Indicator On Lathe Work Piece While Turning?

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Buggy Chief

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Ok, so really new to the hobby and am having challenges turning pieces down to true diameter I am seeking. For example, I have my indicator on the cross slide and determined I need to take .020 off diameter (.010 each side). So I dial cross slide .010 and complete pass on .375 aluminum stock with about 3 inches stuck out from 5c collet and live center on tailstock engaged. Put Micrometer on piece and it reads virtually the same....very frustrating.

My question is, can I put indicator on workpiece opposite side of cutter and it will tell me when the .010 is truly taken off? Any tips are greatly appreciated at this point!! Thanks!
 
An "Arnold gauge " does just that. Never seen one used on a lathe. They are usually found on grinding machines.
A digital read out (DRO) is nice to have on a lathe or mill.
I didn't seem to have the problem you have when I started out. I usually cut to much and then had to start over.
Is something not tight? Does the tool appear to be cutting?
 
Thanks. everything seems tight, but I agree, something is amiss...I was thinking it was because it was such a small piece at .375, but I have a live center on it. How tight do you put live centers? Do you touch just until it starts spinning or really snug it up?

Once I have the dial indicator where I want it, I even lock the cross travel bed down. I admit, I need more practice, but I was trying to turn down a piece of .375 round aluminum stock down to .3125 and felt like I have everything dialed in but getting frustrating. Thanks again for input.
 
Buggy Chief said:
Do you touch just until it starts spinning or really snug it up?
Click to expand...

Not to tight. It will raise the work piece if to much pressure is applied. Snug is good.
Is the tool sharp? Is it on center?
Is the compound possibly backing off or rotating away from the work? If there is some backlash in the compound threads and you reversed the compound last it will likely move away from the work taking up that backlash, so move the compound towards the work to be sure that backlash is taken up.
Tool holder rotating/slipping?
 
I wonder if part of your problem is backlash in your leadscrews .

On a piece of scrap take a skim cut with your dial at zero , and at the end of the cut turn the compound out two full turns .
And then back in two full turns plus .010 or what ever you want for the next cut .
And see what happens .

Of course if you are already doing this it won't help .
When new to the hobby it's fairly easy to not know about or forget that backlash is present in either new or used machines to some degree
 
"Is your tool sharp" seems a very RELEVANT question. Many of you are using carbide to do everything,when it isn't necessary. And,carbide as you buy the cheap,brazed on tips stuff,isn't ready to use. It isn't really sharp enough without honing.

Why don't you grind up a HSS bit and hone the edge with a FINE India stick. Then try it on the aluminum? The key is to get the cutter VERY SHARP. Otherwise it may be rubbing and not really cutting,or not really cutting deep as it should.

There is special carbide (usually inserts) that are sharper,and made for aluminum. But,I would not bother with them unless I was running a factory,and making MANY,MANY aluminum parts.
 
Sounds like you are pushing the material away as opposed to cutting it, either the cutter is not sharp (most likely), you machine is not rigid or you have slop in the cross slide (also check your cutter height that it is on center) as others have mentioned. I do not have the patience to grind tooling most of the time, I use sharp (ground edge) carbide inserts and can easily peel 0.001" off of aluminum repeatably. The inserts on eBay are cheap (about $4) and a trigon insert can last me a year on softer materials. The added benefit is that the tool alignment stays the same when you switch out the insert.

You are spinning aluminum at fairly high RPM, I doubt and indicator would give a reliable reading with the machine running and would wear the indicator tip. I would work on a solution to why the cutter is not cutting.
 
Ok...all good ideas. I was using the insert for steel. Am going to switch to the insert for aluminum and try that. Again, new to this and triggered the thought that I have more inserts in my kit and need to change to the aluminum. AS the poster said above, I was using the same insert for everything. Will report back this weekend as am doing the "family" thing for the holidays.
Thanks for all the input as this is great!!!
 
Am I missing something? You cant use your indicator to measure the diameter. And it would be a bad idea anyway. A piece of swarf is sure to hook it up and rip it into the chuck or similar.
#1 Check your gibs
#2 Check your compound for tightness.
#3 Check your toolpost is locked solid. And that the tool is secured. (QCTP?)
#4 Is your tool on centre, (height)?
#5 Do you back the tool out? If so, do you come out a good number of divisions and then wind back in to the same dial graduation that you finished the cut on, before adding on your .010"
And .375 minus .020 is not going to give you .3125. Unless you mean you are just trying take this down to dia with .010 cuts. Thats a pretty light cut for ally. If you are looking for a tight tolerance, good (surface) finish, diameter. I would take a .025 cut, (.050) off the diameter, measure, take your next cut (depending on your measurement), about .005, leaving you with 001-002 thou to clean up at high RPM with cutting fluid for a mirror finish
What lathe are you using?

Cheers Phil
 
Similar to the comment from Bosephus, set your piece of 3/8 up with the tail stock.
Turn the lathe on to about 300-600 rpm. Bring your tool up to the work just until you see a scratch on the surface.
Go back to the tailstock end and advance the cross slide by about 5-10 thou. and make a cut down your workpiece.
Back the cross slide out and measure the diameter of the piece. Figure out how much still needs to come off and advance the cross slide and cut again.
Don't try to make the measurements with an indicator. Use your micrometer and all will be well.
 
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