Smooth Finish on Metal????

[Justturnin]

I am trying to get a smoother finish when turning metal on my metal lathe. I am practicing on a piece of scrap threaded rod. I have already turned the threads off and have a straight shaft that I am trying to get a smooth finish on. I have tried running her at 300, 600 and 1000 rpm w/ different auto feed rates. I have tried taking off different amounts from 15/1000's to 1/1000's but I just cant get a smooth finish, there always seems to be some ridges in the metal that I can see and feel. I am using water soluble oil and keeping it wet. I am getting consistent curls and breaks on the waste. I am using a HSS cutter.

Got any advise? Need more details that I dont know to give? Running a Grizzly G4000 9x19 lathe

 

[tjseagrove]

Where I went to engineering school, we used a rounded tool on a slow feed that gave us a smoother finish.

 

[Ed McDonnell]

How about some pictures of the finish you are getting (showing the ridges) and the tool you are using? It would help narrow down the possibilities. Especially if you ground your own tool.

Is your cutter dead on center (if you do a facing cut, do you get a clean face or is there a nub left)?

Ed

 

[mredburn]

I suspect your cutter profile is thwarting you. For the best finish a small radius on the tip of the cutter or a very slight flat surface will probabaly help. If your trying to do a finish cut with a point it wont work well. You may have to file or sand the ridges off.

 

[Justturnin]

Thanks guys. I think you are all correct. I think my tool was ground too much. I reground to a 10* and got a better cut. I was also below center which I corrected. Next I am going to knock that point off. Sad think is I ran through that piece of steel getting this far. I need to get another one going to try the rounded edge. My goal is to learn how to make a nice finish cut. My lathe also has a good bit of play in the saddle that I need to figure out how to eliminate as much as I can. It's not a commercial machine so I know I will not be able to get rid of all of it. I do have a great start to try some new things.

 

[Haynie]

My best finish cuts come from a slow feed and barely taking angel hairs off the metal. This could be the wrong way but it words for me.

 

[Paul in OKC]

Metal being used plays a lot in the factor of finish. All thread may be good to practice general cutting with, but...... Diameter you are cutting to, how much is hanging out of the chuck, and as said above tool factors. Small radius is usually the best tip for the tool. I find that small 'fuzz' cuts are not the best. Higher rpm, and around a .005-.006 feed on one of these lathes should do well. And if all else fails, that is what emmory rolls are for =8^).

 

[BradG]

Chris be sure to check your carriage and cross slide to make sure everythings tight and theres no play... if one of those bolt has shook itself loose you will get that wobbled appearance on the surface as its chattering away. as others have said could also be the angle of your cutter, a blunt cutter, or too low... though id put money on there being play on your carriage

 

[mson]

I would use a metal file to remove the ridges then use emory cloth. You will need to allow a few thousanths for finish filing and emory cloth.

here is a utube video that shows filing on a lathe at 2:21 mnutes.

1937 Maytag Engine model 72 rebuild #15 - YouTube

 

[Janster]

Also, is the rod supported in the tailstock? If you have much unsupported length at all, your finished cut will not be smooth. Be well and good luck!...Jan

 

[Justturnin]

Thanks everyone.

Jan, the piece was supported by the TS w/ a 60* bevel to get a good grip.

My next steps are to fine tune my grinding and to tighten down the saddle a bit more. Last time I tightened it I was barely able to move it but the play was gone. I need to find that sweet spot that allows it to move freely but also allows the cross slide to move easily. I am going to try to play with it a bit more Monday.

 

[mson]

Before you make a cut, you might try pulling your tool post (by hand ) toward you to get the slack out. Also, in cranking in the compound, always keep the dail into the work as there is usuall a few thouanths slack there.

 

[BradG]

Thanks everyone.

Jan, the piece was supported by the TS w/ a 60* bevel to get a good grip.

My next steps are to fine tune my grinding and to tighten down the saddle a bit more. Last time I tightened it I was barely able to move it but the play was gone. I need to find that sweet spot that allows it to move freely but also allows the cross slide to move easily. I am going to try to play with it a bit more Monday.

undo the locking nuts, and use an Allen key to wind in all the adjustment screws until they make firm contact, then wind them back out a quart turn.

With your Allen key still in and being held still, tighten the locking nuts back up again. should allow it to still move without the wobble get this right and you wont have to worry about remedying a poor finish, it'll be ready for sanding straight after your final cut.

 

[Hexhead]

Sounds like that edge on the tool is not correct, this can cause you to get curls in the metal with a dull tool but you're actually scraping the metal off instead of cutting it and this makes for a rough surface. Not taking a deep enough cut can also set up a vibration that will make for a rough surface. It's going to be difficult to get a smooth surface with play you talked about. Different metals have different characteristics, sometimes you just have to experiment. You are doing that so I know you'll succeed hang in there it's not learned overnight.