Parting Question: Seems Feed Is Really Fast.....

[great white]

My setup is an atlas TH42 with an AXA QCTP. Using a parting blade, edge polished on a wet stone to make the cutting point as clean and sharp as possible. I've tried a curved, flat and no back rake angle on the tool. Seems to make no difference other than curling or throwing the chip.

It seems I have to feed into the stock really fast in order to minimize chatter. Spindle speed doesn't seem to make a big difference either, fast or slow. Slow just gets big chatter marks and noise, fast makes finer chatter marks but an intolerable "screech" sound to go with it.

I mostly just work in 6061, but it seems I REALLY have to hog in the parting tool to keep chatter away.

Minimizing tool and work stick out doesn't seem to make a lot of difference. Still chatters unless I feed uncomfortable fast into the material.

I've locked down all my carriages and even gone so far as to lock down the gibs on the compound.

The feed is so heavy that I worry about it digging in. Sometimes it does if the chuck doesn't have a death grip on the piece.

Am I doing something wrong?

I've watched parting videos and they seem to not have to feed as fast I I do to keep away chatter.

I know the atlas isn't the most rigid structure out there, but I've watched videos where guys cut off just fine on a 10/12" atlas and not have any significant chatter. At least not the way mine does.

I'm kind of perplexed. I've gone through most I've what I've found online and I still get chatter....

 

[Randall Marx]

How fast are we talking about for spindle speed? Remember that speed needs to be about half of turning speed for parting. Also, are your spindle bearings adjusted well? That could cause chatter here.

 

[TomS]

I agree with what Randall says above with the caveat that your parting blade needs to be perpendicular to the lathe centerline, the tip needs to be on center, and use a liberal amount of cutting fluid. Loading the parting blade with a heavy in feed can reduce chatter, and sometimes eliminate it, if your machine is up to it. How wide is your parting tool? Going to a narrower blade might help. I use a 3/32" wide blade on my 12 x 36 and have no problems.

Hope this helps.

Tom S.

 

[Bill C.]

Make sure your blade doesn't extend to far beyond the diameter of the stock plus maybe a 1/4" of an inch. If the chip curls up on top of itself them the setup is a good one.

Parting can be a challenge no matter what your skill level is.

 

[f350ca]

There seams to be a geometry thing, and maybe a combination of slop in the gibs of some lathes that they just don't like parting. My first lathe was a 14x40 Taiwanese, I could never get it to part well, same thing chatter grab etc. I bought a heavy 16 x 80 Summit, it parts effortlessly, still couldn't get the 14 x 40 to part. Sold the 14 x 40 and bought a wore out Colchester Student, it had no trouble parting. Sold it and bought a Hardinge HLV, again no problems parting, except it will run out of power. From my experience it might just be the lathe.

Greg

 

[pineyfolks]

These old-school tool holders will surprise you with their results. Instead of digging in the tool springs away and reduces chatter.

 

[mikey]

It sounds like you're doing everything right. The only thing I can think of is that you may not be quite on center. If your tool is a tad high it can require higher feed pressure to cut. Try taking a very light facing cut with the corner of your tool at the current height and see if there is a tit on the work.

If you're using that horrid tool holder that holds the tool at an upward angle you may want to increase the front relief angle a bit more; this can make a difference.

 

[stupoty]

My lathe can just about handle power parting in aluminium on the slowest feed, on steel it's plunging too quick I find.

The blade being just a little to high definetly stops me from parting, i had to set it quite low the otherday (maybe 50-75 th) to get a good cutting action on mild steel, this does leave a big ish nib but it was small enough i could snap the last bit off the stock in the chuck.

Parting holow stuff is much easier i find , especialy if the cutter is set a bit low as it tends to get dragged in a bit which can be unplesent towards the centre of the part.

I like to peck part, i dive in quite fast then withdraw at the first sound or feal of unhappyness and use a brush to clear all the chips and add more cutting fluid.

I like parting off brass the most it's amzing

Stuart

 

[great white]

I've fooled around with my on center a fair bit. Doesn't seem to make a difference where I have it.Horrible screeching chatter.

Spindle bearings are adjusted IAW the Atlas manual instructions.

I don't' run out of power, I'm running a Baldor CDP 3440. 3/4 horse. Runs super smooth.

I use the simple formula 4XSFPM/diameter = spindle rpm to set my rpm for cutting. Doesn't seem to matter if I do half it or double it, I still get chatter.

I do think I am using the references "horrible angled holder". Looks like this:



Can't remember off hand what the tool width is.

So, how should I try and adjust the rake if using this tool? more angle or less on the cutting surface? I'm not really understanding how less angle could be helpful. Doesn't that mean the chip edge would be broader/blunter?

 

[David S]

GW your lathe is larger than mine. I part all the time on my Atlas 618 with brass and aluminum. My parting tool is 0.040" wide, so may be too narrow for your application. Also the there is no top rake. Rather than the tilt that you show, mine is not tilted.

David