Broaching a Bolt Action Reciever, Raceways, Lugways, ya someone had to do it.
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    Default Broaching a Bolt Action Reciever, Raceways, Lugways, ya someone had to do it.

    I have wanted to do this for years. And every couple of years I do a search on it in all the usual gunsmithing forums and nothing, a big fat nothing burger.
    NO MEAT, all air bun!

    Oh there are posts on the topic with lots of ideas and suggestions, including some very wacky ideas but no real info about well, BROACHING lugways.
    Usually the replies center around, you could EDM it, you could single point shave it out with a shaper, you could make a full dia bolt, DuMont will make you broaches < $$$$$$$$$$$$$$$$$$ not economically viable.
    Or more amusing 'why not just buy a gun it is cheaper'.
    Everything BUT broaching a receiver. LOL
    LET'S MAKE IT A POINT TO KEEP ALL THAT NOTHINGNESS OUT OF THIS THREAD.

    The exception being the blessed Raymond Benwood.
    http://jpfo.org/filegen-a-m/boltaction.htm
    Thank you Raymond!!

    He did it. He used modified std keyway broaches. He documented it with pics, drawings and dimensions. And although I don't think it was all that precise, it did give me lots of ideas and inspiration. His goal was a survival type weapon, not a target rifle or work of art.
    He also broached with a minimum number of broaches, no surface grinder and a bottle jack shop press. St. Raymond must have the patience of Jobe.
    I wanted more of a production type system of broaching and I do have a 6x12 manual surface grinder so I have a lot more options than he had.

    The hunt, I started gathering used but sharp 1/4 C Push-Type Keyway broaches, 7/16 and 1/2 D broaches and chucking reamers off Ebay. I was going to need a pile of broaches and wanted to keep the cost down in case my plans ended in failure......they have before. LOL
    Most were very sharp, some even new, all but 1 are DuMont. Typically I paid about $35 a broach delivered using BIN, Best Offers, buying in lots and selling off what I didn't need.
    A dull std keyway broach is worth nothing unless you can sharpen it yourself because the cost of sharpening is the cost of a new broach. But that doesn't stop Ebay sellers from trying to sell them, usually at 2/3rd the cost of new with $40 shipping.

    While gathering those I built a broaching press. 2.750" bore, 16" stroke, electric/hydraulic pump. Pull the lever down and it goes. I have the relief set to 2500psi, = almost 15,000lbs force. Yet the ram moves slow enough to spot trouble.
    I wasn't looking forward to broaching and pump, pump, pumping on my 32 ton bottle jack shop press with 6" stroke. The mere thought of that makes me want to go lie down on the couch.

    The 1st problem is that std broaches don't fit down a 45/64" hole. So they would have to be ground down to fit, substantially weakening them in stiffness. I did a bit of experimenting with an ugly, somewhat dull Guinea Pig broach that had the 1st tooth broke off. I was going to be cutting way beyond what Dumont recommended.
    Maximum length of cut for a std C broach is 2.5", I would be doing 3 times that!
    Ds are 6".

    http://dumont.com/our-broaches/push-...ican-standard/
    ^DuMont's site has a lot of good info.

    Also the cutting forces are at least 50% higher broaching hardened 4140 steel vs mild according to the DuMont rep.
    The 2nd problem is the depth of cut for each tooth on a std broach is about 0.0035" I would reduce that down which would reduce the broaching force required, require more passes but hopefully give a better finish.
    3rd problem is D broaches are 13.5" long and I have a 12" surface grinder.
    I shortened the D broaches to 12" which also helps the unsupported length and deflection and found that with a maximum of 0.032" difference between the 1st shortest tooth and the last tallest tooth (about 0.002"/tooth) that the forces were reasonable and a sharp D broach cut without difficulty or excess deflection. A std D broach is about 0.065" total cut. So about 1/2 of std.

    That worked so well that I tried 0.045" 1st to last tooth, SCARY!! Poor Guinea Pig got halfway in and the projecting part was deflected into an S shape. I put on a face shield over the safety glasses I already had on, put up a piece of plywood to hide behind, pulled the lever and forced it down 1" at a time, backed off, another 1" until it made it through. Luckily I didn't break the broach, chip off a tooth or have GP permanently fused in my blank.
    So it is 0.032" max for me on the D broaches!! and that works well as a uniform increment to end up with a 1" lugway, Remington and left lugway of a Mauser. The right lugway of a Mauser is deeper for the extractor.

    Anyway, here we go. 1st I made up a receiver blank holding fixture. I wanted something where I could support a long boring bar at the front and rear, where I could easily see through the bore, blow out chips, quickly remove and replace blanks and not clog up my 3 jaw with chips.
    Basically a barrel vise mounted to a threaded backing plate. All welded up on the lathe, while positioned on an arbor, concentric and final bored in place. I have aluminum bushings bored in place to locate the blank, all marked to go back in the same locations.





    Works even better than I hoped. Integral recoil lugs, square bridges, etc,, can fit around the 2 mounting points.
    Eventually I will pipe oil through the headstock for the reaming operation,

    For blank material I am using 4140 pre hardened to 36 Rc. No butter soft steel, heat treating with old leather boots, dead bones, apricot pits and newt's eyes for me. Nor having to deal with warping (or worse), FFL transfers, shipping and all that.
    Nope plain old 4140 that any heat treater does tons of every year.
    I have a good stash of 4140 prehard, most of it was 28-32 Rc, one piece about 4ft long was 36Rc. That is what I am making my initial receivers from. To me 28-32 is a bit soft and I find most 4140 PH is down at the 28 end.
    My 1st receivers will be Rem clones, since they are easy and I have a few PTG bolts purchased from the PTG bargain bin years ago.
    Then I am moving on to squarebridge Mausers and more challenging actions.
    I really have no desire to make every part of an action, just the receiver if I can buy bolts, trigger guards, etc,, at reasonable prices.
    I have been eyeballing those ugly and cheap Springfield 04 bolts. Thinking about regrinding the bolt body to remove all those hideous undercuts, monstrous safety lug and making a petite action.
    Sort of a MiniMauerfield, I wonder if that name has been copyrighted? LOL

    1st I drill a 11/16" hole in the 3 jaw, the drill wanders but I have come to accept and work around that. Eventually I will setup my lathe for gundrilling, but I am not there yet.
    ^I contacted 2 barrelmakers, neither was interested in drilling receivers. They only want to make barrels and drill their version of 4140 that is alloyed for easier drilling. So let's not go there.

    Next I turn the OD to 1-3/4" on centers which fits my aluminum bushings. So now the bore is at least concentric at each end. Mount in fixture and bore using a 2ft piece of 5/8" casehardened Thomson linear shafting for a boring bar with a HSS bit. The boring bar flexes, chatters BUT does make a straight concentric hole even if it is rough and not uniform diameter along the length. The boring bar is supported by a bronze bushing at the lathe spindle which helps.
    Next I ream with an assortment of reamers from 43/64" to 45/64" in 0.012 to 0.015 increments. I scored some real oddball sized reamers off Ebay which makes this easy. Double and triple reaming works wonders.
    Then rough bore out the barrel tendon to reduce the broach cut length.
    OK, got a straight hole 45/64" (Mauser or Remington) with a great finish.


    ^The geometry.

    All 4 of the C broaches are narrowed to 7/32" and all the D broaches to 7/16". Then the back of all the broaches are ground to reduce the depth of cut of each tooth, reducing the force required to push it through,the bending stresses on the broach and to make the broaches in stepped sizes so I will not have to use shims.
    I want to roll my broaching press onto a plastic tarp in front of the solvent tank. Press a broach through, put the oily, chipped filled broach into the solvent tank, grab the next broach press it through, etc... Broaching is kind of a oily mess without dinking with shims and other stuff.
    Hopefully 30 minutes a receiver.

    I seat of the pants decided that the arbors would have 0.180 of material left at the bottom, this left only 0.072" in shear (see diagram above) when a previously cut lugway doesn't support the back of the arbor. That isn't much, but more than Raymond left with his bushings.
    My arbors travel with the broach, helping support the projecting end, Raymond made long conventional keyway bushings that the broach traveled through so the bushings do not support the projecting and spindly end of the broach.
    Unfortunately there isn't much off the shelf pre ground material for making arbors in 45/64". O1 and W1 seem to be about it. Not ideal, but I really don't want to turn a bunch of spindly arbors, have to heat treat etc... so I guess it is O1 until I find something off the shelf that is better. I would like something 5 points of so harder than the receivers.

    On to the broaches.
    I take four 1/4" C broaches and grind the sides down to 7/32" each, stack two of them side by side in a 45/64" diameter arbor made from O1 drill rod with a 7/16" slot. They don't make C broaches over 5/16" wide and anything over 1/4" has chip breakers which when the broach is narrowed would be out on the corners. So you have to use 1/4" broaches and stack. Bonus, you grind off any small imperfections off the corners.

    The height of the 1st tooth on broach #1 is 0.0450", the last 0.500". I start broaching at the tang end with the C broaches because of the rough boring for the barrel tendon doesn't allow lining up the index marks accurately. Index lines are on arbor and receiver blank. The 1st broach with barely cut out two corners 0.050 deep. De-bur the corner of the cut and rotate the broach 180 degrees using the index lines and make cut #2. De-bur the 2nd cut too otherwise a sharp corner galls the arbor. I use Moly EP grease on the backside of the arbor and Mobile sulferized cutting oil on the teeth. It takes about 2500lbs to force this through.

    Broach #2 is the same as #1 but the 1st tooth is 0.500" and the last 0.525, it cuts a much wider chip than #1 so the depth of cut was decreased.
    Rotate 180 and repeat.


    ^ Broach #1 with two stacked 7/32" broaches just before oiling up. Since these only cut at the corners the two 7/32" broaches can be swapped so you have two more cutting edges before resharpening.


    After using broach #1.

    I now have a rectangular hole 0.700" high, large enough for the D broaches. The next 6 D broaches do not use arbors but are only guided by the existing slot.
    Seeing what a project it was to grind down the C broaches on a manual grinder I took 11 D broaches to a grind shop, they put them on a Blanchard grinder and slabbed them all down EXACTLY to 7/16" wide for $220. Best money I ever spent!
    F & F Grinding, Portland OR. < No affiliation etc....
    ^That is MEAT guys, who, where, what and how much $$$.

    Next I started grinding the back of the D broaches.
    Broach #3, 1st tooth 0.700, last 0.732.
    Broach #4, 1st tooth 0.732, last 0.764. etc...etc... see the drawing above.


    ^Grinding fixture to grind the back of a broach. 1st tooth is shimmed up using feeler gauge to get that 0.032 slope.

    Days passed moving that grinding table back and forth sneaking up on my dimension but I now have my 6 broaches ground at the correct slope and heights.


    ^Broach on left is a std broach for comparison, then broaches #3-#8.


    ^D broach going down the hole. The D broaches probably from being shortened tend to kick out a bit and cut deeper when exiting the blank. So the last inch of the lugway isn't straight. To mediate I swap the receiver so the barrel end is up when using the D broaches. The last inch of the lugway gets cut away when the receiver is finished.


    ^This is where I want to end up. Rectangular hole 0.900 high. A D broach is not high enough to cut beyond 0.900" without an arbor or shim. So if it is a Remington clone I will now broach the 0.4375" slot out to 0.450"ish, use an arbor and a eyeball centered 5/16 D broach and finish with the arced final broach.
    If a Mauser, deepen the right lugway, 5/16 and then the arc.



    ^Hard to tell with my crappy camera and the flash I can't turn off (sorry I spent all my money on broaches) but the finish is very good even without any lapping or polishing.

    Currently waiting on some 45/64" O1 and have to grind the arced broach in the lathe with a toolpost grinder.
    But I have made it over the big hurdles and am home free.

    Comments are welcome.
    Suggestions are welcome too IF you have read the links and IF you are offering up some meat.
    But the interwebs really doesn't need another broaching thread filled with nothing burgers. LOL
    I am going to post this over at accurate reloading too, since PM and accurate are probably the most serious gunsmithing forums.

  2. #2
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    Dude, that's awesome well thought out and well executed!!!! hands down one of the coolest things ive seen on here in awhile.

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    Very interesting.

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    Thanks fellas!!

    Well had some rainy days so I made a bit more progress.
    I reground broaches #3-#8 so that they could be used for both a Rem and Mauser. Broaches after #8 will be specific for a Rem or Mauser.
    The many change was now having a .850" square lugway vs .900". I also allow more clearance between the following broach.
    Example: #4 1st tooth is .002" smaller than the last tooth on #3. Sometimes it was difficult starting the next broach. Not now.


    ^Revisions.


    ^ Rem on left, Mauser on right. I cut the tang end back after broach #2 to reduce the cut length for the D broaches.

    Finally got the arbor and arched broach ground for the mauser.

    ^ Grinding arched broach on the lathe with a toolpost grinder. Depth of cut is .002" for the rougher teeth, .001 for the finish teeth.


    ^More grinding.

    Broach #9 for a mauser opens up the left lugway to .875", for the extractor. As stated up the thread that lugway will have to be 'shaved' with a single point tool.

    ^Finished arched broach and both mauser lugways broached.


    ^Mauser bolt slides in snugly, finish is good and with polishing should be perfect. I made the mauser from a piece of 4140PH that was closer to 28 Rc instead of 36 Rc that the Rem receivers are made from.
    The broached finish wasn't as good on the softer metal. I did this also on some 1018 mild steel and the finish was far worse with lots of rough 'tears'.
    36 Rc for me!

    That is it for the mauser broaching.

    On to the rem.

    The rem lugways are .446" vs the mauser .435" so I open up the lugways with this broach.

    ^ Dimensions shown on broach. 1 pass, rotate 180, add .060" shim, rotate 180. 4 passes. Since it is removing very little material I could make deeper cuts.

    Still have to grind one more rem square broach then the rem arched and the broach grinding will be done.
    Last edited by Doug W; 06-20-2018 at 12:30 AM.

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    Now THAT is gunsmithing! Well done and nicely written up.

    Prepared to sell any of those?

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    Quote Originally Posted by lkydvl View Post
    Now THAT is gunsmithing! Well done and nicely written up.

    Prepared to sell any of those?
    Thank you!!

    Well to be honest, I don't think I would make any money with my old manual machines and process.
    If I sold a blank for $150 I would probably net $20/hr. lol

    More likely is I will make up 10-12 for myself and sell off all the broaches, reamers etc and someone else can go in the biz or make what they want and pass it on.

    Really, making rem clones is easy but too much competition in the market already.
    And to make a true mauser 98 blank the left lugway can be broached but the right is blind and needs to be shaved with a single point tool.

    https://ia802205.us.archive.or...esrifl00colvrich.pdf

    ^Page 58 describes the process. You need a shaper, vertical slotter, crank back and forth on the lathe carriage... something.

    I will have to finish my right Mauser lugway by shaving (it will mimic a commercial FN, not a original mauser with a C collar) with but will wait until all the excess metal is removed 1st.
    Otherwise you broach right thru the barrel threads. Winchester pre 64 M70s did this, but I don't want to.

    If you did all that and used high end parts to complete the action you might have a, sort of Satterlee Square Bridge that I believe is about $4K for just the action.
    Actions he doesn't post prices, I guess if you have to ask.... lol

    Anyway, that makes more sense to me than making another rem clone, when you can buy one for $900??

    So how many guys have the time, tools talent and DESIRE to make a custom SQ Bridge mauser action?
    I bet not many, and how much would they pay for a shaved lugway blank?
    Probably not enough to compete with my day job.

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    Quote Originally Posted by Doug W View Post
    Link did not work.

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    Quote Originally Posted by ulav8r View Post
    Link did not work.
    Try this.

    https://ia802205.us.archive.org/10/i...00colvrich.pdf

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    Well finally got the Rem arced broach ground. Ended up with .001 per tooth cut. I wanted the final cut tight so I would open up the lugways by polishing, eliminate all tool marks and get the required clearance for dirt and dust.
    So I allowed about .004" or more for that. However the broached finish came out so well, .002" would have been enough and now I have a lot of polishing to do.
    I will wait until I have milled away all the loading port, mag well and aft end material before I start finishing the lugways in earnest.

    Not sure why the Rem lugways finish came out far better than the 1 Mauser I did earlier. Maybe because the Rem receivers are harder 36Rc vs 32Rc on the Mauser or if the .001" cut vs .002 on the Mauser.
    I guess I will figure that out when I make more.


    ^ 3 Rems with PTG bolts.


    ^ Nice tight fit.


    ^Close up.


    ^ Polishing irons made from 4140 Prehard they are the dimensions of the bored and broached hole minus the thickness of emery cloth and .0015 for clearance. 1 for Rem, 1 for Mauser. I contact cement the emery to the iron either to the radius, flat or both to finish. I slobber ATF on everything.
    Works good, but slow and I need to find longer lasting abrasive. Maybe find some zirconium cloth??
    That 36Rc doesn't exactly polish easily.


    ^ Close up of rod.

    Well that is it for the broaching process, I will fine tune it as I go.



    Next hurdle, setting up my manual lathe for gundrilling. Now that I know the broaching works, and works well I want to speed up the drilling and reaming the bore of receiver blanks. And avoid that long winded drilling, boring and reaming process I did in my 1st post.
    Also on the list is gundrilling bolt body blanks to make Kurz length bolts.

    I will start a new topic for that.


    ^ A teaser. The 2hp, 3 phase, 3.4 gpm pump, 25 gallon tank I built for gundrilling, pumping oil through the headstock for receiver bore reaming and eventually a chamber flush system.
    I will be using sulferized cutting oil and a VFD to run it and regulate the output.

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    Very cool project....thanks for sharing

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    Quote Originally Posted by praff View Post
    Very cool project....thanks for sharing
    Thanks! It has been a very challenging project and the results have been better than I expected.

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    Couldn't you put shims under the broaches to remove the last bit of material? That method is used in rifling machines.

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    Quote Originally Posted by MilGunsmith View Post
    Couldn't you put shims under the broaches to remove the last bit of material? That method is used in rifling machines.
    I glued the arched broach in the arbor groove so it wouldn't wander out while grinding the arch.

    I might just make another short arbor with only 4-5 teeth ground larger ( I have some short broach bits and pieces) to open up the lugways a bit more.
    But I really just want to complete these 3 Rems and then move on to Mausers, so I will probably just polish them out for more clearance.


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