Help! Boring a tapered hole?
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  1. #1
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    I bought a Bownell's barrel vise, stock number 080-860-307, recently. I want to make some additional aluminum barrel bushings. I have secured a 21" piece of 6160 2" diameter. My question is; How do I bore a tapered whole through the center of the stock to match a FN FAL barrel that I want to install on a reciever? I would appreciate some ideas! Thanks! Virginia Jake

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    Here's a thought. If you can't measure and determine the exact taper of the barrel you want to clamp, simply bore a piece of the aluminum a little big, then use the barrel as a form and bed it to the aluminum sleeve.
    Clean the bored piece, aply release agent to the barrel (I use Johnson's Paste Wax), then use Marine-Tex or similar epoxy to form the bedding to the barrel OD and you have an exact fit! Let it cure for a couple days and use some resin when clamping it. You should have no problems.

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    Measure the barrel were you want the bushing to fit, and 1 inch farther down its length. Subtract the small end from the larger one, and divide by 2. Set up a stright bar, place an indercator on the tool post and adjust the compound till the indercator reads the same as what you got from the math above in 1 inch of compound travel, drill the throu hole smaler that the smallest dia and bore.

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    "Set up a stright bar, place an indercator on the tool post and adjust the compound till the indercator reads the same as what you got from the math above in 1 inch of compound travel"

    Kurt,
    What do you mean by "Set up a stright bar"? Do you mean, "set up a sine bar"? I have read about this in the past but dang if I can remember how to do it. Can you point me to and article or some thing so that I can re read this procedure? I have turned a couple of 60 degree points on stock in the past using the compound rest. I did not indicate this in. I just used the degree markings on the compound.

    rws,
    I had thought of doing the over bored and filled with Acraglas as this might be a one off project, but then I thought that it might be a good idea to try and bore the hole correctly just for the fun of it. The bushings are three inches long, and 1 3/4" in diameter.

    Thanks for your replys,
    Virginia Jake

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    Not a sine bar, just any round bar that is stright, can even use the OD of the part your going to bore. You do it the same as the 60 deg you turned, rember that 60 deg is the included angle ( both sides ) so the compound is set at 30 deg. thats why you divide the def. between the small an large ends by 2. Find a coppy of "Machinery's Handbook" it has lots of neet stuff in it to read.

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    G’day Virginia Jake,
    I normally do what Kurt suggested, I find it quicker than messing around with epoxy.

    To test my setup I usually use a scrap of anything that is large enough in diameter not to deflect too much over the length you are turning. I then turn the outside of the scrap bar, using the angled top slide so that the difference between the larger and smaller diameters matches that of your barrel over the same distance.

    Good Luck, Paul.

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    Okay fellas, here is what I came up with.

    First I measured one of the barrel bushings that came with the vise that I ordered from Brownell's. I found that the over all length of the one that I measured was 3.015" long. I will round that off to 3". Next I measured the barrel that I intend to make this bushing for. I found that the taper that I want to duplicate is 0.7867" in diameter at the large end, and 0.7418" in diameter at the smaller end (three inches away). Using Kurt's formula: (D-d) divided by L, then divide by 2 where:

    D=large diameter
    d=small diameter
    L=length of taper
    divide by two because we are turning the taper all of the way around at the same time.

    So, plugging in the numbers:
    0.7867 - 0.7418 = 0.0449

    0.0449 / 3 = 0.01496

    rounding up to 0.0150

    0.0150 / 2 = 0.0075

    Check me fellas and make sure that I did that right!

    The next part is what I have questions about. Here is what I have done.

    I have broken out my old machine shop text book. I looked up "Tapers on a Lathe". I read the bits about using a taper attachment, and tail stock set over, and using the compound slide. I think that I am correct in my understanding that tail stock set over only is useful to turn external tapers. I do not currently have a taper attachment. So that leaves me with turning an internal taper using the compound side on the saddle.

    Here's the part that I need your advise on. If I understand this correctly, I should mount a piece of round smooth stock between centers, checking to make sure that it is running true. Next, I think that I should turn the compound slide parallel to the bar, and indicate it to run "0" when advancing the side toward the head stock. Next, I think that I should turn the front of the compound slide toward the round bar mounted between centers and indicate 0.0075" when, a) starting from "0" on the dial and b) advancing 1" toward the headstock, the dial should read 0.0075".

    Okay gentlemen! Do I have this right?

    If this is right, what do I do when my compound side will only advance a little over 2"? I am guessing that I will have to set the apon over toward the headstock at some point, and bore this bushing in steps.

    Your help is greatly appreciated!

    Virginia Jake

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    Hey Paul McC,

    Thanks for your reply! I just re read it for the fourth time! Bingo, the light bulb went on in my head!

    Assuming that I am correct on how to set the compound slide, I can check the set up by turning an external taper first on round stock. If the set up is correct, I can switch over to the boring bar set up and use the same settings. Is that correct?

    Thanks!

    Virginia Jake

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    You could have done the epoxy by now. I make tools all the time when needed, but some things just aren't worth the time and effort. I started doing this when taking off a Rem. barrel. I like to clamp the barrel as close to the receiver as possible, and with the Rem. barrel, that puts it right where the contour is. Kinda hard to machine that radius on the inside of a block. Besides, the epoxy way ensures there will be not scarring of the barrel.

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    rws,

    You are correct sir! I may still do the epoxy dance! I could take one of the big (large internal diameter) bushings that I will probably never use, suspend the barrel vertically, clamp the two halves of the bushing around it, (spacing the two halves of the bushing appart so that the complete assembly measures 1.750" in diameter, damning up the bottom of the assembly and fill that sucker up with epoxy. Question! How would I part the assembly with out scratching the barrel?

    Thanks,
    Virginia Jake

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    Jake, you got it. Yep set the apon over or extend the boering bar.

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    Hey Kurt,

    What a good idea about extending the boring bar! Will that make the bar flex too much?

    About how much should I set the apron over? I think that this is about how this will go.

    1. I'll lay out the center on each end of the 2" round stock that I bought. Then I'll center drill the ends.
    2. I'll mount the round stock between centers, and use a lathe dog and driving plate to rotate the work and turn it down to 1.750" diameter.
    3. I can use a parting tool in my Aloris tool post and partially part off a section 3.025" long. This will give me a little material to remove while cleaning up the parted end. I think that I will remove the work and finish parting it off using a hack saw and a bench vise.
    4. I'll remount the 3" piece on the lathe using a four jaw chuck, and indicate it true using a dial indicator.
    5. I'll face the parted end to clean it up and make the work 3" long. Then I'll center drill this end.
    6. Next I'll mount a Jacobs drill chuck in the tail stock and through drill the work with the biggest drill that I can find in my shop. (I think that will only be 1/2" = 0.500".)
    7. I remember from my machine shop class that I can extend the work piece no further than 2 times the diameter from the chuck and maintain a good rigid set up. In this case I will only have about two inches out beyond the jaws of the chuck.
    8. I think that I should do my taper set up at this point.
    9. I think that I will order a boring bar from one of the supply places, as the one that I have will never even start in a 1/2" hole.
    10. I think that I will have to move the compound slide as far back as I can. I think that I have to move the carrage very close to the work and move the cross slide feed in toward the center of the lathe and start the boring bar in the center of the tail stock end of the through hole in the work. Then I think that I need to back the cross slide towards me until the boring bar just touches down on the inside end of the through hole.
    11. Next, I think that I will need to back the carrage away from the work, zero the feed wheel dial of the cross slide and tighten up the carrage lock nut.

    My old shop manual says that I should take a light cut, back the cutter out, measure the results, then calculate how much more material needs to be removed. Then remove all but 0.002" to 0.005" in one or two roughing cut passes. Finally cleaning up the last 0.002" to 0.005" in a finish pass.

    I think that my lathe is so old and ricketty, and that the boring bar that I will have to buy is so light; I'll have to take four or five light cuts by backing the cross slide back toward me, then running the compound side forward to go from 0.500" to 0.7867" or the largest whole diameter on the tail stock end of the work.

    12. I think that a step will form inside of the work because my compound slide will only travel so far forward. I think that once the tail stock end of the work measures about 0.786", I will have to center the boring bar in the hole, back the boring bar out using the compound slide feed wheel, loosen the carrage clamp nut and move the saddle toward the head stock until the boring bar nose is in the 0.500" through hole. Then repeat steps 10 and 11 until I can see that the this second part of the taper meets the first part of the taper that I will turn.
    13. Next, I think that I should clean up any rough tool marks inside of the work with a bit of emory cloth, and get that last 0.0007" on the tail stock end hole.

    Well that is how I think that it should go! Yes? No? Maybe so!

    Hey rws,

    The expoxy thing is starting to look mighty good, but I still want to do this the hard way just for the heck of it!

    Regards,
    Virginia Jake

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    Well Jake, I would not do it quite that way, but you know your machine, and I don't. On my machings I would just center the 2" AL and leve about 4 to 5" hang out center drill it then drill with the bigest drill I could find thats just under small dia, and .5 deeper than length (3.50") bore then finish the out side in one setup, part it off and be done.

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    Hey Kurt!

    That sounds too simple! I got to thinking after reading your last post; If I only had a steady rest for my machine, I could set it up about four inches from the tail stock end, after turning down the round bar from 2" to 1.750". Then I could back the tail stock off and do exactly what you suggest!

    I have a little bitty steady rest for an old 9" South Bend Lathe. Perhaps I could build a riser block so it will center up on my 10" Sheldon lathe.

    Thanks for all of your suggestions! It is good to have all of you good people to bounce my ideas off of!

    Virginia (thinking of more reasons to make chips) Jake

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    G’day fellas,
    I’m afraid my replies will never be prompt, something to do with living on the other side of the world so I’ve been told (and not wanting to get up at 2am).

    I find it is quicker for me to machine a gradual taper bush than to use epoxy, but I have had times when I should have followed what rws suggested. These cases usually involve complex tapers, my worst "stuff up" being with a N04 MK1 Lee Enfield.

    The barrel would not budge, the steep taper on the Knox form kept caming out, even with a tapered wedge locked onto the flat. My barrel-clamping bush obviously needed to be longer, or two clamps hard up against each other to prevent the steep taper section jumping out. The best option would have been to cast a longer bush in epoxy that would lock onto the Knox form as well as the barrel. That is if I had not been so impatient, and smart enough to recognise it.

    Enter stupid mode, I had two other clamps which fitted perfectly further down the barrel, about 6” from the action (stop sniggering); by the time I gave up, the front sight was at 45 degrees to the flat on the Knox form and the barrel had still not cracked loose. There not being much call for worn 2 groove, reverse gain twist barrels designed for those who hold with a cant (how stupid can one person be?). I relieved the barrel shoulder with a parting tool and fitted a replacement from one of my guns, the gun wet from 6” 100 yard groups to 1.5”. The owner was happy and I was severely chastened!

    The perfect case for a long barrel clamp made from a good re-enforced epoxy, and more patience. My wife tells me that this is God’s way of allowing other people to feel good about themselves.

    Lots of luck (and smart thinks), Paul.

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    Great story Paul.

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    Paul McC,

    "G'day mate! No worries!" Replies are never late and it is always good to here from blokes and shelas "down under"! I don't mean to start a political discussion here but it was my impression that your government had banned most private ownership of firearms! I am glad to read of your adventures in bushing making and barrel wrenching! I must admit that my knowlegde about the British Enfield rifle is sorely lacking. I have no idea what a "Knox form" is! I'll have to read up on that one! Actually I had heard about the trick of partially parting a barrel where it butts up to the reciever to get it loose. What a marvelous thing this internet is! There are so many minds and so much information out there! Thank you so much for your reply!

    Virginia (who is just begining to realize how little he knows) Jake

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    G’day Virginia Jake,

    The term “Knox form” is a British term (and most Commonwealth countries, Canada, Australia etc) for the “thick end” of the barrel where it mates with the action. In the case of the Lee Enfield, it does not have a parallel section, but a relatively steep taper to barrel diameter over about 1.5”; it also has a machined flat that is at the same angle as the taper and is the equivalent of “top dead centre” of the barrel. British armourers would have a purpose built wrench designed to wedge onto this section of the barrel to remove it. As I mentioned, by the time I had given up on this barrel, the first 9” could have passed for a licorice twist.

    Nearly all of the shooting I do is at targets, I use my Lee Enfields in our Service Rifle competition, it is more like the shooting equivalent of a vintage car race because the only self loading rifles around are those used by armed forces personal (if they bother to turn up). I also shoot a little IPSC standard class, and Service Pistol (similar to the PPC match shot in USA).

    You are correct in assuming that our Government does not make it easy for firearms owners in Australia; they are hoping gun owners will get sick of the red tape and give up their “silly ideas” (not my words) of private firearms ownership. For my part, I will continue to fill in the forms and jump through the hoops just to keep them on their toes.

    Catch ya later, Paul.

    (Who, in his 50th year has decided to stop tinkering with guns part time and finally hang out his shingle as a gunsmith. I’ve spent 35 years studying guns and I still don’t know anywhere near enough.)

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    G'day Paul!

    "Good on ya mate!" I am so happy to read that the private ownership of firearms is not dead down under! I mostly shoot in Cowboy Action matches here in the good old U.S.A., but I have been sorely tempted to try out I.D.P.A., or International Defensive Pistol (opps! I don't know what the "A" stands for!).

    I have known for some time that there is a large body of shooters in Austrailia that participate in Cowboy Action sports, but I was given to understand that semi automatic pistols, rifles and pump shotguns were all but banned.

    I hope that your government will not continue to twist tighter it's tourniquet on the civil rights of Austrailia's law abiding citizens!

    Thank you for your explaination of what the "Knox form" is. I think that I know exactly what it is that you are refering too. I was looking at one of the Imbell FN FAL barrels night before last. There are two flats very close to the reciever followed by a short, steep taper for about an inch, followed by the taper that I have been discribing.

    I have begun to wonder, after reading your latest post, if I should go ahead and pour up an epoxy filled collet, and cast it around the barrel near the reciever so that I can make excellent use of these features of this barrel. I have read horror stories about how hard it is to remove these barrels from the receiver stub and conversly, how much torque (120 foot pounds or more) it takes to install them properly. I do not want to destroy this barrel! Thank you very much for your input. I have learned a lot.

    Best Regards,

    Virginia (who's glad to have made your acquaintance) Jake


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