PM-1640TL problems getting reasonable surface finish

[jeremysf]

I’m having a problem getting good surface finish with my PM-1640TL. I don’t have enough experience to figure out what I’m doing wrong and am looking for ideas or to have my expectations reset. I am assuming based on seeing other PM-1640TL user videos on YouTube that it really should not be very hard to get great results over a wide range of speeds and feeds using carbide inserts and mild steel.

So, in detail, I’m trying to turn 1/2” mild steel with carbide inserts, and I always get some variation of the above picture, where there is inconsistent depth of cut. The chips vary somewhat with the speeds and feeds, but generally speaking are are super tight, regular and curly and bright. I am not really ever able to get them to break and be individual chips, which seems to be the issue maybe?

Things I have tried:

- Depth of cut from 0.001” to 0.040”
- 80 rpm to 1200 rpm
- Fine feed (0.004) through to coarse feed (0.22)
- Different carbide inserts and tool holders (right hand tool, and universal tool)
- High speed steel tool (pre-ground from the retailer and my own grind from blanks, sharp nose radius and large nose radius)
- 3 jaw vs collet chuck
- Tail support vs no tail support
- Two different sources of material
- Coolant vs no coolant
- Adjusting tool height from below center, to on center, to above center
- Tightening the v-belt tension
- Cross slide at 0, 45 and 90 degrees
- Making sure tool holder is square to chuck
- Making sure the tool post is tightened
- Making sure the chuck is tight
- Fixing the VFD frequency to 60hz (disabling the potentiometer speed control in the Hitachi VFD)

The depth of cut variation is like a thou or so. It’s more than just showing spiral tool marks, and it varies wildly.

The setup appears quite rigid and overkill to my (inexperienced) naked eye.

If I use emory paper to smooth down the result to debug it, it takes like 15 min with 340 grit and I am able to see during that process that some of the “banding” are quite deep grooves (and take forever to remove).

Ideas on what I’m doing wrong?

 

[jwmelvin]

Using something other than 1018/A36 would probably help considerably. Have you tried other materials?

 

[jwmelvin]

Also, what inserts have you tried? Specific inserts make a difference and you may try some intended for aluminum, as they have a much sharper edge. Without seeing a good picture of your HSS tool it’s hard to say much about it.

 

[jeremysf]

Not yet, but ordered a range of different materials from onlinemetals.com to try out.

 

[woodchucker]

So I had a problem last week. I bought some metal from someone here years ago. I tried HSS, with and without a chip breaker, different geometries, then went to cnmg, then wnmg... trying all different speeds and feeds. I had similar but bigger curls. I could not get it to break a chip. I hate curly long strands... dangerous in multiple ways. Especially when they wrap. I was unsuccessful, I finally decided to use the WNMG and just keep using the crossslide to knock out most of my roughing. then move over and rough.. it worked. But I decided I could not do that for more than one.. So I ordered the DCMT holder that I showed in what did you buy and stated it's problem.. with the HSS, CNMG , WNMG I was taking off small, then bigger, and bigger chips...

First time with the new DCMT, chips... short small chips. Now to play with how far I can go. I did try to go as fast as it would spin, with a fast rate, and it stopped breaking them, went to curly stringy again.

Sometimes you just have to keep trying, and not every insert or even HSS geometry will work.
It's hard, to impossible to troubleshoot from our arm chairs the situation without watching it. speeds and feeds are usually close, but sometimes you really have to try different things.

I like blue or straw colored chips. It removes the heat from the metal as much as possible. It also means you are doing well, being efficient.
Pushing a tool is usually good, it doesn't build heat as much. Rubbing builds heat.

Harder metals break chips easier. Some metals are just plain bendable, so the chip won't break.

BTW the ultimate cheat is to auto feed, and stop the feed every once in a while to break the chip.

As far as your bar showing different looks, to me it looks like the curly is getting in the way, or you are running out of oil.

With coated carbides you can run dry.. give it a try.
Give it a try with constantly wicking more oil.

just keep trying. You'll be learning.. and if all else fails... keep something soft around to punch... not the wife or kids.

 

[jeremysf]

Thank you! Love this community!

 

[maspann]

If that is cold rolled rod, it is difficult to get a consistent surface finish. Try getting some free machining steel bar (12L14) and see what result you get. There are several vendors on Ebay that have small quantities you can buy that won't break the bank.

 

[Larry$]

12L14 turns beautifully. I've had some mystery metal that was terrible turning. The chip breaker design on carbide inserts will determine what your ideal DOC should be. Ideal cutting tables exist for all sorts of metals, mostly based on surface feet per minute. I have no experience with name brand inserts and only rarely use the Chinese ones I have. Since I don't do production turning HSS works fine for me.
You might try grinding a shear cutting tool and see if that helps.

 

[woodchucker]

If that is cold rolled rod, it is difficult to get a consistent surface finish. Try getting some free machining steel bar (12L14) and see what result you get. There are several vendors on Ebay that have small quantities you can buy that won't break the bank.

12L14 is cheating, it's impossible not to get a good look, thats why its free machining.
you will learn to do things with it... but you won't learn about breaking chips in hard to use materials with it.

So if you just desire to make things... 12L14 will get you there, any of the free machining will. They will make you think you are the greatest..
But dealing with an unknown metal, or tough to machine metal will test your patience.. Just remember it's a hobby.
And remember like everything in life, the tough things make you appreciate where you came from and where you are at.

 

[Aukai]

Wait till a friend sends you a Thompson bearing rod to turn, and not tell you what it is