Q About Uneven Travel On Cross Slide Table

[auto.pilot]

I just purchased the Grizzly cross-slide table shown in this link:
http://www.grizzly.com/products/6-x-18-1-2-Compound-Slide-Table/G8750

I'm using it on a wood lathe and have attached a poor picture. In theory, this set-up should allow me to make a very flat and uniform cut across my workpiece, which is 7" deep. My problem is that the travel is not uniform. Turning the hand wheel, the table veers slightly inward, then back out. The result is a wobble and zig-zag pattern on my part. I initially dismantled the table to removed the packing grease. Nothing appears to be bent.
Wondering if it's possible to make some gib adjustments to fix it. I have almost zero experience. Appreciate any and all thoughts.

Thanks

Jim

 

[David VanNorman]

Your tool should be on center. I just looked at your picture. That tool that is hanging out is your problem. Can you set that table where you can have your tooling go strait at the piece you are turning.

 

[auto.pilot]

the picture is not the full or correct set up. The tool is actually on center (I think).

 

[brino]

I gotta agree with David......

It looks like:
1) your tool is well below centre(though maybe it's just the angle of the picture?!?!), and
2) you are using a long boring bar when a tool post and short, straight tool would be much more rigid

-brino

EDIT: another thought....with your picture I cannot tell, is that a solid cylinder or just a thin walled shell? If the latter, it could be flexing under the tool pressure.

 

[T Bredehoft]

From your description it's possible that as you turn the crank you inadvertently put pressure, first on one side, then the other, giving a in and out cut.

 

[John Hasler]

I have what appears to be another of those tables. When I first tried to use it for milling I got a .1" pattern on everything I milled due to the table rocking on the ways as I turned the cranks. I ended up scraping the ways, replacing the steel gibs with brass ones, and redesigning the bearings for the screws.

 

[chips&more]

Don’t think the tool being off of center is your problem. I think it’s all in your translation stage (TS) or loose boring bar or tool bit. Grab the boring bar and see if you have any movement from it or the TS when you apply a slight force to it. Any play in that thing will telegraph into your work. When operating/using, a constant hand wheel pressure is a good thing. A constant force on direction on the TS is another good thing. And also adjusting the gibs on the TS is also good. Are your head stock bearings OK?…Dave

 

[hman]

If the pattern of hills and valleys on the wood is about the same pitch as your lead screw, I'd say it's either a loose gib(s), or possibly the rigidity of how the cross slide table is mounted to the lathe. Try watching the end of your tool (no workpiece in the chuck) as you crank the slide. You can also grasp the ends of the slide and try to move it around. Any wiggle will show up on the workpiece.

I downloaded the instructions for the table. They do include a procedure for adjusting the gib screws, but they're kinda sparse. I adjust each screw by running it in and out near its inward limit, so I can see/feel where it bottoms out. Then loosen by a slight amount (think 1 hour on a clock face) and carefully hold it in place while tightening the nut. Do all the screws on one axis this way, then check that the crank doesn't bind. If so, one or more are too tight. After adjusting both X and Y, grasp and try to move the table (twisting around the Z axis). If it moves, look carefully and decide which axis is loose, then re-adjust accordingly. After you've done this whole exercise a couple times, it becomes easier to judge how tightly to set the screws, etc.

If this does not solve the problem, check the mounting of the slide table.

 

[RJSakowski]

If you are getting a cyclic pattern, it is most likely caused by loose ways combined with sideways forces when turning the crank. A small side movement will be amplified by the 7" extension of your tool. Hopefully the ways are consistent enough that you can tighten them without binding at some particular point. As chips&more said consistent hand wheel force is a good thing. You might consider driving the table with a cordless drill. That way the force will be balanced. If possible lock the other axis down to prevent it moving. Otherwise tighten those ways as well.

Bob

 

[mike837go]

As the owner of a brand new Grizzly brand tool, I strongly advise the following:
1) Disassemble the whole thing and remove all the packing grease from all parts
2) Remove all the gib screws and clean all the sprue from the tips so that they all have a round nose
3) Run an oil stone over the gibs to remove all burrs. Especially at the ends.
4) Slowly and carefully reassemble with light machine oil. Start from the bottom and work upwards. Watch the orientation of the gibs
5) Tighten the gib screws one at time. Each one should be the same load as if you are using a feeler gauge. Zero clearance without interference.

Then see how the thing performs.

Then go back and tram it.

You'll be good to go after that.