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Thread: Broach square holes with D-bit

  1. #1
    Supporting Member thehomeengineer's Avatar
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    thehomeengineer's Tools

    Broach square holes with D-bit

    Hi All

    I am currently in the process of motorising my bead roller and thought I would also do the same to my slip rollers and ring roller using the same motor by simply bolting which ever tool I intend to use to a table and using vee-belts.

    The issue I have is the slip rollers were made along time ago and I didn't consider ever powering them until now. There is currently a square drive which an old vice handle fits to. This doesn't allow enough round shaft to fit a vee-pulley to. So I decided to make an adaptor to drive of the square and locate of the 20 mm diameter shaft but allow enough room for a 1-3/8" 2012 taper lock bush to fit with a 1/4" keyway.

    So I thought I would share with you all how I broach square holes on the mill using an indexing head and a cutter ground like a D-Bit.

    The first operation is to turn the adapter and bore/Drill a hole to finished sized square this is sized across the flats (A/F).
    A D-Bit is then ground from a round piece of high speed steel (HSS) to half its diameter.
    The component can then be centred over the indexing head on the mill. The tool can be held in a chuck and the machine placed in low gear to prevent the spindle from rotating. Even better if you have a brake.
    It is now a case of moving the quill of the machine up and down in conjunction with one axis taking very small cuts. The two photos below show the procedure for cutting the square.

    Complete setup on mill
    Broach square holes with D-bit-img_4327.jpg

    Process for cutting
    Broach square holes with D-bit-img_4338.jpgBroach square holes with D-bit-img_4339.jpg

    Cutting square
    Broach square holes with D-bit-img_4325.jpg

    Finished hole to size
    Broach square holes with D-bit-img_4330.jpg Broach square holes with D-bit-img_4331.jpg

    Square drive shaft and fitted adaptor
    Broach square holes with D-bit-img_4328.jpg Broach square holes with D-bit-img_4329.jpg Broach square holes with D-bit-img_4332.jpg

    I have used this method for cutting different size squares and have made several size broaches. The large one was made from mild steel and a piece of parting off blade silver soldered to the mild steel shank . This was used to cut a square slot in cast iron on the axle boxes of my 3" scale Foden steam wagon.
    Broach square holes with D-bit-img_4337.jpg Broach square holes with D-bit-img_4336.jpg

    Square cut and gauge piece used to check fit along with the D-Bit
    Broach square holes with D-bit-img_4323.jpg Broach square holes with D-bit-img_4324.jpg

    This method works really well and is very accurate, Like everything there are some drawbacks The deepth of square is limited by how far you grind the tool and the longer the tool more flex so more patience is needed. Plus side very cheap to make and almost any size can be cut rather than buying expensive square broach which will only cut the size it was intended for and the shape. Using the D-bit hexagons, slots etc. can be cut.

    I hope you can make use of this post and thank you for taking the time to view
    The Home Engineer
    Attached Thumbnails Attached Thumbnails Broach square holes with D-bit-img_4332.jpg  

  2. The Following 10 Users Say Thank You to thehomeengineer For This Useful Post:

    Carnel (01-17-2020), Corm (01-17-2020), DIYSwede (01-16-2020), high-side (01-17-2020), Jon (01-16-2020), old_toolmaker (01-15-2020), Philip Davies (01-17-2020), rgsparber (01-16-2020), Scotsman Hosie (01-18-2020), Sleykin (01-17-2020)

  3. #2
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    Thanks thehomeengineer! We've added your Broach to our Machining category,
    as well as to your builder page: thehomeengineer's Homemade Tools. Your receipt:




  4. #3
    Supporting Member old_toolmaker's Avatar
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    old_toolmaker's Tools
    thehomeengineer,

    You have done a very nice job of broaching! I have used this technique on several shapes including triangular shapes. Thanks for posting!
    Dick


    Links to some of my plans:

    http://www.homemadetools.net/forum/f...6068#post65876 OFF-SET TAILSTOCK CENTER PLANS
    http://www.homemadetools.net/forum/s...995#post112113 SMALL TURRET TOOL POST PLANS
    http://www.homemadetools.net/forum/l...994#post112111 LARGE TURRET TOOL POST PLANS
    http://www.homemadetools.net/forum/m...383#post110340 MINI-LATHE CARRIAGE LOCK PLANS
    http://www.homemadetools.net/forum/s...191#post106483 SMALL QC TOOL POST PLANS
    http://www.homemadetools.net/forum/q...849#post119345 QUICK CHANGE LATHE TURRET
    http://www.homemadetools.net/forum/m...949#post119893 MINI LATHE COMPOUND PIVOT MODIFICATION

  5. The Following 2 Users Say Thank You to old_toolmaker For This Useful Post:

    Crusty (01-16-2020), thehomeengineer (01-16-2020)

  6. #4
    Supporting Member Crusty's Avatar
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    Crusty's Tools
    I'm a fan of D bits too. Need to mill an unusual shaped channel - make a D bit with the desired profile. Need to make precise holes - make a D reamer from the same shaft that will go into the hole. And now there's a D broach.

    I've been using Thompson QS shafting intended for linear guide purposes because I've found that it's hard enough for D tools without a subsequent hardening process but not too hard to machine to the desired shape. Granted it will wear quicker than a properly hardened and tempered bit but for my projects it holds its dimensions long enough.

    I only make one size square hole with my rotary broach (") using a HSS bit and it serves its purpose for that.

    Broach square holes with D-bit-rotary-broach.jpg
    Last edited by Crusty; 01-16-2020 at 10:05 AM.
    If you can't make it precise make it adjustable.

  7. The Following 2 Users Say Thank You to Crusty For This Useful Post:

    old_toolmaker (01-16-2020), thehomeengineer (01-16-2020)

  8. #5
    Supporting Member old_toolmaker's Avatar
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    old_toolmaker's Tools
    Crusty,

    Is that shop made rotary type broach for the 1/4" square hole?
    Dick


    Links to some of my plans:

    http://www.homemadetools.net/forum/f...6068#post65876 OFF-SET TAILSTOCK CENTER PLANS
    http://www.homemadetools.net/forum/s...995#post112113 SMALL TURRET TOOL POST PLANS
    http://www.homemadetools.net/forum/l...994#post112111 LARGE TURRET TOOL POST PLANS
    http://www.homemadetools.net/forum/m...383#post110340 MINI-LATHE CARRIAGE LOCK PLANS
    http://www.homemadetools.net/forum/s...191#post106483 SMALL QC TOOL POST PLANS
    http://www.homemadetools.net/forum/q...849#post119345 QUICK CHANGE LATHE TURRET
    http://www.homemadetools.net/forum/m...949#post119893 MINI LATHE COMPOUND PIVOT MODIFICATION

  9. #6
    Supporting Member Crusty's Avatar
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    Crusty's Tools
    I started with an adjustable tool holder bought on Ebay and then made the rest.

    Make Square Holes with a Square Bit


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    If you can't make it precise make it adjustable.

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