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How dangerous is this?

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  • How dangerous is this?

    Good evening gents. I apologize for the click bait like tittle but I didn't know any other way to word it. I recently bought a tida td-4a. It's a 10x24 lathe made in tiawain in the early 80s, like the Chinese made jet but heavier, and from what little is out there on the internet, a bit more rigid. It came with a Dorian tool post and the pictures will tell the story. While obviously not ideal, what is the opinion of the fine folks here as to how likely the tool post is to be ripped out of the compound, into the chuck, only to be launched into my pearly whites? I guess it's worth noting the base of the Dorian tool post currently in use fills the slot completely.


    Sent from my iPhone using Tapatalk

  • #2
    if the tee nut fills the tee slot I would not worry about it.


    • #3
      The lathe looks to be somewhat higher quality than some of today's units of similar size. I would not use that compound rest at all. If you have a mill I suppose you could shave those broken areas off all the way back to where they end and braze in some new pieces. Being OCD, I would probably also use some countersunk fasteners for insurance.

      No way to see if you could find a replacement or something close enough to use?

      Dan L
      Salem, Oregon


      • #4
        Not good. The remaining lips at the top are too thin and can break off easily. I would repair by milling off the broken parts and replace with 1/4" thick steel strips on each side with 3 or 4 flathead socket cap screws, then mill the assembly flat with a face mill or end mill. There is plenty of meat for the screws and the repair will last as long as the lathe.
        Kansas City area


        • #5
          Yep, fix it... many ways; I'd use Durabar (quality cast iron), mill off the entire top part and screw on another.


          • #6
            I find it not likely that a tool post T-nut would be ripped out of the compound under normal use and the downward force against the post, but...
            Looking at that compound, there doesn't appear to be much of a lip. It looks to be about 1/8". Way too thin.
            Poor casting, improperly fitting T-nut, swarf or other junk under the tool post when it was "over tightened" etc. could all have played a part in what happened.
            If you can't find another compound then welding may be the last resort.
            But before I did that I would mill a new T-slot out of a block of steel, make it oversize. Mill out the compound to accept the oversize part and screw it down in there. It looks like there is enough material around that slot to do that.

            Not sure what that hole is for in the front but it creates a weak point.

            Last edited by JoeLee; 03-11-2017, 06:37 PM.


            • #7
              It's likely not too "dangerous", but it is likely to be fragile. Might get launched, might just throw pieces of broken compound around.

              Looks like the whole thing was milled down to fit that post, is that a BXA or CXA? . You may simply be unable to use a QC post like that, due to a lack of room. The lips of the slot look like they would be too thin even if they were not broken.

              If you did put 1/4" plate on it, either the post would maybe not fit, or the t-nut would not fit. Do you have a pic directly from the side, with toolpost and a holder in place, showing the end of the slot AND the tailstock all at once? That would give a good idea where you are at.
              4357 2773 5647 3671 3645 0087 1276

              CNC machines only go through the motions

              "There's no pleasing these serpents"......Lewis Carroll


              • #8
                I would inspect the rest of the lathe, you dont do that kind of damage without messing something else up.


                • #9
                  Judging by the way the tool holder is sitting down so low that it seems flush to the bottom of the post itself I'm thinking that someone milled down the compound as well. And by doing so they didn't leave enough thickness.

                  The cutter side is pushing down. But the opposite side is pulling up. And the small residual amount of metal left is not all that much. And if it snapped out that much then what's left might be already damaged and just waiting to let go with a slight tug.

                  Clearly the tool post and size of the cutters being used is not a good fit for that size machine. I'd also second or third the suggestion to mill away the damaged area and repair it as suggested or by brazing on a couple of new slot lips.

                  The repair should be thicker than what is shown and after it's done follow up the repair with the replacement of that tool post for something more suitable to the machine.
                  Chilliwack BC, Canada


                  • #10
                    Originally posted by JoeLee View Post
                    Not sure what that hole is for in the front but it creates a weak point.

                    Holds the indexing pin and spring for the original 4-way tool post.


                    • #11
                      How dangerous is it? Well it got ripped out of there once, do you think it will happen again?


                      • #12
                        Do a cost/benefit risk analysis.

                        What is the chance it will fail, again? Probably somewhere between 1% to 50%.
                        What is the chance it will exit towards the operator? Probably 25 - 50%, especially if you see it start to wobble and make a grab.
                        What is the chance that it will do harm to the operator? Probably 90% to 95% ... it ain't gonna be nice.
                        What is the chance that it will hurt a lot? 95%
                        What is the chance of lost time? 80%
                        What is the chance of permanent injury? 10% to 40%
                        What is the chance it will kill you? 1% or less.

                        SO... now, figure out the costs of the losses...

                        Pain - I don't know, how much is being in severe pain for several days worth to you? Would you allow me to stab and mash your hand with a toolpost and cutting tool for $10,000 ???
                        Lost time - Assume you are out of work for 3 days. Will your boss understand? Will you lose pay?
                        Permanent injury - how much is losing a finger, or losing the use of your hand, or losing an eye worth to you? $10K to $200 K ?
                        Death - Well, most people behave as if their life is worth about $500K. Of course, if you have good life insurance you might consider doing your widow a favor...

                        So, multiply it all out... The chance of pain is about 0.1% to 20%... I'd put it on the higher end. If you are a gambling man, at 0.1% the expected loss for not repairing the lathe is only $10. If the repair costs more than $10 take the risk. BUT, at 20% the expected loss for not repairing the lathe is $2000. If it costs less than that, repair the lathe.

                        For permanent injury it's down to 0.01% to 0.04%... if you look at the negative payout, it's only a few bucks. The if I were a business owner risking your life, I'd go for it... And that is why juries assign penalties of over $10 million... At a potential payout of $10 M I'd be looking at a risk evaluated at around $1000 to $4000. Well worth spending the money to fix the lathe...

                        Same thing with death. The chance of death is really low... 0.001% or so... (of course these numbers are back of the envelope guesses, and could easily be wrong by a factor of 10). A gambling man would probably take the chance... But, if you have a wife and kids, you might want to consider how much it's worth it for your kids to grow up having a father... then again, the life insurance and re-marriage reduce that problem...

                        ME - I'd fix the damn thing before I used it. But I have an artificially inflated sense of self worth. I figure I'm one of a kind and pretty darned valuable.

                        It's up to you.


                        • #13
                          I had a similar thing happen, except the bolt holding it to the compound broke. i was cutting something on the order of an inch diameter at maybe 500 rpm and the chuck would have had to exert about 500 pounds of force on the tool to snap the 1/4-20 bolt due to the leverage.

                          I was quite surprised the 0.2" thick cast iron the bolt was threaded into held.

                          Anyhow: its fairly likely that if such a thing were to happen, the tool post would be caught by the chuck jaws and something will break, given that the chuck and spindle has fairly significant rotational inertial. would it be launched at the operator? i doubt it. if it did, what velocity would it have? 100, 500 feet per minute? 500 fpm is a 10 minute mile, that's 6mph. when people look at a lathe they might ponder the velocity of the periphery of the chuck, which often exceeds the surface speed of the cutting operation by significant factor, but its unlikely for anything to be launched at the operator at that speed unless its caught by the chuck.

                          weird **** happens, its not really possible to imagine every possible failure mode.
                          Last edited by johansen; 03-12-2017, 01:55 AM.


                          • #14
                            My thoughts exactly.

                            And it does look like the compound was milled down for the tool post to fit. That was wrong, wrong, wrong. The tool post is the member that should have been milled down. If you do repair it as Toolguy suggests, I would leave the steel thicker and either get a new tool post or mill that toolpost down.

                            Originally posted by Toolguy View Post
                            Not good. The remaining lips at the top are too thin and can break off easily. I would repair by milling off the broken parts and replace with 1/4" thick steel strips on each side with 3 or 4 flathead socket cap screws, then mill the assembly flat with a face mill or end mill. There is plenty of meat for the screws and the repair will last as long as the lathe.
                            Last edited by Paul Alciatore; 03-12-2017, 01:56 AM.
                            Paul A.
                            SE Texas

                            And if you look REAL close at an analog signal,
                            You will find that it has discrete steps.


                            • #15
                              I agree that it looks like the top's been milled to lower the height for the over-sized tool post. It need not be cutting forces alone that's pulled the top off but clamping forces too.

                              If I had to repair that and retain the use of that post I would mill off the remainder of the I would mill off the broken remains down below the top of the slide, mill the bottom of the slot deeper to accept the tee nut then either fix a pair of steel plates to form the top of the tee slot or make a single steel plate with an oval slot in it. A flat nut could be slid into the slot now and the bolt passed through the slot into the nut. Otherwise you could fit a square plate with a fixed-position bolt though it. Less versatile but more sturdy.
                              Peter - novice home machinist, modern motorcycle enthusiast.

                              Denford Viceroy 280 Synchro (11 x 24)
                              Herbert 0V adapted to R8 by 'Sir John'.
                              Monarch 10EE 1942