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Trouble removing lead screw and thrust on 5400 mill

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bfk

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#1
My Sherline is from the 1990s, back when there was no saddle lock. I ordered the 4017U upgrade to add the lock but before I got it out the bag I read on here that there's an even better option, the 4017Z which includes a backlash adjustment. So I swapped it out for that. So far so good. Step 2 of the instructions says to remove the countersunk screw that hold the whole leadscrew assembly on. I cannot get that screw loose. I've been dripping Liquid Wrench, and now Kroil on it for about five days, but it will not budge. The only Allen key that fits is 1/8", which fits the matching screw on the Sherline lathe.
I throw myself upon your mercy in the search for ideas. Any thoughts? Other than patience, which is possible, but getting a bit thin.
 

mikey

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#2
I would suggest using a hex socket, preferably Bondhus that fits hex screws better. If you have a hex key that fits, chop off a short piece and fit it into a regular 1/4" socket and beg/borrow/steal an impact gun. You know the kind that drives screws and will hold a 1/4" square headed adapter. Use that to gently loosen the screw.

Another option is a hand impact driver but I would prefer the gun.

It might help to heat the screw with a soldering gun a few times and drip in some penetrant. I can't recall the name but one that is touted as highly effective is a 50:50 mix of acetone and ATF. Heat it, drip some on when it cools and then heat it a second time, then try the impact gun. Bet it will come out.
 

Gadget01

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#3
If that stubborn screw won't bust loose with a sharp/sudden twist on it, which often works better than gradually applying increasing force, stop. More force will probably do more harm than good and you may quickly use up your daily allowance for colorful metaphors. Purchase a new replacement screw and have a tap for the threads on hand before proceeding.

Drill the head off the stuck screw. You don't have to drill the entire head off- just get the metal thin enough so a little blunt-force trauma can finish the job. This should free the leadscrew assembly and leave you with a stud that no longer has a great deal of locking force on the threads. If it's not quite free enough to remove by hand, thread on a pair of jamb-nuts, tighten against each other, and Bob is now your uncle. Another method that has worked well for me is to cut a slot on the end using an abrasive cut-off wheel until your flat-blade screwdriver fits. Start loosening by just a few degrees then back off. Reapply liquid wrench as needed. Once free, chase the threads with a tap.
 

markba633csi

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#4
Heat and a moderate whack on the wrench with a piece of wood. Always works for me.
Mark
 
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