centering
 

Ok guys how can i get my holes centered when drilling with my lathe? i have a problem or o am not doin something right i have a live center on and the round stalk chucks up pretty close when i put in the drill bit all is tight but it starts to wobble you can watch the drill bit flex around i am thinking it is the drill bits even in the drill press they wobble on the end all the bits are new and they wobble bad bits? or should i be useing something else? any help would be great

Re: centering
 

Drill bits are flexible by design.
You just want to establish the center point with a center drill bit. This is how it looks like: http://mini-machine.com/tooling-cent...rill%20set.jpg
After that the normal drill bit will find the center and do what it is supposed to do.

Kerst

Re: centering
 

clyde just what kerst said . I tend to drill the hole a little smaller then finish it with a boring bar , drill bits tend to deflect a little

IHSteve

Re: centering
 

For nice clean and accurate holes one can use a reamer to finish the hole.

kerst

Re: centering
 

so thats my whole problem .....lol i thought that was it but wasn't shure thank you a bunch guys

Re: centering
 

Is the tail stock aligned with the center of the chuck?

Re: centering
 

I agree, use center drills to start holes on the lathe.

Also check tailstock alignment. To do this take a piece of barstock as long as you can put between the tail center and about 3/8" in the chuck jaws. First short chuck it in the chuck and center drill for the center to run in. Then chuck by the last 3/8" (so the chuck jaws, aren't forcing the piece off at an angle) then take a light skim cut all the way across the piece (you can take a cut from each end be be sure and get the exact same dial reading). Then measure each end with a mic and check for the tail end being bigger or smaller then the chuck end.

If it is not the same on both ends then you will need to adjust the tailstock and recut the test piece until it is. This adjustment depends on your lathe style as to how it is done, but I usually throw a dial indicator on the tailstock body to be able to measure and read how much I actually moved it (move about half the difference of diameters)

Re: centering
 

I agree to what has been said above, also good quality, sharp, drill bits are important to a good hole. If you need real accuracy, reaming will help. Fred

Re: centering
 

A master machinist showed me this one. Just put centres in both headstock and tail stock. Bring tail stock up to headstock. If the tail stock is centered you should be able to hold a razor blade between the two points. If not, then just adjust the tail stock till it does, and your done. Now if your lathe bed is warped then that's a different fix. You'll need a precision level and shims to make it true over the entire length. Then go back to step one. Hope this helps.

Re: centering
 

I have checked that 1 when you told me about it and it was way out . I still get a little run out at the chuck but that could be the adapter plate . I'm having trouble getting the right 1 . but for now my lathe does quite well for a 100+ year old lathe


IHSteve

Re: centering
 

Everyones advice is spot on. Now I will throw a curve at you. Anyone use Titex drills? They are 3 flute carbide drills that do not require a center drill. They are great for aluminum, brass, cobalt chrome, and titanium but lousy in stainless. I have never gotten good results in any type of stainless.

Lynn

Re: centering
 

Haven't tried those, but do use Stub length drills quite often and try to avoid the cheap import brands as they flex and break all the time, but the better stubs are pretty good.

In the vertical machining center I rarely center drill holes unless the position tolerance is tight, but the lathe you always seem to have a little nub point left in the middle which is the main cause for drills wandering in the lathe and the center drill cleans that off easily.

Re: centering
 

I have heard that 135-degree split point drills do not require center drilling. Is this true? Also I cut mostly alum. on my lathe and it seems to cut better with the tool .020" above center. Does this make any sense? If so-why.

Re: centering
 

135 deg drills are a bit stronger than 118 deg and seems like I can push them harder and they work better in some steels. Split-point drills help prevent walking the most.

Running the tool a bit above center probably does 2 things for you. First as the tool flexes it moves to be on center rather than below, and 2nd being above center makes the tool edge a bit more of a positive rake which aluminum like better

Re: centering
 

Not sure about the 135-degree point drills. Always use c'drills except for the Titex drills in both the lathe and mill.
Tool above center might be due to rake of the tool. Are you using ground tooling or carbide insert tooling? I have some insert tooling that my Sherline lathe wouldn't cut air with. No idea why as they work great in other machines.
I see that pugs beat me to answering!

Lynn

Re: centering
 

Thanks to both of you-pugs-that makes sense.tc1cat-I am using the carbide insert tools. They work great for me. For what little steel work I do I gring my own tools. Seems to get a better finish. I use the cheap import carbide tools and when they get a little wear on them I just put em in the trash.

Re: centering
 

i can hold the razor blade between centers and the lathe is all level i checked that all last night i found the steel stock i use may have slight bends in it when i only use a peice about 8 inches everything works great but a longer peice it all goes waist side and the centering bits are still off centered when i have a long peice in the lathe bad steel?

Re: centering
 

Clyde , boring always works best near the chuck . If you are boring a piece that will not fit through the spindle bore , you should have a center rest ( Please correct me if I'm wrong ) the farther away from the chuck with out the tail stock engaged your piece will want to drop due to gravity and slight play in the spindle bearings .

IHSteve

Re: centering
 

What size hole are you drilling? and how deep?

Re: centering
 

i was working some 3/4 in cold roll making top rollers i was drilling a 1/4 inch hole through the center has to be in the steel i trued up another peice and then used the centering bit all is good i drilled my 1/4 inch hole 2 1/2 inches into the cold roll no problems tonight all is well in clyde land lol thank you all for the help .........needless to say i am no machinest but i am starting to make some decent parts finally lol

Re: centering
 

Sounds like your on your way. Only other thing is, if the drill bit isn't ground exactly true on both lips it will walk over. Best to drill under then bore to size.