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  • #16
    If at all possible utilize thru coolant boring tools.
    This is a 3.973" bore 10" deep using a 2 1/2" diameter bar, the starting bore is large enough that I use poor mans thru coolant.
    1/4" nylon tubing taped to the tool, this is not ideal (-:

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    • #17
      Originally posted by Texasbowhunter View Post
      One thing I would like to find is having the inserts that I presently use to interchange with the boring bar....
      I use ccmt insets for my boring bars and also have a turning tool that also uses them. With the turning holder, the geometry of the insert allows turning and facing with the same tool.

      That insert isn’t ideal for every situation and won’t make a “smooth” flat bottom when the bars are used in the boring head but it covers most of my use.

      I have also used endmills as boring bars in the past. Just set it up so one flute edge is cutting and angle it a little so there is clearance when you go in.

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      • #18
        I'm another one in the camp of people who've always heard the 4:1 rule, that the bar can stickout 4 times it's diameter. A half inch bar can go out two inches, a 1 inch bar can cut 4 inches deep, etc. Course, that's a rule of thumb and not a definitive thing
        if I could only have one bar though, my vote would be for a 3/8" bar. Anything the hole is too small for the bar to fit in to, drills and reamers aren't cost prohibitive. That size bar also get me a inch and a half deep, which is plenty enough for most of what I do. Course, this isn't true for all shops, I doubt that the people here with gigantic pacemaker lathes are going to be getting by with just a 3/8" bar for the size of work they do

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        • #19
          I do like oxford stated, I prefer bars with CCGT inserts, same as my regular turning tools. Of course the HSS style is much cheaper and more customizable if you need something in a pinch.
          25 miles north of Buffalo NY, USA

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          • #20
            I've gone up to 8" no problem with my 1" bar. Sharp HSS helps.
            21" Royersford Excelsior CamelBack Drillpress Restoration
            1943 Sidney 16x54 Lathe Restoration

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            • #21
              I made an 5 ACME internal threading bar to go in the start size hole for a 1" X 5 ACME nut. The laydown inserts for that pitch normally fit a bar that is much too big for the start bore of 0.800", and the bar was made from a bit of steel that was lying around. It turned out to be austinitic stainless steel, very soft, but it was plenty stiff enough. I haven't got around to using it myself, but another guy has used it successfully on leaded bronze (sae660 gunmetal).
              It could be used as a boring bar at a pinch. The depth-diameter ratio is 4.5:1.

              Click image for larger version  Name:	_IGP2795.JPG Views:	0 Size:	446.5 KB ID:	1949831
              Last edited by old mart; 07-03-2021, 09:34 AM.

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              • #22
                Originally posted by The Metal Butcher View Post
                I've gone up to 8" no problem with my 1" bar. Sharp HSS helps.
                I don't own a 1" boring bar, but I have 1" stock and I can easily imagine it boring to a depth of 8". Limiting it to a 4" depth (4x) seems unreasonable. It seems that using a linear relationship between depth and diameter is too simplistic, so I did some Googling. Which led me down a rabbit hole to "second moment of area".

                My superficial take-away is that the deflection of the end of a cantilevered circular bar is inversely proportional to its "second moment of area", which is itself proportional to the forth power (!!!) of the diameter. But the deflection is directly proportional to the cube (!!) of the length, which is being assumed to be 4x the diameter. So a 1" bar extended 4" will deflect proportionally to 4^3/1^4 and a 1/2" bar extended 2" to 2^3/0.5^4. The relative deflections would be (4^3/1^4)/(2^3/0.5^4) = 1/2. I.e., a 1" bar extended 4" will deflect 1/2 as much as a 1/2" bar extended 2". So in this case, a simple 4x depth limit is too conservative.

                What about the general case? Let "k" be the ratio of depth to diameter & "d" the diameter. Then deflection will be proportional to (k x d)^3/d^4 = k^3/d. And for a bar of diameter d2 to have the same deflection as a bar of diameter d1: k2^3/d2 = k1^3/d1. Which leads to k2/k1 = cube root (d2/d1). So the case where a bar's diameter is doubled, the depth ratio increases by a factor of 1.26. E.g., doubling the diameter of bar with 4x depth would allow a 5x depth (a 1" bar at 5" would be same as a 1/2" bar at 4"). Whew - it's easy to see why people use a fixed rule of thumb.

                If we assume that a 1/4" bar is good to 1" depth (4x), then:
                d k depth
                1/4 4 1
                3/8 4.6 1.7
                1/2 5 2.5
                5/8 5.4 3.4
                3/4 5.7 4.3
                1 6.4 6.3
                2 8 16 - - - - - - Arrrggghh - this list was formatted, but the extra spaces were removed when posted! How to get around it? "TAB" doesn't work

                IOW, 4 or 5 times is good until you get to 1" bars, then it's too conservative. And since the material, DOC, feed, etc play into it, it's your feel for it that it boils down to.

                Thanks for readin', Bob
                Last edited by Bob Engelhardt; 07-03-2021, 11:22 AM.

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                • #23
                  The 4 X the diameter is taken from commercial suppliers like Sandvik, who expect users to be taking maximum cuts which put huge loads on tooling. using sharper inserts and small depth of cuts will enable you to get much deeper safely, but not economically. Most home shop people are not against the clock all the time.
                  The ratio between the insert size gets smaller as bar sizes increase, so that is in favour of using the biggest bar that you can.
                  Last edited by old mart; 07-03-2021, 12:14 PM.

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                  • #24
                    Originally posted by rickyb View Post

                    All steels have the same modulus of elasticity so all deflect the same amount. Hardness of steel comes into play by increasing the load at which permanent deformation occurs. Since a boring bar won’t get near to yield loading, all steels will behave the same, soft or hard. Localized stresses in the holes of old school bars can reach yield and loosen the inserted bit.

                    lower deflections and less chatter in a bar of specific size can only be had by using materials with a higher modulus like carbide.
                    Why do people always feel the need to argue about this ? ? ?

                    -D
                    DZER

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                    • #25
                      Inserted boring bars can be had cheaply, sometimes less than the cost of the material.
                      These bars are on the smaller side (the largest is 16 mm dia., 5/8") and use the CCMT inserts, which are also good for turning.
                      https://www.aliexpress.com/item/32949053137.html?

                      and here's an assortment up to 20mm
                      https://www.aliexpress.com/item/4000841814096.html

                      I've ordered a lot of very economical inserted tools from Aliexpress and eBay, none have disappointed.
                      Last edited by MrWhoopee; 07-04-2021, 01:09 PM.
                      It's all mind over matter.
                      If you don't mind, it don't matter.

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                      • #26
                        The assortment from aliexpress in MrWhoopee's post are great value, and the inserts can be picked up cheaply too.
                        One thing about long bars in deep holes is the greater leverage which will tend to amplify any loosness in the cross slide plus the top slide. That is why I have a larger toolpost attached directly to the cross slide to take the 25mm boring bars and the 16mm solid carbide shank bar.


                        Click image for larger version

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Views:	80
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                        • #27
                          Arrrggghh - this list was formatted, but the extra spaces were removed when posted! How to get around it? "TAB" doesn't work


                          If we assume that a 1/4" bar is good to 1" depth (4x), then:
                          Code:
                          d     k     depth
                          1/4  4      1
                          3/8  4.6   1.7
                          1/2  5      2.5
                          5/8  5.4   3.4
                          3/4  5.7   4.3
                          1     6.4   6.3
                          2     8     16
                          At the end of the project, there is a profound difference between spare parts and left over parts.

                          Location: SF East Bay.

                          Comment


                          • #28
                            As mentioned here, solid carbide bars are much heavier and stiffer, so they can go about 8 diameters deep. Even the small ones. I have bars in a variety of sizes. Many were picked up on sale or snatched off ebay for a song.

                            When you shop for boring bars, watch out for variations on the theme of "carbide boring bars" which, on closer inspection, have a carbide chip soldered to the cutting end of a steel bar. Once it's ground to the right shape, the carbide chip becomes the cutting edge.

                            A common SOLID carbide bar will be mostly carbide with a steel end brazed onto it to hold the carbide insert. In those cases the insert is the cutting edge. Carbide is brittle, so don't drop them or you might find your $20 boring bar fractured into several $2 pieces.

                            Dan
                            At the end of the project, there is a profound difference between spare parts and left over parts.

                            Location: SF East Bay.

                            Comment


                            • #29
                              Originally posted by Doozer View Post

                              Why do people always feel the need to argue about this ? ? ?

                              -D
                              Because one side is objectively correct and the other isnt

                              Comment


                              • #30
                                Originally posted by Bob Engelhardt View Post

                                I don't own a 1" boring bar, but I have 1" stock and I can easily imagine it boring to a depth of 8". Limiting it to a 4" depth (4x) seems unreasonable. It seems that using a linear relationship between depth and diameter is too simplistic, so I did some Googling. Which led me down a rabbit hole to "second moment of area".

                                My superficial take-away is that the deflection of the end of a cantilevered circular bar is inversely proportional to its "second moment of area", which is itself proportional to the forth power (!!!) of the diameter. But the deflection is directly proportional to the cube (!!) of the length, which is being assumed to be 4x the diameter. So a 1" bar extended 4" will deflect proportionally to 4^3/1^4 and a 1/2" bar extended 2" to 2^3/0.5^4. The relative deflections would be (4^3/1^4)/(2^3/0.5^4) = 1/2. I.e., a 1" bar extended 4" will deflect 1/2 as much as a 1/2" bar extended 2". So in this case, a simple 4x depth limit is too conservative.

                                What about the general case? Let "k" be the ratio of depth to diameter & "d" the diameter. Then deflection will be proportional to (k x d)^3/d^4 = k^3/d. And for a bar of diameter d2 to have the same deflection as a bar of diameter d1: k2^3/d2 = k1^3/d1. Which leads to k2/k1 = cube root (d2/d1). So the case where a bar's diameter is doubled, the depth ratio increases by a factor of 1.26. E.g., doubling the diameter of bar with 4x depth would allow a 5x depth (a 1" bar at 5" would be same as a 1/2" bar at 4"). Whew - it's easy to see why people use a fixed rule of thumb.

                                If we assume that a 1/4" bar is good to 1" depth (4x), then:
                                d k depth
                                1/4 4 1
                                3/8 4.6 1.7
                                1/2 5 2.5
                                5/8 5.4 3.4
                                3/4 5.7 4.3
                                1 6.4 6.3
                                2 8 16 - - - - - - Arrrggghh - this list was formatted, but the extra spaces were removed when posted! How to get around it? "TAB" doesn't work

                                IOW, 4 or 5 times is good until you get to 1" bars, then it's too conservative. And since the material, DOC, feed, etc play into it, it's your feel for it that it boils down to.

                                Thanks for readin', Bob
                                Fantastic post Bob! Thanks for posting. I was thinking it wasn't a linear relationship, but too tired to do any in-depth thinking. And you've shown it is infact not!

                                Originally posted by Doozer View Post

                                Why do people always feel the need to argue about this ? ? ?

                                -D
                                Because they haven't see a stress and strain curve. I've even argued with Adam Booth about that. In one video he was having chatter issues so he switched to his favorite bar which stopped it. He explained how it was more rigid. I explained in the comments how it was not and provided references but he wasn't having it. Later in his next video there was a 2 minute spot bitching about the "haters" or "trolls" which was clearly directed at me. Well sorry bud, but the laws of physics never stop working.
                                21" Royersford Excelsior CamelBack Drillpress Restoration
                                1943 Sidney 16x54 Lathe Restoration

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