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View Full Version : Threading (half nut) Lever problem on 12 x 36 import lathe.



homeshop99
01-02-2009, 03:10 PM
Hi,

I have a fairly new 12 x 36" Import lathe. My problem is although I can engage the power feed screw and it will start to turn, however I cannot turn the lever which engages the half nut on the carriage. This worked briefly, like ten times then quit working after I tried using the cross slide feed. I noticed even when it was working the half nut lever was in the horizontal position when disengaged (not up), and down when engaged(as expected). It is currently frozen in the horizontal position.

Anyone with a 12 x 26 lathe encounter this before? I tried to remove the carriage lid, by removing the 2 bolts on the far side of the rails, the 5 hex cap screws, but was stopped from removing it, by the 2 inner bolts holding the carriage to the rails on the users side. I could get a wrench on them, but there was not enough room to remove turn the wrench.

How do I remove the carriage? Do I loosen the threading rod, and other connecting rods which run from the gear head to the cap at the end of the bed and slide the carriage off the end of the bed?

Thanks for any advice.

Ken_Shea
01-02-2009, 04:24 PM
What about looking at the exploded parts view that usually accompanies equipment like that, perhaps that may offer some help on what/how things are connected.

Ken

Fasttrack
01-02-2009, 04:28 PM
Are you sure there is something wrong? What model lathe, exactly, do you have?

The reason I ask is because you won't be able to engage the half-nuts when a feed is selected. Since the feed and the thread work through two different gear trains (feed is accomplished through a series of gears while the threading is accomplished by directly "connecting" the carriage to the leadscrew), they have a built in protection that prevents a user from engaging both and breaking something.

Make sure your feed direction (if equiped on the apron) and the feed/lead (meaning cross slide feed and longitudinal feed respectively) are set to a neutral posistion and then try to engage your half nuts. I am assuming that you only have a leadscrew with a keyway and not a leadscrew and feed rod. If you have both, you'll also want to make sure that thread is selected instead of the feed on the headstock.



On re-reading... I'm pretty sure the issue is with user-machine interface. Remember that there is a difference between a feed and cutting a thread. You do NOT engage the half-nuts to feed the carriage. The half-nuts are only engaged to cut threads. If the cross-slide feed is selected, there will be a mechanical stop the prevents the half-nut from being engaged. Every lathe is slightly different, but for yours (this is purely a guess) there is probably a lever that selects feed/lead and another lever which engages the power feed. Trying to engage the half-nuts will not accomplish anything if your set up for autofeed/lead

Robin R
01-02-2009, 05:16 PM
I think Fasttrack has the right idea, but if just setting the feed levers in the correct position doesn't fix it, a minor adjustment might be needed. I had removed the half-nut lever from my lathe and after re-installing it, the half nuts wouldn't engage. It turned out that the lever was not timed quite right and the mechanical interlock wasn't disengaging, a minor adjustment to its position got things working again. It might be that some bedding in has occurred on the lathe in question, so some fiddling with the interlock is needed, so it can disengage properly.

torker
01-02-2009, 05:37 PM
You do NOT engage the half-nuts to feed the carriage. The half-nuts are only engaged to cut threads.
Huh??? Yes you do....on that type of lathe. How else to you feed the carriage? If I don't engage the half nuts on mine...it just sits there...I can swear at it all I want but the sukker will not cut :D
The CROSS SLIDE will not feed with the half nuts engaged...you can't even engage them when the cross feed is engaged(I think you meant that part ok). Maybe that is the problem...
Is is possible that something has come apart in the apron and the half nuts aren't dropping in.
Seems to me you have to slide the carriage all the way to the end...undo the ends of the rod and screw...then it should slide off. I read about it somewhere...seems to me that's how the apron has to come off.

Fasttrack
01-02-2009, 06:06 PM
Huh??? Yes you do....on that type of lathe. How else to you feed the carriage? If I don't engage the half nuts on mine...it just sits there...I can swear at it all I want but the sukker will not cut :D
The CROSS SLIDE will not feed with the half nuts engaged...you can't even engage them when the cross feed is engaged(I think you meant that part ok). Maybe that is the problem...
Is is possible that something has come apart in the apron and the half nuts aren't dropping in.
Seems to me you have to slide the carriage all the way to the end...undo the ends of the rod and screw...then it should slide off. I read about it somewhere...seems to me that's how the apron has to come off.


You mean to tell me your lathe feeds from the half-nuts? :eek: I mean, thats how my little Smithy works, but its a piece of junk. Almost every decent lathe (I know nothing about turret lathes) feeds off of either a key in the leadscrew or a second, independent, feed rod. I've seen people mistakenly (not implying anything of the kind for you) use the half-nuts to drive a carriage (actually cutting something like 108 tpi), but that leads to a heavly worn leadscrew and half-nuts, which, in turn, leads to those goofy looking threads! All the lathes of 12" or larger that I've used has a lever to engage the feed, which goes through a completely different gearing in the apron than the half-nuts - which have no gearing. I'm not trying to make any suggestions about you or your equipment, I'm just surprised!

BTW Homeshop99 - Welcome aboard! :)

sidneyt
01-02-2009, 06:28 PM
First of all don't take the machine apart. At least not yet. Put the parts that you took off back on the lathe.

If your lathe is a Grizzly G4003, Harbor Freight 33274 (I own one), Enco 110-2078 (or similar), or one of several others that are virtually identical to the above, download the manual for the Grizzly:
http://grizzly.com/images/manuals/g4003_m.pdf
and read very carefully starting on Page 14 about the operation of the lathe.

Highpower
01-02-2009, 06:41 PM
Note #4, thread or feed lever. You can't do both at the same time... :)

Thread position powers the lead screw - feed position powers the feed bar.


http://img.photobucket.com/albums/v82/Highpwr/Projects/feed_lever.jpg

torker
01-02-2009, 08:43 PM
Fasttrack...feeding with the half nuts is nothing new...I've owned a few SB9C's...they feed with the half nuts...there are millions out there. They must be just poor quality :D
I see by that pic...that's a different lathe than mine. My 14X40 is a change gear lathe....and it uses the half nuts to feed...the keyed shaft runs the cross feed....near as I can tell anyway. I cannot engage the carriage feed until the nuts engage....you can feel them click in the same with threading..
Oh...had to add...FT...where did i say anything about my lathe being decent???? LOL! ROFLMAO!!!

homeshop99
01-02-2009, 11:30 PM
Just to clarify, it is the threading rod half nut that won't engage.
The feed rod works fine. My original post was confusing on re-reading.

I've tried adjusting the feed lever to the carriage/crosslide and
neutral positions. The feed mechanism seems to work fine. In any
position the threading lever remains frozen. I expect the interlock
might be stuck or some other problem related to the feed lever as the
problem started when I tried using the feed lever.

Thanks to all that have responded to my query.

Fasttrack
01-03-2009, 02:16 AM
Fasttrack...feeding with the half nuts is nothing new...I've owned a few SB9C's...they feed with the half nuts...there are millions out there. They must be just poor quality
I see by that pic...that's a different lathe than mine. My 14X40 is a change gear lathe....and it uses the half nuts to feed...the keyed shaft runs the cross feed....near as I can tell anyway. I cannot engage the carriage feed until the nuts engage....you can feel them click in the same with threading..
Oh...had to add...FT...where did i say anything about my lathe being decent???? LOL! ROFLMAO!!!


Well I can see it on small machines - and, admitedly, the only SB's I've used have been heavy 10's - but I was really surprised to hear of that on anything as large as a 12, let alone a 14! But if it gets the job done, it gets the job done!


Homeshop99 - Hmmm... I assume its nothing as simple as just not getting it meshed correctly. (The lead screw obviously has to be spinning). I can't really speak from expierence when it comes to this particular lathe, but for the four lathes I've had to tear apart, this is the process I go through:


Remove tailstock - careful because some are very heavy ... like 250 lbs heavy!

Remove feed rod/leadscrew support (in one case it was neccessary to remove the entire leadscrew and feed rod to pull the carriage) and make sure you support the leadscrew and feed rod once you've removed the carriage so they don't bend from their own weight

Crank carriage to end of bed for removal - consider removing compound and cross-slide to reduce weight

You may need to remove the pinion gear if the rack is "closed" on the end - this is usually accomplished by bending a tab on a locking washer and then backing off a jam nut and then sliding the handwheel and pinion shaft out of the apron

Use engine hoist (or forklift) to aid in the removal carriage and lower onto blocks, suspending the apron about a 1" above the ground

Remove apron bolts and seperate from carriage, being careful not to crush fingers

Once free, call good buddy or apprentice to pack apron onto table for further inspection and work

This is just a rough sketch of what I had to do to disassemble a Pacemaker (the heavy one), a 16" Victor (still pretty heavy), a 14"? Cinci Traytop (getting more managable) and finally a SB Heavy 10 (light!)

The half-nut mechanism may be a little tricky to get apart. In fact, I made a video of the procedure for my Pacemaker. It took me a while to find the place for the slide pull since I had no idea what to expect and the bolt holes had grease globbed in them, even after a cleaning.

Removing the support
http://i108.photobucket.com/albums/n22/fasttrack237/Pacemaker/100_0500.jpg

Removing handwheel and pinion
http://i108.photobucket.com/albums/n22/fasttrack237/Pacemaker/100_0493.jpg

Here you can see a brass arm - that is what reverse the direction of the feeds by the action of a double bevel gear set-up. Unless this is in the neutral posistion, it physically blocks the half-nuts from closing.
http://i108.photobucket.com/albums/n22/fasttrack237/Pacemaker/100_0536.jpg

I'll post the video just for kicks once I get it uploaded. I'm sure you can figure out how yours works just fine with out any help though. They are not too complicated, this was just the first time I'd been in an apron.

http://i108.photobucket.com/albums/n22/fasttrack237/th_100_0556.jpg (http://s108.photobucket.com/albums/n22/fasttrack237/?action=view&current=100_0556.flv)

(whew its hard working with one hand!)

Highpower
01-03-2009, 12:30 PM
I realize this is just echoing everything that Fastrack has already mentioned, but....

The feed lever (#8) is what interlocks with the thread (half-nut) lever (#9). The feed lever must be in the neutral (center) position in order to engage the half-nuts. With the lathe off - you might try putting a slight amount of pressure on the thread lever while working the feed lever up and down to see if the half-nuts break free. If not, you'll have to dig into the apron to see why the interlock or half-nuts are not working or stuck.

You might also have a look at the rear side of the apron with a mirror and a strong light to see if anything looks amiss with the half-nuts or gibb, before you start tearing everything apart....

Best of luck! :)



http://img.photobucket.com/albums/v82/Highpwr/Projects/feed_lever.jpg

homeshop99
01-03-2009, 02:43 PM
I've tried every combination of I can think of to get this working, including threading shaft on and off, all types of feed levers positions etc... Wiggling things.

The threading lever remains frozen. I'm convinced its broken at this point.

The carriage its self looks to be about 100-150 lbs I'm guessing. The mirror was a good idea but this appears to be a sealed unit with oil. So I'll have to remove it. Its still on warranty, but I believe its a parts only warranty. Still I'll try to get some technical support from the vendor before dis-assembly.

Thanks to FastTrack for the apron removal overview, its more or less what I expected.

Thanks

Highpower
01-03-2009, 03:44 PM
The mirror was a good idea but this appears to be a sealed unit with oil. So I'll have to remove it.

I only mentioned it because the half-nuts are on the outside of the apron, not internal. The lead screw does not run through the apron, but just behind it...

A broken gib or half-nut would be visible from the exterior.

Fasttrack
01-03-2009, 11:31 PM
Let us know what you find out, HomeShop99!

homeshop99
02-15-2009, 08:47 PM
I just wanted to give an update on this.

I removed the carriage and took it apart which except for one
nasty roll pin went pretty well. Turned out it was something called a
"safety shifter" that was broken. Basically this is a cylinder with 2
disks that keeps the half nut and feed rod from being engage at the
same time. One of the disks broke in 2 places, from what looked like
metal fatigue, which was weird since this was essentially a new lathe.
Maybe bad part? Anyway I made a new safety shifter using my mini lathe
and lathe is up and working again.

Carld
02-15-2009, 09:02 PM
What brand and model lathe do you have. It's important to know that.