Announcement

Collapse
No announcement yet.

Repairing Draw bar

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

  • Repairing Draw bar

    I have a Bridgeport milling machine and the threads on the draw bar are worn down which are 7/16 * 20. Can I take a 7/16 * 20 grade 8 bolts and cut it to length and cut a corresponding amount off of the draw bar and weld it on? Will it hold, will it be true enough, and are the threads strong enough. I would like to do this because 1. cost $60+ for a new draw bar versus $1.25 for a bolt and 2.The satisfaction of repairing this.

  • #2
    Sure

    Sure - why not.

    Or use a bit of high-tensile "all thread".

    Comment


    • #3
      Why not buy a piece of appropriate-diameter pre-hardened 4140 and make a whole new drawbar?

      But your idea ought to work, I think. I'd probably turn down a spigot on one piece and drill a corresponding hole in the other piece to help ensure alignment.
      ----------
      Try to make a living, not a killing. -- Utah Phillips
      Don't believe everything you know. -- Bumper sticker
      Everybody is ignorant, only on different subjects. -- Will Rogers
      There are lots of people who mistake their imagination for their memory. - Josh Billings
      Law of Logical Argument - Anything is possible if you don't know what you are talking about.
      Don't own anything you have to feed or paint. - Hood River Blackie

      Comment


      • #4
        Cut it off up at the larger diameter, drill and ream a slipfit hole in that piece, get some 7/16 diameter stock, thread the end 7/16-20, insert other end into the hole you drilled and reamed, drill a hole through the diameter of your larger diameter and 7/16 shaft in assembly and pin it. Done. They sell them this way, (pinned) so you can repair them but you can do it yourself, assuming you have a lathe or a 7/16-20 die.

        Comment


        • #5
          Originally posted by Dale
          Can I take a 7/16 * 20 grade 8 bolts and cut it to length and cut a corresponding amount off of the draw bar and weld it on? Will it hold, will it be true enough, and are the threads strong enough.
          Dale Welcome, I made that repair on a BP clone several years ago. What I did was cut the draw bar and bolt at a 45 deg. angle and then fixtured the parts and brazed them. It held together for the remaining time I owned the machine and as far as I know it is still holding.

          Steve

          Comment


          • #6
            You can use a bolt to repair it or MSC has new ones for $16-$25 depending on length

            http://www1.mscdirect.com/CGI/NNPDFF...9935&PMCTLG=00


            Enco is even cheaper $14-$25
            http://www.use-enco.com/CGI/INPDFF?P...MITEM=209-9016
            Experience is something you don't get until just after you need it. ..

            Comment


            • #7
              Originally posted by SGW
              Why not buy a piece of appropriate-diameter pre-hardened 4140 and make a whole new drawbar?

              But your idea ought to work, I think. I'd probably turn down a spigot on one piece and drill a corresponding hole in the other piece to help ensure alignment.
              I second this approach. Also, silver solder would do the job nicely, rather than welding. Draw bar just holds collet in tension so it is not actually driving the cutter.
              Jim (KB4IVH)

              Only fools abuse their tools.

              Comment


              • #8
                Originally posted by SGW
                Why not buy a piece of appropriate-diameter pre-hardened 4140 and make a whole new drawbar?

                But your idea ought to work, I think. I'd probably turn down a spigot on one piece and drill a corresponding hole in the other piece to help ensure alignment.
                Thanks for the suggestions. I will combine some of the suggestions. I did not know that Enco or MSC carried them.

                Comment


                • #9
                  Originally posted by MaxxLagg
                  Cut it off up at the larger diameter, drill and ream a slipfit hole in that piece, get some 7/16 diameter stock, thread the end 7/16-20, insert other end into the hole you drilled and reamed, drill a hole through the diameter of your larger diameter and 7/16 shaft in assembly and pin it. Done. They sell them this way, (pinned) so you can repair them but you can do it yourself, assuming you have a lathe or a 7/16-20 die.

                  Yes, this is a good method of repair and is used by Kurt.http://www.kurtworkholding.com/downl..._DIY_Guide.pdf

                  Comment


                  • #10
                    High Quality Tools makes replacement drawbars for most of retailers. They usualy have cheaper prices too.

                    Comment


                    • #11
                      Id wonder, would one even want grade 8 threads in a drawbar?

                      thats a lot of screwing and unscrewing into all your collets, endmill holders, boring bar shanks, etc. Not to mention the little hammering required to pop R8 or MT tooling out.

                      What im trying to say is I think the grade 8 threads would last longer, but insted wear out the threads in all your collets and such. those could be harder to spot wear on untill one criticaly fails and ruins your work. And then you'll be questioning every collet/boring head/face mill you own.

                      I think the idea of applying a coupleing nut thats pined or something similar to the drawbar and adding a length of grade 5 allthread rod would be a much better idea. Drawbars *ARE* considered consumable, thats why they are sold at so many tool stores. and yea some are $60+ but others are only $30~
                      Play Brutal Nature, Black Moons free to play highly realistic voxel sandbox game.

                      Comment


                      • #12
                        Don't try to pin it because the pins shear at the worst time. Silver solder or braze it together. Or buy a new one and I vote for the new one.
                        It's only ink and paper

                        Comment


                        • #13
                          During my apprenticeship, I learned to make drawbars out of 41 40 or even 1018 steel. The 1018's were actually preferable in many cases because of the abuse they took, and the idea that if one failoed, the collett or end mill hopder or boring head threads would survive with just a quick clean-up with a 7/16-20 tap. I still do this today, make my own drawbars. Before that though, bought probably 18 (I have 6 bridgies in a teaching shop) of the Bridgeport OEM type drawbars, they "went south" very fast in a teaching environ.

                          I make my own this way...Buy some 3/4 hex stock from a supplier like MSC, if just one bar, probably 12 inches will do, cut off 4 inches. Drill and ream a 7/16 hole in one end 2 inch deep, face and .125 chamfer the other for the wrench end. Buy 7/16 stock to the length requitred (probably have to buy 12 feet), cut off to your length desired PLUS two or three inches. Thread one end of the 7/16 stock 7/16-20 about 1.5 inches up using single point (whats a die?), lightly polish the other end and .100 chamfer.

                          Assemble....put 7/16 stock in reamed 7/16 hole in 3/4 hex, put in vise (I use a double vise situation, one clamped to hold the hex, one just floating and lightly "strap clamped" on the mill table to hold the 7/16 stock steady), ream a hole through both the head of the drawbar and the rod up 1" from the ream end. Put 3/16 roll pin in to hold together.

                          Next step, make a 1", 1/2" and 1/4 bushing for your Bridgie head, 1" diameter, .490 diameter, chamfer the edges .060. Use these to space the drawbar from the "head spline". Theas also allow you to cut the drawbar if the thread becomes damaged.

                          I was taught this years ago, many would prefer 4140 for the home shop, and in my home shop had I a bridgie, I woudl probably use the same. However, the 1018 in my teaching shop prevents that scary "overtightening" condition noobs tend to use, or that using the drawbar as a collett out hammer, which damages the end threads - which is why the spacers.

                          I will probably repair two to four drawbar ends during the few week of a noob class, then will not have to do it again until the next noob class but for the rare occurance. Before I made them, I had to buy new bars at the equal rate. With the Bridgeport OEM types of MSC Knock offs, they also caused collett or end mill holder problems, lost a few of these until I went home made. Brutal honesty, every problem I have with my home mades, I had with the store bought ones.

                          Just my 2 cents, do as you wish, for in machining, there are 1000 plus ways to skin a cat, and probably 999 ways are correct if they work for that operator (unless unsafe, then all 1000 ways are wrong).
                          CCBW, MAH

                          Comment


                          • #14
                            I used to buy new drawbars,2 at a time,one to run and one for a spare.

                            Then I switched to repairing them by welding on the grade 8 bolt.TIG or Mig is the best,they can be tweaked straight after the fact.

                            The bought bars typically lasted about a year,the welded ones three years.

                            No damage to collet threads whatsoever,

                            So that's x's 3 for welding on a bolt.
                            I just need one more tool,just one!

                            Comment


                            • #15
                              Well, perhaps I just don't know any better, but all I do is weld up the entire threaded area with either a mig or an AC-DC using a 7018 rod. I then put it in the lathe and turn the weld down to clean it up. Then use a micrometer to see how much more to turn down so that it is 7/16 when finished. You can then either single point or use a die to cut the threads. It works for me just as long, if not longer than a bought one.

                              Comment

                              Working...
                              X