Some lathe questions...

[Ray C]

Sometimes you have a very long bar and it's too long to be supported by just holding in the chuck. When this happens, it's time to use the center support but a problem there, is sometimes you have a piece with a surface so uneven that the pinch bars or rollers can't be used.

Ray

i cant see why one would want to center drill not using the tailstock.

why not use a dial indicator instead of a caliper?

 

[Bill C.]

So I'm using a mini lathe and had some questions I'm hoping you could answer.

- I have a QCTP with a boring bar holder. Is there any reason I can't use a boring bar for facing jobs? It seems like the boring bar is already configured for essentially that job. Plus it would save me extra tool holder for my QCTP.

- Currently to center a tool bit I'll take repeated facing cuts until it doesn't leave a nub. Is there an easier and faster way to do this?

- Does anyone have a good way to fasten a digital caliper or scale to the crossfeed? I'm having a hard time figuring out a way to do it while still allowing the compound to rotate freely when needed.

- If I'm working on a large diameter piece it would be really helpful to center drill it's end for the center before I put it on the lathe. Is there a way to do this accurately?

You can use a drill press to center drill the center of your piece. If you are boring a hole in a piece of plate stock, after locating the center use a center punch to mark it then center drill the mark. Use a higher speed for the center drill. I have used a center punch to locate the center then used the tail stock with a live center to hold the piece while closing the jaws around the part. I was using a four jaw chuck. Also if you are making a crank shaft you would layout several centers to help speed up the locations. Good luck

 

[onecut jimmy]

Sometimes you have a very long bar and it's too long to be supported by just holding in the chuck. When this happens, it's time to use the center support but a problem there, is sometimes you have a piece with a surface so uneven that the pinch bars or rollers can't be used.

Ray

What is a center support? I may have missed something in my 70 plus years of machining.

 

[kd4gij]

What is a center support? I may have missed something in my 70 plus years of machining.

Steady rest is what I think he is talking about.

 

[dian]

and such a "long" bar can be drilled in a drill press?

if your afraid of sag, why not pull the workpeice up by a spring or piece of rubber? but that is splitting hairs. if you have a 10 x 1000 mm rod to cut, locating the centre will be irrelevant.

 

[onecut jimmy]

Steady rest is what I think he is talking about.

That's what I thought. But who knows modern language sheesh.

Are we talking about a piece of steel 10 mm in dia and 1000 mm long.

That would ne .394" dia x 39.4" long.
Are we trying to turn the entire length to a smaller size? or by cutting it do you mean something other than reducing the diameter of the entire rod?

 

[onecut jimmy]

That's what I thought. But who knows modern language sheesh.

Are we talking about a piece of steel 10 mm in dia and 1000 mm long.

I got my thinking cap on . We have a bar which is one centimeter in diameter and one meter long. Besides center drilling it . What else do you want to do with it.
Also you say you have a mini lathe . How big is the spindle hole on that lathe?
Do we have a real life problem here or a hypothetical situation?
Ther are a couple of solutions for either but we need to know what the machine limitations are, so we can work around them.

 

[onecut jimmy]

i cant see why one would want to center drill not using the tailstock.

why not use a dial indicator instead of a caliper?

Dian I have to agree with you.
I am in the USA and don't use meterics very often. But can you help me here. Isn't 10mm 0ne centimeter and1000 mm
one meter? If all he has is aMini Lathe and I have no idea what that is. We really need machine statistics to be able to understand his problems.
Or am I missing something?

 

[DMS]

You got the numbers right, 10mm is 1 cm. 1000mm is 1meter, or 100cm.


For center drilling, I would pass the material through the headstock, clamp it in the chuck with very little sticking out, then center drill. Keep the speed _VERY LOW_, a piece that long will tend to whip. Once you drill that way, reverse and drill the other side. If you have a mini lathe (I'm assuming a 7x), you are still not going to be able to turn it between centers; I think the best you could do is have the tailstock support one end. For a piece this slender you are still going to need a follower or fixed steady, depending on what type of machining you are doing. 10mm should pass easily through the headstock of the minilathe, The grizzly version is 20mm, and I think that is typical.

 

[dian]

i was just trying to make a point, that the best was to centre drill is in the lathe. even if there is some sag, he accuracy will be better than scribing and centre punching, especially if you can pass the work through the spindle. if you cant, it wont sag.