lathe aligement problem

[Deny1950]

Hi i was wondering if someone can give me some idea of the problem? If i take a cut out of a shaft and then turn it end for end and take another cut they do not match up, just as if the head of the lathe is off to one side. the bed was leveled with a ordinary level? The chuck is a d5 and is adjustable with 4 setscrews, and they are all the way to one side and it is out by 1.5 thou where to from here? Thanks in advance Denis

 

[Mark_f]

put a bar in your chuck about 10 inches long. put a live center in other end. Take a LIGHT cut. (.005"). Mic the chuck end and the tail end. If they are different, adjust the tail-stock half the amount it is different. Take another cut. Do this until the ends are the same. Do not remove the bar between cuts or until you are aligned. I did my lathe this way and I can cut a bar with .0003" / foot. Try to use a substantial sized bar. I used 1 1/2 " diam. use at least 1".

Mark

 

[Wobbles]

Just a few informed guesses....
• If you are turning between 2 centers, then maybe your centers don't align. Align the tailstock.
• If you are using a "self-centering" chuck, they usually don't, due to...
........► Wear on the internal scroll gear
........► Jaws not being placed back in correct order (jaw slots are numbered)
........► General jaw and scroll gear wear... Age of the chuck
........► Jaws not clean when clamping work piece


Suggestions...
• Try using a 4-jaw and zero the work in with a dial indicator
• Watch the YouTube videos on truing a "self-centering" chuck
• If it's a short piece, try using collets

The easiest way to keep all surfaces concentric is to cut all surfaces in a single setup. If you know you can't do that, then turn the piece between centers, using a dog and faceplate.

:thumbzup:

 

[Don B]

Hi i was wondering if someone can give me some idea of the problem? If i take a cut out of a shaft and then turn it end for end and take another cut they do not match up, just as if the head of the lathe is off to one side. the bed was leveled with a ordinary level? The chuck is a d5 and is adjustable with 4 setscrews, and they are all the way to one side and it is out by 1.5 thou where to from here? Thanks in advance Denis

You will need to supply a little more info before anyone can can truly help you, when you say "the cuts do not match up" do you mean both end are tapered, or did they wind up not being eccentric to each other, or possibly both, was the work free floating or was it supported by a center (it could be bedway twist, tailstock alignment or a combination of both) how large was the cut (is it a deflection problem)
A picture of the chuck and these 4 set screws would be good as well to see what's going on.
An ordinary level is fine for general leveling of the lathe but if you where using the level for bedway alignment (to remove twist) an ordinary level just won't do.)

 

[Deny1950]

H don the cut was made of the chuck only short piece, and it was not eccentric like a cam. I have a pratt bernerd chuck on a KCB 1540 lathe, it is a Tiwanes make, nice heavy lathe. I would like to post pics but don't know how sorry.

 

[Don B]

H don the cut was made of the chuck only short piece, and it was not eccentric like a cam. I have a pratt bernerd chuck on a KCB 1540 lathe, it is a Tiwanes make, nice heavy lathe. I would like to post pics but don't know how sorry.

I think the first place you need to start then is make yourself a "lathe alignment test bar" it's just a stout bar with a couple of raised collars, you take a very light cut on one collar don't move the cross slide wind the saddle up to the other collar and take a cut, this will tell you if you have a twist in the bedways (i.e. The diameters of the collars are different) if so you will need to do some shimming under the mounting legs/lugs at the tailstock.

 

[donthack]

To help us help, how did you hold your stock to cut? You said it was a short cut, did you indicate run out before cutting? And is this a new install, or some issue that has recently started? Sooner or later someone will figure it out, the people on this site always do!

 

[Deny1950]

I guess i am not explaining it right, it has nothing to do with tail stock, because i did not use it for the cut in question. it was a short 2in piece of heavy tubeing did a light cut turned it end for end toke another cut. The two cuts did not match up, on the second cut it toke more of one side and almost nothing on the other side. This is not a new problem.

 

[joconnor]

I'm guessing you are using a self centering chuck that is not centering perfectly. If so that is normal since they are not perfect, however some are much better than others. I you want it to line up you will have to use a four jaw chuck and dial gauge. Have fun!

 

[chainsawd]

I once had a similar problem with a small atlas lathe, whereby alignment on lathe varied every time I used it.The problem was in the wooden mounting trestle that the lathe was fixed to and with expansion and contraction due to hot , humid and cold weather the lathe would vary considerably in accuracy.
I still use the same wooden trestle but have fitted heavy steel slipper plates between the trestle and the lathe mounting feet and with the use of shims and a precision level and the lathe bolted down tight the problem was rectified