Levelling a lathe on my concrete bench...
Today is the day I mounted my 12x36 Chinese lathe on my concrete machine bench.
These lathes have 6 mounting points, 4 under the headstock and 2 at the far end.
I got everything apparently level easily enough but on further checking I found the lathe bed was arched upwards (very slightly of course). I presumed this was due to the 4 jacking nuts under the headstock not being adjusted correctly.
My level has a vee bottom and does not sit well on the ways (cross wise is OK) so I put it on the top of the cross slide and wound the saddle between the limits of its travel while adjusting the outermost jacks at the head stock end. That seems to have done the trick.
Now the point is, I have never seen any of the on-line accounts of how to level a lathe ever check for this condition of arched (or swayed) back and I dont think a short test bar would find it either. It might show as a tail stock centre high or low but you would have to check that in two or more places to find if the bed was arched. You migh even be able to get an arch backed lathe to pass some of the common tests perfectly.
Sure your not 'tensioning' the lathe? (Squishing the tailstock and headstock mounting points togethor)
Also, I used 123 blocks to put my level onto the ways.
Seems strange to have four adjustable feet under the headstock. Presumable it now only sitting on the two outer ones. Do you have a photo of such an arrangement? I guess an arching (or sagging) bed doesn't get discussed because usually there is no way to adjust for it.
When checking my lathe I always put the level on the cross slide for checking both the longitudinal and transverse level. After all it's not the bed that matters it's the cutting tool tip moving in the same plane. The documentation for my German built lathe shows the use of the carriage.
If you can adjust the "arch" of the bed then you have a means of adjusting for wear.
I dont think so, the holes in the bench are much bigger diameter than the bolts that pass through them.
Originally Posted by Black_Moons
Phil, the lathe is nothing special and very many of the Chinese lathes of this size are mounted like this. Four mounting holes, one at each corner of the head stock foot and two mounting holes, one front and back of the tailstock foot.
These machines are usually mounted on two steel stands which would not give much support against sagging but my solid concrete bench is one solid surface. I have bolts sticking up from the bench top with nuts under the lathe feet as the bench top is not perfectly plane.
You did it right. releasing the tension on either the two end bolts or the two bolts by the chuck would have fixed it. I suggest you check it every month for maybe 6 months to be sure everything is staying put.
It's only ink and paper
Originally Posted by The Artful Bodger
Perhaps I missed a post, but I'm wondering how you coped with the misaligned holes?
lathe fixing by aardvark_akubra, on Flickr
That of course if the headstock end, the tail stock has just two bolts.
It looks a bit suspect standing on those bolts like that and I am sure there would be more rigidity if there was tension on those bolts. I did intend to pack with concrete but that would leave no scope for future adjustment. Hmmmm.... I guess it is not going to go anywhere.
Any ideas of how to fill this gap? Fitted wooden blocks would keep the swarf out and would be soft enough for a bit of future tweaking if required.
Allan, only the two holes that are overhead the end of the bench have embedded threaded sockets, the other holes are right through and big enough to accommodate the misalignment when I use 12mm bolts. I off-centre drilled and tapped the heads of a pair of bolts for the problem positions and I set those bolts in bog so they are not exactly rattling around in their sockets.
Ever think maybe its arched because you jacked up the inside bolts and tensioned the outside bolts?
Repeat after me: Metal is as rigid as a wet noodle.
Btw: I think theres a serious danger of snaping those bolts when you start doing serious offset/unbalanced turning.
No way those bolts would snap. Look up the tensile strength of even common grade bolts for that size.