Lathe Accuracy

[David Haughs]

This may be a silly question but before I run off and replace my lathe, I have to ask it. I purchased a Rikon 70-100 mini lathe several years ago. Recently I am noticing that while drilling, yhe point of the drill does not contact the center of my work piece. If I just lightly contact my work with the point of my drill. it scribes a small circle on the work piece. When I bring my tail stock up to the head of the lathe with centers in both pieces, the points are ever so slightly off. I assume the error is magnified as the tail stock is slid away from the head of the lathe.
Is there a way of adjusting this? I'm thinking that it might be easier to just buy a better lathe and if I do buy a new lathe, how can I insure I get one that is accurate?

[Bill Dufour]

Most likely the quill is not aligned with the headstock. is it high or low compared to the headstock? or is it in or out?. It could easily be out in two directions. A quality metal working lathe tailstock will be two pieces a base and the upper portion. these can be shimmed and angled relative to each other. Many allow the quill to be set over to allow taper turning of a few degrees.
For wood working the accuracy is just not needed. What diameter does the dead center make?
Bill D.

[Bill Dufour]

How are you holding the drill? have you tried changing the alignment. is it all drills or just some. are you using a chuck to hold the drill?
Bill D.

[Perry Hilbert Jr]

Is it possible that you have a minor piece of debris stuck in the tail stock taper. it would throw the center off slightly as well as a drill.

[Marvin Hasenak]

Insert a spur drive on the headstock and your live center in the tailstock, slide the tailstock up and see how close the 2 points are. Take a pic, from the top and from the side, that will show you how far out of alignment the 2 parts are.

[Jay Mullins]

Often the problem like this can be the bed being out of alignment ( usually twisted ) if the point of the tail stock center and the drive center are not matching up horizonaly, simply raise one side of the lathe ( headstock end ) and the opposite corner of the tailstock end of your lathe. I had to adjust my lathe like that today.

Jay

[David Haughs]

Thank you. All great inputs. I used an old spur drive when I first checked alighment so I changed it out and inserted a new, shart spur drive. Now the alignment of the spur drive with the live center is perfect. So now I have to figure out why drills are off center when starting a hole. I am using a brad point drill with a very sharp center point. the point scribes a circle about 1/16 " diameter. The other thing is that when turning a spindle, the cut is very smooth close to rhe spur drive or chuck. By the time I get to the live center at the tail stock, the tool feels like it bouncing up and down. If I turn a pen with the point at the tail stock, the point is out of round. The pen insert is smooth with the wood except on one side where the wood is a little larger than the insert. In other words it is off center. I bought a new mandrill and do not over tighten. BTW, When drilling, I am using a jacobs chuck on a MT2 taper made for the lathe. Thanks for all the good ideas.

[Marvin Hasenak]

I think it might be your drilling procedure. I start my hole using a short center bit. I use jobber bits, the regular ones that 99% of the people buy. I quit using brad points on the lathe, they cause problems. As to the spindle problems, if you get the item too small in diameter you will get chatter from the turning, that us sort of normal, I control it with my freehand. The pen problem, check to see if the mandrel is bent, a common problem for new people, being rough with the mandrel and over tightening can mess it up.

Check the lathe to see if it is level, you might not even see it, but if one corner is higher than the other 3, the bed will warp. The farther you tailstock is pulled back, the more the warp effects the centers.

Put your location in your profile, you might be lucky and have someone close that can help you.

[Kyle Iwamoto]

Aren't you over thinking this? Use the tailstock center point to mark the drill point. Works every time. Since your lathe is "straight". That's what I do.

[Dan Hunkele]

Use the tip of a skew with the sharp edge at about 45 degrees to make a drill center hole. It will automatically find center. There is a little play in the tailstock to make to move easily. Pull I towards you and align it on the rail closest to you for best straightness. It is possible to get the tailstock slightly askew.

[Michael Mills]

You stated the centers (drive and live) were off by a small amount. Is it the same amount when you install your chuck and check the point of the bit to the drive center?

If you have the lathe bolted down it may be a twist as Jay suggested. You can make winding sticks to check for twist with the tail stock removed. Here is a video on winding sticks and how to use them. If you have two rulers the same you can use those (that is what I used).
https://www.youtube.com/watch?v=ZKAxSouPGtE

[John K Jordan]

The problem with point alignment it is only good for that specific spot the tailstock is clamped to the bed. If the bed is twisted evenly all the way down, untwisting can fix it. If the bed is twisted unevenly or otherwise deformed, it may not be possible to align it.

Before assuming it's out of alignment, though, I'd check carefully. Be sure the quill is clean, lubricated, and without excessive play. Be certain there are no burrs or dents on the bed or on the contact surfaces on the bottom of the tailstock. Check alignment with a sharpened rod in the Jacob's chuck. Be sure the rod is straight. See if the point is in the same place even when the chuck is removed, rotated, and reseated and when the rod is removed and replaced. Try a different Jacob's chuck. If inconsistent check the taper on the Jacob's chuck for a burr or other deformity. You can also put the Jacob's chuck with pointed rod in the headstock and see if it consistently misaligns with a drive center point in the tailstock.

If all that is consistent, perhaps check the bed for twist with winding sticks. A twisted bed on a large lathe can be fixed by adjusting one leg (cast iron is surprisingly flexible). I don't know if the leg adjustment method would work on a mini lathe with a short bed. I did have a lathe once that I fixed with shim stock. If you can borrow access to a large surface plate you can check for bed twist with a dial indicator.

From a photo I found of that lathe it appears the headstock is bolted to the bed. If so, I might try loosening all the bolts and see if the headstock can be moved or twisted so it is in alignment all the way down the bed.

JKJ

[Dean S Walker]

I have run into this with my little jet some years ago. The solution was a very small piece of dust in the taper that holds the chuck on the taper adapter. I cleaned that and cleaned the mt tapers on tail and head. most of the problem went away. The second problem was me. I advanced the bit too rapidly bad news for brad point bits. l slowed my feed rate down and switched to normal drills and started in a divot made with a skew.