I need a knurled nut !

[canadianhorsepower]

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]

1. [SIZE=-1]In-feed rate (or axial feed rate for knurling from the turret)[/SIZE]
2. [SIZE=-1]Sharpness of the knurl teeth[/SIZE]
3. [SIZE=-1]Hardness of the material[/SIZE]
4. [SIZE=-1]Included tooth angle of the knurl (a sharper angle penetrates easier)[/SIZE]
5. [SIZE=-1]Width of knurl face (a narrow face penetrates easier)[/SIZE]
6. [SIZE=-1]Method of knurling (bump from cross-slide or end knurling from turret)[/SIZE]
7. [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]

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[canadianhorsepower]

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]

1. [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]
2. [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]

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[rhankey]

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.

 

[MachineTom]

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.

 

[tornitore45]

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.

 

[Rivergypsy]

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

 

[Knurly]

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

 

[Knurly]

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

 

[MachineTom]

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.