Poor facing surface on lathe

[memphisjed]

I am with ekretz here. The clunkidty clunk rhythm matches a surface finish change on the horizontal section witnessed by blinking light.

Something is loose or tight between motor and material.

 

[eKretz]

I agree that the machine doesn't sound good. Wasn't sure if that was just an artifact or if it was really making bad noises.

 

[Avenues]

Here is a diagram of the lathe I have:
Logan Lathe 955

I would need to play with it a bit more but I’m pretty confident the chuck is on tight, I’ll measure this tomorrow. I did some more measurements in the axial direction and I could pull it out about .006” and push it in another .005”, so a total of .011” of travel. That seems to be a likely culprit, although I’m not ruling out my inexperience making things worse, as has been kindly pointed out. Not sure what to do next but look over the design and see where I can possibly tighten something. Open to suggestions!!

As far as the sounds, I can disengage the power feed and it’s much quieter…but yeah it’s not a quiet machine.

Thanks for the help everyone!

 

[Mechanola]

Even with axial play it should be possible to make a straight cut. This is a rubbing tool and you still don’t put on coolant. Aluminium you either hog very aggressively roughing, then no coolant’s needed, or skive it slowly with a sharp tool under coolant.

I am a professional turner and I’m telling you not to play around. Take it seriously and adopt the geometry engineers have contemplated. None of the angles of the tool in the video is correct, top rake, side rake, lead (or approach). Get away from carbide when you can’t have the necessary speeds.

To set the tool post simply loosen it, push it up to the chuck, claws removed, tighten.

 

[eKretz]

Even with axial play it should be possible to make a straight cut. This is a rubbing tool and you still don’t put on coolant. Aluminium you either hog very aggressively roughing, then no coolant’s needed, or skive it slowly with a sharp tool under coolant.

I am a professional turner and I’m telling you not to play around. Take it seriously and adopt the geometry engineers have contemplated. None of the angles of the tool in the video is correct, top rake, side rake, lead (or approach). Get away from carbide when you can’t have the necessary speeds.

To set the tool post simply loosen it, push it up to the chuck, claws removed, tighten.

I definitely disagree. Never going to get an accurate and straight cut with that much end play at under 5 lbs of force without getting very lucky. The tooling is fine. It doesn't need to be optimal to cut a flat face. A quick Google search would appear to show that this machine uses ball bearings. (Edit: didn't notice your manual link, definitely ball bearings). I'd check into why you have so much end play as step 1.

 

[Tyrone Shoelaces]

I used a roughly 3ft long crow bar between the back of the chuck or spindle flange and the headstock casting. Apply moderate to firm pressure on the end of the bar. I’d be expecting less than 0.001” end float.

I’m still talking about HSS tools but I usually got a better finish feeding out from the centre to the edge of the work. Anybody else notice that.

Regards Tyrone

 

[Mechanola]

That depends on the tool geometry. When your lead angle is smaller than 90 degrees turning towards axis it’s no wonder.

 

[BT Fabrication]

its your tool, cutting aluminum needs to be knife edge sharp...

 

[Sam I]

I wonder if the noise is caused by tight changewheels. I've got a manual in the back of the workshop and it can be quite fussy with the spacing. Try loosening them slightly. One trick is to put a sheet of paper between the gear teeth before meshing then tighten everything up. That should then leave a small gap when the paper is removed. I've seen bad finishes (albeit not that bad) caused by the gears binding before so could be worth a check for the 5 minutes it takes.

Once you've got it set rotate everything by hand and check for tightness. If one of the gears isn't concentric to the gear bore then it could cause a binding.

If you've tried feeding by hand as well as under power then this probably isn't your issue but it wasn't clear from my half arsed skim read of the thread whether or not you had tried that previously.

 

[projectnut]

Here's a copy of an inspection sheet that came with a Sheldon lathe I purchased several years ago. It should give you an idea of what to expect as far as tolerances are concerned, and how to measure them.

As for tool radius the rule of thumb is that the tip radius should be a minimum of 1 1/2 times the distance it moves with each revolution. An example would be that if the tool moves .002" each revolution the tip radius should be a minimum of .003". This will allow the tip to partially overlap the previously cut material as it cuts new material. I would also use a lubricant like WD40. Cutting dry often results in chips being welded to the tool resulting in a poor finish.

 

[boslab]

I’m with Tyrone, also I use a RH knife to cut away from the Chuck a lot, I get a better finish pulling the carriage than pushing, but I have an old lathe, worn like me I suppose, we’re both past our sell by date by a few decades.
Mark

 

[Conrad Hoffman]

The spindle should be stiff as hell axially. I don't know if the 955 has internally preloaded bearings like my 211, or an adjustable preload. I suspect the latter. Just for fun, stick a center in your stock so the spindle is loaded to the rear and then make a face cut. Don't hit the center. Better? Same? If better, check with the Logan forum to see how to adjust the bearings if possible- https://groups.io/g/Lathe-List/messages

 

[eKretz]

The spindle should be stiff as hell axially. I don't know if the 955 has internally preloaded bearings like my 211, or an adjustable preload. I suspect the latter. Just for fun, stick a center in your stock so the spindle is loaded to the rear and then make a face cut. Don't hit the center. Better? Same? If better, check with the Logan forum to see how to adjust the bearings if possible- https://groups.io/g/Lathe-List/messages

The parts diagram shows Belleville washers in the assembly. Probably going to have to come apart. Guessing that the bearings are stuck and preload has been lost.

 

[Ray Behner]

I'm back, but only because eKretz forced me into it. He said he had a big stick and knew how to convince me.

I suggest the dreaded TGP. (321 or 2 for example) That's all I use for finishing Al. They're not worth two dead flies on steel. I know you don't have Vari-speed, but on my VS Sheldon I'll finish the cut backing out. Starting somewhere around 2000+ rpm. These pieces are 134mm "5.25"ish. I'll take .002 off and bring the R's down as I go out. They look like CD''s. Yes this is a very accurate and tight machine, but you can possibly make a big difference on about any machine with a positive insert.

 

[GregSY]

I don't like the choice of insert, and the lack of any oil, but those should not cause the lousy surface finish...not that bad, anyway. I agree, there is something wrong with the lathe. As noted above, the tool height could also be off but I'm not seeing that in how it travels across the part. It actually looks like it's giving a decent cut, until you turn the lathe off and then it looks like poop.

 

[Avenues]

The spindle should be stiff as hell axially. I don't know if the 955 has internally preloaded bearings like my 211, or an adjustable preload. I suspect the latter. Just for fun, stick a center in your stock so the spindle is loaded to the rear and then make a face cut. Don't hit the center. Better? Same? If better, check with the Logan forum to see how to adjust the bearings if possible- https://groups.io/g/Lathe-List/messages

Thanks for this suggestion, I'll try this when I get home tonight with the center in place.

I don't like the choice of insert, and the lack of any oil, but those should not cause the lousy surface finish...not that bad, anyway. I agree, there is something wrong with the lathe. As noted above, the tool height could also be off but I'm not seeing that in how it travels across the part. It actually looks like it's giving a decent cut, until you turn the lathe off and then it looks like poop.

Lol yep. I have probably taken about an inch off that aluminum with all the different tool iterations and DOC, feed rates, lube (WD-40), different angles, spindle speeds, etc...Not to say that I've removed all operator error, but I would hope there would be some changes between all the iterations. I have also played with the tool height as suggested, leaving it inline with the spindle axis to just below and I still don't see any difference.

 

[eKretz]

I'm back, but only because eKretz forced me into it. He said he had a big stick and knew how to convince me.

I suggest the dreaded TGP. (321 or 2 for example) That's all I use for finishing Al. They're not worth two dead flies on steel. I know you don't have Vari-speed, but on my VS Sheldon I'll finish the cut backing out. Starting somewhere around 2000+ rpm. These pieces are 134mm "5.25"ish. I'll take .002 off and bring the R's down as I go out. They look like CD''s. Yes this is a very accurate and tight machine, but you can possibly make a big difference on about any machine with a positive insert.

It was my pleasure. And good to see you again!

 

[Tyrone Shoelaces]

I'm back, but only because eKretz forced me into it. He said he had a big stick and knew how to convince me.

I suggest the dreaded TGP. (321 or 2 for example) That's all I use for finishing Al. They're not worth two dead flies on steel. I know you don't have Vari-speed, but on my VS Sheldon I'll finish the cut backing out. Starting somewhere around 2000+ rpm. These pieces are 134mm "5.25"ish. I'll take .002 off and bring the R's down as I go out. They look like CD''s. Yes this is a very accurate and tight machine, but you can possibly make a big difference on about any machine with a positive insert.

Talking about surface finishes and “ CD’s “ I was talking to a kid at the high school I worked at before retirement. He was facing up some bar. I said ” You’ve got a finish like an LP there son “.
The kid said “ What’s an LP ? “
Makes you feel your age !

Regards Tyrone

 

[GregSY]

The kid said “ What’s an LP ? “

Because people can't fathom the difference between Craig and Greg, I find myself often telling people, "Greg - like Greg Brady"

That stopped working some years ago...now I have to first assess how old the person is and adjust accordingly.

 

[AlfaGTA]

Just replace the spindle bearings, manual has them priced at $8.64..................................
I am in the spindle excess play camp...Rough finish sure,surface material tearing or smearing,but a..bad tool, poor geometry , lac of coolant will not give the ridges i see in the video unless the effective depth of cut is changing ie spindle moving axially....
First thing is to determine where all that play is coming from....if its internal in the bearings or if the bearings are moving in the head stock housing.

Cheers Ross