Off by 0.005

[johnn-e]

I have a 7 X 12 mini lathe. I am turning some aluminum 7 inches long down to 3/8 using a dead center. At the chuck the aluminum measures 0.005 bigger than at the dead center.

Any help would be appreciated

[mactec54]

Hi johnn-e

You should be able to ajust the tail stock on your lathe to get this at .000 or closer than what you have, there will be 2 screws one on each side of the tail stock near the bottom, put a indicator on the barrel of the tail stock loosen one screw (just slighty) & tighten the other untill you get it moved on the indicator the amount you need, every time you move the tail stock you will most likely will have to ajust it, if you don't have a indicator then you will move it a little & take a cut, untill you get it right

[johnn-e]

Thanks Mactec54

[Dano523]

A couple of things that you may want to look into as well.

If you are using a three jaw self centering chuck, here is a mod so you can true the chuck a lot easier during mounting. Granted that the there is a lot of detaining going on in the post , the added 4 set screws will be a god send in the end. Instead of dial indicating the chuck out surface, I dial off a piece of true straight rod held in the chuck jaws instead when mounting the chuck.

http://www.toolsandmods.com/chucks-repair.html

Once I have the jaws trued with no run out, then 45* point cut a short piece of stock, and then true the tail stock out to it. When truing the tail, grab a razor blade and use it between the points to see if the points are true to each other or not. In the case from side to side, the tail stock set screws work fine (if the bed is level and not twisted), but in the case of up and down of the tail stock, make sure to shim both ends of the tail stock on the mount. This will insure that that they stay true with the tail stock all the way in, and also moved all the way out.

Note: in a three jaw design, the jaws may not stay true with different diameter pieces chucked up (nature of the beast). If you use a few different sized straight rods for dial indication truing as you mount the chuck, you should be able to get the chuck within .0005 across the board for the small range that the chuck has. If you need to go for a zero run out on a specific piece, then it's just a mater of remounting the chuck for that diameter rod (tail stock will already be trued).

Lastly, if you are using the compound set at 0 degrees for small cuts, make sure it's a true to the work piece. Dial indicator works best here, but if you want to set it fast (within .001), a Parallel off the chuck face to the compound works in pinch as well.

[KIMFAB]

First off get a 4 jaw chuck and center your piece. Now you are ready to adjust your tailstock.
Loosen the screw(s) that allow the tailstock to move away from the bit. Bring them back and loosely snug them down.
Now tighten the screw(s) on the other side. You will only be moving the tailstock a bit so don't get crazy.

[MrWild]

First off get a 4 jaw chuck and center your piece. Now you are ready to adjust your tailstock.
Loosen the screw(s) that allow the tailstock to move away from the bit. Bring them back and loosely snug them down.
Now tighten the screw(s) on the other side. You will only be moving the tailstock a bit so don't get crazy.

Don't need a four jaw chuck for this. Once you've made a cut on a part, the shaft is true to center. If the diametrical difference is .005, the tail stock only gets moved .0025. It is best to do the adjustment with a indicator on the shaft so you know with precision how far you've moved. Moving and then a test cut is just wasting time as you will do this several times before you get it right.

[RotarySMP]

First do a check of the headstock alignment, and start on the tail stock.

Here's how I did my 7x12. Those tailstocks are really crap! I am sorely tempted to buy a lump of cast iron an make a new one from scratch.

http://www.wrathall.com/Interests/ma...ent_check1.htm

[KIMFAB]

Don't need a four jaw chuck for this. Once you've made a cut on a part, the shaft is true to center. If the diametrical difference is .005, the tail stock only gets moved .0025. It is best to do the adjustment with a indicator on the shaft so you know with precision how far you've moved. Moving and then a test cut is just wasting time as you will do this several times before you get it right.

No he doesn't need a 4 jaw chuck for this but if he is capable of measuring and concerning himself with .005 in 7 inches he will need one for other stuff.
We are trying to get him orientated here.

[Dano523]

Not having a 7X12 lathe I can not comment on the tail stock, but until he gets it centered with the head stock (both up and down and side to side for it's full throw), cuts from one end of the piece to the other are going to be a problem in regards to being unified (tool cutter no longer on the same plain up and down on the piece). I pointed out mod to true up the three jaw self aligning chuck, but someone may have to list a post for the mod needed on the tail stock.

Going front to back may not be enough to accomplish the needed task, and may find that shimming or lapping of the tail stock is needed to get it to align up/down correctly as well.

As for the 4 jaw, it will be need in time for off axis cuts, or odd blocks, but his current problem is all tail stock currently.

To add, not a big fan of dead centers in the tail stock. With the work piece in rotaion, and the end stock center fixed, you could have a bit of elongating going to the end center hold point on the piece, causing the variation in cut as well (tail stock end of the piece walking out .005 under cutter pressure by the time the cutter reaches it).

[MrWild]

To add, not a big fan of dead centers in the tail stock. With the work piece in rotaion, and the end stock center fixed, you could have a bit of elongating going to the end center hold point on the piece, causing the variation in cut as well (tail stock end of the piece walking out .005 under cutter pressure by the time the cutter reaches it).

True, and being a newbee, he might not even be lubing the dead center with high pressure grease. Lube the tail stock dead center? what's that? They make a special high pressure grease just for dead centers, but you can probably get by with disk brake wheel bearing grease as its easy to find in any auto store.

[Torsten]

I have a 7 X 12 mini lathe. I am turning some aluminum 7 inches long down to 3/8 using a dead center. At the chuck the aluminum measures 0.005 bigger than at the dead center.

Any help would be appreciated

Unfortunetly that is pretty common.
The quick fix is to ajust your Tailstock in or out by half the distance your diameter is out.
You will need a Indicator on the side of the Tailstock spindle to controll the amount for adjustment.
Also note that the Locking screw for the Tailstock Quill will affect the amount of missanlignment.
Make sure this screw is locked before machining and durring adjustments.
Good Luck

[johnn-e]

Thanks everybody, a 4-jaw chuck and a live center are on the list. I decided to get a milling attachment instead for some basic mill cuts hopefully it's not a waste of money.

I wasn't expecting to get this information on the problem. I'm happy people at cnczone share their experience.

Thanks again everyone