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Getting twist of of lathe with only 2 mounting points

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GunsOfNavarone

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#1
I was going to post this under Grizzly, but there are so many clones, others have dealt with this hurdle.
So my table i have my lathe to is substantial, I believe it holds 2k lbs...2 inch butcherblock, heavy steel legs that are braced. I have the table level with a machinist level and the top surface is true/smooth.
The lathe (Griz G0602) is bolted down via 2 mounting bolts at either end of lathe, running under direct center of lathe. They are just lightly tighten, no more. !!!!¡¡¡¡When cutting the rest shape (barbell) out of 6061, the tailstock end is +.004 bigger than spindle end.¡¡¡¡¡!!!! I believe that means the fix is lifting tailstock side/front. *I did level the lathe with machinist level as well* There really isn't a way to do this, again there is only one mounting point and it is under the centerline. Also, this is not being cut with any assistance of the tailstock....this is chucked only.
From the factory, the readings are;
Parallelism of tailstock to longitude motion in
Vertical plane .026
Horizontal plane .028
Spindle can action .018
Spindle nose run out .0175
Spindle taper run out at
Nose test bar .018
End test bar .0285
Parallelism of spindle centerline to longitude motion of carriage
In vertical plane .0485
In horizontal plane .027
Difference in center height between headstock and tailstock .058
I assume these are metric readings, and they are more, but n case there were follow up questions...
 

Mitch Alsup

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#2
Oxtool has a video on leveling a lathe--which is about removing the twist in the rails not getting the lathe perpendicular with respect to the center of the earth.

I leveled my lathe using a level (duh) and a torque wrench to make sure all 8 machine pads were holding the same load.
 

GunsOfNavarone

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#3
Yeah. I watched his video a couple weeks ago, but having 8 adjustable legs versus none, I'm kinda at a dead end..changing my tables level has no bearing on the lathe mounted to a 2" thick table top, twist. Hmmmm..if be better taking a torch to the ways, but I won't do that!
 

ddickey

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#4
Can you shim up one side of the lathe between the table top and lathe base?
 

GunsOfNavarone

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#5
It's not the greatest picture, but there really is just a center pod, only about 3" wide. Doesn't really seem as if it will have the ability to counter the twist. I guess I can find with it, such a nightmare to level again if it doesn't help. I'm sure someone else has had to do this on a Chinese mini lathe.
 

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TerryH

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#6
I just did my G0752. I made levelers from 1/2" plate with leveling bolts. Mounted 1/4" plate on the bottom of the feet. Very simple to get the bed perfectly parallel with this system. I'll make a step by step post later today but here's a preview...









 

GunsOfNavarone

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#7
Interesting, having some adjustable feet would be glorious! I’d be interested how it all connects at bottom. These 4 adjustable bolts are not connected in any way to bottom of lathe? What is the raw steel bar running along bottom of lathe in 2nd to last picture? I would guess you still have it (the lathe) bolted down to table top, this just extends that connection? I would guess a much simplified version would be to loosen my 2 mounting bolts and cram a shim under front right and crank it down on top of it...that would tweak the beds in essentially the same manner. I just installed this a couple weeks ago...seriously don’t want to start over. Yeah, any diagrams of detailed pictures would be great when I get around to starting from scratch again.
 

TerryH

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#8
Interesting, having some adjustable feet would be glorious! I’d be interested how it all connects at bottom. These 4 adjustable bolts are not connected in any way to bottom of lathe? What is the raw steel bar running along bottom of lathe in 2nd to last picture? I would guess you still have it (the lathe) bolted down to table top, this just extends that connection? I would guess a much simplified version would be to loosen my 2 mounting bolts and cram a shim under front right and crank it down on top of it...that would tweak the beds in essentially the same manner. I just installed this a couple weeks ago...seriously don’t want to start over. Yeah, any diagrams of detailed pictures would be great when I get around to starting from scratch again.
The leveling bolts are not connected to the lathe bed. They bear on the 1/4" plate on the bottom of the feet. There is a 4 1/2" x 1/2" thru bolt going through the original mounting hole and extending all the way thru the bench top.

You can use shims to accomplish the same result but it will be a trial and error operation.

I'll make a detailed post later today.

 

GrayTech

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#9
Personally I would forget the level and just shim it until it stops cutting tapers. Once that's done level by using the table feet.

Sent from my H3123 using Tapatalk
 

RJSakowski

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#10
I have the 602 lathe and face the same issues. I plan to put 5" x 7" x 7/8" steel risers under the feet. The primary reason for this is for better access to the lower motor mounts. As shipped it isn't possible to service the motor without lifting the lathe which will destroy any alignment. The additional clearance under the bed for cleanout will be nice too. Just need to get the tanks filled so I can make the rough cuts.

My stand is made from steel with a full width section of 7" channel running under the lathe and covered with a sheet metal skin. The risers will placed on top of the chip pan and bolted through to the channel and should provide a solid base for the lathe mount. Terry's alignment method would be a good addition.

My stand has leveling feet, using the same concept. The issue with them is they tend to walk on the floor when trying to make an adjustment. OK for rough adjustment but it sucks when trying to get those last few thousandths. I also have a typical four point alignment and have decided to go to three points for the stand. This will prevent twisting the stand and adding stresses which telegraph up to the lathe mount. The third alignment point will be under the tailstock and the original corner feet on the right end will be adjusted for light contact to prevent any rocking of the stand.
 

ttabbal

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#11
Keep in mind, leveling isn't a one time deal. Over time you have to adjust it. So shims can be a bit of a pain. With adjustment bolts it's much easier, which means I'm more likely to do it.
 

John281

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#12
Terry, that's a great addition to the lathe. I'm curious how much twist you found. From what I gather, eliminating twist is more important than being level and it may take some back and forth to eliminate twist and have the ways level in two directions. I think that's where your setup will really simplify the process.
As RJ mentioned above, the lower, right motor mount nut is inaccessible (on the G0752) with the lathe sitting on the chip tray. By elevating the lathe slightly, I wonder if it's now possible to access that nut. That would be another bonus.
 

RJSakowski

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#13
The 602 has an adjustable headstock. The mounting holes in the headstock are slightly oversized to allow the adjustment as are the grooves for the V ways. There are two setscrews (412 in the parts diagram) on the backside of the headstock which work against the mounting studs to facilitate movement of the headstock in a controlled fashion.

Caution should be used in making this adjustment as it also affects the ability to cut a flat face. I would check that before determining that an adjustment was required. This can easily be done by mounting the faceplate and installing a 1/2 x 1" bolt and nut in one of the faceplate slots. Position the bolt to the outside of the slot for maximum sensitivity. I domed the head of the bolt and polished it to make easier for a test indicator to ride on the head and for more reproducible measurements.

To use, I set up a test indicator on the cross slide positioned so that it can sweep ther face of the bolt when the faceplate is positioned with the bolt nearest the front and horizontal to the spindle axis. Rock the faceplate to hind the point of greatest deflection of the test indicator. Move the cross slide slightly to find the point of greatest deflection. Zero the indicator. Rotate the faceplate 180º and repeat the process. If the reading is zero, the cross slide ways are perpendicular to the spindle axis and a facing operation will yield a flat face. If the deflection is greater at the rear, a concave face will be cut and if is less a convex face will be cut. The only adjustment possible on the 602 for this is rotation of the headstock. Because of that, I would not recommend using this adjustment to correct for turning a taper. I made that mistake early on correcting a taper turning issue and ended up cutting a convex face.
Some machinists advocate cutting a slightly concave face to prevent a part from rocking when placed on end on a flat surface. I do not. I will check my cross slide perpendicularity first and then deal with any taper turning ossues as being caused by bed twist.
 

TerryH

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#14
Terry, that's a great addition to the lathe. I'm curious how much twist you found. From what I gather, eliminating twist is more important than being level and it may take some back and forth to eliminate twist and have the ways level in two directions. I think that's where your setup will really simplify the process.
As RJ mentioned above, the lower, right motor mount nut is inaccessible (on the G0752) with the lathe sitting on the chip tray. By elevating the lathe slightly, I wonder if it's now possible to access that nut. That would be another bonus.
Thanks John. There was minimal twist. I did not measure it before. In my situation the back of the bench was slightly lower so all the adjustment was done with the rear levelers. I'm not sure about access to that bolt but I'll check it when I get home. I definitely like the additional space under the bed one way or the other. Should make cleaning much easier.

I posted a thread with the leveling plate information...

https://www.hobby-machinist.com/threads/lathe-leveling-parallelism-using-shop-made-levelers.72014/
 

RJSakowski

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#15
Terry, that's a great addition to the lathe. I'm curious how much twist you found. From what I gather, eliminating twist is more important than being level and it may take some back and forth to eliminate twist and have the ways level in two directions. I think that's where your setup will really simplify the process.
As RJ mentioned above, the lower, right motor mount nut is inaccessible (on the G0752) with the lathe sitting on the chip tray. By elevating the lathe slightly, I wonder if it's now possible to access that nut. That would be another bonus.
Yes, you should be able to access the motor mounting bolts. Because of the fins on the motor housing, using a socket wrench with even a 1/4" drive isn't possible.

A box or open end wrench can access from the side but there is limited range of motion. At least 40º is needed for a 12 pt. wrench. The near side side are no problem but the inside nuts would require removal of the splash guard to access them.

By raising the lathe by 3/4 or 7/8", a wobble extension or a flexible drive could be used. Even then, the clearance is such that a very shallow socket would be needed. It is also likely that the motor cooling fins may have to be bent or cut away for access.
 

GunsOfNavarone

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#16
Terry, that's a great addition to the lathe. I'm curious how much twist you found. From what I gather, eliminating twist is more important than being level and it may take some back and forth to eliminate twist and have the ways level in two directions. I think that's where your setup will really simplify the process.
As RJ mentioned above, the lower, right motor mount nut is inaccessible (on the G0752) with the lathe sitting on the chip tray. By elevating the lathe slightly, I wonder if it's now possible to access that nut. That would be another bonus.
I'm seeing that too. I take out some twist, need to work on leveling and vice versa. When I though it would be difficult to take out twist...HA!, more the contrary. Every time I touch about anything, the twist changes. It feels like I am adjusting, calibrating and leveling more than actually making anything. If it wasn't for the test barbell, I wouldn't be making any chips!
 

TerryH

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#17
Terry, that's a great addition to the lathe. I'm curious how much twist you found. From what I gather, eliminating twist is more important than being level and it may take some back and forth to eliminate twist and have the ways level in two directions. I think that's where your setup will really simplify the process.
As RJ mentioned above, the lower, right motor mount nut is inaccessible (on the G0752) with the lathe sitting on the chip tray. By elevating the lathe slightly, I wonder if it's now possible to access that nut. That would be another bonus.
The nut is easily accessible now. Hope I don't need to access it any time soon though. :grin:
 
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