SIEG X2 Y Axis Stock Screw Dimensional Drawing?

MetalMuncher

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Does anyone know where I can find a CAD type drawing of the stock Y axis screw for a SIEG X2 mill? I am specifically interested in the end machined for the hand wheel and support block, and the dimensions of that machining.
 
Or, alternatively, a supplier of 20 TPI ball screw kits machined to use the original hand wheels of the SIEG X2? I'd like to convert only my Y axis screw to a ball screw, but I have no interest in converting to CNC. I also don't really need to do the X axis, as it works smoothly and already has a power feed on it. So I am looking for a single kit for just the Y Axis.
 
Just a heads up regarding the use of ball screws in Manual Mill (Non-CNC) setup. Ball Screws are two way. What I mean is turning the screw moves the Nut/Table, but also pushing on the Table will turn the screw. Unlike Acme or Square Treads, which are "one way", where only turning the screw will move the Nut/Table, just like worm drives.

I bring this up because, without something to hold the screw in position (such as a Stepper or Servo) you will alway have to make sure the table is locked or any pressure will move it.

Based on your second post, are you looking to improve the "smoothness" of the Y axis?
 
I did not know that. Thanks! I do have a power drive on the Y axis, but it has a disengagement clutch to make it easier to use the hand wheel.

Yes, my goal is to get around the miserably poor smoothness of Y axis movement when the gibs are anywhere near reasonably snug.

My opinion of how they overlooked adding a rear carrier bearing on the screw is about as low as it could be. There is certainly room for one. I've thought about making one, but converting to a ball screw would be easier. I have a Phenom thrust bearing kit on the screw, and that helped a little. I can get fairly smooth movement with a lot of patience in the adjustment procedure for the front screw support block and for its acme nut, but their intended design for the nut retention screw to not be torqued down fully is another miserably poor design. And the smooth movement I do achieve is always a time bomb waiting to change, usually in the middle of some involved machining project requiring a lot of Y axis movement.

The whole reason I designed a power drive interface for the Y axis is to help with how difficult turning the Y axis screw can get when it starts to go out of perfect adjustment in the middle of some project. Sometimes even the power drive won't turn it. Then I have to tear things down and redo the adjustment before I can complete the project in progress. I'd like to find an affordable way to eliminate this problem. This mill is highly customized, so I doubt I'll ever look toward a different mill.
 
Sounds like you've done a lot of work to your mill. Versus the leadscrew, could your issues be more related to your ways and gib?

Could the Gib benefit from stoning or flattening/smoothing on a surface plate. Regarding the ways.... could they also be stoned or going to the extreme, you could consider scraping?
 
I won't consider scraping, but the gib strips have already been polished on a surface plate. The problem is not there.

As I mentioned, when I can get all the planets to align while hitting that infinitescimle sweet spot adjusting the screw support block and acme nut retainer, I get very smooth travel. The problem is that the acme nut moves, as per their stupid design, and in so doing it binds on the screw. If I torque the nut retainer down, then it also binds. If I leave the nut retainer too loose, it also binds. It has to be tightened to some imperceptible magical amount that has no definition, so it can't possibly be expected to remain as such. The only reason for such a (ridiculous) set up is because they KNOW the acme nut and its slot are poorly machined, so this was their half baked solution....to allow the nut to wander around instead of being held in precise alignment.

I have to wonder if it would even work to put a carrier bearing on the far end of the Y screw so it can't wander off being parallel to the ways. It may come down to their not making the ways perfect either. But I've seen so much discussion on converting these X2 mills to CNC that I feel using a ball screw must be improving on the poor original design, or there would be tons of dialog on CNC not working with these mills. So I am thinking the problem is not in the ways. It is in the original acme screw and nut.

It has occurred to me today that I have a way to create a CAD drawing of the screw's hand crank machined end myself. When I converted this mill to inch scale many years ago, I kept the original metric acme screws. The shaft dimensions for the crank end will be identical. I can measure the old metric shaft to get the dimensions and draw it up myself, without taking my mill apart. I would need this drawing in the event I decided to order a customized ball screw to fit the mill's Y axis, so I could provide the vendor with the drawing for their custom machining.
 
Your comment " I have to wonder if it would even work to put a carrier bearing on the far end of the Y screw so it can't wander off being parallel to the ways" made me wonder... Could you leadscrew nut and Y axis bear block not aligned, given the lead screw moves off parallel to the ways as you move the axis?

The reason I mention it is, I recently refurbished a Syil X3 CNC mill, which is built on the chassis of the Sieg SX3 ( the big brother to your X2). The owner sold it because it was loosing steps on the X axis and he was unable to determine the cause. What I found was the Ball Nut was originally mounted slightly Off center and Low, from the centerline of the lead screw, causing the screw to bind towards the ends of travel. I took me about a 1 week of chasing to figure it out. In my case the bearing block at the end of the lead screw made it worse, since it prevented the screw from deflecting as it got closer to the bearing block.

Hope this helped... Good Luck
 
I am wondering if you are familiar with the way the SIEG X2 Y axis screw and nut are constructed? There is no way to "align" the nut. The manual tells you it is SUPPOSED TO move. They tell you to only "snug" its retention screw so that the nut is pretty much loosely held in whatever is the closest to a real alignment. Its poor design. They do that, coupled with the lack of a tail end carrier bearing, so the screw can move around "if needed".

It's like how some people only fasten one end, and the head screw, on a DRO scale, because they don't want to take the time and patience to properly get the scale fastened such that the head travels perfectly aligned from end to end with both ends and the scale head firmly screwed down. If you try to fasten the nut retainer screw tightly, the screw will bind at some point(s) in travel. My statement that the screw goes off parallel is an assumption, I admit, as it is forced in some direction by the movement of the acme nut in its loose holder, as it suddenly grabs in the slot. Ideally, wanting something to be able to move around in a slot should not incorporate the end of a screw trying to hold it in place, but should incorporate lubricated polished bearing surfaces to guide it along a desired path if it does move, precisely adjusted to eliminate chatter. Imagine if, instead of a nice smooth flat gib strip, the ways on the mill table axis were held in tight tolerance instead by only the tips of the gib screws themselves against the ways. That's essentially what SIEG did on this acme nut.

The X2 Y axis nut looks like an inverted tombstone. The threads for the screw are toward the rounded end. The squared off end sits upward in a slot that is wide enough to allow the tombstone to rotate many degrees left and right of being perpendicular. In fact, it can rotate beyond the point where it comes out of the slot in the carriage, if not careful when adjusting it. This allows for flexing of the screw (which ideally should never be needed) to accommodate whatever travel errors are occurring along the screw path, likely due to the fact the screw isn't rigidly constrained. This is a top heavy orientation. If the "snugged" retention screw loosens (it hides behind things you must remove to access it), the square top end of the tombstone "flops over" to one side or the other. Note that the alignment of the tombstone nut is the only thing holding the screw parallel to the ways, since the screw is free floating at the tail end. So when the nut tries to flop over, it pulls the screw sideways with it, and that is what causes it to bind, usually bringing a halt to any project until you disassemble, re-align and re-assemble things again. Typically, when the nut "moves" to one side, it never "moves" back the other way because of the retention screw grabbing at its surface as it slides past the screw end. That nut needs to be held in place vertically so it can't flop over. On the X axis, the squared off (heavy) end of its tombstone nut hangs down instead of pointing up, so gravity helps keep it centered. Perhaps what they should have used on the Y axis is a circular disc, with the acme threaded hole in its center, rather than the crazy inverted tombstone design they used. Hmm. I wonder if that idea would retrofit?

It is interesting you mention the X3 uses a tail carrier bearing. Perhaps they realized how essential that is. When they did, they should have applied the idea to any further X2 models produced. I've been through 3 different base castings along my upgrade path to the wider table and then a fixed vertical column. Every one of them lacks the tail bearing, and has this same problem with the Y axis screw binding. This "floppy nut" issue causing the binding is intrinsic to their design, it is not just a single incident on one casting. If they would have used the same design they use on the X axis, which has a bearing at both ends, and moves as smooth as butter, there would not have been this issue.
 
I have the factory Y axis and X axis leadscrews out of my Sieg X2 if you want me to get you any dimensions with a picture or something? I installed the LMS imperial leadscrews and now have a larger table abd solid column so I will never use them again if you are interested in one or both of them.
 
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.
 
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