Sieg X2D Z axis question

[Razzle]

Hello all. I have been lurking for a while but finally had a question that I wanted to ask. I recently purchased a sieg X2D from LMS. I am now performing initial tear down to clean the shipping oil off and start the lube and tune process.
During this I noticed that the Z axis is very smooth when raising the head, but is a little jerky when lowering the head. I played with the gib a little bit but couldn't seem to make it any better.
So my question: Is this normal or am I missing something. It has the gas shock assist.
I would like to occasionally use it in drill press mode so I can get rid of my HF benchtop DP. I am limited on space so I am trying to be efficient.

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[RJSakowski]

Hello all. I have been lurking for a while but finally had a question that I wanted to ask. I recently purchased a sieg X2D from LMS. I am now performing initial tear down to clean the shipping oil off and start the lube and tune process.
During this I noticed that the Z axis is very smooth when raising the head, but is a little jerky when lowering the head. I played with the gib a little bit but couldn't seem to make it any better.
So my question: Is this normal or am I missing something. It has the gas shock assist.
I would like to occasionally use it in drill press mode so I can get rid of my HF benchtop DP. I am limited on space so I am trying to be efficient.

Sent from my Pixel 3 XL using Tapatalk

It's a combination of stiction and backlash in the gearing. The gas assist is probably contributing to the matter. There are three forces at play when you move the head. Gravity, friction, and your force from cranking the head. They will always add to zero. Gravity is always pointed down and friction is always in the opposite direction of motion. Your cranking force is equal to the vector sum of the those two force. Stiction or static friction is always greater than dynamic or moving friction.

When you are cranking up, the friction and gravity are both directed downward and the forces add. You will notice a very slight reduction on the force required to move the head as the head begins to move and static friction changes to dynamic friction.

When you are cranking down, the friction is directed upward and subtracts from gravity. As the head starts to move, the static friction is now dynamic and therefore decreased and the head will fall, limited by the backlash in the gearing. It then becomes static friction again as you crank to remove the backlash and the process begins again.

The gas assist magnifies the problem as it counteracts the gravitational force reducing its effect. This brings it more in line with the stiction force and makes the jerking more noticeable.

Solutions to the jerking? Reduce the backlash in the gearing. Reduce the gas assist force. Better lubrication of the z axis ways. Possibly the gib on the z axis is overtightened.

 

[higgite]

Hi Razzle,

If adjusting the gibs and lubing it up good doesn't solve the problem, I'd suggest calling LMS and get their input on whether that seems normal for that machine or not. If it's not, they can help you get it sorted out. They have always been very helpful when I've called them with a problem or a product query.

Tom

 

[homebrewed]

One source of backlash on these machines is the rack and pinion drive. Some folks have shimmed the rack using multiple layers of PSA-backed aluminum and claim it helps, but you can't reduce the backlash to zero.

These machines reinforce the "lock all axes except the driven one" adage, because all of the axes have some backlash. The feed mechanisms are either rack/pinion (Z) or threaded rods/tapped nuts (X,Y). Due to the backlash, adding DROs is often one of the first things new owners do. And be very cautious when it comes to climb milling, or just plain avoid it altogether.

 

[Razzle]

Thank you all. This all makes alot of sense
I take it that there is no easy way to measure the lash between the rack and pinion? So shimming is just trial and error until a happy medium is found? I haven't pulled the head off of the column yet. Been trying to get the gunk cleaned off without going that far.

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[homebrewed]

I take it that there is no easy way to measure the lash between the rack and pinion?

The description of the mod indicated it was a trial-and-error procedure. Unfortunately, it doesn't appear that I bookmarked that web site.

If the fine feed didn't have its own huge amount of backlash you could use the fine feed dial in combination with a dial indicator on a mag base to get a feel for how much backlash the rack&pinion have but unfortunately the fine feed backlash is even worse than the rack and pinion (mostly due to the castle nuts that are part of the fine feed mechanism). If you engage the fine feed and then stick a wedge in between the castle nut teeth you're a step in the right direction, but you still have backlash in the worm gear to contend with.

 

[RJSakowski]

You can assess the contributions of the rack and pinion and of the fine feed mechanism in this way. Lock the z axis securely and engage the fine feed mechanism. Use your hand to bias the downfeed lever to prevent its movement and gently move the fine feed dial to the left and right. Stop when you detect some motion in the downfeed lever. Read the dial in the clockwise and counterclockwise extremes. The difference is the contribution of the fine feed mechanism to backlash. No releas the downfeed lever and move the fine feed dial to left and right, reading the dial at the extreme of motion. The difference in the readings is your total backlash. The contribution from the rack and pinion is the difference between the total back;lash and the contribution from the fine feed mechanism.

On my mill/drill, I have .0087" of backlash in the fine feed mechanism and a total backlash of .0225" for .0138" of rack and pinion backlash.

 

[Razzle]

Great procedure. I will be using that. Thank you very much.

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