Surface finish problems

[Todd]

Years ago I had an old worn out Logan and just could not get even a mediocre finish on steel. Aluminum & brass were fine. After trying carbide just about every conceivable HSS grind I suspected the machine was just not rigid enough. I made a toolpost that attached directly to the cross slide and eliminated the compound all together. The old Logan instantly became a different machine finally putting a decent finish on steel. Not a mirror, but totally smooth to the touch even when using the same tooling the had previously failed so miserably.

Good point, another way I get around this on interrupted turning especially on my 10L is to tighten the gib for my compound, pretty much locking it. Definitely helps with rigidity

Todd

 

[markknx]

To start with let me say my mill is a G0602 10x22 from grizzly. (should have stated that before) Also let me state this is not a deep spiral it can be removed with a quick 2 or 3 steady paasses with some 400 grit emory. I am more concerned it is a warning of something not right.

Went over all gibs All were tight, the carriage had some slop at the bed ways more so to the head side. So I removed the clamping plate, Checked it with a mic. Sure enough it was not stepped as much on the front side. so when tight it was not clamping the way. So I milled about .005 off the low side and was able to get things alot better as far as the slop. But could not get it all as I think the bed ways are not perfect.

Yes I always back out .010 before backing the carage up.

The spiral pattern is sill there after all above I also tried new carbide bits, rehoning my hss bits(knew it was not the bits I ground haha) It did seem to go away when I fed with the compound instead of the carriage. I will do more tests on this today and will check for gear binding mentioned below. theone thing I do not know how to check is the head bearings. and do not know if this could cause this or not.

BTW the set up in the photos is the same as when the cuts were made.

 

[Ray C]

...


...It did seem to go away when I fed with the compound instead of the carriage. I will do more tests on this today and will check for gear binding mentioned below. theone thing I do not know how to check is the head bearings. and do not know if this could cause this or not.

BTW the set up in the photos is the same as when the cuts were made.

A couple things could be wrong. The carriage is possibly not secured to the ways properly. I could also be that the leadscrew is bent and as it rotates, it influences the carriage enough to show-up in the cut. Instead of a bent leadscrew, the halfnuts might not be adjusted at the right height or, the leadscrew could be at an angle from where it starts at the head and terminates at the end of the bed. Finally, it could be the leadscrew bearings.

At one time or another with various lathes, I've encountered most if not all these problems.

Ray

 

[Bill C.]

This can happen with mild steel especially materials intended for construction use. These metals have very low carbon content and are very "gummy". You should always use auto-feed instead of moving the carriage by hand. For a shaft that diameter (it looks to be about 1" diameter or 2.5cm) using high speed steel cutter, I would spin about 600 RPM and set the feed rate to about 0.003 to 0.006 IPR and set the depth of cut at about 0.005 to 0.010". If the diameter is less than 1", you'll need to spin at higher RPM but the feed rate and depth of cut can remain the same.

Of course, you need a properly ground bit and the piece must be supported at the end with either a live or dead center. If you don't support a long piece at the end, there is no way it will ever cut cleanly as it vibrates while being cut.

Once again, with mild and "gummy" steel, sometimes you never get a great finish and the best you can hope for is an even finish that might not be very smooth but is consistent.

Ray

Good advise Ray. I would hit it with some Emery cloth and a little cutting oil as well.

 

[markknx]

Thanks ray I will check into those. I think I have a quick way to check the bend theory. It would seem that if it is the leadscrew is bent then the speed of the carriage (the ratio of spindle to leadscrew) would effect the angle of the spiral. so ifI speed up the feed it sould chage the spiral's pattern. I am thinking it will lower the angle. If this works then I will be sure the feed is involved in the problem.
Thanks again for the imfo
Mark

A couple things could be wrong. The carriage is possibly not secured to the ways properly. I could also be that the leadscrew is bent and as it rotates, it influences the carriage enough to show-up in the cut. Instead of a bent leadscrew, the halfnuts might not be adjusted at the right height or, the leadscrew could be at an angle from where it starts at the head and terminates at the end of the bed. Finally, it could be the leadscrew bearings.

At one time or another with various lathes, I've encountered most if not all these problems.

Ray

 

[Ray C]

Hmmm... Thinking: :thinking:...


I think the ratio is set so speeding up won't make a difference. Just try looking at the leadscrew with and without the halfnuts engaged. If you engage the halfnuts and notice that the leadscrew has to move up, down or sideways at all in order to engage properly, that is a high probability it's your problem. Engaging the halfnuts should not have any influence on the leadscrew. It's easiest to check when the carriage is in the middle of the bed. Also check at the extreme ends too. Heck, sometimes you can clearly see it bending/wobbling when the halfnut is not engaged.

Any chance you can post a better picture of the imprinting you're getting? If I could see it, it would tell me more. -Trust me, I've been through all this on a couple of my first lathes.

Ray

Thanks ray I will check into those. I think I have a quick way to check the bend theory. It would seem that if it is the leadscrew is bent then the speed of the carriage (the ratio of spindle to leadscrew) would effect the angle of the spiral. so ifI speed up the feed it sould chage the spiral's pattern. I am thinking it will lower the angle. If this works then I will be sure the feed is involved in the problem.
Thanks again for the imfo
Mark

 

[markknx]

Just ran some cuts. Speed did not seem to change it, but hard to tell doto less smooth surface. cut both by hand using the carriage and the compound. Still see this. (I think when I used the compound before I fed much slower) Removed the compound and used my ball turner for a few cuts still see this spiral. so that take the compound out of it. Also would seem to rule out leadscrew and half nut. Leeving carriage, cross slide(which is tight) or something in the head. I have ruled out chuck out of round because that would seem to fix itself after a cut the depth of therun out.(am I thinking right here?) Could be a bearing, if there were a flat spot it would keep the same rythem. I do not no if play would cause this. I may be able to find this by chaging the dia. of the piece. it would seem that the spaces between the spiral line would get bigger as the dia. increased( is this right?) also at a higher surface speed if it is chatter from something loose it should increase. Now I am rambeling so I will end my thoughts here and wait for imput.
Thanks again to all those that gave imput, and those that will.
Mark

 

[itsme_Bernie]

AlrightI have been noticing a twisted pattern arround the part. not threading but a very faint twisted or spiral effect in the finish. About 1 twist per 3-4" reducing spead from 560 down to300 made it less. pronounsed but sill there. The effect happens on both SS and mild steel. the test parts where 3/4 . Don't know ifyou can see it in pics I can but it is hard to see and I know what it looks like.
View attachment 63977View attachment 63978

I don't know if I'm seeing what you are saying- but the marks I see might be from the chips exiting the cut in front of the cutter- and getting between the cutter and the workpiece. If you picture it, that would interrupt a cut for just that little bit of time, like a few turns.

This might be getting out of bit-grinding 101 and into bit-grinding 102 . If with carbide it might be a mixture of lack of experience affecting setup, or it could be the carbide quality. Someone on the site here recently said that almost all carbide bits we get are
Pretty dull until we hone them at home.

Bernie

 

[markknx]

Bernie,
Are you refering to the scratch like marks or the spirals that have a twist you can really only see them right at the top of the light reflection.(think barber pole stripes) they are not really a grove but more like a pattern of light chatter marks. I might just be looking to hard at them because they come out with 400 or even 600 grit paper. (and I mean in 3 or4 passes.) I think I just started getting a finish that was smooth enough to see this effect. The lathe may not have changed it may just be I am getting a cleaner cut using HSS a long with other thingsi have changed such as feed,spindel speed, and bit stick out. All things I picked up on here from all the great people. If you are looking at the spiral what is the fix to keep the chip behind the cutting edge? I think the bit was ground at 10deg. on both releifs with 10deg. end angle, 0 side angle and i do not recall side rake I think +8-10,
Thanks for your imfo, and help,
Mark

 

[itsme_Bernie]

Bernie,
Are you refering to the scratch like marks or the spirals that have a twist you can really only see them right at the top of the light reflection.(think barber pole stripes) they are not really a grove but more like a pattern of light chatter marks. I might just be looking to hard at them because they come out with 400 or even 600 grit paper. (and I mean in 3 or4 passes.) I think I just started getting a finish that was smooth enough to see this effect. The lathe may not have changed it may just be I am getting a cleaner cut using HSS a long with other thingsi have changed such as feed,spindel speed, and bit stick out. All things I picked up on here from all the great people. If you are looking at the spiral what is the fix to keep the chip behind the cutting edge? I think the bit was ground at 10deg. on both releifs with 10deg. end angle, 0 side angle and i do not recall side rake I think +8-10,
Thanks for your imfo, and help,
Mark

Hey Mark-

First of all- good problem to have, right? You are obviously getting better if your machine is the problem and not you! Seriously, that's great.

Ok- I have to say that I am having a hard time seeing which mark is spiral, and which are scratches from the pics. So +1 from me about closer pics.
****Pic Tip- you can put a magnifying glass in front of your phone or camera- just play with the distance from the workpiece, and camera to magnifying glass****

Looking at the pics, I WAS referring to irregular scratching.

But reading more of the thread here about your spiraling issues, I would start by saying to try to make the problem repeat, so you can scientifically rule things out.

Ray has most of possibilities nailed down for you. I will mention a few I haven't seen mentioned yet.

One- when you are running the lathe with the carriage feed, do you HEAR a "chugging" sound, or is the gear noise completely regular? If it is chugging, listen to Ray' suggestions, and also check that ALL the gear teeth on the feed gears are clean, and COMPLETELY. Free spinning. Or at least all smooth and the same all around.

Two- it looks from your pic like your machine has roller-spindle bearings. My suggestion is NOT as likely, but if your issue is the same whether in carriage feed or hand feed, you might have an issue with the cage in one of your spindle bearings, or with one of the balls/rollers. Not the most likely candidate. Or foreign matter in the bearing race. How do these bearings feel when the belt is loose? Is it completely smooth spinning by hand? Or jumpy or gritty?

Is there any way to measure if the irregularity is a deeper cut or raised up?

Hmmm.... Fun brain teaser!!

Three- Is the spiral almost exactly the same if you hand feed the carriage at somewhat irregular speeds, compared to feeding it really evenly, like you were trying to do?


Bernie