Tapping 1/2-13, about 1" deep, cut tap (new), in 1" rnd 6061, held in what seems to me to be a pretty sturdy 5C collet fixture (china), judging from the stout handle (as opposed to another one I have that closes with a bendable 5/16 rod ditty). Clamped in a vise.
Problem is the material starts to spin in the collet.
Is this job just too demanding for a 5C collet fixture?
If not, then the problem must be either the collet, the fixture mechanism, or both. How to tell?
What tap drill size? Coated tap? Spiral flute tap tap? Chips packing in the bottom, and the tap binding? Depending on torque requirements of the threads, I'd try a .437 tap drill. It shouldn't be spinning in the collet just cutting aluminum.
Chips might be grabbing on the way *out*. Regular plug tap. I don't know if the tap is coated, but I do know it's not TiN. I do have a TiN coated tap. Should I try that?
I'll also peck tap, and blow out the hole/tap during a dwell or sumpn, mebbe rough up the inside of the collet. I spose a spiral tap or roll tap would help, but it would be nice to solve the problem with what I got.
That used to happen to me when tapping that big by hand if I didn't use a cutting fluid like tap magic as opposed to some crappy tapping oil. That stuff makes the tap handle 50% easier to turn.
That's another good point. The soup I use for coolant has already demonstrated itself to be poor for tapping in alum, under even less demanding conditions. Tap Magic fixed a crappy thread problem when I switched taps/coating. I'm told WD40 is proly as good, and I have a gallon of liquid WD.
ALSO, what's a good speed/feed for this, given spinning problems? I'm using S780.2 F60. ( 60 x 13 = 780). Mebbe even slower?
How many do you have to do? If it's only a few, then maybe some Loctite will help hold things. And how new is your tap? Old taps are some of the most expensive tools you can own.
Order of magnatude for taps by amount of torque/power to drive.
1 roll tap, has to cold form material into thread form, extremely high pressure on tool and part, exponetionally higher as tap size increases
2 straight flute tap, direct cutting forces on tool and part.
3 spiral flute tap, decreased cutting forces by introducing dual positive tool geometry/ lifting chip away from part, great for blind holes.
4 spiral point or "gun tap", further reduced cutting forces by high dual positive tool geometry, driving chip downward thru hole.
A 5c collet for that size thread is asking a bit much, even if your using anything but a gun tap.
Well, let's see. You've got a smooth hard collet, a smooth surfaced workpiece made of something that just naturally tends to slide nicely against smooth hard steel, and a relatively small mechanical advantage in the clamping mechanism, compared to something like a screw-driven vise or a scroll chuck. What did you think was gonna happen?
Here are some possible solutions, ordered from cheapest and least likely to succeed, up to expensive and guaranteed to work.
Scuff up the ID of the collet with some 320 grit sandpaper
Machine some axial grooves in the ID of the collet with a small carbide endmill, or a dremel-style grinding wheel. The grooves might mark the workpiece OD. And if the work still spins, it'll get chewed.
Buy a soft "emergency" collet and bore it to size. Bore it slightly undersize, actually, so it grips in 6 places instead of just three. Don't put too nice a finish on it.
Speaking of coefficients/tinsel strenghts / brute force & ignorance, Would a Titanium 6AL4V angle plate or fixture be stronger than a cast iron or forged steel (store bought)? It shure would be allot lighter. The forged steel has always been the best, but I'm liking the lightness of TI, only bitch is,its non magnetic.
Being a machine phixer, I wonder if a mistake of an operator or programmer would cause more damage hitting it. I love carbide boring bars, when our operators fk up, the lathe isn't always tweeked, carbide tends to just snap, steel hangs in there a bit too long.
2" dia tuned steel boring bars are cool, with the hollow section they break off okay and don't always knock everything out. (About 50/50)
Interesting question. It's been my experience that Titanium (specifically 6AL4V - 6%Alum. 4%Vanadium), is not anywhere near as "strong" or "stiff" (as regards deflection), as steel or cast iron when made to the same dimensional constraints. Now it may be as "strong" or "stronger" if made to near the same mass/weight as the steel or cast iron angle plate. But then there goes your main reason for choosing Ti in the first place. Also, while surface grinding Titanium might be "pretty" in the sense of creating your own fireworks display, with bright colorful sparks, you have to work harder to get a good finish. Plus the embedibility or proneness to scratching when sliding a large piece of titanium on a mill table seems to be much greater (surface is softer in other words). Traditionally cast iron has been credited with having vibration damping qualities. You wouldn't want your angle plate to go into some sort of sympathetic harmonics or "ring" while face milling your parts. But let me check some basic facts to see if they support, or refute, my personal experience regarding "stiffness".
Titanium is a light metal having a density of about 4540 kg/m3. This compares to steel at 7900 kg/m3 and Aluminum at 2710kg/m3. Titanium has a Modulus of Elasticity of 110 x 10 9 Pa. compared to steel at 210 x 10 9 Pa. Therefore Titanium has a significantly high deflection under the same load than steel. ====================================================================
According to the above data Titanium weighs almost 60% of steel and is a little over 50% as "stiff". So to bring the "stiffness" up to steel standards you'd probably have to double the thickness. Adios light weight.
In grinding, the difference between titanium and other metals is the activity of titanium at high temperatures. At the localized points of wheel contact titanium can react chemically with the wheel material. The most important facts to consider in order to prevent this and ensure successful grinding are:
Effective use of coolants. Water based soluble oils can be used but, in general, result in poor wheel life. Solutions of vapor-phase rust inhibitors of the nitrite amine type give good results with aluminum oxide wheels.
Correct wheel speeds. A good guide is to use one half to one-third of conventional operating wheel speeds to get the best result with titanium.
Selection of proper wheels. Silicon carbide wheels can be used at
4000-6000 surface feet per minute to give optimum surface finish at minimum wheel wear but the high speeds essential with these wheels produce intense sparking which can cause a fire hazard unless the work is flooded with coolant. However, vitrified bond A60 wheels, hardness J-M have been successfully used at speeds of 1500 to 2000 surface feet per minute while removing as much as 0.08 cubic inches of metal per minute. ====================================================================
In other words, it's a PITA to grind unless you're set up for it. Otherwise be ready to dress the wheel often and take light finish passes.
A large Titanium angle plate probably wouldn't be cheap as regards material OR manufacturing. All these reasons may be why I've personally never seen any commercial Titanium angle plates on the market. It's be a cool idea if it were practical though.
"John R. Carroll" wrote in news:jYednRHfTsVW1hLXnZ2dnUVZ snipped-for-privacy@giganews.com:
Or send the collet to these guys -
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Once coated you'll break other stuff before the part slips. Cheap and permanent too.
Also worth mentioning that 5C collets suck in applications where cutting forces are pulling the work away from the collet (pulling the collet off of its taper).
Well I dont know if anyone has mentioned it, I did not look closely, The 5C collet is not a "heavy duty" holder IMO. Its precision repeat holder as far as cheap collets go, been around forever. There are a few different kinds of holders I've run across. Hex, square, & various specialty stuff like end mill sharpening fixtures/ lathe closeres ect. They all have different types of closing mechanisms. Some with cam levers or just a knurled ring with spanner holes. Thats the best. You can really tighten the shit out of with a small spanner wrench. But most don't have one so the knurl is buggered up from pipe wrenches & channel locks. If the work piece slips after that & tools are sharp, better just clamp in a V block in a Kurt, my preference when milling round in a CNC. My V blocks name is "V8" with 3/8" c-bored mounting screws in both directions . The U clamps have tapped holes on 45deg to aid in holding if necessary. Best collet holder? R-8 that SOB holds- because of the pulldown stud, just cant work much bigger than 7/8". I think there is a 1" "emergency" R-8? not heavy duty at all. CRACK!
Hell ya, I'm sure I could get a stack of pizza's for a company lunch once a month with the right scrap guy, but that involves me,just about putting the shit in my 3door Fucus & taking it to the right scrap yard. Hey all I can do is suggest. Me: FNG - only 6mo.
Gil=A9 Charter Member of OFAT =3D=3DOld Fart American Toolmakers=3D=3D using the "old world" ways with today's technology building Tomorrows Dreams
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