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Half-nuts take time to engage

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redvan22

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#1
Hi,
On my Microlux 7x16 mini lathe, when I attempt to engage the half-nuts, with the default gearing just to turn down stock, they seem to not lock immediately but take a moment and then engage with a clunk. I'm planning on doing some threading in the near future and this behavior doesn't make me feel confident.

I came across something (article, post, not sure) that delved into resynchronizing the lead screw with the thread dial and half-nuts but I cannot remember where.

Any help would be greatly appreciated.

Red.
 

JimDawson

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#2
The half nut needs to wait for the threads on the screw and nut to align before it can fully engage.

Will the half nut engage when the thread dial is on a line? If not you can normally loosen the thread dial and and rotate it then re-engage with the lead screw.
 

Ken from ontario

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#3
On my Microlux 7x16 mini lathe, when I attempt to engage the half-nuts, with the default gearing just to turn down stock, they seem to not lock immediately but take a moment and then engage with a clunk
When that happens to me (when turning / not threading,LMS 5200) I just wiggle the cross slide handle left and right ever so slightly and that always makes the half nuts to engage.
 
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Technical Ted

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#4
There's a couple ways that come to mind for syncing the half nuts with the reference lines on the dial. Start by setting up for an even thread on your QCGB or change gears. Turn on the spindle at a slow speed. Engage the half nuts and let the carriage start to move down the ways. Stop the spindle but leave the half nuts engaged. Now, on your threading dial, either loosen the dial or the gear that goes into the lead screw and manually rotate the one you loosened until one of the numbered lines line up with the reference mark on the edge of the threading dial. Once lined up, tighten things back up. You're done.

If you can't loosen either of these, you can add/remove spacers where your threading dial mounts to change the spacing between the carriage and the threading dial. This spacing will change the timing/sync as well because it changes the relationship between the carriage and the lead screw.

Edit: if I'm misunderstanding what is happening and the half nuts do engage, but the carriage doesn't start to move right away, you have some other problem... Something must be loose in the drive train someplace.

Good luck,
Ted
 

4ssss

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#5
That's what I was about to say. The thread dial needs to be adjusted.
 

higgite

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#6
If you’re trying to engage the half nuts with no regard to the threading dial, the half nut threads and the lead screw threads will most likely not mesh until the the lead screw rotates into position for the half nuts to “fall into the groove”, so to speak, as you gently press on the engagement lever. If that is what you’re experiencing, it is common when engaging the lead screw for turning and does no harm as long as you don’t try to force them to mesh. Gentle pressure on the engagement lever will allow the half nuts and lead screw threads to mesh when the lead screw turns enough for the two threads to line up. Cutting threads is a different story. Then you have to watch the dial and engage the half nuts when the correct line on the dial lines up with the witness mark on the dial housing.

Tom
 

Bob Korves

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#7
The lines do not need to match up, they just need to engage in the same visual relationship every time. It is just a reference to make sure the lead screw is engaged the same for every pass. I also engage the half nuts slightly early causing them to ride on top of the lead screw threads until the half nuts drop into the threads, better a slightly early engagement than a too late one. I also start the pass with the tool far enough away from the work that I can easily disengage the half nuts before entering the work if I do not like the picture I am seeing. In that case it is easy to just start over and try again, no damage done. For newbies, or if it has been a while since threading, it is well worth doing passes with the tool backed off from the work, over and over again, until the brain gets up to speed on what is happening, and the muscles are able to disengage at the wanted position on each pass. It makes the job a lot less nervous or scary. A lot of this depends on the spindle speed and the traverse rate. Go really slow until you think you can safely go faster. Faster only get the work done somewhat faster, and often helps the surface finish.
 

4ssss

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#8
All these technical responses are just making the guy more confused than he is. There's a set screw on the gear that engages the lead screw. Loosen it, and engage the half nut. Turn the number dial to any number or line and re-tighten the set screw. Easy and done.
 

redvan22

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#9
4ssss,
Thanks.
You nailed my thoughts EXACTLY!

However, all good avenues of thought to consider.

Thanks all.
 
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