ball screw questions

[mechhamo]

These are just my opinions.

I just didn't see the need for the 32mm diameter ballscrews. I have only really said to avoid the 3205 (even though it would work, it just won't perform as well as the 3210). That's just from an inertial math perspective. Not sure if you'll find a 3208 size from Taiwan or China.

i think you are correct it seems to be hard to get a 3208 , i looked in the tbi motion catalog and the ball nut type they recommend for milling is a sfm and the only size available in that nut type from them is a 3205 but there are other types of ball nuts that are 3210 but i don't know if these types of nuts are suitable for a knee mill cnc conversion,there is so many different types and i don't know which type is best suited for a particular application and it seems to have pros and cons for each, do you no what types of ball screws are best suited for what i'm doing or can be used.

I took another look at this since you were saying that you wanted to be able to use the mill manually. and because you want to reuse the end support bearings.

it does not matter if dial markings are not useable i can use the DRO and i don't think it will be a problem i hope


For the 3210 a gear ratio of 3:1 is better, but 2:1 is also fine. It would still be a great performer. With a 3:1, assuming a max of 3000 RPM on the servo, you'd be looking at rapids of 10000mm / min or around 400 IPM max.

i did a critical speed test using a a root diameter of 28.5 and got a critical speed of 2900 at 3.1 ratio the max screw speed would be 966rpm what would this relate to in IPM

For the 3205 (just in case you really want the 5mm lead for using the mill manually, perhaps Jim can give an opinion of this), the performance is actually better with a 2:1 gear ratio, something I had not considered doing on a 5mm lead. So assuming 3000 RPM on the servo, 1500 RPM on the screw, that would give a top speed of 1500x5 or 7500mm/min or around 300 IPM.

The fact that you're throwing 750W servos at this makes your life easier. Also the facts that you don't need the fastest acceleration or top speed.

The 3210 will out perform the 3205 but if you want the 5mm lead for manual operation, then you could do that instead. Both would work.

At the last place I worked we had the folding handles on our mill conversions. Real easy to get hurt by a handle without something like that.

i have the type of handles that you have to push in to engage they will rotate but would free wheel if caught on it i hope this works for me.

Perhaps ask these guys for a quote as well for comparison.

https://bstmotion.aliexpress.com/store/314742?

regards wayne

[mechhamo]

hi nic

after sending detail drawings of both shafts and the type of nut i wanted to use to TBI Motion they got back to me

with a price * DFM03205-4* *760 long* was $271 US dollar*delivered and ends machined to my specs (left helix)

and* DFM03205-4* * * *were $376* US dollar*delivered and ends machined to my specs

both screws are ground c5 grade with DFM ballnuts yeah ha !!!!!!!

[NIC 77]

Sounds like you're happy?

If so, that's great! I hope it works out for you. Please let us know how it goes. C5 ground ballscrews sound very decent, and I'm sure you told the salesperson that you wanted them for a mill, so no axial play. My guess is that those prices are around twice the cost, or a bit less than that, of the more inexpensive ballscrews from China, but they are for sure way way less than anything from Germany or Japan and the quality is probably fantastic. Probably a good choice if you don't want to mess around, or risk it. Did you figure out what you will do about driving the quill? Unfortunately, I can't be of much assistance there.

To answer your question if you have a servo that is capable of 3000 RPM, then with 2:1 gear reduction, your ballscrew would spin at 1500 RPM at max speed. With a 5mm lead, 1500 (Revolutions / minute) x (5mm / revolution)

= (1500 x 5) (revolutions x mm) / (minutes x revolutions), the revolutions cancel out and you get 7500 mm / min.

7500 (mm / min) / 25.4 (mm / inch) = 295 inches / min max speed.

If it were me I'd go with the 2:1 gear reduction on those. That will give you a bit better acceleration potential and you don't need a top speed over 295 IPM for rapids on a mill. You could probably run that at 0.3G or more linear acceleration just based on continuous torque and have more cutting force than your spindle could handle. Although you may tone it done from what it can actually do to be within your comfort level and what your mill can handle, as Jim has said in his posts.

Have you sourced your belts and pulleys yet? Could that not effect your end machining?

Probably the first thing you should do when you get your ballscrews is to get them in the bearings and give them a spin to make sure that they are not bent.

Also, you should make a post here to give us a review of your experience with the TBI ballscrews.

When you place your order you can specify in which orientation you would like the nut to be. If you don't specify and it comes the opposite way, then you have to take the nut off and flip it around. There is always a risk of loosing balls when you do this, and it's best to simply tell them the orientation that you want so you don't have to mess around with this if that's at all possible.

[mechhamo]

Sounds like you're happy?

If so, that's great! I hope it works out for you. Please let us know how it goes. C5 ground ballscrews sound very decent, and I'm sure you told the salesperson that you wanted them for a mill, so no axial play. My guess is that those prices are around twice the cost, or a bit less than that, of the more inexpensive ballscrews from China, but they are for sure way way less than anything from Germany or Japan and the quality is probably fantastic. Probably a good choice if you don't want to mess around, or risk it. Did you figure out what you will do about driving the quill? Unfortunately, I can't be of much assistance there.

yes it was a case of me knowing what i needed and wanted before i could order so i downloaded the TBI catalog and studied what ball nut was designed for milling, as the part number said DFM series (designed for milling) it is a double nut which has a outer diameter smaller than others because of the double nut which i need to keep that size down otherwise the yoke that i have to make will become to large to fit in and the bed will hit it.
the only problem was if i wanted a left helix for the x axis they only do the DFM nut type in a 32mm ballscrews.

i have thought about the z axis and i am thinking at the moment how i can engage and disengage quill from manual to cnc have got any thoughts on that.

To answer your question if you have a servo that is capable of 3000 RPM, then with 2:1 gear reduction, your ballscrew would spin at 1500 RPM at max speed. With a 5mm lead, 1500 (Revolutions / minute) x (5mm / revolution)

= (1500 x 5) (revolutions x mm) / (minutes x revolutions), the revolutions cancel out and you get 7500 mm / min.

7500 (mm / min) / 25.4 (mm / inch) = 295 inches / min max speed.

If it were me I'd go with the 2:1 gear reduction on those. That will give you a bit better acceleration potential and you don't need a top speed over 295 IPM for rapids on a mill. You could probably run that at 0.3G or more linear acceleration just based on continuous torque and have more cutting force than your spindle could handle. Although you may tone it done from what it can actually do to be within your comfort level and what your mill can handle, as Jim has said in his posts.

yes i think the 2.1 ratio will be my choice, the speed will be faster enough for what i will need considering a cnc knee mill is not ideal and is never going to be able to run speed like a linear rails but i had the mill and decided it won't be perfect but it will be very helpful for me.

Have you sourced your belts and pulleys yet? Could that not effect your end machining?

i have not sourced them yet but if anyone knows a site to get them from please let me know,the x axis has the power feed mounted and there is plenty of shaft sticking out to mount drives, i am thinking of milling up a complete new end housing with the same bearing mounts as the the old end plate but will also carry the drive motor and be able to fix a cover,the x axis will be able to be done by removing the dial wheel because i don't need it as it has a dro

Probably the first thing you should do when you get your ballscrews is to get them in the bearings and give them a spin to make sure that they are not bent

thanks for that info i sure will.

Also, you should make a post here to give us a review of your experience with the TBI ballscrews.

i will put photos up when i get them and of the installation as well i got the ground screws because i thought it would give less noise in operation

When you place your order you can specify in which orientation you would like the nut to be. If you don't specify and it comes the opposite way, then you have to take the nut off and flip it around. There is always a risk of loosing balls when you do this, and it's best to simply tell them the orientation that you want so you don't have to mess around with this if that's at all possible.

will do for shore kind regards wayne