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Posted: 11/7/2007 3:20:10 PM EDT
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Well over the summer I had a hankering to make a 608. I thought a good place to start with the project would probably be the front handguard cap since I had lost access to the waterjet over the summer, so I wasn't able to cut any of the pieces for the stock. The reason that a new handguard front cap is needed is because a standard one is about 1/8 of an inch too small. A new one is needed to match the same i.d. as a standard slip ring so that a straight tube can be used for the handguard. standard cap sitting inside a slip ring.  My first attempt to use a lathe that I was by no means familiar with yielded this piece of thoroughly trashed aluminum.   Today I was a little more successful as I was back to the machinery I'm used to and my mentor was close at hand to answer my questions. The process for making one was pretty straight forward. I chucked the hunk of 2" aluminum in a rotary table mounted on a milling machine and made the interior to the dimensions I thought I'd try first. I chose to do the inside on a mill because it would have been a real headache using a boring tool on the lathe, without drilling a one inch hole through the center. After the inside was done, chucked it in a lathe and cut it off, then mounted it backwards in a smaller lathe because the big lathe's jaws wouldn't go small enough to fit on the inside. Next up was trimming the right right overall length. Finally it was on to radiusing the front edge and deburring.  As you can see I still need to make the hole in the center a little larger as well as cutting the hole for the gas tube.   A picture of the 2" round stock that I made them from.  More to come later. please let me know if the pictures as too big, I'll make them a little smaller. |
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Man, you get to have too much fun! My metalwork is currently limited to chopsaws, air tools, welders & plasma cutters (Not that they haven't found a 1911 cross their path a time or two...   )I would love to get into machinework. I'll have to start a thread about good mini-mill candiates...  |
I was just going to let it rotate, but I suppose I could put one or two small engagement points in the front cap then cut one or two small recesses in the handguard tube to keep it from rotating. I wasn't that worried about it because the handguard is round so it wouldn't have a right way to be oriented, but you do bring up a valid point, one that I didn't even think about. |
The slip ring and foreend cap are different sizes. It would then be tapered, or have a "step" in it. The handguards aren't a problem. |
With the step in the front you would also then have to bore out the inside of the back of the tube because of the increased wall diameter so that it would clear the barrel nut and gas tube. And it turns out that a bigger one-off slip ring might need to be made because the standard slip ring might not have enough room for the tube to clear the gas tube. Yes black nylon would be nice, but flame retardant G-10 FR4 would be nicer
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Would it matter??? As long as the front cap remains stationary, the handguard could rotate as much as it wants...not desirable, but tolerances/clearances etc would dictate that *some* would rotate...  unclemoak - Were the original 608 handguards (or just handguard, I guess) knurled??? Some of the (admittedly poor quality) pics look like they may have been... I love these reverse-engineering projects!!! 
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How's that compare in price to the uni-directional carbon fiber tubing I e-mailed you about? |
I found some for about $90 for what I think was 42" |
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I was back in the shop today making a little progress. I was thinking about the handguard situation a little over the past week and came to the conclusion that there just wasn't going to be enough room in the slip ring to accommodate the gas tube and the round handguard tube. So today's task was to make a new front cap and a one-off slip ring. The i.d. of a standard slip ring is 1.75", so I stretched this one out to 2". Old front inside the new front cap.  Old and new slip rings.  Not a lot of room.  Plenty of room.  Mistake made from not measuring both sides.  Mounted.  Comparison of old and new. 
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I may be wrong but it looks like this uses a standard flat slip ring. Maybe the handguard cap itself has a step that the handguard tube fits over http://retroblackrifle.com/images/608-6-sm.jpg |
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Just by eyeballing this photo above, and comparing the FSB height of a carbine I have to the pic, it does look like an oversize front cap... I like designers who think unconventionally... Unclemoak's threads are always intriguing...they make me think... I wonder how a handguard like the one in the Tool Room pic above would look mated to an XM607 stock???...Hmmmmmm.... |
I took some time to take some pictures to see what was going on, to see if I could find a size that was close to the original. When compared to the BAFT picture above, the 1.75" front end cap looks a little small. If you take a look at where the top of the cap touches the front sight you will understand what I mean.  The 2" cap looks a little closer. When you take into consideration that the cap I have picture is slightly bigger than 2" i.d. and that it's machined aluminum instead of stamped steel, it might sway you to believe either way. I took a measurement and my cap extends above the sight edge by .085", the sight being 1" front the center line of the bore to the edge I'm referencing, which could believably be corrected if I stamped on out of steel..........(as I start looking into making stamping dies)  I by no means consider myself an expert in retro black rifles, I'm just presenting what I've found. |
Just out of curiosity, how did you come up with these numbers? |
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It isn't 100% acurate but I did a simple ratio calculation. I used the picture form the first page. I then went and measured a dust cover which is .75" from the top of the dust cover to right above the dust cover pin. Then I opened the 608 picture in CAD and measured the dust cover on there to be .4375". After that I measured the part I wanted to know the size of on CAD. So for instance lets do the stock length, which was 3.0625". So.... 3.0625"/0.4375" x .75 = 5.25" 608 but stock length It isn't the most acurate because the pic was such low quality that it was hard to pick specific corners or hardpoints, but heck if you can't get your hands on the gun it might be better then nothing and it will work on almost anything. Lunch |
I do the same thing, but I pick the longest value in the pic that I can...it reduces the error from pixelization (that fuzzy effect at the very edge of the pic or object)...since you know the length of the trapdoor, it would be better to use that value than the height... |
Yeah my door was short due to being 9mm. But you are right the longer the better, along with if a better pic can be found. Lunch |
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Today I decided to make another front cap and slip ring because I just wasn't happy with the last set I made. While making the last set, I didn't realize that my caliper wasn't zeroed, so I accidentally made them .02" too big on the I.D. and of course I thought it was my fault for being stupid. So I made another set today. The set I made today turned out a lot better. The I.D. measures 2.005, which is right where I wanted it. There was a few mishaps though. When I was using the cut-off tool on the front cap, I somehow managed to chunk the carbide insert and metals bits started flying everywhere. After that I just thought it might be better to cut it with the bandsaw instead so I didn't ruin my part. Another thing that I did differently on these ones was the addition of the grooves on the slip ring to mimic those on a standard slip ring. Since mine is about .1" longer than the standard, I decided to throw an extra groove on it to make it look proportional.   
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Was a little bored and decided to draw up the parts in CAD after finally being able to put it back on my laptop. A word to the wise, 8GB worth of software bogs down a machine that only has a 40GB hard-drive. On a lighter note you have to love colleges for handing out probably a several thousand dollar piece of software.
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Thought I'd post some new pictures. Mocked up on a carbine length barrel I had laying around. I ordered some material for the handguard today. Hopefully it will work out because it wasn't too cheap.  Not tighten the whole way. I'm debating whether or not to make the handguards long enough so that the slip ring almost touches the upper.  Plenty of room for the 1/8" wall tubing,  The next phase. Hopefully I can get the pieces cut before I lose direct access to the waterjet while I'm out for an internship this spring.  I need to order some rifle buffer tubes to make sure my dimensions are correct for the stock. Then figure out how to drill them to make them look 601 style. 
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Material - Garolite Garolite Material - Grade G-10 Garolite Backing - Plain Back Shape - Tubes Tube Type - Round Wall Thickness - 1/8" Length - 39" Length Tolerance - +9" Inside Diameter - 1-3/4" Inside Diameter Tolerance - ±0.016" Outside Diameter - 2" Outside Diameter Tolerance - ±0.014" Opaque - Yellow-Green Operating Temperature Range - -40° to +325° F Impact Strength - Not Rated Tolerance -Standard Hardness -Rockwell M: 110 Specifications Met -Military Specifications (MIL) and Underwriters Laboratories (UL) MIL Specification -MIL-I-24768 and MIL-P-18177 UL Rating -UL 94HB Note -Poor electrical insulator. Straightness Tolerance -Not Rated This stuff was a good bit pricier than other forms of Garolite they had, but this particular type high the highest operating temperature. Hopefully a combination of this and some duct (not duck) tape on the inside will be enough to stand up against the gas tube. |
No Probably about it. Solidworks is a $5K software. |
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Today I had the hankering to learn how to single point thread, which in layman's terms, means to cut threads on something with a lathe using a single v-shaped cutter. Basically most of the work involved consists of arranging 6 or 7 levers on the machine to combine a certain amalgamation of gears so the cutter moves at the desired threads per inch rate. After you have that all squared away you have to look up how deep you need to cut the threads, which is determined by the thread pitch. In my case, since I wasn't threading anything important, I went with 16 threads per inch and they needed to be cut .081 inches deep. So hopefully my new found skill will come in handy when I need to cut down some barrels here in the near future. If you do it right, your part should come out with some nice looking threads. 
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You're getting way too technical...Set your tool head at 60º and set the cross slide at 0...feed the tool head in at about .001" per cut (you only want to cut on the front of the threading bit)...Use the slowest spindle speed you have...Return the cross slide to 0 each time...take a file to the threads occasionally, to knock the sharp edge off...and when it starts looking like a thread, try a nut on it...repeat as needed until the nut just goes on...
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I might have to try that when I get my skills a little more refined. Today I tried to cut some 1/2 28 threads on a piece of round stock. I don't know what the heck I did, as the threads look great, but the O.D. is way too small. Got a lovely package from McMaster today. I thought it was going to be by handguard tubing, but it was the 100 1/16 x 1/4 stainless roll pins I ordered.  Hopefully the tubing will get here in the next day or two. |
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