heres how to get 0.0001" precision on your ancient hobby lathe

[george wilson]

I won't lock it since Nelson didn't. But,I'll be glad to see this long,convoluted list of repudiations go on down the list and vanish. And this after criticisms were asked for in post #1.

 

[John Hasler]

I won't lock it since Nelson didn't. But,I'll be glad to see this long,convoluted list of repudiations go on down the list and vanish. And this after criticisms were asked for in post #1.

IMHO it's one of the best discussions we've had in months. Nothing wrong with a bit of argument as long as it doesn't get personal.

 

[george wilson]

When a person just will not listen to sound reasons why a ground surface is called for in high precision,it gets to be a bit of a pain.

And,that last statement about the HF mike being made of the same materials as a Mitutoyo(is it really?),so it must be as good, was right off the wall. I can list a dozen reasons why the HF mike probably is not as good. But,why bother?

 

[John Hasler]

When a person just will not listen to sound reasons why a ground surface is called for in high precision,it gets to be a bit of a pain.

And,that last statement about the HF mike being made of the same materials as a Mitutoyo(is it really?),so it must be as good, was right off the wall. I can list a dozen reasons why the HF mike probably is not as good. But,why bother?

He didn't say it was as good. He just said it would expand at the same rate due to both being made of invar.

 

[george wilson]

There's no telling what crappy grade of metal was used in a real cheap instrument. There are lots of home brewed grades of cast iron out there in Asia.

 

[BRIAN]

Hi all
Just so us at the small end of the shop can get something out of this intense discussion I looked at the title and went into the shop
, turned the compound to the required angle, then then took apiece of HSS and roughly made a shear tool didn't even hone it.
Found the worst piece of hot rolled steel that I scrounged from the local blacksmith and took a cut with a carbide tool just to remove the rubbish, ended up with the normal B--- A---- finish.

placed my new shear tool in the lathe and took a cut of .002" WOW It started to look smoother ,another two passes and I had a acceptable (to me) finish.





Now if I am trying to make two parts fit together I need to take fine cuts, so now I try the compound just one division and it takes off a very fine sliver so I now measure the size to see if I can take off a controlled amount.
My daddy's mic that he bought just after the war. WW1 not WW2, will not measure down to these sizes. so I had to turn to my cheepo metric mic that measures down to.01mm This is a figure almost non existent in my usage.

Repeated cuts show I can happily hold a .01mm change in diameter so the cut must be half that, Boy am I pleased.
This is going to help me when it comes to making the crank for my engine.
The argument about shop environment ETC don't mean a thing to many of our members Just trying to make chips

Just remember the title said ( ancient hobby lathe ) and this thread is a big help to those starting out on this never ending hobby.
.Brian.

 

[higgite]

I think it has been a good discussion for the most part. But, what I'm taking away from it is that the theory is solid (you can't argue with math), but the application to hobby lathes is pretty iffy for frog hair precision purposes. ymmv

John, off topic for an instant... 408 yards... in 3 quarters... not too shabby.

Tom

 

[Micke S]

I think the idea of a superior finish versus an accurate diameter are being mixed up. One does not necessarily come along with the other. A tool post grinder will not correct pitch error in the tool post screw or the tool post ways not being straight.

Do you really think diameter and surface finish are mixed up, and has anyone so far claimed that a tool post grinder has the capability to correct pitch errors and defective ways ? ondering:

 

[chips&more]

I think it has been a good discussion for the most part. But, what I'm taking away from it is that the theory is solid (you can't argue with math), but the application to hobby lathes is pretty iffy for frog hair precision purposes. ymmv

John, off topic for an instant... 408 yards... in 3 quarters... not too shabby.

Tom

That’s it exactly. It looks good on paper, using the offset compound and all. But in the real world, it’s basically dream land trying to hold 0.0001” with variables like a worn out lathe, tool bit material, tool bit geometry, tool pressure, operator finesse, type of job/material, ambient conditions…to name a few. But it’s fun talking about it…Good Luck, Dave.

 

[John Hasler]

There's no telling what crappy grade of metal was used in a real cheap instrument. There are lots of home brewed grades of cast iron out there in Asia.

That's easily determined. Cool the instrument to 50F, measure a 1" block, heat to 100F, measure again. By my calculations if it's invar he'll see less than a tenth change, if steel or cast iron perhaps half a thou.

Your Mitutoyo might do much better, of course.