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  1. #1
    Join Date
    Apr 2009
    Location
    Kingswood
    Posts
    422

    Default Carbide Tips for Screwcutting

    Hi all,
    Spent some time today grinding a 60 degree HSS tool and screwcutting 15 mm x 1 mm pitch for a nut on an arbor.
    (Said arbor fits into a vertically mounted rotary table for gear cutting in a small vertical mill)

    I have only used HSS on my Sheraton 9A to date, but it occurs to me that carbide tips for screwcutting may be far superior.
    I have used carbide during a TAFE course and my impression is that it is good for removing metal, but not good for shaving that last 0.02 mm to size.

    Any comments on carbide thread cutting tips for typical hobby use very welcomed.

    If yes, what grade of tip ?

    And where can I get them ?

    Happy machining,
    John.

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  3. #2
    Join Date
    Aug 2008
    Location
    Charlestown NSW
    Age
    65
    Posts
    899

    Default

    John
    For home use I would (do) stick to HSS. Sure, it takes a little while to initially grind up the tool but once its done it should last for years with the occasional touch up. In the long term it will also be a lot cheaper than running carbide.
    I've been more or less out of the trade for a few years now so I'm not up there with current carbide technology but I don't think the basics would have changed all that much. Carbide works best with a bit of speed and a bit of depth to the cut. It's hard to take a real fine cut with it. Your lathe is a belt head I think? If so it was designed for high carbon and HSS tooling. You will probably find it works best with that.
    After a while you will end up with a selection of threading tools. I have a quite few, including some specials.

    hope this helps
    regards
    bollie7

  4. #3
    Join Date
    Apr 2009
    Location
    Kingswood
    Posts
    422

    Default

    Thanks bollie7 for the comments.
    I asked the same question of the teacher at TAFE.
    Apparently the teacher uses a Hercus at home, always with HSS.
    The only job using carbide is large diameter cast iron because the lathe cannot run slow enough for HSS.

    So, HSS it is.

    Happy machining,
    John.

  5. #4
    Join Date
    Apr 2008
    Location
    NSW
    Posts
    356

    Default

    Carbide threading inserts are prone to chipping on the edge and flacking bits off.
    The edge security is not as good as a normal turning insert because they are sharp on the cutting edge's and point . Top quality ones like Sandvick work better and cheap inserts from who knows where are not so good.
    It is very easy to just clip the forward edge on a shoulder or at the end of a cut and chip or break them.
    I am currantly in the process of abandoning them for HSS ground tooling as they are just too expensive and easy to break.
    At about $75 per packet of five I find them outrageous.
    The volume of a pizza of thickness 'a' and radius 'z' is given by pi z z a.

  6. #5
    Join Date
    Mar 2009
    Location
    Melbourne
    Posts
    295

    Default Carbide

    Dear Steam. You can get carbide tips with the correct form to cut any thread. But they are fearfully expensive and then there is the holder for the tips to consider. I have just cut two 1 1/4 7 TPI threads for a locomotive project using said tips borrowed from work and it was a pleasure. But out of the average machinists cost range. If you can get second hand tips these can be braised on too mild steel blanks. The key to grinding the tips is to have two grinding wheels one a general purpose wheel for grinding the mild steel part of the tool and a silicon carbide (green wheel) for the tip. The carbide tip do not like the general purpose wheels and the edges of the tip will chip. The softer silicon wheel will leave a clean sharp edge that will produce the skim needed to give an excellent finish. The braising method was how I obtained my first tip tools during my appernticeship. This was after pleading with the foreman on bended knee for a used tip. The tradesmen who used the repacement tips had to return each used tip befire getting a new one. These tips were sweated on with tobin bronze not silver solder as was used on the manufactured article. Another usefull tip In times of emergency or dire need a piece of Tool steel can be arc welded to the end of a piece of Hex mild steel to form a quick and reliable boring bar. No quenching is required just use as finished.
    Hope this has been of help 4-6-4

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