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newbee ?-- plz define trepan

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  • newbee ?-- plz define trepan

    NM

  • #2
    Are you refering to trepaning tools? If so you can basically think of them as grooving tools that feed axially rather than radially. Clearance it extremely important. Try SPI(Swiss Precision Instruments). Their catalog has good pictures of high speed ones. Or is this about primitive brain surgery?

    ------------------
    Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.

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    • #3
      A hole saw, for instance. Cutting out a slug of material to make a large hole instead of boring it out as chips.

      On a lathe, you can do it with a suitably ground lathe bit with the work mounted on a faceplate. As S.D. says, toolbit clearance can get to be an issue.


      ----------
      Try to make a living, not a killing. -- Utah Phillips
      Don't believe everything you know. -- Bumper sticker
      Everybody is ignorant, only on different subjects. -- Will Rogers
      There are lots of people who mistake their imagination for their memory. - Josh Billings
      Law of Logical Argument - Anything is possible if you don't know what you are talking about.
      Don't own anything you have to feed or paint. - Hood River Blackie

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      • #4
        There are very goods trepaning tools available from distributors to cut larger holes in materials. They are rather specialized and very expensive. A poorly designed one is very dangerous to use - as such all commercial versions are a balanced designed (two cutters, dynamic balancing).

        Annular cutters are a better choice and safer to use. They do require a special shank to hold the cutter. High quality milling tools.

        Automatic Boring heads can be used to cut large holes as well - big money.

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        • #5
          What sort of job are you wanting to do?

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          • #6
            Thanx for the replies. I saw the word in a procedure and didn't understand. So, its basically parting axially?
            Bob

            P.S. To all grammarians: please excuse that last comment.

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            • #7
              Yep.

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              • #8
                See:
                http://www.aucegypt.edu/faculty/gaaf...Trepanning.doc
                for a definition of trepanning.

                I have been looking into the best way of making 2â€‌ diameter holes in آ½â€‌ 6061-T6 aluminum plate on my mill. Trepanning appears to be one solution. Looking at SPI Type 2000 trepanning tool for the mill. I have an SPI Val-Cut trepanning tool for the lathe that uses a 6mm cutter bit that works well. I have been using a 1 15/16â€‌ piloted annular cutter with the mill, (Technically this is trepanning.) followed by using a boring head to finish the hole to size. I think that the SPI 2000 trepanning tool will allow cutting a hole closer to the desired 2â€‌ diameter so only a finish cut with the boring tool will be needed.

                Don Clement
                Running Springs, California
                Owner: Clement Focuser

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                • #9
                  Don

                  A 2" annular cutter will be dead on, as long as the arbor is not bent. I have seen them to 6" diameter and 4" deep. A diamond core drill will also work in Aluminum very well and provides a finely finished surface if done at high speed. Carbide drills are ideal for Aluminum. APT has spade drills that are reasonably cheap (HSS, coated HSS, & Carbide blades) and produce accurate holes.

                  [This message has been edited by Thrud (edited 12-08-2002).]

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                  • #10
                    I should measure the accuracy of the 1 15/16â€‌ diameter hole made with the annular cutter. The hole needs to be 2.000â€‌ –0.000" + 0.004â€‌. So if the annular cutter proves accurate, then a 2â€‌ annular will work. Finish cut with a single pass of the boring head. The annular cutters are one piece HSS with a آ¾â€‌ diameter shank. If the annular cutter works, it would be much less expensive than an SPI 2000 trepanning tool with a 5mm bit that would cut through آ½â€‌ plate. KBC has the Polish made HSS annular cutters on sale for $53. SPI 2000 trepanning tool with a 5mm bit is about $180. Diamond would work with aluminum but the big problem that I have found with aluminum is getting the chips out of the annular slot. Do diamond cutters have good chip clearance?

                    Don Clement
                    Running Springs, California
                    Owner: Clement Focuser

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                    • #11
                      I've found that it helps to drill a "chip drain hole" tangent to the final o.d. somewhere along the cut, so the chips can fall through.
                      ----------
                      Try to make a living, not a killing. -- Utah Phillips
                      Don't believe everything you know. -- Bumper sticker
                      Everybody is ignorant, only on different subjects. -- Will Rogers
                      There are lots of people who mistake their imagination for their memory. - Josh Billings
                      Law of Logical Argument - Anything is possible if you don't know what you are talking about.
                      Don't own anything you have to feed or paint. - Hood River Blackie

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                      • #12
                        I don't know about aluminum, but I used a "hole saw" to rough out a hole in a 5/8" thick piece of bronze to make an eccentric strap for a pump. This was on a lathe, I don't have a mill. I backed up the workpiece with a piece of Oak fastened to the cross-slide, used a hole saw several thou smaller than finished hole was to be and slowest back gear speed, and hand fed it by pressing on the back with the tailstock ram. I took it very slow and easy, withdrawing the work after about a dozen revs and blew out the chips, then started again, It took awhile, but it worked! Only had about 60 thou to finish with the boring bar. Boring head in mill will do even better!!

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                        • #13
                          You can use ordinary bi-metal hole saws to cut to full depth if you first drill about four holes (or more for large sizes)in the waste piece so that the holes just break into the cutting path of the saw. This allows the chips to clear. Also be generous with cutting oil.
                          I've drilled holes through structural steel over an inch thick this way.
                          The advantages are, You don't need an expensive solid bit, or a really large drill, you can drill relatively large holes without a magnetic drillpress, also holesaws are shorter than equivalent size bits,(and cheaper) so its good for tight spots. The main disadvantage is very slow speed and a good deal of pressure to make sure it cuts (no problem for a press)Twist drills tend to pull themselves in once started, especially in soft material.

                          I used a treppaning cutter (single point) to cut out a chuck backplate blank from steel plate about a month ago, in the horizontal mill. 5" diameter, it came out nice. Drilled and started the tap in the mill at the same setting. This was to mount a real three jaw on the Taig.
                          I sometimes use large hole saws for making turning blanks. If you don't want a center hole just make sure its secure and start it in real slow and keep backing it out until your about past the teeth gullets, then it wont be able to skid out anymore, and you can feed it in. Make sure the chips are cleared, either by constantly backing out or by drilling chip clearance holes on the waste side.
                          Also when useing holesaws on metal its better to remove the pilot bit and replace it with a piece of rod. This helps keep the saw aligned better and cannot enlarge the pilot hole by milling sideways. Use plenty of cutting oil.

                          I know that this is all elemntary to most of you, but I've seen alot of ruined holesaws and really messed up work. So it will help someone (maybe)

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                          • #14
                            Don
                            With a core drill the piece could be dammed and fluid filled and the piece cut. The diamond will grind the aluminum to fine powder just as it would stone or concrete. If you want to try this method out, buy a small core drill from a lapidary store - we can get them up here for under $20. If this works to your satisfaction , then you could get a larger core drill. There are Starrett Structured tooth carbide and Diamond holesaws, but I cannot vouch for diameteral accuracy - that is something you would need to test yourself.

                            Of course, you could just get a 2" carbide drill. Garr Carbide, Kennametal, and Sandvik Coromant all do custom tools and might be able to build a holesaw/reamer for you.

                            If it was me I would machine a "Forstner style" bit braze carbide where I needed it and send it out to a good CNC sharpening shop.

                            Lee Valley Tools www.leevalley.com has HSS forstner bits that might work in Aluminum - they have a saw tooth edge so they should not chatter too much, but would need lots of coolant or lube - worth a try. I have not tried this with mine but could if you are really interested.

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                            • #15
                              I cored a آ½â€‌ thick test piece of aluminum with the 1 15/16â€‌ HSS annular cutter from KBC tools. The test piece was clamped in a vise and the annular cutter mounted in a آ¾â€‌ R8 collet on the Rockwell mill. Speed was the 270 RPM. Mist coolant was used. Quill feed was used for the annular cutter. Cutting went pretty smooth. I did have to back the cutter out a few times to clear the chips. Results were not good enough for a single pass finish cut with a boring head if I were going to use the 2â€‌ annular cutter. My target hole is 2.002â€‌ –0.000â€‌ +0.002â€‌ The hole from the annular cutter is > 0.010â€‌ oversize.
                              I am going with the 1 15/16â€‌ annular cutter and two passes with a boring head. I already have the cutter and boring head, so there is no additional cost with this method. I need to make ~200 holes.

                              Don Clement
                              Running Springs, California
                              Owner: Clement Focuser

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