Repeatability/Indexing

[mickri]

I often read about the need/want of indexable tooling. Usually in connection with QCTPs. I think that I understand the concept. Yet often wonder how important is this in a hobby shop where we are often making one thing. Not hundreds as in a production shop.

So educate me on the importance of repeatability and indexable tooling.

 

[RJSakowski]

I don't worry about indexing other than tool height with my AXA QCTP because I am constantly changing the tool post rotation to optimize cutting. The OEM four way tool post had fairly repeatable indexing but I prefer the ease of tool height adjustment of the QCTP vs. repeatable indexing.

I expect that a wedge type QCTP is more repeatable than the piston type which I have. For rough turning or facing, I will change tool holders without concern for referencing. For precision work, I will make a light cut and measure before a final cut.

 

[pontiac428]

On single point manual machines it is as close as you can get to being completely irrelevant. On manual mill tools with multiple inserts, you can see one way that repeatability in setting cutters is desired. On CNC you usually have to back off your offsets by some tenths when replacing inserts regardless, so you can account for wear. Real commercial tools (Kennametal, Iscar, etc.) do not have much issue with repeatability.

 

[WobblyHand]

Question for @mickri do you mean insert indexing or part indexing? Not sure if either, or something else entirely. Just trying to refine the question so you can get better answers.

 

[mmcmdl]

For manuals , set the height and forget it . For CNCs , as @pontiac428 stated , top of the line tooling is certified meaning changing a tool in the turret will get you within .005 or so . Changing inserts in such tool would still need to be backed off and re-comped with the touch of a button .

 

[mickri]

Does it matter if you are using inserts? I don't think so but I don't know either. I have never used inserts and don't intend to. Grinding HSS tool bits is very easy with my belt sander. I can grind any shape that I want to. Another plus is HSS tool bits last forever. A light touch up is all it takes.

What I am asking about is repeatability when you change tooling with a QCTP. I was reading a thread this morning about QCTPs. The original poster asked about the repeatability/indexing of various types of QCTPs. Maybe someone can explain the pros and cons of this. And when it might be useful.

 

[akjeff]

I often read about the need/want of indexable tooling. Usually in connection with QCTPs. I think that I understand the concept. Yet often wonder how important is this in a hobby shop where we are often making one thing. Not hundreds as in a production shop.

So educate me on the importance of repeatability and indexable tooling.

Speaking for myself, if nothing else, the convenience of it all. This is assuming the lathe is not only equipped with a QCTP, but also a DRO with a memory/tool library. Hobby or not, I like doing things quickly and efficiently, and don't like repeating tasks that can be avoided if possible. Unless I'm making a part in the lathe that needs to be on size to within 2-3 thou, I can pretty much make the complete part without touching a caliper or a mic. A heavy, rigid machine teamed up with a quality QCTP( Aloris BXA in my case ) and a good DRO is a pretty nice thing to operate.

 

[pontiac428]

QCTP repeatability matters to me as far as staying on center goes. I've used different systems, and most repeat well enough. To be completely honest, a couple thou above or below center isn't going to be noticed. I care more that it does not move once set. Tool setting on the lathe has a lot of wiggle room in reality. I care not at all about tool lengths, because I set my handwheels with a touch-off automatically in the workflow when changing a tool.

The idea of keeping a tool library in a manual lathe DRO is about the same as wearing a conductor's hat and blowing a whistle when playing with model trains. If that's your thang, more powah to you. That's charm and flavor, but it's not what makes the train go.

 

[OTmachine]

On QCTP’s, Wedge over Piston Type. Common Shop Practice in places that I have worked were: roughing cut to about .020 to .030 oversize, reduce feed per revolution, measure, divide remaining amount in half to take semi-finish cut, measure and adjust to take finish cut based on the amount of material taken on semi-finish cut. And if I have to take a small amount to size a part, I prefer HSS with cobalt.

 

[akjeff]

QCTP repeatability matters to me as far as staying on center goes. I've used different systems, and most repeat well enough. To be completely honest, a couple thou above or below center isn't going to be noticed. I care more that it does not move once set. Tool setting on the lathe has a lot of wiggle room in reality. I care not at all about tool lengths, because I set my handwheels with a touch-off automatically in the workflow when changing a tool.

The idea of keeping a tool library in a manual lathe DRO is about the same as wearing a conductor's hat and blowing a whistle when playing with model trains. If that's your thang, more powah to you. That's charm and flavor, but it's not what makes the train go.

You can usually be counted on to respond to posts with ignorant, snide remarks when folks have the audacity to do things in a different way than you, and you didn't disappoint with this thread. Enjoy life on Luddite Island.