# I need a knurled nut !



## Knurly (Aug 5, 2013)

Hi
I'm trying to find a little assistance with a simple metalworking problem . I have an old and rare Sony microphone which has been abused during it's lifetime and now requires some very simple parts to get it back to health .

Specifically I need a small hollow circular 'nut' that serves as a strain relief for a cable that passes through it . It's difficult to find an engineeing firm interested in such a small job . I was wondering whether anyone here would like to offer assistance or might know where I could find some . I'm happy to offer remuneration .

Many thanks , Knurly .


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## Cogsy (Aug 5, 2013)

It doesn't look like an overly difficult piece to make, if you've got the right tools that is. Maybe you should include your location as there are members on here from all over the world.


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## canadianhorsepower (Aug 5, 2013)

Cogsy --is right looks like a ten minutes job
and anyone with a knurl can do this.. I think


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## Knurly (Aug 5, 2013)

Thanks Cogsy & CanadianHP . I'm in London . There's a little bit more to it , but the knurled nut is the crucial piece . It screws into a thin walled , possibly spun , metal housing . The thread has , over time , gouged the 'meat' from the hole it used to mount in and is now too loose to fit properly . I'd imagine the easiest solution is to simply increase the OD of the threaded portion .

The mic is a 1950's Sony C37A , a venerable and expensive piece of gear . Plenty of it's internal metalwork could stand replacement , but the 'nut' is the fundamental problem . I can post other photos for those who are interested .

Thanks again , Knurly .


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## canadianhorsepower (Aug 5, 2013)

sure post some more pictures and dimensions

cheers

Luc


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## Knurly (Aug 5, 2013)

Luc
  Here's a few more . It's obvious that the mic internals have been desecrated over the years . Apart from the knurled nut and the horrible mess made of the mounting hole , there is an internal bracket (obscured by gaffer tape) that is fundamentally the wrong shape .

  The cable clamp needs to allow the cable to exit at an angle , rather than at 90deg to the rest of the the frame . This is the flaw that causes many of the problems with maintaining these mics . Note that the heads of the cable clamp screws have been totally stripped , so it's may be easy to release but it'll be impossible to tighten .

  I'll measure up some dims .

Thanks , Knurly .


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## Till (Aug 5, 2013)

That's a ten minute job but as long as you don't enter your location in your profile, nobody will make the nut for a crate of beer...


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## Knurly (Aug 5, 2013)

Dimensions : The 'nut' is 14.25mm in diameter , 10.9mm in diam on the threaded portion , which has 2mm of thread , and 8.45mm 'thick' .

Knurly


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## Knurly (Aug 5, 2013)

Till said:


> That's a ten minute job but as long as you don't enter your location in your profile, nobody will make the nut for a crate of beer...



Thanks , Till . A very sensible nudge . Is there a bureau in Hamburg that can dispense crates of beer ? It'd be so useful to be able to arrange such a thing with a Paypal payment .

I often work with a guy , Hansi , who also from Hamburg . Maybe I can get him to drop by ? The only caveat is that it may arrive as half a crate of beer , Hansi's quite a thirsty chap .

Knurly .


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## mcostello (Aug 5, 2013)

Old and venerable works for Us.


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## canadianhorsepower (Aug 5, 2013)

Knurly said:


> Dimensions : The 'nut' is 14.25mm in diameter , 10.9mm in diam on the threaded portion , which has 2mm of thread , and 8.45mm 'thick' .
> 
> Knurly


 
the 8.45 thick does that include the thread of 2mm

the rest of the stuff can easily be fix with a small build up of silver solder
or even Devcon liquid metal

it's to bad your not close to mt place that's the kind of work I like doing


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## Knurly (Aug 6, 2013)

Luc
The 8.45mm includes the 2mm of thread . In the past someone had tried to build up the hole using solder , but used normal tin/lead solder . Doh !

Yes indeed , I'd quite like to be much closer to Ottawa ! That's the problem with this little job , it's proving very difficult to find a local 'light engineer' and I know that at some point anyone taking on the task would like to actually see and handle the various bits .

By the way , I like your photos in that thread about your new engine . Knurly .


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## Woodster (Aug 6, 2013)

If you can get it to Letchworth (daytime) or Hemel Hempstead (evening) I could have a look at it for you. 
Message me for more information.


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## ornithorhynchus (Aug 6, 2013)

Hmmm. Why don't you silver solder it!
Its quite easy.
Or maybe bronze.
I'll look tomorrow, I may have a nut for you or two.
Don't hold your breadth though, i've had a clean out.
Shadow.


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## tornitore45 (Aug 6, 2013)

Two crucial points

Must the nut be threade last after the can is all closed or can be preassembbled with a tin nut inside?

The knurling is not a standard diamond pattern or little piramids, rather is the conjugate made up od piramidal indentations.  If exact restoration is desired that can be a problem.


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## chucketn (Aug 6, 2013)

Anyone know where to get wheels that make the pattern in Knurly's picture? 

Chuck


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## canadianhorsepower (Aug 6, 2013)

I don't see it any different then the one we use.
It looks like a regular knurl that was machine down after to remove
the spike


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## chucketn (Aug 6, 2013)

The wheels I bought from LMS don't make the line between the diamonds, at least on the knurls I've made. Maybe I'm not doing it right. Here's my latest effort: http://s571.photobucket.com/user/chucketn/media/Drawbar%20Wrench_Hammer/handle2_zps22186cab.jpg.html

Chuck

Edit: Maybe it's an optical illusion, but it looks like a positive ridge between the diamonds, mine makes a groove.


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## canadianhorsepower (Aug 6, 2013)

chucketn said:


> The wheels I bought from LMS don't make the line between the diamonds, at least on the knurls I've made. Maybe I'm not doing it right. Here's my latest effort: http://s571.photobucket.com/user/chucketn/media/Drawbar Wrench_Hammer/handle2_zps22186cab.jpg.html
> 
> Chuck
> 
> Edit: Maybe it's an optical illusion, but it looks like a positive ridge between the diamonds, mine makes a groove.


 
Chuck, you didn't go deep enough you would have the same pattern
then only machine it on the lathe to remove the excess of spike
you also need a constant flow of air and taping fluid when doing this
do you have the clamping style knurler??


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## chucketn (Aug 6, 2013)

Yes, Luc, I have a clamp type knurler that I built as well as single and double wheel bump types. I prefer the clamp type on my 7x14 lathe.
Can't remember now, but think I only bought medium wheels from LMS for the one I made.

Chuck


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## canadianhorsepower (Aug 6, 2013)

_*BLANK DIAMETER SELECTION
        FOR CIRCULAR PITCH KNURLING WHEN KNURLING FROM THE "CROSS SLIDE".*_​

[SIZE=-1]The following formula can be used to determine         an approximate blank diameter for proper tracking. This blank diameter         can be adjusted for optimal results once good tracking has been established.         It is advisable to do all test rolling at the same speed and feed as is         planned for the production run.[/SIZE]​
[SIZE=-1]Knurl Diameter [ideal] = 
                  Blank Diameter / #Teeth [part] x #Teeth [die] - C.F.*[/SIZE]

[SIZE=-1]* C.F. = Tracking Correction Factor [/SIZE]​
[SIZE=-1]This correction factor takes into account the fact that         the tips of the knurl teeth have penetrated below the blank diameter by         the end of the first revolution. Several other formulas can be derived         to calculate almost any aspect that may be required. (For approximate         C.F. values see Table         II.)[/SIZE]
[SIZE=-1]#Teeth [part] = ( Blank Diameter                 x #Teeth [die] ) / ( Knurl Diameter + C.F. )[/SIZE]

[SIZE=-1]Blank Diameter = ( #Teeth [part]                 / #Teeth [die] ) x ( Knurl O.D. + C.F. )[/SIZE]​
[SIZE=-1]The approximate tolerance for the knurl diameter should           be: [/SIZE]

[SIZE=-1]± (.5) x (C.F.) x (Knurl                 Diameter / Blank Diameter)[/SIZE]​
[SIZE=-1]If the finished diameter of the part is known, an approximate          blank diameter can be determined by subtracting the proper value from Table         I.[/SIZE]

_*BLANK DIAMETER SELECTION
          FOR DIAMETRAL PITCH KNURLING*_​
[SIZE=-1]Blank diameters for diametral pitch knurling dies are         more easily computed, since they are always common fractional sizes. The         formula is as follows:[/SIZE]
[SIZE=-1]Blank Diameter = ( #Teeth [part]                 / Diametral Pitch )[/SIZE]​
[SIZE=-1]American Standard ASA B94.6-1984 describes the diametral         pitch knurl system. Diametral pitch knurls are designed to track uniformly         on fractional size stock up to 1" in multiples of 1/32" or 1/64".         They are held to closer tolerances for this purpose. 

        The American Standard recommends that the use of 64 Diametral Pitch knurls         be avoided as much as possible, and that preference be given to the use         of 96 D.P. knurls for simplification of tooling. (For Equivalent Normal         Circular TPI see Table         III.)

        The number of teeth that will be rolled can be easily determined by multiplying         the blank diameter by the Diametral Pitch of the knurl. Example: A 96         D.P. knurl will roll 96 x 1/2 = 48 teeth on a 1/2" diameter stock.[/SIZE]
*[SIZE=-1]D.P.[/SIZE]*
*[SIZE=-1]Blank Diameters 
                for Uniform Tracking[/SIZE]*
[SIZE=-1]64[/SIZE]
[SIZE=-1]every 1/64"[/SIZE]
[SIZE=-1]96[/SIZE]
[SIZE=-1]every 1/32" (also every                 1/96")[/SIZE]
[SIZE=-1]128[/SIZE]
[SIZE=-1]every 1/64" (also every                 1/128")[/SIZE]
[SIZE=-1]160[/SIZE]
[SIZE=-1]every 1/32" (also every                 1/160")[/SIZE]​
[SIZE=-1]NOTE: Unfortunately the above formulas do not hold precisely         for all conditions. Sometimes apparently identical knurls from different         manufacturers will not track on the same blank diameters due to a difference         in the sharpness of the teeth. Also, it is possible for the number of         teeth rolled on a part to change as the knurling tool wears. How deeply         the knurl penetrates into the work blank on the first revolution is the         main factor in determining if an adjustment should be made to the basic         formula.
[/SIZE][SIZE=-1]
        Some factors which affect this penetration are:[/SIZE]

[SIZE=-1]In-feed rate (or axial feed rate for knurling from             the turret)[/SIZE]
[SIZE=-1]Sharpness of the knurl teeth[/SIZE]
[SIZE=-1]Hardness of the material[/SIZE]
[SIZE=-1]Included tooth angle of the knurl (a sharper angle             penetrates easier)[/SIZE]
[SIZE=-1]Width of knurl face (a narrow face penetrates easier)[/SIZE]
[SIZE=-1]Method of knurling (bump from cross-slide or end             knurling from turret)[/SIZE]
[SIZE=-1]Bevels on edges of part or knurl tool (affects knurl             penetration from end)[/SIZE]
[SIZE=-1]A change in any of the above variable may correct (or         cause) a mis-tracking problem. [/SIZE]
[Close this window]​ ​


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## canadianhorsepower (Aug 6, 2013)

*Speeds & Feeds for Knurling
*​[SIZE=-1]
      For convenience, Knurling is often performed at the same speeds used for       turning operations when using high speed steel tool bits. But to prevent       seizing of the rolls on the pin, we recommend a maximum surface speed of       about 150 SFPM (Feet/Min) or 50 m/min. You may find you get longer knurl       life and improved appearance by slowing down the spindle to about 50 SFPM       (15 m/min) for harder steels and stainless. CARBIDE knurl pins are strongly       recommended for all high speed knurl applications. DOWEL pins with a plus       tolerance SHOULD NOT be used because of the possibility of the knurls seizing       up and breaking. 

      For BUMP knurling with a SINGLE TOOL HOLDER from the cross-slide, the       infeed would normally be .001-.004"/rev (.025 - .1mm) to roll the part       complete 5/20 revolutions. When knurling stainless steels, it is important       not to roll any longer than necessary as this material work hardens as       it is formed. The total amount the tool penetrates into the workpiece is       approximately 50% of the tooth depth of the wheel (which is shown in TABLE       1). You may have to travel more than this amount to allow for the flexing       of the part or holder due to rolling pressure. Some trial and error will       be required. 

      If you are using a two die STRADDLE HOLDER, the infeed rate should be 5       or 10 times faster because the wheels are coming in tangentially instead       of head on. Before knurling, the holder should be set so that the distance       between the two wheels is smaller than the workpiece diameter by approximately       the depth of the knurl tooth. Then to knurl, move the holder so that the       two wheels are as close to the centerline as possible to minimize the knurling       pressure on work spindle and cross slide. To initially find the centerline       using a two die straddle holder, you may use this method: 
[/SIZE]       
[SIZE=-1] Bring the preset holder and knurls towards the           workpiece up to just touch a flat plate of any thickness inserted between           the knurls and workpiece. 
[/SIZE]
[SIZE=-1]Remove the plate and advance the holder the thickness             of the plate + 50% of the diameter of the knurl wheels + 50% of            the diameter of the workpiece. The two knurls should then be over            and under the centerline of the workpiece.[/SIZE]
[SIZE=-1]
        If you will also be axial feeding to produce a knurling pattern that is         wider than the knurling wheels, chamfers should be on the edges of the         wheels. If the knurling doesn't go up close to a shoulder, the use of         our CONVEX axial feed wheels is strongly recommended to further reduce         the knurling forces, extend tool life and improve the cosmetic appearance         of the workpiece. The normal axial feed rates would be from about .004-.020"/rev.         (.1 - .5 mm/rev). The slower feed for stainless steels and tough or semi-hardened         steels and faster for mild steels, brass or aluminum. When using CONVEX         axial feed wheels, even faster feeds may be used. 

        END KNURLING from the turret (axial feeding only) is usually done at        .005/.030"/rev (.1-.7 mm/rev), using the slower range for coarser        Knurling on high-alloy steels, faster for finer pitches and on brass,        aluminum        or mild alloy steels. Normally the dies are fed off the work about twice        as fast. 

*CUT TYPE KNURLING* is done at similar speeds and feeds as pressure knurling,        but the method of initial contact is critical if clean knurling is to        be produced. Please click below for recommended speeds and feeds.[/SIZE]​[SIZE=-1]
        Speeds and Feeds for Cut Knurling 
[/SIZE]​*
      IMPORTANT:*[SIZE=-1] If you are having problems with double or       mis-tracking, it usually can be solved by increasing the infeed on bump      or cut knurling. For end-knurling from the turret, increase the axial       feed rate. The deeper and wider the penetration of the knurling wheel into      the workpiece on the first revolution, the more likely it will fall into      step the next time around. 

      An estimated best workpiece or knurling wheel diameter can be calculated,      but it may not always work the first try. Variations in the material hardness,      sharpness of the crest of the knurling wheel teeth, width of knurling,      initial      in-feed rate, or spindle speed all affect the initial tracking. 

      Another common way to correct a mis-tracking problem is to grind or stone      a small flat of up to .004" (.1mm) or slightly more on the crest of the      knurl wheel teeth. This also may actually improve tool life because the      wheel is less likely to chip out. Usually, the flat in the root of the      rolled workpiece is not noticeable. [/SIZE]       
[Close this window]​


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## rhankey (Aug 6, 2013)

It is somewhat amusing reading all the engineering that is going into what appears to be a rather simple "nut".

Perhaps I am wrong, but I am not convinced the "nut" threaded directly into the sheet metal microphone shell, as the hole looks too perfectly round.  I don't know how thin the metal shell is, but I can't imagine it would have had much more than a single thread contact, which would have been a problem waiting to happen, and almost certainly would have resulted in a non-round hole when it did eventually wear out or pull through.  Also, if that was how it was constructed, the "nut" would have needed threading all the way to the shoulder, which does not appear to be the case.  It would seem far wiser to have the "nut" attach to a thin inner nut, thus sandwiching the microphone shell.  I'd almost bet that was how it was originally constructed, and over time the inner nut has been lost.

I'm not sure whether the goal is to faithfully restore the microphone to exactly how it was originally constructed, or if it is ok to make some minor improvements along the way that don't materially alter the outward appearance.


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## MachineTom (Aug 6, 2013)

A quick glance at ebay shows item #271243958888 available for the small change of $4500 USD.

Many nice photos, and the outer nut shown by OP, is way different than on this mint looking model from 1959. On the first shot of the mic you can see straight knurls, and the threads appear to be coming out from the mic, and the nut screws on to those. So there was a threaded boss likely brazed for the inside to which the cap was threaded, Possible material was AL. tough to say.


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## tornitore45 (Aug 7, 2013)

About the art and religion of knurling...

So much geometry calculations and theory is expended to determine the correct blaqnk diameter to end with a last statement that basically says:

"There are many variable involved such as material hardness dies shape wear and sharpness that it may not work on first try, if that is the case a more aggressive start may be succesful."

I learned from a pro that told me knurling is not like cutting gears, is a deformation process where the true pitch diameter is practically unknown.
Just drive in aggressively and the system will find its own happy place for a clean knurl.

Since following his advice I had good tracking knurls on any diameter.

If you have production on a CNC machine, obviously you need repetibility but this is a whole new bowl of wax.  You can fine tune the formulas with experiment on diameter, feed and speed and go from there and change tool before it wears to the point of not tracking.


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## Rivergypsy (Aug 7, 2013)

Just to throw another option in, I'm in Ely, Cambs if you need a hand still


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## Knurly (Aug 7, 2013)

Yes indeed , rhankey , the knurled nut 'bites' directly on the thin metal shell . I don't think the shells were threaded .

To assemble the mic it's necessary to feed the cable through the shell and the nut , but the nut can only be screwed in once the shell has been fully fitted . Because of the minimum bend radius of the cable , it is impossible to feed the cable through the nut while it's fitted to the shell . This also means that there can be no internal fixing .

The perfect nut would be made of something pretty 'hard' with a thread pattern that accounts for the lack of a mating thread and the thinness of the shell .

The metalwork for this mic is all wrong , but there very little can be done about it without redesigning the mic . To keep it vintage I can't alter it too much .

Knurly


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## Knurly (Aug 7, 2013)

Tom , it sure is an expensive mic , which is why it deserves radically better maintenance that it has had . The cable exit and strain relief are a serious design flaw . Every one of these mics I've seen has the same problem .

The mic is free to rotate on it's 'strirrup' type mount , but the cable passes through a loop fixed to the base of the stand , just above the 3/8" thread mount . This isn't just tidiness , it stops the weight of the cable from unintentionally adjusting the position of the mic .

The cable must be multicored , to allow power to be fed to the 'tube' . It must also be well screened and have a rational impedance . All of these factors combine ; the cables get destroyed over a few years and must be replaced . That's when things go wrong .

Knurly


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## MachineTom (Aug 8, 2013)

If I was to fix this, First I would ream the hole is the shell round, using an adjustable reamer so the size would not be noticeably larger, likely .010 or so. I would then knurl a piece of stock that has a blank diameter same as the hole, turn off a portion of that knurled area leaving a step, while keeping a press fit of around .005-7" in the turned section, then make a cap nut as in the photo, straight knurls, radius end. 

A couple hours to get it right. alot less to do a shoemakers job of it.


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