How Would You Make This Part?

BottleBob wrote:


    Thanks to all who replied and for the alternate procedures to possibly doing this part. Not to put too much on it, but I liked hearing all the options people posted. If I had to do more than two parts I would have done them differently.
    First, one of the manual guys squared up the blocks and finished ALL the outside dimensions, while I programmed. (We needed work for the manual dept. and it shortens the lead time)     I used a 6.5" X 3.5 X .5 alum block held in a vise as a subplate/fixture. I figured I'd hold the parts down by 4-40 screws with plastic washers to not mark the finished surface. Drilled and form tapped the holes in the fixture, plus drilled and reamed some 3/16" holes for dowel pins to locate the parts. 2 pins wide spread on the back X axis, and one pin in the middle on the left side.     Put the blank against the pins, and held it down by a couple of Kant-Twist clamps, then drilled all the holes, and tapped the two 4-40 Heli-Coil holes half way through with a cut tap. Didn't want to form tap them since there was too much chance of the form tap deforming the already finished outside surface. Took the drilled blank off to remove the long chips from the two tapped holes, chamfered the holes and put the blank back on and screwed it down with the 4-40 screws and squished the plastic washers snuggly.     Used a .250 two flute high helix end mill to radius the four outside corners then used a .500 two flute end mill (7,500 RPM @ 80 IPM and .050 DOC) to rough out the center leaving .050 on the walls to finish. Then went in with the .250 end mill again leaving about .005 on the walls to finish and roughed out the inside front notches as well. Finished with a .125 high helix end mill 7,500 RPM 20 IPM and .050 DOC. The notches in the front were finished with a .125 3 flute ball end mill, profiling the floor.
    Doing the holes was a 4 minute cycle time, the pocketing & finishing of the walls was a 34 min. cycle time.
    Checked the part and the center of the right side wall was .058 and the center of the back wall was .059 (they were supposed to be .050 +- .010. The walls were within print BUT just barely, and I don't like being on the edge of a tolerance since it can adversely affect other operations down the line. So I added two more 3/16 dowel pins, one in the center of the back wall, and another at the center of the right wall.     Did another blank, the walls now came out fine (within a couple of thou) BUT the front left corner was being deflected by the last pass with the .500 end mill since it was pealing up the last .050 of floor and the plastic washers weren't holding the part securely enough to resist movement. SOOO, I changed the program to only leave .010 on the floor and used another op. to take the .010 off, plus I switched to steel washers. I didn't originally want to do that at first since I was afraid that at 7,500 RPM the steel washers would notch the .125 end mill, but I went with them anyway.     That's my two original blanks down, so I had Salvador make another two blanks while enduring all the resultant kidding for scrapping his first two blanks. "Hey Salvador, I'm giving you job security, right?" LOL
    Anyway, put another blank in and ran it, and it was dimensionally fine, with no feelable notching of the end mill. So ran the second one.     Deburred the parts, flipped one over, put a Jo block stack between the front "pincers" and screwed it down to do the notches on the back side... well now the top side.
    Next were the two front edge 4-40 Heli-Coil holes. We have some 3"+ tall vise jaws that have a series of .250 dowel pin holes in them. So I put a couple of dowel pins in to locate the side wall of the part, and put another dowel in so that the underside of the where the tapped holes would go would be supported. Put the jaws in the vise and a part against the dowel pins and tightened the vise. I put a Kant-Twist clamp near the top of the jaws to more securely hold the part and edge found the the jaw and part and was ready to machine.     The holes were blind with .250 worth of material but the callout wanted .190 min. full thread depth. So I programmed to drill within .020 of breaking through, then helixed in with a .094 end mill to get a flat bottom and machine tapped down .150 and finished the tapping of the holes manually. Ground a tap flat on the end to get another couple of threads in the hole.
    And that's pretty much it. Geeze, that was an awful lot of writing for such a simple part. And I even left out a few things. LOL     
--
BottleBob
http://home.earthlink.net/~bottlbob
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wrote:

Typo?
Think it S/B 6.5" x 3.5" x .750"
Tom
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On Sat, 20 Sep 2008 18:46:46 -0700, snipped-for-privacy@aol.com wrote:

Sorry I should have read your whole post first.
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Hi Bob. Just wandering. Could you have checked the wall thickness before taking the part of and adjust it? Also something about the washers. You can get small aluminum washers for pop rivets. They would be great for this kind of work and you would not have to worry about damaging your cutter. Nice work. Jerry

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Jerry wrote:

Jerry:
    Good point. Actually, I did check the walls before I pulled it off, and noticed the centers were fat. And yes, I could have made some extra programming passes, but they would have to have been heavy in the middle and tapering off on the ends. I decided it was easier, faster and more accurate in the long run to add supporting pins in the area that was deflecting. Plus this little holding fixture might have to be used again in the future if they want a couple more of these puppies.

    Yep, aluminum washers would have been better, but I couldn't wait a day for delivery. This particular problem has not arisen before, but I should probably order some alum 4-40 washers - just in case for the future. Good point Jerry.

    Why thank you.
    *IF* I had more of these to do (like anything over 10), I'd probably use 5/32" dowels in the larger holes and hold the parts down with thin aluminum clamps around perimeter.
    Just another OPINION while I'm here, wire EDM'ing would do the perimeter, but you'd still have to make a locating fixture to do the upper and lower "notches". So if you're going to make a fixture anyway, you may as well make the the whole part with it and not have to worry about outside processing matching your existing holes, being off center etc.
    Oh, here's something I didn't add in the original explanation. There was a .050 thick strip that "appeared" to screw on the front my part. It's kind of like the back wall reproduced and attached to the front by the edge 4-40 Heli-Coiled holes. Well after my part was done, which had 1/16" radii next to the Heli-Coils, as per the model/print, the strip had square corners - as per the model/print for THAT part. But the strip wouldn't fit flush with my part due to the radii holding it off.     Now we didn't have an assembly drawing/model showing just how, or even IF, the strip actually mounted to my part. It just looked to me like it should. A few job shops would just ship the parts as is, since they were made to print. But we often save the engineers bacon by catching boo-boos before they are shipped, preferably before they are reproduced in metal. So we called the engineer about the possible problem, and if it WAS a problem we would offer two solutions. Either radius the ends of the strip, or square the corners where the strip contacts "my" part. Yes, it WAS a problem, and they chose the squaring the corners solution. So I used basically the same setup I used for doing the edge holes but I had to lift the part above the vise jaws. I didn't want to just rest the part on top of a pin, I wanted to hold the part by the side of the .030 front lip for better support. I just happened to have a 2" long 1/2" wide hardened strip that had a .010 relief in the middle, so I put that on the top of the jaws and raised the part until it contacted the relief. That made the part sit .010 above the vise jaws while being held by about .020 of the rest of the lip.
    I don't know if ANY of that last part was really understandable. As you all know, this is what every machinist goes through day after day, week after week, as a matter of course. It seems that when written out, you've got to write a book length explanation on how to tap a simple hole. LOL
--
BottleBob
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Great work, Bob. 3 ring binder worthy for sure. How much did the part move in the 6 inch dimension after being released from the fixture?
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Joe788 wrote:

Joe:
    Thanks. I don't know if it qualifies as a machining tip, it was just a quick and dirty setup. Tom Brewer sent me some zip files this morning that show an excellent way to make these things in production, I hope he posts them.
> How much did the part > move in the 6 inch dimension after being released from the fixture?
    As far as moving, the walls came out pretty straight, but the part was really flexible. A little tweaking brought in the dimension between the "pincers". It was going to be sandwiched between top and bottom flat plates (which were made by a couple of other guys in the shop), with screws going through all pieces. Plus, a front strip. So the assembly was sort of self-aligning.
--
BottleBob
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wrote:

Here ya go;
http://tinyurl.com/3q22yf First operation complete
http://tinyurl.com/3qopxr Pocket milled in jaws
http://tinyurl.com/3kb74s Loaded for second operation
http://tinyurl.com/3edkrs Second operation complete
http://tinyurl.com/3tx2bs Loaded for third and last operation
http://tinyurl.com/42h8jn Part Complete
http://tinyurl.com/4nvre6 Unloading completed part
For a production run I would make tooling to run multiple parts complete, exactly how would be determined by job quantity, machines & tooling available.
Tom
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Wow.....
What program did you use for this? Did you draw the vise, or is the vise a kind of intra-program clipart?
I ackshooly learned sumpn! Good show!
--
PV'd, as usual, but now I got butt another inferiority complex!



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On Tue, 30 Sep 2008 16:38:03 -0400, "DrollTroll"
SolidWorks
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On Tue, 23 Sep 2008 22:46:04 -0700, snipped-for-privacy@aol.com wrote:

=======Very nice. Thanks for closing the loop.
Unka' George [George McDuffee] ------------------------------------------- He that will not apply new remedies, must expect new evils: for Time is the greatest innovator: and if Time, of course, alter things to the worse, and wisdom and counsel shall not alter them to the better, what shall be the end?
Francis Bacon (1561-1626), English philosopher, essayist, statesman. Essays, "Of Innovations" (1597-1625).
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On Sep 30, 1:41pm, F. George McDuffee <gmcduf...@mcduffee- associates.us> wrote:> Very nice. Thanks for closing the loop.
What "loop" would that be?
Jon Banquer San Diego, CA http://jonbanquer.blogspot.com /
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