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Machine leveling

Richard S

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#1
I've just joined the Forum, this is my first post. I just bought a used 920 jet lathe. The manual for it that I've downloaded indicates that it should be leveled or the stand(which I have) should be bolted to the floor. Elsewhere I have read the lathe bed May twist if this procedure is not followed.
I found no discussion of this topic when I searched hobby Machinist and see no evidence in pictures of casually placed machines. I've shimmed the machine so all four feet share the load of the lathe but I'm loathe to Bolt the machine in place--dedicated space being at a premium.
 

francist

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#2
Hi Richard, welcome. I agree the search capabilities on the forum can sometimes lathe a bit of functionality, but I just did a quick forum search using "lathe levelling" and found two pages of threads on the topic. It is a frequently discussed subject here and I'm sure there will be many replies, but in the meantime this may give you a few older posts to look at.

-frank
 

RJSakowski

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#3
I've just joined the Forum, this is my first post. I just bought a used 920 jet lathe. The manual for it that I've downloaded indicates that it should be leveled or the stand(which I have) should be bolted to the floor. Elsewhere I have read the lathe bed May twist if this procedure is not followed.
I found no discussion of this topic when I searched hobby Machinist and see no evidence in pictures of casually placed machines. I've shimmed the machine so all four feet share the load of the lathe but I'm loathe to Bolt the machine in place--dedicated space being at a premium.
Bolting the stand to the floor accomplishes two things. It prevents the stand from moving during use and it tends to stabilize the stand and lathe blessing the possibility of your previously adjusted lathe losing its adjustment. This is more important on a light stand/lathe is unintentional shift in position is more likely. However, there are many lathe setups where the lathe is free standing. My lathes are set on heavy stands which are not easily moved and are free standing.

Leveling a lathe is important to prevent twisting of the bed. A twisted bed will turn a taper on a cylinder because the cutting surface is rotated towards or away from the spindle axis. A left hand twist will rotate the tool into the spindle as you move towards the tailstock, causing a smaller turned diameter at that end. Sometimes twist is intentionally added to correct for a non-level condition. It is preferable to level the lathe as best you can before using any twist. Leveling precisely requires a machinist's level with sensitivities in the .005"/ft to .0005"/ft range. This is far more sensitive than a typical carpenter's level. Since these levels are fairly expensive, most hobbyists use a two collar test or procedure known as Rollie's Dad's Method to determine correct alignment.

The two collar test basically involves turning an area on a cylinder near the headstock and one near the tailstock. If the lathe is aligned, the two diameters will be equal. The RDM method uses a bar of uniform roundness and diameter along with a suitable indicator to measure the distance to the spindle axis near the headstock and near the tailstock. It involves some simple calculations but turning isn't required and the bar doesn't have to be free from runout. Note that the bar isn't supported in the tailstock in either of these tests. For that reason, a fairly stout bar to minimize deflection is required.
 

Richard S

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#4
I appreciate the input guys. I'm awaiting the arrival of a dial indicator so it looks like I can proceed.

I still find myself hesitating to bolt it down and dedicate the space permanently. In the past I have grouted heavy equipment in place and I wonder if I could get away with that here here. This 920 with its base is just shy of 300 lb.
 

mikey

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#5
Richard, I have noticed two basic camps on this subject. One group says you should mount the stand on a solid footing, like concrete, and bolt it down. Clearly, this is the ideal but to say it is the only way - no, it's not.

The second group are guys with small shops who have to move the lathe from time to time. For this purpose, leveling casters like Foot Master, Carry Master and others are popular. While not ideal, sometimes you just have to move the lathe and casters allow that. I use this method and have to re-level the lathe when I re-site it and it can be either fast or agony, depending on the Universe's sense of humor on that day. A good precision level helps.

Yet another group mounts their lathe on a rolling tool chest; I suppose they're a sub-group of the first camp. Most of these guys obviously have small lathes like your 9 X 20. Moving the tool chest does not disturb the level of the lathe so you might consider this. If you go this route, make sure the surface you mount the lathe on is solid and unmoving and you should be okay. We were just discussing this in this thread:

http://www.hobby-machinist.com/thre...put-under-a-benchtop-lathe.60245/#post-496728

Good luck, whichever way you decide to go.
 

T Bredehoft

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#6
There is a very small minority that don't worry about leveling their lathe, I do no work longer than 3 or 4 inches long in my lathe, and have the tailstock adjusted for almost no taper. If I need better I achieve it with paper or file. It's a small lathe, 6 by 20, flat ways, on a wooden stand. No wheels, no leveling feet.
 

TakeDeadAim

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#8
With a lathe that small it comes down to the bed rigidity. If the lathe on the stand cuts with no or tolerable taper then leave it alone. If not then it will need to be leveled to correct that. Sometimes, such as my 13x40 it is on leveling screws but no hold downs to the floor. It is level to my Starrett 12 in machinists level and cuts 0/0 over 12".
 

Richard S

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#9
I appreciate all the responses. I'm somewhat reassured that if I proceed to check for level, I can determine how rigid the Lathe bed and base are. Starting out I don't anticipate turning long pieces.
With a lathe that small it comes down to the bed rigidity. If the lathe on the stand cuts with no or tolerable taper then leave it alone. If not then it will need to be leveled to correct that. Sometimes, such as my 13x40 it is on leveling screws but no hold downs to the floor. It is level to my Starrett 12 in machinists level and cuts 0/0 over 12".
 

mikey

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#10
I appreciate all the responses. I'm somewhat reassured that if I proceed to check for level, I can determine how rigid the Lathe bed and base are. Starting out I don't anticipate turning long pieces.
Richard, leveling the lathe tells you nothing about rigidity. It only tells you if the lathe is level or not relative to how the lathe is mounted or sited. After leveling, you usually will either take measurements or take very fine test cuts on a 2-collar bar; this allows you to fine tune and/or confirm that the lathe is level.

Rigidity is a whole other thing.
 

joshua43214

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#11
Getting the base level and equally on all feet is a good idea just for its own sake. It is not necessary, but it is "best practice." It is especially important that the base bears evenly on all feet otherwise it can cause issues with the finish.
Bolting the machine to the floor is often good, but some folks have had to unbolt theirs because of local vibration from a freeway, trains, etc. and put the machine on rubber machine feet. Mine is bolted down, and it improved my finish quality.

"leveling" a lathe is a bit of a misnomer. The object is not so much to get the beds level as it is to get the machine setting on the base with no stress. Having the beds level can make other set ups easier since you can use a level to see if your work is in the machine right at times. But as already stated, Army mobile machine shops, and navy machine shops are anything but level. The reason we call it leveling is because using a level is the easiest way to remove twist. Short of using a level, you would have to resort to some other complicated method.

A "leveled" lathe will have no twist in the beds. This is accomplished by using a machinist level over the beds and adjusting the feet until the ways are free of twist (as measured by the level). if the machine cuts a taper with untwisted ways, the headstock is out of alignment. If it is very minor, many people will twist the bed to compensate, best practice is to loosen the headstock and align it.
Only after the headstock is made to be in alignment should the so called "two collar" method be used to center the tail stock.

So, level the base, level the lathe, align the headstock, align the tail stock.

There are tons of threads hear on it, and plenty of videos on the internet.
Just use your common sense, there is also a lot of poorly informed info out there.

-Josh
 

Richard S

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#13
Josh thanks for the very clear explanation of the mechanics. I was wondering about the distinction between being level and having the ways coplanar. I can see the convenience of having a level reference. Presumably on a lathe like mine one has to have reference spacers to get above the V ways to measure the bed for level.
 

mikey

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#14
Josh thanks for the very clear explanation of the mechanics. I was wondering about the distinction between being level and having the ways coplanar. I can see the convenience of having a level reference. Presumably on a lathe like mine one has to have reference spacers to get above the V ways to measure the bed for level.
Not really. Just remove the compound and set the level on your cross slide.
 

ddickey

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#15
Why would you need to remove the compound Mike? Just lay the level along the cross slide.
 

mikey

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#16
Why would you need to remove the compound Mike? Just lay the level along the cross slide.
My level is almost 12" long with a relieved section in the middle. It has to sit on the ends of the level and there isn't enough bearing surface with the compound in place. Most precision levels are similarly relieved in the center so ... the compound has to come off.
 
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