New lathe giving me fits!

rwskinner · Feb 19, 2018

I bought a new Acra 21x60 and I have been using it a couple months. So far, everything has been going fairly well until I try to bore. All my bores are picking up tons of chatter even on light cuts. Using the same exact set up, feeds, speeds, and tooling my Leblond doesn't chatter at all. Feed and speeds are set up properly for the job as I do this same job on the Leblond on a regular basis.

Now, the Acra is cutting great in the outside turning, it's only the internal boring causing the issue. I checked the gibs on the cross slide and the compound and even have them locked to make sure they aren't too loose. I snugged up the gib on the front of the apron a tad tight to eliminate that area as well.

The job requires this 1.5" boring bar to be extended about 7" out from the holder. Most cuts are 0.050" from diameter or less in mild steel. Never a problem on the Leblond.

What all should I check? I put an indicator on the top of the apron and ways and check for excessive play then from the cross slide to the apron, then the compound to cross slide and I'm not showing any deflection (mainly because I have it all pretty tight right now).

Now on the back of the apron, I can pry it up off the ways about 0.004" so that needs to be tightened up some. I have to remove the back splash guard and take some time to adjust this out closer.

I put some 2" pipe in the 4 jaw chuck for leverage and put an indicator on the outside of the chuck. I am picking up about 0.002" on the outside of a 16" chuck but that is prying pretty hard. Is that too much? Parts are turning true and concentric so far.

Are the two items out of whack enough to cause all these problems? I've ran some pretty worn out iron over the years that never acted like this so I'm not real sure.

Ideas and help would be appreciated.

Richard

JST · Feb 19, 2018

Assuming this has rolling element bearings (ball, roller), that 0,002" seems like a lot. Possibly the spindle preload is not set correctly? We need to know how you measured that.

I have absolutely no knowledge of that particular machine, so I'm no help as far as specifics on "how to" adjust or check that per factory.

But, before getting excited, maybe you can describe just what you did, where the indicator is, what the indicator is based on, what it is measuring to, and whether that 0.002" is a TIR, or a one-direction measurement.

I am not sure why a preload problem should show up more with boring than turning. I CAN see why it might be that way with a carriage, crosslide, compound, or toolpost problem. Leverage is different.

rbjscott · Feb 19, 2018

Bore on the back side to see what happens.

Spruewell · Feb 20, 2018

Check the center-line of your tool. If you are running the same tools and tool holders from one machine to the other, there could be a difference in the overall heights of the toolposts relative to the centerline of the spindles. The other thing to consider is the mass and rigidity of the carriage, cross, compound, and tool post.

rons · Feb 20, 2018

rwskinner said:
I bought a new Acra 21x60 and I have been using it a couple months.

The job requires this 1.5" boring bar to be extended about 7" out from the holder. Most cuts are 0.050" from diameter or less in mild steel. Never a problem on the Leblond.

What happens with quality of cut as boring bar extension changes from 1" to 7"?

I'm not a firm believer in prying.

Somebody I knew owned something like your new lathe. Had a built-in frequency drive and could feed with a ton of different settings. The one thing I remember him saying was that he made a big fuss about setting the machine level on the four feet.

thermite · Feb 20, 2018

rwskinner said:
until I try to bore. All my bores are picking up tons of chatter even on light cuts. Using the same exact set up, feeds, speeds, and tooling my Leblond doesn't chatter at all. Feed and speeds are set up properly for the job as I do this same job on the Leblond on a regular basis.

Now, the Acra is cutting great in the outside turning, it's only the internal boring causing the issue. I checked the gibs on the cross slide and the compound and even have them locked to make sure they aren't too loose. I snugged up the gib on the front of the apron a tad tight to eliminate that area as well.

The job requires this 1.5" boring bar to be extended about 7" out from the holder. Most cuts are 0.050" from diameter or less in mild steel. Never a problem on the Leblond.

What all should I check?

If your Lelond is a "Regal" some among us class that as a light/medium.

Even so, is the Acra even as heavy, most especially in carriage, cross, and compound?

A photo of your TP or bar mount, and overall setup could help PM to better help you.

Beside other good advice already posted, as to tuning it for better stability, you may have to consider fabbing a monolithic bar mount that replaces the compound.

rwskinner · Feb 20, 2018

The spindle does have 3 bearings and I really don't think it's in the spindle either but I did want to mention it. The 0.002" I measured there is more deflection than clearance. In other words, pulling on the pipe can get up to 0.002" deflection but it goes back to zero as soon as I release the bar like it's spring loaded, again most likely because I'm flexing it.

FYI, I mounted a mag base to the ways and put my indicator plunger on the outside diameter of the chuck at 90 degrees (pointed towards the back splash guard). 2" pipe was about 3 feet long.

JST said:
Assuming this has rolling element bearings (ball, roller), that 0,002" seems like a lot. Possibly the spindle preload is not set correctly? We need to know how you measured that.

I have absolutely no knowledge of that particular machine, so I'm no help as far as specifics on "how to" adjust or check that per factory.

But, before getting excited, maybe you can describe just what you did, where the indicator is, what the indicator is based on, what it is measuring to, and whether that 0.002" is a TIR, or a one-direction measurement.

I am not sure why a preload problem should show up more with boring than turning. I CAN see why it might be that way with a carriage, crosslide, compound, or toolpost problem. Leverage is different.

rwskinner · Feb 20, 2018

Reducing boring bar extension from 7" down to 4" solves the problem, but you can no longer reach the work.
This is why I think the carriage is lifting. Boring on the back side may also prove this, I think.

I don't have a VFD on this machine but I have changed RPM, Feed, Speed and everything else under the sun including moving to 1/64" radius finishing inserts and then to ultra sharp HSS to make it more free cutting. It helped, and I thought it I was making progress but it looked like a knurling tool went thru the bore when I was done.

Lathe was leveled with Starrett 8" machinist level on 4 feet then the other two feet just ran down snug.

<<What happens with quality of cut as boring bar extension changes from 1" to 7"?

I'm not a firm believer in prying.

Somebody I knew owned something like your new lathe. Had a built-in frequency drive and could feed with a ton of different settings. The one thing I remember him saying was that he made a big fuss about setting the machine level on the four feet.>>

rwskinner · Feb 20, 2018

rbjscott said:
Bore on the back side to see what happens.

Yes sir, on the next one I plan to do exactly that. That ought to tell real quick if the back of the apron is lifting. I sure don't see how cause it does it on even light cuts but it was something I wanted to try.

rwskinner · Feb 20, 2018

They are both in the same weight class. Actually, the Acra is a tad heavier. Both are only 6,000# lathes with chuck. Both have 14" wide bed/ways but I do have to admit the saddle on the Leblond has a larger, wider foot print. The Acra has a smaller saddle and apron with the push pull knobs for feed control like the Clausings did.

thermite said:
If your Lelond is a "Regal" some among us class that as a light/medium.

Even so, is the Acra even as heavy, most especially in carriage, cross, and compound?

A photo of your TP or bar mount, and overall setup could help PM to better help you.

Beside other good advice already posted, as to tuning it for better stability, you may have to consider fabbing a monolithic bar mount that replaces the compound.

rwskinner · Feb 20, 2018

Yes, I had to raise the height of all the tooling for the Acra. The plan was to slowing move everything over to the Acra and eventually get rid of the Leblond but that might not be the case until I figure out this annoying issue.

Spruewell said:
Check the center-line of your tool. If you are running the same tools and tool holders from one machine to the other, there could be a difference in the overall heights of the toolposts relative to the centerline of the spindles. The other thing to consider is the mass and rigidity of the carriage, cross, compound, and tool post.

Demon69 · Feb 20, 2018

rwskinner said:
I bought a new Acra 21x60 and I have been using it a couple months. So far, everything has been going fairly well until I try to bore. All my bores are picking up tons of chatter even on light cuts. Using the same exact set up, feeds, speeds, and tooling my Leblond doesn't chatter at all. Feed and speeds are set up properly for the job as I do this same job on the Leblond on a regular basis.

Now, the Acra is cutting great in the outside turning, it's only the internal boring causing the issue. I checked the gibs on the cross slide and the compound and even have them locked to make sure they aren't too loose. I snugged up the gib on the front of the apron a tad tight to eliminate that area as well.

The job requires this 1.5" boring bar to be extended about 7" out from the holder. Most cuts are 0.050" from diameter or less in mild steel. Never a problem on the Leblond.

What all should I check? I put an indicator on the top of the apron and ways and check for excessive play then from the cross slide to the apron, then the compound to cross slide and I'm not showing any deflection (mainly because I have it all pretty tight right now).

Now on the back of the apron, I can pry it up off the ways about 0.004" so that needs to be tightened up some. I have to remove the back splash guard and take some time to adjust this out closer.

I put some 2" pipe in the 4 jaw chuck for leverage and put an indicator on the outside of the chuck. I am picking up about 0.002" on the outside of a 16" chuck but that is prying pretty hard. Is that too much? Parts are turning true and concentric so far.

Are the two items out of whack enough to cause all these problems? I've ran some pretty worn out iron over the years that never acted like this so I'm not real sure.

Ideas and help would be appreciated.

Richard

You mentioned in following posts that if you extend the bar 4" rather than 7" it cuts fine, and that it turns OD fine, unless im missing something im thinking thats a good bet for it not being spindle bearings.

Assuming the machine is levelled properly, Im thinking the problem is likely a lack of rigidity in the carriage → tool holder somewhere. Ie wear in slides, tool post not seating well to the compound etc etc. You said you indicated for movement in the slides, did you check for side to side movement too? It could be anything thats flexing under pressure, depending on how you indicate, what you see 7" out you might miss at 1" out. Be nice to see some pics of the machine, maybe give us an idea of how you clocked the assembles too :scratchchin:

rwskinner · Feb 20, 2018

I have the compound slide parallel to the bed in order to give it the most support and keep it from rocking side to side. I removed the splash guard this morning and tightened up the back gib strip on the saddle and took that 0.004" down to 0.0005". Carriage moves a little stiffer but still moves fine.

I check side to side on the following...
Saddle to Bed, Saddle to cross slide, cross slide to compound, and total, compound to bed. If there is any movement I can detect it and it would be only a tenth of a thou or so.

Demon73 said:
You mentioned in following posts that if you extend the bar 4" rather than 7" it cuts fine, and that it turns OD fine, unless im missing something im thinking thats a good bet for it not being spindle bearings.

Assuming the machine is levelled properly, Im thinking the problem is likely a lack of rigidity in the carriage → tool holder somewhere. Ie wear in slides, tool post not seating well to the compound etc etc. You said you indicated for movement in the slides, did you check for side to side movement too? It could be anything thats flexing under pressure, depending on how you indicate, what you see 7" out you might miss at 1" out. Be nice to see some pics of the machine, maybe give us an idea of how you clocked the assembles too

Tyrone Shoelaces · Feb 20, 2018

I'm not a turner by trade but to my machine tool fitters eye that's a fair bit of stick out for the rigidity of the set up. I'm wondering what it would be like with a positive rake tool instead of that negative looking throw away tip.

Regards Tyrone.

Bobw · Feb 20, 2018

Stupid question... Are your jaws slightly sprung? Grabbing a little harder
at the back of the chuck than at the front of the chuck..

This may sound stupid, but I have a 3 jaw that I use to mill with, its a POS, and
its sprung a bit.. When I'm grabbing something with the full length of the jaws
it gets pretty choppy.. I just take a piece of plastic masking tape and wrap it
around the part so that the front of the jaws grab it, and I don't have any problems.

Demon69 · Feb 20, 2018

rwskinner said:
I have the compound slide parallel to the bed in order to give it the most support and keep it from rocking side to side. I removed the splash guard this morning and tightened up the back gib strip on the saddle and took that 0.004" down to 0.0005". Carriage moves a little stiffer but still moves fine.

I check side to side on the following...
Saddle to Bed, Saddle to cross slide, cross slide to compound, and total, compound to bed. If there is any movement I can detect it and it would be only a tenth of a thou or so.

View attachment 221097
View attachment 221098

Wow looks near new, I thought we were talking about an old beater.

Im thinking to indicate each connection starting with the tool block.
Green: indicate to the back of the bar top and side, pressure the bar tool end up and down and side to side.
Red: Indicate from the block to the back of the compound and do the same. It could be somthing as simple as the Tslot has pulled a bit and not allowing the block to seat properly.

The problems seem occur when the tools stuck out, so try an replicate that distance from the fulcrum in your indications, see if you can locate the 'big one' starting with the simple stuff, eliminating things step by step.

thermite · Feb 20, 2018

Photos tell a clear story, thank you for those.

What jumps out at me right away:

- Regardless of the level of "goodness" or lack thereof in a(ny) Acra, and "heavy" is not evident, this one is also a raised swing model.

You'll be about as steady as stand-up shagging on stilts as far as deep boring goes with that tribe. Any make.

- Compare the long-axis length of the carriage and its "wings" of your LeBlond and your Acra. Similar effect. Stand with both feet tight together, small child can knock you over. Try again, Sumo-wrestler's wide stance, not happening.

- bar is hung offset to the supporting mass under the TP, it is a lever on short (cross) axis as well as long.

If the inserted tool is also Neg Rake?

You don't HAVE a boring setup at all, Pilgrim.

You've only built a rather BAD tuning-fork!

Minimalist answer? Go back and use the LeBlond. Even so, look to correcting the setup.

Rigidity in a boring op is akin to (what I have been told) lubrication is to those interested in proctology.. and similar persuasions:

Too much .. is almost enough !!!

You really do not want to "go there" without whichever one as is most appropriate.

rwskinner · Feb 20, 2018

I was shocked at the raised swing also however if you really look around almost all new lathes are starting to be that way. So basically I have a $30k POS. Nice. Yes, the saddle on my Leblond is 20.5" wide and it's only 17.5" wide on this one and I realize every little bit that counts.

Recommendations on a good 1.5" boring bar with positive rake would be great. Seems everywhere I search those all point towards a negative rake insert. I get small boring bars with sharp positive rake inserts all day long but I have to admit I'm no expert at all on the subject.

I was picking up significant chatter even with a sharp HSS bit. I use that lots of times when I have to take a super fine finish pass or to sneak up on a bore diameter....

thermite · Feb 20, 2018

rwskinner said:
I was picking up significant chatter even with a sharp HSS bit. I use that lots of times when I have to take a super fine finish pass or to sneak up on a bore diameter....

CAVEAT: This MAY make the problem worse. I do know my imitations... but.. it worked on clapped-out War One era Niles because..one can add mass to a saddle already hard to lift..

Go to sharp HSS-Cobalt. Rotate the bar 180 degrees on its long axis, chipbreaker/top of the cutter now down, not up, lathe still to be run in "Forward", not reverse. Inherently sound and vibration deadening Mark One human right arm pulling pre-load on the TP toward the operator. Sandbag on the away side of the cross.

Won't take long to see if it helps or hinders. Doesn't have to cost anything but a risked part or close-enough dummy from drops.

Mind.. we HAD NO compound rest on any lathe more than about once in several weeks.

Massive 4-way that needed an overhead crane to mount or de-mount directly to the cross in place of a compound, rather. And no, it isn't at all difficult to thread that way.

OTOH, the lathe, the work, the bar, and the tool were all scaled accordingly.

Terry Keeley · Feb 20, 2018

My Toolmaker buddy turned me on to these high rake Iscar inserts, they turned boring on my small machines from ugly to a joy:

ISCAR Cutting Tools - Metal Working Tools - TPGT-SP

These are for finishing but I'm sure something in that line (probably with a bigger nose radius?) would be great for bigger cuts.

ps: What inserts/bar are you using?

New lathe giving me fits!

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Aluminum

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Diamond

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Aluminum

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Titanium

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