Ballscrew and Parts sourcing -experienced users please respond

[Ninhil]

I'm sourcing out my own parts to build my ballscrews and mounting hardware for a seig X3 machine.

I am looking at McMaster.com for these parts because I'm not wanting to spend a fortune on conversion kits. My questions are bolded.

5/8" BALLSCREW:
item# 5966K26
Price Per Inch: $1.27


What is the length in inches I need to order in ballscrew for the X3 for X,Y and Z axis? (Total length including what needs to be machined off)

I will need to machine down the ends of these Ballscrews to fit the flex coupling to the motor shaft. Also there is some material machined of of the ends and I see some sort of stopper is mounted.
What is the machined shaft diameter? Also what lengths need to be machined along the shaft endls along the axis of X,Y and Z?
What are these stoppers I see set onto the ballscrews?


5/8" BALLNUTS:
item# 5966K16
Price Each: $23.85



ZERO-BACKLASH FLEXIBLE SPIDER SHAFT COUPLINGS:
Plain Aluminum Item# 9845T2
Set Screw Glass Fiber Item# 9939T1
Price Each: Somewhere near $15



To connect the couplings to the NEMA 23 motor shaft, you would need a 1/4" couple on one side. For the other side I'm unclear about because I have no idea what the shaft diameter I will need to machine the Ballscrews to. 5/8" ballscrew diameter is O.D. right?
There is also an option to choose from a coupling that sets on the shafts with a set screw, or to choose the aluminum coupling with no set screw. Which one would you recommend? I think the motor shaft is ground flat on one side, but that would mean the ballscrew would also need to be machined flat on one side as well, right?
It also looks like it is appropriate to choose the proper spider to connect the couplers. I suppose choosing the proper in/lb is of greatest concern. There are also angular tolerances and hardness properties. Less hardness leades to greater cushioning I believe. Angular tolerances leads to better backlash resistance I believe.


GAS SPRING:
15.23" 90lb force
Item# 4138T55
Price Each: $19


What Length Spring should I order? I see the X3 has 14-7/8" of head stock travel, so there would need to be at least 15" Total Gas Spring Length (Dimension A). Also, The Compression length needs to accomidate the mill at it's lowest stroke (Dimension B). This leads me to pick Item# 4138T55. Can anybody tell me if this is correct?
I picked the 90lb Gas Spring force because of what I've read on another thread on the forums. Is this a good value to go with?



ANGULAR CONTACT BEARINGS:
(2 Per Axis Back to Back)
ITEM# 7201B 12x32x10
Cost Per Axis: $15


As for the ballscrew mounting blocks, and motor mounts, I'm going to engineer this fine man's solidworks files to work with stepper motors.
Bob Berg's Site: http://www.rlberg.com/millprt/



I really appreciate all the help I've been getting from the members of this site. I am really getting very close to summarizing all of the parts I need and then go through with this X3 Build!

[Ninhil]

When I mentioned the ballscrew lengths, this is what I was talking about.

Perhaps this becomes more obvious when I get the machine in front of me and I remove the ACME threads.




edit: perhaps the machined length of the ballscrew at the motor connection is 10mm. This will match the ID of the Bearing I listed. BUT....

But what about the coupler? I'm still confused as to what coupler size I should use. Its probably best to use the largest diameter machined down from the ballscrew I imagine.

[S_J_H]

Mcmaster is a good source , SDP-SI is a real good source as well. I like OLDHAM type couplers which you can get from either source. 6ft of ballscrew should be enough. Your questions about the machining I can not answer though. If you are going to try and duplicate the conversion you linked to I would think the owner of that mill might be able to help with those specific questions. There is no set length or shaft diameters that can be used universally to determine what needs to be machined off the ballscrews. That all depends on the conversion design. I have no idea what those stopper things are. Might be a bearing or collar. I have no such animal on my mill. Steve

[lewisd]

re things on the end of ballscrews
top one is a split ring about 3/8 inch thick that has a set screw that will make it clamp down on the 12 mm shaft so shaft is snug againt a bearing. I do not know what they are called.
The lower one looks like a spanner nut threaded on shaft(does the same thing as above but can be adjusted very precisely to squeeze bearing just the right amount. If you have room to get tool in to adjust, this is best. My z shaft has very little room on bottom to service so it has the clamping type and my x and y has threaded ends because you can get to ends easily to tighten nut up against bearing.

[Deviant]

Both of those are shaft collars with set screws.

It's not how the ballscrews should be held in place.

There is a huge discussion on this regarding the cncfusion conversion kit and their methods.

Ideally, you'd have the screw machined to exact length needed. Then each end would be turned down to slitfit into a bearing. There's much discussion on the type of bearing.

Most of the spindles are designed with angular contact bearings. I'd guess you could continue that practice, but you'd really need some mechanical engineer to tell you why you really need one of the other.

Now that you have the ballscrew to length. And supported on each end with a bear. You need to decide how your going to contain it.

In the example picture above. It's contained by smooshing that collar against the bearing then cranking down the set screw.

The most accepted practice that I have seen involves one end of the screw being turned down over a longer length. Now you have the bearings to support the screw. That bearing fits into a pocketed plated. On the opposite side of the plate is another pocket where an additional bear will be fitted.

Now you have the screw supported with dual bearings sandwiched around the mounting plate. Now you have to keep it from moving in and out. This is done by threading the part beyond the second bearing. You can then apply a certain amount of pressure to the thread/nut and secure the screw.

Past the threaded part is where the screw is turned down to support connection to a motor. Through some type of coupler. Generally these are machined flat one one side to allow for a sets screw.

I hope that my description is good enough.

[Ninhil]

Originally Posted by Deviant Both of those are shaft collars with set screws. It's not how the ballscrews should be held in place. There is a huge discussion on this regarding the cncfusion conversion kit and their methods. Ideally, you'd have the screw machined to exact length needed. Then each end would be turned down to slitfit into a bearing. There's much discussion on the type of bearing. Most of the spindles are designed with angular contact bearings. I'd guess you could continue that practice, but you'd really need some mechanical engineer to tell you why you really need one of the other. Now that you have the ballscrew to length. And supported on each end with a bear. You need to decide how your going to contain it. In the example picture above. It's contained by smooshing that collar against the bearing then cranking down the set screw. The most accepted practice that I have seen involves one end of the screw being turned down over a longer length. Now you have the bearings to support the screw. That bearing fits into a pocketed plated. On the opposite side of the plate is another pocket where an additional bear will be fitted. Now you have the screw supported with dual bearings sandwiched around the mounting plate. Now you have to keep it from moving in and out. This is done by threading the part beyond the second bearing. You can then apply a certain amount of pressure to the thread/nut and secure the screw. Past the threaded part is where the screw is turned down to support connection to a motor. Through some type of coupler. Generally these are machined flat one one side to allow for a sets screw. I hope that my description is good enough.

I understand. This relly helps to explain whats going on here. Thanks!



So from what I gather so far:

BALLSCREWS:
I'm going to need somewhere around 6' of ballscrew. It would be nice to know how much I need for each axis. I can just order the machine, and copy the length of the ACME Screws for this... Unless someone already knows. I can order the screws from McMaster cut to length. This will also save on shipping.

SHAFT COUPLERS:
1/4" is needed on the side that couples to the motor. What Diameter should I use to couple to the Screw? 1/2"?

GAS SPRING:
Is that one I spec'd out suitable?


Again, I appreciate all the help!

-Brandon

[Deviant]

As it was posted above.

There is no "set" screw length. That depends on your setup. ((Will you be using stock location of the existing mounting plates. Or will you hollow them out to steal a little extra movement or mounting depth))

I.e. if you use a double ballnut with double angular contact bearings. Your length could be longer than someone that uses stock bearings with a single nut.

Additonally, depending on how you attach your motor, you could need a longer or shorter shaft sticking out beyond the bearing location. I.e. You have a 2-1 pulley system vs direct connect.

The couplers depend on your design. If you use bearings that have an inside diameter of 12mm, with a 10mm thread section for preload nut. Then I'd assume that your shaft portion will be somewhere between 0-10mm's.

You need to decide what size ballscrews, bearings and motor shaft your using. Then research what premade couplers exist. I.e. if they only offer 1/4 to 1/4 or 1/4 to 1/2. Your decision is already made.

As for the gas spring. I don't know. I've read of people using 75lbs. You need to know how much the head weighs, then decide how much of that you want to left. If the head is 75lbs but you use a 95lb gas spring.. You increase the work to lower the head, but make it easier to lift.

Ideally, I'd think you'd want it even, or slightly on the weaker side to allow gravity to help with chatter/kickback on the head.

The last part is only my assumption.

((Edit, cause I can't spell/type))

[Ninhil]

Originally Posted by Deviant As it was posted above. There is no "set" screw length. That depends on your setup. ((Will you be using stock location of the existing mounting plates. Or will you hollow them out to steal a little extra movement or mounting depth)) I.e. if you use a double ballnut with double angular contact bearings. Your length could be longer than someone that uses stock bearings with a single nut. Additonally, depending on how you attack your motor, you could need a longer or shorter shaft sticking out beyond the bearing location. I.e. You have a 2-1 pulley system. Couplers depend on your design. If you use bearings that have an inside diameter of 12mm, with a 10mm thread section for preload nut. Then I'd assume that your shaft portion will be somewhere between 0-10mm's. You need to decide what size ballscrews/bears and motor shaft your using. Then research what premade couplers exist. I.e. if they only offer 1/4 to 1/4 or 1/4 to 1/2. Your decision is already made.

ahh i see now. so 6' it is!
@1.27 per inch, this aounts to $91.44 of material.
shipping may be higher on 6', but at least i wont have any lengths cut too short.

Originally Posted by Deviant As for the gas spring. I don't know. I've read of people using 75lbs. You need to know how much the head weighs, then decide how much of that you want to left. If the head is 75lbs but you use a 95lb gas spring.. You increase the work to lower the head, but make it easier to lift. Ideally, I'd think you'd want it even, or slightly on the weaker side to allow gravity to help with chatter/kickback on the head. The last part is only my assumption. ((Edit, cause I can't spell/type))

I'm also going to assume the weight should be even or slightly more than head weight. This is to keep the ball nuts held against the screws, am I right?

CNC Fusion says it is used for making raising and lowering the spindle head easier. SO... How much of a difference does this really make?

[NC Cams]

Unless you preload the ball screw support bearings, you're going to have direction change slop issues to contend with that backlash comp will NEVER get rid of. You can preload them by either shimming them or sending them to KAF Manufacturing in Stamford CT and have them preload them DB for you.

I"d go with about 150 lbs of TOTAL preload for the each set of 2 bearings (distributed 75lbs per bearing). This is NOT that much as a true ball screw bearing can be set with as much as 500 lbs of preload. The 150 is pretty much a "standard", accepted value for a true, milling machine grade mills.

To determine how much to shim is not doable by calculation - you have to dead load the bearings axially and measure the individual raceway offsets. KAF can do this for you, individually grind them, and then they etch the chevron markings on OD to denote proper positioning.

I don't recall what the cost is - its been a while since I had any done - but it is reasonable all things considered. Since you're already sparing no expense for the bearings (true ball screw bearings go up to $800/set), you should be able to afford precision/professional preloading services.

All things considered (as in time wasted, hurt parts, screwing around), having a proper preload ground into the bearings is simply good money well spent. YOU WILL NOT REGRET IT.

[Ninhil]

Originally Posted by NC Cams Unless you preload the ball screw support bearings, you're going to have direction change slop issues to contend with that backlash comp will NEVER get rid of. You can preload them by either shimming them or sending them to KAF Manufacturing in Stamford CT and have them preload them DB for you. I"d go with about 150 lbs of TOTAL preload for the each set of 2 bearings (distributed 75lbs per bearing). This is NOT that much as a true ball screw bearing can be set with as much as 500 lbs of preload. The 150 is pretty much a "standard", accepted value for a true, milling machine grade mills. To determine how much to shim is not doable by calculation - you have to dead load the bearings axially and measure the individual raceway offsets. KAF can do this for you, individually grind them, and then they etch the chevron markings on OD to denote proper positioning. I don't recall what the cost is - its been a while since I had any done - but it is reasonable all things considered. Since you're already sparing no expense for the bearings (true ball screw bearings go up to $800/set), you should be able to afford precision/professional preloading services. All things considered (as in time wasted, hurt parts, screwing around), having a proper preload ground into the bearings is simply good money well spent. YOU WILL NOT REGRET IT.

I've read about threading the ballscrew shaft, placing a nut and washers on the screw, and inserting a spring in between the washers. This presses against the bearings.

I probably will be doing this myself, and not sending these parts to a shop for their analysis. But thanks for the info.

[Barbs]

Hello,
I'm a mechanical engineering major and for my senior project I have been assigned the task of designing a gantry style table top cnc mill. I've never designed a mill, so I am trying to get some more information about the technical details in designing a mill.

Originally Posted by Deviant Both of those are shaft collars with set screws. It's not how the ballscrews should be held in place. There is a huge discussion on this regarding the cncfusion conversion kit and their methods. Ideally, you'd have the screw machined to exact length needed. Then each end would be turned down to slitfit into a bearing. There's much discussion on the type of bearing. Now that you have the ballscrew to length. And supported on each end with a bear. You need to decide how your going to contain it. The most accepted practice that I have seen involves one end of the screw being turned down over a longer length. Now you have the bearings to support the screw. That bearing fits into a pocketed plated. On the opposite side of the plate is another pocket where an additional bear will be fitted. Now you have the screw supported with dual bearings sandwiched around the mounting plate. Now you have to keep it from moving in and out. This is done by threading the part beyond the second bearing. You can then apply a certain amount of pressure to the thread/nut and secure the screw. Past the threaded part is where the screw is turned down to support connection to a motor. Through some type of coupler. Generally these are machined flat one one side to allow for a sets screw.

I was confused about some of the thing brought up in this post. What is a bear?
I can't visualize the "dual bearings sandwiched around the mounting plate".
or the "threaded part beyond the second bearing"
Any link to where I can see a good example of this?

I was particularly interested in this post:

Originally Posted by NC Cams Unless you preload the ball screw support bearings, you're going to have direction change slop issues to contend with that backlash comp will NEVER get rid of. You can preload them by either shimming them or sending them to KAF Manufacturing in Stamford CT and have them preload them DB for you. I"d go with about 150 lbs of TOTAL preload for the each set of 2 bearings (distributed 75lbs per bearing). This is NOT that much as a true ball screw bearing can be set with as much as 500 lbs of preload. The 150 is pretty much a "standard", accepted value for a true, milling machine grade mills. To determine how much to shim is not doable by calculation - you have to dead load the bearings axially and measure the individual raceway offsets. KAF can do this for you, individually grind them, and then they etch the chevron markings on OD to denote proper positioning. I don't recall what the cost is - its been a while since I had any done - but it is reasonable all things considered. Since you're already sparing no expense for the bearings (true ball screw bearings go up to $800/set), you should be able to afford precision/professional preloading services. All things considered (as in time wasted, hurt parts, screwing around), having a proper preload ground into the bearings is simply good money well spent. YOU WILL NOT REGRET IT.

What exactly is meant by preloading the ball screw support?
Preloading them how? press fitting the bearings in place?

"you have to dead load the bearings axially and measure the individual raceway offsets."
Huh?

It's kind of a big project and all the little details are starting to get a bit overwhelming.
Some good issues were brought up in this tread and I'm just trying to get a little more info on these issues.

[phantomcow2]

There are indeed a lot of details.

Check google for documentation about preloading bearings.
I don't know what the cost is to get regular bearings preloaded. BUt it may be more economical to simply buy a duplex already preloaded from New Hampshire Ball Bearing. Plus, your original bearings will probably be of higher quality than generics. All of Danaher Motion's duplex bearings are NHBB.
That said, I successfully preloaded 3 pairs of 10$ VXB bearings, and the results are fantastic.