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  1. #21
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    Re: Threading tungsten carbide rod

    One good starting point will be the input power: if you have some estimate of the input power you can estimate the "nominal" current. The nominal current and power is estimated over some meaningful interval.

    The output frequency also should be estimated to get a meaningful RF power output. This is not a conventional spark and a conventional spark plug is not appropriate.

    Conventional spark plugs need a dead time to recover (consider a conventional discharge tube like a photo flash Xe tube discharge). Or, you can also consider a simple GM tube as a model.

    I am afraid there is no "correct method" to get the "nominal current" for the discharge. You need to design your own devices- perhaps.

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    Re: Threading tungsten carbide rod

    Recently obtained https://www.ebay.com/itm/Set-of-two-...72.m2749.l2649 and will space them with 3M electrical tape to ~2-3mm and will fasten capacitor bank to sharpened ends with these https://www.ebay.com/itm/10pcs-Screw...72.m2749.l2649

    The issue with spark gap tubes is their limits on discharges, these drill bits should last much longer since turning them to a clean facing side will permit operation.

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  3. #23
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    Re: Threading tungsten carbide rod

    Take care to avoid corona. They can drain significant energy from your setup...


    (your links do not work)

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    Re: Threading tungsten carbide rod

    Quote Originally Posted by c_mitra View Post
    Take care to avoid corona. They can drain significant energy from your setup...


    (your links do not work)
    These links might work https://www.ebay.com/itm/Set-of-two-...p2047675.l2557 fasteners are https://www.ebay.com/itm/262370628135/
    Product listing image 3/4" X 4.0" Tungsten Carbide CNC bits




    The drill bits will be parallel to each other mounted to a high speed fan. The curvature of the bits will be optimal for airflow. Or you meant something other than gap quenching?

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    Re: Threading tungsten carbide rod

    The tools are hardly made of bulk tungsten carbide, at best cemented tungsten carbide. The temper color reveals steel.

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    Re: Threading tungsten carbide rod

    Going to send them back if they are strongly magnetic going off density of tungsten carbide they should each be ~175grams and 188.57g nominal for 3/4inx4in cylindrical tungsten carbide. Might as well get the small high purity tungsten if these aren't solid carbide.

    Seller said they are solid carbide bits.
    Last edited by Zak28; 27th May 2019 at 09:04.

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  7. #27
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    Re: Threading tungsten carbide rod

    The temper color reveals steel...
    I too think so.

    Tungsten carbide is about double the density of steel; you just take the weight of a similar sized bit and compare.

    But if it is steel, you can slowly anneal the bits, thread them and temper them back. Success not guaranteed but possible in principle.

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  8. #28
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    Re: Threading tungsten carbide rod

    They each weight 355g, each have an engraving 3/4 31271 and nominal whole carbide cylinder for this size is 452.61g (previous figures were incorrect) they are weakly magnetic to my 50x20mm super magnet.

    They appear and measure entirely carbide.
    Last edited by Zak28; 31st May 2019 at 00:14.

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    Re: Threading tungsten carbide rod

    measure the actual volume and find the density and see if the density is correct

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    Re: Threading tungsten carbide rod

    Quote Originally Posted by wwfeldman View Post
    measure the actual volume and find the density and see if the density is correct
    Not sure how to obtain actual volume.

    Also tried to sand the shank end of the bit with rotary sander and it ruined the sand paper and didnt grind the shank.

    I did grind a HSS tap die and it rapidly removed the HSS from the die tap. I even held the sander to the drill bit for quite a long duration and it didnt grind any of the shank but creased and ruined the sandpaper accumulating the fine grains from the sand paper at the shank incident to the sand paper. The HSS die would likely have been mostly sanded away for the same duration.

    Last edited by Zak28; 31st May 2019 at 02:02.

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    Re: Threading tungsten carbide rod

    they are weakly magnetic to my 50x20mm super magnet.
    The weak magnetism is very likely due to nickel or cobalt that are used as binders.

    The density test is quite definitive. You cannot change the density.

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    Re: Threading tungsten carbide rod

    Quote Originally Posted by c_mitra View Post
    The weak magnetism is very likely due to nickel or cobalt that are used as binders.

    The density test is quite definitive. You cannot change the density.
    You disregarded the hardness aspect of the drill bit. Cemented cobalt would have likely been ground off with the sander also. Not sure if there are industrial steel alloys which surpass carbide.

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    Re: Threading tungsten carbide rod

    Quote Originally Posted by Zak28 View Post
    Not sure how to obtain actual volume.
    Drop the object in a vial containing water. The rise of water level tells you volume of the object.

    Or, start with water level at the top. Drop in the object and the amount that overflows tells you the volume. Or else gauge the volume by the amount of water needed to refill the vial.

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    Re: Threading tungsten carbide rod

    The bit displaces ~29g of water. Made this measurement with electronic weight scale.

    The seller mentioned its an iron cored bit. Seems thats what solid carbide bits are. Or are there non cemented completely carbide bits available?

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    Re: Threading tungsten carbide rod

    Cemented cobalt would have likely been ground off with the sander also...
    Not quite correct.

    You start with WC in the powder form. You cannot melt or cast that stuff. The powder is mixed with nickel or cobalt as binder. Then it is sintered (high temp and pressure) but I do not have the details.

    Even tungsten wires are made like that- the metal is obtained in the form of powder and then it is sintered into a rod and the rod is drawn into wires. At no stage the metal is melted.

    The binder is quite small- perhaps less than 10% and can be dissolved away with nitric acid. Regular steel will fully dissolve in nitric acid. But this is a destructive test.

    All WC bits or buttons or any other stuff must have some binder present. It can be ground only with diamond powder or tools.

    - - - Updated - - -

    The bit displaces ~29g of water...
    That makes the volume as 29cc. The mass was reported 355gm. The density works out as 12.2g/cc which rules out iron or any iron alloy. Official density of pure WC is 15.6 but that is without any binder.

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  16. #36
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    Re: Threading tungsten carbide rod

    Quote Originally Posted by BradtheRad View Post
    Drop the object in a vial containing water. The rise of water level tells you volume of the object.

    Or, start with water level at the top. Drop in the object and the amount that overflows tells you the volume. Or else gauge the volume by the amount of water needed to refill the vial.
    Used narrow glass jar, dropping this bit in would have likely caused it to fracture. A tap form this bit can likely fracture tempered glass quite quickly, infact quicker than specialty tools to fracture said glass.

    Quote Originally Posted by c_mitra View Post
    Not quite correct.

    You start with WC in the powder form. You cannot melt or cast that stuff. The powder is mixed with nickel or cobalt as binder. Then it is sintered (high temp and pressure) but I do not have the details.

    Even tungsten wires are made like that- the metal is obtained in the form of powder and then it is sintered into a rod and the rod is drawn into wires. At no stage the metal is melted.

    The binder is quite small- perhaps less than 10% and can be dissolved away with nitric acid. Regular steel will fully dissolve in nitric acid. But this is a destructive test.

    All WC bits or buttons or any other stuff must have some binder present. It can be ground only with diamond powder or tools.

    - - - Updated - - -



    That makes the volume as 29cc. The mass was reported 355gm. The density works out as 12.2g/cc which rules out iron or any iron alloy. Official density of pure WC is 15.6 but that is without any binder.
    The official 15.63g/cm^3 density figure made me point out the cored iron.

    Glad you mentioned 12.2g density and also the excellent volume methodology mentioned by another user earlier. Obtained 2 pairs of these https://www.ebay.com/itm/273150336079/ only bottom bits as they will fasten nicely unlike the top most bit.

    Is carbide less prone to destruction than is pure tungsten from the ion bombardment found whilst operating as a spark gap for tesla coils?

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