How to get a better finish?

[Shootymacshootface]

What mikey said and use your tailstock. A file with a handle different grits of emery cloth and some scotchbrite can work wonders when needed.

 

[benmychree]

Probably, 1/4" tool bits would be appropriate for that lathe, I have a 9" Monarch, and use 1/4" bits on it; plenty good for the size of machine, less grinding required. For cutting fluid, I use Tap Magic. and yes, as above, filing and polishing are part of lathe work, for sizing and appearance.

 

[mikey]

If the tool is ground up near the tip where all the cutting takes place then yes, that is what matters. However, I see no reason not to grind the tool properly. When you learn to fully use that tool and learn to angle it toward the tailstock to take fine finishing cuts more of the side cutting edge is engaged. At least be sure the first 1/4" of the side cutting edge is fully formed.

Insofar as tailstock support is concerned you will find that the finish will smooth out when you get to the inner 1/3 of an unsupported work piece, and the closer to the chuck you get, the smoother the cut. With a live center the cut is smooth all the way and your accuracy will improve.

I've not ever used an Atlas 618 so I'm not sure of its capabilities but I use 3/8" square tool bits on my little Sherline lathe and can easily take 0.040-0.060" deep cuts in mild steel when roughing. I would imagine your lathe would be capable of better than 0.025" cuts if everything else is okay.

I use 3/8" tools on my Sherline and Emco lathes and it works fine for me. Takes me all of 3-4 minutes to grind a tool so not too long.

The tool post is important, Craig. The tool can only cut if it is held rigidly and on small lathes with low horsepower and rigidity, it is important to get the tool on center height as well.

You can use just about any readily available cutting fluid. I use Tapmatic Gold most of the time but you can also use Sulfur bearing threading oil from the hardware store if you prefer; stinks, though. Use WD-40 on aluminum and none for brass.

Brass tools have zero rake on top so the tools are quick to grind. Hone them well, though.

 

[catsparadise]

Have a look on the web for details of a shear tool. Dead simple to grind (only 2 faces to grind). Only takes off a few thou at once but you can use one to get a much nicer finish on a lot a steels that wouldn't behave otherwise. I use one quite often to tidy up EN8 (medium carbon - not easy to make it shine!).

Rob

 

[BaronJ]

Hi Guys,

I agree about using a shear tool to get a good finish. I tend to use it when machining shafts to run in PB bearings.

This is mine. 10 mm square HSS M42.

Craig: The cutting edge is the vertical one with the backwards slope. Looked at from the chuck side, it looks like a "L". Apart from the backwards slope angle, about 20 degrees, the only relief is behind that vertical edge. I forget the exact amount, but ten degrees is enough.

 

[Shootymacshootface]

Have a look on the web for details of a shear tool. Dead simple to grind (only 2 faces to grind). Only takes off a few thou at once but you can use one to get a much nicer finish on a lot a steels that wouldn't behave otherwise. I use one quite often to tidy up EN8 (medium carbon - not easy to make it shine!).

Rob

I learned something new today!
Thanks mate!

 

[rgray]

Re aluminum or brass. I got a handy pdf from steves-workshop.co.uk that walked me through the process of grinding a tool. However, it says that steel, brass and aluminum all need very different side and back rack. Eg 0 back rake for brass, 15 degrees for steel and 35 degrees for aluminum. (Suddenly, I see a LOT of grinding in my future.) I really need different bits for each of these metals?

Craig

Almost all my tools are 0 backrake for both my manual lathes. I do have a few carbide inserted tools but use mostly HSS tools and 3/8" is what I use most of on my 12x 36. Most tool holders for my small lathe (Ames) have 1/4" hss bits.
I have 1/8"-1/2" bits. The 1/8" are used in my small (and large) boring bars and I have a quick change holder with one out each end that comes in handy now and then.
I had a hss face mill for the mill that had me grinding a tool like you show as it had to cut in a circular path. Sold the face mill but had extra 3/8" tools ground for it that I kept and they work good on the lathe, but not greatly better than my zero back rake tools. So I am usually cutting with flat top tool bits.

 

[Soggy618]

Old thread, new question ...

I'm researching getting a finer feed on a 618 and am looking at the page in the MOLO for threading on the 6".
They give a table listing feeds of .008", .007", .006", .005", .0021" (wait for it) ... then nothing. But in the text they
refer to a feed of .001046" and say there should be 6 rates shown. I'm pretty sure I can count to 6 (using both hands
and my nose as a pointer) but this table only has 5.

Any help would be appreciated.

 

[SLK001]

+1 on using a shear tool. The only trick to using it is cutting less than 0.001" per pass. Try to get to 0.0005" per pass. I turn on the lathe, then advance the shear tool slowly until it just creates a whiff of a cut, then start the longitudinal feed. The cuttings will look like angel hair and can even float in the air. Be careful that you don't breath in any. Always use a cutting oil and a high sulphur oil does best for cutting, but it is getting very hard to find. Oakley still makes some for pipe threading. Also, the tool edge wears quickly, so check it before every use.

 

[Shootymacshootface]

Any Ace Hardware store will have a house brand high sulfur cutting oil for pipe threading in quart bottles, or 1 gallon jugs. It's smokey, but it works well enough.