Steady Rest Question

homebrewed

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I believe the rule of thumb for stick-out of work from a lathe chuck is 3 diameters or less. A steady rest operates a little differently than a chuck so I'm wondering if the same rule of thumb applies or not? Is this established by flexure of the work or how firmly the chuck grasps the work?
 
It's flexure. Part of it is the work wet-noodling at high RPMs (search for the whomp-whomp-whomp video of the bar sticking out the aft end of a lathe spindle), and part of it is deflection from the tool during cutting. With a chuck and a steady, you have a long base of aligned stock, so you don't have to worry so much about the work whipping around, but there will still be deflection from the tool.
 
The rule of thumb is based on beam flexing. The lathe has 3 (or 4) such cases::

a) fixed-free--part is held on one end in chuck and unsupported at the other end
b) fixed-pinned--part is held in chuck and supported by center or steady rest
c) fixed-fixed--the part is held in the chuck and another chuck is holding the part from the tail stock (Seldom seen)
and a variant not generally encountered in beam equations
d) fixed-moving-pinned--this is the follow rest version

Fixed-free is supposed to allow 3× to 4× length compared to part diameter.
Fixed-pinned has 4× less flex than fixed-free and should allow 12× length to part diameter.
Fixed-moving-pinned has even less flex than the steady rest--when setup properly this has less flex than the fixed-fixed (below)
Fixed-fixed has 2× less flex than the fixed-pinned (steady rest)
 
Great info -- thanks!!

FYI, my inquiry is based on my dislike of excess waste of raw stock. I only need about a 1" section of 1.5" rod turned down (to make a plug gauge), but the raw material is 12 inches long. And it's too large in diameter to go through my 3-jaw and 4-jaw chucks. So to ensure a good grip in my 3-jaw I will need to dedicate about 1 inch over & above the portion I want...and that scenario will repeat every time I use some of the raw material!

My follow rest cannot accommodate a rod this diameter so I'm looking at making a steady rest. I have just about everything I need on hand, except for the bearings and a few fasteners so I should be able to save some money compared to buying a steady rest. I hope....
 
Just some unsolicited advice. As the owner of a Sherline lathe, I am all too familiar with stock being too large to pass through the spindle. Hell, my spindle bore is only 3/8"! So I understand what you're saying BUT I wanted to remind you that a steady rest is not a substitute for a chuck and you will not be able to hold tolerances very well by trying to machine beyond the end of a steady rest.

My suggestion is to just waste the material and cut what you need to work from the chuck. Been there, done that.
 
I would cut off a piece of stock 1 1/2 long. Then face and drill a 1/2 hole thru. Then use a piece of 1/2 threaded rod thru part and spindle with a washer on back end of spindle and clamp stock together with a nut on both ends. I have held pieces over 6 inches dia this way. Sometimes I just drill and tap the slug I’m working on If it is too long to drill thru. And Mikey a 3/8 threaded rod will work as well.
jimsehr
 
Just some unsolicited advice. As the owner of a Sherline lathe, I am all too familiar with stock being too large to pass through the spindle. Hell, my spindle bore is only 3/8"! So I understand what you're saying BUT I wanted to remind you that a steady rest is not a substitute for a chuck and you will not be able to hold tolerances very well by trying to machine beyond the end of a steady rest.

My suggestion is to just waste the material and cut what you need to work from the chuck. Been there, done that.
A good point. In addition, I could save some time (now) by avoiding the need to make or order a steady rest.
 
I would definitely get a steady rest. You need it so you can hold long, large diameter pieces steady enough to face and center drill it for tailstock support. No matter how big your spindle bore is, it will always be too small for some projects and a steady rest is a must-have accessory for your lathe. And you do not need roller bearings for the arm tips; brass works fine and will not steer a work piece like an off-alignment bearing will.
 
I would cut off a piece of stock 1 1/2 long. Then face and drill a 1/2 hole thru. Then use a piece of 1/2 threaded rod thru part and spindle with a washer on back end of spindle and clamp stock together with a nut on both ends. I have held pieces over 6 inches dia this way. Sometimes I just drill and tap the slug I’m working on If it is too long to drill thru. And Mikey a 3/8 threaded rod will work as well.
jimsehr
Not a bad idea -- thanks!

I just remembered I have an expanding mandrel set that could work for this. Your comment nudged my memory -- I don't use it very much because the sizes rarely match the ID of stuff I'm machining. In this case I can drill/bore as needed.
 
Mikey,

Yes. I can do what I need this time around using an expanding mandrel but I'm also working up an order for material to make a steady rest. It makes sense to make one because ones made for the mini lathe are, in my opinion, too small anyway.
 
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