New mini-lathe user question

S

shorton

Active User
Registered
Joined
Nov 25, 2013
Messages
81
I'm a mentor for a small high school robotics team. I just got a min-lathe for the kids to use, but first I have to learn how to use it :). I'm an old engineer (so not a complete dummy) but I'm no machinist by any stretch. I have a small mill, a CNC router, so I understand speeds and feeds, but have no metal lathe experience.

I've read all about grinding my own HSS tools, and I plan to work up to that. But right now I don't have a suitable grinder, or time, so I've taken a temporary measure and bought some insert tooling from LMS. I also ordered some HSS inserts as I understand at the mimi lathe speeds HSS will likely be better. I will be using some 1" 6061 Alu rod to start playing with.

My first question is on positioning a tool. I'm not sure what position to orient an insert relative to the workpiece. That is, what angle to orient the shaft of the tool relative to the axis of the workpiece. Can someone explain or point me to a photo of how I should orient the/a triangular tool? I'm going to use these for now:
http://www.littlemachineshop.com/products/product_view.php?ProductID=1669&category=
The come with carbide, but with their advise I also ordered:
http://www.littlemachineshop.com/products/product_view.php?ProductID=1724&category=-1550042347

Thanks,
Scott
 
Those cutting tools are designed so that the user places the top edge of the tool exactly perpendicular to the center line of the workpiece. In practice you can get away with a hair under the centerline, but never over.
 
canerodscom said:
Those cutting tools are designed so that the user places the top edge of the tool exactly perpendicular to the center line of the workpiece. In practice you can get away with a hair under the centerline, but never over.
Click to expand...

Thnaks, but not that angle. I understand it's supposed to be level with centerline. I mean looking down (top view), tool holder relative to the rotation axis. Maybe called lead angle? I'd like to orient to face and turn if possible.
 
Yup, the correct term is lead angle. In general, a turning tool is used with the shank of the tool perpendicular to the lathe axis, which is why there are different shapes for different tools - roughing, facing, finishing. However, you are free to use what works for you. For example, you can angle the tool CCW to face such that the cut is performed by just the tip, the turn with the same tool by moving it CW so the tool shank is perpendicular to rough, then turn CW a bit more to finish. How much is a bit more? It is advisable to use as much lead angle as you can as long as you don't have chatter, at least according to Machinery's Handbook and my own experience anyway.
 
Thanks, "more" lead angle would be clockwise then right? So the shank leans towards the chuck?
 
shorton said:
I'm a mentor for a small high school robotics team. I just got a min-lathe for the kids to use, but first I have to learn how to use it :). I'm an old engineer (so not a complete dummy) but I'm no machinist by any stretch. I have a small mill, a CNC router, so I understand speeds and feeds, but have no metal lathe experience.

I've read all about grinding my own HSS tools, and I plan to work up to that. But right now I don't have a suitable grinder, or time, so I've taken a temporary measure and bought some insert tooling from LMS. I also ordered some HSS inserts as I understand at the mimi lathe speeds HSS will likely be better. I will be using some 1" 6061 Alu rod to start playing with.

My first question is on positioning a tool. I'm not sure what position to orient an insert relative to the workpiece. That is, what angle to orient the shaft of the tool relative to the axis of the workpiece. Can someone explain or point me to a photo of how I should orient the/a triangular tool? I'm going to use these for now:
http://www.littlemachineshop.com/products/product_view.php?ProductID=1669&category=
The come with carbide, but with their advise I also ordered:
http://www.littlemachineshop.com/products/product_view.php?ProductID=1724&category=-1550042347

Thanks,
Scott
Click to expand...

Welcome, If you decide to use HSS tools in the future be sure to have a bowl of water to cool the bits off. They will get hot to handle by hand. I've used course grit wheels to rough out my bits before but it helps to use a fine grit wheel to finish and touch up.

What type of robotics do you you teach? I always found that to be an interesting project.
 
Bill C. said:
Welcome, If you decide to use HSS tools in the future be sure to have a bowl of water to cool the bits off. They will get hot to handle by hand. I've used course grit wheels to rough out my bits before but it helps to use a fine grit wheel to finish and touch up.

What type of robotics do you you teach? I always found that to be an interesting project.
Click to expand...
The kids participate in a national program designed for middle and high school students called BEST (Bettering Engineering Science and Technology) www.bestinc.org Our kids won all categories except one at our local competition and then got 2nd place in the robot category at the Championship at Auburn University last December. The kids have to do everthing themselves. Including me, we have a couple of ME mentors but we have to do some touge biting and let them figure out their problems themselves. But, we work toward giving them the tools they need to do it. And teach them that "tools" does not just mean hand and power tools. It means understanding how to do things, that they can slot, or press fit, or make a gear, and what a gear does, or understanding torque, etc. The more they know how to do, the more they can apply that to their designs. So I have a lot of fun teaching them basics. And I learn a few things along the way myself :) . I've learned to not argue about math subjects with the little brainiacs that got perfect ACT scores LOL.
 
One of the best sources I have seen for learning the basics of the lathe is the old "standard", "How to Run a Lathe" by South Bend Lathes.I believe there is a copy in the downloads section. Even though it's written for SBs the information is mostly universal to manual lathe operations and tooling. It will answer many of your questions even ones you didn't know you had yet.

Hope that helps.

-Ron
 
Last edited:
ScrapMetal said:
One of the best sources I have seen for learning the basics of the lathe is the old "standard", "How to Run a Lathe" by South Bend Lathes.I believe there is a copy in the downloads section. Even though it's written for SBs the information is mostly universal to manual lathe operations and tooling. It will answer many of your questions even ones you didn't know you had yet.

Hope that helps.

-Ron
Click to expand...
Got it, thank you.
 
The angle makes very subtle effects and most times doesn't make much difference at all until you are trying to do something really specific. One thing to remember is that you want most of the cutting force parallel to the long axis when not facing off a part or parting off. Especially with thinner stock. If you have the majority of the force perpendicular to the axis (the direction of the cross slide) you will get more deflection in the part and it will be hard to get it to a constant size. You also should turn towards the most rigid part of the lathe when you can. The headstock is the stiffest part and you also tend to push the stock into the chuck instead of pulling it out. You only turn the other way when you have a specific reason to such as cutting to a face on the tailstock end.

The rest of the angles are really just for clearance and to be able to get into places more than for any consideration of cutting. You can orient the tool to be able to direct the chip and to present the cutter to the work at a certain angle. This would include a radius or a form tool. One other way the angle will make a difference is if you want to make it have a shearing action which can help at times. Sometimes reducing the angle can make it easier to get a good finish when you are getting a rough cut surface. I use this effect when I want to cut threads off of a piece of stock (like turning a threaded rod down to attach to coupling.) I present the side of the tool at a slight angle and turn so the rotation is going opposite the helix of the thread to prevent the tool from trying to follow the thread.
 
You must log in or register to reply here.
Back
Top