way too much friction and the ball nuts were not turning properly on the ball screws. If I remember correctly, this took me from around .0025 backlash in my whole setup including ballscrew and AC bearings down to around .0015.

[109jb]

.004 seems very high for ballscrews, are you sure that is in the ballscrews and not the combo of the ballscrews and AC or thrust bearings?

I have repacked a single ball nut with larger balls, and what I did was measure the existing balls, and ordered the next two larger sizes I could buy, they were cheap. I then tried each one, and only the one size up worked. The second size got in there, but there was way too much friction and the ball nuts were not turning properly on the ball screws. If I remember correctly, this took me from around .0025 backlash in my whole setup including ballscrew and AC bearings down to around .0015.

Thanks. I did check and the 0.004 was almost entirely in the ball nut/screw. Keep in mind that these are probably the absolute cheapest rolled screws I could find at the time. I know that the nut is a Thompson, but the screw is unknown as there was no marking on the package. These came from McMaster Carr. I bought them several years ago. It may be that the ones I have that have not been installed are better as they were ordered at different times than the ones in my G0704. I will have to wait and see what the actual backlash on these particular screws is. With double nuts my G0704 has about 0.0005" backlash with the gibs adjusted how I like them. If I loosen them up I can get down to about half that.

When you say you ordered the next 2 larger size balls for your screws, what do yo mean by that. For example did you order 0.001" larger and 0.002" larger, or 0.0005" and 0.001" or something else?

Thanks again

[AVRnj]

Thanks. I did check and the 0.004 was almost entirely in the ball nut/screw. Keep in mind that these are probably the absolute cheapest rolled screws I could find at the time. I know that the nut is a Thompson, but the screw is unknown as there was no marking on the package. These came from McMaster Carr. I bought them several years ago. It may be that the ones I have that have not been installed are better as they were ordered at different times than the ones in my G0704. I will have to wait and see what the actual backlash on these particular screws is. With double nuts my G0704 has about 0.0005" backlash with the gibs adjusted how I like them. If I loosen them up I can get down to about half that.

When you say you ordered the next 2 larger size balls for your screws, what do yo mean by that. For example did you order 0.001" larger and 0.002" larger, or 0.0005" and 0.001" or something else?

Thanks again

It was a while ago, so here is what I remember. Lets say the balls measured something like 0.1", I don't remember exactly. I was not able to find balls in that specific of increments like you mention, it was weird, maybe something like 0.105", 0.16", etc. so I basically just bought the next 2 biggest sizes I could find above the measurement I took. Does that make sense?

Also, I am sure you know this, but also make sure to measure them with a good micrometer.

[N4NV]

I need to do the same thing to get rid of the backlash on my Hiwin ballscrews. Where do you buy oversized balls and what grade do they need to be?
Thanks.

Vince

[ebrewste]

I have purchased balls from ball-tec before. They have an amazing selection of balls.
Baltec - Home
I think chrome steel balls are the right ones for a ball screw. I used grade 25, though it's been too long to remember the details of why.

Bal-tec

Bal-tec - Ball Material Selection

[arizonavideo]

Baltec is great if you know the exact size of balls but they charge way too much, often .24 per ball.

[Andreiir]

Why u don't buy a ground c5 , c3 ballscrew ?
Is more easy to use it , and u have w little backlash .

- - - Updated - - -

Why u don't buy a ground c5 , c3 ballscrew ?
Is more easy to use it , and u have w little backlash .