Thread: Vertical lift screws binding in old horizontal mill

I bought an old mill recently, the details of it are here - http://www.woodworkforums.com/f65/new-mill-122675/

I dont know much about it except that its badged "Geo. Hatersley and Sons - Keighley England"

The vertical lift screw is binding badly. Its almost impossible to wind it up or down. I have pulled the mechanism apart and its a screw within a screw type. The central screw is 1 3/4 inch by 4 TPI and is driven by the powerfeeds or manual handle. I believe that in theory when this inner screw unscrews all the way it should then begin to unwind the outer screw, which is 4 inch by 4 TPI, giving the knee an extra 15 inches or so of lift.

In practice however, both screws are binding badly. The outer screw is worse, as when you try to raise the knee the inner screw just winds itself out. Im not sure how the design is meant to prevent that from happening as unless there are some parts missing it would seem impossible. The attached diagram shows all the parts that exist in this very simple screw as of this point in time.

Re a solution - I thinkt the first step is to free up the nuts and screws a bit. I have done a visual inspection of the inner nuts and they appear damaged. I havent got the outer nut off yet but will do so tonight. Both screws are in excellent condition though. I am looking for suggestions on how to free up these nuts and screws. The coarsest screw my lathe can cut is 8 TPI, so if running a pass or two to clean up the nut is the answer then i'll need help with that and am willing to pay.

If there is another answer, please let me know.

I believe the second step is to make a couple of caps to prevent the inner screw from winding itself, or the inner nut out. This is easy and I can do it at home.

If anyone thinks there is something glaringly wrong with what I propose or understand of this mechanism, please let me know. See attached pic for a better understanding of whats going on.

Cheers,

Brendan

hey your mill is most likely older than me, we're allowed to move a little slow
And a nice buy for $500.
You dont say if you have cleaned it all and tried it again?
I'm just guessing here, I've seen a machine with this set up but not had it apart.
Is there a taped hole in the end of the inner screw?
You say that bronze nut is pinned, is it pinned into a slot?
If the bronze nut can't rotate how can lift?
Was there anything between the bronze and steel nuts?
I'm wondering like you, what the bronze it there for. Could it some how(say by squashing a piece of felt) stop the inner screw from turning until the outer screw had moved full travel?
Is the steel nut part of the outer screw? If not how is it fixed to the outer screw?
oh and find your camera
Yes not much help, but its an interesting problem
Stuart

Ha ha, slow I could handle. Two hands and all my might to move the table up an inch a minute is a sign that somethings obviously wrong!

Yep, should have mentioned. The first thing I did was to clean/degrease the screw and nuts but still no good. I can see with my eye that the brass nut is damaged, and that the top 5 threads of the steel nut are broken ( I think I did this), but the bottom threads of the steel nut look good but I cant wind the bugger on. Im yet to get a visual on the condition of the large 4 inch nut.

I took photos of all of this but as I mentioned I have misplaced my camera. I thought id try get the discussion rolling whilst I look for the damn thing (hopefully its not under the mill!). Re your questions....

Is there a taped hole in the end of the inner screw?
No, this is what I was expecting to find. This is what I plan on adding if I go with the solution I outlined above.

You say that bronze nut is pinned, is it pinned into a slot?
Yes, the bronze nut contains a slot down its entire lenght (approx 2 inches) that corresponds to a slot in the outer 4 inch screw. It came with one pin identical in length to the bronze nut but the other pin was missing. the interesting bit is that the steel nut contains a matching slot, but only about 3/4s of an inch long. The steel nut is about 5 inches long. This arrangement prevents the bronze nut from spinning in the outer screw when the inner screw winds. See attached jpg for a diagram.

If the bronze nut can't rotate how can lift?
By not being able to rotate lift is achieved. Nut is stationary and inner screw attached to mill knee at upper end, and runs through bronze and steel nuts at the other end. Thus the inner screw forces the knee up or down as it winds in and out of the bronze nut. The nuts I keep referring to are circular by the way.

Was there anything between the bronze and steel nuts?
No

I'm wondering like you, what the bronze it there for. Could it some how(say by squashing a piece of felt) stop the inner screw from turning until the outer screw had moved full travel?
I imagine the two nut setup has something to do with it. If for instance the bottom steel nut was pinned to the inner screw, it would rotate with the inner screw and come up as the knee lifts, until the point where it hits the bronze nut that is pinned to the outer screw, causing the lot to bind and the outer screw to start winding. I could not find any evidence however of the bottom steel nut being able to be fixed to the inner screw.

Is the steel nut part of the outer screw? If not how is it fixed to the outer screw?
No, not fixed...slides up and down the outer screw as the inner screw winds said nut up and down. The attached paint artwork may explain things better.

Brendan

I'm missing something here. How is the downward force from the knee on the inner screw transferred to the outer screw? You say the steel nut "slides up and down the outer screw as the inner screw winds said nut up and down" so that cant be transferring the load. There is nothing between the Bronze and steel nuts. The bronze nut is only held from rotation by the pin and is the same Dia as the steel nut. What am I missing?
Stuart

I dont think your missing anything - in current setup, from what I can tell, the steel nut is completely redundant. It goes up and down and round and round in the same manner that the inner screw does. Perhaps, as it contains slots, it is meant to be pinned to the bronze nut, which is definately meant to be pinned to the outer screw. Maybe they were shimmed apart just enough to make this a very tight fit, ensuring that the outer screw spins first.

I think the downward force from the knee gets transferred to the outer screw when the inner screw winds all the way in. At this point the inner screw cant travel through the bronze nut any further and then then the outer screw would start turning.

Dave has a mill with a similar setup. He is going to tell me which screw winds first. I have a hunch that this is what is supposed to happen.

Starting with the knee at its lowest point...I.e bottomed out. Both screws are wound down inside each other. When the handled is turned to lift the table up, the inner screw rotates. The brass nut is designed to be stiff, so the load is transferred to the outer screw first. The captive outerscrew which contains the integral, pinned bronze nut unwinds for about 15 inches until it is maxed out. During this period the bronze nut and inner screw rotate together. Upon the outer screw maxing out, the bronze nut would become stationary and the inner screw would start unwinding through the bronze nut. This would continue until the knee maxes out in height, which would occur BEFORE the innerscrew had a chance to wind itself out of the bronze nut....hence why the inner screw doesnt need to be captive.

My hunch is that what is wrong with mine is the outerscrew has seized in its nut (which it has) meaning the innerscrew unwinds itself fully without ever transferring load to the outer screw. In the process of unwinding all the way and thumping back down, the bronze nut has become damaged and even stiffer than its meant to be. See attached diagram for explanation.

Hi Brendan,
I thought I would post this here instead of the other thread.
I have had a look at the shaper and the top of the large screw has a collar on it which contacts a collar on the top of the small screw under the knee when wound down. I would say it is the friction between these that makes the large screw turn first until it stops at the end of it's travel then the small screw takes over.
I tested it and if the small screw goes first it stops at the end of it's travel and the large one takes over. So there must be something in there to stop the small screw coming out.
I had a look at the mill and it's hard to tell because I cant wind it down as it"s gunked up as I haven't cleaned it yet. A the moment as it come the large screw is fully extended and the small one is half.
It does not have a collar but the small screw threads at the top stop short about 5-8mm. It might be this that locks into the large one when down to make the large one move first.

Dave

Here are a few pictures of the shaper and mill screw.

Dave

sounds as if it works on the same principal as a screw jack

"stop the inner screw from turning until the outer screw had moved full travel?"
This I get.

I was asking about what carries the load not the torque. i.e. what stops the bronze nut sliding down through the outer screw in the same way the steel nut does?
IF the bronze nut sits on a shoulder or a taper(as I am guessing it must) and carries the load weight of the knee, the steel nut may just be there to supply the extra resistance to make the outer nut turn first. That would explain why it is pinned to the bronze nut.
I cant really see the pin being used as a backlash or preload adjustment as you say it only has two holes, at 4tpi that's 1/8 between adjustment points.

Of course that doesn't explain how its thread could have been damaged.

Of course I still maybe missing something.
Stuart

Hey Dave,

The screw setup on your mill appears to be the same as mine.

Im reasonably confident I know how it works. Now the only problem is these binding nuts. For whatever reason, they are far too tight and cleaning them hasnt helped. Would taking a very light cut through the nut threads with a correctly formed tool be a good idea or is this inviting disaster? Any other suggestions for freeing these up? Would putting some valve grinding paste in the nuts and then winding them up and down be a bad idea?

Brendan

I don't think grinding past would hurt as long as you use the full length of the screw while doing it. It might not take much to get it working. I would machine up a adapter to go onto your drill and run it back and forth with it. If it doesn't free up after 5-10 minutes with the drill and past it probably isn't going to work.

Dave

Did you get the outer one apart yet?
Could there be a burr on the inside Dia of the steel nut that is pressing against the minior Dia of the outer screw?
Some of the old greases seem to set like concrete, it may take some shifting.
Stuart

I have both screws turning in their respective nuts very freely. The outer nut and screw was bound up with lots of swarf, including one piece about 30mm long that I suspect was causing most of the binding.

The inner screw was binding due to the damaged bronze nut - not sure how it got damaged. The very bottom thread of the inner screw was also damaged but I have fixed this now (ground down the damaged parts til the steel nut could thread over it very easily).

I am going to fix the problem by using a design similar to what I proposed in my original post of this thread. Ill take photos as I go and try to get them up here in a timely fashion.

Some photos of the machine and the screw jack can be found here:

http://www.woodworkforums.com/f65/ne...75/index2.html

OK, its all back together now and working as anticipated. You can still feel the weight of the knee when winding up, but the action is smooth and feels good. One of my first projects will be to restore the power lift mechanism of the knee, possibly by adding a motor to do the work for me. There is room inside the knee for a starter motor sized motor, otherwise plenty of room under the knee for something bigger.

In the meantime though, what is the best sort of lubricant for a screw jack like this?

19brendan81 You've me confused again. You mill has power feed on X,Y and Z. Why do you need to add a starter motor?
Stuart