Grizzly mini, strange table flatness issues.

[Cowbell]

As I've started delving more into precision work, I've run into some real strange issues with the flatness/alignment of my table.

To start with, I trammed the thing using the standard technique of sticking a dial indicator on the spindle and rotating in between extremes of the table, tapping the vertical column to get it perfectly aligned.



My dial indicator has hash marks of 0.0005", and after endless tweaking and checking, I got it so that it ready to <= 1 hash mark on each end of the rotation. As far as my beginner's eye can tell, it's perfectly trammed.

Then I mounted the dial indicator directly under the spindle so that X motion of the table was perpendicular to the direction of the indicator head to eliminate push/pull drag. What I find here is extremely puzzling.

As I travel over the RIGHT side of the table (that is, from the middle out to the right end) there is extremely little deviation in the indicator. <= 1 hash mark. However, as I travel over the LEFT side of the table (from the middle to the left end) the deviation is large and seemingly linear. Over the 5-6" of travel, the deviation is well over 0.003". You can actually see the dial smoothly moving as you turn the feedscrew.



This really puzzles me.

a.) if I can get the reading during tramming to be pretty much spot on, why would I see a difference as the table travels?

b.) why would one half of the table appear to be nearly perfectly flat, while the other half deviates so sharply?

About the best I can come up with is that the table isn't sitting in it's grooves cleanly and as it crosses the midpoint, it tilts ever so slightly. But I can't feel this, and putting weight on the left end of the table doesn't seem to change things at all.


What goes on here? Is this kind of thing normal on such a low end mill? What options do I have? It would suck to have to restrict usage of my mill to half the table

[phil burman]

a) When you tram it you are only checking that the spindle axis is at 90 degrees to an imaginary plane that passes through the points on the table touched by the indicator. Try the same test at different positions along the x axis.

b) It may not have been machined flat or it may have warped after machining. Use a straight edge of known quality to check the flatness of the table.

Here's a test procedure with acceptance criteria that you may find interesting/useful.

http://www.tormach.com/document_libr...C_addendum.pdf

Regards
Phil

As
This really puzzles me.

a.) if I can get the reading during tramming to be pretty much spot on, why would I see a difference as the table travels?

b.) why would one half of the table appear to be nearly perfectly flat, while the other half deviates so sharply?

[cncuser1]

check the gibbs to make sure that they are not rubbing where they are not supposed to.

I found that my gibbs were installed crooked and rubbed in the wrong places, causing friction, in an extreme case they may cause movement too.

[acondit]

Cowbell,

I found that on my Mill-Drill when the table was all the way to the right, the weight pulling down lifted the table about 0.001 under the spindle. It actually raised it about 0.001" in the 4" width of the vise. If I adjusted the gibs enough to stop that it was too tight to use.

I repositioned my vise to the middle of the table and that helped with thing being machined in the vise.

Alan

[OwenL]

Table sag from the weight all the way to the oposite side and loose gibs.
Gib keys that are not true lifting the table as they travel.
Table actually not ground flat and true [thicker at one end v/s the other]

just throwing out things to check for.
Owen

[mjarus]

Well I just experienced the EXACT same thing today! I finally got around to tramming my table. Fiddled with it forever. Then I ran the X axis with the indicator in the spindle. Same problem except I get .004 on the left side instead of .003. I have a HF X2.

So, really miffed I came inside to search the forums and lo and behold same problem by someone else (so if I am crazy I have company)!

On another note I have adjusted my gibs so I don't think that is a cause... the X-axis would actually move if you shook it with your hand, I adjusted the gibs and now it is fine.

I think it would be odd that 2 machines would be out by almost the same amount in the same area if it were just an issue of a crap ground table. Maybe they made ours back to back in a training class?!

Anyways, I will give anything a shot. If I can't figure it out, back to HF I go...

mjarus.

[50062040]

what you just proved marjus/cowbell was the the t slot or edge which the dial indicator was touching while doing measurements is not parallel to travel direction.

i dont know if this is common but it shouldnt be a problem.

[Cowbell]

I'm not sure I follow. Assuming, under ideal circumstances that a table is perfectly flat, it shouldn't matter if the slots are parallel to travel direction. The table should be able to move in any arbitrary direction in XY and the plane of it's surface shouldn't change at all.

Or do you mean that the non-paralellism is the result of the table being twisted or otherwise distorted around X?

Either way, if you mount something on the "good" half, you get flat horizontal travel in both X and Y. If you mount it on the "bad" half, you get large, linear divergence in Z (height) over 5-6 inches.

The more I think about it, I just can't see what could cause this except for a non-flat table.

[mjarus]

i dont know if this is common but it shouldnt be a problem.

Could you explain more please? Doesn't that mean that, for example, if you place a piece on the table that is square to the table it will cut deeper on the left hand side of the piece than the right?

As an added note I checked the table with a long parallel and it seems flat. I just checked it by the looking for light underneath the edge method. Probably not the most accurate, but it is all I could think of. I figured I should be able to see some light under a .004" gap. Maybe not.

Any other ideas?

mjarus.

[mjarus]

Ahh posted the same time as cowbell...

Anywho, cowbell... I tried to check for table flatness. See above post. Looked ok.

mjarus.

[Cowbell]

I just checked with paralells too. They do indeed appear flat. But, running the table for the Nth time, the results are the same. <= 0.0005" over the 4-5 inches of travel on the right side of the table. > 0.003" over the 4-5 inches of the left side of the table.

Also - when the dial is at maximum error, I find that I can't even budge the dial more than 0.0005" by pulling up/pushing down on the table by hand. To me this implies the gibs/rails/whatever are highly snug. Yet the deflection is still here.

Man. Very confusing.

[50062040]

apologies, i assumed the readings were from the sides of the t slot