[TXFred]

I want to surface grind the table on my mill, and I am trying to come up with a good way to do this.

What I have been contemplating is getting a cup style grinding wheel and mounting it in the mill's spindle. I would then put the mill's head slightly out of tram in X, so that only one side of the grinding cup would contact the table.

Does this seem like a good plan, or am I setting myself up to mess up my table?

What is the best grinding material for cast iron?

Is there a better way to do this, short of taking the table off and putting it on a real surface grinder?

Fred

[luv2ride]

Ooh, this is a good question and I am very interested also.

[neilw20]

Unless the gibs and slides are perfect you will end up with a roller coaster surface. Put it on a surface grinder, or live with the scratches.
This is the limit of my machine repairing itself.
SX3 Spindle nose grinding pictures by neilw20_2008 - Photobucket

[luv2ride]

Unless the gibs and slides are perfect you will end up with a roller coaster surface. Put it on a surface grinder, or live with the scratches.
This is the limit of my machine repairing itself.
SX3 Spindle nose grinding pictures by neilw20_2008 - Photobucket

I was thinking something similar but if the grinder is in the same place and the gibs are tight, wouldn't it be flat? Probably wishful thinking, nothing is ever that easy.

[LongRat]

If you put the mill head slightly out of tram in X you will by definition not produce a flat surface on the table, but a dished one in the Y direction. No matter what you do it is going to be difficult to hit the entire table surface with the mill. I think either a bigger mill or (better) a proper surface grinder would be required.

[TXFred]

If you put the mill head slightly out of tram in X you will by definition not produce a flat surface on the table, but a dished one in the Y direction. No matter what you do it is going to be difficult to hit the entire table surface with the mill. I think either a bigger mill or (better) a proper surface grinder would be required.

When surface grinding, you make many passes with small stepovers. That would eliminate the dishing.

[neilw20]

That is fine, but on most machines you can't get the center of the spindle outside of table area, and you must be able to at least do that.

[QSPSB]

Just a thought... Couldn't you just purchase a new table. Then just clamp it down to a tooling plate that can be moved around.. or better yet.. do you have a cross slide table you could clamp down and go that route...

But then again... Z-axis height may pose to be a problem as well

Just a thought

[headsmess]

hows about the old tried and true lap-lap?

sheet of fine emery, same heavy duty plate glass, patience, and some kero? or screw the emery and just smear paste on the glass...

what you CANT control is tapering. keeping the thickness the same all the way down the length of the table. can get pretty darned close though

*sighs and shakes head over accident years ago involving end mill and table that still bears the (deep) scar*

[M250cnc]

That is fine, but on most machines you can't get the center of the spindle outside of table area, and you must be able to at least do that.

Quite right.

So why do you need to grind the table ?

Phil

[TXFred]

Here's why I need to grind it. I took a dial indicator and checked the height at positions along the table. I get a variation of 0.0016" over the entire table. I would like to get that number under 0.0005"



(I had to put that in as an image file because if I posted it as text, the spacing would get messed up.)

I do have access to a surface grinder, so I am going to use that with some fixtures to get the table level on the magnetic chuck. I was hoping to find a good way to use the mill to grind the table, but as pointed out, there are many obstacles to overcome.

Cheers,
Frederic

[M250cnc]

Frederic,

I think it will be very difficult to take of the table and set it up to reproduce those errors to then grind the table flat.

You may do even more harm to the flatness and reminds me of when i had to try and convince my boss that the surface grinder i was using was not grinding flat.

As you know you can grind the chuck on a surface grinder so in theory it would be flat, WRONG you grind it parallel to any errors inherent in the ways and if these are worn badly then the table is not flat.

You can prove this yourself with a quality parallel on the table run the DTI over it, any deviation is coming from the ways as you are working from a known flat surface.

The upshot is i got a brand new machine.

Phil

[Boots]

We had our Milling table Machined Flat in a Bridge Mill at a local Machine Shop. You don't really need to grind it to get it flat and smooth but you will need to take it off the machine to do it properly. Canting the head will make the table wavy as mentioned above no matter how slight the stepover and when you move the table from one side to the other in the X it will droop from lack of support resulting in the removal of too much material on the ends. No,,, the Table needs to be supported properly and clamped in a "Relaxed State" with no tortion or twist. We only paid 175.00 to have it machined. They took off .025 with a 12 in. Face Mill. Looks like a brand new table.