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Another machinist question

Discussion in 'Uncategorized Threads' started by quicky, Mar 24, 2008.

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  1. quicky

    quicky Member

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    Here is a question for a machinist more practiced than I: I have to drill and tap for a 1 1/4" x 7 thd. in a pump casing made of nihard. I have carbide tools I can perhaps bore a hole with but have only high-speed steel to tap with. There were holes tapped in the original casing from the factory but I do not know how they were done. I have thought of boring a larger hole and putting a kind of reverse hose barb arrangement inside the hole, then pouring babbitt into the hole and doing the threads in the babbitt. There is somewhat of a safety risk with hot liquor in the pump, we had an operator burned when the rotten threads pulled out of the case earlier, so I do not know if babbitt would be a safe alternative. A new casing is on order but won't be available until the end of May. Thanks, Quicky
     
  2. Haskins Bill

    Haskins Bill TS Member

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    Here is a thought. Is there any way you can mount the pump on the face plate of a lathe and bore and then cut the threads with a boring bar? I am guessing you are doing pipe threads, so you will have to use the taper atachment to chase the threads. I have done that in the past but it was external left hand pipe threads in bronze. Babbit does not have much of any strenth and will surely pull out under pressure. Maybe you could have a fitting welded to the outside of the casing that has the internal threads you need. I am assuning that the orginal threads that pulled out were one inch and you need to go one size larger to salvage the pump. Is 'nihard' a cast iron? Did a lot of this sosrt of things years ago at Allied Chemical/Plaskon in Toledo to salvage obsolete equiment. Good luck Bill
     
  3. 320090T

    320090T Well-Known Member

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    Is the pump casing turnable, meaning chucking it up in a lathe? If so, cut the thread on the lathe. Just tossing some ideas out....

    Bill beat me to the button but thats ok.
     
  4. TOOLMAKER 251

    TOOLMAKER 251 Active Member

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    Tap with a cobalt tap, Nihard usually is around Rockwell c low 50's to mid 50's no problem for a cobalt tap. It would make it alot easier if the tap was under the centerline of a mill or on center of a tailstock so you can keep the tap centered when you run it in.
     
  5. chrisg

    chrisg Member

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    I used to drill Molybdenum by heating to a dull red with a torch and drilling before it cooled. You could tap it the same way although the threads may be a little tight when cool, but you should be able to run tap back in it and chase the threads then. 1 1/4-7 is not a pipe thread, so obviously this is not a fluid sealing hole. You should be OK with this method.
     
  6. slowdp

    slowdp TS Member

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    "There is somewhat of a safety risk with hot liquor in the pump" - I assume this is not liquor for drinks - babbitt has lead in it. Better keep the lead for shot.
     
  7. quicky

    quicky Member

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    I will need to put the intake chamber on a horizontal mill and turn out the broken threads with a carbide boring tool. The hole is blind and about 7/8" deep. The original threads were 1" x 8tpi. I don't have a lathe with a large enough swing to turn the entire intake chamber around that hole centerline. My bigger lathe only turns 34" over the ways.

    There are warnings on the intake chamber concerning heating and welding. The bolt was previously welded in the field as a stop-gap repair that failed. Ni-hard cannot be welded safely.

    I will check into a cobalt tap and may be able to warm the casing somewhat. Cobalt should be able to tap fairly warm.

    When I was involved with a foundry casting HH20 we used to use a grooved piece of mild steel as a core in the mold. We would heat it bright red, place it in the mold in place of the Furan core, close the mold and pour the iron. That iron was about 700 Brinell and unmachinable as cast. The mild steel core provided a way to machine a tapered bore for mounting on a shaft. We had to heat the mild steel core and pour quickly so a cold piece wouldn't create stresses and also assure that the iron wouldn't chill and not flow around it.

    Keep the ideas coming, perhaps we'll stumble into a winning combination. Quicky
     
  8. dwmiller

    dwmiller TS Member

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    NIHard castings are a High Nickle/ Chrome iron casting with a good amout of Carbon and Carbide substraight. This part has been heat-treated and drawn to 52to 57 Rockwell C. Tapping with any tap will be tough. Especially a coarse thread like a 7 pitch and with a dia. of 1 1/4". Couple options: talk with the casting manufacture and see if it can be annealed, then re-heat-treated. Best option. Annealing will bring the hardness down so that it can be worked. Last option go to a machine shop that can Thread mill the casting. Using a carbide thread mill might be your only option. The annealing process should be done by a heat treat shop as to rapid of cooling can crack the casting as can heating outside of the tempering range.

    Good Luck
     
  9. JEB

    JEB Active Member

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    Can you make a counterbored hole in the casting? If so, how about doing that and making an oversized plug with a flange. Thread the plug id, freeze it in dry ice and press it in. Then drill a dutchman centered on the edge of the flange and casting, use a cobalt or T-15 drill, secure it with a pin that has also been shrunk. If you cannot bore out the hole, is there someone near with a Bullard or horizontal boring mill? They should be able to help you.

    JEB
     
  10. austin fatts

    austin fatts TS Member

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    Is it possible to make a threaded plug, maybe with 7/8-14 type thread. Then bore out the old thread to the 1.250 dia and press in the plug and then possible stake the plug?? Maybe you don't have that type of room and it probably is a sealing fit.

    Austin
     
  11. chrisg

    chrisg Member

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    You did not originally say it was a blind hole. Forget about tapping it because you won't have enough thread depth with the lead on the tap to be safe. Even if you use a bottoming tap it will be short, not to mention next to impossible to cut with no tap lead. The only way to do it right is with a thread mill as dwmiller stated. With that you can get full threads right to the bottom of the hole. Where are you located? I could fix you up if you are close.

    http://inlinethumb51.webshots.com/41330/2044315020055382454S425x425Q85.jpg

    This is what I would do it on. My newest acquisition. Mazak QT350MYII. 4axis Mill Turn Center. You can see in the picture I am threadmilling the outside holes on this part. I can do the same on the front just using a horizontal holder instead of a vertical one. I think I have a 7 pitch thread mill in stock to use also!
     
  12. chrisg

    chrisg Member

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    Sorry about that. Here is what I am talking about.
     
  13. j l c

    j l c TS Member

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    You could possibly mill the threads if someone near you has a capable CNC
     
  14. quicky

    quicky Member

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    The loctite/plug option is probably a good one. The only reason I hesitate about it is that, as good a Loctite is, we have a safety problem. In the last instance someone tried to use a liquid metal to secure the old stud in place. It is simply a take-up stud to adjust runner clearance in a pump intake. As the liquid metal failed it allowed the pump bearing column to move away from its setting in the case and the expeller rubbed the back of the intake chamber and the pump failed catastrophically, burning an operator who was trying to switch valves on an adjacent spare pump. The liquid temp. was > 180 degrees F. and luckily the operator was able to get to a safety shower nearby and get cooled off before the burns went past 2nd degree.

    I hesitate to press or shrink in a plug because of stresses which may cause failure in the casting. An EDM would be great...any near S.W. Wyoming? I know of none but will certainly check around! Thanks for all, Quicky
     
  15. austin fatts

    austin fatts TS Member

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    I agree there are some very good LOCTITE products available, but with heat involed I would be suspect of LOCTITE over the long haul. May I ask at how threading with a EDM is accompished?? Does it interpolate the threads similar to a thread milling op?? Doesn't someone build shotguns in Sturgis SD?? Contact them.

    Austin
     
  16. dwmiller

    dwmiller TS Member

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    A Robo Sinker EDM is a great idea. Trouble is they are not that common unless you have a lot of mold shops in your area. Look in the phone book for your area under mold makers. Most will have a Robo EDM attachment. If not Thread Milling is the way to go.
     
  17. 100straight

    100straight Member

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    Do you have any clearance on the inside of the casing? If so, maybe you can bore the casing and then machine a steel insert with a lip on the inside so it cannot be blown out. I'd machine it a couple thousandths oversize, pre-thread it, heat the casing, freeze the insert, and put it together quick with a locking agent of some sort (ie. locktite).

    Another option, if you don't have any inside clearance, might be to bore the casing from the inside with a tapered reamer, then machine a tapered steel plug to fit. If I were using this method I would press the plug in place, and then drill three angled 3/16" holes through the plug and into the casing. I would drive 3/16" spring pins into these holes to lock the plug in place.

    Just a couple of ideas I have used before. Hope they help.

    Shoot well and often,

    Mark.
     
  18. quicky

    quicky Member

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    I have sent the casing to a shop in Salt Lake City for EDM threading. This looks like the best option at this point. Thanks everyone! Quicky
     
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