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thru boring a 6" chuck for direct bolting to rotary table

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  • #16
    Hey that's some helpful math to aid my layout. or scare me off my present plan. I may have to drill and tap - which is fine too. .654 from the jaw centerline - I dont see how that can work with jaws that have to be close to an inch. I need .125 clearance and .1875 (half of bore) so .312 from edge of jaw. .812 from center. So I'm thinking I can go the edge but it sounds too tight.


    Originally posted by old mart View Post
    When I wanted to mount 3 jaw scroll and 4 jaw independent on a 4 tee slot RT, the four jaw just needed front mount holes, bolts and tee nuts. The three jaw problem was solved by mounting the front mount chuck using tapped holes directly into the RT. I should have removed the top to examine it properly, as one of the holes happened to intercept a lubrication drilling which I had not noticed. So a second set of holes were drilled in full thickness metal. Before tightening the three jaw, I gently clamp the jaws onto a MT2 arbor fitted in the centre of the RT. That centralises the chuck and the screws can be tightened. It might be possible to find a position for 4 threaded holes in the top of a 3 slot RT to mount a 4 jaw independent directly. If the threaded holes are no closer than 1/8" from a tee slot, it would be feasible.
    Drilling the chuck with three holes will result in 2 of them being 15 degrees from the centreline of 2 of the jaws. The further out the holes are drilled results in that 15 degrees being a larger measurement. If the holes in the chuck are drilled on the 5" diameter, 2 of the holes will be 0.654" from the jaw centreline. That may be enough with a 6" chuck.

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    • #17
      Wow loved watching this video link, that guy is just too cool. I'm planning to center the table and lock in on the spindle. As far as then mounting the 4 jaw I dont have the foggiest clue. I've never gone down this road. really lookiing forward to having the ability to grab work this way. I'm also ordering a MT3 draw bar style blank so I can mount a small 3 jaw for round stuff and 5C collets.

      Thanks on 1/64 over. Makes sense.

      Sorry but I'm not understanding what butting 3 cap screws in a 4 jaw means... coming in from bottom?

      the Insane step drilling was bc I read about semi steel and thought it might be pretty hard. my science was bad on the sizing I guess. Doozer has been talking me out of my tree on this matter ;-)





      Originally posted by The Metal Butcher View Post
      I wrote this before the rest of the discussion but got sidetracked, so I'm gonna post it anyway as is:

      You might find this video useful: https://www.youtube.com/watch?v=MGCBrhsUVu0

      At any rate, it's not that critical. Especially if you're going to bump it in anyway. In fact, I would go 1/64th over. Working overly-tight when there is no reason for it does nobody any favors. I guess since it's a 4 jaw it doesn't matter if the body runs out, whereas it does on a 3 jaw.

      PS, have you checked butting 3 caps screws in a 4 jaw? 4 and 3 don't generally jive, but maybe you can fit them in.

      Lastly, what's with the insane step drilling? 3/8" is a pilot drill in cast iron. Hell, 5/8" is a pilot drill in cast iron unless your tools are small. 3/16" just means a lot more chip clearing and chances for wander.

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      • #18
        Ive been thinking about how to do this - so thanks. I can center the table, it's really clear conceptually. But the chuck and these mounting bores are tough. I have a lathe - I think you are saying turn a double ended allignment pin that is a tight fit to both RoTab and Chuck center bore? They make Mt3 machinable blanks up to 1.5" diameter, might not be quite enough for chuck so I can turn a delrin sleeve. But am I reading you right? cause that makes the whole set up wicked clean if so.



        Originally posted by Bented View Post
        Drill the mounting holes with substantial clearance, .010" per side minimum, these holes do not align the chuck to the center of rotation.

        If you do not have a lathe mill a pilot that fits the thru hole of the table in place flip it over then mill a diameter that tightly fits the chuck bore, this will center the chuck whilst the bolts merely hold it down.

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        • #19
          Originally posted by Bill White View Post
          Ive been thinking about how to do this - so thanks. I can center the table, it's really clear conceptually. But the chuck and these mounting bores are tough. I have a lathe - I think you are saying turn a double ended allignment pin that is a tight fit to both RoTab and Chuck center bore? They make Mt3 machinable blanks up to 1.5" diameter, might not be quite enough for chuck so I can turn a delrin sleeve. But am I reading you right? cause that makes the whole set up wicked clean if so.




          Exactly, many rotary tables have straight pilot bores rather then tapers.

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          • #20
            Follow up:

            Click image for larger version

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            I got it on there a couple days ago. The CME/Sanou chuck (8" 4 jaw) is not a bad for $122. I laid it out by strapping a bolt thru center (thanks Doozer!) and decided to tap into the Rotary platter using the 4 existing bores (thanks Old Mart!). After dialing chuck to table, I marked and drilled for a 3/8 tap. I had never drilled CI on my mill, at 600 rpm it was like butter, just turns to dust! I kept the vacuum handy cause that dust is evil. With my layout one bore had to fall very close to one of the 3 slots in the Rotab which leaves the threads showing a tad but with plenty of meat to grab. So much for perfect- I could not find a geometry that was any better. So much for square pegs in round holes.

            Only issue turns out to be centering the Rotab, I got an MT3 arbor with a machinable blank end that I planned to turn down so the end fit an R8 collet - but I had never tried to chuck a morse taper, wobble wobble. Someone said get a piece of copper pipe, slit it down the side as a crush sleeve. So I'll try that

            thanks to you guys for the help. Appreciate it!

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            • #21
              Ps. now thats it on there I'm not sure I have any use for it - so why do I feel so much better knowing I have it??

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              • #22
                Oh yeah - bolt circles! OMG the time I have lost laying out those buggers!

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                • #23
                  I hope you can counterbore the holes to get a set of SHCS screws just underflush.

                  It is common for people to be afraid of modifying their tooling but they miss out on having something that does the job much better.

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                  • #24
                    Originally posted by Bill White View Post
                    Follow up:

                    Click image for larger version

Name:	Screen Shot 2021-05-13 at 7.43.06 AM.png
Views:	112
Size:	843.2 KB
ID:	1942683

                    I got it on there a couple days ago. The CME/Sanou chuck (8" 4 jaw) is not a bad for $122. I laid it out by strapping a bolt thru center (thanks Doozer!) and decided to tap into the Rotary platter using the 4 existing bores (thanks Old Mart!). After dialing chuck to table, I marked and drilled for a 3/8 tap. I had never drilled CI on my mill, at 600 rpm it was like butter, just turns to dust! I kept the vacuum handy cause that dust is evil. With my layout one bore had to fall very close to one of the 3 slots in the Rotab which leaves the threads showing a tad but with plenty of meat to grab. So much for perfect- I could not find a geometry that was any better. So much for square pegs in round holes.

                    Only issue turns out to be centering the Rotab, I got an MT3 arbor with a machinable blank end that I planned to turn down so the end fit an R8 collet - but I had never tried to chuck a morse taper, wobble wobble. Someone said get a piece of copper pipe, slit it down the side as a crush sleeve. So I'll try that

                    thanks to you guys for the help. Appreciate it!
                    That blank MT needs to be turned between centers. Holding tapered shanks in chuck jaws is a poor method, even with copper sleeves. as soon as you start cutting, the workpiece will tend to loosen!
                    I cut it off twice; it's still too short
                    Oregon, USA

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                    • #25
                      The 6" RT that I have has a MT2 centre, and I have a test bar with centres and a MT2 end. When setting up the RT, I use the bar which is a short one, about 7" long, to set the axis of the table in line wtih the spindle. It is within 0.002" tir which is good enough for most of my work. The test bars are useful for mills and lathes.

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                      • #26
                        Looks like you have a Delta Rockwell mill. Those are a super nice medium
                        size machine. There is a Youtube guy what has one that is vertical and
                        horizontal. I forget his channel name. But what a great combination machine.
                        I have a VanNorman mill that swivels from H to V, but with 2 separate spindles
                        it is more handy.
                        So how are those Sanou chucks? I know they are China but I have heard they
                        are a bit better than no name China chucks.

                        --Doozer
                        DZER

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                        • #27
                          I only have a 7 x 12 at home and replaced the original 80mm three and four jaw chucks with 80 (3) and 100 (4) mm chucks made by Sanou. The 4 jaw got machined to fit directly on the spindle, they are a big improvement over the original, also Chinese made chucks. Not the precision associated with the top brands, but good value for money.

                          The holes in the top of the RT could do with some grubscrews with screwdriver slots in them to screw in as swarf protectors when the chuck is off. If you broke through when drilling the top, you should dismantle the RT and give it a good clean and relube.
                          Last edited by old mart; 05-13-2021, 02:42 PM.

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                          • #28
                            Mart, Yup. I did not like screwing holes in my 1970 Rockwell Mill to mount a cheap asian DRO- but it's the best thing I ever did. I'm still resisting mounting a scale to my 120 yr old Seneca Falls lathe. Bought the scale and started using a push dial indicator instead of drilling holes, actually the DI is pretty hard to beat on a lathe.

                            I don't need to counter bore this Mart, it's front mount/counterbored from factory. I just took out the M10 bolts and dropped in 3/8 after I tapped the Rotab. Took a couple hrs of being careful with DI and getting the holes layed out- but really a simple, quick job. Thanks for the encouragement!

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                            • #29
                              Originally posted by Bill White View Post
                              Ps. now thats it on there I'm not sure I have any use for it - so why do I feel so much better knowing I have it??
                              My wife insisted the only reason I needed tools was to make more tools. Better hobby than spending time in the local bar.

                              Mike

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                              • #30
                                Tim, Thanks for that! It's funny when you get great advise its always like "duh! why didnt I think of that!" But I actually read a whole thread on the subject over at PM and no one mentioned it there. So it's not obvious, but it is smart! Would a copper sleeve still help
                                anything between centers?

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