Lathe finish is unacceptable.

[terrycan]

You guys are doing some great work with your Patriots. I bought a new one recently. Been having trouble with the lathe finish.

It faces very well with a nice finish.

The problem is with diameters. The X axis (dia.) appears to pulse back and forth about .0005. This leaves an unacceptable finish.

I have been a machinist since 1974. The set up, feeds and speeds are good.

Any body hear of this problem with other Patriots?

Any suggestions on how to identify the problem?

Terry

[bowman1964]

You guys are doing some great work with your Patriots. I bought a new one recently. Been having trouble with the lathe finish.

It faces very well with a nice finish.

The problem is with diameters. The X axis (dia.) appears to pulse back and forth about .0005. This leaves an unacceptable finish.

I have been a machinist since 1974. The set up, feeds and speeds are good.

Any body hear of this problem with other Patriots?

Any suggestions on how to identify the problem?

Terry

I had similar problems with mine. Multiple things were causing excessive backlash.
First my tool post compound slide was too loose. Simple fix was tightening down gib screws until it wouldn’t move. That helped the lathe finish. Until I had time to scrape and get the proper fit.
I also had a loose lathe spindle giving be a bad finish. Check that and tighten if necessary.
Next problem is the ways and beds were not fitting tight enough. I had scrapped them until I had good contact.
My ball screws were too loose. I have tightened my Y axis with larger balls. This was a simple thing. I still need to order a few more sizes of balls to tighten it up some more.
If the x bed is not getting at least 75% contact you will have excessive play that is hard to control.
I actually got me a torque screw driver so I could set the gib screws to an even pressure. Thought it would help. It did but not worth the cost for the gain I got out of it.
I took out the mill spindle and repacked the bearing and tighten up the spindle play I had.
I had cut my first full cnc part a couple of weeks ago. It came out great except I could see tool chatter in the finish. I am hoping the finish will now be better since the spindle work.

I am still tweaking. So it’s not perfect…YET.

[txcncman]

You guys are doing some great work with your Patriots. I bought a new one recently. Been having trouble with the lathe finish.

It faces very well with a nice finish.

The problem is with diameters. The X axis (dia.) appears to pulse back and forth about .0005. This leaves an unacceptable finish.

I have been a machinist since 1974. The set up, feeds and speeds are good.

Any body hear of this problem with other Patriots?

Any suggestions on how to identify the problem?

Terry

Thanks for today's humor. I got a good chuckle from this.

[instructor37]

Terrycan,
A bit more detail would help. Or post some pictures of your setup and the finish problem you are having.

[terrycan]

Here are some photos. Sorry about the focus. Will get some better quality photos soon.


Terry

[instructor37]

Terrycan,
A couple things-
Even though its probably OK, I would keep the work back closer to the chuck-looks like there is more sticking out than necessary. Also, How long is the rod? Does it extend out past the rear of the spindle? A long small diameter rod with no support on the other end can set up a vibration- if thats the case, a simple bushing made from wood or plastic with a hole equal to the rod OD that fits into the spindle end will help.
Your toolpost doesn't look like ours- is it a home grown? Even though it looks plenty solid, I would try a cut with the factory toolpost just to compare results.
A good close up photo of the finish might get you some more advise as well.

[terrycan]

instructor 37

Thank you for your input.

The stock is 303ss .75" dia X 6". Don't believe bar whip is the problem.

The tool is less than a hair below center.

Have turned the stock closer to the chuck. The finish is the same.

The stock is sticking out so a dial ind. could be on the stock when I took a cut. This showed .0005" deflection in the spindle.

Mounting the dial ind. on the tool post showed an oscillation of .0005" when I took a cut.

The tool post is solid to the table. A dial ind. on the table and tool post proved this when I took a cut. The tool post is a Shars (Aloris style). I made the aluminum block with my Patriot.

Convinced this is a hardware issue.

Can email you a higher resolution photo.

Have over years machining experience. However no machine repair experience. This should be a very basic problem. I don't know how to identify the problem.

Terry

[terrycan]

[txcncman]

Looks like you might have some slop in your Z feed also.

[terrycan]

Thank you to all for your input.

Still have the finish problem.

Tried different feeds and speeds with no difference.

RPM 300-1000 FEED/rev .0005"-.007"

The ind. shows a smooth motion in Z.

The ind. shows oscillation of .0005" in X.

Believe the problem is in X.

Does any one know how identify if this is a gibb or ballscrew issue?

Terry

[wilsonrj22]

Just a thought, have you removed your chuck and checked spindle flange face with your indicator. If needed make a light facing finish pass on the spindle flange. Just fishing, if the 3 mounting holes on flange might be out? Rotating chuck on flange 1-bolt hole clockwise, retighten and check? If same, maybe rotate again 1-bolt hole clockwise, retighten and check.

Do you get same results with your 4-jaw after prepping the faceplate?

-RJW

[SaskFab]

Could you clarify if the 1/2 thou runout on the barstock is on the area you have already turned or is it on the raw surface?

You've listed a range of speeds and feeds you've tried, but at what depth of cut? Also, you've tried 300 to 1000 rpm, but with .75" diam the surface speed is quite low. Depending on your choice of insert, a good finish may be impossible, especially with a light cut.

I don't know what type of inserts you have tried, but I would advise trying a few others as well. Have you had this machine very long and have you been having trouble with all materials that you turn?