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hornluv
02-23-2004, 05:57 PM
I was turning threads the other day and I noticed that with each pass, the half nut disengaged itself just a bit. I noticed this problem only after my threads came out a little wrong and I spent a long time wondering what was going on. Is there a way to tighten up the handle that engages it or otherwise keep it in place besides just holding it down?

Thanks,
Stuart

BillH
02-23-2004, 06:14 PM
Half nuts on what? A southbend?

metal mite
02-23-2004, 07:05 PM
What ever happoned to Halfnut?
He was a very talented mechanic.
mite

CCWKen
02-24-2004, 03:14 AM
They could be worn to the point that the feed screw is pushing them open. If not, you should be able to adjust them.

hornluv
02-24-2004, 03:15 PM
"Half nuts on what?"

The lathe is an Enco. I bought it new in 2001. So far this is the first problem I've had with it.

"the feed screw is pushing them open"

That is what it seems to be doing. I can't imagine they've worn since 2001, since I really don't turn many threads. How do I go about adjusting them?

Thanks,
Stuart

lynnl
02-24-2004, 05:35 PM
Are you seeing the hand lever actually visibly moving to dis-engage the halfnuts as the carriage travels? ...or can you feel it, with light hand contact on the lever as it travels, while threading?

Does this lathe have a separate feed rod for non-threading powerfeed? If so, there's probably an interlock device to prevent engaging powerfeed while the halfnuts are closed. This is just a wildass guess on my part, but that's probably where I'd start looking for the problem.

Alistair Hosie
02-24-2004, 05:43 PM
Stuart start off by getting a book on the model if you can.
I had a boxford with a problem whereby the crosslide would not traverse although it was designed to do so.
I ended up having to take the saddle assembly apart and found out that the previous owner had swopped the threaded feed rod inside and replaced it with a smaller one.
You have had this since new thereby you will, or should have a book showing the assembly in detail and then you may be able to see where the problem lies. If the unit is so new it should not be wear. Enco is a good little lathe and the fact it is small should make the disassembly and reassembly (IF NEEDED) quite straight forward I wish you luck try and find other Enco owners first though there may be a club for them you should inquire or contact Enco themselves and inquire good luck Alistair

hornluv
02-24-2004, 11:30 PM
"Are you seeing the hand lever actually visibly moving to dis-engage the halfnuts as the carriage travels?"

Yep. When the carriage starts moving you can see it jump up just a bit. Not enough to completely disengage it, but enough that it significantly increases the amount of space between the threads of the screw and the nut. Since it jumped a little with each pass, I ended up with a really thick thread at the beginning of the cut that gradually thinned out after about one revolution. Not sure why it thinned out.

"Does this lathe have a separate feed rod for non-threading powerfeed?"

Yep as well. Would the interlock device be housed in the apron? Why would this be the problem and not just the nut being too loose? What would be the solution to the problem?

Alistair, I have the books, although, the translation of the book from the Chinese was apparently done by the person who knew the most English at the factory and that wasn't much. They were so kind as to include a book of exploded views though. Those are usable.

Thanks,
Stuart

JCHannum
02-24-2004, 11:47 PM
Some backlash is normal. Always start the feed with the tool a few threads before the start of the work to allow things to catch up with themselves. As long as the nut is engaged with the thread of the lead screw, it will advance the distance of the pitch with each revolution.
What are you threading? If it is long and slender, are you using a center in the end? Is the part secure in the chuck, and not being pushed back under the pressure of the cut?
If the threads are a standard size, I will single point about 90% of the thread and finish with a die in the tailstock just to clean it up.

BillH
02-24-2004, 11:59 PM
..

[This message has been edited by BillH (edited 02-24-2004).]

hornluv
02-25-2004, 02:55 AM
The part is actually already done but the halfnut issue still remains. I was cutting 20 TPI on a diameter of 3 inches internal and external. The part is a little hard to explain. It is soldered to the bell of a French Horn so the bell can be cut off and made detachable. You can see a picture of the part at my website. The part in question is the little bronze deal around the throat of the bell in the picture at this link.

http://www.4hornsmen.com/deharohorns/screwbell_conversions.htm

Stuart

[This message has been edited by hornluv (edited 02-25-2004).]

lynnl
02-25-2004, 01:15 PM
"....Would the interlock device be housed in the apron? Why would this be the problem and not just the nut being too loose? What would be the solution to the problem?..."

Yes, the interlock will be housed in the apron. I don't have my manual available right now, and it's been 4 yrs or so since I tore into mine, but on my old Leblond: when the lever is moved to engage the halfnut, it forces a rod over sideways to prevent closure of the mechanism that controls the powerfeed. Likewise when the powerfeed is activated it forces that rod in the other direction to prevent closure of the halfnut. And as I recall the ends of that rod are kinda wedge-shaped. What I'm suggesting is that (POSSIBLY) vibration or looseness is causing that rod to shift and partially force the halfnut open. Maybe not. Maybe, as you say, it's just a matter of the halfnut being too sloppy of a fit.

Depending on how much space you have, you may be able to slip an inspection mirror up between the backside of the apron and the lathe bed, and shine a flashlight up in there to illuminate the area, and try to observe it in operation. (OBVIOUSLY, EXERCISE GREAT CARE IN DOING THAT!) Maybe you'll get lucky and that'll reveal the problem.

JCH: re your statement "..As long as the nut is engaged with the thread of the lead screw, it will advance the distance of the pitch with each revolution." ...
If the nut is gradually disengaging, won't that be gradually increasing the effective pitch of the leadscrew? ...as the point of engagement between nut thread and screw thread moves outward along the flank of the 29deg acme thread? Seems to me it would have the effect of retarding the motion of the carriage slightly.

hornluv
02-25-2004, 03:37 PM
"...as the point of engagement between nut thread and screw thread moves outward along the flank of the 29deg acme thread? Seems to me it would have the effect of retarding the motion of the carriage slightly."

That is exactly what it seems to be doing. I guess my lathe is retarded then.

JCHannum
02-26-2004, 12:02 AM
lynnl, he says the lever jumps a little when the carriage starts to move. I assume it stays in same position for the rest of the thread. Hence, leaving space for the backlash to settle out before starting the cut should let it settle out.
Try chasing a thread on a test piece while holding the lever down and see if that makes a difference. That should tell you if the problem is in the lever/halfnut assembly.
I appreciate your take on the instruction manual, they can be very entertaining at times, but often not too informative. There usually is nothing too exotic in the apron, and dismantling may reveal the problem.

Alan in Oz
02-26-2004, 03:57 AM
There are several things that can be done to check the slop in what appears to be the half nuts on small Asian lathes that I've had experience with: With the machine stopped engage the half nuts fully and then move the apron wheel handle back / forward and note any movement relative to the bed, there maybe slop in the nut itself, the leadscrew can be loose ie: end play which may require adjustment / shimming at the tailstock end block that the shaft rotates in. Another area, when the half nuts engage / disengage they slide up / down usually in a dovetail arrangement on the backside of the apron, some have an adjustment to take out play on one side of the dovetail. The nut halves are usually actuated by 2 pins in rotary disk on the backside of the apron this being connected with the half nut handle on the front of the apron. Several possibilities, pins can be loose in the disk itself or a loose fit into the slideways on the half nuts allowing the half nuts to walk open slightly during use or the half nuts are not closing completely onto the lead screw due to insufficient clearance on the mating faces of the half nuts ie: not being relieved fully. Some apron half nut handles have a spring detent to hold them in position this may not be engaging due to handle position on the shaft etc.

As someone already mentioned if you can get a good light / mirror and a look at the half nuts while undertaking the above then its fairly easy to see where the play is. Hope this helps.