A thread on threads (screw threads, that is)

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  • A thread on threads (screw threads, that is)

    I had to replace one of the hex button screws on top of the BT3 fence (they are for aligning the fence to the blade). Anyhow, the screws appear to be 1/4"-20 but when I got the new screw home it only threads half-way in. The new and old threads line up by eye "exactly" and also screw into the same 1/4" nuts BUT again on the application on the fence, it only goes in 1/2 way... and it goes in easily until that point.

    SO... what is that a symptom of? And, should I use a 1/4" 20 tap to re-thread (i.e. clean up) the holes? Cautionary notes and alternatives requested.

    Thanks,
    David
    Never met a bargain I didn't like.

  • #2
    David

    Check the parts list to see if it is a 1/4 x 20. If it is being cross threaded it probably won't go half way. Could it be too long, or hitting something? Take the BT3 bolt and see if it threads into a 1/4 20 nut. BT3 may be metric.



    "I'M NEVER WRONG - BUT I'M NOT ALWAYS RIGHT"

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    • #3
      Originally posted by cabinetman
      David

      Check the parts list to see if it is a 1/4 x 20. If it is being cross threaded it probably won't go half way. Could it be too long, or hitting something? Take the BT3 bolt and see if it threads into a 1/4 20 nut. BT3 may be metric.



      "I'M NEVER WRONG - BUT I'M NOT ALWAYS RIGHT"
      The FAQ says everything on the BT3 is SAE, not metric.
      for some reason, I'm a firm believer in the FAQ.

      Look in the articles section here. This parts explosion of the BT3100 says its a 1/4-20 x 5/8 button head.
      http://www.bt3central.com/articles/f...32_r_sheet.pdf


      so that says you have the right screw. Something else therefore is wrong.
      1) Why are you replacing this screw? Sounds like something traumatic happened.
      2) Did it come out OK?
      3) or ???
      Last edited by LCHIEN; 08-08-2006, 10:18 PM.
      Loring in Katy, TX USA
      If your only tool is a hammer, you tend to treat all problems as if they were nails.
      BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

      Comment


      • #4
        Originally posted by LCHIEN
        1) Why are you replacing this screw? Sounds like something traumatic happened.
        2) Did it come out OK?
        3) or ???
        Dang it Loring, why did you have to ask? I was trying to skirt around this issue of the "why" since everyone (i.e. you) already know I managed to break a roll pin on the mortiser. OK OK, yes it's true! I was trying to loosen the screw in order to align the fence and I managed to strip the hex head. Both screws were very resistent... should have used WD40 but they weren't rusted or anything... the first one came after some effort, the 2nd didn't.

        Anyway, I was able to extract the screw and remove it. No damage to the threads as far as I can tell... and before you finish the thought... you should know that the new screw won't go into either screw hole so it seems unrelated to the incident (about which we will never speak again!)

        Btw, I think part of the trouble is due to the way the fence is constructed. There is a spring on the inside that is applying pressure in effect pulling the outer aluminum shell one way and the inner casting (in which the screws seat) the other way.

        Now, I'll ruin the other surprise to be elaborated on elsewhere... I also have a BT3000 (we're previously discussing a new BT3100 bought in April or so) and that older machine does have rusted over screws... one of which came loose with WD40, the other sits there mocking me. I refuse to strip that one out. (So, I will need advice on getting that one out... without the drill!)

        So...
        1) what to do about the new screw? shall I re-tap it to 1/4-20?
        2) what to do about the old BT3000 screw that won't come loose either.

        Btw, I have so far opted to replace the screw with another hex button screw... but since the 2nd machine is also trouble... I am thinking maybe going with a Set-type hex screw (deeper, larger hex) or a hex-head bolt type of screw. (i.e. the first uses allen wrench, the 2nd socket wrench)

        Thoughts??
        Never met a bargain I didn't like.

        Comment


        • #5
          I suspect you've got the wrong thread!

          The type of screw that you've purchased is also available with a 1/4-28 thread, in addition to the 1/4-20 thread that is spec'd, and would perform in the manner that you've described.

          I would check that Screw very carefully to make sure it is, in fact, the proper thread.

          A 1/4-28 Screw would partially engage, very much as you've described, but would not fully engage as it should. Visually, the difference in the Thread Pitch is less than 1/64" and would be very hard to see, if you're not used to looking at that sort of thing.
          Last edited by gmack5; 08-09-2006, 02:45 AM.
          Stop thinking why you can't and Start thinking how you CAN!
          Remember, SUCCESS comes in CANS!
          George

          Comment


          • #6
            Far as getting that old screw out: One thing I'd try is cut a slot in the head with a Dremel. Then try a large flat screwdriver. Another option is cutting or grinding its head on two sides to create flats a wrench can grab. I second the 14-28 theory. Had a similar thing happen when I bought wrong nuts to use with a 3/8" threaded rod.

            Comment


            • #7
              He says the threads of the old and new screws line up exactly by eye; the difference over only one thread would indeed be difficult to see but over four or five it would be obvious. Also, a 1/4-28 wouldn't go halfway in before stopping but would stop almost immediately.

              David, where did you buy the screw? And have you tried another one? That it won't go into either hole provides what I regard as the best clue. You may just have a bad screw. Lately the quality of the fasteners you get at regular retail outlets like HD and Lowe's has been CRAP. The other day I was putting together something-or-other and found a couple of the bulk-purchase hex bolts I had on hand suffered the exact same problem you're encountering.

              Re: getting the other screws out ... I never can remember exactly how this goes, so you may need to do some experimenting ... I think the fasteners on the BT are SAE, but I found that the nearest metric-size allen wrench fits the screw head MUCH more snugly than the "correct" SAE size. Either that, or the head is in fact metric. In any case, try both SAE and metric wrenches and use the one that fits tightest. The one I use goes in so snugly that at first blush it almost seems like it's too big.
              Last edited by LarryG; 08-09-2006, 08:28 AM.
              Larry

              Comment


              • #8
                Originally posted by davidtu
                Dang it Loring, why did you have to ask? I was trying to skirt around this issue of the "why" since everyone (i.e. you) already know I managed to break a roll pin on the mortiser. OK OK, yes it's true! I was trying to loosen the screw in order to align the fence and I managed to strip the hex head. Both screws were very resistent... should have used WD40 but they weren't rusted or anything... the first one came after some effort, the 2nd didn't.

                Anyway, I was able to extract the screw and remove it. No damage to the threads as far as I can tell... and before you finish the thought... you should know that the new screw won't go into either screw hole so it seems unrelated to the incident (about which we will never speak again!)

                Btw, I think part of the trouble is due to the way the fence is constructed. There is a spring on the inside that is applying pressure in effect pulling the outer aluminum shell one way and the inner casting (in which the screws seat) the other way.

                Now, I'll ruin the other surprise to be elaborated on elsewhere... I also have a BT3000 (we're previously discussing a new BT3100 bought in April or so) and that older machine does have rusted over screws... one of which came loose with WD40, the other sits there mocking me. I refuse to strip that one out. (So, I will need advice on getting that one out... without the drill!)

                So...
                1) what to do about the new screw? shall I re-tap it to 1/4-20?
                2) what to do about the old BT3000 screw that won't come loose either.

                Btw, I have so far opted to replace the screw with another hex button screw... but since the 2nd machine is also trouble... I am thinking maybe going with a Set-type hex screw (deeper, larger hex) or a hex-head bolt type of screw. (i.e. the first uses allen wrench, the 2nd socket wrench)

                Thoughts??
                Yeah I always ask the hard question .

                First of all, to address the other comments, a 1/4-28, while the same diameter and thus confusing, looks quite readily different in thread pitch than a 1/4-20, you can easily tell by eyeball when side-by-side, so I don't think that's the issue.

                Another issue - in the past, for stuck screws, other BT'ers have used a sharp rap with a punch on top of the screw before loosening.. Penentrating oil (not WD-40) may help, too.

                If you manage to round off the hex recess, use a dremel tool and a rotary blade to cut a slot so you can use an ordinary screwdriver to back it out.

                As for determining whether the screw is bad or the hole is bad,
                if the screw goes into other 1/4-20 holes OK (e.g. the second hole, and 1/4-20 nuts, etc) then it is probably OK. If other screws, just for testing, go into that hole in the Fencetop OK, then that hole is probably OK. If either test fails, then you either need a new screw or to clean out the hole with the correct sized tap. It should be obvious which to do! So if you already said the new screw won't go into either hole, you need a new screw or to run the bad screw through a threading die (we only tap holes). If you don't have a threading die to rethread the screw, examine it carefully and see if there is a shard of metal in the threads you can pick or file out, sometimes you can use a nut to rethread a bolt (not truly recommended because the nut is no harder than the bolt!).

                It's rare but ocassionally you get the one screw that seems to be OK and the one hole that seems to be OK, but they just won't mate. perhaps because they are each at the opposite end of tolerance range or something. In that case just swap screws.

                P.s. with the price of screws being relatively cheap (compared to the time and gas to go to the store again) I never, ever just buy one...
                you have two in the fence, you already broke one, you may drop the other etc. Murphy says if you have a spare you won't need it but if you don't, you will.

                I also standardize around 1/4-20 in my shop, I have drawers full of hex head bolts in different lengths, nuts, wing nuts, tee-nuts, knobs, all-thread, etc in 1/4-20 size.
                for new and old jigs and repair work.

                P.S. I suppose it doen't hurt to ask - the new screw is the same length as the original? that is 5/8" long?
                You do know the rip fence has some hardware inside that a long screw may hit.
                Last edited by LCHIEN; 08-09-2006, 10:47 AM.
                Loring in Katy, TX USA
                If your only tool is a hammer, you tend to treat all problems as if they were nails.
                BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

                Comment


                • #9
                  To get the stuck screw loose first try a sharp hammer blow while trying to turn the screw. If that does not work try to tighten before trying to loosen. Next you may want to try heat, do so carefully!

                  If all of the above does not work then it is time to use the dremel approach.
                  Donate to my Tour de Cure


                  marK in WA and Ryobi Fanatic Association State President

                  Head servant of the forum

                  Comment


                  • #10
                    Originally posted by LarryG
                    <SNIP>
                    David, where did you buy the screw? And have you tried another one? That it won't go into either hole provides what I regard as the best clue. You may just have a bad screw. Lately the quality of the fasteners you get at regular retail outlets like HD and Lowe's has been CRAP. The other day I was putting together something-or-other and found a couple of the bulk-purchase hex bolts I had on hand suffered the exact same problem you're encountering.
                    </SNIP>
                    QFT, I bought a box of toggle bolts w/ the screws in the box the other day at home depot I think there were 4 or 5 bolts and screws in box, I think 2 of the screws would actually thread in to the bolts, 1 screw was the wrong size completely.

                    Comment


                    • #11
                      I'm wondering if the reason that the screw only goes in half way is that it is hitting something.

                      Example. On my Old Wrangler, there are two bolts on each side of the windshield. If you remove both at the same time, a bracket inside can get out of place making reinstallation very difficult. Many attachments go on this sot and all tell you to remove them one at a time so that something is always holding the bracket in place.

                      So, Could it be that something has shifted inside just enough to not allow the screw to continue on it's true path?
                      Mike
                      Lakota's Dad

                      If at first you don't succeed, deny you were trying in the first place.

                      Comment


                      • #12
                        Resolution--

                        Thanks to everyone for your excellent suggestions and advice. You guys are the best!

                        Long story short, I was able to get the old fence's screw loose today just by applying a reasonable amount of pressure w/ the allen wrench. Maybe WD40 worked overnight, maybe I was just in a better mood to do it w/o stripping it.

                        Regarding the new fence and the screw that stripped and couldn't be replaced b/c the new screws (not screw, btw, but screws) didn't seem to want to go in... once I got the old fence screw to give I took it out cleaned it up and screwed it into the new fence's hole and it must have cleaned out the threading (for some reason the new fence's 2nd screw tho it went in both holes fine didn't seem to cleam 'em out)... and so now all of the four new screws I'd bought screwed in fine.

                        The new screws are, for the record, 1/4-20 x 1/2" .. the original screws are a hair shorter than this but with the washer and fence in place the new screw does not come down too far to hit the bar inside, so no worries.

                        Fence works fine again. NOW, to adjust that 1/32" misalignment that started all of this. Talk about "ask for an inch, take a mile!"

                        I now have an arsenal of ideas to attack the next stubborn screw. Thanks again!

                        Regards all,
                        David
                        Never met a bargain I didn't like.

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