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  1. #1
    Grits's Avatar
    Grits is offline Stainless
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    I have a Series I BP with a 1 HP motor. The largest flycutter I have is 2 1/2" in diameter.

    Question is, how big can I go and maintain enough rigidity with a 3/4" shank. I want to machine a big 'un.

    Thanks

    Grits

  2. #2
    J.Ramsey is offline Cast Iron
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    With a 3/4 straight shank maybe 4 to 5 inch,I have a 10 incher I made mounted on a 1.5 x18tpi R-8 shank that I use on motorcycle cyl.heads and stuff like that,with the large cutting dia.extreme care must be used because it's like running a lawnmower without the deck.I believe flex will be the issue with a 3/4 shank.

  3. #3
    Grits's Avatar
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    J Ramsey

    What type shank the R8 have when you started with it and if it is odd-ball, where did you get it? The R8 was my first thought.

    Grits

  4. #4
    J.Ramsey is offline Cast Iron
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    Grits
    Enco and Grizzly both have them, look in the boreing head section,when I bought mine they were about 18 dollar's.

  5. #5
    smallshop's Avatar
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    When making big fly cutters (we call these fly bars) make them rectangular with two cutters. keep 'em balanced! they're quick to make. make from two pieces. The shanks should have a head so the bar won't fly off after welding. Weld shank on both sides of bar (requires a big chamfer).

    this is an 8 inch one and would need conservative speeds and feeds with that 3/4 shank.

  6. #6
    Carl Darnell is offline Titanium
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    smallshop, do you have much trouble setting the cutters even? How do you set the cutters? I have thought about doing a double cutter but setting the cutter with a dial indicator is kind of hit and miss. I am thinking 8" or 9" is as large as I want.

    Years ago a friend had a Van Norman head broach that I made a special sharpening tool to sharpen the cutters while they were in the broach head. That way he didn't have to take the cutters out, sharpen and then dial them in. He loved that tool and said it saved him hours each time he resharpened the cutters. I guess I could make a similar sharpener.

  7. #7
    crossthread's Avatar
    crossthread is offline Stainless
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    I would think that if you loosened the setscrews and allowed both cutters to drop down on either the table or the flat section of your mill vise and then tighten them, they would be pretty close to even.

  8. #8
    bronto48 is offline Hot Rolled
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    Carl--if you would describe in detail the sharpening tool you mentioned, I believe a lot of us would be very interested.

    crossthread--decades ago when I apprenticed, we had an R-8 "flycutter" for our Bridgeport that accepted up to 6 cutter bits (I think 5/16 or 3/8 square). This one was made so that the bits were mounted more vertically than most flycutters. Its action was sort of between that of a flycutter and a very large end mill. I generally used just 3 carbide tipped cutters for machining aluminum and would set the cutters exactly as you suggest--lower the cutter head over the mill vise and let the tips of each bit rest on the vise while tightening the set screws. Worked fine.

    I used that cutter with preference over anything else we had in the shop because I could resharpen it myself (no tool cutter available in that shop), and change relief angles if the next job was steel or something tougher/harder than aluminum. The added benefit was I did not have to fear a rebuke from the boss if I had used an end mill and dulled or chipped it accidently.

  9. #9
    smallshop's Avatar
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    "smallshop, do you have much trouble setting the cutters even? How do you set the cutters?"

    I surface ground the bottom of the head square to the shank. Then you can use a planer gage (or something homemade) to set tools.You can resharp this way without moving the head and still be at the same z location in your setup. Some guys intentionally set one cutter up higher but out farther so it acts like a rougher and the other acts like a finisher. I haven't tried it so I can't comment.

    This design would adapt easily to a solid R8 shank and would be more solid.

  10. #10
    Carl Darnell is offline Titanium
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    I can tell you that setting the tips of the cutters on the table and tightening them they will NOT be even. I have tried that.

    Setting one high, one low will work as one will always be cutting and the other may cut sometimes depending on feed and speed.

    I think I have some photo's of the attachment I made for him. He would sharpen the tools the normal way for Van Norman then put the cutters in the head and dial the tops in then dress the side of the cutters to the same length. It gave a real nice finish after that.

  11. #11
    jabezkin is offline Stainless
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    On a double flycutter I always set one higher and farther out from center, the lower one further in for a light finishing cut. Had to be stout and not too big a dia.

  12. #12
    Carl Darnell is offline Titanium
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    For anyone interested I started a thread about the Van Norman tool rather than steal this thread.

  13. #13
    Grits's Avatar
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    I ordered an R8 boring head shank, from Enco, today. I have an idea using two indexable tool bit holders. If I build it right, it may have a rougher and finisher, I have quite a bit more head scratching before I say too much.

    Grits

  14. #14
    toastydeath is offline Hot Rolled
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    The sky is the limit on larger flycutters, even with a 3/4 shank. If you can keep it balancedand control the depth of cut precisely (using an indicator), it will work. .0005 and .0002 depth of cut with a dead zero rake, radially and axially, can be done on very wide flycutters with a sharp PCD or CBN insert. Use only one cutting tool, not two, and save it for finish passes. The benefit to using high-end inserts is that surface speed becomes irrelevant. You can run it as fast or as slow as you feel comfortable.

    On a milling machine with excellent spindle bearings, you can produce a near mirror finish (with custom bearings, you can produce a mirror finish) using PCD/CBN inserts, and eliminate grinding.

  15. #15
    J.Ramsey is offline Cast Iron
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    Grits
    I'll agree with toastydeath except the 3/4 shank part, the one I built the bits are 90 degrees like the smallshops drawing. I have not had the need to use two bits other than one of them I insert upside down for balance purposes. I have run mine as fast as 2400 rpm, no vibration what so ever,taking.050 cuts on aluminum, normally I turn it about 800 rpm, finish cut of about .002 to .010 and it leaves a mirror finish. Just be careful of the large dia.Anything on the table,shop towels,tools,lexan guards ect that come into contact with it will be eaten and thrown across the shop if your lucky enough that it misses you on the way by. When I get my set up done I set the table feed and stand back,It will throw chips twenty plus feet.Like I said previously, compare it to running a lawn mower without the deck.A lot of difference between a one eighth inch end mill cutter and a 8 to 10 inch one.

  16. #16
    smallshop's Avatar
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    One other thing....with big flycutters you really have to have your head indicated dead on. if not you'll see why....

  17. #17
    Close Work is offline Cast Iron
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    We have two fly cutters with R8 shanks that are 6-8" in diameter. We use two tools with one higher than the other. One of the fly cutters will hold 4 tools but I have never seen it used with 4. That one has some device for easy adjustment of tool angle. If I get time I will try to post a picture of that one. Both of these fly cutters are complete circles and not bars. We have other fly cutters as large as 30" which run on larger machines. All the fly cutters are full disks and the thickness is no less than 1/8 of the diameter. (8"dia. means 1" thick) Bars become wings at speed and flutter which degrades the finish as well as carry blobs of chips and then throw them off which further causes balance and finish problems.

  18. #18
    smallshop's Avatar
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    I've used bars for years with no problems. I have never used one over ten inches though. 30 inches sounds a bit scarey....

    Another reason a flybar is nice is you can orient it to go in a cnc turret without hogging two more spaces......

  19. #19
    John Garner is offline Stainless
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    I'd be mighty inclined to put straps over the open slot ends shown in smallshop's drawing. A toolbit chucked from a flybar will poke a hole in just about anything in its way, leaving the very out-of-balance flybar behind.

    Then, assuming the flybar will be operated with normal "forward" spindle rotation, putting the toolbit clamp screws into the other side of the slots, so that they bear on the "tops" of the toolbits, might be better.

    John

  20. #20
    J.Ramsey is offline Cast Iron
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    Smallshop
    You'll see why? I have a Storm/Vulcan 85B block mill
    sixteen carbide cutters,just had the bits dressed, had to take it to Tulsa OK.The head/spindle is trammed .006 +,over 18" dia.cutting head, just a slight hollow cut so speak.The factory recommendation so the back side doesn't wipe or double cut
    I always thought fly cutting was with a single point tool.Three bits or more it is a face mill?

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