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hmcl281
03-03-2008, 02:12 PM
was trying to mill the back of this trigger frame a few days ago and for some reason the end mill grab it and pulled it. it was too big for me to lay it flat in my vise so i had mill it vertically. it was not center but towards the back of the vise. i used a 1/4 end mill meant for aluminum with about 1200 rpm and a very slow feed and small cut. was it the fact that it was not in the middle of the vise that cause it to bet pulled towards the end mill? i tighten the work piece pretty tight in the vise.

http://i100.photobucket.com/albums/m11/hmcl281/pbnation%204/silver%20half/DSC03083.jpg

SGW
03-03-2008, 02:22 PM
You say "not in the middle of the vise." Depending on the condition of the vise, that might have caused most of the clamping force to be essentially line, or even point, contact, which let the piece pivot even though it was "pretty tight."

mochinist
03-03-2008, 02:25 PM
I would bet the vice didn't have a good bite on it regardless of how tight you had it.

aboard_epsilon
03-03-2008, 02:29 PM
i know its a pain ...
but some jobs require you to spend a lot of time making jigs ..

all the best.markj

hmcl281
03-03-2008, 02:39 PM
i know its a pain ...
but some jobs require you to spend a lot of time making jigs ..

all the best.markj


sorry i'm new, what r jigs?

Doc Nickel
03-03-2008, 02:50 PM
Ditto what SGW said.

The Ego frame is basically a hollow channel- even the best you could have hoped for is full contact on the two thin edges on the opposite side, but what you probably got was contact on the front edge only, with minimal grip on the back edge (thanks to the vise jaws twisting.)

Meaning you were trying to support a piece almost 6" long, and some 4" away from the vise, by a thin strip of aluminum barely 1/8" wide.

Minimal contact with the vise, the exaggerated length which gave the mill extra leverage, and a thin cross section of what was clamped, letting flex allow the part to move.

Expensive lesson, I'm sorry to see it.

Quick cure: Get two plates of aluminum, as wide as your vise jaws, 4" or 5" tall, and at least 3/8" thick. Clean them up so there's no burrs or rough edges.

When clamping something like a grip frame, where you have to mill the long axis like that, drop the two plates into the vise with the grip between them. Clamp the vise like normal, then add a C-clamp or a deep-reach Vise-Grip or other extra clamping to the plates above the vise jaws. You don't have to go overboard, one heavy C-clamp kept fairly snug will work wonders.

You'll still have a bit of leverage on the part, so even retained like this take light cuts and go slow, but it'll add to the security of the vise hold considerably.

Doc.

Doc Nickel
03-03-2008, 02:53 PM
sorry i'm new, what r jigs?

-A jig is a fixture specifically designed to hold an odd-shaped part.

In this case, you'd probably have something that looks like an angle plate, where the frame could bolt or clamp to a wider surface, for more holding power.

Also, this isn't PBNation. We actually spell out words like "are", and capitalize when needed, here. :D

Doc.

SGW
03-03-2008, 02:54 PM
Actually, I think it would properly be a "fixture," not a jig...but I may have that backwards....

Anyway, a fixture (or maybe it's a jig) is a purpose-built THING to hold a specific part for machining. In the case at hand, it might be a flat plate with a couple of strategically-located pins that would slide into the holes in the part and locate it precisely, and solidly.

wierdscience
03-03-2008, 02:58 PM
Couple things you could do.One is to place a piece of paper or thin cardboard between the part and the movable vise jaw to make better contact and conform to the work's surface.

And add support in the form of blocks or machinist's jacks under the areas the arrows point to in the pics.The jacks can be bought or just made uop from threaded rod couplers and bolts from the local hardware store.

The horizonal line represents the vise jaw and the two arrows indicate the points to locate the supports.

http://img.photobucket.com/albums/0903/wierdscience/DSC03083.jpg

aboard_epsilon
03-03-2008, 03:02 PM
sorry i'm new, what r jigs?

they are sometimes lash-ups of spacers and bolts to hold the peice directly to your table

or can be another whole lump of metal milled to enable the work peice fit into and be milled without any chance of it coming loose ...this is usually when you have a few to do though

you have several holes in the workpeice that can be used to clamp it down directly to the table ...


once youve worked out, how to do that .....you then level it with parallels and offcuts ect and shims or machine jacks ..

he he what are machine jacks ...is the next question

smiller6912
03-03-2008, 03:06 PM
I was taught that, a jig is used to guide a tool and a fixture is used to hold a part. Does that sound about right to y'all...........

ahidley
03-03-2008, 03:09 PM
Climb milling will grab it

aboard_epsilon
03-03-2008, 03:14 PM
as i understand a fixture is one complete part .......made of many

so a number of seperate things holding the thing to the table ...would be ................?

i could not think of anything else to call it.

jigsture or fixtures maybe ...
perhaps we should invent a new word for it

all the best..markj

hornluv
03-03-2008, 03:19 PM
Just out of curiosity were you doing conventional or climb milling? Conventional is when you feed against the cutter rotation, climb is when you feed with the cutter rotation. Due to backlash in the table screws and nuts on a manual machine, climb milling will grab a part and take progressively deeper cuts, ruining the part and probably your endmill as well. For that reason, it is best to stick with conventional milling on manual machines.

aboard_epsilon
03-03-2008, 03:26 PM
yeah to understand climb milling

just place a block of metal in the middle of your table ........if you were milling the sides of this block ......you would be going counter-clockwise around it .

that's conventional milling

remember that .............and apply the method to everything you mill.


only cncs can do etch a sketch......as they have no backlash


all the best.markj

hmcl281
03-03-2008, 03:37 PM
i'll try to remember the information about the punctuation. sorry but i do it in all of my non formal typing. i will try to remember when i am on this forum.

thanks for the reply and the infomation.



-A jig is a fixture specifically designed to hold an odd-shaped part.

In this case, you'd probably have something that looks like an angle plate, where the frame could bolt or clamp to a wider surface, for more holding power.

Also, this isn't PBNation. We actually spell out words like "are", and capitalize when needed, here. :D

Doc.

Peter N
03-03-2008, 03:39 PM
Generally understanding is that a fixture secures the part in a certain orientation, or a number of orientations, in an accurately repeatable position. For example, a CNC mill on production work for raw castings will use a fixture to locate the casting in the same table position and datum every time to machine the features.

A Jig on the other hand usually has some provision for guidance of the tool in relation to the part, i.e. a drilling jig using bushes to correctly align the drill path.

Peter

hmcl281
03-03-2008, 03:45 PM
Climb milling will grab it


i think it was standard milling, but i could be wrong.

hmcl281
03-03-2008, 03:47 PM
Just out of curiosity were you doing conventional or climb milling? Conventional is when you feed against the cutter rotation, climb is when you feed with the cutter rotation. Due to backlash in the table screws and nuts on a manual machine, climb milling will grab a part and take progressively deeper cuts, ruining the part and probably your endmill as well. For that reason, it is best to stick with conventional milling on manual machines.

it was conventional milling

hmcl281
03-03-2008, 03:50 PM
for some reason it is easier for me to use the end mill as the center point and i would feed the stock clockwise. is this correct?




yeah to understand climb milling

just place a block of metal in the middle of your table ........if you were milling the sides of this block ......you would be going counter-clockwise around it .

that's conventional milling

remember that .............and apply the method to everything you mill.


only cncs can do etch a sketch......as they have no backlash


all the best.markj

mochinist
03-03-2008, 03:51 PM
I climb mill all the time with no problems on a manual machine, maybe say on smaller hobby machines dont climb mill, but saying that for all manual machines is just false information.

Oldbrock
03-03-2008, 04:15 PM
My first take on looking at the part was that the two flanges on the bottom of the casting must have been different sizes which meant you were only holding on one thin section with the other one free to rotate about the held one. mike the two flanges and I think you will find a difference. If there is, that's one of your problems. Fixtures are for holding a part for machining so that you can do the same operation to as many parts as needed. To me jigs are for repeatable drilling operations. A toolmaker will probably elaborate on that. Peter

Your Old Dog
03-03-2008, 04:26 PM
If I had to vice that, I'd try to make a filler piece for the inside of the frame so that when I really put the meat to the vice it wouldn't crush the frame.

I had the same thing happen but was able to work around it and make it look intentional ! Mine was caused by inadvertantly climb milling.

http://raymondswan.com/dp/climb2.jpg

hmcl281
03-03-2008, 04:32 PM
If I had to vice that, I'd try to make a filler piece for the inside of the frame so that when I really put the meat to the vice it wouldn't crush the frame.

I had the same thing happen but was able to work around it and make it look intentional ! Mine was caused by inadvertantly climb milling.

http://raymondswan.com/dp/climb2.jpg


i was also afraid i would crush it if it was too tight

IOWOLF
03-03-2008, 04:43 PM
-A jig is a fixture specifically designed to hold an odd-shaped part.

In this case, you'd probably have something that looks like an angle plate, where the frame could bolt or clamp to a wider surface, for more holding power.

Also, this isn't PBNation. We actually spell out words like "are", and capitalize when needed, here. :D

Doc.

Thank You Doc, I was staying out of this one.

A.K. Boomer
03-03-2008, 04:57 PM
All good info, I might add a few things, The higher you go out of the vise without other support the more this will happen -- for the record I have a bike part with marks on it like YOD's

Other things to consider is a dull cutter will generally increase the work load on the piece.

One more thing, flute spiral --- the straighter the flute the more the piece will be pushed off to the side, the more spiral the more the piece will be sucked up into the mill head.

Thats a tough one, thats an intricate piece, But on the bright side i bet you dont do this again for quite awhile and maybe never --- All of us have done a little learn time at the school of hard knocks.

If you have to risk a flimsy setup do it with a very light cut conventionally and a sharp cutter.

Uncle O
03-03-2008, 08:45 PM
I climb mill all the time with no problems on a manual machine, maybe say on smaller hobby machines dont climb mill, but saying that for all manual machines is just false information.


Yes I love to climb cut, it is my preferred way to machine, You just have to use your experience. some set-ups and depths of cut you just know are going to try and grab, and should be done with due care.

BobWarfield
03-03-2008, 09:15 PM
some set-ups and depths of cut you just know are going to try and grab, and should be done with due care.

That's been my experience. Finish is a lot better when I climb mill, right up until it grabs, and then something unhappy usually happens. For that reason, I limit myself to 3/8" or smaller cutters on my mill before I'll climb mill. I also limit cutter engagement to less than twice the mill diameter. In other words, with a 3/8" end mill, I don't want to mill the side of more than 3/8" x 2 = 3/4" high. Also keep the DOC to a minimum.

Better safe than sorry!

When I get ballscrews and eliminate the backlash, it will be climb all the time.

Best,

BW

hmcl281
03-03-2008, 10:46 PM
thanks for al the replies. a lesson learn.

hornluv
03-04-2008, 02:18 PM
for some reason it is easier for me to use the end mill as the center point and i would feed the stock clockwise. is this correct?

That's climb milling. If you visualize it by looking down at the table from the spindle, the cutter will be turning clockwise. If the workpiece moves clockwise around the cutter, you'll be climb milling (because the workpiece is moving in the same direction as the rotation of the cutter), counterclockwise would be conventional milling.

hmcl281
03-04-2008, 09:58 PM
That's climb milling. If you visualize it by looking down at the table from the spindle, the cutter will be turning clockwise. If the workpiece moves clockwise around the cutter, you'll be climb milling (because the workpiece is moving in the same direction as the rotation of the cutter), counterclockwise would be conventional milling.


thanks for pointing it out. for some reason when i read coventional and climb milling i mix the 2 up. will remember to go counter clockwise with my work piece.

i bought a wider wide mouth vise so it should prevent the problem i had with the trigger frame.

thanks for the replies and point out some of my errors.

Uncle O
03-04-2008, 11:27 PM
A visual aid.....

http://www.hanita.com/hanita_protected/tec00006.htm

oil mac
03-05-2008, 07:00 AM
I guess i was lucky, Some years ago, i was at a works closing down sale, and i managed to purchase acouple of angle plates, and even better a couple of box angle plates, some people call these things cuboids.

I find these items of plant are invaluable for cases where one wishes to bolt on to them a component, which allows a very flexible system of being able to hold the workpiece by being able to place tee bolts where one conveniently wishes to grip the component whilst milling, and also this gives a powerfull holding medium, and one is also able to place stops where appropriate, to stop work spinning, also one can in some cases rotate table to work on another face on component.
A most powerful work holding medium. Another point is having a good well built & accurate vice, some of the far east efforts are crap.

NickH
03-05-2008, 11:09 AM
In addition to your vice buy a clamping kit of the correct size for your table's T slots, a set of parallels, at least one pair of 3 2 1 blocks and a few sets of cheap feeler guages and get a basic book on vertical milling

This is a good one for beginners -

http://www.amazon.co.uk/Milling-Complete-Course-Workshop-Practice/dp/1854862324

Take a look at -
http://www.industrialhobbies.com/

click on Production Notes on the left, have a look at Tips and Techniques too, it's not all relevant but you'll get some good ideas

Most importantly of all have fun!
Regards,
Nick