Mounting live center easily

[Dan]

I had a hard time without a hole in the middle of my material so I came up with this,...
Turn the jaws around and loosly chuck up the peice thats to large to fit through the chuck,
Turn it slowly by hand and center the tailstock end then tighten the chuck, then
Put a deadcenter in the tailstock and ram in against the material this "centerpunches"
a dimple and with a countersink bit in the tailstock chuck drill a good sized hole for the live center.??

 

[Maryak]

Dan,

First, Welcome to our forum.

Second, may I ask are you new to machining ???

Best Regards
Bob

 

[Dan]

Yes very new to the proper techniques. I got started with a drill press and a circular auto body air cutoff grinder making odd screws and such. Then i got fed up with that and found a clarke mini-lathe for 275 at the hardware store.

I had aviation mechanics in high school and the instructor had a lathe but used it very little, made those little aluminum nose cones for model rc airplanes, and thats about all the formal training Ive had, other than sitting through six hours of video I downloaded from the MIT video library.

 

[malcolmt]

Hi Dan and welcome

Can i ask where you are from ?
I have read through your post's and I'm having difficulty working out what you are trying to do. if you have the facility can you post a picture of your set up so we can see how we can help.

Kind regards

Malcolm

 

[Maryak]

Dan,

Thanks for that, I re-read my 1st post and it sounded pompous to me and for that I apologise. :bow:

Your method is not one I would choose.

There are several ways of getting a centre hole in a long piece of round stock which won't go through the lathe spindle.

Use Jenny or Odd leg calipers to find the centre by setting them near to the radius and scribing an arc in 3 or 4 places from around the circumference. Where these lines x over meet etc. the centre of their meeting place is the centre of the end, hold it in a vice whilst you pop this point with a centre punch.

Set up in vee blocks on a surface plate, scribe several lines, (at least 3), ending up with a point similar to the Odd leg method.

If you don't have a fixed steady for your lathe either of the above should get you there without running the risk of jamming your dead centre in the tailstock.

The best is to set your material running true near the chuck, attach the fixed steady to the lathe bed and adjust it so that the end of the stock nearest the tailstock is running true, drill with your centre drill and replace the drill chuck with the live centre. This assumes a that the stock is not so long that you can't get the drill chuck into the tailstock and have the tailstock remain on the lathe. Then it's those above and a dead centre with grease.

Oh I nearly forgot, black ferrous metal is not normally held in a 3 jaw chuck. To keep it accurate hold only unmachined non ferrous stock, machined ferrous/non ferrous stock or brightstock.

I hope this helps get you going. ??? ???

Others will give you their versions and pick the one(s) you are comfortable with.

Best Regards
Bob

 

[Dan]

Thanks bob,

I have heard about the two arcs and straight edge with a intersecting center point double line method and nicknamed it " The old cat eye trick", maybe slamming the tailstock into the head aint such a good idea but it lead to a better idea and a chance to build another tool for the tailstock. Ill keep working on it until its perfected.

again thanks, thats what im looking for is more know how to

 

[ScottM]

Hi Bob,
Can you explain what you meant?

Thanks - Scott

Oh I nearly forgot, black ferrous metal is not normally held in a 3 jaw chuck. To keep it accurate hold only unmachined non ferrous stock, machined ferrous/non ferrous stock or brightstock.

 

[Maryak]

Scott,

I'll try :

Steel straight out of a steel mill has a residue from the forming process called mill scale, which is pretty hard, covering the outside of the stock, this plus some inaccuracies in the mill die mean that the piece you get is not truly round. Cast Iron also has a very hard outer skin left by the casting process and again is not truly round.

Putting these materials in a 3 jaw self centreing chuck puts an uneven strain on the scroll in the chuck, the scroll may be damaged by this and the accuracy of the self centre compromised.

Non ferrous materials are generally softer than steel and most of them don't have a skin which is harder than the steel chuck jaws so the inaccuracies are overcome by the strength of the chuck v the strength of the material and the chuck is not strained.

If in doubt use a 4 jaw independent chuck and machine a chucking piece for it to go into the 3 jaw chuck.

Brightstock is steel which has been accurately made to size before sale. It is bright to look at, (not black), and is covered in a preservative compound to prevent oxidation prior to sale. It also requires much more gentle handling in transit and storage hence the big bucks when you buy it.

Hope this helps. ??? ???

Best Regards
Bob

 

[IanN]

Hi,

OK, I'll bite -

Steel straight out of a steel mill has a residue from the forming process called mill scale, which is pretty hard, covering the outside of the stock, this plus some inaccuracies in the mill die mean that the piece you get is not truly round. Cast Iron also has a very hard outer skin left by the casting process and again is not truly round.

Putting these materials in a 3 jaw self centreing chuck puts an uneven strain on the scroll in the chuck, the scroll may be damaged by this and the accuracy of the self centre compromised.

Why does gripping material not truly round in section strain the scroll?

Assuming the work is free to move in the jaws as they are tightened it will shift until the force exerted by each jaw is equal, then it will stop moving. If the jaws all experience the same tightening forces then they will all be stressed and strained equally and the scroll will experience symetrical forces. Any non-radial component of the gripping force is taken by the slots that the chuck jaws slide in, not by the scroll.

I agree that the scroll will be damaged by overtightening but I don't see how it can be damaged by gripping a slightly non-circular section.

Ian.

 

[ScottM]

Bob,

Thanks for the reply. I understand what your saying now you are talking about "mill scale", yes it is hard, hard to remove as well!
I don't agree that it will cause damage to the scroll, as Lan said that's cased by too much clamping force.
Since a three jaw has three points on contact with the work it will have almost equal pressure between the points (assuming the work piece is more or less round or hex).

- Scott

 

[Maryak]

Ian and Scott,

Thanks for your explanations. :bow:

I am sorry I don't have a better reason for not doing it than the one I gave in my original post.

Each to there own.

Best Regards
Bob

 

[IanN]

Hi Bob,

My comments were not an explanation, just my opinion - I thought I was missing something.

Ian

 

[Cedge]

Dan
I've read through this thread several times and "IF" I'm reading things right, an answer hasn't quite been given to your question.

First off it appears that you are using a 3 jaw chuck on a lathe and want to center drill the end for additional support. If so, then your description seems to be doing things a little backwards.

Once a piece of round stock is chucked and the lathe is turned on, it is quite common to find the work piece turning off center... that wobbling thing we all know so well. Disregarding Bob's caution about uneven chucking, it's best to lock the metal down enough to prevent it slipping or worse... climbing out of the chuck..... that's a bad thing.

Once the piece is chucked, mount the tail stock drill chuck and a center drill. Run the center drill into the end of the work piece and watch how it reacts. If it is not offset, the center drill will begin to drill a hole dead center of the rotation, turning off small twin spirals of swarf, indicating a nice even cut.

If the tail stock is offset, the center drill will do one of two things. It will visibly move to the center which can be seen in the movement of the bit or flex in the tail stock bore. It might also begin cutting a small circular ring with a high point in the center. Either one indicates that you need to check the tail stock alignment.

Assuming the center drill begins a nicely centered hole, continue to drill until the larger part of the drill's taper is cutting metal close to its shoulder. You now have a center point that will accept the live center without having to bang anything into anything else. Replace the drill chuck with a live center and you are ready to true the work piece.

Yup....center drilled and the wobble is still there. That is what a lathe does.... it remove wobbles. As you begin cutting the long side, the work piece will become concentric with the center drilled hole and you have a nice stable surface to work with.

Easy.... safe and far more effective than trying to manually locate the center before locking the chuck.

Now.... if I missed the point of the question, then all bets are off....LOL

Steve

 

[Tin Falcon]

Dan :
Welcome sounds like your question was answered.
Here are a couple of links to the basic manuals used to to teach military folk machining basics. These are large pdf downloads broken down by chapter. Military manual are generally easy to read and understand this may help you with many shop basics. But you are welcome to ask questions here as often as needed.


Army machining manual
http://www.metalworking.com/tutorials/ARMY-TC-9-524/9-524-index.html
Navy Repairman Manual and lots lots more you need to scroll down a bit to find it
http://www.metalworking.com/DropBox/
Tin

 

[T70MkIII]

Thanks for the links, Tin Falcon - great resources!