Dial test indicator question

[fcs]

Interesting. I had planned to move to collets, maybe it will be now instead of someday. I’ll have to think this thru. I thought the Sherline chuck would be more accurate than what I’m finding. Thanks for the help.

Frank

 

[mikey]

The older Sherline chucks were more accurate, I think. I have a 35 year old 3 jaw with around 0.001" TIR but that means very little. On first operations work, it is dead on accurate.

You may want to look into a Beall ER32 chuck if you're going to be holding ground rods. ER chucks are not as potentially accurate than a 4 jaw but they are much faster.

 

[fcs]

The Beall Chuck seems like a good solution. Add a few good quality collets and I’ll be on to the next problem. I’m lapping small diameter pieces so I don’t need to go past 0.250.

The 3 jaw chuck has consistent high & low spots according to the dti. So there SHOULD be some way to reduce nonconcentricity from .005 to maybe .002. I will work on it. I might not be skilled but I’m stubborn.

Thanks again.

 

[mikey]

Frank, if the chuck is truly out of spec then send it back to Sherline instead of messing with it. If you do anything structural to it, like lap something, then they won't exchange it.

If I were you, I would chuck something up in it and turn it. Use a short piece of aluminum or mild steel and turn it down a little, then measure the run out of the work piece over that turned section without removing it from the chuck. It should read zero. If it does, then there is nothing wrong with the chuck.

Can you please try this and report back?

 

[fcs]

I turned about 2.5 inches of a 5/8 in aluminum bar. I didn't get a smooth cut (I'm at the bottom of the learning curve on speeds and feeds and depth of cut), but there was <.0005 deviation from concentricity at both the jaw end and the free end of the cut. The bar measured .5990 at the jaw end and .6003 free end with a micrometer.

So it seems to me that the chuck is OK, except it holds the work about .005 out of concentric.

 

[mikey]

Frank, before we go into your results, which turning tool did you use and what were your depths of cut to get these results?

Next, do you own an dial indicator and do you have a holder that will place that DI on the centerline of your lathe? If not, you should buy the DI and make a holder. You need this to measure and also to dial in work pieces in a 4 jaw anyway.

To be clear, you did a first operation turning on a long work piece without tailstock support. This is fine, that's what we want. However, we also need to be careful on what and how we measure and what it tells us. If we measure the run out of the work with an indicator in one spot while turning the work by hand (not under power), it tells us how concentric the work is with the spindle centerline. If you do this, I have little doubt the reading will be zero and that your chuck is fine.

Now, if we measure the OD of the work piece and see a difference then that can have multiple other causes but they are NOT due to the chuck. Your headstock may be off-axis, the lathe may not be level, you may be having excessive deflection due to the long work piece and the radial cutting forces from your turning tool to name a few.

So, which turning tool did you use? If carbide, what is the nose radius? What were your depths of cut on each pass? Can you please show us the tool? I will tell you now that if you are not using HSS tools on your lathe then you are not going to realize the potential of that lathe, and this applies to the amount it will cut and the accuracy to which it can work.

Your measurements show the larger OD on the free end of the bar. This may very well be due to deflection but it can also be due to headstock misalignment. Much depends on the tool in use and the depths of cut you took; hence, my question above. If we can rule out the tool deflecting then we can move the headstock, probably clockwise, a tiny bit and get the cut to be dead on accurate. Once we get that done, level the lathe well and we can go into how to do that if you aren't sure how to do it.

The Sherline lathe can be adjusted pretty precisely but you have to approach it systematically.

 

[brino]

@fcs

Hi Frank,

I only have three things to add.

1) Don't worry too much about using the wrong terms here; you will not be flamed. Beginners are always welcome!
2) I have the Beall ER-32 collet chuck for my Southbend 9" and like it very much.
3) Stick with @mikey, he knows of what he speaks and will invest the time to help you figure out any irregularities.

Welcome to the group!

-brino

 

[fcs]

Mikey, you are running way ahead of me here. I will answer these questions in a minute.

What I have determined from what I've done and what people here have stated so far is: (1) A 3 jaw chuck can't be expected to produce concentricity. I didn't understand this. Mine doesn't, which is too bad for me wanting to hold a mandrel, but its the way it is. Collets are the proper solution. (2) After turning a piece of stock, the result is concentric. This shows the chuck is good.

This is really all I care about at this point. The rough finish on my turning, I will read more and experiment and learn. If it gets to the point I can't make progress, I will holler for help. The possibility of alignment issues I will deal with when I need to. I know there is a lot of info on this forum I can mine. Much of it, for Sherlines, from you.

Frank, before we go into your results, which turning tool did you use and what were your depths of cut to get these results?

I used the HSS tool that came with the lathe. The only one I have. I did read an extensive discussion (I think on this forum) about turning aluminum. I learned that for a smooth final finish you must use HSS, and you must use carbide, and you must feed slow, and you must feed fast. And the bit must be very sharp, and that you must have a radius point, and you should not have a radius point.

Next, do you own an dial indicator and do you have a holder that will place that DI on the centerline of your lathe? If not, you should buy the DI and make a holder. You need this to measure and also to dial in work pieces in a 4 jaw anyway.

To be clear, you did a first operation turning on a long work piece without tailstock support. This is fine, that's what we want. However, we also need to be careful on what and how we measure and what it tells us. If we measure the run out of the work with an indicator in one spot while turning the work by hand (not under power), it tells us how concentric the work is with the spindle centerline. If you do this, I have little doubt the reading will be zero and that your chuck is fine.

Yes I have dial indicators and 2 magnetic bases. I don't understand what it means to put the DI on the centerline of the lathe. When I used the DTI to measure concentricity, I had the point as near as I could eyeball to the center of the piece as viewed from above and perpendicular to the piece. I turned the headstock by hand. Is that what you mean?

Now, if we measure the OD of the work piece and see a difference then that can have multiple other causes but they are NOT due to the chuck. Your headstock may be off-axis, the lathe may not be level, you may be having excessive deflection due to the long work piece and the radial cutting forces from your turning tool to name a few.

So, which turning tool did you use? If carbide, what is the nose radius? What were your depths of cut on each pass? Can you please show us the tool? I will tell you now that if you are not using HSS tools on your lathe then you are not going to realize the potential of that lathe, and this applies to the amount it will cut and the accuracy to which it can work.

My depth of cut was ~.005. Material was 7075 aluminum. Lubricant was lamp oil.

Your measurements show the larger OD on the free end of the bar. This may very well be due to deflection but it can also be due to headstock misalignment. Much depends on the tool in use and the depths of cut you took; hence, my question above. If we can rule out the tool deflecting then we can move the headstock, probably clockwise, a tiny bit and get the cut to be dead on accurate. Once we get that done, level the lathe well and we can go into how to do that if you aren't sure how to do it.

The Sherline lathe can be adjusted pretty precisely but you have to approach it systematically.

I look forward to working on these things a little farther down the road. I am having fun learning. Thanks again. I'll be back with new questions when I get stuck.

 

[Dabbler]

@fcs I don't want to mess with your investigation.

There are a few things, though. Unless you spend big$$$ even a collet chuck with cheap collets can be expected to run out. the cheaper the collets, the more expected runout you'll probably get. (there are exceptions, but they are low probability)

Even with a collet chuck/collets in the thousands of dollars, with many hours getting it perfect, collet to collet, you will still expect runout of a couple of tenths. For a one off, the 4 jaw - indicated in - is still king.

I have a lot of confidence in @mikey I'm sure he'll get you there.

 

[mikey]

Mikey, you are running way ahead of me here. I will answer these questions in a minute.

It appears I've overwhelmed you, which was not the intent.

What I have determined from what I've done and what people here have stated so far is: (1) A 3 jaw chuck can't be expected to produce concentricity.

A 3 jaw scroll chuck will produce concentricity on a first operation/first turning. It will not do so otherwise.

This is really all I care about at this point. The rough finish on my turning, I will read more and experiment and learn. If it gets to the point I can't make progress, I will holler for help. The possibility of alignment issues I will deal with when I need to.

Understood. I won't throw more at you. If you want help, ask.

I used the HSS tool that came with the lathe ... My depth of cut was ~.005. Material was 7075 aluminum. Lubricant was lamp oil.

Okay, useful info, thanks.

Yes I have dial indicators and 2 magnetic bases. I don't understand what it means to put the DI on the centerline of the lathe. When I used the DTI to measure concentricity, I had the point as near as I could eyeball to the center of the piece as viewed from above and perpendicular to the piece. I turned the headstock by hand. Is that what you mean?

What I meant is to place a DI so the body of it is horizontal so you can see what you're doing. Putting the tip on the centerline height of the spindle axis is self evident. When you get ready to use a 4 jaw, this is how the DI is positioned.

I look forward to working on these things a little farther down the road. I am having fun learning. Thanks again. I'll be back with new questions when I get stuck.

Just so you know, I've have been exactly where you are now and I understand how confusing this stuff can be. My intent was to clarify, not to overwhelm or upset you. Take your time, learn and then come back and ask questions. When you're ready, we are here. There are other Sherline guys here, too; it doesn't have to be me answering you.