How to accuaratey set up square stock in the lathe.

[atomarc]

I have 36 inches of 1 1/2" square bar that has features that must be turned in the lathe. I screwed the first victim up and don't want to ruin my second attempt.

I dialed the first attempt in using the 4 jaw and a DTI but must have missed the mark a few thou's.

On this second attempt I'm going to center drill each end in my mill, finding dead center with my trusty Haimer. I then plan on installing the bar in the lathe between centers and using a dog, turning the features.

Am I setting myself up for complete failure..sure seems like it would work, and bypass all that fussing around with the 4 jaw and indicators.

What do the pro's think?


EDIT. Title is certainly a spelling disaster...sorry!


Stuart

 

[Booze Daily]

I do a couple jobs out of square stock.
I bored out some soft jaws to hold W&S collet pads.

 

[atomarc]

That's a very clever setup, although in my case, it's a one-off and I'll probably never see the job again.

Stuart

 

[michiganbuck]

Between centers is the best way.

If you can get a good central location for center drilling on your mill then fine. I think a center drill can drill a tad off-center. ..
or Center drill in the lathe with the part indicted off the flat sides held in a 4jaw and tool bit scalped..then center drilled...with the part tail end centered also when doing the out end. Yes turn the part about and do the other end the same.

The square part OD corners are not much good to indicate to.

Checking a long part for straightness may be also good.

 

[TGTool]

Between centers seems like a perfectly good plan if you want to go that way.

Centering rectangular stuff can be annoying because of the different factors that can come into play. As Michigan says, corners are unreliable. Flats can be squirrely because you have to get the indicator out of the way to check the next flat, and if the indicator is above or below center you get other strange changes finding zero.

My approach is to set the indicator point as nearly on center as I can, rock the chuck back and forth to get the minimum indicator reading and zero both indicator and crosslide. Then you can back out if you need to, or move the carriage to access another flat. You should be able to center in just a couple moves, then just crank the chuck jaws to zero for the other two flats. Of course there's always the prospect that the square isn't exactly equal both ways so you'll have to split the difference on one set of flats.

 

[Garwood]

How square and straight is the material?

I do like above and use an indicator with enough travel to pull out of the way of the corners as I rotate and when I start getting close I use the toolpost to press against the stock to square it up so all my measurements are taken at identical spots, then it doesn't matter if I'm perfectly on center with the indicator either.

I usually center drill long stuff like that on a mill.

 

[atomarc]

Well...as long as the general consensus it that this procedure isn't bunk, I'll give it a go. The material is 12L14, it's straight and true as near as I can tell.

Stuart

 

[michiganbuck]

I have had such poor luck getting a center drill to get .002 and better that I keep a Norton 60* stone handy to move the center. I just put the center lap in the tail and chuck the right end, then with pushing downward go back and forth a few times.

I got used to doing this when I would get in tenths repair grinding job that had no grind stock ..and it having a bad center.

 

[cyanidekid]

you are trying to get + - .001 on sq stock you don't know is flat and square (to a fraction of that)? if you want that kind of result repeatably, you need to have some idea what you are starting out with, even if you had precision ground stock, you would still need to inspect it on a good surface plate.

as far as setup, a decent 4 jaw should get you well within that easily, and unless you need to work it along the length, what is the advantage of working between centers? in fact to mount it between centers most of us would chuck it up in that 4 jaw to center drill it first ( if available lathe size allows that).

 

[Overland]

I'm missing how you would use a mill to drill centers.
Do you have enough "headroom" on a vertical mill ?
Can you get the table high enough on a horizontal ?
Personally I'd use a 4-jaw in the lathe; just trying to understand how you would use a mill.
Thanks
Bob

 

[cyanidekid]

I'm missing how you would use a mill to drill centers.
Do you have enough "headroom" on a vertical mill ?
Can you get the table high enough on a horizontal ?
Personally I'd use a 4-jaw in the lathe; just trying to understand how you would use a mill.
Thanks
Bob

If it doesn't fit through the headstock, and it's too long to hang out of the 4 jaw, we do it on the mill. if it's too long for our Z, get out that 90 deg. head.

 

[michiganbuck]

If it doesn't fit through the headstock, and it's too long to hang out of the 4 jaw, we do it on the mill. if it's too long for our Z, get out that 90 deg. head.

I guess an odd way would be to set a mill vise on the lathe to hold the part end to be center drilled and a center drill bit in the lathe spindle/collet/chuck using a Haimer or the like edge finder off two flat sides. yes, likely need something to hold the out, tail way end straight.

 

[gbent]

I'm missing how you would use a mill to drill centers.
Do you have enough "headroom" on a vertical mill ?
Can you get the table high enough on a horizontal ?
Personally I'd use a 4-jaw in the lathe; just trying to understand how you would use a mill.
Thanks
Bob

On a turret mill you hang the work off the edge of the table and swing the head around and tram the head to the stock.

 

[atomarc]

The front of the table on B-ports is ground and has a T-slot in it. Mount a small precision machinist vise there and you can clamp up long stock in a vertical plane and fiddle with the ends.

Stuart

 

[Garwood]

I'm missing how you would use a mill to drill centers.
Do you have enough "headroom" on a vertical mill ?
Can you get the table high enough on a horizontal ?
Personally I'd use a 4-jaw in the lathe; just trying to understand how you would use a mill.
Thanks
Bob

Bridgeport is easy. You can swing the ram to the side or you can tip the head over 90 and raise the knee up.

HBM is handy for that stuff too. I tend to use HBM before turning the BP ram because on my mill it throws tram way off.

 

[atomarc]

Thanks for all the ideas. Being a one-man job/repair shop, these chores are by the hour and if I turn in a $1000 bill for turning a simple piece of square bar, the customer is liable to send Guido to break my kneecaps. Height gauges, toolmakers button and gauge blocks would bring the whole Sicilian family to my door step...although I do love Italian food.

Don-Stuart

 

[Bill in PA]

When I indicate flat-sided parts on the lathe, I use a ball bearing indicator point. Rolls easily over the corners.



Bill

 

[Georgineer]

The traditional way is to get (or turn) a piece of round stock with the same diameter as the across-flats measurement of your square stock. Centre the circular piece in the four jaw chuck in the usual way. Slacken two adjacent jaws and remove the round piece. Insert the square piece and tighten the same two jaws and there you are.

I can't tell from your description whether the 1½" stock will go through the lathe mandrel, but if it does you can centre-drill while it's in the chuck before sliding it out for support from a centre.

George

 

[ballen]

For one or a few, I do exactly what TGTool said in post #5. It just takes a minute or two, assuming that you know how to center something in a universal 4-jaw chuck.

This method assumes that your 4-jaw chuck is in good shape, and not bell-mouthed or distorted. You should check this:
If the cylindrical feature that you are turning on the square stock is located some distance away from the chuck jaws, then after you are done centering the square stock, be sure to run an indicator up and down the length of the stock (Z direction) between the location of the chuck jaws and the location of the feature. If you see any significant deviations you'll have to address those first, for example by grinding the chuck jaws.

 

[cyanidekid]

Bridgeport is easy. You can swing the ram to the side or you can tip the head over 90 and raise the knee up.

HBM is handy for that stuff too. I tend to use HBM before turning the BP ram because on my mill it throws tram way off.

geez.. rotate the head to center drill one piece(or even 50pcs) of stock?! the 90deg. attachment is enough of a pain, and center drilling is a perfect light duty use for it.

rotate the head if you HAVE to for actual milling.