Whats going on with this cut?

[SamI]

A couple of thoughts from me:

• Try a tool with a smaller nose radius. It's hard to tell from your photo but that tool looks to have a large radius on it. If your tailstock is out by a couple of thou then this could be the difference between the tool rubbing at the tailstock end and cutting at the headstock end.
• When taking a cut with a centre the tailstock can push back slightly. I notice this when taking heavy cuts in roughing operations but if everything isn't locked down firmly then this could easily cause a problem on lighter cuts, especially if the tool is rubbing and not cutting. When the tailstock pushes back it allows the bar to deflect as it is no longer being fully supported by the centre. When this happens you will usually notice that the very end of the part has a slight taper to it
• Sometimes bizarrely a deeper cut (within reason) will cause less deflection to the bar than a lighter cut. I believe that this is due to the radius of the insert being fully sunk into the material which minimises the reaction force in the stock pushing back into the cutting tool. I'm sure I read a good explanation of this on here somewhere but maybe some one who can explain this a little better can comment?

 

[Tozguy]

i have 0.002 runout at spindle end, have 0.004 at the tail stock end.

Is this runout in the work piece? before turning or after?

But i tried moving the alignment a tiny bit to remove that runout and just keeps jumping around.

TS must not be jumping around.

so why would i be getting a cut not concentric while twisting at the same time?

You are not using the right insert for this job. What Sami said. This might explain it better than I can.

Sandvik Coromant

www.sandvik.coromant.com

Also, the chuck jaws need to be straight for this type of holding.

 

[Tozguy]

• Select an insert nose radius that is smaller than the cutting depth
• 
  
  

 

[Opie_7afe]

For the runout, it is in the work piece after turning..

Ill try a ccmt or a dcmt inserted tool instead of the wcmt.

 

[projectnut]

You didn't mention what type of lathe you are using, but it looks like to be an older model. Is it possible either that the chuck and tailstock are either not at the same height, or the bed is worn more at the headstock end? In most cases older machines have more wear at the headstock end. When setting the tool on center at this end it will rise above center at the tailstock end. Either condition would cause the tool to be at center at one end and above center at the other end thus cutting more material when on center and less when above center.

I have one older lathe with almost .015" wear on the bed at the headstock end. The wear is steady for about 6" then slowly tapers off. The machine works fine when making short pieces, but it requires considerable effort to make a part that is long enough that it spans the transition point.

 

[tjb]

You cannot align the tail stock by sight.

Make a spool for alignment.

Simple to do.

Find some scrap 2 in OD x 3 inches long...anything close in material or size will do.

Place in chuck and face it off, center drill then take finish cut to make it look nice, use power cross feed if you have it.

Flip it and repeat.

Now place in Chuck with about 3/4 length exposed and support with tail stock.

Remove about 1/4 the diameter in the center leaving a coller at each end.

Now place a center in the headstock or place a chunk of your drill rod and make a point, this will be your driving center.

Place the spool between centers and take light cuts as it will slip otherwise.

Cut only enough to make it round .

Measure diameter if each cooler.

If the tail stock end is larger tail stock needs to come forward and if smaller then back.

Make tiny adjustments and insure locked before cutting.

When both are exactly same tail stock is in alignment with headstock.

Now save the spool and NEVER cut again, just place a dial indicator in tool post and measure.

We made ours 20 years ago and is is still primary alignment tool.

Sent from my SAMSUNG-SM-G930A using Tapatalk

Can you post a photo of your spool?


Regards,
Terry

 

[Opie_7afe]

Lathe is an atlas 10d

 

[tq60]

Can you post a photo of your spool?


Regards,
Terry

Material does not matter, just find a chunk of something about size of d battery

Sent from my SAMSUNG-SM-G930A using Tapatalk

 

[Cadillac]

Tailstock pressure when the material heats up can bow the material.
Dial in the tailstock by the variance in the rod you are cutting. Take measurements of od at chuck and at tailstock. Move tailstock half the reading. Might get you better than eyeballin it. When making the test bar aluminum donuts would be better than steel. Less chance of wear on tool in the cut.

 

[Opie_7afe]

So i think i got it worked out got off work super early so had some time..first thing the tailstock was way off by atleast 1/8" and headstock bearing had a good bit of up and down play so took caps off and peeled away a shim on each side and much better, was like a loose tie rod end where you feel the clunking. Now have to adjust the motor, belt is too loose and have some slippage.