SIEG X2 Y Axis Stock Screw Dimensional Drawing?

Mulling over this whole "floppy tombstone" design of the Y axis screw and nut, I decided to look into what the "genuine article" uses to move the Y axis. Looking at the design of this Bridgeport Series 1 hardware, its pretty obvious nothing is intended to wobble around "if needed" as SIEG's design does. There has to be a way to eliminate this hassle in the X2 Y Axis. Some kind of rigidly adjustable nut in place of their design. The saddle doesn't wobble around when it slides, and the screw, although only held from one end, is held rigidly from that end, passing through a bearing block in close tolerance to its shaft. So the screw can't wobble around any appreciable amount. The only thing that tries to move is the silly tombstone nut held "loosely" in its over-sized slot. Perhaps something to make the slot a closer fit, and not allow the tombstone to rotate more than a few degrees might help. Or, re-design the nut with the same goals in mind, so it nearly fills the slot?

Bridgeport Y Axis Screw.png
 
An alternative to modding your Y axis drive with a ball screw/nut is to make a new block that uses real thrust bearings like this. I made something similar and it totally transformed the feel of the Y axis. If you make a simpler one-piece bearing block you may lose a bit of range on the Y axis, but worst-case it's not much -- somewhere around .2" if you make the block the same thickness as the OEM part. I made mine out of 6061 and it works just fine.

The reason you may lose a bit of travel on Y: the thrust bearing OD puts it a bit proud of the base so it fouls the table. The design at the link I provided moves the thrust bearing out a bit, but at most you only get a few tenths (of an inch) more range because the feed nut comes up against the base....so there's only so much you can do.

The method for adjusting axes for minimum drag on these machines is to loosen the set screws that hold the feed nuts, run the table up close to the hand wheel and tighten the set screws. You also may find it helpful to (at the same time) loosen/re-tighten the bolts that hold the bearing blocks in place. The built-in manufacturing slop takes care of the rest.

Yes, clear evidence of a poor design, but we're talking about an inexpensive hobbyist-level machine here. Consider it an opportunity to get creative :).

Edit: To give proper credit, I did not design the block shown in the link (a member of the 7x12MiniLathe@groups.io group did that). I just made one like it.
 
That's a beautiful thrust bearing modification!

I already have a thrust bearing mod on mine, sold by Phenom. It is not as involved as the lovely one you showed, but it does help.

Regarding losing some Y axis, when I switched from just having the LMS Large Table to also having the Solid Column (which requires switching the base casting as well) I found that I could actually increase the Y axis travel range by spacing the front bearing block, supporting the crank end, away from the column by an extra half inch using a spacer block I made for that purpose. That almost made up for what I lost by having the DRO X axis glass scale mounted to the back of the table.

I have found with a lot of patience, trial, and error, that adjustment method you mentioned will allow me to actually tighten down the retention screw on the Y axis nut much more than the loose grip they suggest. It's a balancing act between all three screws and the angle you put on the Y axis screw by lifting or pressing down on the crank wheel while you tighten them. But eventually I find that even with the nut retention screw tightened reasonably, the nut still eventually moves, usually at the very worst possible moment while in the middle of a project, and can result in binding the screw shaft so badly you have to stop and fix it.

Rather than going the ball screw route, I am currently thinking about ways to "stabilize" the Y nut so it can move a little, but would be constrained such that it can't cock over in any direction enough to bind the screw. Perhaps a pair of springs bored one into each side, to keep it from rotating very much. I've also toyed with the idea of making a new nut with its weight mass centered at the bottom, instead of at the top. The X nut has its weight at the bottom, and it never moves on me at all. Being top heavy, the Y nut is begging to rotate all the time.

Agreed, it is a hobby level machine, but that doesn't mean it needs to be "thrown together cheaply". They've sold enough of these to have been worth more thought and a better design here. I know the X3 has a support bearing at the rear end of the Y shaft. They wouldn't have added that unless they realized it is needed, probably through complaints about the lack of it on the X2. They could have offered an X2 upgrade to add that bearing.

Creativity is how we take these "once inexpensive" (no thanks to the current establishment's tariffs) tools and make them into something truly useful. Thus the many modifications this machine has seen since I bought it years ago. This Y axis binding is pretty much the last annoyance I am trying to remove.

:) I Thank you all for your suggestions!
 
Correct me if I am wrong but you dont want the leadscrew nut to move. The set screw should be tightened to keep it from moving. What I do is run the Y axis all the way forward and then all the way back and figure out where the nut works best in both directions and then tighten it down. If it moves it allows a lot of slop which is no good unless you have DRO’s. If its positioned wrong it binds really bad in one direction but not the other.
I just measured the threads and they are .615”.
Have you looked into Phenom Engineering’s Y-axis bearing upgrade? It does not completely solve the problem but it does help tocsmooth out the motion.
I am working on getting you those dimensions. I am hoping too
Mulling over this whole "floppy tombstone" design of the Y axis screw and nut, I decided to look into what the "genuine article" uses to move the Y axis. Looking at the design of this Bridgeport Series 1 hardware, its pretty obvious nothing is intended to wobble around "if needed" as SIEG's design does. There has to be a way to eliminate this hassle in the X2 Y Axis. Some kind of rigidly adjustable nut in place of their design. The saddle doesn't wobble around when it slides, and the screw, although only held from one end, is held rigidly from that end, passing through a bearing block in close tolerance to its shaft. So the screw can't wobble around any appreciable amount. The only thing that tries to move is the silly tombstone nut held "loosely" in its over-sized slot. Perhaps something to make the slot a closer fit, and not allow the tombstone to rotate more than a few degrees might help. Or, re-design the nut with the same goals in mind, so it nearly fills the slot?

View attachment 278979
 
EDIT: I wrote a reply before I read your latest replies so disregard everything excpet the thread major diameter

Correct me if I am wrong but you dont want the leadscrew nut to move. The set screw should be tightened to keep it from moving. What I do is run the Y axis all the way forward and then all the way back and figure out where the nut works best in both directions and then tighten it down. If it moves it allows a lot of slop which is no good unless you have DRO’s. If its positioned wrong it binds really bad in one direction but not the other.
I just measured the threads and they are .615”.
Have you looked into Phenom Engineering’s Y-axis bearing upgrade? It does not completely solve the problem but it does help tocsmooth out the motion.
I am working on getting you those dimensions. I am hoping too
 
I too have a scale on the back of the table. I really didnt loose much travel since I have the read head standing up and tight up against the back of the table but I am curious as to how you added travel to the Y-axis. How much travel do you think you gained? Is this simply a 1/2” spacer? Any other mods required?

That's a beautiful thrust bearing modification!

I already have a thrust bearing mod on mine, sold by Phenom. It is not as involved as the lovely one you showed, but it does help.

Regarding losing some Y axis, when I switched from just having the LMS Large Table to also having the Solid Column (which requires switching the base casting as well) I found that I could actually increase the Y axis travel range by spacing the front bearing block, supporting the crank end, away from the column by an extra half inch using a spacer block I made for that purpose. That almost made up for what I lost by having the DRO X axis glass scale mounted to the back of the table.

I have found with a lot of patience, trial, and error, that adjustment method you mentioned will allow me to actually tighten down the retention screw on the Y axis nut much more than the loose grip they suggest. It's a balancing act between all three screws and the angle you put on the Y axis screw by lifting or pressing down on the crank wheel while you tighten them. But eventually I find that even with the nut retention screw tightened reasonably, the nut still eventually moves, usually at the very worst possible moment while in the middle of a project, and can result in binding the screw shaft so badly you have to stop and fix it.

Rather than going the ball screw route, I am currently thinking about ways to "stabilize" the Y nut so it can move a little, but would be constrained such that it can't cock over in any direction enough to bind the screw. Perhaps a pair of springs bored one into each side, to keep it from rotating very much. I've also toyed with the idea of making a new nut with its weight mass centered at the bottom, instead of at the top. The X nut has its weight at the bottom, and it never moves on me at all. Being top heavy, the Y nut is begging to rotate all the time.

Agreed, it is a hobby level machine, but that doesn't mean it needs to be "thrown together cheaply". They've sold enough of these to have been worth more thought and a better design here. I know the X3 has a support bearing at the rear end of the Y shaft. They wouldn't have added that unless they realized it is needed, probably through complaints about the lack of it on the X2. They could have offered an X2 upgrade to add that bearing.

Creativity is how we take these "once inexpensive" (no thanks to the current establishment's tariffs) tools and make them into something truly useful. Thus the many modifications this machine has seen since I bought it years ago. This Y axis binding is pretty much the last annoyance I am trying to remove.

:) I Thank you all for your suggestions!
 
That’s interesting about the leadscrew. I thought it was ACME but I guess thats why I was never able to find much information about it.

I am also using the 2” column riser block and have not noticed any difference in rigidity but I am only using 1 spacer. I think you are the first person I have heard to of ever used 2 spacers. Your mill must have a ton of travel! I have been contemplating upgrading the studs as I feel they are not adequate. I cant remember what size hardware I got to replace them with. I have not gotten around to doing it yet but I will soon because I need to re-tram the column. When I trammed it I used LMS’s plastic shim stock. I know, it was stupid but it was all that I had at the time. I now have Steel shim stock to replace it with and I am hoping it makes it a little more rigid although I think its rigid enough for even 1/2” end mills and slightly larger.

There is one thing you could tell me, since you offered. Are the screws 5/8" diameter? I've been trying to remember that, but hadn't yet dug into finding out.

If you're interested, I've learned that the shaft thread technically isn't ACME as I had thought. ACME doesn't offer the 20 TPI you have now. They are a thread called Unified Standard. I had been looking for a tap or nut and none of the ACME sizes at all use 20 TPI. But there are many of the Unified Standard diameters that use 20 TPI. So I am thinking they are UNS 5/8 - 20 TPI.

I am re-thinking an upgrade to ball screws, given the above information on how they can rotate under a load if manually operated instead of using stepper motors. Now I am considering adding a rear shaft bearing to the Y axis screw instead. I think that might eliminate the screw binding I get when the axis nut shifts in the middle of a project.



You're going to like the upgrades you did!

BTW, if you're wondering can you stack the 2 inch riser blocks LMS sells for extending the solid column, I'm using 2 of them stacked up. I had to find a new longer air spring for lift, but it all works together very well. One of the most major drawbacks to these mini mills is a serious lack of Z axis travel. I also bought a second rack gear, cut it to fit, and mated it to the original, so I can move the head the extra distance of travel toward the table. Later testing seems to indicate there is no concern for flexing with the stacked riser blocks under the solid column when taking heavy milling cuts.
 
EDIT: I wrote a reply before I read your latest replies so disregard everything excpet the thread major diameter

Thanks! In the interim, I was reading a lot of forum posts looking specifically to see if anyone had ever added a rear support bearing on their Y axis screw. I didn't find anything about that, except that many feel this is an acceptable way to do it, supporting the screw only at the crank end. My personal opinion disagrees. But I did find mention of the axis screws being 5/8-20 (on the ones with inch conversion screws).

Here is a link to a slew of information on threads, including where I discovered that there were no 20 TPI listed under standard ACME sizes, but several 20 TPI across the range of UNS thread. Thus, knowing we have 5/8 screws now, I concluded they are UNS 5/8-20. A tap for that thread is available on McMaster-Carr if anyone needs one. Also the 37/64 drill bit required for it.

https://www.gewinde-normen.de/en/20-un-thread.html
 
I too have a scale on the back of the table. I really didnt loose much travel since I have the read head standing up and tight up against the back of the table but I am curious as to how you added travel to the Y-axis. How much travel do you think you gained? Is this simply a 1/2” spacer? Any other mods required?

I gained 0.540". If you will excuse the fact that my CAD drawings are meant only for my own use, and therefore probably do not adhere to any kind of accepted "standards" for CAD in the outside world, I can add a drawing of what I made.

This may or may not work for anyone else. I make no promises. And understand that is is MOVING the travel range of the Y axis, not EXTENDING it. This steals 0.504" off the back end and moves it to the front. The problem is that the rigid column base puts the table closer to the column than it was with the stock column that pivots on the shaft and nut. Because I was losing the 1/2 inch due to the scale thickness (glass scales) I didn't want to give that up. The X2 mill, even with the large table upgrade, has such a meager travel on the Y axis, every little bit counts! It is basically just a spacer, with 3 holes in it, made to fit in between the crank support block and the base casting. I made mine out of aluminum, one of my favorite materials to work with.



Mini Mill Y Axis Screw Extender.png
 
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