Bar pushing back

runner1957 · Mar 31, 2021

Hi all, I have a sandvik 880 drill, 34mm, running 2200 rpm and .0065 feed, 4140 annealed, in a doosan TTSY mill turn. Running less than 70% spindle load. Using Hardinge A80 collet chuck, 2-5/8" round serrated collets, max force for the chuck, according to hardinge is 10,100 pounds force. Samchully cylinder calcs out at 300psi hydraulic for 10,549#. Drill's running like butter, besides slowing the feed, what can I do to stop the material from sliding back. This is a barfeed application. Can't dead stop it. Moves back about .1-.25"

Thanks

Unrelated, anyone got good tricks for getting thread chips out of bores? Using the machine....not my hands....??

Booze Daily · Mar 31, 2021

How long is the bar? Are you using a spindle liner?

chucker · Mar 31, 2021

If you have a lot of vibration form your bar feeder that could cause it, I would clean the collet chuck and make sure you do not have chips preventing from closing, also make sure your not at the end of stroke on your chuck, you may need to go one more turn on your collet or tighten up your draw tube.

Bobw · Mar 31, 2021

Booze Daily said:
How long is the bar? Are you using a spindle liner?

That's what I was thinking, if its whipping a bit, it can walk back, no matter how hard you grab it.

I guess that begs the question. If there is a single short piece in the chuck, does it still
move back? How far is your stickout.

Off the wall thought. Are you drilling deeper than your flutes and packing them?

Orange Vise · Mar 31, 2021

What's the Z-axis servo load when drilling?

Is this drill thru-coolant fed?

SIM · Mar 31, 2021

Yup...a hard smooth bar and collets can be a headache...even serrated.

When I have that problem I bring out the chuck. My take is pressure on three jaw points may dig in a bit and beats having pressure dispersed evenly all the way around. I might be wrong on the reason...but the chuck does work better for me when bar pushes.

We used to cut lots of A22...Kinda like Nitronic 50. Smooth ground, true shafts 10'-20 feet long. Material needed to be pushed to chip...but with tailstock it would push back...and since the overall length was the full length a pushback was very costly.

Nerdlinger · Mar 31, 2021

You could try sending that collet out to carbinite to get coated. A #1 coating adds .003” per side so your collet would a little on the small side but that could actually help since the corners might be a bit more likely to dig in a tad. Or you could order a collet .006” oversized and then send it out for coating. They’ve always worked well for us. Good luck!

runner1957 · Mar 31, 2021

Ok,
Bars are 40", short bar lns feed, correct spindle liner, spins at 4000 pretty smooth.

Not a lot of vibration, the hardinge is about 1/2 turn off max, can go no tighter
No whipping, nothing hangs out of the back of the spindle, barfeed leaves a remnant just a little longer than the collet, maybe 2" or so. Part is out of the collet 4.18", cutoff runs less than an 1/8" from collet face. I am running close to the max depth of the drill, as spec'd by sandvik. 1000psi coolant ,nice little chips blowing out of the hole.

Didn't look at the z load. Spindle load is around 70%. Lots of coolant. Gotta love the sound of it.

I don't have any chucks for this machine, its going to live its life on a diet of barstock, 2-5/8" and smaller. TT1800SY, got two flex 80 hardinges, they go to 3", i havea couple of jobs we will hand load slugs of 3". Got a bigger doosan for bigger parts, with dual chuck.

carbonite? Found the web site, sent an inquiry, looks very promising.

Thank you everyone!!

mmurray70 · Mar 31, 2021

Have you tried different inserts? Stainless grades usually have sharper edges which means lower Z axis force. I havent tried this in a drill, but Sandviks 11xx grades for stainless do fairly well in steel too. Might be worth a try.

Sandviks 870 drills cut with very little Z load as well. Might be another option.

david n · Mar 31, 2021

Are the bars oily? Sometimes it’s as simple as degreasing the barstock......

CORONA VIRUS · Apr 1, 2021

runner1957 said:
Hi all, I have a sandvik 880 drill, 34mm, running 2200 rpm and .0065 feed, 4140 annealed, in a doosan TTSY mill turn. Running less than 70% spindle load. Using Hardinge A80 collet chuck, 2-5/8" round serrated collets, max force for the chuck, according to hardinge is 10,100 pounds force. Samchully cylinder calcs out at 300psi hydraulic for 10,549#. Drill's running like butter, besides slowing the feed, what can I do to stop the material from sliding back. This is a barfeed application. Can't dead stop it. Moves back about .1-.25"

Thanks

Unrelated, anyone got good tricks for getting thread chips out of bores? Using the machine....not my hands....??

Try a smaller drill. How are you doing the threads? Tap? Single point? If doing single point threading from bottom to top.

HuFlungDung · Apr 1, 2021

Would sandblasting the bar stock be an effective way to increase the friction factor?

david n · Apr 1, 2021

Something doesn't smell right here..............What is an A80 collet chuck? FlexC? I have two FlexC systems and they have the kungfu grip.............I only run smooth collets too. Low carbon, 4140, 303, 304, Ali and I never have push back. Running any where from 7/8 to 1-3/4" Ø insert drills. And I don't baby it...................I did have some really smooth 303 push back once, but I forgot to crank up the clamp pressure from the previous job. Are you sure your pressure is actually what the gage says? Does the collet chuck/draw tube nut have enough travel?

toolsteel · Apr 1, 2021

I havent paid attention to the load meters enough to compare....I am curious....if this drill can be run offcenter like many inserted drills would that affect the load???

litlerob1 · Apr 1, 2021

What diameter is the Stock in your 2 5/8" collett pads?

R

Nerdlinger · Apr 1, 2021

Iscar (and others) make a “multifunction” tool that kind of looks like those insert drills that use the two little square inserts but this one only has one insert that passes past center a bit so it can drill on center and then use it as a boring bar to open up ID’s (or OD’s for that matter.). They’re kind of weird but they really cut down on the cutting forces because it’s only like half of a drill lip. Just a thought. Good luck!

CarbideBob · Apr 1, 2021

Nerdlinger said:
You could try sending that collet out to carbinite to get coated. A #1 coating adds .003” per side so your collet would a little on the small side but that could actually help since the corners might be a bit more likely to dig in a tad. Or you could order a collet .006” oversized and then send it out for coating. They’ve always worked well for us. Good luck!

Carbide Surfaces does this also, a sort of grit in the collet that way increases the ability to stop "slip" and makes much longer collet or chuck jaw life.
Others that do diamond or CBN plate which sort of the same.
Problem with such is can you live with tiny indents on the clamped surface? Often fed in and recut so that scaring not a problem.
Bob

Ox · Apr 5, 2021

runner1957 said:
Hi all, I have a sandvik 880 drill, 34mm, running 2200 rpm and .0065 feed, 4140 annealed, in a doosan TTSY mill turn. Running less than 70% spindle load. Using Hardinge A80 collet chuck, 2-5/8" round serrated collets, max force for the chuck, according to hardinge is 10,100 pounds force. Samchully cylinder calcs out at 300psi hydraulic for 10,549#. Drill's running like butter, besides slowing the feed, what can I do to stop the material from sliding back. This is a barfeed application. Can't dead stop it. Moves back about .1-.25"

Thanks

Unrelated, anyone got good tricks for getting thread chips out of bores? Using the machine....not my hands....??

My first thought was worn pads.

Have these pads got many miles on them?

I have worn out a few sets of regular serrated pads.
Well, maybe not worn "out", but rather ran into the next up /32" anyhow.

Not that the pads are too worn to work, but rather the collet bottoms out at the point that it tightens up.

Is this a pull-back or push-to-close (dead length) set-up?

If push to close (and I am not sure how Hardinge does the dead length on these for sure w/o looking) but typically on dead length chucks, they will build up fines in front of the moving sleeve and eventually limit travel.

I replaced my dead lengths with pull-backs.
VERY seldom will I git that one job that needs dead lengths, and then they see daylight, but not often.

-------------

Think Snow Eh!
Ox

CarbideBob · Apr 5, 2021

This is not a uncommon problem,

Omega · Apr 5, 2021

I usually spin the od on a belt sander to rough it up a bit, usually works pretty good

Bar pushing back

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