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View Full Version : How to stop chips from WEDGING between boring bar & bore wall?



KiddZimaHater
09-15-2014, 09:58 PM
GGRRRR...
This has been driving me nuts FOREVER!
Time to tap the Brain-Trust here.
...............
I run a lot of 6061 Aluminum parts, that require boring deep blind holes.
As soon as I get halfway down into the bore, stringy chips will wedge themselves between the boring bar and the bore wall. Resulting in the boring bar 'bumping' out a little, thus screwing up my '0' dial reading, and Pi$$ing me off.
The only way I've conquered this mess is to 'Peck' in & out by hand, to clear the chips. A real pain-in-the-arse.
Hate it!
I'm running at my max RPM, 1600.
I've tried .005, .008, .013, .015, .025, .035, .050, and .100 Depths of cut.
I've tried hand feeding.
I've tried auto feeding at .005, .008, .013, .015, .020 Per Rev.
And damn-near every possible combination of said feeds, & DOC's in my gear train.
I don't have a coolant setup, so I cut dry. Spraying with WD-40 helps a little.
I'm using a CCGX-32.51-ALH10 Insert (Supposedly) designed for Aluminum Turning.
Egad man!! Nothing seems to work.
Any tips??
................
Here's a picture of what I'm talking about:
...................
https://imagizer.imageshack.us/v2/628x454q90/540/ot1Arv.jpg

Arthur.Marks
09-15-2014, 10:01 PM
Any air in the shop? Through coolant bars if only used with compressed air?? Just a thought from the sideline...

jlevie
09-15-2014, 10:20 PM
If you don' t have a coolant set, when you could use a boring bar with coolant fed to the cutting end or flood coolant fromt the other end of the bore to flush out the swarf, the only option left it peck bore.

Toolguy
09-15-2014, 10:21 PM
Got a picture of your insert? I use Tapmagic for Aluminum for a cutting fluid and a fairly heavy feed rate, maybe .008 to .015 per rev., depending on diam. A good chipbreaker on the insert helps. Then .003 to .005 for a finish cut and then a spring pass. For all but finishing you need to form a thick enough chip to curl up and break off often. Then you have a bunch of little chips instead of a bird nest.

PixMan
09-15-2014, 10:27 PM
Get a boring bar that takes a DCGT32.5x insert. That allows a LOT more room around the insert, far reducing the chances of chips getting caught there.

If not feasible, get a different insert. I suggest a Walter CCGT32.51-PF2 grade WK1. It'll break chips in aluminum like you've never seen.

Bob Ford
09-15-2014, 10:39 PM
Have you tried boring from the bottom out?

Bob

mattthemuppet
09-15-2014, 11:28 PM
I'm no expert, but perhaps an HSS tool with a steep negative top and side take (shopping back and sideways from the tip, think that's right) with a a small chip breaker might help the chips curl away into the bore. That's what seems to happen with the ones I've ground from blanks, probably more by luck than design!

boslab
09-16-2014, 12:07 AM
Turn the tool over and cut at the back, I do, you can see better as well, flood coolant helps wash the crap out, stick a rubber bung with a swivel pipe fitting on the ass end of the mandrel bore and a gallon of coolant on a shelf if no pump, plastic tube clamp to regulate, has worked for me
Mark

JRouche
09-16-2014, 12:34 AM
How bout an inexpensive chip grabber. Bought one from enco, five bucks.

Its spring steel and kinda like a "slim jim" for unlocking cars.

Its sold as a chip puller for the pan but I think it could be inserted into the bore when you get to the 30% mark and grab the chip bundle out before it becomes a massive birds nest. Even while running. No need to stuff the tool in deep. It will catch on the front edge of the mass then you give it a pull and all should follow.

I know it sounds hap hazard but IMO I dont think as much a hazard as it sounds.

Just a quick thought, JR.

http://www.use-enco.com/CGI/INSRIT?PMAKA=KN825-0005&PMPANO=0720648&PMKANO=384&PMKBNO=3439&PMPAGE=8&PARTPG=INLMPI

wierdscience
09-16-2014, 12:54 AM
I run CCGT-AK 32.52 inserts for that.Much better chip breaker and mirror polished just for Aluminum.

http://www.kbctools.com/can/pdf/c0251.pdf

I run .014-.018 ipr and a .100"doc for the roughing passes and drop down to .004 ipr and .005" doc for a finishing pass.

With a shot of WD-40 depending on speed it will either break the chips,or turn out tight spirals that snap off at 2" intervals.

Like Pixman mentioned clearance around the boring bar will help also.

Running the bar upside down on the backside of the bore as Boslab mention will also help for the reasons mentioned.

becksmachine
09-16-2014, 12:59 AM
What the hell makes you think you are so special to be avoiding the very same crap all the rest of us have had to deal with??

:)

There is no cure all for this problem. It is conceivable that you would find a combination of feed, speed, depth of cut, and chipbreaker configuration that would break the chip, at a particular diameter in your part. Which will then not work at another diameter in your roughing process, thus converting any time spent achieving the aforesaid condition, into wasted time. Otherwise minor differences in materials will also convert those precious minutes into wasted minutes. And it most certainly won't work on any finish passes. Which may not be an issue as the finer "baling wire" produced by the finer finishing passes does not have as great a tendency to cause problems.

Using a brazed tool in an appropriate bar will allow for greater clearances between bore wall and bar surface, and combined with flood coolant, will help minimize the problem in that it will make it harder for the rubbing chips to create a galling condition.

Boring towards the tailstock has it's merits, but is not for the faint of heart in that it is difficult to measure the resulting bore diameter until the cut is finished.

The most effective method I have found is to try to drill as close to finish bore size so there is a minimum of material left to remove. This may or may not be applicable in your case, in other acronyms, YMMV.

Dave

J Tiers
09-16-2014, 01:01 AM
Hmmm... I don't have that problem with Bokum and Criterion solid HSS boring bars. I do have an insert bar, but have not used it with aluminum.

The Bokum bars seem to "aim" the chips out of the hole better than some. Inserts with differently radiused corners will change the way the chip is aimed depending on the depth of cut vs radius.

But in general 6061 is relatively "gummy", and I have not found any good chipbreaking methods that work consistently with it.

If you cannot aim the chip, aim the bar.... tilt it a bit so it isn't parallel to the bore. The insert bars seem to have less clearance or stickout of the insert past the diameter of the bar, and may need help.

With the bokums, the tiddly little scrap of chip your picture shows would be no issue at all. Tilting may be bad practice, and give a non-flat bottom of the hole, but it will also give you less hassle with chip wrapping when you have a fat bar and an insert that barely sticks out past it.

Old Hat
09-16-2014, 02:11 AM
Have you tried boring from the bottom out?

Bob


Boring towards the tailstock has it's merits, but is not for the faint of heart in that it is difficult to measure the resulting bore diameter until the cut is finished.

The most effective method I have found is to try to drill as close to finish bore size so there is a minimum of material left to remove.

Dave

As soon as you said "deep blind holes." I wondered how the thread will go.

Do you know what a jig-bore reamer is?
Using one, or a doctored up End-mill, or a modified drill as short as you can make it...........
prep your holes leaving as little on the walls as you can and still take a quallify~ing bore cut.

Then as Bob Ford suggested back-bore the remainder. ***
It wasn't that challenging pre DRO so there's no reason it should be all that nasty now.
================

PS you (most of you) default right to insertables. I find that sad.
Why get involved in a trade / hobby, and disregard one of it's fundamentals?
ie, hand formed boring and turning bits and bars.

It's like building a house on the grass, with no foundation.

***Boring and back-boring have pros and cons about equall.
Back-boring shouldn't be relagated to the last-resort drawer.

oldtiffie
09-16-2014, 09:02 AM
Invert the tool (mount it up-side down) in the tool-post at centre height with lathe running forward and feeding inward/forward.

The chips may be inclined to drop clear.

"Spring" or jamming are of no real consequence until the final/finishing cut.

cameron
09-16-2014, 09:59 AM
"Spring" or jamming are of no real consequence until the final/finishing cut.

Now THAT'S what I would call wishful thinking.

Rosco-P
09-16-2014, 12:08 PM
Invert the tool (mount it up-side down) in the tool-post at centre height with lathe running forward and feeding inward/forward.

The chips may be inclined to drop clear.

"Spring" or jamming are of no real consequence until the final/finishing cut.

This makes the most sense to me. When boring in plastics the result is often the same as you are experiencing. As suggested I'd also make a chip hook. A section of hacksaw blade with the teeth ground off would be good raw material for making the hook.

DR
09-16-2014, 01:21 PM
What you're experiencing is a very common machining problem, you're generating stringy chips. You need to break the chips. Are the chips piling up on top of the insert or are they rolling off? If they're piling up a little lubrication can help with the rolling action that'll help in breaking.

The obvious way to break chips is by upping the rpm's, but you say you're at top speed right now anyway. Increasing the depth of cut and the feed rate to create thicker chips that are more likely to break. Using short bursts of feed will create smaller nests of chips.

By drilling the bulk of the material away prior to boring and only having a small finish boring pass is another solution.

Another solution is to switch to a material that is more machinable than the 6061 I assume you're using. 2011 or 7075 are both better for machining.

Looking at your picture, the inner wall doesn't look smooth like I would expect from a aluminum cutting insert. Is your setup rigid? Is the extension of your boring bar at the absolute minimum for the depth you're boring to? Is the bar flexing away from the cut, if so, get a larger diameter bar.

RPM22
09-16-2014, 07:20 PM
I machine and bore a lot of plastics, and since this happens all the time, I keep a pair of fine forceps at hand, so I can keep pulling out the chip for as long as possible before the bored hole gets too deep to reach. It helps that with delrin there is only one chip - this will probably be frowned on as too dangerous, but I have never figured out a better solution - a chip hook sounds workable too

Richard in Los Angeles

KiddZimaHater
09-16-2014, 07:59 PM
I've tried the upside-down boring bar, bore on the backside trick before with some success.
But, after one scary crash, the saddle tried to lift-up, off of the bed. YIKES!!!
Boring upside down, and the 'lifting' action has given me the Heebie-Geebies ever since. :eek:

J Tiers
09-16-2014, 08:42 PM
The idea that the chips simply fall away on the reverse side is plain-out naive wishful thinking for your type of chip..... It's perfectly true with well fractured little "6" shaped chips, but not at all true of long stringy thick chips that are gonna do what they do regardless of gravity.

Tilt the bar, or use an HSS bar with more space for chips. Not everything needs inserts..... particularly not 6061, which cuts as well with HSS as any other cutter.

DR
09-16-2014, 09:22 PM
.................................................. .................................................. .................................

Tilt the bar, or use an HSS bar with more space for chips. Not everything needs inserts..... particularly not 6061, which cuts as well with HSS as any other cutter.

Actually, the insert he's using is better for aluminum than anybody on earth can grind in HSS. Very high positive, razor sharp, with mirror polish and deep chip breaker. (I believe the OP made a typo in his insert spec, he said CCGX, I bet he meant CCGT like most of us use for CNC machining aluminum.)

KiddZimaHater
09-17-2014, 01:08 AM
You're right DR.
Should've read CCGT-32.51-ALH10
OOPS...My typo.
After reading your responses, I think the major culprit is the material itself. (6061)
It cuts stringy.
Even when drilling holes with the drill press, the chips are stringy.
Funny how different lots of 6061 will cut completely different.
One batch, stringy as hell. the next batch makes nice little '6's

Old Hat
09-17-2014, 02:35 AM
Actually, the insert he's using is better for aluminum than anybody on earth can grind in HSS.

Got that "dislike button ready yet!"

DR
09-17-2014, 06:27 AM
Old hat, It's fair to assume you disagree with me on CCGT inserts, so what nonsense about the "old ways" of grinding HSS bits for aluminum are you planning on telling us? Maybe the part about how carbide can't be honed sharp enough like HSS can (that's always a good one)? Please let us know.

BTW, for those who don't know exactly what a CCGT insert looks like Google on it for some nice pictures.

Doozer
09-17-2014, 08:25 AM
I think with a HSS grind that a lot of positive side rake would help aim the chips out of the bore.
Also makes for a nice shearing action with the softer aluminum. I never seen a carbide insert
with that much side rake like that which I am envisioning, hence the reason for HSS. You can
custom grind to fit the situation.

-Doozer

BTW, the CCGT is a nice insert, and is available in many high positive verities.

J Tiers
09-17-2014, 08:45 AM
Actually, the insert he's using is better for aluminum than anybody on earth can grind in HSS.

Probably you do not have any decent HSS boring bars..........

If carbide can be formed that way, HSS can be ground that way. And there will be more chip room, which is the actual problem.

PixMan
09-18-2014, 06:25 AM
Probably you do not have any decent HSS boring bars..........

If carbide can be formed that way, HSS can be ground that way. And there will be more chip room, which is the actual problem.

Perhaps, but I've never seen a HSS tool with a form like this that wasn't done with EDM. This is the Walter PF2 chipbreaker I mentioned earlier, in a CCGT32.51 (CCGT09T304 in ISO.) Used in a DCGT that would give better chip clearance against the wall of the bore, it breaks chips in aluminum at pretty reasonable depth of cut and feed rate.

http://img.photobucket.com/albums/v466/kenm10759/Dads%20shop/IMG_0976-r.jpg

elf
09-18-2014, 06:31 PM
Probably you do not have any decent HSS boring bars..........

If carbide can be formed that way, HSS can be ground that way. And there will be more chip room, which is the actual problem.
Can you share photos of the cutting tip on your boring bars?

Black_Moons
09-18-2014, 08:52 PM
Use a boring bar with more clearance (smaller shaft), Or tilt the entire lathe up 20+ degrees so the chips all fall out :P

Inserts with a good chipbreaker can help.

KiddZimaHater
09-18-2014, 09:32 PM
OOPS. Ignore this post :o

becksmachine
09-18-2014, 11:00 PM
Perhaps, but I've never seen a HSS tool with a form like this that wasn't done with EDM. This is the Walter PF2 chipbreaker I mentioned earlier, in a CCGT32.51 (CCGT09T304 in ISO.) Used in a DCGT that would give better chip clearance against the wall of the bore, it breaks chips in aluminum at pretty reasonable depth of cut and feed rate.




Old hat, It's fair to assume you disagree with me on CCGT inserts, so what nonsense about the "old ways" of grinding HSS bits for aluminum are you planning on telling us?
BTW, for those who don't know exactly what a CCGT insert looks like Google on it for some nice pictures.


Actually, the insert he's using is better for aluminum than anybody on earth can grind in HSS. Very high positive, razor sharp, with mirror polish and deep chip breaker.

Ok, here are a few examples pulled out of the "special"drawer.

Never underestimate the inventiveness of a desperate machinist with a die grinder.

Or was that a tool and cutter grinder??

The chip breaker(s) on an insert are often more bi-directional, but as far as breaking the chip, they have no advantage over something that can be ground in HSS.

Dave

http://i1042.photobucket.com/albums/b422/becksmachine/tool%20grinds/IMG_2270.jpg (http://s1042.photobucket.com/user/becksmachine/media/tool%20grinds/IMG_2270.jpg.html)

J Tiers
09-18-2014, 11:04 PM
Can you share photos of the cutting tip on your boring bars?

Standard Bokum bars, nothing too special, but they work. I think I have posted a pic before, maybe not. Mostly due to more clearance, I'll bet, but they do seem to get more of the chip to come out instead of wrapping around the tip.

yeah, here is a picture from the business end of one of them. The cutting tip is the part away from you in the pic.

http://img.photobucket.com/albums/0803/jstanley/tooling/Boringbargrindbokum_zps0d869730.jpg (http://smg.photobucket.com/user/jstanley/media/tooling/Boringbargrindbokum_zps0d869730.jpg.html)