What are cheap method to turn the threads off a bolt?
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  1. #1
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    Default What are cheap method to turn the threads off a bolt?

    I "make" and sell this tool:

    cam_bolt_04.jpg


    Not a lot of them, but enough that I'm annoyed about the concept that I know there's something I'm doing wrong.

    The consistency is poor. I have a holder that's got some threads, I screw in the bolt, chuck the holder in the lathe (cheap 12x36) and I machine off the threads at the end. It breaks the general rule of being 3x the diameter out from the chuck but I've got the process down pretty well. I've been doing small batches of these for 6 or 7 years. I use a bar with an insert on it behind the part, run the lathe clockwise, first cut of 0.030" off from the end by hand, then move the cross slide in another 0.020" and I use the power feed to cut away from the chuck. I've played with speed and feed as well as depth of cuts to get it almost perfect. But there are always lines in the final part. I've always sucked at machining steel, so I don't usually fret it.

    What are the various ways a small shop could machine this bolt? I'm taking off about 0.050" from the outside of the threads, or 0.100" diameter overall.

    Or is my issue that it needs finishing? (I'm not too excited about more operations, honestly)

    Thanks for your thoughts - long time reader, first time asker,
    Chris

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    Is the "holder" you screw the part into slit so it can give some squeeze onto the screw? I suspect it isn't. If its not thats your problem right there. the clearance in threads is allowing the bolt to weeble wobble as it gets turned.

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    I my experience, store-bought bolts can be made of some pretty gummy steel, and it may be difficult to get a god finish.

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    If you are going to use a holder +1 for split, springy & unthreaded. Best would be a cylindrical collet affair with three slots made slightly bigger than the end knob and long enough that when the head butts up at the end leaving only a little more than the the aprt to be turned down showing. Position slots opposite the jaws in the three jaw, turn on the coolant / lube and take it down in one pass. Commercial bolt metal is made to be worked hard and fast. Pussying around gets you nowhere.

    I've done a few jobs similar stye in small quantities, 10 to 20 or so in a batch. Never bothered with a holder. Straight in the three jaw, nipped up with a bit too much sticking out. Push back with "pusher" in the parallel to bed QC holder station until saddle hits appropriate rod in 6 way turret bed stop. Tighten up. Pull pusher off QC. Fit tool and set to cutting dept. Quickest way to set cut if you don't have a cross slide stop, few lathes do, is to adjust the dials so cut depth is on zero. Click bed stop round to cut position and have at it. Probably do two in the time it took to read that. A hate-em job so it gets done fast!

    Clive

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    You did not state what size screw. Perhaps a ¼ - x 1 ½? Plus United States is not a very good location perhaps add the state.
    You might measure the screw solid portion diameter.

    Take a slug of ¾ dia x 3/4" long CRS and drill it 1/2" deep with + .003 to the average shoulder size. Then drill the remining ¼” for the thread tap drill and tap it to the thread. Now split the part perhaps with a hack saw (or better) long way.
    With this you screw in your bolt, put it in the 3 jaw. One hand tight the T wrench and turn the part, using perhaps 1 1/32 radius tool bet or insert. The saw cut will allow to hold the screw tight. Will tighten up on the thread and be as solid as you might get..

    Might drill slug with 6.5mm or an F drill for about .257..for the shoulder part/ OK
    might just sharpen a 1/4 drill with point .002 off center and get a slip fit.

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    your kidding right? this is machine shop 101.
    make or buy a split bushing for the Dia of shoulder.
    place bolt into split bushing with just enough needed hanging out to cut.
    then cut.
    with a 5c collet on a lathe you can make one ever min or so with a chuck every 2 mins.
    its stupid simple

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    Chamfer tool & Roller box - job done.

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    I needed to make a short run of these on a 10x48 lathe.

    library-punch-pin.jpg

    I was starting with .250 stock, and had to cut the .092 pin portion at 4.7 l/d ratio without the benefit of a tailstock or other support. I stole a technique from Joe Pieczynski ( YouTube ). I was using HSS to cut O-1 drill rod and took a .079 cut in from the end toward the headstock. This way all the cutting forces were compression into the chuck, not pressure against the remaining stock. Joe went from 1/2" to .030 in the video. Here's the start of the money shot: YouTube .

    I was trying to do the entire pin in one clamping, so I actually had about 1.2" hanging out of the chuck when I cut the .092 x.440 pin portion.

    I just read the posts that came up while I was typing. If you are making a bushing or using a collet, don't plan on the nominal size of the bolt if you are holding on the un-threaded portion. I found out the hard way when I was converting hex bolts to square head bolts. Most threads are rolled, and the diameter of the bolt is probably significantly under nominal size in the un-threaded portion. I know on the 1/4" bolts I was using the size was below what a .250 5C collet would hold.
    Last edited by wheels17; 04-25-2019 at 05:17 PM. Reason: One more comment....

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    There is these things called "Lathes" there all the rage these days.

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    I agree with the others that thread clearance is the source of you problems. A nut on the last threads could help.
    But if the guess that is a 1/4 20 thread is correct I think I could turn it in 2 or 3 passes while holding on the shank(unthreaded)with a collet. A positive rake insert or tool bit would not push the screw so hard that you would have problems. I think you are over thinking this by trying to hold it with a threaded bushing.

    If holding the shank does not work out then I would chuck on the threads with a collet. It is not really that long.

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    How about a box tool or hollow mill?

    Tom

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    How about turn the end down then use a live center with a female cone or a follow rest.
    Bill D.

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    There are quite a number of different stock bolts available and you don't say which you are using. From what looks like a pressed on head, I am guessing that you are using some kind of SHCS (socket head cap screw) which means that it is probably harder than a common, hardware store, grade 3 bolt. Grade 5 perhaps or even grade 8?

    The threads on most bolts are produced by a rolling process and the steel alloy is probably selected with that in mind. So it is not going to be ideal for turning in a lathe. That does not mean that you can't turn it but it does mean that it is not ideal for that.

    I have made parts from the common, grade 3 bolts and the finish is a problem. For my parts I made a custom collet that first grips the bolt by the OD of the threads. It does not use a female thread form, just a bore with a slightly larger diameter. It does not distort the threads on the bolt because there are enough of them for a good grip. I believe this would also be the case with your part: you do not need a female thread in your collet. And avoiding screwing it in would save time in your process.

    Even with the sharpest tooling, you are not going to get a "perfect finish". I don't even though my custom collet does hold them very firmly with no wiggle room. And I use a tailstock center as well. The bad finish is just due to the steel alloy. I leave about a half thousandth for abrasive finishing. I use strips of sandpaper that are wet with cutting oil in a shoe shine rag fashion. Starting with a 150 grit and working down to about 600 or even 1000 grit I can get a very nice finish, approaching a mirror finish if I take enough time at it. I am only talking about a minute or two of machine time per part. Of course you can stop when you feel it is good enough. If the diameter must be constant with a tight tolerance, then you may need to use a lap. But for a cosmetic finish the sandpaper strips will be just fine.

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    Da fuk?! It's a cap screw with a press on cap....make a split collet to go in the chuck, leave the threads showing and turn the threads off using an inserted tool. Yikes why make it complicated.

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    Quote Originally Posted by Limy Sami View Post
    Chamfer tool & Roller box - job done.
    That's cheating! Nobody and I mean nobody has a turret lathe just sitting in their
    basement....

    Oh. Wait.

    Never mind.

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    Quote Originally Posted by wheels17 View Post
    I needed to make a short run of these on a 10x48 lathe.

    I just read the posts that came up while I was typing. If you are making a bushing or using a collet, don't plan on the nominal size of the bolt if you are holding on the un-threaded portion. I found out the hard way when I was converting hex bolts to square head bolts. Most threads are rolled, and the diameter of the bolt is probably significantly under nominal size in the un-threaded portion. I know on the 1/4" bolts I was using the size was below what a .250 5C collet would hold.
    Again Machine shop 101.

    Measure the size of the shank that your going to hold on(which I assumed was obvious) MAKE Split bushing to that size.
    if you have a 5 c collet then you can Make a split bushing to fit into lets say a 3/4" dia 5c collet so you dont have to tighten the chuck and loosen the chuck with a chuck ket everytime. plus you can have a nice stop set-up for length in a 5c or other collet.

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    Quote Originally Posted by plastikdreams View Post
    Da fuk?! It's a cap screw with a press on cap....make a split collet to go in the chuck, leave the threads showing and turn the threads off using an inserted tool. Yikes why make it complicated.
    Exactly, someone is machinist

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    Quote Originally Posted by Delw View Post
    Exactly, someone is machinist
    Not the op

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    Simple.
    1. Make a properly dimensioned & toleranced drawing of part.
    2. Post it at the "resources" sub-forum.

    Easy Peasy

    No more pissing around with bad finishes, etc.

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    The OPs threaded bushing shouldering out to hold the part, Then turning into the right hand thread seems likely to loosen the hold (back out the thread) and free the part if any aggressive turning is done.

    Might not be a bad idea to simply split that bushing for a better holding device,holding in the 3jaw, with not threading screw so tight so it might lock on threads and not need shoulder step hold

    Agree tool geometry rake angles, sharpness, nose radius are in play for best surface finish, the OPs problem.

    I have run some poor finish jobs with a small flat nose hone of perhaps .010 at the intersect place of a HSS tool bit for better finish.

    Simply running a test part held in the 3 jaw to the shoulder would tell if holding on the shoulder with a split bushing with all threads sticking out would work, would help, or would not.

    Split bushing so less cranking the chuck for part change, getting past the 3/8 screw head.(guessing it may be 1/4")


    Some times you see a guy grinding on top of a threaded part the way the grinding would un-screw the part, when often just grinding on the other side for screw-in direction would be safer.

    *Question to the Op..what are you using to hold the cap?


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