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Sieg SX2P (LMS hitorque 3900) feed screw question

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chris.trotter

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#1
I'm working on a power feed, went to screw the X (long) axis feed screw back in from the other side, discovered there was a small lock washer kinda thing right at the transition from thread to spindle end (where the handle slides on). Had to forcefully remove it (verrrrrry carefully), and now I can thread the feed screw in from the other side.

However, I now need to replace that. No prob! Except it's not on any parts diagrams or lists anywhere... It kinda looks like its purpose was to prevent the feed screw from trying to pull itself too far in at the feed screw nut?

Like here's my machine: Parts diagram PDF
(they call it the Y axis)

The feed screw shoulder right before the thread has nothing in the parts diagram there. (see red arrow)

washer-thingy.png


Anyways, I'm probably just going to fabricate something, but super curious why it was on my machine, but not in the diagrams. Even the LMS diagrams have nothing for any of the clones of this machine.

BTW, this is what I've done which required me to screw it in from the other side...in hindsight maybe not the best solution.
apr17-feed_screw_gear.png


Why I'm asking this is that after reassembly, there is an enormous amount of backlash. (could also be that my modifications aren't allowing the handle nut to fully pull everything together) Is there a definitive guide to "eliminate backlash in a mini mill"?
 

Richard King 2

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#2
If the machine didn't have backlash before then the factory added that washer to eliminate the backlash. Those drawings from the mfg's. have a lot to be desired in most cares. They may have to put different thickness washers on different machines. I suspect your an Engineer by trade and expect everything to be perfect as we are used to here in the North America, but working with Asian Machines you have to have an open mind and one never knows what to expect.
 

chris.trotter

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#3
Ya, that's possible. Also more possible is that I've just not reassembled things correctly. The backlash I'm seeing now is 5x the thickness of that washer. :)

I am no engineer, and am totally ok with this being what it is - like I said, was just gonna fab something up. Just have no experience and therefore don't know what to expect, so hoped the wiser amongst us would help out. As has happened. :)

I'll take another crack at it tonight with the knowledge that the washer is 'just gettin' er done'. :D
 

homebrewed

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#4
The X axis of these mills has a thrust washer on the feed screw. It greatly reduces friction so you can tighten up the nut (on the other side of the hand wheel) to get a minimal amount of backlash without making it too hard to turn the crank.

Your machine may not be exactly like mine (an SX2), but most in this category do NOT have thrust washers on the Y axis. It is very easy to over-tighten the nut on the Y axis and make it overly difficult to turn the crank. This shortcoming has been the subject of a number of mods.

Sources of backlash on the X axis include the nut on the hand wheel (too loose = backlash), loose set screws that hold the feed screw nut in place, and the normally-present clearance between the nut and feed screw. You can address the former two things but not the latter (at least, not with the stock pieces).

BTW, the thrust washer should have three components. Two hardened "races" and a thingie between them that holds the bearing balls. It looks to me like you don't have all the pieces back in there. Sometimes the pieces on the right side get pulled out when you remove the end piece. Maybe they fell out when you tore that part of the table down?

Mark
 

chris.trotter

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#5
Interesting - I have a pair of thrust washers the previous owner gave me (but never actually installed). Pretty sure my 'major backlash' is just improper reassembly at this point.

@homebrewed I'll look up how to add them, thanks!
Also, do you refer to X/Y axis as per their manual, or the common perception (reverse). I feel like all my exposure so far has been that the long part of the table is X, short is Y. Incorrect?
 

homebrewed

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#6
PS the thrust washer probably is item #21 on the parts diagram. See what it is supposed to be.
Mark
 

homebrewed

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#7
Interesting - I have a pair of thrust washers the previous owner gave me (but never actually installed). Pretty sure my 'major backlash' is just improper reassembly at this point.

@homebrewed I'll look up how to add them, thanks!
Also, do you refer to X/Y axis as per their manual, or the common perception (reverse). I feel like all my exposure so far has been that the long part of the table is X, short is Y. Incorrect?
The long axis is the X, short axis is the Y. So moving the Y axis will move the table toward/away from the operator.

To be clear: each thrust washer has three separate components. So if you have two complete thrust washers you should have: 4 races, which look a lot like plain old washers; and 2 bearing ball cages. If you DO have two fully complete thrust washers it is possible that your Y axis uses one, too...and it isn't installed correctly, either.

Mark
 

chris.trotter

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#8
Huh, ok will try and install both tonight. Yeah, I have two complete thrust washers, still in original plastic baggies.

Thanks!
 

homebrewed

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#9
Huh, ok will try and install both tonight. Yeah, I have two complete thrust washers, still in original plastic baggies.

Thanks!
Not knowing what the previous owner was up to, it is possible that he/she just got a spare for the X axis. If your Y axis currently has very little backlash you probably don't need to tear into it. Examination of the parts diagram did not reveal a thrust washer but maybe your machine's Y axis has been modified? There is at least one aftermarket upgrade to add a thrust washer to the Y axis.

Good Luck tonight!

Mark
 

chris.trotter

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#10
So I reassembled things - the fitment of the feed screw seat (item 24) was a bit tight, causing the screw not to seat properly. I jiggled it in, and was finally able to reassemble properly. Downside of adding the thrust washer is that it reduced the amount of thread sticking out for the handle lock nut. I removed the nut's washer and there is just enough thread, but it's pretty tight now. Workable, but tight. Another issue is that the thrust washers I have are obviously the wrong size for this machine - they are probably 2-3mm too large on the ID. I will attempt to make a little bushing/spacer thingy.

On the plus side I got the power feed gear dealy attached (properly this time, I hope), and as a grand finale to the evening did fly cutting on a piece of aluminum for the first time - and a wide one, at that! (6x2") Cannot believe how much faster/easier it cuts compared to steel.

2018-04-18 20.17.18.jpg


2018-04-18 20.17.29.jpg


2018-04-18 20.53.20 HDR.jpg


Thanks guys!
 

homebrewed

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#11
Congrats on getting your 3900 mill up and going!

It does appear that your thrust bearing is not the right one. There shouldn't be anywhere near that big a gap between the dial and the mounting bracket (#'s 18 & 24 on the parts diagram). The thrust bearing should fit into pockets in the dial and bracket. That's why you don't have much for the nut to thread onto.

It looks like your mill is usable for the moment, but you may want to think about getting the right thrust bearing. As it is, it would be awfully easy for swarf to get into the bearing. Are both of the thrust bearing sets you have the same? Maybe one of them is a different (hopefully more compatible) size. If not, LMS would have the right one.

BTW when the nut is snugged up tight to remove backlash the thrust bearing is under load so you don't want to use it dry. Put some lube in there. I use lithium grease. Unfortunately, grease attracts swarf so right now you have a version of the devil's dilemma.
 

chris.trotter

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#12
Just to be clear, it's a Sieg, not LMS 3900 (same kinda thing).

Yeah, it crossed my mind. Saw other kits come with a plastic shroud to prevent swarf from getting in, but they also clearly mount where I've placed them. I'll look up replacing it (LMS has some), but I mean, this was "free", so might as well use it for the time being. :)

Thanks for the pointer on grease - had wondered about that when installing. Will do.
 

homebrewed

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#13
OK, not sure why I was thinking you had a 3900. That just makes my comments more relevant :).

Free is a very good price! Have fun!

-Mark
 
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