Gratuitous swarf photos

OOOOO!!!! Very very nicely done so far, and an excellent series of photos.

Well done Sir! Well done indeed!

Gunner

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner

Quite amazing. Is it really that easy to hobb gears?

Jim

I like it! But, being a novice, I have to ask: Why do you appear to be turning from the center to the OD for facing operations? Does the carbide cutter "like" that better? Thanks

Cool shots.

One thing - your feed rate for the stainless is probably too low. Your insert seems to have chip-breaker geometry. If the chips are not breaking, you are not feeding hard enough. What's your SFPM and IPR? Mind you, your machine may not have the power to run that cutter correctly, and I'm not sure that insert is capable of breaking stainless chips so YYMV. Just a thought.

Further, unless you're trying to achieve a certain angle with the leading edge of your cutter (bad idea IMHO), you shouldn't set the cutter to anything but ~90º from the work. You're increasing the load because of the longer cut length, but not increasing your material removal rate. You're using a finishing insert which has a reduced capability to withstand cutting forces. You're more liable to break it in a "decent" cut.

You should systematically increase your feed rate until you get fairly low edge life or your insert just breaks off - then back it off a bit. You'll usually find your surface finish will be best when the insert is cutting as it was designed, and you don't have to deal with razor blades in your face (I nearly cut my right index finger off with such chips, seriously). Obviously you need a rigid and powerful machine.

HTH.

Regards,

Robin

Very cool. Thanks!

It depends on the SS grade. If a manufacture can develop a reliable chip breaker for 316 for example..or 304...he can make a shitload of money.

Gunner

"Pax Americana is a philosophy. Hardly an empire. Making sure other people play nice and dont kill each other (and us) off in job lots is hardly empire building, particularly when you give them self determination under "play nice" rules.

Think of it as having your older brother knock the shit out of you for torturing the cat." Gunner

Hey Jeff,

Pix and chips both look great. Do more when you can. You've got style.

I doubt that the tap you used as the hob would be making any more or different cuttings than in regular use. It is not a type that is very common around here, or maybe it's for a specific job with which I am not familiar. The shank has flutes like a drill bit. What are the flutes supposed to do when it is used in its "normal" mode?

Take care.

Brian Laws>For those of you who like to watch, here is a three-page photo essay showing

Get the chips out of the hole :-)

Mark Rand RTFM

No, it's a damn nuisance. Jeff is just making it look easy!

Whenever I've tried to hob worm wheels they've started out beautifully, then "jumped a tooth" halfway through and demolished themselves. It always took several goes to get a good one.

Ideally you need a tap that's ground for hobbing, with minimal flutes. You don't need the chip clearance but you do need as much rigidity as you can get. I've not done one as big as M10 but in the small sizes I've only ever succeeded by using a centre as an additional support to the far end of the tap.

...

Hobbing is tricky: the pitch of the hob has to be the pitch of the gear at the *minor* diameter, which is less than the gear pitch at the major diameter. But you start the cutting at the outside (major diameter), so there is a conflict. To handle this, the blank can be "gashed" at the correct OD pitch and the hob will follow the gashes, even though they are further apart than the hob teeth. A gash is just a thin slit across the edge of the blank, easily done with a slitting saw. When I tried to hob a 32 tooth straight gear without gashing, I got 33 teeth because of the pitch discrepancy.

Jeff's photo's are of a drill bit with ground/turned threads, yes? If so, was it purchased or made? Hobs are easily made, especially for cutting soft material. It's basically the worm gear, with flutes cut/ground out. Technical Video Rental

a video on hobbing, which is pretty good, if slow (how many times do you have to see the blank advanced and a cut made?).

Bob

If you can't break 316 chips you need a stronger more rigid machine. We run 316 all day long and can pack a 55 gal drum with 500+ pounds of chips. ( they got to be small to do that. .024 feed with .5 inch off the diameter)

John

Yup. Sure is. Either that, or I am blessed with more than my fair share of dumb luck.

(or both)

I've made seven or eight by the method shown, and all have worked fine. Not *brilliant*, but fine. I ruined the aluminium one by lapping it with too-coarse paste, and the nylon one just didn't cut cleanly. All the brass ones, however, have been OK.

-- Jeff R.

Thanks Gunner. Its fun, making chips again.

-- Jeff R.

(blush) Dumb fool luck, actually.

Mine have just been well-behaved. Never attempted to calculate the minor diameter required, just turned the blank to suit the space available and the stock size on hand. It seems there's been enough slack in the system to "take up" the difference when the first revolution is completed.

I did that for my first few, using a conventional straight-fluted tap. It had a countersink drilled into its base, so I managed to support it between centres (very cramped for space). I didn't like the action, though, so I went onto a spiral-fluted tap. No countersink, so not between centres, but it seems to be rigid enough. The blank, however, is not supported well enough. More on that later.

-- Jeff R.

Dunno 'bout the cutter, but *I* like it. I prefer it when the cutter finishes a cut by feeding into clear air, rather than the back of the job - but that's just me.

-- Jeff R.

Thanks Robin. That thought occurred to me, so I increased the speed until the swarf dutifully broke up - but I don't like the sound of a motor crying and begging for mercy, so I went back to slow feed.

I'm using a pretty small school lathe (forget the exact specs) which is not really happy with much more than I am feeding it now.

Quite right on all counts. My excuses:

1) I set up the tool geometry mainly to achieve clearance - of the cutter and the tool post. This is not a huge shaft I'm turning, and things get a bit tight towards the end of the cut. The tailstock gets in the way. Anyways, aside from producing those murderous long ribbons of death, the cut is proceeding very nicely. You know the sound a tool makes when its cutting *happily*? No screeching, no chattering, just a "shhhhhhh" like a breeze through the treetops. Thats what it sounds like, and I like that. :-) 2) Choice of cutter. I'm working at an impoverished government (now *there's* a tautology) school. This year we had to choose between lacquer, abrasives or cutting tips. Lacquer and abrasives won out. I'm lucky I have *any* tips left!

Yup. Right again. Our machines are good - and well set up, but it would be dreaming to call them "powerful".

It did, thanks.

Cheers

-- Jeff R.

Welcome. Its all fun...

-- Jeff R.

(blush again) Thanks Brian.

As Mark said, get the chips out.

Aren't spiral fluted taps in common use in the US and Canada? I thought CNC machines would use them pretty exclusively...

-- Jeff R.

Sigghhhh.

I mean "slow speed".

J.