# Damaged threads issue



## Abody711 (Apr 16, 2022)

I rebuilt the head on my 10 Heavy. I tried putting the chuck backplate on and found out why I have a major issue removing it to begin with. The threads are damaged. I know the threads are 2.25 x 8 tpi. My question is are the threads the same as pipe threads? Would like to run a die on threads.


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## pdentrem (Apr 16, 2022)

Not familiar with the SB 10H but normally I would grind a HSS tool to match the threads and set up the lathe for that pitch.
By hand a quality triangular file and carefully rework the damaged area.
Pierre


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## 682bear (Apr 16, 2022)

Abody711 said:


> I rebuilt the head on my 10 Heavy. I tried putting the chuck backplate on and found out why I have a major issue removing it to begin with. The threads are damaged. I know the threads are 2.25 x 8 tpi. My question is are the threads the same as pipe threads? Would like to run a die on threads.



No, they are not the same as pipe threads.

Like pdentrem said... I would get a triangle file and carefully clean up the damaged threads by hand.

How badly are they damaged?

-Bear


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## benmychree (Apr 16, 2022)

Definitely not pipe threads, use great care with the file, likely best to use a new file.


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## Abody711 (Apr 16, 2022)

I filed some already. I can get the plate screwed but it is not easy. Gone to look at things under a magnifying glass tomorrow. Things looked to be cleanup but I am missing something.


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## Jubil (Apr 16, 2022)

Probably have damage on female side also, harder to detect or repair. 

Chuck


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## C-Bag (Apr 16, 2022)

Check your backing plate closely. I had one that didn’t want to thread easily yet the other 3 did just fine. Turned out either it was dropped or somebody dropped a Chuck or something heavy on the boss and it slightly bent it making it slightly out of round. Luckily it’s not one of the ones is use very much.


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## woodchucker (Apr 16, 2022)

can you load a pic of the damaged threads.
sometimes instead of filing you can roll the thread back , but given that the spindle and thread are hardened.. not easily.
A pic would help determine the course of action.
If it were me, I would rather get the metal moved back to where it needs to go. If you can't, I wonder if a file will actually do anything to the hardened threads... if a file does work great, if not.. it's abrasive time... you can wrap sandpaper around the triangular file and work it. Or if you have a triangular stone..


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## Shootymacshootface (Apr 16, 2022)

I would clean up the threads by hand only. Use a file on the spindle. Make a very sharp hss inside threading tool that is big enough to work by holding it in your hand, or put a handle on one. Scrape the damaged threads inside the plate by hand until it threads on normally. Use any kind of bluing or a big sharpie to see the areas that need to be cleaned up. This is how I clean up the threads on hydraulic rods and piston nuts.
It works good.


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## Abody711 (Apr 16, 2022)

Found a solution maybe. Purchased a thread file on Ebay. Will report back. Thanks for all the advice


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## Winegrower (Apr 16, 2022)

Remember pipe threads are tapered.  I doubt your spindle threads are.


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## SLK001 (Apr 17, 2022)

You might be better off with a triangle shaped stone.  I doubt that a file will do much good because of the hardness of the spindle itself.


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## tq60 (Apr 17, 2022)

Paint it with a marker and see where it gets shiny or Transfered.

Cleanup only where it needs it.

Sent from my SM-G781V using Tapatalk


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## Abody711 (Apr 19, 2022)

Winegrower said:


> Remember pipe threads are tapered.  I doubt your spindle threads are.


I looked up the flare on SAE and NPT and both are 37 degrees. So hopefully will not be an issue.


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## 682bear (Apr 19, 2022)

What does flare have to do with a lathe spindle?

Sorry... Am I missing something?

NPT threads are tapered... your spindle is not... if you run an NPT die over your spindle threads, you will ruin it... and it likely won't be repairable.

-Bear


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## MikeInOr (Apr 20, 2022)

Could you post a couple of pictures showing how the threads are buggered?

The diameter of the outside of the threads get smaller the closer you get to the end of the pipe.  This is what people mean by tapered pipe threads.  People are worried that you will try to use a pipe die on your spindle and ruin it.  I think you might be talking about a file with 37degree faces which sounds right without looking it up to confirm.



NPT tapered pipe thread.

Somewhere there is a video of a guy that likes to single point thread backwards.  I.e. mount the bit upside down then run the spindle backwards which causes the carriage to run left to right instead of right to left.  You might consider doing this with your spindle.  You would be able to line the cutter up with the good threads furthest in from the end of the spindle, then run the cutter through the threads backwards off the end (right side) of the spindle.  To me this seems like it would be much easier to get the alignment of the cutter to the existing spindle threads correct than normal right to left threading.  It would still be a right hand thread like the original just cut the carriage traveling left to right instead of right to left.  ... Just a thought.


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## MikeInOr (Apr 20, 2022)

Go to the ~4:30 mark on this video to get a better explanation of what I mean by threading backwards:






I think that single point threading as described will give you MUCH better results than going at the threads with a file free hand.


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## SLK001 (Apr 20, 2022)

Look... Your spindle is 2-1/4" x 8 TPI.  Is is *NOT *tapered.  It is *NOT *a pipe thread, so give all the pipe stuff a rest.  Your spindle is also harder than a whore's heart, so using a non-diamond file will usually just skate across the threads.  Same thing with trying to single point the threads, also.  You're going to have to use some ultra hard triangle shaped device to dress down the damaged areas.  

Photos showing the damage would help.


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## Jake M (Apr 20, 2022)

A pipe thread die is not going to work, first for the reason already mentioned, most readily available pipe thread dies are tapered, and the spindle nose will not be.

There are straight pipe threads out there, and IF you had a match in diameter and thread pitch, and thread form, then "maybe".....  But you've still got a crest and root modification that's going to give you fits.

The real dealbreaker is this.  Pipe threads don't hit eight threads per inch until three inch (or maybe just under), which is the nominal INSIDE diameter of the pipe, which is actually much larger than nominal.  So if you converted to "bolt thread nomenclature", the first tie you'd ever hope to find with eight threads per inch would be, in bolt terms, in the three and a half inch range.  (They're eight threads per inch for a LONG ways above that, but not below.  To get the right diameter (you can't), you'd be somewhere in between a 1-1/2 and a 2 inch pipe.  Everything in that size range is 11-1/2 threads per inch.

I'm not sure where the 37 degrees for NPT and SAE, but that's maybe bad information, or more likely incomplete.  Somebody's sending you down a rabbit hole.  SAE has a lot of angles, 30, 37, and 45 being the most common seating angles.    NPSM (that is, pipe threads that include such an angle) is always 30 degrees.  But this is a seating angle, it's for free running threads that pull two components together onto a seat.  It is  NOT a threading angle in any way.  The threads are always 60 degree V threads (albeit with modified crests and roots.  Unless you get into British stuff, but that's a whole 'nother can of worms.

The best thing you can do is to put up pictures of the damage.  The solution to a damaged thread that's big enough to work with is rarely a thread cutting die, and this forum will probably be able to offer you dozens of solutions to solve the problem without causing more damage than what's already there.  If you insist on using a die, then to repair a standard 2-1/4-8 thread, instead of reverse engineering pipe thread dies to try to find something that fits (which it won't), how about just seeking out a 2-1/4-8 die?  You're gonna drop a hundred bucks on an "OKish" one either way, triple that for quality stuff.  If you want to google it, take note of how I 'spelled' that, 2-1/4-8.  Google likes that.   But tossing up pictures is free.....


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## Abody711 (Apr 24, 2022)

When I said 37 degrees, I was referring to thread face as someone else mentioned. Did not think it was flared like npt. I received thread file. Did not specify the thread type it was for. I filed the damaged threads and chased the internal threads with the file. Threads aren’t perfect now but face plate screws on with no issue. Only have after picture


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## Abody711 (Apr 24, 2022)

Picture didn’t post


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## SLK001 (Apr 24, 2022)

Cleaning off the dirt and rust will help things go on and off also.


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## Jake M (Apr 24, 2022)

Abody711 said:


> When I said 37 degrees, I was referring to thread face as someone else mentioned.
> Did not think it was flared like npt.



I know what you were referring to.  That's why I said it was bad or incomplete information.  Internet forums (and Google it's self) are great for doing that sort of thing.  Working in text, with minimal context, trying to solve each other's problems...  Things get crossed up and re-arranged a lot. 

Speaking of minimal context...  In this case, I have very little context, but enough context to know what you mean by "did not think it was flared like npt.  NPT is not flared, it's tapered.  While I have figured out somewhat what you mean, "the internet" is just one's and zeros....  If you say flared, you're gonna get "flared", which is a totally different thing.  Here's a piece of advice that isn't about lathe spindles, machining, or anything in particular, rather it's about EVERYTHING you do on the internet....  Pay attention to and learn proper nomenclature, as best you can, just as if it was part of the project you are working on.  The internet will still be a heap of crap with anything else but your best interest in mind, but it'll become a lot more useful tool if the terms you put in match up to the answers you're looking for.



Abody711 said:


> I received thread file. Did not specify the thread type it was for. I filed the damaged threads and chased the internal threads with the file. Threads aren’t perfect now but face plate screws on with no issue. Only have after picture



That looks like it was a heckuva ding, and a pretty good save to me.  I can blow that picture up until the spindle is nine plus inches in diameter, and get a good look at it....  Very nice.  It looks like you've got the "mushrooms" off, without disturbing much if any material that's still in the correct position.  Can't ask for more than that.

I would make a further suggestion.  Two actually.  First, as SLK001 said, I'd be inclined to clean the whole of those threads.  No more with the thread file, you don't want to change any dimensions.  I'd cut a thin strip of scotch brite, cover the ways, run the lathe in reverse, pull that strip tight, and run it through the threads until they polished up some.  From your picture (assuming it's consistant all the way around), I'd probably start with red until it's just clean, and move to gray to finish.  Absolutely not "required", but it'll make it a lot nicer to use.

Second suggestion, it looks like the very start of the partial thread has a chunk that's missing, or reduced to an ineffective amount.  I might consider cleaning and/or removing the section of thread prior to the damaged area (above it in your picture), and carefully round over the beginning of the good thread to such a degree that you'd feel comfortable touching it with your hand while the lathe was spinning.  If you were to google "higbee thread", you'd get pictures of what I'm talking about.  It looks like most of the videos are using machine tools to make those threads (which is cooler, but absolutely not necessary), but when you see the pictures, you'll know exactly what I'm talking about.  Just like my other suggestion, it's absolutely not required, but it'll just it nicer to work with.

EDIT-
Scotch Brite has a LOT of products, and as I think about it.....  I think the colors don't necessarily interchange between the two of them, so let me make a more specific suggestion:

3M  64933

That number will google nicely, I get mine from Napa.  It's a good starter kit to figure out what you need.  It lasts quite a while, but it's not cheap enough to own all of it....  This part number includes the two most useful "flavors".  They cut easily with junk scissors (they ruin good scissors), and are quite good.  Like I said though, cover the ways.  It's a fine, fine abrasive that you don't want packed into your way wipers.....


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## Abody711 (Apr 25, 2022)

The threads are clean under the machinist blue and anti-seize grease


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## Shootymacshootface (Apr 25, 2022)

Abody711 said:


> The threads are clean under the machinist blue and anti-seize grease


I would be very happy with that.


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