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Bought myself a mini lathe..

Hi All:
I am still plodding along with my lathe project. I have my electrical problem solved and the coolant system is working well. I have made a few small parts on the machine and getting back to using a lathe. I now have to get some tooling and some more metal to machine. Now that fall/winter is upon us I will have more time to play in the workshop, it is easier to heat the place than to cool it.

jimf5
in Pahrump
 

NYECOGunsmith

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I thought we talked about that some time ago, conventional versus climb milling that is. Hopefully you found out about it without a bad experience!
 

Pcmaker

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I'm getting better at grinding HSS cutting tools for my lathe.

I've been using 1/4" HSS blanks and now I've switched to 3/8" M42 cobalt blanks.
 

NYECOGunsmith

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Wear a respirator and eye protection especially when grinding those cobalt blanks, cobalt is a known carcinogen and that grinding dust is hazardous to your health!
 

NYECOGunsmith

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That will work. ^^^^^
Also, unless you are going to be turning stuff like pre-hardened 4140, or Stellite, or Monel, or steel alloys that tend to work harden. Otherwise, plain old M2 HSS steel is all you really need.
On the other hand, M42 with 8% or 10% cobalt will stay sharper longer, and they are less prone to chipping if you have to make interrupted cuts.
So for most alloys of steel that are easily machinable, like 12L14 for example, I usually go with M2 HSS, same for aluminum and brass.
For stuff like some (not all) of the 300 and 400 series of stainless steel, 5150, 4140 , or abrasive stuff (things with glass fiber embedded in it for , phenolic, G10, Micarta, for example) etc. then I break out the more expensive M42 Cobalt stuff, particularly if I have to take hefty cuts at high speed and things are gonna get HOT even with a flow of coolant. The edges last longer in those applications.
If it's really hard or nasty abrasive wise, then it's time for Carbide tooling, just don't use Carbide bits for interrupted cuts, they will chip and shatter on you. And you have to (generally speaking ) take a deeper cut with Carbide to get a decent finish.
At least in my experience, TexasJackKin or Earthquake can probably give you a better picture, they are both real machinists, I'm just a hack.
 

Pcmaker

Obsessed Member
That will work. ^^^^^
Also, unless you are going to be turning stuff like pre-hardened 4140, or Stellite, or Monel, or steel alloys that tend to work harden. Otherwise, plain old M2 HSS steel is all you really need.
On the other hand, M42 with 8% or 10% cobalt will stay sharper longer, and they are less prone to chipping if you have to make interrupted cuts.
So for most alloys of steel that are easily machinable, like 12L14 for example, I usually go with M2 HSS, same for aluminum and brass.
For stuff like some (not all) of the 300 and 400 series of stainless steel, 5150, 4140 , or abrasive stuff (things with glass fiber embedded in it for , phenolic, G10, Micarta, for example) etc. then I break out the more expensive M42 Cobalt stuff, particularly if I have to take hefty cuts at high speed and things are gonna get HOT even with a flow of coolant. The edges last longer in those applications.
If it's really hard or nasty abrasive wise, then it's time for Carbide tooling, just don't use Carbide bits for interrupted cuts, they will chip and shatter on you. And you have to (generally speaking ) take a deeper cut with Carbide to get a decent finish.
At least in my experience, TexasJackKin or Earthquake can probably give you a better picture, they are both real machinists, I'm just a hack.
I bought the cobalt blank because I don't want to be sharpening so much and I wanted an all-in-one cutting tool, where it can cut most material
 

NYECOGunsmith

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The 8% or 10% cobalt will do that ^^^ , although it can be a bit tougher to get a really good edge on, so practice!

I like to start a grind on M42 HSS with a Vitrified Aluminum Oxide grinding wheel (properly dressed to a square face, first with a star wheel dresser to get nice sharp grains, and it also removes any tailings or pinnings from previous grinding of softer metals, then with a diamond dresser to get the shape I desire), of about 60 grit, of an I or J hardness level, as I have found the H level of wheel hardness to be a bit soft. Norton makes good wheels, been using them for decades with no complaints. The one I like for most tool bit grinding is the Norton 38A 60J8VBE, although the gray aluminum oxide version of it (that one is white) 32A 60J8VBE is a good one too, a bit tougher, but either one will do. You can actually read those numbers by the way, the 32 or 38 is Norton's model number the 60 is the grit , the J is the hardness level, the 8 is the structure of the grain, and the VBE is their term for Vitreous Resinoid Epoxy, what holds the grains together on the wheel.

The softer the wheel goes with the harder the material being ground, and the faster the wheel breaks down or wears out , and the K level I feel is too hard (the harder the wheel, goes with the softer the material you are grinding, the wheel lasts longer but will likely generate more heat in the object being ground) then for the final grind I move over to the 80 grit wheel, also Vitrified Aluminum Oxide. It's good for fine details, like on a forming bit (concave or convex radius, two side by side V grooves, other shapes) but otherwise is probably best left alone for a beginner, as it can burn the tool bit quickly when free handing a grind if you are not experienced.
Hardness levels run from A through Z by the way, with A being the softest and Z the hardest.

The other factor to consider when buying a grinding wheel is the porosity of it, also known as the grain structure or grain spacing. The lower the number, the tighter packed the grains are, the higher the number, the more open the spacing (the more it looks like a sponge instead of a smooth surface). The open structure also grinds cooler, but won't give a fine finish.

A level of 6, I have found is too tight, and you end up burning the bit, 12 is too open (they run from 1 thru 16 as I recall, with 1 being dense and 16 open like a sponge) , and you don't get a decent finish which then requires more polishing with another wheel or by hand. So I usually choose an 8 when it comes to grain structure, right in the middle.

Never run a grinding wheel FASTER than its rated speed, that can prove deadly, literally , because it can explode and throw shrapnel everywhere.

Running it slower than its rated speed is OK, the wheel will run cooler and act like a softer wheel, but will also wear out faster. Most grinders have shaft speeds of either 1,800 or 3,600 RPM, make sure the wheel(s) you choose are rated for at least the speed of the grinder shaft. When you mount a new wheel, there should be an arrow on the face of it, that arrow points to the heaviest part of the wheel, and when you install it on the shaft, that arrow should be pointing down to the 6 o'clock position.

Then I move on to hand polishing the faces and edge with a medium oil stone, followed by a hard Arkansas oil stone, and if I am being really fussy about the finish on the workpiece, a super fine diamond stone. A bit sharpened like this stays sharp longer and gives a much smoother cut, less chance of swarf welding to the bit, etc.

And don't get too wrapped up in the rake, face, side relief, etc. angles, get it close, see how it cuts, make small changes if necessary and go with it. Some guys can grind accurate angles on a tool bit free hand repeatedly without a protractor tool rest, I can't. For those exacting angles (which over 50+ years I have NEVER found to be 100% necessary, they are just guidelines) you need a fixture and a surface grinder, which is a very expensive tool!

Grind while holding the tool bit bare handed, and dunk it frequently in room temperature water. If you get it so hot that it steams the water when you dunk it, you are risking micro fractures in the tool bit at all sharp edges, not a good thing, so grind for a couple of seconds, dunk, grind, dunk, the tool bit should never get more than comfortably warm in yer paws.
 
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NYECOGunsmith

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Baaaawwaaaahhaaaaaaa! I warned you!
I can make it up to ya, stop by the shop for some lathe and mill lessons.
Enjoy the new lathe, next stop, a 14x40 or larger lathe, and 9x49 or larger bridgeport mill........!
 

Pcmaker

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The difference in quality between my Grizzly lathe and my Precision Matthews mill is very apparent

Now, I'm trying to come up with a workbench design that will hold both the mill and this new lathe, as well as tools. That's well over 1000 pounds.
 

NYECOGunsmith

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Steel I beams for legs, weld on 2x2" heavy wall steel tubing for cross braces, add 1" thick steel plate top, that would be the best.
For a 36" wide by 6 foot long table, it will end up weighing about 2,000 pounds.

Or, more practical for you maybe, go with a set of these legs:
http://www.grizzly.com/products/Shop-Fox-Super-Heavy-Duty-Workbench-Leg-System/D2910

And this top:
http://www.grizzly.com/products/Gri...nch-Top-60-Wide-x-30-Deep-x-1-3-4-Thick/G9914

Put down a 3/4" thick MDF top, then a layer of nice flat 2x12's, then a second 3/4" MDF top to add weight and rigidity, that should do it. That will give you a table that will support the weight and won't flex hardly at all. The weight of the table will help reduce chatter and vibration when you bolt the lathe and mill to it.

You could build it out of 4x6's for legs and cross braces instead of using the Grizzly leg set. My reloading bench is built that way, heavy timbers for legs and cross bracing, and the top a laminate of the MDF , 2x12's and MDF. Very heavy, solid, rigid.

Whatever you build, first measure the distance from the palm of your hands to the floor, when your arms are held at your sides , bent at the elbow so that your forearms and palms (palms facing down) are parallel to the floor.

Then build the bench so that the height of the controls you will use most often on the lathe and mill (more the lathe than the mill, since the mills controls are at both the bottom and top of it) is at that distance, or 1-2 inches below the distance from your palm to the floor as described.
So if the distance from your palms to the floor was say, 41 inches like mine is, and the controls you use most on the lathe are say, 4 inches above whatever surface the lathe rests on, you would build the table so that the top of the table was 37 inches above the floor, 37+4=41.

This will greatly reduce operator fatigue. Bending the forearm down an inch or two from parallel to the floor is comfortable for humans, bending it up gets tiring very quickly, lowering it way down gets tiring too.
 

Pcmaker

Obsessed Member
I guess I should start looking to sell my mini lathe

The DRO is on back order and they're the ones to install it, so it'll be awhile before I get it.
 

NYECOGunsmith

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Should, but if not that design is easy to reinforce.
Just add one or more layers of 3/4" plywood of MDF to the top, and some 4x4s on each of the inner sides of the existing 4x4 legs.
And double up on the 2x4 cross braces.