Best way to machine square end on round stock?

PHPaul

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What's the best setup to machine a square end on a piece of round stock?

I've used a v-block in a vise and used a square to re-set the stock after machining each flat and that's...adequate but not horribly accurate.

I have a rotary table that can be mounted vertically but can't figure out how to mount the round stock to the table.
 
Use a collet block. Mill a side. Rotate 90 degrees. Mill a side. Rinse and repeat until all 4 sides are done.
 
Use a collet block. Mill a side. Rotate 90 degrees. Mill a side. Rinse and repeat until all 4 sides are done.
Yep, I was going to suggest the same thing. If your stock is small enough to fit in a collet (5C is 1 1/16" I think?) it is pretty trivial to do and as accurate as your collet block is for squareness. I bought this kit a while back and am reasonably happy with it: https://www.amazon.com/5C-CB-5C-Collet-Block-Set/dp/B0186MD7L2
 
Clamp in vise with end sticking out.
Side mill two sides to size.
End mill top to size.
Flip part over and clock part into vise with previously milled sides.
End mill 4 side to size.

This will get the squareness very accurate, hitting size is fairly fiddly.
But it requires no special fixturing or tooling.
 
I use the RT to cut hex , square, 7 sided polygons, etc. It can be done with the RT set either horizontally or vertically. I use the RT horizontally for short work and side mill. For longer work, I set the RT vertically and end mill. My RT has a 1.000 center hole and I made an adapter so that I can use either my three jaw chuck or my four jaw chuck. I have a threaded plug and a drawbar to secure the chuck. The chuck for my 4th axis RT for the Tormach has a backing plate with a flange for clamping via the table slots.

To cut the polygon in the horizontal mode. I have my 4" three jaw chuck mounted at the center of the RT. I will mount my stock and set the table so it is off side on the x axis and make a trial cut by moving in the y direction. Rotate the table 180º and make a second pass in the y direction. Measure the distance between the two cuts and adjust the x axis appropriately to reach the final size. Rotate the table by 360º/ no. of faces after each cut. This works well for even sided polygons. For odd sided polygons, where it would be difficult to measure the size, I would make two skim cuts 180º apart and measure across the flats. The x axis center will be 1/2 the measurement.

If the cylinder is already to dimension, the work has to be centered to the RT axis. To that end, a four jaw chuck would be a better choice. I would center the work much like on a lathe by rotating the RT. When the work is concentric with the RT axis, I can proceed as above.

Using the RT in a vertical configuration is done in a similar manner except you are using the end of the cutter.
 
Depending on the length of the square end and the length of the bar. Clamp it in the vice with a V block pointing straight up and side mill all 4 sides in one setup. This will be as accurate as your mill can do. You do not have to do the full side depth in one pass. You can work your way down leaving .005 - .010 for final cleanup pass to make it look pretty.

If the round bar is to long to stand straight up. Clamp the bar to a V block and then put it in the vice with the clamp just out the end of the vice Use a second V block and clamp sticking out the other side of the vice to keep everything square. mill a side then rotate the whole works in the vice for the rest of the sides. You will have to indicate for each side, but it will be as accurate as your blocks and indicating.
 
I have a rotary table that can be mounted vertically but can't figure out how to mount the round stock to the table.

It depends on the diameter and legth of the piece and what equipment you have available.

As others have pointed out, a collet block is easiest, but I would assume if you had one and the work would fit in it you would have used it already. Using the method Asm109 described works well but you will have 2 radiused and 2 square shoulders. If that is a factor you can go back and clean them up after you have it square. Using your original method, rather than a square you can clamp the first flat to a 1-2-3 block or an angle plate to line it up in your vise for each succeeding cut. If it will fit, you could also mount a lathe chuck to your rotary table.

Many different methods, just depends on what you have.
 
Yep, I was going to suggest the same thing. If your stock is small enough to fit in a collet (5C is 1 1/16" I think?) it is pretty trivial to do and as accurate as your collet block is for squareness. I bought this kit a while back and am reasonably happy with it: https://www.amazon.com/5C-CB-5C-Collet-Block-Set/dp/B0186MD7L2
If you are using (or planning to use) ER collets in your shop instead of 5C collets, collet blocks are made in that type, too. Pick one type and stick with it, at least at first, and you will save lots of money, though it can be useful to have both types. 5C is better when you will be using nominal stock sizes off the shelf, ER is better when random diameters will need to be chucked. I do not have ER collets -- yet...
 
Collet block is by far the best choice for ease vs. accuracy. Rotary head is my choice, but a chuck on a RT would be good.

Funny thing about collets. I set up my mill and lathe with ER collets, but I ended up with 50 collets to cover inch and metric. Then I needed a better set of 5C collets for my SO grinder. And then I decided R8 collets were better than ER in the mill, so I got those too... Not what I intended!
 
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