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The Artful Bodger
08-26-2011, 06:27 AM
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.

Black_Moons
08-26-2011, 06:34 AM
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.

philbur
08-26-2011, 10:35 AM
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.:D

Phil:)

The Artful Bodger
08-26-2011, 06:04 PM
Sure your not 'tensioning' the lathe? (Squishing the tailstock and headstock mounting points togethor)



I dont think so, the holes in the bench are much bigger diameter than the bolts that pass through them.

The Artful Bodger
08-26-2011, 06:08 PM
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.

Carld
08-26-2011, 06:18 PM
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.

aostling
08-26-2011, 09:07 PM
Today is the day I mounted my 12x36 Chinese lathe on my concrete machine bench.


John,

Perhaps I missed a post, but I'm wondering how you coped with the misaligned holes?

The Artful Bodger
08-26-2011, 11:23 PM
http://farm7.static.flickr.com/6193/6083960481_977fa7f1cb.jpg (http://www.flickr.com/photos/25239206@N06/6083960481/)
lathe fixing (http://www.flickr.com/photos/25239206@N06/6083960481/) by aardvark_akubra (http://www.flickr.com/people/25239206@N06/), 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.:rolleyes:

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.

Black_Moons
08-26-2011, 11:27 PM
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.

macona
08-26-2011, 11:37 PM
No way those bolts would snap. Look up the tensile strength of even common grade bolts for that size.

The Artful Bodger
08-27-2011, 01:22 AM
Ever think maybe its arched because you jacked up the inside bolts and tensioned the outside bolts?



More than likely..:D

Robin R
08-27-2011, 01:24 AM
Nice looking bench, are you going to paint it before it gets oily. Also have you run the lathe on it and if so, does it seem to give a better finish to the work, less chatter etc.

dp
08-27-2011, 01:59 AM
Use any three mount points to level the lathe on three axes - use all four to take out the warp.

darryl
08-27-2011, 02:46 AM
Hmm- I think what I would do at this point is put a piece of wood under the headstock, about halfway between the bolts, then set the bed down on that. Then I'd do the same under the tailstock, except use a slightly thinner piece of wood and lay that of a piece of rod that's centered under the bed. The bed will now be on a three point support and will take the alignment it wants. The thinner wood piece plus the diameter of the rod should have that end of the lathe at the same height as the head end.

The lathe would be lined up so all bolts will stand through the mounting holes and the bench top without leaning sideways.

At this point I would begin to run the bottom nuts up til they each stop. Once all of them are up, do what you need to to make the studs tight to the benchtop. Then make the rounds again on the nuts, making sure they are all run up about equally. Then I would place felt marker marks on each nut so you can then give each one an extra full turn up. You should be able to remove the wood now, and run the upper nuts down finger tight. Now start checking the bed for warping.

If there's an upward warp, lower the two inside nuts under the head end, turning each the same small amount. Finger tight the upper nuts and check the bed again. When you seem to have the bed level, tighten all the upper nuts at the headstock.

At this point use only the studs at the tailstock end to make adjustments. You can warp the bed up or down, and twist it. Avoid any twisting except when you have detected it with the sensitive level. Always use both nuts now to de-twist, so the average height at that end stays the same. One set of nuts goes up- the other set goes down the same amount. I'm going to guestimate here and say the most you would need to alter these adjustments would be perhaps a quarter turn, but probably much less than that.

If you use this procedure, you can set the lathe bed fairly low to the benchtop. About all the room you need is two threads up on all the bottom nuts, or make what turns out to be the lowest one two threads up. You're never going to need that much adjustment again, once you level it the first time

I agree, that's a pretty large gap to fill with mortar or whatever. Just make up something cosmetic that you can slide into place- maybe secure it with a few beads of dap or similar. You will want to be able to remove it without wrecking it, so don't overdo it.

I'll make a suggestion for this piece- find a piece of birch plywood, the stuff that has lots of plies in it, about 1/2 inch thick. Make it about four inches longer and wider than the outermost part of the beds mounting plates. Cut a notch where it can slide under the bed at both ends and miss the mounting bolts. Push that under the bed from the front and temporarily block it up. Now you can measure the gap from that to the benchtop and saw up some of the same plywood to become the skirt. Make the front skirt full length, and glue that plus the two side pieces into place. For the back skirt, you want it removable so you can slide this assembly out the front for cleaning and adjusting the bed if and when needed. Sand this assembly up nicely and give it an all-around coating with something durable.

The Artful Bodger
08-27-2011, 02:54 AM
Use any three mount points to level the lathe on three axes - use all four to take out the warp.


The level I am using is Czech made 0.17/1000 and I can still get some indication (about a fifth of a graduation) of non flat ways, what should I expect?

dp
08-27-2011, 03:02 AM
Level it with three points measuring on a diagonal, then, if you've chosen the three points correctly, you can unwarp it by shimming the off-level diagonals. The assumption is the lathe is both off level in two axes, and racked.

Like scraping, you are moving the entire plane and you need to work from that perspective. You want both level and flat but to be honest I'll take a flat bed over a level bed any day of the week. Making a lathe level is solving a problem that doesn't exist. Making it flat is the goal. Making it flat and level is cool.

The Artful Bodger
08-27-2011, 03:20 AM
Nice looking bench, are you going to paint it before it gets oily. Also have you run the lathe on it and if so, does it seem to give a better finish to the work, less chatter etc.


I am trying to keep the oil off it and will paint it but I am not sure I will be painting the top surface, just sealing against oil and damp.

The Artful Bodger
08-27-2011, 03:38 AM
Thanks for the advice and suggestions.:)

jugs
08-27-2011, 05:04 AM
http://farm7.static.flickr.com/6193/6083960481_977fa7f1cb.jpg (http://www.flickr.com/photos/25239206@N06/6083960481/)
lathe fixing (http://www.flickr.com/photos/25239206@N06/6083960481/) by aardvark_akubra (http://www.flickr.com/people/25239206@N06/), 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.:rolleyes:

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.

Presumably you went to the trouble of building a concrete bench to give your lathe mass & rigidity ?? but you now stand the machine on 6 x 12mm bolts :confused: so the machine is now effectively supported on a set of tunable (longer = lower frequency) vibrating rods, the only part of the system that is damped by the mass is the bottom end of the bolt, everything else is free to vibrate @ it's natural frequency, giving lots of scope for chatter.

The bolts/studs are in compression but the cast iron foot is in shear & tension ( the only bit in compression is the bit around the hole squeezed by the nuts) so expect stress cracking around the cast iron foot.

I suggest you oil/grease bottom of feet,
Cast concrete under the feet, allow time to cure,
make shims that raise the machine 2mm above the jacking points
Tighten 4 bolts down - I suggest only the 2 @ chuck end to eliminate introducing hogging + tailstock.
so now the machine is clamped to the mass, bolts are in tension, cast iron is in compression, stress & vibration gone away. :D

Because concrete is flexible & moves while curing you will need to do regular checks for twist, warp, taper, re shim a necessary.
Paint/seal all surfaces except bottom of feet with 2pack epoxy to reduce the movement effects of humidity changes.

Peter.
08-27-2011, 08:39 AM
I agree with Jugs completely. Standing the lathe up on posts has robbed the bench of it's primary function.

I would drop the lathe down to about 20mm and re-level it then dry-pack the headstock and tailstock using non-shrink admixture in the dry-packing leaving enough around the studs to release the bottom nuts. Really ram the dry packing in hard with a square-cut batten. Look-up dry-packing it's the easiest thing in the world to do. Basically it's a strong mixture of cement, sharp sand and just enough water to make it clump in your hand when you squeeze it, and break-open when you pinch the clump. Buy the admixture (or ready-mixed) to keep the shrinkage low.

Once that has cured drop out the bottom nuts and pull the top ones down to clamp it onto the dry packing. The dry-packng might shrink a tiny bit but it will do it evenly so there should be no need to shim. If you do you could use foil etc

darryl
08-27-2011, 04:36 PM
Hmm- from the last few posts I've gotten the idea that you could completely bed the headstock onto a layer of cement, which would give full support to the entire underside of it, then leave all adjustments to the tailstock end, which is something that I more or less suggested earlier. I like this idea. Do everything like I suggested a couple posts ago, but then instead of leaving the whole thing open and filling in the gaps with a wooden structure, you would concrete in the headstock end. Build a form around the back, the left side, and the right side of the headstock base. Use whatever temporary clamping you need to to hold this form in place. Have a front piece ready to attach to the front of the form. Then mix up the non-shrinking mortar or concrete and tamp it into place until the gap is filled, add the front form piece, then finish filling the gap and tamping it in tightly.

There's your headstock fully supported over its entire area on the bench. The upper nuts on the studs can still be removed or tightened- if you found that you needed to shim at some point, it could still be done.

The tailstock mounting and adjustments are as before. If there's a degree of settling and stabilizing in the concrete bench over time, you have the option to re-adjust the bed to suit. Then at a later time, say a year or two down the road, you could cement in the tailstock end similarly to the headstock. You would probably use a layer of waxed cardboard under the tailstock base before tamping the cement into the form- that would leave you with a small gap between the base and the cement, which gives room to shim up or down, or apply corrective twist. At the first time an adjustment is required, the cardboard is removed to leave that gap, but until that time it is just left in place.

All of the lathe mounting studs are now cemented into place and become an integral part of the benchtop. The headstock end is fully supported over its entire base area right from the start, and the tailstock end will have about as much support as it could ever get while still having the means to be adjusted. If you did adjust after a few years, the gap left will be very small, and some epoxy could be wicked in if you wanted to enhance the rigidity of the connection between lathe and benchtop at that end.

In my mind, this would meet all the requirements when it comes to mounting the lathe bed most rigidly to the mass of the benchtop. The interface is a perfect fit between bench and lathe, adjustability is retained, and the lathe is fully removable. Because you have essentially cast the gap fillers into place on an already cured benchtop, the filler blobs would be removable as well, taking the mounting studs with them and leaving a fully cleared benchtop. This might be important when it comes to mounting the 'new' lathe.

The Artful Bodger
08-27-2011, 05:47 PM
Relax guys! I never intended to leave it standing on six thin stalks like that.:)

Thanks everyone for the very helpful advice and information.

Darryl, your idea of locking the headstock to the bench and leaving the foot for adjustment is a good one and I will be giving that more thought.

Unfortunately the feet of the lathe are not solid and although I have been keeping a look out for a suitable plate to put under them nothing suitable has come my way yet.

So here is a 'plan' for comment and discussion:-

Prop up the tail stock on the existing bolts.
Put a steel plate under the headstock and a small block of wood under there.
Use the bolts to pull down the headstock level.
Pack concrete under the plate and around the block of wood, the bolts would be wrapped in tape or maybe in tubes.
Bolts to be tensioned after the concrete has cured.

(The purpose of the block of wood is to support the lathe while the concrete cures without the need for jacking nuts.)

The tail stock to be done the same way after a time for the bench and headstock end to settle. Any further tweaking to be done by shims or by wedges under the corners of the bench.

philbur
08-27-2011, 06:11 PM
After all that effort the lathe will still be a POS.:D

Phil:)

The Artful Bodger
08-27-2011, 06:19 PM
After all that effort the lathe will still be a POS.:D

Phil:)


................. :D

........and it still has a single phase motor.....

Peter.
08-28-2011, 04:43 AM
the bolts would be wrapped in tape or maybe in tubes.

I've seen pipe lagging used by concrete gangs but favourite is polystyrene.