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Re: [multimachine] Lead screw alternatives

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  • michael broadbent
    Hi    A six mm leadscrew would be very prone to flex.   In the past i have made cheap leadscrews using 12 and 16mm  screws,a very simple  split nut was
    Message 1 of 18 , May 11, 2010
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      Hi
         A six mm leadscrew would be very prone to flex.
       
      In the past i have made cheap leadscrews using 12 and 16mm  screws,a very simple  split nut was made to take care of back lash .
       
      The nut was a block of steel  tapped to suit screw then cut in half across the screw axisOne half of the nut was bolted to the carrage and the  other half left to be adjustable along the axis 'This was done by having allen screws to set the gap .
      Is this is what you are looking for?
       
      Mikeafloat
       
       
       
      --- On Tue, 11/5/10, BRUCE BELLOWS <bbellows@...> wrote:

      From: BRUCE BELLOWS <bbellows@...>
      Subject: Re: [multimachine] Lead screw alternatives
      To: multimachine@yahoogroups.com
      Date: Tuesday, 11 May, 2010, 16:24



      That bend in the nut allows it to function as a anti backlash nut. A standard threaded screw could probably give very good results using such a nut. I would recommend an unplated screw so the plating doesn't become a future problem.
       
      Bruce

      --- On Tue, 5/11/10, Pat Delany <rigmatch@...> wrote:

      From: Pat Delany <rigmatch@...>
      Subject: Re: [multimachine] Lead screw alternatives
      To: multimachine@yahoogroups.com
      Date: Tuesday, May 11, 2010, 2:26 PM

       
      2 comments about this:

      I have a very expensive milling table that has almost no backlash on the lead screw and it uses a long nut (like an allthread coupling nut) that is cut about 3/4 through from the side and bent slightly closed.

      90% of the machine work in the world is made on machines that are at least  a little crapped out. People learn to live with it.

      Pat



      From: Bruce Bellows <bbellows@rogers. com>
      To: multimachine@ yahoogroups. com
      Sent: Tue, May 11, 2010 7:09:20 AM
      Subject: Re: [multimachine] Lead screw alternatives

       
      A company named EXLAR offer a satellite roller nut that may run with a standard thread form. The threaded shaft may need to be high precision but would probably be cheaper that a lead screw.

      Bruce

      Cassidy wrote:
       
      I will have to build the compound table in our Files section - Drill Press Compound Slide.pdf - if I want to start thinking of building a machine to perform some milling.

      I have checked the prices of lead screws and they are expensive. $100-$200+ per metre which probably is reasonable if you consider that a new Chinese compound table is ~$2000 around here.

      I'm thinking of using M6 threaded rod as an alternative since they're suppose to travel 1mm per turn (from what I've read).

      What do you guys think?

      Regards.





    • Pat
      A great idea Dave
      Message 2 of 18 , May 11, 2010
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        A great idea Dave

        --- In multimachine@yahoogroups.com, "David G. LeVine" <dlevine@...> wrote:
        >
        > On 05/11/2010 10:26 AM, Pat Delany wrote:
        > >
        > >
        > > 2 comments about this:
        > >
        > > I have a very expensive milling table that has almost no backlash on
        > > the lead screw and it uses a long nut (like an allthread coupling nut)
        > > that is cut about 3/4 through from the side and bent slightly closed.
        >
        > Sometimes the nut is bent open by a setscrew in the cut, which makes the
        > antibacklash setting adjustable.
        >
        > Often two nuts with either shims or springs (like Belleville washers)
        > between them are used to limit backlash. The springs allow for the
        > leadscrew to not jam if a small amount of contamination accumulates on
        > the screw, and contamination CAN accumulate on a leadscrew all too easily.
        >
      • Jeff
        Don t forget about about the acme threaded rods in car jacks and trash compactors.
        Message 3 of 18 , May 11, 2010
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          Don't forget about about the acme threaded rods in car jacks and trash compactors.

          --- In multimachine@yahoogroups.com, "Pat" <rigmatch@...> wrote:
          >
          > A great idea Dave
          >
          > --- In multimachine@yahoogroups.com, "David G. LeVine" <dlevine@> wrote:
          > >
          > > On 05/11/2010 10:26 AM, Pat Delany wrote:
          > > >
          > > >
          > > > 2 comments about this:
          > > >
          > > > I have a very expensive milling table that has almost no backlash on
          > > > the lead screw and it uses a long nut (like an allthread coupling nut)
          > > > that is cut about 3/4 through from the side and bent slightly closed.
          > >
          > > Sometimes the nut is bent open by a setscrew in the cut, which makes the
          > > antibacklash setting adjustable.
          > >
          > > Often two nuts with either shims or springs (like Belleville washers)
          > > between them are used to limit backlash. The springs allow for the
          > > leadscrew to not jam if a small amount of contamination accumulates on
          > > the screw, and contamination CAN accumulate on a leadscrew all too easily.
          > >
          >
        • David G. LeVine
          ... This is a case of I can not tell a lie. These are not my idea, they are industrial standards. Sorry, I am not that good. However, I do tend to point
          Message 4 of 18 , May 11, 2010
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            On 05/11/2010 04:32 PM, Pat wrote:
            > A great idea Dave
            >
            > --- In multimachine@yahoogroups.com, "David G. LeVine"<dlevine@...> wrote:
            >
            >> <snip>Often two nuts with either shims or springs (like Belleville
            >> washers)
            >> between them are used to limit backlash. The springs allow for the
            >> leadscrew to not jam if a small amount of contamination accumulates on
            >> the screw, and contamination CAN accumulate on a leadscrew all too easily.
            >>
            This is a case of "I can not tell a lie." These are not my idea, they
            are industrial standards.

            Sorry, I am not that good. However, I do tend to point out good ideas
            from time to time.

            The basic plan is to take two nuts and tighten them loosely on the
            leadscrew. Put dowels through the two nuts so they can not rotate with
            respect to each other. Shim or use springs to preload to the desired
            level. Since the nuts are fixed in orientation to each other, the
            preload is either fixed or the leadscrews are bad. It is interesting to
            note that errors will tend to average out with the shimmed nuts, but not
            with the spring preloaded nuts.

            If the two nuts float (nut-spring-support-spring-nut), errors will
            average out, but the errors due to flex will be worse (the stiffness is
            lower with the springs in place.)

            Ideally, huge ball screws would be best, but the price is incredible,
            literally.

            Do not use 1/4-20 or M6-1 leadscrews, they are not stiff enough, they
            will "whip" as you do fast moves and will flex during cutting.
          • Cassidy
            Very good point, Bruce.
            Message 5 of 18 , May 12, 2010
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              Very good point, Bruce.

              --- In multimachine@yahoogroups.com, BRUCE BELLOWS <bbellows@...> wrote:
              >
              > That bend in the nut allows it to function as a anti backlash nut. A standard threaded screw could probably give very good results using such a nut. I would recommend an unplated screw so the plating doesn't become a future problem.
              >  
              > Bruce
              >
              > --- On Tue, 5/11/10, Pat Delany <rigmatch@...> wrote:
              >
              >
              > From: Pat Delany <rigmatch@...>
              > Subject: Re: [multimachine] Lead screw alternatives
              > To: multimachine@yahoogroups.com
              > Date: Tuesday, May 11, 2010, 2:26 PM
              >
              >
              >  
              >
              >
              >
              >
              > 2 comments about this:
              >
              > I have a very expensive milling table that has almost no backlash on the lead screw and it uses a long nut (like an allthread coupling nut) that is cut about 3/4 through from the side and bent slightly closed.
              >
              > 90% of the machine work in the world is made on machines that are at least  a little crapped out. People learn to live with it.
              >
              > Pat
              >
              >
              >
              >
              >
              >
              >
              > From: Bruce Bellows <bbellows@rogers. com>
              > To: multimachine@ yahoogroups. com
              > Sent: Tue, May 11, 2010 7:09:20 AM
              > Subject: Re: [multimachine] Lead screw alternatives
              >
              >  
              >
              > A company named EXLAR offer a satellite roller nut that may run with a standard thread form. The threaded shaft may need to be high precision but would probably be cheaper that a lead screw.
              >
              > Bruce
              >
              > Cassidy wrote:
              >  
              >
              > I will have to build the compound table in our Files section - Drill Press Compound Slide.pdf - if I want to start thinking of building a machine to perform some milling.
              >
              > I have checked the prices of lead screws and they are expensive. $100-$200+ per metre which probably is reasonable if you consider that a new Chinese compound table is ~$2000 around here.
              >
              > I'm thinking of using M6 threaded rod as an alternative since they're suppose to travel 1mm per turn (from what I've read).
              >
              > What do you guys think?
              >
              > Regards.
              >
            • Cassidy
              Thanx Jeff, another option to consider.
              Message 6 of 18 , May 12, 2010
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                Thanx Jeff, another option to consider.

                --- In multimachine@yahoogroups.com, "Jeff" <jhan5en@...> wrote:
                >
                > Don't forget about about the acme threaded rods in car jacks and trash compactors.
                >
              • Cassidy
                Thanks to all for giving me direction. I m feeling very optimistic about this. Regards.
                Message 7 of 18 , May 12, 2010
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                  Thanks to all for giving me direction. I'm feeling very optimistic about this.

                  Regards.

                  --- In multimachine@yahoogroups.com, "David G. LeVine" <dlevine@...> wrote:
                  >
                  > On 05/11/2010 04:32 PM, Pat wrote:
                  > > A great idea Dave
                  > >
                  > > --- In multimachine@yahoogroups.com, "David G. LeVine"<dlevine@> wrote:
                  > >
                  > >> <snip>Often two nuts with either shims or springs (like Belleville
                  > >> washers)
                  > >> between them are used to limit backlash. The springs allow for the
                  > >> leadscrew to not jam if a small amount of contamination accumulates on
                  > >> the screw, and contamination CAN accumulate on a leadscrew all too easily.
                  > >>
                  > This is a case of "I can not tell a lie." These are not my idea, they
                  > are industrial standards.
                  >
                  > Sorry, I am not that good. However, I do tend to point out good ideas
                  > from time to time.
                  >
                  > The basic plan is to take two nuts and tighten them loosely on the
                  > leadscrew. Put dowels through the two nuts so they can not rotate with
                  > respect to each other. Shim or use springs to preload to the desired
                  > level. Since the nuts are fixed in orientation to each other, the
                  > preload is either fixed or the leadscrews are bad. It is interesting to
                  > note that errors will tend to average out with the shimmed nuts, but not
                  > with the spring preloaded nuts.
                  >
                  > If the two nuts float (nut-spring-support-spring-nut), errors will
                  > average out, but the errors due to flex will be worse (the stiffness is
                  > lower with the springs in place.)
                  >
                  > Ideally, huge ball screws would be best, but the price is incredible,
                  > literally.
                  >
                  > Do not use 1/4-20 or M6-1 leadscrews, they are not stiff enough, they
                  > will "whip" as you do fast moves and will flex during cutting.
                  >
                • wildstrumph
                  Hi, Speaking of alternatives to lead screws, why do we see lathes with just lead screws and lathes with lead screws as well as feed rods, but we don t see
                  Message 8 of 18 , May 12, 2010
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                    Hi,

                    Speaking of alternatives to lead screws, why do we see lathes with just lead screws and lathes with lead screws as well as feed rods, but we don't see lathes with just feed rods?

                    --
                    brian
                  • Gordon Haag
                    Would 1/2-20 make a stiff enough leadscrew?
                    Message 9 of 18 , May 12, 2010
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                      Would 1/2-20 make a stiff enough leadscrew?

                      On Wed, May 12, 2010 at 9:52 AM, wildstrumph <no_reply@yahoogroups.com> wrote:
                       

                      Hi,

                      Speaking of alternatives to lead screws, why do we see lathes with just lead screws and lathes with lead screws as well as feed rods, but we don't see lathes with just feed rods?

                      --
                      brian


                    • Ian Newman
                      Hi, On a lathe the leadscrew is used to provide the feed to cut threads, therefore any wear on the leadscrew reduces the accuracy of threads produced. To
                      Message 10 of 18 , May 12, 2010
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                        Hi,

                        On a lathe the leadscrew is used to provide the feed to cut threads, therefore any wear on the leadscrew reduces the accuracy of threads produced.

                        To prevent un-necessary wear on the leadscrew an alternative drive is provided for use when the accuracy is not needed (i.e. for automatic fine feed) - any wear on this part of the drive will not degrade the threading accuracy.

                        Of course having two feed mechanisms increases the cost, so cheaper machines use the leadscrew for both functions.

                        Ian.

                        --- On Thu, 13/5/10, Gordon Haag <nodrog19@...> wrote:

                        From: Gordon Haag <nodrog19@...>
                        Subject: Re: [multimachine] Re: Lead screw alternatives
                        To: multimachine@yahoogroups.com
                        Date: Thursday, 13 May, 2010, 0:23

                         

                        Would 1/2-20 make a stiff enough leadscrew?On Wed, May 12, 2010 at 9:52 AM, wildstrumph wrote:> > > Hi, > > Speaking of alternatives to lead screws, why do we see lathes with just > lead screws and lathes with lead screws as well as feed rods, but we don't > see lathes with just feed rods? > > -- > brian > > >


                      • wildstrumph
                        ... While this certainly makes sense, it doesn t address the presence of lead-screw-only lathes and absense of feed-rod-only lathes. If a lathe is to have
                        Message 11 of 18 , May 13, 2010
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                          --- In multimachine@yahoogroups.com, Ian Newman <ian_new@...> wrote:
                          > On a lathe the leadscrew is used to provide the feed to cut threads, therefore any wear on the leadscrew reduces the accuracy of threads produced.
                          >
                          > To prevent un-necessary wear on the leadscrew an alternative drive is provided for use when the accuracy is not needed (i.e. for automatic fine feed) - any wear on this part of the drive will not degrade the threading accuracy.
                          >
                          > Of course having two feed mechanisms increases the cost, so cheaper machines use the leadscrew for both functions.


                          While this certainly makes sense, it doesn't address the presence of lead-screw-only lathes and absense of feed-rod-only lathes. If a lathe is to have only one feed mechanism, why is it always a screw instead of a feed rod?

                          --
                          thanks
                          brian
                        • Stan Stocker
                          Greetings, The leadscrew allows thread cutting. The leadscrew can also support carriage advance. A feed rod setup only provides drive to the carriage. For
                          Message 12 of 18 , May 13, 2010
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                            Greetings,

                            The leadscrew allows thread cutting. The leadscrew can also support
                            carriage advance. A feed rod setup only provides drive to the
                            carriage. For threading, the half nut clamping on a leadscrew provides
                            a more reliable and accurate approach than the worm wheel driving the
                            handwheel pinion with all of its assorted freedoms of motion, backlash,
                            and single point of drive. The half nuts also average out errors over
                            the length of the halfnut.

                            If you ONLY needed power carriage advance, and had no interest in
                            threading, then it would be possible to do a drive by feed rod only.
                            The downside is that driving by the feedrod actually required more parts
                            and more hard to make parts than the simple carriage advance via half
                            nut on a leasdscrew. So the feedrod only version does less for more
                            money from a machine design perspective.

                            If I wanted cheap carriage feed only, I'd be looking at chain or cable
                            drive with a separate low speed drive motor or a stepper on the handwheel.

                            Cheers,
                            Stan

                            wildstrumph wrote:
                            > --- In multimachine@yahoogroups.com, Ian Newman <ian_new@...> wrote:
                            >
                            >> On a lathe the leadscrew is used to provide the feed to cut threads, therefore any wear on the leadscrew reduces the accuracy of threads produced.
                            >>
                            >> To prevent un-necessary wear on the leadscrew an alternative drive is provided for use when the accuracy is not needed (i.e. for automatic fine feed) - any wear on this part of the drive will not degrade the threading accuracy.
                            >>
                            >> Of course having two feed mechanisms increases the cost, so cheaper machines use the leadscrew for both functions.
                            >>
                            >
                            >
                            > While this certainly makes sense, it doesn't address the presence of lead-screw-only lathes and absense of feed-rod-only lathes. If a lathe is to have only one feed mechanism, why is it always a screw instead of a feed rod?
                            >
                            >
                          • David G. LeVine
                            ... The question is FOR WHAT? For a CNC 36 lathe holding 0.0005 accuracy? Nope, no way. For a manual operation only, unimat type lathe? Yep, that ll work
                            Message 13 of 18 , May 13, 2010
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                              On 05/12/2010 07:23 PM, Gordon Haag wrote: Would 1/2-20 make a stiff enough leadscrew?

                              The question is FOR WHAT?

                              For a CNC 36" lathe holding 0.0005" accuracy?  Nope, no way.  For a manual operation only, unimat type lathe?  Yep, that'll work well.  If left to flop around (only one end supported), and run at high speed, you are looking for trouble at 36", for a 2" drive with handwheels running to no more than 10 RPM, it should be fine.



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