How to center round stock in mill

[werowance]

Sorry for the newb question but I need to learn how to center round stock in the mill in order to mill a grove across the center of the face of the round stock

I have been cheating by taking my rotary table with collet chuck and a pice of drill rod and chucking both ends in my mill chuck and the rotary table chuck and then bolting down the table with good results to center both. But I need to learn how it's supposed to be done and stop what I call cheating

So that said how do I center it in my vice to center of mill head?


Thanks
Bryan

 

[10K Pete]

Dial indicator in the mill quill, rotate around the part and read run-out.
Move part as required to achieve zero.
Rotating mill quill by hand, of course!!

Pete

 

[Brian Rupnow]

Or--take a short piece of 1" round cold rolled stock stock and drill/ream a 0.500 hole through it in your lath. Get a piece of .5" cold rolled (which is actually about .0005" undersize) x 3" long. It must be a "good sliding fit" into the hole in the 1" round stock. Bolt the rotary table down to the mill table and hold the 1" round stock in the 3 jaw chuck which is attached and hopefully centered on the rotary table. Put the .5" cold rolled in the spindle chuck. Now use the X and Y table movement to move the rotary table around until you can extend the spindle and have it enter the hole without any binding (spindle should not be turning when you do this.). I used that method for many years until I put DRO's on my mill.----Brian

 

[Cogsy]

Or you can use an edge finder quite accurately. Find the edge on one side - say x travel direction - (try and get it close to the middle by eye) then move in half the diameter. Now repeat for the Y direction and again move in half the diameter. Now repeat for the x direction again, then one last time for the y direction. Each repitition gets you closer to the true center.

The more times you repeat it the more accurate you get but just doing it twice gets you really close - I can't remember where I saw the math for it but repeating it 4 times gets you to within something ridiculous like 0.0002" (as long as your edge finder is accurate/repeatable).

I used to do it like this but now I use a coaxial indicator, just because I've got one.

 

[kf2qd]

Get hold of a COAX indicator. It is used for centering on ODs and IDs and even Center Punches with the included tips. And you use it with the spindle turning. Once you use one and get the hang of it, there is no better or faster way to do it.

 

[Blogwitch]

Get hold of a COAX indicator. ??????

A dire suggestion for many people new to machining and not really knowing what they have.

I own a largish Bridgy clone and even I struggle to get one of these under the throat (14") at times, especially when using a chuck mounted onto an RT, to such an extent, I have had to make shortened probes for it.

Don't just run out and buy one, make sure your mill has enough throat to take one.

I tend to use the round bar (or square, oblong or hex) in a horizontal position sat on a parallel in my vice (usually more stable) and use slitting saws or edge and face cutters for cutting cross slots.
Touch on top face of horizontal bar with cutter, raise the piece part (or lower quill) by 1/2 thickness of cutter plus 1/2 diameter (or thickness) of bar will put you spot on centre, then just cut to depth with the cutter from the side.

Hope this helps.

John

 

[werowance]

Thanks. I'll try dial indicator tomorrow and probably eBay for a coaxial indicator tomorrow

Brian, your method sounds much like mine but with improvements as it was difficult to remove the drill rod I used to center both up and then tighten down the rotary table. I like the rod with sleeve approach. Would be easier than my way. How accurate do you normally achieve when you do it this way. I never checked when I did it because it was always just simple "close enough" work until now.

Problem with my mill is its a combo lathe. Similar to a smithy. It's hard to see a dial indicator on the back side when I rotate it and have really never seen a coaxial indicator. Once I look it up I might retract that statement but I definitely don't own one yet.


Someone mentioned dro on their mill. I have a dro on mine but not sure how I would use it to find the center on something round. Only thing I can think of is you would have to use a edge finder with it. Yes works great for cross drilling but don't know how to find center of face instead of side

 

[Brian Rupnow]

How accurate can you get?--well, if the 1/2" round cold rolled steel is .0.4995" diameter, and it's going into a hole that is 0.5000 diameter, the maximum out of center condition you can have is .00025". That is better accuracy than many lathes have for runout.---Brian

 

[canadianhorsepower]

Someone mentioned dro on their mill. I have a dro on mine but not sure how I would use it to find the center on something round. Only thing I can think of is you would have to use a edge finder with it.

That's all you need.
use your edge finder and touch one side let say on the X axe
zero it on your DRO then go and touch the other side of your rod
on the X axes again. then touch your YELLOW X button and on your Key pad
you have a button that shows 1/2 press on it It will do the math for you
and give you the number that if you bring it to 0 will be the center on X
then do the same thing for Y axes.

of course you can use that for any shape of material you have
enjoy

 

[werowance]

Thanks Canadianhorsepower I guess what I don't understand is using an edge finder on the round part. As the part is round how do you know you found the edge of the furthest distance of the circle? My edge finder is one of those led light finder.

Maybe I could find the edge of the solid jaw of my vice assuming the vice is square on the table. That way I could find the exact half point on one axis. Then the edge finder would hit the highest point on the other axis then move in to the half point that way?

Looks like with a circle you would have to have at least one square surface to get started with?

 

[Brian Rupnow]

Use the edge finder to touch one side of the round part. It doesn't have to be on center. Retract the quill so your edge finder clears the top of the part. Now crank the table over so your edge finder can be lowered again on the other side of the part. Crank your table until the edge finder will touch the corresponding point on the other side. It will then tell you what is half way between those two contact points to center it. You don't need to worry about whether you are in line with the center of the part to start this process.

 

[werowance]

Thanks Brian. That makes perfect sense.

I appreciate everyone's help

 

[MachineTom]

Save your money, don't bother with a co-ax. It will just take up space in the drawers.

Edge finders are repeatable, and quick to use. Accuracy is in the hands of the operator.

Many ways to do this job, Quickest, With the stock vertical in the mill vise, stock against the fixed jaw, vee block against the moveable jaw. Assuming the vise jaws are aligned with X axis, edgefinder to the fixed jaw, hit it again to be sure. Mark your settings, subtract the .100 or half the finder stem, whatever it is, then move Y axis half the diameter of the part, you on center in Y. Since its a slot you don't need X center, if you did, place a 123 block on the vise jaws, square the block to the jaws, move Y to center, then edge the 123 block, Subtract the 123 block, the .100 and half the stock diameter. All this in less time than finding the co-ax in the drawer.

You should also have a .500 finder with the cone point end, to use on larger diameter round stock, used when horizontal, position of holes and punchmarks...

 

[abby]

Brian I don't quite understand your figures , a piece of cold drawn steel measuring 0.495" ( lets forget the 1/2 a thou as this is totally unreliable unless measured under inspection room conditions ) placed into a reamed 1/2" hole.
There is a clearance of 5 thou. This allows for an eccentricity far greater than the run-out of anything useable as a lathe.

 

[Brian Rupnow]

Brian I don't quite understand your figures , a piece of cold drawn steel measuring 0.495" ( lets forget the 1/2 a thou as this is totally unreliable unless measured under inspection room conditions ) placed into a reamed 1/2" hole.
There is a clearance of 5 thou. This allows for an eccentricity far greater than the run-out of anything useable as a lathe.

My bad Abby---I meant to type .4995".---fat finger syndrome. I have corrected my post.--Brian

 

[Jchesley]

If you have a lathe then you could center drill the part, then once it is in the mill use a center finder on it. the center drill hole would be removed as you cut the part.

 

[Cogsy]

Looks like with a circle you would have to have at least one square surface to get started with?

If you use an edge finder, you can eyeball the centre in one direction (say X) to get started, find the edge and move in exactly half the diameter. This will get you sort-of close in X. Use that 'center' for the other direction (Y) and you will be very close to correct. Now use that 'center' for X again and you will be almost spot-on. Repeat as many times as you want for increased accuracy but realistically, once you've done it a couple of times you will see you keep returning to exactly the same point - you have found the centre. Probably took me longer to type than the procedure does to find center.

I do like my coax for finding the centre of holes though.

 

[kf2qd]

Save your money, don't bother with a co-ax. It will just take up space in the drawers.

Edge finders are repeatable, and quick to use. Accuracy is in the hands of the operator.

Many ways to do this job, Quickest, With the stock vertical in the mill vise, stock against the fixed jaw, vee block against the moveable jaw. Assuming the vise jaws are aligned with X axis, edgefinder to the fixed jaw, hit it again to be sure. Mark your settings, subtract the .100 or half the finder stem, whatever it is, then move Y axis half the diameter of the part, you on center in Y. Since its a slot you don't need X center, if you did, place a 123 block on the vise jaws, square the block to the jaws, move Y to center, then edge the 123 block, Subtract the 123 block, the .100 and half the stock diameter. All this in less time than finding the co-ax in the drawer.

You should also have a .500 finder with the cone point end, to use on larger diameter round stock, used when horizontal, position of holes and punchmarks...

I tend to do round stuff in the lathe and rectangular stuff in the mill, but when I do have to line up on a round feature in the mil the comes out every time. I got a clone model and it cost under $100 and has always done superb.

 

[Dave Sohlstrom]

Put your part in the vice. load your probe in the spindle. Go to the probing page and tell it to find center of a round boss. After complete Dros are set to 0,0 , done.

Oh wait you have a manual machine use an edge finder as others have suggested.

Dave

 

[Philipintexas]

I use an edge finder, but, I put the shaft in the spindle collet/chuck and the point in the rotary table chuck after they are very closely aligned visually. This upsets the two halves of the center-finder. By sliding my finger-nail up/down over the separation line on both X/Y axis I can detect any misalignment and move that axis accordingly. For total accuracy I can mike the separation line 90 degrees apart to attain perfect alignment. The finger-nail test is pretty accurate and usually is on the mark. It's quick and as accurate as you are. Probably doesn't need to be said, but don't rotate anything while both halves of the edge-finder are chucked in different devices....