Announcement

Collapse
No announcement yet.

Twist drill vs spade tipped drill - for holes larger than say 1 inch dia?

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Twist drill vs spade tipped drill - for holes larger than say 1 inch dia?

    I have frequently seen spade drill bit holders and drill bit tips, both carbide and HSS tips at auction. Here is an example of a spade drill tip: https://perfcarb.com/products/spade-...-spade-drills/

    I have a set of MT twist drills by 64th up to 1 inch. Above that I have a few misc twist drills - nothing much over 1.3 inch in dia. I have never seen a hole being drilled in metal using a spade drill. Occasionally I need to drill a large hole prior to boring the hole to size. It can be quite slow to open up a 1.3 inch dia hole to 2.2 inch dia using a boring bar. Does a spade drill require much greater power / force to push the drill into the work?
    Metro Detroit

  • #2
    Just on cost alone I'd opt for the spade bit option. Once we get over 1" the twist drill cost rises at an alarming rate.
    Chilliwack BC, Canada

    Comment


    • #3
      On larger holes I usually use a hole saw then bore it from there. Hole saws can be quite slow, specially in thicker material because you have keep stopping to clear the cuttings from the teeth.
      Larry - west coast of Canada

      Comment


      • #4
        Spade drills definitely require more horsepower than standard drills. If you have trouble opening up a
        small bore like that I doubt that a spade drill would be very effective.

        I have a small but fairly robust lathe (13x40, 4 HP, 3400 lbs.) and, as long as the hole was less than
        about 3" deep I could rough out a bore of that size in two passes. Drill to 1-1/4" and make two roughing
        passes about .200" deep to get within finishing range.

        I could probably run a small spade drill on my machine but they're expensive and, for the relatively small
        number of holes I drill, I couldn't justify the cost...
        Keith
        __________________________
        Just one project too many--that's what finally got him...

        Comment


        • #5
          Originally posted by Cuttings View Post
          On larger holes I usually use a hole saw then bore it from there. Hole saws can be quite slow, specially in thicker material because you have keep stopping to clear the cuttings from the teeth.
          If you want to go that route get yourself some annular cutters. They work very well, require relatively
          low horsepower and clear chips well. They are more expensive than hole saws but for lots of
          applications they will finish close enough to size that you don't need to touch the hole with anything
          else.

          New, sharp hole saws actually cut pretty quickly but you need to turn them slow and flood them with
          coolant to get the best performance...
          Keith
          __________________________
          Just one project too many--that's what finally got him...

          Comment


          • #6
            Another vote for an annular cutter. Up to about 1.5 inches I know they aren't horrifically expensive, $20-30 for something serviceable. Only downside is annular cutters are depth-limited, so if you need to go deeper than 2 inches that's a problem

            Comment


            • #7
              My own practice to date for anything bigger than 1" is to drill to 1" and then bore it in which ever machine is used for the 1" hole. So boring bar in the lathe or boring head in the mill.

              Which reminds me that I wanted to make a boring bar for my boring head that uses both of the holes for better stiffness. The goal being heavier cuts for things like you're talking about here.
              Chilliwack BC, Canada

              Comment


              • #8
                Originally posted by aribert View Post
                .................................................. ........... Does a spade drill require much greater power / force to push the drill into the work?
                Yes, Absolutely, but it is also the cheapest way to drill large holes because you basically are only buying the tip of the drill
                Also the spade drills are easier to sharpen. We regularly drilled 4 to 5 inch diameter holes in 4140 forgings in one pass. It was done on Lathes that had 25 to 50 HP and lots of coolant. Look at the length (?) of the cut edge and that gives you an idea of the HP required along with the feed rate
                . In metal work calculations, it takes about one HP to remove one cubic inch of steel per minute
                Also before you jump on doing it, you better look at the Tailstock taper and whether it can hold against the torque forces in Spade Drilling which are very high .
                Rich
                Green Bay, WI

                Comment


                • #9
                  I often use step drills (Unibits) to drill larger holes up to about 1-1/2 inches. They are especially good on thin materials and tricky stuff like copper. They usually cut clean and straight, and can also debur the hole. For deep (not blind) holes I go part way in one direction and finish drilling from the other side.

                  Another option might be to use a small side cutting end mill and a rotary table.
                  http://pauleschoen.com/pix/PM08_P76_P54.png
                  Paul , P S Technology, Inc. and MrTibbs
                  USA Maryland 21030

                  Comment


                  • #10
                    Insert spade drills are excellent but they require a great deal of power to use effectively.
                    Do not drill a smaller pilot hole first just push them through as they do not behave well making a hole larger.

                    A 2 1/2" spade drill through 3" of low carbon steel in about 6 minutes per part, this is of course using a 25 HP spindle W&S turret lathe.
                    If your machine does not have the power do not even try (-:

                    Holding the part is more difficult then the drilling, this is a 5" through the spindle machine and such an operation would push the part through the chuck if it was smaller then the opening.
                    Last edited by Bented; 10-08-2021, 06:36 PM.

                    Comment


                    • #11
                      Same machine, 1-7/16 hole with a twist drill in one shot.
                      Power is your friend.
                      https://bented.smugmug.com/My-First-Gallery/i-QpnSStf/A

                      Comment


                      • #12
                        Originally posted by Cuttings View Post
                        On larger holes I usually use a hole saw then bore it from there. Hole saws can be quite slow, specially in thicker material because you have keep stopping to clear the cuttings from the teeth.
                        To be efficient with a hole saw you need to drill some relief holes for the chips to fall out while cutting. They will cut quite fast when you do.

                        I usually lay out for a 1/2” hole to just touch the edge of the diameter hole saw I am using and then use a 31/64” drill bit to drill the hole with. Example would be, 3” hole saw, I would drill (2) 31/64” diameter holes 180 degrees apart on a 2.5” diameter circle.

                        1 hole is usually fine but 2 is better. It is also better to “shim” the hole saw to the arbor so it sits tight and the drive pins still engage.

                        Mentioned above annular cutters up to 1.5” aren’t terribly expensive and very efficient for through holes up to 2” thick or so.

                        Comment


                        • #13
                          Originally posted by oxford View Post

                          To be efficient with a hole saw you need to drill some relief holes for the chips to fall out while cutting. They will cut quite fast when you do.

                          I usually lay out for a 1/2” hole to just touch the edge of the diameter hole saw I am using and then use a 31/64” drill bit to drill the hole with. Example would be, 3” hole saw, I would drill (2) 31/64” diameter holes 180 degrees apart on a 2.5” diameter circle.

                          1 hole is usually fine but 2 is better. It is also better to “shim” the hole saw to the arbor so it sits tight and the drive pins still engage.

                          Mentioned above annular cutters up to 1.5” aren’t terribly expensive and very efficient for through holes up to 2” thick or so.
                          This is a very good idea. It will work on thin materials too and likely produce a smoother cut because chip packing is greatly reduced.

                          Comment


                          • #14
                            Originally posted by LKeithR View Post
                            Spade drills definitely require more horsepower than standard drills. If you have trouble opening up a
                            small bore like that I doubt that a spade drill would be very effective.

                            ..
                            The horsepower required to drive a drill depends solely on the metal removal rate. If a spade drill requires more HP than a twist drill i is because the penetration rate is higher. If fed at the same rate (inches per revolution) there should be no difference between the HP requirements.

                            Comment


                            • #15
                              Look into APT Multi-Tool.
                              Mike
                              WI/IL border, USA

                              Comment

                              Working...
                              X