Negative rake on a 10EE?

I mostly use HSS on my 10EE but I have a project coming up where I will need to remove a lot of steel so I purchased a Dorian MCLNR08-3A 1/2" shank tool holder and some CNMG 322-PM inserts. The holder is negative rake which is new to me.

I did some test cuts on 1" to 1.75" mild steel of a couple different varieties and while I got fairly satisfactory results at ~1500RPM at ~.030 DOC (shiny, reasonably smooth cuts) but the whole lathe rung like a bell. You could actually put your hand on it anywhere and feel the whole 3200 lbs vibrating a deep ringing that didn't change much with RPM.

I have a 5HP VFD driven motor that did not slow down or complain in the least. I don't think it noticed.

I did everything I could think of to reduce potential chatter. The 8" chuck was tight everywhere with the work close, I checked all the gibs, there's no unnecessary overhang on the tool, etc. Like mentioned above it wasn't at only one RPM so it doesn't appear to be a limited harmonics issue. It only did seem to ring when the RPMs were fast enough for the SFM to be in the range where the carbide "worked" correctly and it would go from rough finish to shiny only with RPM change.

I know the insert gave effectively a small amount of positive rake but I'm wondering if it's a little too blunt. I know carbide isn't as sharp as HSS but this particular kind of insert seems bit dull even for carbide.

I'd love to hear the experiences of anyone using negative rake tooling successfully on the 10EE especially if it's an insert that will work in my tooling

Thanks,

Will

wfrancis said:

I'd love to hear the experiences of anyone using negative rake tooling successfully on the 10EE especially if it's an insert that will work in my tooling

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I used the Hell out of neg rake on L&S, Niles et al when it was all we could get that could survive against corn-cob stick weld. Average 30" swing, 15 to 50 HP, and a 4-way direct on the cross that wanted two men and the traveling crane to swap out.

I would no more take neg rake to a 10EE than put snowcat tracks on my Jaguar.

When not HSS-Cobalt, go and get modern, positive-rake carbides or ceramics, and she'll be happy and smooth as such things can be, even if not otherwise 'perfect' as to RPM, speeds, and feeds..

Bill

Try CNMP322 or CNGP322 inserts.

Your 10EE will thank you!

Mike

I run CNMG, DNMG , VNMG and WNMG on my 10EE with no issue. I do get some ringing with some small boring bars occasionally but they are positive rake. !/2" shank is perhaps where the problems stems all my neg rake tool holders are 3/4 or 1 inch.

Steve

I also use WNMG and CNMG inserts on the EE. Mostly use 1/32 R inserts, 1/16"R or larger can cause chatter or screeching.

I use an Aloris BXA tool post, with 3/4" shank tools. 2" 1018 CRS 700 RPM, .05-.075 DOC .010"/turn or more (or max on my round dial).
Yes there is chip noise and a rooster tail of hot properly broken chips flying off.

The top of the cross slide was hollowed out from use of the old style tool posts.
Many turning problems went away after I ground the top flat.

If using the T/S, most EE's I have worked with were worn from years of use with drill chucks with a necked down area in the center of the arbors.
A quick spin with a full length taper center with magic marker stripes along it's length will reveal if there is uneven wear along the length of the taper.
I had the taper hard turned on a CNC lathe with CBN inserts. Rock solid now.

1/2" shank tools are much too flimsy for these kind of cuts in my book.
Also the back end of the tool shank should not project out of the back of the Aloris slot, this can cause ringing if it sticks out 2X the section (1" on a 1/2" shank) or more.

Bill

Thanks for everyone's comments.

I have an AXA toolpost so 1/2" is typically the largest tool shank I can run, though it looks like there might be some "oversize" 5/8" holders I might be able to use. My investment in AXA is pretty decent so I'm not likely to upgrade to BXA just for this.

I can't find CNMP 322 or CNGP 322 inserts. Seems like both of those really start at 4XX. If there's a source that's not MSC, McMaster, Ebay or Amazon that I'm missing please let me know! I looked on the websites of some of the major manufacturers (Kennemetal, Sanvik, etc) which wasn't encouraging, either.

I'll look into a positive rake holder.

Will

Kennametal has CNMG322FF KCU10 or KC5010 (Fine Finishing with 20° positive top rake)

CNMG322FN KCP10 (Finishing Negative with 10° positive top rake)

If you change toolholders, get MCLNR124A and mill the 3/4 square shank down to suit your AXA block.

There are many insert choices in CNM*/CNG*-432 (1/2 inch IC) inserts.

Mike

To solve the problems with using 3/4" tools on an AXA tool post, I made a holder that accepted 3/4" tools with a dovetail that fit the AXA.
Slot is .760" tall and .750" deep. The sets screws are centered on the 3/4" dim.
Lower lip is .280" tall, material is 1045.
The BXA blocks are 1/8" taller than the AXA, and the 3/4" slot width means the block will be over 1/4" wider than the AXA.
Works like a charm.

Bill

The 4XX size inserts are the workhorse in the industry. Smaller inserts are harder to find, and don't have the selections available.

wfrancis said:

My investment in AXA is pretty decent so I'm not likely to upgrade to BXA just for this.

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Don't have to 'entirely' upgrade, so long as the AXA suits your majority needs.

MIGHT make sense to acquire a used-but-good BXA and at least two holders as 'problem solvers' to utilize well-regarded and recommended alternatives.

Not likely to be the last-time-ever that you have a need for more rigidity or ability to utilize different inserts..

Bill

wfrancis said:

I have an AXA toolpost so 1/2" is typically the largest tool shank I can run

Click to expand...

There is another neat trick you might consider - buying oversize tool holders - 1"-2" - and machining the AXA QC TP dovetail directly into the tool holder. Those large tool holders are often available used for cheap. The challenge may be finding compatibility with your preferred inserts. Bonus - you have the option of changing the engagement geometry and final height depending on where you locate the dovetail.

http://www.practicalmachinist.com/v...s-tool-holders-290091/index2.html#post2366150

Sounds to me like not enough feed causing the tool to rub rather than cut. What was the feedrate? The surface speed (390 - 690 fpm) is also on the low side for mild steel. Push things harder. Surface finish during roughing cuts doesn't matter so don't let that drive cut conditions.

Before buying new inserts or taking drastic steps, try doubling the DOC (.060 radial, .12 on diam), feed at .008-.020 IPR, and start with 1700 rpm (800 fpm at 1.75" OD). This is a ~3hp cut. Up the feed until the chips break in 6s and 9s. Then up the RPM until the chips come off blue. If you have power leftover up the DOC until it starts to complain or bog down.

I've run CNMG 432 inserts in a 1/2" holder on a South Bend 10L with a 1hp motor. Of course they were getting underused but if a South Bend can do that a 10ee should not be complaining.

So the BXA is the tool post of choice then?

I had a similar problem with cutoff inserts in aluminum. It turned out that when I ran out of the correct inserts, the owner of another shop gave me a few. At first I didn't realize they were honed (ie deliberately dulled) for steel and did not cut the aluminum to their full width. With both sides rubbing, the insert bounced back and forth slightly, making it sing and leave a matte finish.

Bill

I'm happy to report I had some time at the shop today and tried a much heavier DOC, like .060" per side, and it worked beautifully. Almost alarmingly so with heavy, hot chips really flying. The motor still didn't care.

I think I will get some of those fine finish ones as well. I bet they need a lot less DOC.

I still might look into a beefier tool post though, once the idea got into my head about getting a BXA it would open up some other tooling for me.

Thanks everyone!

Go to a 4 insert and holder as you get many more options and may find the carbide bits cheaper.
Whittle down the shank as needed. Not a big deal, most shanks are 40-48 4140 and easy to cut to whatever you need.

A premium top of the line coated grade CNMG/CNMP-432 in big quantity goes for under 4-5 bucks in my world but you are not buying 80,000 a year.
Sometimes you can tail onto another big user's blanket and get good prices on the common inserts so ask your salesman what is available at low prices.

The holder may be negative, the molded chipbreaker turns it into a positive cutting tool. On a normal G there is a flat land that you have to get past in feed per rev. to get this positive action. P inserts have very small or no land so work better when you are HP limited on feed per rev.
Downside the P is a weaker edge, chips easily and will flank wear faster.
Bob