Backlash Or Just Poor Technique?

[chevydyl]

Funny how that works eh wreck, I get great finishes with roughing depths, with no cut on the back drag, but when I take 10 thou or so not a great finish but it will cut on the back

 

[John Hasler]

Yep. It's going to be sensitive to the diameter of the workpiece. Dropping by 0.1" on a 4" diameter piece is equivalent to dropping 0.025" on a 1" piece. In either case you've reduced the rake and rotated the cutting forces by 2.86 degrees.

Makes me think about a toolholder that would maintain a constant angle as the tool advanced into the work rather than a constant height.

 

[pstemari]

Makes me think about a toolholder that would maintain a constant angle as the tool advanced into the work rather than a constant height.

That's why putting tools on center is standard. The angle remains constant.

Sent from my Nexus 6 using Tapatalk

 

[John Hasler]

That's why putting tools on center is standard. The angle remains constant.

Sent from my Nexus 6 using Tapatalk

That's not what I meant. Jim wants to put his tool slightly below center such that the forces balance out and the tool is neither rocked back nor pulled under. However, the optimum amount by which to set the tool below center decreases as the diameter of the work decreases. This probably boils down to an optimum angle between the horizontal and the plane defined by the centerline and the cutting edge (in fact some references enjoin one to set the tool a certain number of degrees below center for some operations). A holder such as I speculated about above would maintain this angle by advancing the tool upward along a line from the initial setpoint toward the centerline.

 

[kingmt01]

There is such a tool. It has been around a long time but the name slips my mind ATM. The tool holder is about $200 but uses a piece of HSS. It looks great but I can't bring myself to spend the money.

 

[JimDawson]

That's not what I meant. Jim wants to put his tool slightly below center such that the forces balance out and the tool is neither rocked back nor pulled under. However, the optimum amount by which to set the tool below center decreases as the diameter of the work decreases. This probably boils down to an optimum angle between the horizontal and the plane defined by the centerline and the cutting edge (in fact some references enjoin one to set the tool a certain number of degrees below center for some operations). A holder such as I speculated about above would maintain this angle by advancing the tool upward along a line from the initial setpoint toward the centerline.

That sounds like an interesting design project. The biggest problem I can see is anchoring the tool in position while still being able to change the height as the cross slide advances. Hmmmmm.....going to have to think about that.

 

[kingmt01]

It isn't that the tool moves in height as the tool advances. It is the angle that the tool is held in the tool holder that it always keeps the correct tangent to the work.

 

[kingmt01]

Found it. This is the tool holder

As soon as I remembered tangent I remembered what the tool was called.

 

[John Hasler]

It isn't that the tool moves in height as the tool advances. It is the angle that the tool is held in the tool holder that it always keeps the correct tangent to the work.

Change the rake as a function of X movement? Not quite the same effect, I think.

 

[kingmt01]

I may be wrong but I believe by dropping the tool that is pointed straight you are changing the tangent & that is what keeps the tool from being pulled in & pushed out.

Then again I'm probably not much more knowledgeable then the other beginners. I do most things by feel & I get lucky often. That is what makes it look like I know what I'm doing.