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Matt
02-04-2003, 05:18 PM
While turning a length of 2" stock today with a right hand cemented carbide a friend who was watching suggested cutting in the opposite direction (towards the tailstock)with the same tool assuring me that the finish would be much better and that he does this regularly on his lathe. What do you think?

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Matt

Oso
02-04-2003, 05:35 PM
Sounds like a brass magnet.

Tool form, material and speed affect finish. Direction does not, unless your friend never sharpens his tools. The unused side would still be sharp................

DR
02-04-2003, 08:36 PM
Yes, we do this all the time on our CNC lathes using CCMT32.5x inserts. That's an 80 degree diamond.

For instance on your part we might take a heavy cut towards the headstock, feed in a couple thou' and finish back towards the tailstock. This works especially well on aluminum. Stainles and steel also.

Oso
02-04-2003, 10:31 PM
OK, den why duz it wurrik?

Maybe the cutting angle? Got to be something with the toolbit.

Matt
02-04-2003, 11:04 PM
I should have mentioned in the original post that the cemented carbide I was using has side rake that makes it a right hand tool only, not like an insert(diamond)which can cut in either direction.

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Matt

Thrud
02-04-2003, 11:51 PM
Matt

It depends on the type of insert and its retention method. The geometry of most toolholders is designed for one direction only, but this is not always the case. Some toolholders are designed for any direction of tool path cutting - these were refered to tin the past as "copy lathe tools". These days they are used for CNC machines doing complex profiles with single tools - some heavy cut-off blades are used this way.

The old style inserts that were clamped only have a tendency to slip out if used in the wrong direction as well as becoming excessively negative. This is why pin & clamp, screw retained, and levered pin are used on most inserts these days. Large face mills are often clamped inserts - so never run these backwards! http://bbs.homeshopmachinist.net//biggrin.gif

JCHannum
02-05-2003, 10:24 AM
Did you try it? Did it work? Then it works. If it didn't work, then it doesn't work, but it might in a different set up.
Feeding the tool backwards sometimes can have a burnishing effect on the workpiece. It depends on the geometry of the tool and the material being cut.

kap pullen
02-05-2003, 01:08 PM
We used to turn shafting for the cardboard box industry tword the tailstock.

Set the rough shaft in the four jaw, and steady at the tailstock end.

Line up the steady, center drill, and set the center.

Slide steady back to the chuck.

Start the cut tword the tailstock from close as you can get to the headstock.
When she starts to chatter, move the steady out, and set on the just turned area.

Do that twice on a 4.5 dia x 120" shaft, and redo it again for the finish cut with a positive finish tool.

Reset the steady at the tailstock end, to finish the journals (bearing and gear dias).

Reset and finish the other end.

Standard practice for shaft work, least where I worked.

We used those old slab style negative inserts with 1/4 doc per side, and .022 "/rev feed at 300 sfm.

Makim plentyum bluechipps, c's and 6's like in the book.

Dosen't relate to the post, but could resharpen the tool instead of running it backward for a finish.

You're lible to get chatter with that lead angle unless using a tracer type tool.

kap

Matt
02-05-2003, 06:19 PM
Again with the inserts! I never said I was using an insert tool. Cemented carbide designation AR 8.

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Matt

bspooh
02-05-2003, 07:43 PM
a very heated discussion....

brent

C. Tate
02-05-2003, 10:13 PM
Matt,
Insert,cemented carbide or hss makes no difference. Like OSO says finish is directly related tool geometry, cutting speed, feed rate, and rigidity of your set up. If you try it and works go for it.

[This message has been edited by C. Tate (edited 02-05-2003).]

[This message has been edited by C. Tate (edited 02-05-2003).]

Kevin45
02-15-2003, 07:25 AM
It will work and I do it quite often. It lets the shaving or chips fall completely away from the tool instead of falling onto the tool and taking a chance of pinching. Also it kind of burnishes the material coming back across even though it is taking a cut. One other thing, never use a sharp tool. Always break the edge ever so slightly and put a radius on it. I keep a diamond hone in my toolbox just for this purpose. It is unbelievable just how much difference the smallest radius will make on a tool. When it is sharp it will tend to dig in and leave what I call a furry cut. With a slight radius and the proper feed and speed you will get a reflective cut.

Kevin