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Thread: Drilling center holes on a lathe
03-21-2012, 03:35 PM #1
Drilling center holes on a lathe
I need some suggestions on how to accurately drill center-holes in round stock so I can mount it between centers on my lathe without using a chuck (I don't have a chuck).
I am thinking of bolting a block of wood to the faceplate. Turning a hole into the block of wood the size of the piece I want to center drill then support the other end with some type of homemade steady rest which will then allow me to use the tailstock to drill the hole, flip the piece around and drill the other end. It just seems that there must be an easier way to drill the center holes then to go through all that and am wondering if someone could tell me the proper way to do it.
03-21-2012, 03:53 PM #2
If you are going to spend any amount of time without a chuck, then maybe you should make up a V-block with a flange that you can mount on the face plate. It will still be tedious but it will be a lot more repeatable than a block of wood.
You could also put a block of steel on your face plate, bore it to size, slot it and with some method of compression use it as a De-facto collet.
The easiest thing is to just buy a chuck. If you get a four jaw chuck you'll save money and develop a valuable skill.
03-21-2012, 04:16 PM #3
A way you could do it: use a center head on a combination square and scribe a bunch of lines across the end of the bar. Where they intersect should be the center. Prick punch it lightly, on both ends, then mount it on very sharp center points and spin it on the centers and indicate runout. Mark the direction of runout. Then dismount the part and prick punch it again, leaning the punch at an angle to the surface, and attempting to skid it a little sideways as you slightly deepen the impression. Test, repunch, etc, until you are close enough for your purposes.
Then lightly centerpunch on top of the prick punch mark to flatten the impression a little bit, enough so you can get a small center drill to find its way to center.
Mount the center drill in the headstock drill chuck, and set the part up on the punch marks, and apply light drilling pressure with the tailstock while you hold the part from rotating, with the spindle running. Flip end for end and drill the other end. Done.
I imagine it takes a lot of skill to get a perfectly centered hole this way, but then, the original method of accurate work was to turn the OD after the centers were already present, and not to do things ass backwards like this.
Joe Miranda liked this post
03-21-2012, 04:24 PM #4
The way to do this is described in "How to Run a Lathe" (look for it on Amazon). You should get it and read it.
You have limited choices but it is still possible.
Lay out the centers of your stock as accurately as you can with a scribe. You can use the center head from a combination square set, a hermaphrodite caliper, or a surface gage on a flat plate.
Center punch the centers as accurately as you can.
Mount the work on end in a drill press and drill the centers.
Lay out and center punch the ends of the work as above.
You need a drill chuck mounted on the same Morse taper as the center that fits in your spindle. You can get such a setup quite inexpensively from places like tools4cheap.net
Mount a combination center drill in the chuck.
With your left hand holding the work and the right end of the workpiece center punch hole held firmly against the dead center in the tailstock.
Feed the work on to the drill mounted in the headstock with the tailstock handwheel.
Flip the work and repeat.
Get "How to Run a Lathe" an get a drill chuck mounted on the correct morse taper.
Here is the procedure with pictures, starts at top of page 19:
How to run a lathe, for the beginner: how to erect, care for and operate a ... - South Bend Lathe Works, South Bend, Ind - Google Books
Last edited by David Utidjian; 03-21-2012 at 04:33 PM. Reason: added stuff and fiks speling
03-21-2012, 04:31 PM #5
03-21-2012, 04:36 PM #6
As far as doing it backwards it is because I am turning #2 tapers out of drillrod so I can make my own tooling such as centers, drill pads and mounts for jacobs chucks and I am doing the turning by hand(meaning using a handheld graver to do the cutting) and trying to do much truing up kicks my but and keeps breaking the tips on my graver.
harrytm liked this post
03-21-2012, 04:39 PM #7
The standard approach is to unceremoniously clamp the bar to an angle plate or v-block and drill on it a drill press. If the bar is too long for that or you have no drill press then you would use a steady rest on the lathe. To clamp a round bar on a faceplate you round a strip of copper and then wrap it around the end of the bar to protect it and act as a gripper. Then you use 4 set screws just like a four-jaw chuck. The set screws are attached to the faceplate in what are called "screw dogs". I have attached a picture of a screw dog. It is a 90-angle with two holes. One is used to bolt onto the plate, the other is threaded and holds the set screw. You can make the screw dogs yourself.
As an alternative to set screws, you can make soft jaws in the same way using the right angle dogs, but having a jaw of some kind instead of a set screw.
03-21-2012, 04:55 PM #8
I am curious about one thing. Probably this is a mathematical issue alone. But...
I take a bar , say a relatively short bar, 4" by 1/2". I chuck it up in a 3jaw, or worse, do some manual drill job to get the center holes done.
Now the centers will be in the bar, approximately to 4 thou on center. But it WILL have SOME excentricity.
I put it between centers. Since the centers are perfectly coaxial and the error will not be the same on both sides, the workpiece will have to revolve at a relative angle other than 0°. The workpiece will NOT be coaxial. This means that the center holes will not bear on the full surface but only a point.
Now i figure that elastic deformation and some wear against the hardened centers will correct this if the excentricity is minimal. Like those 4thou.
But what if i end up with 10thou because that good ole drill press is a piece of crap, frankly......and that on a short sturdy bar that cant bend to compensate....
Where do you draw the line.....
03-21-2012, 05:00 PM #9
03-21-2012, 05:30 PM #10
Your only real problem is if the sides of the bar are irregular. In this case you stuff the bar inside of tube that is regular, and it is the tube that gets clamped to the v-block/angle plates.
03-21-2012, 05:35 PM #11
The center holes will be coaxial. Nice.
They will still be excentric. And that will still give an angular error as long as the excentricity is not at the same index on both ends....
03-21-2012, 05:36 PM #12
What are you planning to drive the center drill with: your teeth?
03-21-2012, 05:42 PM #13
03-21-2012, 05:46 PM #14
It seems as if the emperor has no clothes.
A lathe without a chuck!!!!
Why the f.. are we not asking about how to mount the chuck.
03-21-2012, 05:56 PM #15
Excentric....friggin German spelling when you replace "tric" with kraut equivalent "trisch" . Sometimes it resurfaces
Coaxial.....well youre damned right, its late here and I should be sleeping....the axes of rotation would be parallel and NOT coaxial....bahhhhh
They WILL be parallel because no normal way of drilling a center is going to be exactly on center. Chucks, V blocks, everything.
And in that case the workpiece will no longer be coaxial with the machine axis, because chances are the eccentricity is not on the same angular index on both ends......
03-21-2012, 06:02 PM #16
We are no longer in the 17th century. We have had screw cutting lathes for over 200 years. If I am reading you correctly it seems you are starting so far behind the curve that you will never catch up. You would save much time by getting a minimum wage job and using the money to buy some better tooling or even a clapped out 100 year old lathe.
03-21-2012, 06:31 PM #17
I'll either cut it with a graver or temperarely mount a 3 jaw chuck to a morris taper cut out of wood and attach a dog to the chuck so I can prevent it from spinning and the wooden morris taper is only there for alignment.
this is meant to be a reply to HuFlungDung
03-21-2012, 06:37 PM #18
03-21-2012, 06:53 PM #19
The way it used to done is to file the stock to a cental point at each end and then use female centers in the lathe. No drilling required. Start with stock slighlty larger than what you need as the piece will not run true at first but can be turned to be concentric with the 2 ends.
I agree with David about spending the time to make a little scatch to buy some actual metalworking tools. My favorite lathe, a Stark #4, was only $300 a few years ago on the CL, so it doesn't take that much.
03-21-2012, 07:15 PM #20