Looking for a different way to tap a big hole!
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  1. #1
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    Default Looking for a different way to tap a big hole!

    Hi All,

    I'm sure there is a joke in the title somewhere, not too sure about these things.

    I make a part where it requires a 1-1/2" NPT female thread in silicon bronze, it REALLY tough stuff with about 30% the machinability of steel. 4130/4140 is easier to machine than this for reference, at least from my experience.

    I've used brute force a number of times, raw torque, bore the hole, taper ream the hole to size, and skip tooth tap. Regular tap will not work. I made a special "tap holder" from 2" hex stock, and use a 2" box wrench as the tap arm. It will stall a 7.5HP lathe in the lowest gear, it's just raw torque. It's really a hard way to do it, hard on everything, not to mention me. It's stressful to do that way.

    So we send them out to a machine shop, over the year we do about 500 pieces, batches of 75 or so at a time. $20 a pop and they do good work. The problem is they are going out of business, and it's a good time to look at options. They single point thread it on a CNC Mori something. I cannot buy their machine, and it will not fit in my shop. A little tight for space, not an option.

    So I'm looking at options.

    Currently the best idea is to CNC retrofit a spare Bridgeport and thread mill it. I have the Bridgeport (bought it from the shop), done plenty of CNC retro's in the past, very comfortable with it. It will fit in the budget, less that what I spend to send them out now. Plus I get a fun CNC mill to do some other small chores here and there, CNC mill is a handy thing to have around.

    But of course it's sometimes good to hear from others, If I convince myself this is the ONLY solution, we all knows how that goes. I don't want to drink my own kool-aid.

    So can anyone think of a better option CNC retro a mill and thread mill this large 1-1/2" NPT in silicon bronze? for under about $8K?

    All good ideas welcome.

    Thanks in advance.
    Aaron

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  3. #2
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    Quote Originally Posted by Aaron-M View Post
    So can anyone think of a better option CNC retro ...
    It'll be way cheaper and faster to pic up something that already works. In fact Ox has a running 5VC750 that will do the job nicely and cost less than what you are considering.

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    Post a picture of the part.

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    Definitely thread milling this large NPT is the way to go. As far as retro-ing a B-port..? I don't know. Not that it can't be done, but .... I would say get an inserted tool with correct pitch, faster than single pointing fo' sure.

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    Agree with inserted thread mill, but retrofit B-ports are so 1990, Small VMCs can be had on the same budget.

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    Can the part not be fixtured on to a lathe with a TA? .............taper thread screwcutting's very little different to parallel .

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    Limy's suggestion is good. A hydraulic tracer attachment will work even better if your lathe doesn't have a taper attachment. I would be a little leery about roundness of the tapped hole and its ability to hold pressure if thread milled on a retrofit bridgeport.

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    What about the hydraulic tapping arm from Flex Arm?, they are capable of doing up to 2"NPT they are almost $20K but well worth it for volume tapping. its a GH-60 model.

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    I have a factory retrofitted CNC knee mill. It does have ball screws and servos. I have thread milled thousands of 3/4"-10 holes in 1018 steel with it. I used a single point thread mill to keep spindle load and chatter down. You can just take a bunch of shallow passes and fight your way through anything.

    Thread milling is certainly more fun with a full form tool and 2 second cycles on a VMC. But run what ya 'brung and get 'r' done. ;-)

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    How about thread forming? Maybe use a series of taps to reach full diameter.
    Bill D

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    Quote Originally Posted by Bill D View Post
    How about thread forming? Maybe use a series of taps to reach full diameter.
    Bill D
    Thread forming 1.5" NPT in alu bronze?
    Not for faint hearted if you actually manage to find such a tap.

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    Good morning All:
    I agree with all of you who have invoked threadmilling as the best option.
    I also agree with gbent's point in post #7 about the roundness of a threadmilled bore done on a homebrew machine, and the potential consequences for sealing.

    AaronM; you have set some boundaries in your first post:
    You have a budget.
    You have space constraints.
    You do about $10,000.00 worth of these a year.

    The needed quality of these (implied not stated), the shitty material, the quantity, and the money you can get for these all imply you cannot fuck around with this without losing your ass.
    At 20 bucks apiece and a shop rate of 80 bucks an hour you have to drop a good part off the machine every 15 minutes and that doesn't even account for the carbide you use, the coolant you use, the setup, the handling, the inspection etc etc.

    You also state you've had good success with an outside vendor but they are going out of business.
    What is stopping you from just finding a new vendor?
    CNC lathes and CNC mills are a dime a dozen in every machine shop in the country now; there must be 10,000 shops in California who can do this for you.

    On a different tack, can this be a spur to get a machine of your very own too?
    If you do, I concur with all who have said you need a real machine...I think this is a bad project to cheap out on.
    A retrofit Bridgeport is marginal to do this kind of job at all, and in my opinion, it's a hopeless proposition if you expect to make money on these.
    A Haas like my 2001 Minimill would fit into a space not much bigger than the Bridgeport and could eat these parts for breakfast.
    I don't know just what my old machine is worth anymore, but I'm thinking you could get lucky and pick one up for 8 to 10K.
    You could also find a Hurco or a Fadal or a Milltronics or any other low end budget machine and be way ahead for this job and for others.

    Cheers

    Marcus
    Implant Mechanix • Design & Innovation > HOME
    Vancouver Wire EDM -- Wire EDM Machining

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    Maybe, it should be a "No Quote"......

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    Quote Originally Posted by MattiJ View Post
    Thread forming 1.5" NPT in alu bronze?
    Not for faint hearted if you actually manage to find such a tap.
    Thanks for the response. I obviously know nothing about thread milling except that it exists and not do to try it in cast iron. I guess it takes as much or more force then a cutting tap.
    Bil lD

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    Thanks for the options, Lots of good ideas.

    BT thanks, those are cool, can't use a flex arm, torque is torque. It doesn't have enough, plus we have to hold it, to squeeze it that hard is difficult.

    Blue, sorry, we never show our parts, not our thing.

    Thread forming takes more torque than cutting, maybe an internal geometric die head? Is there a such thing.

    Quote another machine shop in California, Not a chance, this isn't my first outside machine shop, last one screwed up a lot of parts. "The usual guy who runs them in in jail for a while, you got what you got...", California is an absolute waste of matter in the universe. That's why I can't get a new/bigger machine. I will be leaving this state Dec 31, 2021. Can't get too much extra stuff to move. New shop, get New VMC, make payments, no problem.

    So this is more of a 2 year solution, than a lifetime commitment.

    A Haas mini doesn't look too bad, and you're right it will fit in the space. A used 1997 Haas mini at the machine dealer down the street is $39,360. Yes boys and girls, $40K over 5 years, so there is some finance going on, but not cheap. I can get a TORMACH!!!! Think of the fun there!!! Even looked at those AutoMate CNC things, not bad, just have to move it again in 14 months.

    I Really, Really looked at/for a CNC lathe, just space and overall usefulness. Mill is more overall useful than a lathe. I was considering doing a 4th axis while I was at it this way you just set it at a constant rate, do a -Z cut and use the X to set the taper. Takes out the concentrically issue. Plus it's still NPT, it's a tapered thread for a reason, teflon tape anyone?

    KB, I think we're of the same mind, I got what I got. Single point and go. I just don't see another option.

    I didn't know if BP or someone made some cool clock work thing, remember we made a lot of cool things BEFORE CNC. I have a 1954 Delta/Milwaukee drill press mounted on a cast iron table that I am just about done rebuilding. It had something called a QuadDrill, like a turret for a drill press, just about the slickest thing you've ever seen. Great tool. Not like a Burgmaster, just different and really cool.

    I have a turret late, with a 1" bore, and can make a year's worth of parts in a day in a single setup. Is it faster than a screw machine with a chain feeder? NO, does it cost $250K. Nope.

    So, think simple, is there a PRE-CNC way to single point a thread?

    Thanks
    Aaron

    BTW: Just so you can think outside the box a little, Silicon Bronze doesn't play well with just about ANY drill bit bigger than 3/8". You can knock down the sharp edges and it will work without grabbing (much), but then it takes a lot of power to drill. BUT, if you get one of those $15 step drills, with the STRAIGHT cut up the size (not spiral) and grind it so size on a tool post grinder, you'll make reamer perfect holes all day long. It took a lot of really expensive bits to figure that one out.

    Thanks Again.
    Aaron
    Last edited by Aaron-M; 10-02-2020 at 10:34 PM. Reason: Added tip

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    Quote Originally Posted by Aaron-M View Post
    So, think simple, is there a PRE-CNC way to single point a thread?
    Sure, a thread mill. But they cost more and are harder to find than an nc machine.

    Why don't you just pick up a 325 Tree or similar off craigslist for five grand, then sell it off in two years ?

    btw, there are people in California who can do this. I could name four or five off the top of my head but don't want to embarrass them ...

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    I would single point them on a manual lathe with a TA , you should be able to do 5 in a hour...Phil

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    Thanks Emanuel,

    Looked that up, that's not too bad. Like a tool room mill.

    What is a thread mill in your context, what would be a machine name or something to look up?

    Yes, there are people in CA who can do this, just time to bring it in house, we've been over that barrel a few times and we're not playing that any more.


    Phil,
    I don't have a lathe it will fit in. The big lathe I use to tap them occasionally is my Dad's, so not my shop.

    Thanks
    Aaron

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    Quote Originally Posted by Aaron-M View Post
    What is a thread mill in your context, what would be a machine name or something to look up?
    Lees-Bradner, Wanderer make big ones, Pratt & Whitney made smaller ones and internals ? Externals are a lot more common, but even "common" in this case is pretty rare. Not to rain on that parade but pickin's are slim in the old-world threadmilling market.

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    If you are desperate enough, you could use a torque multiplier. You would need to have a way to drive it so that the tap stays in alignment (the reaction arm tries to push the tap over).


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