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hwingo
02-25-2011, 01:46 AM
Bear with me fellows,

I’m about to ask a question that likely make little sense. :o

Let’s assume you have a 12” long 2” diameter (or even longer) round prefabricated part that CAN be held in a lathe’s 4-jaw chuck but is too large to fit inside the spindle. The piece mics the same diameter at both ends and holds true at any distance between the two ends. You need to do some work on the end; just pick a need ….. turning the end OD a little or boring a hole in the end as an example.

When you set up the piece, it is required that the piece be dialed in and run true. The problem is, if it’s dialed in next to the chuck’s jaws, run-out is .015” at the end. If you dial in at the end, run-out is .015” at the jaws.

What is the correct way of setting up this piece. Do you dial in at the end where you will be working and damned the area being held by the chuck? Lets make it a little more difficult, the work piece is a pipe with the ID being too large and too thin to run a live center. What now?

Harold

38_Cal
02-25-2011, 01:50 AM
At 12" long you need to support the outboard end with a steady rest...and dial in both ends!

David

lbhsbz
02-25-2011, 01:52 AM
I would first find a bull nose live center big enough to fit the workpiece, or turn up a piece to fit into the end of the workpiece such that you can you can use a live center (or dead center) to hold the tail end true. Use a steady rest. Use the tailstock center and your 4 jaw to dial everything in, then set up your steady rest, remove tailstock, go to work.

hwingo
02-25-2011, 01:59 AM
SUPER!

Now a followup question. How do you keep the steady rest from marring the area where it is riding? The tips on my steady rest are brass. Every time I attempt to use my steady rest, the three plungers eventually cut an unwanted grove in my work piece.

Harold

isaac338
02-25-2011, 02:02 AM
Oil, or spend a day building tips with ball bearings on them!

lbhsbz
02-25-2011, 02:16 AM
You can also find a bearing to press over the shaft, set your steady rest fingers on the outer race of the bearing, then press it off when you're done machining

Black_Moons
02-25-2011, 02:32 AM
To avoid damage from your steady rest, Make a spider that grabs onto your workpeice with 3 or more set screws, Put padding under each set screw to avoid damage to workpeice.

Mike Burdick
02-25-2011, 02:49 AM
Make a cathead similar to this...

http://www.stevenson-engineers.co.uk/files/steadypost7.jpg

... it was made by John Stevenson and he discusses it in the following thread:

http://bbs.homeshopmachinist.net/showthread.php?t=33552

.

SGW
02-25-2011, 08:56 AM
If you need to work on the end, you need a steady rest. Get the end in the 4-jaw running true. Slide the steady rest up next to the chuck and adjust the fingers, then slide it out to support the end. If you try to adjust it in its final position it will always look as though it is correct but it can be misaligned which will make the work wobble and walk it out of the chuck.

Adjust the fingers so they *just* touch, and apply oil. You shouldn't get significant wear on the work.

vpt
02-25-2011, 09:55 AM
I'd go with the bull nose live center unless you have to work on "face" end of the pipe.

hwingo
02-25-2011, 10:09 AM
If you need to work on the end, you need a steady rest. Get the end in the 4-jaw running true. Slide the steady rest up next to the chuck and adjust the fingers, then slide it out to support the end. If you try to adjust it in its final position it will always look as though it is correct but it can be misaligned which will make the work wobble and walk it out of the chuck.

Adjust the fingers so they *just* touch, and apply oil. You shouldn't get significant wear on the work.

Good suggestion. I could see this method working better on smaller diameter stock. One would think, as diameter increased so would the difficulty of sliding the rest near the end (less flex in 2 or 3 inch diameter than say half inch or 1 inch stock. Am I thinking right on this?

Harold

Carld
02-25-2011, 11:09 AM
hwingo, if you have brass tips on your steady rest then put a length of 1" wide emery cloth around the work under the fingers and clamped between the jaws of the steady rest with the smooth side toward the work. Put oil between the emery cloth and the work and keep close attention to the pressure the fingers are applying to the work to keep it centered. You don't want them to get loose or tight and keep the chips out of the area with a piece of cardboard over the work and against the steady rest.

This works very well for quick setups. You can also make a sleeve to go over the work or a cat head but all those take a lot of time and care to set up and get centered.

fciron
02-25-2011, 06:41 PM
I had a similar issue lately and when I got out my new-to-me bull-nose center it turned out to have what appears to be a 1-1/2 morse taper. (I assume it's a different taper standard.)

I turned a short tapered plug with a center hole and stuck it in there. Turning a tapered plug meant very little measuring was required. ;)

http://farm5.static.flickr.com/4076/5443940128_3082593e2b.jpg (http://www.flickr.com/photos/fciron/5443940128/)
Shrunk on collar (http://www.flickr.com/photos/fciron/5443940128/) by fciron (http://www.flickr.com/people/fciron/), on Flickr

http://farm6.static.flickr.com/5298/5443335633_15777f9c5a.jpg (http://www.flickr.com/photos/fciron/5443335633/)
Fixed! (http://www.flickr.com/photos/fciron/5443335633/) by fciron (http://www.flickr.com/people/fciron/), on Flickr

Oldbrock
02-25-2011, 08:01 PM
Good solution fciron, make sure the face of the plug is running true and you're good to go. You can now true up the od of the piece for a steady. Peter

fciron
02-26-2011, 03:22 AM
Thanks!

I used my largest center drill when making the plug. Then held it against the live center in the tailstock to guide it into the hole. I could have used a third arm, but everything lined up nicely in the end.

fciron
02-26-2011, 03:32 AM
Good suggestion. I could see this method working better on smaller diameter stock. One would think, as diameter increased so would the difficulty of sliding the rest near the end (less flex in 2 or 3 inch diameter than say half inch or 1 inch stock. Am I thinking right on this?

Harold

I missed this earlier. If you open the chuck so the workpiece can move, then you're not flexing anything.

In theory, if your workpiece is straight and your lathe bed is straight and your steady rest is adjusted properly, then there should be no interference when you slide it down the bed anyhow.....it could happen. ;)

Forrest Addy
02-26-2011, 04:21 AM
I've done countless jobs like this. It's a common second operation where finished OD material is cut to lengths and center drilled for keyways, splined, end work, etc.

Shade tree lathe hands make the mistake of "swallowing" the work - gripping it deep in the jaws. The jaws ALWAYS splay unevenly under load making it nearly impossible to keep the extended end of the work concentric with the spindle axis. If the work is long and flexible the unequal grip will spring it making imposible a part that's straight in the relaxed condition. If you want the work to stay straight, grip a short part of the length on copper pads centered in the plane of rotation and use a steady to hold the work concentric under cutting forces. The copper is soft and ductile and will not mar steel or bronze alloys but it yields enough to allow part movement during set-up.

Here's how I'd do it. I have a collection of bronze buhings with saw cuts in one side. They're a little over size but the bore is concentric with the OD. The saw cut allows them to squash down a little with the steady jaws and the bushing will support the work without marking it.

I'd 4 jaw the work gripping about 1/2 inch on copper pads or a single wrap of 6 ga wire in the jaw serration. Dial in next to the chuck, dial in the extended end by bumping it with a copper or other soft hammer, back and forth a few times until both ends dial in dead nuts.

Slip on the bushing, set up the steady with just a little tension on the bushing. Keep the bushing oiled. Slip on a cardboard chip flinger to keep chips away from the bushing. Center drill, drill and bore, whatever. If significant thrust loads are expected use a chuck jack or otherwise block the work from axal movement.

With a bushing in the steady jaws you can run keyseated stock, splines etc or any other work with an incomplete diameter.

Next time you're in the bearing supply house dig through the seldom used stock for bushings having oddball OD that never sell. Make them an offer for a range whoe ID's will suit you; nominal ID's for example. They are REAL handy on a lathe steady.

If protection from steady jaws is a cncern and you haven't got a bushing, a strip of motor insulation, plastic, brass shim, etc around the work and clamped in the steady joint to prevent its rotation with the part works nearly as well but be careful, chips appear in the best guarded places.