Striped finish problem

[jim rozen]

Half thou on the spindle clearance is good. What spindle speed, and feed rate are you running when you obtained the most recent photo? Where in NE PA are you located?

 

[michiganbuck]

Did you rule out the bent lead screw..does it look bent? do you feel anything odd when just feeding and not engaging the pat with a tool?
Tool bit looks a lot better, It could use some side and back rake, but now seems not to be the culprit causing the marking.

Did you say what RPM is used?
Does the motor pulley seem in balance and running round/true?
Is there anything wrong with the belt, like retainers upside down?

 

[jim rozen]

Can't tell from that photo but if he used the print I provided it will have side rake. My experience back rake is not needed in a situation like this, and only complicates sharpening the tool.
If it does *not* have side rake then it's basically a brass tool and will cut terribly in steel.

 

[michiganbuck]

The tool holder angled into the part feed, angled to the left can cause pressure chatter.
Angled to the right will avoid that problem (or straight) , along with being central on the saddle so not having the compound length off saddle center and extending way out to the left.

Some saddles are like a rocking chair long ways.

Re: JimRozen
To be sure the side cutting edge has about 10* clearance is important..anong with some top rake, perhaps 10 and 8..

I don't think you quoted RPM or how hard the material is.

 

[tommy1010]

I have a 3ph 1/2HP 1725 RPM motor you can have for free. I live in NE Pa also.

 

[jim rozen]

Rocking chair ways - something not investigated, how snug are the gibs on this machine?

 

[michiganbuck]

It is an interesting thread, and it will be good to find out what solves the problem.
One thing we failed to mention is to tap tap the tool holder with a small hammer to see if it is/feels solid.

 

[chipss]

You're sure the slides are tight.
Headstock bearings tight.
Tool sharp as a knife.
Tool tip height is on the centerline of the spindle.

Now lets look at the chuck. Does the machine have a lot of time on it? It's hard to see but are the jaws bell mouthed? Although the work is clamped tight it can wiggle around as the jaws typically wear more at the tips. Have a different chuck you can try? Most of these machines also have a 4 jaw laying around so give that a shot.
Or set the machine up to machine a piece between centers and see if you still get your pattern.

If you think it is the chuck you can trap the jaws and grind the ID a few thou if you are so equipped to eliminate the bell mouthing. It won't help concentricity on a scroll chuck but it does help work holding.

 

[k3vyl]

A tool with no rake is not good on a SBL. The belt driven lathe doesn't have what it takes to use them. Those tools can work fine on a geared head machine. I use them on my Regal, but not on the SBLs.

 

[eKretz]

You're sure the slides are tight.
Headstock bearings tight.
Tool sharp as a knife.
Tool tip height is on the centerline of the spindle.

Now lets look at the chuck. Does the machine have a lot of time on it? It's hard to see but are the jaws bell mouthed? Although the work is clamped tight it can wiggle around as the jaws typically wear more at the tips. Have a different chuck you can try? Most of these machines also have a 4 jaw laying around so give that a shot.
Or set the machine up to machine a piece between centers and see if you still get your pattern.

If you think it is the chuck you can trap the jaws and grind the ID a few thou if you are so equipped to eliminate the bell mouthing. It won't help concentricity on a scroll chuck but it does help work holding.

That's what I was going to suggest checking next. Looks like chatter from work that isn't tightly held to me. Put a center hole in the end of that part and stick a center in there and take another light cut. If that chatter goes away you have a rigidity problem. First place to look on a machine that old is the chuck jaws

 

[camaro_dan67]

I want to try the 3 phase motor idea next. I have a furnas drum switch model RSB2 but the 3 phase diagram is wiped off of it. Anyone have this diagram?

 

[dalmatiangirl61]

I want to try the 3 phase motor idea next. I have a furnas drum switch model RSB2 but the 3 phase diagram is wiped off of it. Anyone have this diagram?

There are 2 configurations for drum switches, no idea how that model is meant to be wired. Use an ohmeter and map it out, if you can't do that, you probably can't wire it. The 3 phase wiring is pretty easy, the single phase wiring takes a bit longer to wrap your brain around.

 

[camaro_dan67]

I finally got around to finishing up the 3 phase motor swap. This was the result from a .015 depth of cut with a Hss bit. I'm not sure of the feed. I did 3 cuts like this with the same result each time. So far I'm happy with it. I will try different tool types and angles to see what the results are soon.

 

[michiganbuck]

Sometimes that finish can be the tool edge not being sharp enough and so pushing material back into the part rather than pealing it off.
A positive rake angle can help.. and a nose radius.
*Post #43 looks like a flat-top tool bit with lacking a side cutting edge, and a back rake.

A hard very fine grit hone can put on the needed very sharp small nose radius.
A little lard on a small paintbrush for the final cut can also help.

You might try around 500 RPM and a .003 feed per revolution and work up ad down RPM to fr the sweet spot for the material.

 

[camaro_dan67]

I know my last picture the surface finish looks torn. I realize this is tool sharpness/geometry. The main focus of that picture was to show that the helical stripes are gone. The lathe now sounds completely different all I hear when it runs is the sound from the straight cut gears. With the old single phase motor it sounded like a washing machine running with a constant hum.

 

[michiganbuck]

Angles are not fussy, often 2 degrees error is Ok..But for steel they need to be very sharp. 60grit wheel or a fine stone for a few swipe to make a sharp edge.
Most/many lathe hands don't even protractor a turning bit. Yes, a threading bit is fussy.
https://littlemachineshop.com/images/gallery/instructions/grindingtoolbits.pdf