# Threading ?s



## Naiveambition (Nov 15, 2017)

A part I'm working on requires a one inch thread, and having trouble laying it out so ,  

As u can see in pic only the center of the bar is threaded,    and mating to the female part.      My issue is the chart calls for 8 tpi and 12 is lowest on my lathe , plus With the nut only being a 1/2" this only leaves four threads.  No stress on the part so I don't need a deep , large thread.  

I would like a more compact thread..  Can I just pick say 12 or 24 tpi and still achieve a fit with the sizing I have now.  My parts are sized to what thread limit charts call for.         
     1" bar for external threads and 59/64 for the nut


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## bazmak (Nov 15, 2017)

Thread form and TPI(pitch ) are the main criterier everything else
forms itself.If you are making the male and female you can do anything you wish.If you want imperial then whit at 55o and tpi for a fine thread BSF
will give charts for any other dims or a non std pitch and you will have to calculate any missing dims.All that changes is depth of thread or cut


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## goldstar31 (Nov 15, 2017)

Deleted- Poster gave confusing details


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## Picko (Nov 16, 2017)

If you're making both parts it will not matter what pitch you use.


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## Naiveambition (Nov 16, 2017)

Yes I am making or threading both parts.    I know what I want it to look like just don't know what thread I'm looking for.   Granted I work in imperial.  And topping it of this is my first thread job ever!!  Gonna try on a test peice first and hope and pray. 

Something similar to the photo is the intended target.    As you see they are very shallow threads.   Im guessin around 20 tpi .  So when I say a 1" thread I mean the outside diameter, not trying to cut the normal thread for a inch bolt per se.
Probably a little deeper and longer but the same style.   

How would I know my depth of cut?   Just pick a depth and mate the other part?


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## bazmak (Nov 16, 2017)

It depends on the lathe is it metric or imperial. If you want 1" thread
 then you can still cut metric pitch at 60o and whatever pitch you want
If metric then each thread is an equilateral triangle ,so depth of cut = pitch
and you would be cutting an M25.4 thread at say 1mm pitch= 25.4 tpi
The thread is best determined by what your lathe will cut pitchwise and if 
metric or imperial. Personally it is easier and cheaper to cut metric form at 60o
on any diameter depth = pitch. Make a male piece by eye till it looks rigt then cut a female and check for fit. All trial and error


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## ShopShoe (Nov 16, 2017)

Since you are creating a thread of your own, what others have said above is true. Make one thread and then make the matching part. 

The pitch of whatever thread you make will depend on the change gears (either manually set or with your lathe's threading gearbox). Use a chart to choose a pitch and set the gears for cutting.

If you use a 60-degree cutting tool, then you are OK for either metric or imperial thread forms. 

The diameter of the part you are threading really has no relation to the pitch, other than when making standard fasteners or fittings. If that is an issue, consult a reference source like Machinery's Handbook.

If you want to measure a known thread, you can buy inexpensive thread-pitch gauges. They might not be a bad investment if you will be wanting to know about other threads later. If you are thinking of buying a tap and die set to add to your shop it may include one. Useful little tools.

You can attempt to measure your TPI with a ruler (also called a scale). If you have a magnifier that may help you.

--

My first attempt a thread-cutting was making a brass barrel for a ballpoint pen. I used a ruler and guestimated a thread pitch to use based on my lathe's change-gear chart. It was a strange "kinda-square" thread form, so I ground external and internal toolbits to make the form and went from there. The whole pen, with two internal and two external threads to be cut, took less than three hours, including the toolbit grinding. One aborted attempt.

--ShopShoe


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## Sansspaceship (Nov 16, 2017)

Hi,
Not sure if you are aware, but given your description of the problem thought that I would mention a common tool &#8216;thread gages&#8217; you can buy them pretty much at any tool store they allow you to check threads to on say a bolt or part like in your photo. They will only set you back a few bucks, and give you a better idea of the tpi you are looking for visualaly.

Sorry if you know about them, wasn&#8217;t trying to be a smart ar*e :hDe:

You haven&#8217;t talked about trying to cut the thread yet, but if it&#8217;s your first one don&#8217;t don&#8217;t get disappointed if you make a meal of it.  It will seem like more art than science for the first few you cut. If you run into problems I picked a lot of tips up from the gunsmith forums, when starting out theading .... as to get them right it&#8217;s not quite as simple as just plunging in a 60 degree threading bit.

Hope it does well, and please share your finished parts with the forum.

edit - shop-shoe posted just before me :thumbup:

Cheers,
.adrian


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## Edke6bnl (Nov 16, 2017)

I have only done a dozen threads myself but I like to experiment on pvc first to get the motion and moves down.


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## john_reese (Nov 16, 2017)

It sounds like you have the freedom to choose your pitch and thread form.  Make your decision then start in on it.

You may scrap a couple parts but you will become proficient in short order.

A suggestion for the female part.  Leave it a bit long.  Bore that excess length to the major diameter of the thread.  When the threading tool just marks that diameter your thread is on size.  Cut off the excess length after threading.  If using a sharp V tool instead on a truncated V, be sure to calculate the major diameter based on the sharp V.


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## mfrick (Nov 16, 2017)

If your really into threading you can use thread wires to get a correct depth them make the mating part to fit.


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## Wizard69 (Nov 16, 2017)

Im wondering what this part is for.   Everybody is saying you can use whatever pitch you want which is true to a limited extent.   However 8 TPI has me wondering if there was a specific reason for the pitch.  It comes down to what the part was designed for.  

By the way your machine may or may not be able to cit the pitch.   If you get creative with the change gears you can often come up with many other pitches.  

Perhaps the most important suggestion here is to get a copy of Machinery's Handbook and study threading.  If you learn the formulas involved you can do threads in any size or form you want.    Probably the second most important thing to do here is practice on cheap materials PVC was mentioned above but others will do.  

One other thing i noticed, one of your pictures had a ring with graduations.   If that is your nut or part of it you cant change pitch and expect that the graduations will work.   It would help a lot to clear up what you have here and what it does.


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## Chiptosser (Nov 16, 2017)

You can make it to the thread that you choose, and you machine has available.


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## pp2076 (Nov 16, 2017)

Wizard69 said:


> Perhaps the most important suggestion here is to get a copy of Machinery's Handbook and study threading.


Google has an old version for download at https://www.google.com.au/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwj92a3KyMTXAhWLF5QKHdM4DXoQFggoMAA&url=http%3A%2F%2Fwww.woodworkslibrary.com%2Frepository%2Fmachinery_handbook_for_machine_shop_and_drafting_room_1914.pdf&usg=AOvVaw2Iv-I-fWAoLI4ZjQmMjcOC

Newer version here: https://www.google.com.au/url?sa=t&..._Edition.pdf&usg=AOvVaw1EVKaLZxinM4PjoUGeoTvJ


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## Naiveambition (Nov 18, 2017)

Well tried to do my threads today.    Started with I'm guessing acetal rod or something similar and came out great.   Was amazed I got on first try.  So now I'm feeling confident and went to my metal pieces.  

 Here's where it all went to [email protected]&t     Broke every carbide tip I  used(3 different kinds)  for various reasons,   Hss blunted Fast as usual for me.   Machine kept kicking out of gears when it would jam losing its spot.  And ruin my peices.   With all theses issues I don't ever want to thread again,   I love taps!!

Even though I will try again since I have to have these parts. But:wall: I still can't really figure out what went wrong   The minor diameter would not produce a nice valley  being flat.  The nut was okish but the the rod was terrible . This was where all my issues were.  may go to alum.   I'm pretty sure that they were stainless of some sort, and may be part of why :fan:    I  got a load of it from a guy that worked on space station parts and have no idea what hardness it is or if I work hardened it

As for the part use.   I'm making a half scale ma duece .22 (from ccs on the web)and the piece I'm on is the barrel ring that holds the cooling pipe.    The threaded peices are purely cosmetic and have no real job.  This is why I can choose any thread that will work vs what my tap chart was at 8tpi.   The peice I'm holding will thread into the collar around the barrel..


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## ShopShoe (Nov 18, 2017)

Anybody else please chime in.

My Guesses:

1. Trying to cut thread in one pass? You need to make multiple passes.

2. Too big a cut on each pass?

3. Rigidity of the tool at the workface? 

4. Speed too fast? Some ( Me included) have made a hand crank to turn the lathe for really slow operation (Small lathe, and of course the lathe is unplugged.)

5. Maybe still not the right cutter (or sharpness) for the Stainless or exotic metal you have.

6. Maybe not the right lube for the metal, cutter, and speed you are using.

It would really help if your friend could tell you exactly what the metal is.

Perhaps it's academic at this point, but if the metal is difficult to thread on the lathe, it would probably be a problem with a die or tap, unless you are looking at specialty dies or taps (read as expensive.)

--ShopShoe


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## Hopper (Nov 18, 2017)

Naiveambition said:


> ...
> ... I'm pretty sure that they were stainless of some sort, and may be part of why :fan:    I  got a load of it from a guy that worked on space station parts and have no idea what hardness it is or if I work hardened it
> 
> ...



You are fighting an uphill battle there. Stainless can be a real pain to machine. Well worth buying some nice mild steel bar that you know is a standard grade and should machine well. Using scrap and offcuts is always a bit of a lucky dip.


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## Sansspaceship (Nov 18, 2017)

Will add a few thoughts, in addition to the comments from shopshoe:

A) Run a file across your stock, if it skips or doesnt scratch .... I would be looking for new stock! How does it turn down in normal operation with a normal cutter, test number 2?

B) are you plunging straight in i.e is the cutter engaged on both sides of the V.  If so You might want to have a look for some gunsmithing videos as mentioned In my earlier post. But in short setup you cross slide at 59 degrees (may be different on some lathes). Then setup the cutter ensuring its central.  Start cutting using the cross slide, so you are engaging only one side of the V at anyone time, that is after your initial cut.

Cutting, threads takes practice and some skill - but once you have it down, believe me a tapped thread isnt anywhere near as nice for mateing two parts... especially if you are cutting both threads.

If you have a ridged machine - dont baby the carbide bits, but your speed must be slow... I cut threads on the slowest speed available on my lathe.

Good luck - dont get disappointed it just takes a bit of research and some practice.  

Cheers,
.adrian


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## Sansspaceship (Nov 18, 2017)

Hopper said:


> You are fighting an uphill battle there. Stainless can be a real pain to machine. Well worth buying some nice mild steel bar that you know is a standard grade and should machine well. Using scrap and offcuts is always a bit of a lucky dip.



Agree with this comment from hopper, as will be easier than learning on SS, I would go with 12L14 over 1018 in your generic CRS.


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## Sansspaceship (Nov 25, 2017)

Hi - just thought I would ask if you had any further luck with your threading adventure?

Cheers,
.adrian


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## Naiveambition (Dec 1, 2017)

Adding some closure to this thread.     

I was able to accomplish my threads but not without some complications and discoverys.    
For this mission I switched to alum. The male thread went as planned but the female still presented issues.  1st being I found my leadscrew clamp was busted and with cuts under.01 it was fine but any more it would slip out of sync and kick the gearbox out of gear losing my place.   So after fabing up another solved my issues there.   The second issue was most likely cutter geometry.  Was not cutting nice clean chips,  more of a tear style chip.   Under power it was enough to stop my little 7x10 so had to resort to hand turning the lathe and finally made it thru.    

I chose 20 tpi and cut till I had one full turn on the dial or .1 I think..  Now granted I made my own 60* guage for setting the tool and prob made mistake of using small top rake.   So not perfect but worked in the end will need some more practice but at least the steps are down and work on the finer points.

Here's a pic of my parts    The iPad cam has no definition so they do look better than the photo.


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## Sansspaceship (Dec 4, 2017)

Glad you had some success, will leave others to comment on cutting geometry as grinding cutting tools isn&#8217;t one of my strong areas. But something is definetly wrong if it gouging and not cutting, my initial thought would be too deep a cut, without enough horse power (as alu can be gummy) but won&#8217;t comment past that as am only guessing without more details.

Anyway good luck with you project, thanks for the update.

Cheers,
Adrian


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## BaronJ (Dec 4, 2017)

Hi, From looking at your picture of the threads in the ring, make sure that the tool has enough clearance under the front and side edges.  It looks as if it is rubbing and tearing the thread.  I've had this problem with home ground tool bits.  The problem gets worse with smaller holes.  I have started to buy small carbide threading bits, which gets around this problem nicely.  You still have to watch the hole size though.

HTH.


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## JCSteam (Dec 4, 2017)

Just throwing this out there, with regards to the comment of Ali been gummy, have you tried cutting Ali with WD40. It stops the Ali cold welding itself to the tip, which may be another cause of the dragging that you've experience. For the sake of a couple of quid for a tin may be worth a try.
?? It did wonders on a part that I was turning, plus the chips just rolled off the cutting tool. 

I by no means profess to be an expert, this is just my observations from my own work.


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## Sansspaceship (Dec 6, 2017)

JCSteam said:


> Just throwing this out there, with regards to the comment of Ali been gummy, have you tried cutting Ali with WD40. It stops the Ali cold welding itself to the tip, which may be another cause of the dragging that you've experience. For the sake of a couple of quid for a tin may be worth a try.
> ?? It did wonders on a part that I was turning, plus the chips just rolled off the cutting tool.
> 
> I by no means profess to be an expert, this is just my observations from my own work.



I might have added a bit of confusion by bringing up the gummy alu comment. To clarify I was just trying to read between the lines with the OP comment that he wasnt getting good chips and it was more tearing which to me might have appeared gummy.

But you point is extremely valid though, when I first started with alu I used wd40 and it works great. Now I use a fog buster as just run it generally set and forget after program proofing on the mill which is where I cut most of my alu, but yes coolant would be recommended when starting out. Although i have had quite a bit for success roughing dry.

The other thought I had was if it wasnt any of the culprits that have been mentioned by any of the previous posts it could be non heat tread alu, which can be a bear to cut and might explain the tearing, in my experience  you want T3 or T6 (common) alu in a 2011, 6061 or 7075.

I too am no expert, but always interested and keen to learn about cause and effect of stuff like cutters and material.

Cheers,
Adrian


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## DJP (Dec 6, 2017)

I'm sure that there are many cutting fluids available but if you want a 'home brew' try one part kerosene, one part Varsol and one part Automatic Transmission fluid.


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## mcostello (Dec 6, 2017)

My experience is that any kind of light oil will work, penetrating oil bought at garage sales for a pittance works best as it soothes My wallet at the same time.


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## rlukens (Dec 20, 2017)

It's an absolute must to have the compound rest set at 29 degrees. Make all your advancements with it, not the cross slide. Otherwise your plunging the cutter straight ahead and cutting on both sides. For your last pass, maybe move in on the cross slide a thou or two to clean up both sides of the "v".


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## Cogsy (Dec 21, 2017)

Why is it 29 and not 30 degrees for a 60 degree thread? I've always wondered this, every time I see the 29 degree figure quoted. I've never tested it myself, having only every cut smallish threads on the lathe and never having an issue with plunging straight in, but it would satisfy my curiosity to know.


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## BaronJ (Dec 21, 2017)

Hi Guys,

This controversy over 29-30 degrees and the insistence that this must be, verses plunging straight in, only serves to confuse and confound, newbies in particular.  I would suggest that most of us would only cut relativity fine threads, say more than ten or twelve TPI, so plunging in is not a big issue, and I admit that this is exactly what I do !

For large threads cutting on the forward face, which is what happens when using a 29 degree top slide angle does, lowers the cutting forces because it creates back edge clearance.  Doing Acme and square threads is an altogether more complicated proposition.

JM2PW.


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## goldstar31 (Dec 21, 2017)

ONE of the problems is that AFTER screwcutting in the lathe that it should be finished with a ground die.
The other possibility is that most lathes have 'protractors' which are inaccurate and the next exiting point is that the leadscrews on most older lathes are- em- knackered.

One way to find out what is happening is to cut a sample in half and use a high quality comparator which we all have -after we have carefully filed the quality control sample. Said he laughin' and scratchin'

Of course, we are all still reading something like McGraw's book Statistical Quality Control with a copy of  Schlesinger for bed time reading. 

In case of doubt-- YES:hDe:

Norm


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## john_reese (Dec 21, 2017)

Here is my take on threading.
If feeding from the cross slide you have chips from both sides of the tool meeting and jamming together.  Not good, especially on coarser threads.
In feeding from the cross slide a 30* angle may seem right, but it is likely you would see"steps" on the flank of the thread.  By setting the compound slightly less than 30* the trailing edge of the tool shaves a tiny amount off the flank of the thread eliminating the "steps"
In general I set my compound 1/2* less than half the included angle of the thread.

On CNC the feed is always straight in but is commonly fed to cut alternate flanks of the thread.


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## rlukens (Dec 21, 2017)

The tool has a 60 degree "point"... 30 on each side of center. Plunging straight in will cut equally on the left and right side of the tool. If you watch in slow motion, you will see the chip from each side curling towards each other. They collide, push back, and snap off. Although not the end of the world, this does give rise to a ragged thread.
Why 29 and not 30 degrees? Only because backing off of 30 by 1 degree wipes the right side of the thread slightly on each pass.


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## Cogsy (Dec 21, 2017)

goldstar31 said:


> AFTER screwcutting in the lathe that it should be finished with a ground die


 
I was watching a professional machinist cutting a thread on his industrial lathe a few months ago and he did not follow with a ground die, of course the fact that the major diameter of the thread was around 450mm (18 inches) probably limited his options...


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## goldstar31 (Dec 22, 2017)

Whilst I can appreciate that a very small number of people are still engaged in Screwcutting- as you say 60 degrees and whatever, there are vast numbers of people making and using 'non standard' threads and these, if they are studied carefully have rounded crests.

If you read what the vast majority of people should be reading-- and doing something about it, the sea is full- endemic proportions of screwtop bottles. Again in my cupboard of my real needs, I note  that all the 'lightweight' glass has closures which would cut through the lacquer on metal closures and as for the plastic ones, cause difficulty or annoyance if not some thing like 85 R3 which was the standard in the past.

On a more perhaps mundane level, Britain still has 55degrees, 47.5 and still uses metric sized threads in what can  be laughingly called' 'British Association' 

If I have ruffled a few feathers, might I humbly apologise.

Norm


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## Hopper (Dec 22, 2017)

No need for setting the topslide at an angle. You can have five bob each way by leaving it in the standard position. When screwcutting, advance the topslide by half the amount the cross slide is wound in. EG, if taking a 10 thou deep cut on the cross slide, advance the topslide by 5 thou. This combination moves the tool bit in a path equivalent to a bit under 27 degrees, so works perfectly for both 60 degree and and 55 degree threads. Most of the cutting is done on the leading edge, with the trailing taking a light clean up cut so no steps are generated.


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## mcostello (Dec 22, 2017)

I hardly ever finish off a thread with a die. If the lathe is set up to thread I will finish that way. More practice means better parts for Plan B.


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## rlukens (Dec 22, 2017)

Hopper said:


> No need for setting the topslide at an angle. You can have five bob each way by leaving it in the standard position. When screwcutting, advance the topslide by half the amount the cross slide is wound in. EG, if taking a 10 thou deep cut on the cross slide, advance the topslide by 5 thou. This combination moves the tool bit in a path equivalent to a bit under 27 degrees, so works perfectly for both 60 degree and and 55 degree threads. Most of the cutting is done on the leading edge, with the trailing taking a light clean up cut so no steps are generated.


Agreed, but without DRO's (I'm old) how can you accurately advance in the "Z" direction.


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## Herbiev (Dec 22, 2017)

Cogsy said:


> I was watching a professional machinist cutting a thread on his industrial lathe a few months ago and he did not follow with a ground die, of course the fact that the major diameter of the thread was around 450mm (18 inches) probably limited his options...



Come on Cogsy. We all have an 18 inch UNC die hidden away somewhere :hDe:


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## RichD (Dec 22, 2017)

Check out this guy...his videos are short and to the point. I already know a bit about threading, but darn if I didn't learn more tips from this guy.

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=2&cad=rja&uact=8&ved=0ahUKEwj8usX6jp_YAhXC5lQKHRrJD_gQtwIIMDAB&url=https%3A%2F%2Fwww.youtube.com%2Fwatch%3Fv%3D-hqYyPWSltk&usg=AOvVaw21gNbsNihEWLJRonx3hf0Z

I usually try to cut the female thread first if I can, then make the male piece last. Depending on the job, you can test fit the female threads onto the male thread and adjust as needed for a good fit.


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## john_reese (Dec 23, 2017)

If I have sufficient material to do it I like to turn a portion of the work to the minor diameter of the thread.  When the threading tool just marks the minor diameter, the thread is to size.  I cut off that portion after threading.  I use a similar approach on internal threads.


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## Timehunter (Jan 16, 2018)

For a down and dirty depth of cut for 60 degree U.S. threads....
0.866 divided by number of threads you want.
Should get you there...


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