Newbie needs help with mini-lathe

Brass is one of the easiest metals to turn. When things are right, it cuts like butter. When things are wrong, you dig in.

The things that must be right include having the tool dead on center height. If the tool is too high, you rub. If too low, you will dig in, no matter what your tool geometry is. I suspect this is you key problem - the tool is low.

Ideally, you want a tool with zero to maybe 5 degrees of side rake only - no back rake. You also want fairly large relief angles, on the order of 12-18 degrees. Brass likes really sharp tools so grind the relief angles and then hone the sides and the flat top and the tool will cut well. Also hone a nose radius; for brass, this is not that critical but I prefer a smaller nose radius, maybe 1/32". Find a 1/32" drill bit and make the nose radius like the bit. With all this said, a standard tool with side and back rake will work but your set up must be rigid and it must be on center height.

I don't think cutting speeds are all that critical for brass. I tend to run fast, maybe around 1000-1200 rpm on a piece like yours and I run much higher for smaller work. The material is so soft that just about anything will work fine.

As for drilling, I think dubbing your drills is a good idea if you insist on using a pilot drill. If you go straight to your main drill without a pilot then it will drill just fine as is.

If any of this is unclear, let us know. For now, look up using a 6" rule to find center height.
 
It looks like you're using a knife tool, which works fine for some stuff (facing, very light cuts) but for general use, a more conventionally shaped tool with a bit more side cutting edge angle would work better for you. May I suggest you look at the tool we ground in this thread? Grind it the same but don't grind the top rake angles. Put a nose radius on it, hone it and I bet it will work well for you.

Also, its hard to tell but it looks like you have a little nub on the face of the work. This suggests that your tool height is a little low. Fix that and the tool will work better for you.
 
Knife tool? I thought this was a basic turning tool?

I did have a very small nub in the center of the face. I'll try raising it up a bit.
 
I didn't read the entire thread so i apologize if this is a repeat.....

I had the following similar issue on my lathe which turned out was caused because the "torque" setting pot was apparently never properly adjusted from factory which caused me to experience exactly what you are experiencing on your lathe!

If your lathe is anything similar to the harbor freight benchtop lathes and you continue having motor stall problems then you may need to get into the control circuit board to see if there are 2 or 3 adjustable "pots" on that circuit board which will allow you to fine tune (increase or decrease) both speed and Torque settings which will keep the motor from stalling out so easily!
 
Devils: Looks as though your tool is hanging out there too far- these small machines are limiting in that the carriage "arms" aren't very wide. Try rotating the compound to be at around a 45 degree angle and crank it almost fully back. Bring the tool bit closer in to the tool post also, that should help.
Do whatever you can to bring the cutting edge as close to the center of the carriage (when looking down on it) as possible
 
I don't "think" the motor has a power issue. It was jammed when it stalled, but I can take a look.

I'll try making the tool bit closer to the tool post.

Just curious, how do carbide bits compare since the geometry can't be changed based on material.
 
devils4ever said:
Knife tool? I thought this was a basic turning tool?

I did have a very small nub in the center of the face. I'll try raising it up a bit.
Click to expand...

Yeah, that tool is called a Knife Tool. Have a look here; we discussed this tool and others in some depth.

Regarding carbide inserts on a little 7X lathe, you can certainly use them. Lots of hobby guys do. However, you lack the speed, power and rigidity to use them well. HSS will typically outperform inserted carbide on small lathes. Another option is brazed carbide tooling that can be sharpened to near-HSS sharpness. You can alter the geometry of these tools if you have the right equipment and know what you're doing and the tools will easily outlast HSS; they probably won't outperform HSS, though.
 
To catch a rubbing tool, color all cutting faces with sharpie marker. If you get any more than a thin shiny line on the face, you are rubbing. That will make the cutting terrible.
 
I had great success tonight! I ground a 3/8" tool blank without touching the top surface. It's not pretty, but it works. I reduced the overhang to a minimum, rotated the cross-slide and centered it to give maximum support. I increased speed a little and raised the bit to slightly above the center-line.

The cut was smooth and has a nice finish. Thanks to all! You guys are great!

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