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Idea for new project

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  • Idea for new project

    I have an idea for a new project. I could make good use of a high speed lathe with more capacity than the Unimat. The single biggest disadvantage of the SB9 is the low speed available. Max rpms are 658 and with plain bearings speeding it up is not an option.

    So, I have come up with an idea that should be pretty usfeul, especially for turning and polishing brass and aluminum in smaller sizes. It is a spindle through the spindle with roller bearings at each end. It will be simple and inexpensive to make. It is powered from the SB motor. At least on my machine there is around 1 1/2" of shaft sticking out past the primary drive pulley on the motor making it possible to add another pulley to drive the high speed spindle. I have also figured out a way to tension the belt automatically when the regular flat belt is tensioned.

    The through hole on the SB9 spindle is slightly greater than 3/4" so it will allow a 3/4" spindle to pass. I will shrink on a collar to act as a bearing stop and chuck register. I intend to use a 3" chuck, probably a three jaw but maybe a 4, or maybe both

    The cool thing is that both spindles can run at the same time so I still have power carriage feed for long cuts. The only real disadvantage is the second spindle will not have a through hole although I will bore it 1/2" at least several inches deep. The entire rig should only take a minute to mount on the lathe.

    It may be a while before I get around to this, I have to finish my other projects first.

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  • #2
    I'm not so sure about both spindles turning at the same time. Anything less than perfect concentricity in any of the parts will show up as runout in the new spindle. Worse still, the runout will wander around as the spindles rotate with respect to one another.

    Even the mighty four jaw chuck won't be able to cure that kind of runout.

    One thing which might help is to use a larger bearing on the right end. If the inner race is mounted directly on the original spindle, the overhang would be less, and the part that fits around the outer race could be permanently attached to (and machined concentric with) the new spindle.


    [This message has been edited by winchman (edited 05-17-2004).]
    Any products mentioned in my posts have been endorsed by their manufacturer.


    • #3
      Roger, the concentricity should be perfect. The part that goes on the original spindle is threaded to fit and register and then the seat for the bearing is turned. It can't not be concentric and should go on the same way every time, just like a chuck. Overhang isn't much of a problem here as this would be for small stuff at around 2500 rpm.
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      • #4
        Evan this may be a better idea. More work, but better IMO. Build a complete second head that can take 5cs internally that clamps on the bed in front of the SB headstock. This head would only need to have a ingle sheeve and a vaariable speed motor or a multiple sheeve set up. Clamp it to the bed just like the steady rest. In fact if you set every thing up correctly you could use this just like a steady for long thin pieces. Use a bed plate that would mount on the ways and use fitting spacers to get it on centerline. Given the job you've been doing on the indexing fixture this should be no problem!
        Forty plus years and I still have ten toes, ten fingers and both eyes. I must be doing something right.


        • #5
          An interesting idea Evan. It would be very useful for polishing but I think that there is a posibility that the 3/4" spindle shaft will flex under even light cutting loads. If you are like me you will totally ignore that possibility and build it anyway . After all it's the only way to know for sure .
          To invent, you need a good imagination - and a pile of junk. Thomas A. Edison


          • #6

            I considered that but it would really cut down the distance between centers. I'm going to try my idea since it is easy and relatively cheap.

            George, I also considered that and if it is a problem then I can make a new longer nose piece with two bearings to help reduce flex. All it costs is a few $ worth of steel.

            [This message has been edited by Evan (edited 05-17-2004).]
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            • #7
              That sounds like a dandy idea Evan. I was just wondering though; How will those SB9 gears like spinning up to say 2000 rpm for polishing? I wonder if the headstock train would have to be balanced?


              • #8
                Gears? The regular spindle turns at the regular speeds including the gears, or I slip the belt and it doesn't turn at all. The high speed spindle is supported by the stock spindle but is not connected rotationally (is that a word?) because of the bearings. The high speed spindle merely takes drive from the motor and spins the chuck on its end. the low speed stock spindle can do whatever it I set it to do, as per usual. The main thing that can't be done on the high speed spindle is threading, but then I never thread at 2500 rpm
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                • #9
                  As far as the shaft goes, you're just looking for a rod less than an inch diameter. Is there some close-grained cast that would be better? How about a rod from a front end strut, would that be fat enough?
                  I seldom do anything within the scope of logical reason and calculated cost/benefit, etc- I'm following my passion-


                  • #10
                    I don't think it would make any difference. The modulus of elasticity is typically the same for all forms of iron alloys. I will use normalized 1018 crs and case harden the spindle nose.
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                    • #11
                      My 9c has the 2 step motor pulley setup, and my top RPM I believe is around 1020?
                      You could get a tiny bit more speed out of your lathe, however on mine, I never go faster than 400 something anyhow. I use my little Mini lathe which can go up to 3,000 rpm with the Bison 3 jaw and zero setable backplate for that stuff.


                      • #12
                        Evan: If you're concerned about the lack of "beef" in the new spindle nose, how about a larger bearing housing where the bore of a large bearing sits over the OD of the entire existing 1-1/2x8 nose. The new spindle end would spin on the OUTER race of the large bore bearing, but still be driven by the small shaft thru the old spindle.

                        A bit more work but now your 3/4" drive shaft is only a drive shaft ... and the large nose has all the beef that a larger, camlock or other spindle end would offer ... with the new, high speeds

                        This beefy arrangement would be limited in stiffness only by the SB 1-1/2x8 thread and register area ... pretty good.

                        I was thinking bearing selection would be a bear but you could use tapered rollers and pick up the preload by keeping the "thru" shaft in tension.

                        I'll drop a cross-section sketch in here if I get a chance.



                        • #13
                          I'm not sure that your idea would be easy to make work. I think this would be a high precision job.

                          If what you want to do is polish consider making a speed lathe out of a wood lathe. These are relatively cheap and turn at high speeds.

                          The other option is to speed up you SB. I don't understand why you say this is not possible. It seems to me to be a matter of pulley ratios and motor speed. The bearings should be fine if you can supply them with sufficient oil. The advantage of the journal bearing over other designs is running at high continuous speed. Provided enough oil is continually supplied ;-).


                          • #14

                            That would be a workable option but I don't have a suitable bearing in that size range. A bearing that size would cost $$$. Also, the adapter would be getting up to pretty large size to machine from steel on the SB.

                            I only intend to run a 3" chuck on it to do small stuff, mainly aluminum. What I really need is something equivalent to a machine halfway between the Unimat and the SB. I figure I can build my idea for about $20 or less, not including chuck.
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                            • #15
                              On the subject of chucks, does anyone have an idea what the speed rating of a 5" early (1980s) Bison three jaw chuck would be?
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