[men8ifr]

Standard ballnut?

Double with shim to preload?

Standard with oversize balls?

And details on backlash, performance, problems please

[rcheli]

I used a CNCFusion Deluxe kit on my mill which came with nuts that had oversize balls. I have only .0005 backlash. With a double nut I would have had to sacrifice travel. If I was building a router where I would have more room I would consider double balls.

[arizonavideo]

For the PM-25 and G0704 kits that I make you don't loose any travel with the double nuts.

Stock single nuts can be fairly bad sometimes so you have to get re packed ones, I did that for overt 5 years. .0005" is a really good number for single nut re packed but most will be under .0015" depending on load.

The re shimmed double nuts can give the best results and later on ,if the screws and nuts wear some, you can re shim them which most the time is easier than trying to fit a ball size on a single nut. They cost a little more but if you use the mill a lot then doubles are the way to go.

[dazp1976]

Small home mill I used 1605 C7 w/single nuts. Used thrust bearings and ended up with 0.03mm backlash (0.0012"). I can live with that. (lengths of 280mm / 450mm / 500mm)
However I did use those springy type couplings so I have ordered some plum ones to try out and see if comes down.
I may have just got lucky with the screws.

For the next one I'm going to machine the base a bit and try double nuts and better couplings. Fitting them as close to the underside of the tables as I can and using AC bearings. I don't mind the C7 screws too much but I don't do many circles which is when the backlash is an issue.
It seems to me if you fit them a bit low down to easily clear obstructions you can get a bend effect on the screw which makes the whole thing a waste of effort and exaggerates backlash further.

If the machine makes a little money then yes I may put up £200+ for C5 or less screw/nut hardware per axis. But for now £20-30ish for a C7 isn't a bother. As long as it comes straight!!

[men8ifr]

Arizona - thanks for the info as usual, I'm aiming to go for double ballnuts - but ballnut and shaft will be from different places so I need to measure the preload - not sure how to do that yet, I've seen anywhere from 1-10% quoted as a good amount..

Daz - I've just put a post up in the ballscrew section asking about which double contact bearings to use, 'quality' parts i.e. SKF will be ~12-15 each = £72-90 for a 3 axis mill and they are not sealed so would have to machine mounts for external seals and buy the seals as well... I can get branded 'dunlop' angular contact bearings for £6 each and they are sealed but don't want that if they will add to backlash... I have just seen this though https://www.themanufacturer.com/arti...risps-factory/ so seems they are OEM suppliers and that's good enough for me!

For me I will go C5 or better but of course that only affects error at different positions along the spindle, but for IIRC 0.05mm error that can occur in a C7 screw at 300mm but a C5 takes 1.25metres to accrue the same error.

[mactec54]

Arizona - thanks for the info as usual, I'm aiming to go for double ballnuts - but ballnut and shaft will be from different places so I need to measure the preload - not sure how to do that yet, I've seen anywhere from 1-10% quoted as a good amount..

Daz - I've just put a post up in the ballscrew section asking about which double contact bearings to use, 'quality' parts i.e. SKF will be ~12-15 each = £72-90 for a 3 axis mill and they are not sealed so would have to machine mounts for external seals and buy the seals as well... I can get branded 'dunlop' angular contact bearings for £6 each and they are sealed but don't want that if they will add to backlash... I have just seen this though https://www.themanufacturer.com/arti...risps-factory/ so seems they are OEM suppliers and that's good enough for me!

For me I will go C5 or better but of course that only affects error at different positions along the spindle, but for IIRC 0.05mm error that can occur in a C7 screw at 300mm but a C5 takes 1.25metres to accrue the same error.

If you are going with a C5 then you would get the Ballscrew and Nut from the same supplier or you may have a problem with the ( 2 ) parts fitting, a C5 is normally a Ground screw and nut C7 are rolled screws there is a big difference between the two

[dazp1976]

Daz - I've just put a post up in the ballscrew section asking about which double contact bearings to use, 'quality' parts i.e. SKF will be ~12-15 each = £72-90 for a 3 axis mill and they are not sealed so would have to machine mounts for external seals and buy the seals as well... I can get branded 'dunlop' angular contact bearings for £6 each and they are sealed but don't want that if they will add to backlash... I have just seen this though https://www.themanufacturer.com/arti...risps-factory/ so seems they are OEM suppliers and that's good enough for me!

Not sure which I'll go for yet. Once the machine comes in then I can size it all up.
I was first thinking of a couple of 7001 singles, size 12x28x8 on x.y axis which meant I could poss incorporate a BK12 bearing block into the mounting design for the steppers.
However I'm now thinking of 7201 size 12x32x10 for a little more beef. I'd have to then make complete new bearing blocks from scratch this way. Possibly need to take a small area from the front of the saddle to clear the mount too as it will be higher.
I'm considering a 2005 screw on the Z and haven't looked at options for that yet. May just stick with thrusts there tho.
My Seig X2 will be making the parts once I've rebuilt it all. It's not right mechanically after a bit of an accident.

Doesn't really matter whether I have sealed or not as I'm planning to fit grease points in the mounts and they'll be covered anyway for flood.
I'll have to wait and see how the machine measures up first but those are my 2 ideas. Been delayed coming into uk 3 times already
Prob be the Dunlop bearings for me as their thrust types have been ok. Can't afford much else atm but the FAG caught my eye too.

I hope to get it going by next Feb/Mar. A disability makes me the slowest person on the planet!
See if I can earn a bit of £ from it and then look at it again in terms of upgrading the lot.
It's all a bit of a punt

[men8ifr]

C5's would be rolled, anything better would be 2nd hand and come with a single nut (which may have backlash...)

I have the nominal size for the ballnuts (3.175 IIRC) I'll ask what the screws use!

[men8ifr]

The benefit of the angular bearings over flat thrust bearings is that the lay-out is very simple for the double set , combined with sealed bearings make it all very easy to machine the required mounts and shaft - don't forget the seals will not just keep lube in they need to keep everything else out!

I also looked at tapered bearings but they are not sealed and are wider so cost more in material when making the mounts.

[mactec54]

The benefit of the angular bearings over flat thrust bearings is that the lay-out is very simple for the double set , combined with sealed bearings make it all very easy to machine the required mounts and shaft - don't forget the seals will not just keep lube in they need to keep everything else out!

I also looked at tapered bearings but they are not sealed and are wider so cost more in material when making the mounts.

If you are looking for simple, this works well and is sealed, this is a double row AC Bearing

[mactec54]

C5's would be rolled, anything better would be 2nd hand and come with a single nut (which may have backlash...)

I have the nominal size for the ballnuts (3.175 IIRC) I'll ask what the screws use!

I doubt that you will be able to get a matching fit with anything like this C5 rolled is at the max for accuracy for a C5 and is hit and miss on the accuracy

[men8ifr]

I doubt that you will be able to get a matching fit with anything like this C5 rolled is at the max for accuracy for a C5 and is hit and miss on the accuracy

For double ballnuts I don't think the size of the balls is critical (unless they were too big) , only thing that would be critical I think would be the diameter that the balls run in (possibly) and the pitch (definitely) , but the pitch should be very well controlled, even better controlled on a C5 screw than a C7...

But of course I expect to need to adjust the preload

[dazp1976]

If you are looking for simple, this works well and is sealed, this is a double row AC Bearing

I'm kind of stupid Never really got how these work tbf.
Is it just a case of holding the outer part of the bearing really tight in the bearing block and then the inner bearings don't move laterally?
Which would be best to use too, face to face or back to back?
I assume you'd want a heavy preload one as well.

[mactec54]

I'm kind of stupid Never really got how these work tbf.
Is it just a case of holding the outer part of the bearing really tight in the bearing block and then the inner bearings don't move laterally?
Which would be best to use too, face to face or back to back?
I assume you'd want a heavy preload one as well.

A good fit in the housing is ok but also can be just a slide fit and have a retainer on the front face .0002" to .0003" would be the max you would need undersize for your Bearing fit in the housing

The Bearings I posted in the snip are 2 row AC Bearing that are Back to Back which is the best way for any type of thrust loading like this

These bearings have no preload unless you get the more expensive ones which have the inner races split then you can add preload,so it is best to use these at each end of the Ballscrew and then you can put the Ballscrew under tension / which will give these Bearing a small preload, not much is needed 4 inch pounds is normally enough

[Heavymetalcnc]

For double ballnuts I don't think the size of the balls is critical (unless they were too big) , only thing that would be critical I think would be the diameter that the balls run in (possibly) and the pitch (definitely) , but the pitch should be very well controlled, even better controlled on a C5 screw than a C7...

But of course I expect to need to adjust the preload

I have never seen a C5 rolled ball screw. The only C5 I have ever seen was ground. Who is selling a C5 rolled ball screw? The C6 I use has a pitch tolerance of +/-.0012 over 12". Is this the one you are talking about?

[mactec54]

I have never seen a C5 rolled ball screw. The only C5 I have ever seen was ground. Who is selling a C5 rolled ball screw? The C6 I use has a pitch tolerance of +/-.0012 over 12". Is this the one you are talking about?

Yes there are quite a few different manufactures that make them here are 2 that make a good C5 Rolled Screw

[Heavymetalcnc]

Yes there are quite a few different manufactures that make them here are 2 that make a good C5 Rolled Screw

Ummm...... I don’t want to come off as a jerk here, but I just looked those up. They are precision ground. A good precision ground ball screw costs about 10 times more than a rolled one.

[mactec54]

Ummm...... I don’t want to come off as a jerk here, but I just looked those up. They are precision ground. A good precision ground ball screw costs about 10 times more than a rolled one.

They make both Ground and Rolled in the C5 you can always tell a Rolled screw from a Ground screw the Rolled screw has the grove on the lands of the screw the Ground screws do not

They have C5 Rolled screws as do many other manufacturers, I saw the TBI C5 rolled screw at IMTS just last month, Bosch make a C5 rolled screw also as I have some

[mactec54]

Ummm...... I don’t want to come off as a jerk here, but I just looked those up. They are precision ground. A good precision ground ball screw costs about 10 times more than a rolled one.

Here is one TBI is a Taiwan Company that has been around since the late 80's

https://www.aliexpress.com/item/Taiw...a-eff2b092fa35

[dazp1976]

Just out of interest I've been looking around in the u.k. for screws. Had a quote for a double nutted C5 of £215 + £90 to have it end machined, then add vat. Think I'll pass.
I'll stick with the Chinese C7 at 1/6th the price for now. I know these have an error of 0.05mm. The C5 I looked at have error of 0.018mm so C7 isn't a total disaster.
Those Chinese double nuts though, the way the sleeve is held and rotates about is a bit laughable.
I'll have to come up with a shim and see if I can fit in a separate clamp type bracket I reckon to hold it to the machine in it's own right. That should help no end.

No word on expected date of this new machines arrival yet (again). Was supposed to be the 15th!.
One job that will need looking at is the Z travel. I like to use direct collets at times due to being able to get runout down to 0.004mm quite easily compared to the ER32 chuck systems. However looks like the lowest the Z will go is about 75mm above the table which is a bit high for direct collet use.
I'll have to extend the column slot and put some little extension brackets on the front of the head so I can fit some longer gas struts. I'll add the struts at a later date though. For now just do the slot. Once I get the head off I'll weigh it and get some struts that are rated 50% heavier. That should assist against backlash too as they'll hold the head firmly against the nut.
Something like this:
http://farm8.staticflickr.com/7008/6...d0b35522_b.jpg

Just been bench testing my electronics for it and having to go with Win XP. Still can't seem to get it reliable with Win7 for some reason.
Need to re-solder some connectors as the ones I have are a little under rated for the 1600 oz/in Nema 34. I may have to get some different x,y steppers too as the 425 oz/in may not be enough. Oh the joys of diy.