Thread: 1/8" thick round plate

How would you go about making a steel plate, 1/8" thick 3" diameter with a 1 1/4" hole in the middle? The edge is what I am interested in - it needs to be very smooth and will have index marks engraved on it. I have a mill and a lathe. Thanks.

Part it from a 3" diameter bar with a 1 1/4" hole through, which you've already fininsh turned the periphery as nice as you need.

Al

Rough the plate blank about 1/16" oversize from a piece of plate, hold it in the 3 jaw using the outside jaws, then trepan the hole in the middle to the size and finish that you want.

Change the jaws and holding it through the centre hole turn the out side to size and finish.

CD.

Originally Posted by Charles Dolan

Rough the plate blank about 1/16" oversize from a piece of plate, hold it in the 3 jaw using the outside jaws, then trepan the hole in the middle to the size and finish that you want.

Trepanning tool:
http://www.ibiblio.org/ecolandtech/m...nning_tool.jpg
http://www.ibiblio.org/ecolandtech/m...hop/Valcut.jpg
Cutters available in cobalt steel:
grooving
inside round
outside round

Change the jaws and holding it through the centre hole turn the out side to size and finish.

CD.

How precisely flat does it need to be? ERA's approach would be a heck of a lot easier and better, but if you don't have any 3" round stock and you do have some flat plate of the proper thickness, you can rough out an oversize blank on the band saw; drill a hole in the middle; make a mandrel to mount it on the lathe; and turn the edge. Depending on how well you rough out the circle, the interrupted cut may generate quite a pounding until it begins to clean up. Then mount it in a four-jaw or clamp to a face plate, making sure it is centered and as flat as possible, and bore out the 1-1/4" hole in the middle. Alternately, reverse these last two steps -- first mount the rough blank on a face plate or 4-jaw and drill/bore the 1-1/4" hole, then mount it on a mandrel cut to 1-1/4". Either way, the flatness of the result will depend on how flat the plate was to begin with, and/or on how well you mount it in the four-jaw for boring.

On edit -- I had let this sit a while, while I dealt with some other things, so hadn't seen Charles Dolan's approach. It is similar to mine, except that I would probably just drill and bore the center hole, rather than trepanning it ... and I hadn't thought about holding the piece from the inside with the jaws. That may depend on your chuck -- I don't think I could do that with the chuck on my lathe, not unless the hole was bigger than 1-1/4". Also, if you need the center hole to be perfectly concentric with the outside diameter, holding it inside with the jaws of a 3-jaw will often be off by a few thou. I guess you could hold it with the jaws of a 4-jaw from the inside, depending on the size of chuck, and depending on whether you could indicate it adequately. Hmmm ... obviously, more than one way to skin this cat!

I've done a few projects similar to this with a hole saw, keep in mind you need to measure the saw's ID for your disk OD. Drill your small hole first (undersize), change saws and drill the big one Voila! your first disk. If you are using sheet, cut to strips as long as the travel on your mill and just work your way to the other end. When alls done finish ID and OD on the lathe. BTW I suggest making your own heavy saw mandrel with a shank sized for a collet. A slow down feed and plenty of coolant, or even peck to clear chips from the teeth.

Originally Posted by rmw

How would you go about making a steel plate, 1/8" thick 3" diameter with a 1 1/4" hole in the middle? The edge is what I am interested in - it needs to be very smooth and will have index marks engraved on it. I have a mill and a lathe. Thanks.

I feel like I might do it this way:
Weld a long coupling nut to the back side of some 1/8 inch plate.
Chuck it up in the lathe, with jaws on the nut.
Turn your OD.

Remove it from the chuck and then grab the OD with the outside chuck jaws.
Bore your 1-1/4 inch hole with a boring bar and let the nut fall off.

If perfectly concentric alignment is needed between the OD and hole, use a 4 jaw chuck to grab the OD, then bore the hole......pg

I'd rough the blank oversize using holesaws put thru an 11 gage plate before I used the lathe.

Then finish the ID and make up a precision mandrel that was nearly a press-fit on the ID of the disk, and a keeper to hold it.

Chuck and indicate that mandrel and finish the OD.

I used ERA's method last nite on the first one. Parting through that much material seemed dicey, but it worked. I had already bored the 1 1/4" center. I only had to debur it. I have 3 more similar plates to make, and plan to try trepanning the center on at least one, and the welded nut method on at least one. Thanks all for your help and ideas. Greg

Glad my suggestion worked for you, if you are new to parting, you could try this:

Put a jacobs chuck in your tailstock holding a smallish diameter length of drill rod or anything you think will be strong enough to support the weight of the part you are parting (I often use a pencil) & advance the rod into the hole. Part as you would normally and when the part drops it is captured on the rod and doesn't fall onto the lathe bed putting a ding in your pristine finish.

If you are unsure about a deep groove, part in 2 or more stages widening the groove the width of the tool each time from the headstock. Obviously for this you need more material available to you. This method can allow you to put a nicer finish on the back face of the part as you take a skim off on the last pass.

Hope this is clear.

Al

Originally Posted by Engine Room Artificer

Glad my suggestion worked for you, if you are new to parting, you could try this:
Put a jacobs chuck in your tailstock holding a smallish diameter length of drill rod or anything you think will be strong enough to support the weight of the part you are parting (I often use a pencil) & advance the rod into the hole. Part as you would normally and when the part drops it is captured on the rod and doesn't fall onto the lathe bed putting a ding in your pristine finish.
If you are unsure about a deep groove, part in 2 or more stages widening the groove the width of the tool each time from the headstock. Obviously for this you need more material available to you. This method can allow you to put a nicer finish on the back face of the part as you take a skim off on the lastpass.
Hope this is clear.Al

If I understand correctly, he said he bored the 1-1/4 inch hole first, then parted. A pencil is not going to help much going into that large hole. If the hole was only a quarter inch, the pencil or drill rod would help.
However, the best choice is to bore the 1-1/4 inch hole first (as he did) to reduce the amount of cut off work he has to do. The less he has to plunge that tool into the work the better off and quicker he can get it done, the less heat generated, etc.......pg

Pinion, Don't know if you understood about the pencil idea correctly. A pencil, 1/4 drill, a scriber, or just about anything will work.

PG

The pencil or whatever is to catch the part as it drops to prevent it getting dinged. Sorry for my bad explanation.

Al

Originally Posted by Rstewart

Pinion, Don't know if you understood about the pencil idea correctly. A pencil, 1/4 drill, a scriber, or just about anything will work.

2 sharp centers, one in the chuck, one in the MT holder; align the point tips with a magnifying glass; or put blue on them also

Or put same size precision dowels in chuck and in MT holder. Use indicator to make them
parallel in y & z axes. Use machined plate under MT holder for repeat settings, as Walter suggested.

"align the point tips with a magnifying glass; or put blue on them also"

I hadn't heard of bluing opposing centers before...how does that work?

Originally Posted by matt_isserstedt

"align the point tips with a magnifying glass; or put blue on them also"

I hadn't heard of bluing opposing centers before...how does that work?

It just occured to me; I've never tried it. You'd have to use a loupe or magnifying glass for it to be practical in order to see scoring in the blue.
With off center misses you'd more easily see scoring on the taper then adjust accordingly until the scoring got closer to the point. Turn chuck to make
concentric rings for added visibility.

Or put a sharp center in the tailstock and a 1/2" or so rod with precision-ground flat face in chuck. Blue the face then score a center point with the tailstock center.
Put center in MT holder and try to align it with the established point on the end of the rod. Use magnifying glass.

Or face a 1/2" X 3" round plate in chuck. Bore 1/2" hole in it then turn a 1" X 1/4" recess concentric around it. Press fit a disc of plastic into this recess.
Put small drillbit in tailstock chuck and embed it into & through the center of the plastic disc. Use fine diamond file (mounted in toolholder) to grind sharp taper on end of
drillbit. Attach copper wire to drillbit - to battery - to lightbulb - to center in MT holder. Align center in MT holder with drillbit point.
You have centered the MT holder when light goes on. Again, machine plate to go under MY holder for repeats. Never tried this but it sounds OK.

Or put dielectric sleeve around small drillbit and clamp it in collet in spindle; sharpen point and attach lightbulb circuit as described above. Then align MT holder for center.
This would eliminate any error encountered with discrepancy in tailstock alignment.

For years I used to make 1/4" thick plates of 1018. 5-1/4" diameter with a 5/16 center hole. Typical run was 500 to 1000 pieces.

These were a base for a retail display stand and got powder coated or chrome. All surfaces had to be smooth.

We looked at all sorts of methods. Turned out the best for us was to have a grinding shop with an automatic bandsaw slice off the blanks and double disk grind both faces simultaneously. $2.30 each for the cutting and grinding.

We held the blanks in a step chuck in the CNC lathe and put the center hole in, plus an edge break radius on both sides.

"Turn chuck to make concentric rings for added visibility."

Right there you have to indicate a center into the chuck or rather true a shop-made one with a light cut. Then rely on visual methods.

I submit that the better and faster way to check alignment is with a simple piece of hardware like pictured below, piece of pipe with a dowel pin welded to it, and a test indicator attached. No precision in chucking or making the fixture is required as once rigidly clamped, it rotates as concentrically as the spindle bearings allow.

In this case the picture is shot checking the OD of the tailstock ram, you can also indicate the bore on the tailstock, a tip on a dead center, etc. IMHO, the indicator dial gives a better quantitative analysis of which way and how far to move things.

Originally Posted by matt_isserstedt

I submit that the better and faster way to check alignment is with a simple piece of hardware like pictured below, piece of pipe with a dowel pin welded to it, and a test indicator attached. No precision in chucking or making the fixture is required as once rigidly clamped, it rotates as concentrically as the spindle bearings allow.

In this case the picture is shot checking the OD of the tailstock ram, you can also indicate the bore on the tailstock, a tip on a dead center, etc. IMHO, the indicator dial gives a better quantitative analysis of which way and how far to move things.

That's probably the definitive method. I think I remember your posting this
same information earlier in PM. You described the clamp you made to attach the indicator
(stem or dovetail?) to the dowel on the pipe. Maybe you used this setup on a mill too.
Could you repost that or describe that part with the small handwheel in the pic?

Thanks. LL

Waterjet

(10 characters)