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ptjw7uk
03-09-2006, 06:51 AM
Been browsing the forum and several strands have set me thinking that I may not have my (chinese origin) lathe correctly set up.
The machine as bought was supplied with a stand onto which I set the lathe up, the stand however does not have any built in means of fixing it to the floor. Now in my darkest recesses of my mind I seem to remember being told that the actual bolting down of the lathe can induce twist in the lathe. If this is so how can this twist be checked and is there a correct way of installing a lathe not that my machining skills are much to write home about I would just like to know for knowing sake!!!
Peter

railfancwb
03-09-2006, 07:07 AM
Go to

http://www.atlas-press.com/servicebulletins.htm

where you will find some "how-to" pages discussing leveling and aligning of lathes.

Bolt hole locations will differ, but theory and basic techniques are constant. Note particularly the comments about the importance of a sensitive level; the typical carpenter's level isn't precise enough for the job.

Charles

Carl
03-09-2006, 03:08 PM
The ultimate test of a lathe is whether or not it will turn straight. If the work you are turning has no taper, or the taper is within your tolerances, then all is well.

J Tiers
03-09-2006, 04:43 PM
<font face="Verdana, Arial" size="2">Originally posted by Carl:
The ultimate test of a lathe is whether or not it will turn straight. If the work you are turning has no taper, or the taper is within your tolerances, then all is well.</font>

Pretty much.

There could be opposing errors that cancel out. If adjusted ONLY for no taper, you have no proof that the headstock is even seated right....

Best to have an external reference, and the level (much-hated and regularly ridiculed here) is a good one. That way you know that one part of the machine is right, and can set the others to it, or at least check them against it.

Fasttrack
03-09-2006, 04:53 PM
hmm...i haven't noticed any of those problems with my lathe, but i know its not perfectly level because its on a garage floor which slants slightly downwards so water will drain. (i built the table square, not taking into consideration the effect of the slant) Whats the best way to correct this if my lathe (really a smithy combo machine, yes i know laugh it up) doesn't have feet persay. It is supported the entire length of the way; i'm affraid shimming it might cause it to sag since it wasn't designed to be supported only in the corners. Any suggestions? (gosh thanks Peter, you got me thinking! Hope i can correct any stupid mistakes i've made)

Carl
03-09-2006, 06:02 PM
Level doesn't matter. Level is only a reference in determining whether or not there is twist in the bed. It could be mounted with two legs on the floor and two legs on the wall and as long as it isn't twisted, it will cut straight. J Tiers is right, if you have to shim it to correct a twist, using level as the reference point, then you are using an opposing force to cancel out an error.

Fasttrack
03-09-2006, 06:11 PM
"Level doesn't matter. Level is only a reference in determining whether or not there is twist in the bed. It could be mounted with two legs on the floor and two legs on the wall and as long as it isn't twisted, it will cut straight."

Whew...thats what i originally thought whenever i set up the lathe, but then reading the post i started getting a little nervous! I'd hate to screw up even something as small as the smithy, still cost me several summers of hard work http://bbs.homeshopmachinist.net//wink.gif

ptjw7uk
03-10-2006, 08:39 AM
And where do we get these levels!!
How sensitive do they have to be!!
Peter

J Tiers
03-10-2006, 09:25 AM
The purists will say it has to be a "master precision level" with 0.0005 " per foot sensitivity.

The truth is that it can be a much less sensitive level, because it is a "sanity check" and not your only tool. The fancy ones are fine, but overkill.

So sensitive they are hard to use. Expensive, and the cheaper types may be junk, like the Grizzly one I bought and sent back... base wasn't close to flat, making it useless.

I use a small Starrett with 5 thou per foot sensitivity that I picked up at a sale for $10.

That is about 10 times more sensitive than a carpenter's level, but not crazy-sensitive.

There are otehr ways, too, and possibly some creativity is in oder... you just want to know if the bed is twisted, so in principle you could sight over straight bars, etc, etc.

Tin Falcon
03-10-2006, 03:59 PM
Here is a link I posted last year that may also help. http://www.wrathall.com/Interests/machining/Testing%20lathe%20for%20accuracy.pdf

lbhgti
03-11-2006, 12:38 AM
I suppose this might work for a cheap level, more accurate than a carpenters level. Get two of the smallest diameter graduated cylinders that you can find, and make some holes towards the bottom of each and connect up a hose the length of the bed of your lathe. Put one cylinder at one end and one at the other end and fill halfway up with water. If it is out of level, the water level in the two graduated cylinders will be different and you can correct the level until they are the same. The finer the graduations, the easier this will be. Maybe it won't work, but its a shot.

CCWKen
03-11-2006, 01:24 AM
Ummmmmmm... I think that's how they level trailers around here. I don't think it would be accurate enough unless the cylinders were glass capilary tubes.

Speaking of levels. I've got two Starrett bubble capsules. Is there a way to tell what sensitivity they might be? I might mount one to a 12" test bar and check it out. If it can detect a .0005" shim under one side, that would be good.

I may have to epoxy studs to the bar though. I don't know if I can or want to drill it. Dang, another project to add to the list.

Millman
03-11-2006, 04:31 AM
What the hell? Just how LONG is that Smithy?, 10-25 FT.? I don't think so; just level it. .0005 is close enough until you get into high precision turning large diameters over a given length. If you turn long lengths, you also have to figure in deflection and mass; such as the weight of variable wall diameters, especially long lengths versus wall thicknesses. Small lathe; piece of cake.

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BFH