Southbend Leadscrew Nut Won't Fit, Tool Tuesday Ep.16 

I think you are correct. They cut it undersized for a reason. I have a feeling the seller was supposed to state it was undersized (they probably didn't know).

😃👍Same here

Agreed. I was surprised that Adam didn't clamp the nut in the vice, thread the screw through to midpoint, and measure the lash at the tip of the screw. That being said, Adam has at least 5 hours more time as a machinist than I do, so I'm gonna assume that his method was good enough for the task at hand :)

He wasn't trying to get a super precise measurement. Just something to do a simple comparison of before and after.

Correct the armchair guys always know a better way!

I think he wanted to test the backlash in the nut. Checking in the middle of the screw would have shown the combined backlash. .015 is not that bad for a lathe. A new nut wasn’t necessary.

@@ellieprice363true. But there’s nothing wrong with trying to get backlash out as much as possible.

I’d wondered the same thing.

Or was that a way of "fitting" the nut to the lead screw during manufacture?

"off" WHAT?

They were trying to tighten up the threads by compressing the metal. When it's worn the best temp fix is to slot the nut an hammer it closed a little, just temporarily.

🤣

The shaft (or lead screw) is, in this case, made of steel. Often lead screws are also hardened and ground to final size and finish. The nut is, in this case, made of brass or bronze which is far far softer than steel. It is much smaller and MUCH simpler to make a new nut than a new lead screw. The nut is what one might call a "wear part"... in the same way you replace your brake pads with new ones but not always your brake rotors (not the best analogy but the only one I could think of.) It is the same thing for the longitudinal lead screw on a lathe. Damned expensive to buy a new one every time you replace the half-nuts for threading.

@@utidjian I fully understand that however, what we don't know is, how old is the southbend, what kind of abuse has it had in it's life, what's the condition of said machine, even hardened steel will wear. Just only speaking from experience on the farm. :)

@@Ham68229Lathe and milling machine screws are tough but not hardened. Moore jig borers and grinders and a few other high precision machines would have hardened and ground screws.

@@ellieprice363 Not disagreeing, only stating my experience and I know everyone's experience is different. :)

He said at the beginning of the video he measured the screw and it wasn't worn.

I think he must have stock in a lot of sponsors. At this point the whole channel is highly commercialized.

@@superdavett2 But it is free to watch!

@@jerrydemas2020 Lots of people pay the youtube subscription. Put the Anchorlube in the hole instead of on the tap. It always stays at the front of the tool where it is needed so lots of holes can be prepared without having to coat the tap every time.

Is anchor lube a bad product?

@@charlesgibson4184 Not a bad product - if it was he wouldn't use it. Just sponsored so he gives it more camera time. Blondie Hacks also uses it (I believe not sponsored), so for me, that tells me it is good.

Why do that when he can get the correct tap for $27?

@@utidjian $27 plus wait for Amazon. Any time I can save time and money and get the job done correctly, why would I not go that route?

@@duaneohall Sure... I could see trying what you suggest if I was in the middle of the Indian Ocean on an aircraft carrier and for some reason I had to get the crossfeed screw nut that was in spares working... but that isn't my situation. Nor, I would guess, is it Aboms (Jacks) situation either. I value my time far more than $27 times however long it would take janking around with the wrong sized tool. With the right tool it takes less time to cut the thread correctly than it takes to compose this reply. Anyhow plenty of ways to skin a cat or win our own battles. We are fortunate to each have the choices on how we want to do it.

Agree. Not sure why Abom did this but a great video would have been to do what you suggested. I might have learned something.

Not

😂 It is annoying so it has to been fixed. Maybe you should fix yours to.

@@fearlyenrage Clearly he has some loose nuts, but as long as he is happy we'll accept him as he is.

try relling that to a carbide parting tip while cutting something gummy!

@@donsfromnz6515 That's a South Bend 9 inch cross feed nut, pretty sure he's not parting with carbide inserts, gummy or not...

If you back it out, it'll cut even more off and become looser. This is a one and done deal.

It originally wasn't working, so things could only improve.

@@tmmtmm There are many variables to make your statement universally true, too many to list here. One in particular is worth mentioning and that is a skilled operator will have been taught to avoid this and have the feel to prevent backcutting. The point I was making is that if the tap is inserted at increasing depths all of which are before the parallel finishing teeth engage. When the tap is reversed to back out, the tapered teeth are in a larger threaded hole so they can't cut what they are not touching. Repeat cautiously and gradually from each side of the hole until the male thread goes in. In this case the subject was a leadscrew with a worn center section and virgin threads on the ends. If the nut is opened out to suit the unworn threads on the ends it will always be even sloppier in the middle. In this video he managed to get it sloppy on the full size threads on the end, he never showed the increased play in the center of the leadscrew! I suspect the nut thread was deliberately made to a slightly tighter spec for a closer engagement on the worn area of the leadscrew. My first operation would have been to see if the nut could be forced over the virgin threads and onto the worn area to see how it fitted in the working area. If it was too tight to thread over the full size thread on the end I would consider relieving the end of the leadscrew thread to help, as this portion is not used.

@@tates11 ...Agree. I was rather surprised he didn't begin to tap, back it out and check screw fit, when eventually it begins to fit, tap in the other direction doing the same. Likely to have ended up with a far superior fit.... Not conventional, just being practical...

@@leybraith3561 A bit gung ho.

There are disadvantages with ball screws on this configuration. Left hand ball screws tend to be more expensive. The nut size will be much bigger. The max thrusting force is smaller since ball contact surface is much smaller. The smaller the thread pitch the smaller the balls. 10TPI si about 2.5mm thread pitch. It's hard to have a ball screw with this small thread pitch.

A better solution which I implemented on my lathe (although metric thread) is a split nut. Actually two nuts. One is fixed to the top slide and one is floating. One face of the floating nut is milled at 2 degree angle in relation with the nut axis. The fixed nut has 4 dowel pins in the corners which goes into the floating nut to keep it aligned. Between the two nuts it's a wedge which is adjusted with a set screw from above top slide. The bottom of the wedge is pushed up with a leaf spring mounted on the fixed nut. You adjust the backlash from above - no need to dissasemble anything - by adjusting the set screw. It will push the wedge down against the leaf spring and spread apart the two nuts creating pressure on the opposite thread flanks. I have 0 backlash on my lathe for the reason I put a 1 micron glass scale and DRO

He is very talented at that.

Got that right I need it for my old atlas 10in lathe

@@TheMoody876 Made Adam will have time to work on it. Never hurts to ask.

@ronnydowdy7432 to me it would be more cost effective to sell the atlas and buy something larger and more accurate

@@TheMoody876 okay. Then you should do that if you can.

It's still very hit or miss I feel. Sometimes you get actual razor sharp carbide tools and other times, it says carbide but turns out to be softer than lead. But all in all I'd agree, that they've been producing very decent tools, taps and endmills, especially for the home/hobbyist shop. I've only had bad luck with inserts for the lathe or mill though.

@@nils1953 I’ve found that cutting tools, collets, Toolholders from India to be superior quality than most of the Chinese stuff. Robert

@@RobertBrown-lf8yq that's very interesting! Where do you buy tools from India? I don't think I've ever used any tools made from there.

@@nils1953 I got onto it via Google. Got some 5C collets from them. Bloody first class….. not one burr 😱 So ordered some square and hex collets. Delivery was about six-seven weeks ( probably a special order ??). Ditto for some BT30 ER32 toolholders. I’ll see if I can find their details again and post here.

I think the lead screw is worn causing the slop also. I think in the end, the few tight threads in the middle would snug the backlash. It would be temporary but if he does not use it much, that may get him far down the road with tighter tolerances. If tolerances are that important to him he can buy more Nuts to do the same with.

Isn't that contrary to the "Never back out an Acme Tap" rule? Wakodahatchee Chris

I thought the same.

even applying a measured force on the old nut in the press would have been better than cutting the new nut to fit the non worn part of the screw

Soon as he stuck it in a vise I was thinking I would crush it.

@@LuggageStardate Use a hydraulic hose crimping machine with the appropriate die, it might help. Just a thought.

Could you upsize to 1/2-10 LH ACME and tap out the nut to match?

Have done that on at least four leads crew repairs. Worked just fine. Found and used half ten precision ground acme. Lh stock. More readily available than the 7 sixteenth ​@@mikewilliams5873

My Southbend lathe has some cool history it was originally built and sold to the Keebler cookie company

It really shouldn't matter, but it depends on the size of the object and whether you were able to completely pass the full threads. You risk reaming the threads a tad by repeated passes.

Measuring an OD with calipers is trivial. Any machinist should be able to do it drunk and blindfolded while in their sleep.

The difference is also in the direction of the threading. Regular thread "right tighty, lefty loosey". Left hand thread is just the opposite.

Hes says at 7:35

Lol

When you tap something who already has a thread it will be bigger than the first time you tap it, if he made a new nut and tap it with this tap I'm pretty sure there will be much less play

Still a leadscrew. Robert

backlash is inherent to threads, otherwise they bind and can't be 'threaded'.. to get backlash out of this mechanism it requires a 2nd nut that is being put under adjustable tension / pressure axially to get backlash minimized to near zero and to be able to readjust once things have worn and get sloppy again.. the cheap version of this is to cut perpendicular into the nut without parting it off and using that as the 2nd nut (needs a way to bend it slightly then, usually with a set screw pushing into the cut).

He isn't using a hydraulic press. It's just hand tight.

@@boothbytcd6011 how difficult would it be to clamp it on the pin?

Undersized, right?

I don't think the drill has anything to do with it on those type of threads, a square thread is designed to take the force on the face of the thread not on the outside or inside diameters. On angled threads a totally different matter.

Acme threads are a tapered threadfrom (14.5* per side, 29* inclusive) ​@cameronjohnston5748

yup theres always worn part somewhere depending of use case...

Yes, maybe the new nut was high quality and made in such a way to be a tight fit, and now it is ruined?

That makes perfect sense. New to me, but obvious when you think about it. Great comment.

Or some steel guitar while we're at it. High speed steel guitar!