Question Ball Screw replacement for wearing thread nuts

Hi FaFiNoS,

You've done a first class job there - I tried some time ago (without success I might add) to find some reasonably prices ballnuts to fit the SC2 leadscrews. Apparently Eichenberger also make a one which fit the leadscrews which are also made by them according to another post, they are however much more expensive than the SKF ones you chose.

Do you by any chance have a dimensioned drawing of the adaptors you made - in particular the distance from the mounting face to the centre of the leadscrew?

Did you need to address the problem of lateral restraint of the leadscrew, or is the existing SC2 hardware sufficient to do this?

Regards

Peter

Hi guys,

One more thing. To get the nuts perfectly inline with lead screws bearings/motors you need to grind the carry nuts or gantry (as I did), just little bit, 0.4 - 0.5mm should be enough. I grinded more, around 1mm so my ball nuts not touching gantry at all.

I completely forgot about this Still too excited how machine works Sorry about that.

Attached STL file with all four holders. Please note each holder is designed to specific hole in gantry. Holders with longer part for M6 screw are for Y axis.

That's definitely all, no more modifications.

FaFiNoS

Got a bit carried away with our stepcraft modifications, and ended up building my own cnc from scratch.

Build area 740 wide, 1340 long 250 z , 2.2kw water cooled spindle, linear motion rails×6, blocks x12.

Now it can cut !

Hey Finch,
That sounds like a beast of a machine, any chance of a few pictures?

Hi FaFiNoS,

If you have the adaptor drawings in DXF format, that would be ideal - thanks. I've viewed the .stl file you posted and see that there are two different mounting stud lengths shown whereas I'm sure all the original brass nuts were identical - do you know something I don't!!

Having to mill a clearance slot under each ballnut is a real pain - sounds a though a total strip down of the machine is required, not a job I fancy to be sure.

Peter

Hi Peter,

Holders with longer mounting stud for Y axis. I made them longer when I printed holders from PLA plastic.

Attached DXF with four holders and also DXF with one holder universal for all axes.

The clearance under each ballnut must be done I know It's a pain to disassemble whole machine but no chance to put ballnuts without clearance.
I used small Dremel to grind gantry, 10min and job done.

FaFiNoS

Hi FaFiNoS,

Thanks for the information - had some difficulty getting it into CUT2D - looks very odd on the screen, picture attached.

I have managed to extract the key dimensions using CUT2D and will migrate these into Autosketch later and post a screenshot for reference.

Peter

Hi Peter,

Import to Cut2D looks really odd. Please find attached two DXF files, side and bottom view. Very clean. Hope it help you.

FaFiNoS

Hi FaFiNoS,

Perfect - thank you. All the critical information is there.

Peter

peterg1000 wrote: Hi FaFiNoS,

Perfect - thank you. All the critical information is there.

You're welcome. Good luck!

FaFiNoS

FaFiNoS wrote: Hi guys,

One more thing. To get the nuts perfectly inline with lead screws bearings/motors you need to grind the carry nuts or gantry (as I did), just little bit, 0.4 - 0.5mm should be enough. I grinded more, around 1mm so my ball nuts not touching gantry at all.

I completely forgot about this Still too excited how machine works Sorry about that.

Attached STL file with all four holders. Please note each holder is designed to specific hole in gantry. Holders with longer part for M6 screw are for Y axis.

That's definitely all, no more modifications.

FaFiNoS

Hi, i just machined these ballnut holders from aluminium and bought 4pcs KGT 10x3 FGR RH S A G Eichenberger Carry Nut. I just cant understand what do you mean under grinding 0,4-1mm carry nuts or gantry. Can you show on picture?

Thank you!
Martin

Hi!

I got it working and it runs like a charm. But i cant go over 4500mm/min speeds because it will lose steps. Backlash is almost none. So these ballnuts work plug and play. Some pictures as well. But i am really disappointed in Step-Craft quality I had to put extra washers between y-axis rollers on one side because it was binding at ends. Problem was that x-axis carrier is 500mm wide and it will pull y-axis from side to side. so when i added some extra 1.5mm washers to the left side rollers, now threaded screws line up with bearings and front plate goes on without any hard work. So i am very disappointed in this product. I have had this y-axis alignment 10 times without any success. But at last, when i added those washers and ballnuts, it works. Still some grinding noises and vibrating with z-axis moving down MM-1000 but its not as bad as with copper threaded nut.

All the best!
Martin

I resurrect this (very intriguing) thread for a question:

Any idea about what ballnuts I should buy for my old Steppie SC1 with 8mm leadscrew? The pitch is 2mm.

On the Zapp Automation website there is no detailed size description of the screw to be used with. I guess the first two numbers of the product-code indicates the diameter of the screw, I'm right? (E.g. R1003T3-RSK = 10 mm diameter).


UPDATE
I was wrong, sorry. FaFiNas used the ballnuts from SKF, not Zapp Automation.
After a quick review of the datasheet I discovered that there is no suitable size for 8mm screws with 2mm pitch...

BTW, the ballnuts pointed by FaFiNas are for 3mm of pitch size (SH 10x3R). Maybe he intended the ones for 2mm instead? (I.e. type SH 10x2R)

peterg1000 wrote: Ball diameters are 1.71mm, and the Stepcraft screw looks to be able to accommodate nearer 2mm (cant measure this exactly). I can only conclude that the Eichenberger ball nut uses a larger size since the original experimenter reported little or no backlash.

I am wondering whether to risk £90 on one of the Eichenberger ball nuts !!! Motivation not high at the moment!!

Peter.

Yes. Accordingly to the Eichenberger catalog (page 22 here ) the ball-diameter for types coded as 10x3 FGRHxxx is exactly 2 mm (Look at the column reporting the Dw size).

At the moment I'm evaluating the 8x2 FGRHxxx ball nut for my old Steppi (version 1), the ball-diameter in this case is 1.59 mm. Now I have to check if this balls will fit in the standard leadscrew from Stepcraft...

What is the benefit of a high quality ball screw (with hardened balls) on a unknown lead screw with technically unknown specs and profile?

The backlash goes almost to zero?
Maybe the wearing will progressively augment the backlash, but I think it will be limited to few cents of millimeter, IMO.

At the moment I cannot see alternatives. Buying new "professional" leadscrews will rapidly overcome the value of the machine itself, and it is like firing at a small bird with a big naval gun.

julius wrote: The backlash goes almost to zero?
Maybe the wearing will progressively augment the backlash, but I think it will be limited to few cents of millimeter, IMO.

The backlash with the new nuts is very low and the cost of replacing them is very low. Also it ensures the wear is on a cheap components, as replacing the rods would be very uneconomical. Bronze nuts has been used as a wear component in machines for ages and has a very reliable record with regard of wear. The new nut with adjustable pre-load seems like the best solution.

The balls in a ball bearing is very very hard, and running those on a regular hardened rod will quickly wear down the rod. To me it seems like risking a high replacement cost for a short-lived joy, and there is no going back when you get wear on the rods.

eiaro wrote: The new nut with adjustable pre-load seems like the best solution.

You missed the point here: the new nuts are not available for old SC1 steppies. The old machines use an 8 mm leadscrew instead of 10 mm.

eiaro wrote: The balls in a ball bearing is very very hard, and running those on a regular hardened rod will quickly wear down the rod. To me it seems like risking a high replacement cost for a short-lived joy, and there is no going back when you get wear on the rods.

Two guys of the forum made this mod before, they are quite satisfied.
I'm available to buy new rods/leadscrews one time per year, when it pays in terms of precision. Also, one has to look to quality of the steel used from Stepcraft. It seems good to me, so (maybe) there will be no so huge wearing by adopting ball-nuts...

julius wrote: You missed the point here: the new nuts are not available for old SC1 steppies.

Ah, sorry. I missed that.

julius wrote: Also, one has to look to quality of the steel used from Stepcraft. It seems good to me, so (maybe) there will be no so huge wearing by adopting ball-nuts...

Doing a hardness test on the rod would probably be a good indication.

The original Stepcraft leadscrews are made from Eichenberg , so the quality should be not an issue in this case.
But I agree with you: we need a volunteer to make a duration test....

Yesterday I made some measurement: the leadscrews on the old Steppie (8mm diameter, 2mm step) seems to be perfect to accomodate the 1,59 balls of the KGT 8x2 FGR RH N A G miniature ballnuts from Moore International.

Any volunteer here?
We could collect some money and share the costs of purchasing a couple of that stuff for a test.