KGS 200 Table Lift

[electrosteam]

Thanks to all the advice received here, my SG has been used successfully on its first 'paid job'.
The job was to improve the finish on a tool for shaping the inside curve of a wooden bowl on a wood lathe.
The material is tool steel about 6" long, 2" wide, 7/16" thick, with a long shaft welded to the end for the handle.
The job was placed across the chuck because of the long shaft.

If the table is fully extended towards the operator, and left there for some time to ensure thermal equilibrium, the first subsequent cut is quite heavy, reducing as the table traverses away from the operator.

The appearance is that of a table that has tilted slightly upwards on the side away from the operator.
Note that the table was never moved outside its nominal working envelope.

The slides are inverted 'V' lined with plastic with a manual oil feed, and the machine has had an unknown industrial life.

Is this effect normal, indicative of some wear, or caused by something else ?

Obviously, the table will in future only be left in the fully retracted position.
John

 

[Bob Korves]

The table needs to cross feed for the grinder to do its job. The weight of the overhanging handle on the front (operator) side may have been tilting your table or chuck and causing the problems you were having. Also, your chuck may not be flat in relation to the reciprocating and cross feed motions. Test with an accurate test indicator mounted to the wheel head and indicating the chuck. Ideally the indicator needle will not move anywhere the indicator moves to on the chuck.

 

[electrosteam]

Bob,
If the chuck was previously skimmed with the table lifting/dropping etc, then any test with a DTI off the wheel head will simply follow the grind and show zero problem.

I think I need to do test pieces and measure them on the granite.

Note that I think it is a 5 - 10 micron problem that would not normally cause an issue with any parts I am likely to process.
It is the observing, analyzing, allowing for and, perhaps, correction of the problem that fascinates me.
The subtle variations in cut at times makes me very curious as to what is really going on.

A minor correction, the 'V' ways are not inverted.
Thanks for all the comments,
John.

 

[electrosteam]

Further attempts to get the wooden bowl tool looking good were frustrating.
In addition to the table lift issue, I am getting odd cycles of heavy cut in the middle of a previously finished surface.
One credible hypothesis is that this could be either dirt in the V ways or dirt in the table rollers occasionally lifting the saddle or table.

The table rollers have been fully cleaned and lubricated with a lanolin based product, so the next refurbishment job looks like lifting the saddle off the V ways for inspection and cleaning.
I have no idea on how to go about removing any wear effects, if found.

Is it likely that a slightly heavy cut would produce sufficient local heating that a subsequent cut along the same path would provide more heat, causing a heavier cut, and so on.
Should I defer all machine investigations until after I have got the coolant system running ?

John

 

[electrosteam]

Well, I finally got the customer job delivered, and complementary he was too.

Then I added a 1/10th thou" DTI to the mix to measure a couple of things.

With the DTI on the mast and touching a straight bar on the cross-slide (carriage ?), with the cross-slide at any stationary position, extreme up/down force applied manually to the handles showed absolutely no movement on the DTI.
The conclusion is that the cr0ss-slide is not lifting.

With the DTI on the cross-slide and touching the chuck, rolling the chuck back-and-forth showed no particular lift, only a slow drift due to the chuck not being skimmed, and bumps due to the stylus dragging along the chuck surface.
The conclusion is that the table is not lifting.

So, back to operator error.
Too much heat going into the job (dry grinding) and loss of part geometry awareness.
I suspect that the first dig-in due to the heat left a step for the subsequent cycle to encounter, which then looks worse, and so on.

This gets back to a lack of opportunity to observe, and talk to, other grinding hands doing their job.
Learning in isolation is frustrating, but with the help of you guys and gals, I am sure I can get there.

In future, any dig-in will be left to cool without touching the settings.
Then the re-start will be made from the opposite side.
And, the coolant system will be re-furbished and commissioned ASAP.

John

 

[Bob Korves]

Have you had the chuck off? Sometimes there is corrosion that grows under the chuck and it moves around because of it. If found, a partial grind of the table with the wheel to establish a solid mounting surface, followed by similar grind to the bottom of the chuck, and then remounting the chuck with grease or other rust retardant to keep it from reoccurring will give the chuck a firm foundation.