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  • I whipped up a little rotary broaching tool to use in my lathe, and tried it out to make my first hex head screw. It fits the Rivett lathe's eccentric toolpost, so I didn't have to worry about designing any angles into the tool. The toolpost is set to a 1 degree angle when using it. Centering it turns out to be really easy to do by eye if the the pilot hole is chamfered a little bit. The outer body of the tool is 1/2" diameter aluminum, and the inner spindle that holds the broach is mild steel. The end of the steel spindle is center drilled, and bears against a 1/4" ball bearing seated down at the end of the aluminum body, to act like a thrust bearing. The spindle will hold broaches with 1/4" shank, this first broach I made is a 4mm hex, and was made from O1 steel.

    Here is my 4mm hex head screw that I made to replace some missing hardware from a crib that was given to us, it is made from mild steel:


    And here's a shot of the broaching tool:
    Max
    http://joyofprecision.com/

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    • Max, that's really cool. Can you show some more detail pics of the broach itself, how you make it, and maybe a pic of it in action? I think I need to make one of these, any details you're willing to share would be great. How do you size the broach, is it exactly the size of the hole you want to make, or something smaller?

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      • Made a "hollow line tap" (the industry's nomenclature, not mine). It's obviously not a tap, just a tool for restoring threads in refrigerant line fittings. The commercial set I have is supposed to have the most common sizes but it doesn't have a 7/8"-14, which is what I need most often. So, I turned some "Scrapalloy", put a thread on it, cross drilled for a tommy bar and then hardened it. Haven't had a chance to use it yet, but it will sure as heck beat scraping the gunk out of a fitting with a pick.

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        • Welcome to the forum Tim. Nice job. Did you slot and then thread or the other way around?
          Location: Long Island, N.Y.

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          • Thanks Rich. I threaded first, cut the slots then drilled the hole. I don't have a mill (yet) so any slotting has to be done on the lathe. I figured it would be easier to have only thread to cut through.

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            • Drill press clamps. I got the design from Chrisb257 on YouTube. Having no mill, the rectangular bits were roughed out with a torch and angle grinder. Finishing was done through a lot of tedious four jaw chuck work and filing. All the material, except for some bits of 3/8" threaded rod, were yanked out of the scrap bin at work.



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              • Originally posted by Yondering View Post
                Max, that's really cool. Can you show some more detail pics of the broach itself, how you make it, and maybe a pic of it in action? I think I need to make one of these, any details you're willing to share would be great. How do you size the broach, is it exactly the size of the hole you want to make, or something smaller?
                I haven't forgotten about your request, I have some video footage of the broach in use, and I will be needing to make another cutter in a different size for it, so I will be taking some pics and video of that process too. My foray into making project videos is coming together pretty slowly. I have footage for 3 different short videos already but I think this rotary broach one will be the first that I finish so I'll let you know when it's posted.

                In the meantime, I can at least answer your question about the broach sizing, you make them the size of the actual hole you want to create (so, the size of the wrench you want to use plus a bit of clearance). The only thing different about the tool I made versus the others you can read about online (Mike's Workshop, for example, has a great writeup about these), is that mine is much simpler because it makes use of the oddball tool holder on my lathe. It only needs to be a simple round body, with the cutting tool angle set by using the graduations at the base of the tool holder. My design for the rotary holder would probably only be of interest to others with a Rivett or Hjorth eccentric tool holder.
                Max
                http://joyofprecision.com/

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                • Thanks!
                  Looking forward to the video.

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                  • I spent a bit of time making a die stock to fit a set of unused antique Wells dies that I found on e-bay a while ago. They seem to be an oddball OD (at least, I didn't have any luck finding a commercially made die stock that would fit them), so I made this from some scrap 2.5" round mystery steel and some 1/4" round drill rod.



                    Max
                    http://joyofprecision.com/

                    Comment


                    • Nice work Max, nice find with the dies too they look good quality, never seen dies with a built in adjuster.

                      Paul

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                      • Originally posted by _Paul_ View Post
                        Nice work Max, nice find with the dies too they look good quality, never seen dies with a built in adjuster.

                        Paul
                        Thanks! Split dies with screws for adjustment are fairly common (at least in smaller sizes), but these are the first I've seen with the screw going in through the front rather than the side. I ended up with a pretty decent selection of smaller sizes, just got lucky and caught it right after it was listed with a silly cheap buy-it-now (about $30 including shipping):
                        Max
                        http://joyofprecision.com/

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                        • Mars-Red,

                          Maynot be the correct place but YOU SUCK for this lot !
                          good find, some sizes there that I've never seen.

                          TX
                          Mr fixit for the family
                          Chris

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                          • Originally posted by Mr Fixit View Post
                            Mars-Red,

                            Maynot be the correct place but YOU SUCK for this lot !
                            good find, some sizes there that I've never seen.

                            TX
                            Mr fixit for the family
                            Chris
                            Haha thanks, yeah if I ever need a small diameter weirdo thread pitch I'm probably covered.
                            Max
                            http://joyofprecision.com/

                            Comment


                            • A while ago I needed to form a few holes of various sizes in some clear acrylic sheet, to make a little display holder for some coins (my 7 year old is turning into quite the little numismatist!). I ended up making a quick and simple miniature boring head for use in my LMS mini mill. It had no adjusting screw, and instead of a gib and gib screws it has a split and clamping screw so that the female dovetail is clamped in place over the male dovetail, to lock the position. This was fine for the task at hand, where the exact diameter of the bore wasn't at all critical. Afterward, I got to thinking that I could certainly add an adjusting screw mechanism. It was complicated somewhat by the fact that I had this clamping screw running right through the center of the tool, exactly where I'd want to be placing the nut for the adjusting screw. My solution was an offset nut. It took me several attempts to make an offset nut that fit and worked properly. Finally got the whole thing done, and it works pretty nice. The two black socket head screws shown in the pics are the only parts I didn't make from stock. The adjusting screw (and the tiny retaining screw to keep the adjusting screw in place) are both #4-40. Each graduation around the adjustment screw head represents 0.001" of travel. The bottom of the head is currently bored and reamed to fit a 1/8" diameter boring bar. As needs arise, I'm sure the bottom section of the head will be further machined to accomodate different arrangements.







                              Max
                              http://joyofprecision.com/

                              Comment


                              • Beautiful, mars-red! Did you design it yourself, or are there plans available?

                                Chuck

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