lathe tool height?

[BigDave]

Ok, so I remember we're supposed to set the top of the tool cutting edge right at centerline for od turning.

But I heard somewhere that for id turning, that the cutting edge should be set slightly above centerline. And if so, would there be a difference in cutting edge height for negative rake inserts or not?

I did have the place I bought the new full size mill from remove the Newal Topaz readout and change it to their new 3 axis DP8 digital readout.

I hade them put the reader on the knee for the Z axis and added a Mitutoyo simple digital readout on the quill.

One thing that was lame about the lathe is once I put Valenite ValTurn water soluable cutting fluid in the sump, it leaked several tablespoons a night right throught the cast iron one piece base.

They said they would waterproof the sump with a sealant, and I told them I needed a lifetime guarantee on their sealant.

[C. Tate]

Negative rake tools are designed to run on center in and out. The clearances are built into the seat. Set on center by taking a face cut and adjust untill the little tit in the middle of the face is gone.

[Thrud]

It was suggested to set above center to allow more tool clearance in smaller holes.

Modern insert tooling for small boring and threading bars take this into account so most are still set "on center".

[Lead Screw]

Keep the tip on center unless you need the extra tool clearance. About that leak--- I've never seen a cast iron cooking pot leak unless it had a hole or a crack.

[ShopDawg]

I was shown a quick and dirty trick for finding the center height of a lathe tool when you can't face off the part. (you all may already know this one..)
Eyeball the height, and run the tool in with the lathe off until the tip of the tool is close to the part. Then, take a 6" rule, and hold it vertically between the tool and the part. Gently run the tool against the rule until it clamps it against the part. If the top of the rule tilts away from you, your tool is too high, points toward you, it's too low. Pointing straight up means you got it dead center.
I have also found out on my own, that it best if you use a 6" rule that ISN'T BENT.... (I'm glad I don't have to be smart ALL the time...)

KB

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http://shopdawg.com

[halfnut]

On center heights.

OK, you have boring bar in machine, set it at center. Now look at how it work and how it will flex, look at the cutting forces. It will push it down right, what happens when bar goes below center, hole gets bigger, you are boring oversize now, maybe not much but over, and it might make up for side deflection and you might just be right on, maybe.

The reason for setting a boring bar above center just a tad, is for a little windage or such. When bar deflects it will cut a little under not over.

Then take a free pass, worked with one guy who always made passes of 3, the cut, a free pass, then another. If it just barely fuzzes on the first free pass, I'll skip the second myself.

Hope your coolant pan doesn't spring any more leaks.

We have a new asian made lathe at work, first time I added coolant, I went and got the bucket as usual, mixed it up, tossed in machine, then I had to go and get the mop, dadburn back door on the pan of this machine, I think more went on floor than in sump.

I have got the process down now, I don't like a mop, them things hurt the hands.

[JBELANGER]

Heres a handy "tool" for setting lathe tools on center. All of our manual lathes have these at the shop. Its a block of scrap steel with a threaded rod, or a piece of drill rod inserted into it, and secured with a nut or roll pin. The overall height of the piece matches the distance from the lathe way to the chuck center. Whenever we have to change tools or set tools on center, we place the block on the lathe way and adjust the height of the tool insert or HSS to match the height of the rod. Its very easy and accurate.

[Thrud]

Hardinge has a cheesy tool like that...

When you set your boring bar too high the back rake becomes too negative and produces a poor finish. If you are using bits in a bar make sure the end relief is adequate or the heel of the tool will rub the bore. Also, a smaller bar insures chips can clear out properly. Excessive overhang can lead to chatter from sympathetic vibrations.

With modern insert type boring bars set them on center always.

[BigDave]

Thanks for all the replies, I will fiddle with on center and slightly above and see what the results are.

As to the leak in the cast iron base, the company that sold it to me sent out their guys and opened the sump. Right where the leak was there is a steel disk about 1.25" in diameter that is pressed into the hole and there are 4 stakes marks around it's perimeter. seems it was leaking through there, so some epoxy sealant was painted in the sump, that should take care of it.

[BrianH]

...I really liked the cheezy Hardinge setting tool.....