Bad surface finish on Pinacho lathe

Jorgens · Sep 18, 2017

Hi.

I have a Pinacho manual lathe, which makes a rough/poor surface finish only when i do fine cuts (1/10 mm)or below. When doing roughcuts (1mm and over) the surfacefinish is as should be.
There is no play in the carriage and I just tightened the cross slide without any improvements. The main spindle bearings seems good as of the suppliers spec (checked)
It leaves this surface both with manual and automatic feed.
Any suggestions for further checks/ improvements?

Thanks!

Jørgen

MattiJ · Sep 18, 2017

Looks like typical beginner problem with built-up edge. Insufficient speed and cut depth for the material/cutting tool combo.

Take deeper cut, increase speed if possible or select sharper tool. Or select material with better machinability.

Tyrone Shoelaces · Sep 18, 2017

What speed and feed rate are you running at ? What sort of turning tool are you using ? Given I've never heard of a " Pinacho " lathe what size it, how old is it etc etc.

Edit. Just had a look for " Pinacho " lathes on the " Tony's Lathes " site. It seems a reasonably good sized lathe for home shop work. Given the fact that it's probably getting on for over 40 years old you could be having spindle bearing issues. I've noticed in the past with similar stories of a " heavy cut "being fine but light cuts that are " chattery " the bearings aren't either set correctly or they're on the way out.

Even on a lathe that size a 1mm cut is not a " heavy " cut. 4mm or 5mm might be.

Regards Tyrone.

Tyrone Shoelaces · Sep 18, 2017

Sorry, repeat post, the Internet is playing up this morning.

Regards Tyrone.

michiganbuck · Sep 18, 2017

Also consider edge sharpness, top rake angle, length of part and tool bit stick out, bit centered to part, tool holder and compound more centered on saddle, quality of holding the part, part outer surface dulling the bit (scale or the like), to high RPM causing chuck out-of-balance to affect the swing, intersect of side cutting edge and follow edge causing too much clearance(so a small nose radius at perhaps 7* might help), employ a dead tail center, very dirty lead screw, dirty or dry bed ways, lack of oil in moving parts, vibration from a loose key or motor pulley or the like, lathe nor level or a foot not supported..
Some times a heavy cut can tighten the holding enough to make part secure .. then a light cut allows poor holding to seem loose.. so perhaps the chuck jaw wear and jaw taper.

Good to have a 10x loop so you might look close at the side cutting edge, nose. build -up, smooth sharp edge, chipping, where the bit contacts the part.

And yes the quality of the spindle bearings. The last thing to blame after all is right....
Gear chatter is often an even marking to the part so think it not that.

*Do tell us what solves the problem..

MattiJ · Sep 18, 2017

Did anyone bother to click the picture to bigger size?

It's so rough that if your stroke it with fingernail its screaming "BUE"

And solution is to get rid of BUE formation.

In other words: "why I can't get good surface finish on crappy 1018 steel with carbide insert and less than 0,003" cut depth"

DMF_TomB · Sep 18, 2017

Jorgens said:
Hi.

I have a Pinacho manual lathe, which makes a rough/poor surface finish only when i do fine cuts (1/10 mm)or below. When doing roughcuts (1mm and over) the surfacefinish is as should be.
There is no play in the carriage and I just tightened the cross slide without any improvements. The main spindle bearings seems good as of the suppliers spec (checked)
It leaves this surface both with manual and automatic feed.
Any suggestions for further checks/ improvements?

Thanks!

Jørgen

.
modern carbide inserts assuming you are using a modern designed insert and not a plain insert are made for specific sfpm (rpm), depth of cut and feed rate. when insert new and running hot enough they give a shiny finish. below minimum sfpm the finish goes dull looking. sharp inserts using coolant often run better 800 to 1000 sfpm. they last longer at below 600 sfpm but finish is dull and not shiny. ipt or feed often have to be .0030" per rev or less to get best shiny finish. of course when you run faster >800 sfpm tool life is shorter
.
old timer rule if throwing sparks inserts are dull.

Terry Keeley · Sep 18, 2017

CRS can be a biotch to get a good finish on. What insert/hss cutter are you using?

Brushing on a little cutting oil (Tap Magic etc.) can help a lot. Make sure the tool is on center.

michiganbuck · Sep 18, 2017

some times the direction af the chip flow can tell something.. for mild steel the chip should flow across and to go to the right on a right hand cut towards the chuck on an OD cut..Chip flow going another way can suggest a dull , or a chip in the edge..Yes a sharp neg bit can make a good surface finish on a stout lathe and set-up..perhaps even with better tool life...certainly most often for cast iron...

DMF_TomB · Sep 18, 2017

going too slow rpm you always get a less shiny finish

bustedanvil · Sep 18, 2017

Play in tool holder, feed too fast or rpm too slow. Possibly have it set on threading instead of auto feed for turning can result in that with the slowest feed rate on threading.

Sent from my P027 using Tapatalk

michiganbuck · Sep 18, 2017

Think I have it figured out ... with all the water around and great lakes there you should be not running a lathe but out fishing .
fishing in finland map - Google Search

Jorgens · Sep 18, 2017

Tyrone Shoelaces said:
What speed and feed rate are you running at ? What sort of turning tool are you using ? Given I've never heard of a " Pinacho " lathe what size it, how old is it etc etc.

Edit. Just had a look for " Pinacho " lathes on the " Tony's Lathes " site. It seems a reasonably good sized lathe for home shop work. Given the fact that it's probably getting on for over 40 years old you could be having spindle bearing issues. I've noticed in the past with similar stories of a " heavy cut "being fine but light cuts that are " chattery " the bearings aren't either set correctly or they're on the way out.

Even on a lathe that size a 1mm cut is not a " heavy " cut. 4mm or 5mm might be.

Regards Tyrone.

It`s a 2001 model.

Jørgen

Jorgens · Sep 18, 2017

MattiJ said:
Looks like typical beginner problem with built-up edge. Insufficient speed and cut depth for the material/cutting tool combo.

Take deeper cut, increase speed if possible or select sharper tool. Or select material with better machinability.

Did some checking today, and it`s a combo: First, the topslide has been tightened too much at some point, so i measured a small build up on two sides (where the bolts are) which again means the topslide was "riding" on two edges.. will send it off for grinding.

I did a finish cut (1/10 mm)@ the same rpm and feed as in the attached pic with my alu insert, and the surface became flawless.. :-) Will do some more investigation regarding my current inserts.

Thanks for all input!

Jørgen

Jorgens · Sep 18, 2017

michiganbuck said:
Think I have it figured out ... with all the water around and great lakes there you should be not running a lathe but out fishing .
fishing in finland map - Google Search

Who said Finland?

Tyrone Shoelaces · Sep 18, 2017

Jorgens said:
It`s a 2001 model.

Jørgen

Sorry Jorgen, I was looking at the article on the " Tony's lathes " site were it showed a lathe circa 1970 but didn't mention any subsequent lathes. I assumed the company no longer existed. If your lathe is as recent as 2001 the bearings should ok.

Regards Tyrone

MattiJ · Sep 18, 2017

Jorgens said:
Did some checking today, and it`s a combo: First, the topslide has been tightened too much at some point, so i measured a small build up on two sides (where the bolts are) which again means the topslide was "riding" on two edges.. will send it off for grinding.

I did a finish cut (1/10 mm)@ the same rpm and feed as in the attached pic with my alu insert, and the surface became flawless.. :-) Will do some more investigation regarding my current inserts.

Thanks for all input!

Jørgen

I was talking about built up edge to cutting tool edge:
http://web.mit.edu/2.670/www/Tutorials/Machining/physics/Description.html

Cool video shows edge build-up and surface tearing in slow motion:
Iscar Chip Formation.wmv - YouTube

I also use those very sharp DCGT/CCGT aluminium inserts if I have to skim off 0,02mm from soft steel.
Finishing Cermets like Sumitomo T1200 in DCGT shape work also well.
And bit unconventional approach but re-sharpened Kennametal KY1615 ceramic inserts produce maybe the best surface quality on soft steel of anything what I have tested.

michiganbuck · Sep 18, 2017

Jorgens said:
Who said Finland?

My Bad.. NORWAY

QT: [with my alu insert, and the surface became flawless.] Likely much sharper edge, more clearance under cutting edge..
You might tell the insert first used..

[topslide was "riding" on two edges.. will send it off for grinding.] You might just use your hand scraper edge to remove edges then file or hone back to flat...

ewlsey · Sep 18, 2017

Get some Cermet inserts and all the RPMs you can manage.

GregSY · Sep 18, 2017

I had a 14x40 Pinacho lathe. It was a light duty lathe but worked OK. My friend has it now.

Bad surface finish on Pinacho lathe

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