How perfect are tools?

[Jimsehr]

As and old school machinist I have never checked if my qctp repeats to a thousand or a tenth. Sixty years ago when I ran turrets I trusted that when I indexed the 4 way tool post that it would repeat. Also I always backed off the dia about .010 thousands because nothing is perfect and took a test cut when I changed inserts. More because I worried a spec of dirt or something got in the insert pocket.
I also remember using a tenth indicator and watching a tool jump a tenth or so when the lathe motor switch was turned on or off. Most jobs who cares.
I think it is a bit silly to worry in a home shop when most jobs are one offs.
I also backed off the tool dia when I ran CNC lathes When I changed inserts.

Another rant is when a new guy trying to learn how to grind tools goes to a book showing how it was done over 80 years ago. I have never seen a modern shop using those tool shapes in a modern shop. And some people try to make relief angles to some exact angle. I NEVER check angles when I grind tools andI never have.

And why 118 degrees for a drill point? Why not 120 degrees?

Rant over.
jimsehr

 

[benmychree]

Agreed, Jim; nobody uses the tool shapes that F W Taylor and Maunsel White standardized in the late 1890s when the discovered the heat treatment for HSS and revolutionized modern machining, development of modern cutting tool materials by Krupp (carbide) revolutionized metal cutting just as Taylor had, and also how ceremet and ceramic and CBN and diamond tools have done, it is a continual evolution over the past hundred plus years, and will presumably continue to evolve.

 

[Winegrower]

The tolerance field on most of the inserts I buy and use show 0.005". I don't actually know how that's measured, what it means, or if it's plus or minus, but it doesn't sound like perfect.

 

[mmcmdl]

Rant over.
jimsehr

What was the rant about ? This is common practice in any shop .

 

[Larry$]

I NEVER check angles when I grind tools andI never have.

I'm too lazy to check relief angles. Just eyeball it and go. I do use a fish tail gage for threading tools.

 

[MrWhoopee]

It's the difference between machinists who have worked in the trade and hobbyists who are learning from books or Youtube but have yet to be told "Quit f***ing around and get that job done!" by an impatient boss. I see it here frequently, dithering about tenths when ten thousandths is plenty close. And then there's speeds and feeds. I never met a manual machinist who calculated IPM. I believe those online calculators actually prevent people from developing an intuitive feel for what they are doing.

 

[great white]

I’m certainly not a pro. But I use spindle rpm and the simple calc to determine a starting surface speed and then adjust rpm up or down depending on what I see happening at the tool. Also adjust as the diameter reduces depending on what I see happening at the tooling face.

Parting is a little different for me. I put it in back gear and am usually somewhere in the 100-150 spindle rpm, adjusting up or down depending one what I see at the cutting tip.

When I grind my own hss tools, I “eyeball” it. I only hve a general idea of what it should look like and base adjustments on how it cuts. I’m usually less concerned with angles as much as what the cutting tip looks like. Always seems to work well enough for me.

But then again, I’m just some amateur hack out in his garage making the best chips he can on an old 1950’s Atlas….not joking either. I literally am just an amateur hobby machinist.

 

[Jimsehr]

What was the rant about ? This is common practice in any shop .

I had just read someone had bought a 5c collet and called it junk because it ran out .001 thousands.

I think it is silly to expect everything to be perfect.

I think it is silly to think a cutting tool has to be a certain degree.

I would hate to be a new guy trying to match these standards.

I think it is silly to tell a new guy trying to learn machining to read a book with out dated info about how to grind a tool. Info about a 100 years old.

To me it is like taking a teen out and saying I am going to teach you how to drive
then taking him out to a model A Ford.

Jimsehr

 

[tq60]

Lots of folks stressing to get to the tenth when the tolerance may be substantially different, like 0.010...

Being able to hit that is a learned skill that is needed.

A good operator can used bad tools and still hit the mark.

Sent from my SM-G781V using Tapatalk

 

[WobblyHand]

I don't stress about hitting to a tenth, but I do practice and try to hit tenths on occasion. The only way to get good at something is to practice. Most of the time being within 0.005-0.0010 is fine. However, there are occasions when being on the mark matters. Knowing when it matters is learned via experience. Going overboard with precision when it isn't justified is not productive.