[lcvette]

Well, I was turning down some aluminum to make a index pulse disc for the mill and ruined a part trying to get cute with the boring bar.. My Lathe/mill combo G9729 harbor freight model still has the rotating tool post which I like and hate all at the same time.

It's great for OD turning bit has a strange height for my boring bars. Even with them shimmed as high as they can go they were needing to be rotated to clear the underside of the boring bar. So while sneaking up on the final ID of my part I usually try to make a final cut of around .020" or else the boring bar chatters like hell and leaves a terrible finish. The problem is because the bar requires being rotated down and off center its kind of guess work because the dials no longer coincide with the actual cut depth. So I went over and the fit was too loose so needed to start all over..

So I decided I was going to fix the problem so I could use the wheel markings as intended. After looking at it for a few minutes is decided to flip the boring bar over in the tool post with the cutting edge down and pointed at the backside of the Lathe. This allowed me to get the cutting point at the center height of the spindle axis. I decided to put a dial indicator on the d axis to ensure I was accurate this time. So I made a test cut to see where the minimum depth of cut the Lathe would be happiest at and low and behold it cut smoother with an unbelievable surface finish.. Zero chatter, and I was able to cut from .001" to .100" with no chatter and great smooth cutting and perfect finish..

So the part came out Gorgeous!!! And I learned something new. I also decided to try my parting tool which I never could get to work very well and boom!!! Cuts like a hot knife through butter!!

So for anyone plagued with chatter. Flip the tools upside down and welcome the new amazing fun the Lathe becomes!!!

Hope this helps some of you out! I know my build will now incorporated more of a slant bed design with rear mounted tool post to flip all tools upside down. I imagine a more rigid machine can handle heavier cuts without chatter. But these smaller machines struggle with it. I'm so excited to find a solution I had to share!

Happy chip making!!

Chris

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[Fastest1]

I started using the cut off tool upside down and the lathe turning in reverse a while back. I get great results, quietly too. I dont have problems with the boring bar though.

[lcvette]

Yeah it makes a world of difference.. I started setting my G9729 to run all cutters upside down before I realized it wouldn't work for some of them due to the feed direction being tied to the spindle rotation direction. I was bummed out. Lol... But it will be no problem once converted to cnc..

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[kawazuki]

I'm somewhat confused with the descriptions....... Turning the tool upside down and moving it to the rear, keeping the correct 'normal' rotation shouldn't make any difference! Turning the tool upside down, moving it to the rear and reversing the spindle direction will achieve nothing except polish the surface! I've heard that people have more success with parting when tool is moved to rear, tool up and reverse spindle as tool is pushed down.......but in 'theory' its no different to being mounted normally ? ? ?
I prefer to see what is happening at the tool cutting interface rather than having it all hidden - just personal opinion and what works for me.

[Fastest1]

Kawazuki, I believe the original problem Chris was having was getting the tool tip at the centerline.

I was not referring to using a rear tool post. Merely flip the cut off tool over, recenter the height and reverse the direction of rotation. I never liked the chatter and or unpredictability of running the tool conventionally. You would think there wouldnt be a difference but there is. Try it as a test, then report back.

[lcvette]

The turning the tool upside down you can cut from either direction just depends on spindle rotation. It they are left cutting tools they will need to go to the rear to cut as left cutting. If you have right cutting holders you can front mount them upside down and cut with reverse spindle rotation as left cutting tool holders. My problem as I was explaining it is for a facing operation with a rear mounted tool upside down, my feed would be moving the took in the X + direction away from the part center which is useless... And if I got right hand cutters and ran in reverse with them front mounted, then my Z feed would be in the + direction so I would always have either a facing or OD turning issue with the gear driven feed so could only have one work correctly.

PS.. Don't knock cutting upside down until you've tried it. It takes alot of chatter out and leaves a superior part finish.. I recommend a spring pass for tight tolerance parts..

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[109jb]

It needs to be said. DO NOT CUT IN REVERSE ON A THREADED SPINDLE LATHE!!!!! I know someone will say that there are locking set screws in the backplate, but that is not always true and I wouldn't trust them anyway. Very bad things can happen.

[lcvette]

Good call!!! Should have thought to mention that! As stated try with common sense and only on bolted Lathe chucks!

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