Question about lathe levelling

All discussion about lathes including but not limited to: South Bend, Hardinge, Logan, Monarch, Clausing and other HSM lathes, including imports

Moderators: GlennW, Harold_V

LouStule
Posts: 86
Joined: Fri Sep 11, 2020 7:20 pm
Location: Washington State

Re: Question about lathe levelling

Post by LouStule »

pete wrote: Sun Oct 18, 2020 9:13 pm Square non twisted lathe ways are still very important even with short parts for a couple of reasons. It's debatable how much effort gets expended while setting up the bare lathe beds on a surface grinder with the smaller off shore hobby level machines. But ideally and in simple terms the lathe beds should have the mounting feet machined and/or ground on the better industrial machines while the bed is in a relaxed or neutral state, it's then set on those feet and the ways are ground. So running the machine with a bed in that non neutral or twisted condition accelerates wear to the moving parts. But that twist also affects the tools being used due to how the misalignments get amplified. With turning tools locked into a tool holder, any bed twist will move the tool either into or away from the desired tool location due to the amplification or tool height above the bed ways. Visualize that twist in the ways as rolling the tool tip in a partial arc into or away from the part depending on it's direction. It's that effect that causes a part to be tapered from end to end on a misaligned lathe bed because the lathe carriage has to follow and will replicate what ever alignment there is on the ways. But even with short parts the tools used for internal machining, drilling and reaming from the tail stock, boring bars held in tool holders are usually fairly long. Any twist can then easily result in taper drilled, bored or reamed holes.

This might sound highly critical, it isn't meant that way, I'm trying to be factual due to what I've personally experienced with some of what I've bought. A whole lot of these off shore machines look fairly good on the surface. In some cases there at best a lathe shaped object once you start actually checking what the factory produced using the tests and methods in that PDF link I gave you. EVERYTHING does need to be verified on these machines so you do know what it's alignments are. My Sieg C6 lathe as just one example came with the tail stock barrel pointing up hill .009" in just over 2 inches. Add a morse taper mounted drill chuck to that tail stock and even a short center drill and the length and therefore misalignment is over double that. It was impossible to use any center drill from the tail stock since it would instantly break the tip off. Reamed holes were seriously tapered even with a properly leveled bed. While a vertical misalignment at the tail stock has far less effect in creating a taper turned part for logical reasons, due to that serious misalignment it still refused to turn exactly parallel no matter how I adjusted it. So the reality's are that bed leveling is only the first step in what's required as further checking.

Myself I'd never run parallel turning tests between the head and tail stock using any lathe chuck on the head stock end. It's far better to hold a piece of at least 1" diameter scrap material with what ever chuck you want to use and turn a proper 60 degree point on it. That way it's as concentric and with a true running point on the head stocks exact C/L as the spindle bearings can produce. Use one of the sides of the a chuck jaw to drive the lathe dog that's attached to your test piece. Leave that 60 degree point undisturbed in the chuck until all your turning tests and adjustments are complete.

Once the bed is known to produce a properly parallel turned work piece you then have a starting point for further tests. At that point I'd probably verify the tail stocks quill and how parallel it is in both the vertical and horizontal directions. I'd then start checking the lathes facing alignment. All lathes should be set up to face concave and never convex. It's an extremely small amount on even the best manual and cnc lathes made today. That Schlesinger PDF will show the numbers. From memory it's only .001" - .002" concave over I think a 24" diameter work piece for a tool room lathe and a bit more allowable deviation for lesser quality lathes. No your lathe can't turn anything of that size, but there's a trick to amplify the measurements on smaller diameter parts. Did you get a face plate with that lathe? If so spotlessly clean the spindle nose and face plates mounting surfaces. Mount it to the lathes spindle and make a light but full facing cut from the outside of the face plates rim to the inside hole in the face plate using a new carbide tip or extremely sharp high speed steel tool. To use a clock dial as the best way to visualize this you'd be turning from the 9 o'clock position to the face plates center. Once that face is fully cleaned up withdraw the cross slide to your starting position, now set a 10ths capable or metric equivalent dti's tip just on the far side of the face plates center hole. Use the cross slide to run the indicators tip to the back side of the face plates rim or it's 3 o'clock position. Doing it this way will show DOUBLE the measurement readings of what the facing alignment is. Using the same path the tool took to make that facing cut ( 9 o'clock to center) will only follow the exact same path the tool took and your readings will show zero so it tells you nothing.

Well made high end lathes are purposely set up to have the head stock pointing towards the operator by approximately .001" in 10"-12" from dead true on a test bar and another roughly .001" upwards over the same distance. Those purposely set misalignments are done to help compensate for work piece weight and turning pressures. The lathes cross slides are also aligned to help the lathe face very slightly concave and never convex. That's done so the machine starts to slowly wear towards flat facing cuts and not immediately away or towards a highly undesirable convex facing situation. No I don't expect your lathe to be that accurately made, I'm providing those numbers of what a proper lathe should have. What you measure with that lathe might be just about anything but correct. But the Schlesinger numbers can be at least used as rough guidelines. What's generally known as the Two Collar Test can be used as another rough guideline for your actual head stock alignment, mistakes and faulty test results can easily be made just due to a slightly dull tool, taking more than the barest minimum of cuts, and trying to make cuts on a test piece that's too small in diameter. Any flex at all in the work piece while it's being cut and the test is worthless. For that lathe I think I'd chose to follow the maximum accepted diameter part length to it's diameter without tail stock support. 3-1, or no more than three times the part diameter extending outside the chuck jaws. Something like a piece of 3" diameter 6061 aluminum with a 9" length between the two collars being cut would be the maximum I'd feel confident in trying. Again it takes a minimum depth of cut, very sharp tools and a very good trustworthy micrometer to be 100% sure of your test results. Because of it's much lower cutting pressure requirements, then aluminum and not steel would be my choice of material.

What you find during these tests, what your willing to accept or not, your skills or how much effort you want to invest in correcting anything that isn't quite right is going to dictate how far you go with this. But for information about correcting for wear or built in alignment faults then I don't know of a better YouTube channel than this one, https://www.youtube.com/channel/UCD1jVj ... PHw/videos Those Schlesinger test methods in that PDF aren't the only methods of course. There's others where people have come up with different ways to get to the exact same point as Schlesinger does. I chose to use his methods since there proven to work and are still being used today by just about any manufacturer I know of. I hope some of this will help.
Great info. Thanks!
RSG
Posts: 1541
Joined: Fri Feb 04, 2011 9:59 am
Location: Ontario, Canada

Re: Question about lathe levelling

Post by RSG »

Yes, Pete is a good one for detailed posts. I can't speak for others but I always appreciate his replies.
Vision is not seeing things as they are, but as they will be.
pete
Posts: 2518
Joined: Tue Feb 10, 2009 6:04 am

Re: Question about lathe levelling

Post by pete »

Thanks RSG.
GeoNOregon
Posts: 3
Joined: Tue Dec 25, 2018 12:26 am

Re: Question about lathe levelling

Post by GeoNOregon »

I spent 35+ cutting up dead tree carcasses, and building things from the pieces. In 1990, I bought an MD electronic level, when they first came on the market. I have never looked back.

In my entire life, I cannot think of one single tool which made me a better carpenter, immediately. Imagine this with a bubble level. Start in one corner of a room, in a 10-100 year old house. Mark a level line the length of your 4' level, then continue until you reach a corner, then go all the way around the room. How close would end of your last line be to the beginning height mark?

Anybody with a moderate amount of experience with a bubble level would even try. With the electronic level, I could go around the room, and hit the starting mark, dead nuts.

To level your lathe, or anything, get an electronic level. If you don't have enough use to warrant the $100 for one, go to eBay, and buy an inclinometer from a Chinese vendor for <10.00. I bought one a few months ago, because they are 3" x 3" x 1" deep.

I have checked it against my brand new MD, and it is right on, in accuracy, and has the same measuring features: degrees, in/ft and bubble emulation.

Oh, yeah, a plug for MD Tools. When I got ready to level my lathe a couple years ago, I got out my electronic level, began to calibrate it, and it froze up. Almost 30 years of use, and it was locked up. I contacted to MD to see if there was a way to hard reset the thing.

The response was, 'We not only have no idea IF it can be done, but there is no one here who has ever SEEN your model, in the wild, or in person.

Being the outspoken guy I am, I replied with, 'Well, that makes my level a valuable artifact for historical and research purposes. I'll make you a deal: I'll send you my valuable artifact, and you can send me a new one, in exchange. I can then get back to work, and you will be able to glean knowledge from my old level.

A few days later, I got a reply from 'The Boss' at MD Tools: "Which model would you like?"

MD Tools gave me a brand new level, for my old one, AND through in a carrying case. Total cost: shipping the old level to them.

WHO does that? LOL

Get yourself an electronic level, either a new/used MD, or an inclinometer from China via eBay. You won't regret the expense of either one.

Regards,

GeoD
Last edited by Harold_V on Mon Nov 02, 2020 5:15 am, edited 1 time in total.
Reason: remove undesirable language
LIALLEGHENY
Posts: 363
Joined: Sat Jan 11, 2014 12:36 am
Location: Bohemia, NY

Re: Question about lathe levelling

Post by LIALLEGHENY »

I can tell you from experience that the electronic levels on the market are no where near accurate enough to level a lathe correctly. I make a weldment for Thompson/ Danaher for the solar industry. The job requires that angles and flatness be held to extremely high accuracy. When the first pieces were shipped to their facility I got a call saying the parts were no good.....when I question how the Inspection department was checking the parts I was informed that they were using electronic level, and protractor. They didn't want to listen and sent the parts back. I had them checked again and shipped them back, got the inspection department on the phone and had them check the manufacturers specs on their electronic equipment. I also told them to get a good Starrett level and protractor........They got back to me a few days later.....my parts were good, the electronic levels were not accurate enough.

The key to leveling a lathe , as has been stated, is to prevent twist, and to keep it straight from one end to the other. You could tilt the lathe at 10 degrees as long as both ends are accurately at 10 degrees.

Nyle
atunguyd
Posts: 199
Joined: Tue Oct 20, 2009 9:39 pm
Location: Durban South Africa

Re: Question about lathe levelling

Post by atunguyd »

GeoNOregan,

With all die respect I doubt that a digital level would work.
Are you referring to this level?
http://mdbuildingproducts.com/product/4 ... ying-case/

The specs claim it is accurate to 0.1 degrees.
That's 6 minutes of a degree. The less sensitive machinists levels are typically accurate to 80 seconds of a degree. That's 1.33 minutes or 0.022 degrees.

It would be great if a digital product could be this sensitive but I think they are just not (well not on the price ranges we are talking)


Sent from my SM-N975F using Tapatalk


John Hasler
Posts: 1852
Joined: Tue Dec 06, 2016 4:05 pm
Location: Elmwood, Wisconsin

Re: Question about lathe levelling

Post by John Hasler »

I agree with Nyle and atunguyd. There are electronic levels that are the equal of the machinist's bubble levels but they are even more expensive. Those cheap digital levels are suitable for leveling sewer lines and building foundations.
Mr Ron
Posts: 2126
Joined: Tue Dec 22, 2009 12:36 pm
Location: Vancleave, Mississippi

Re: Question about lathe levelling

Post by Mr Ron »

Assuming you are able to get a level indication and add shims, will the "twist" immediately "untwist" or do you have to wait for the bed to normalize? I'm thinking there is spring back for a bed that has been twisted out of level for a long time.
Mr.Ron from South Mississippi
atunguyd
Posts: 199
Joined: Tue Oct 20, 2009 9:39 pm
Location: Durban South Africa

Re: Question about lathe levelling

Post by atunguyd »

Mr Ron wrote:Assuming you are able to get a level indication and add shims, will the "twist" immediately "untwist" or do you have to wait for the bed to normalize? I'm thinking there is spring back for a bed that has been twisted out of level for a long time.
I assume not simply because the amount of twist that we are talking is still well within the elastic deformation range of the cast iron bed. If it were enough to have permanently twisted the bed I am thinking it would be possible to see this story the naked eye (no need for any level).
However this is just something that makes sense in my head.

Sent from my SM-N975F using Tapatalk

Post Reply