Milling Machine DRO

[YYCHM]

@YYCHM i‘ve been wondering if a DRO makes the round column issue disappear. What’s your experience?

Disappear in what way?

 

[Johnwa]

I assume that if you have a position that you can re-zero the DRO to, then losing position when raising and lowering the head wouldn’t be an issue. It would be a bit of a PITA to have to re-zero though.

 

[PeterT]

I don't think so John. The work is DRO registered in XY but the mill head has no idea where it is relative to spindle axis once its been raised or lowered around the post & potentially swiveled round it. That's why the stabilizing arms or other mechanical fixes.

But you know.... assuming the head can only drift by pivoting around the post (vs any nod or tram change as a function of being raised or lowered) - if you could hook up a sensitive 'radial' displacement DRO so the mill head knows where it was relative to the post, that might work. Click zero/null before raising head, raise head, display says drifted 1.2345 degrees. This time, rather than kick the cat, rotate back to 0.000 readout, lock head. Theoretically its back inline relative to table XY work which hasn't changed. The trick is you need some kind of zero reference encoder strip up the entire column that wont interfere with normal movement.

 

[YYCHM]

I assume that if you have a position that you can re-zero the DRO to, then losing position when raising and lowering the head wouldn’t be an issue. It would be a bit of a PITA to have to re-zero though.

No, the DRO doesn't help with the spindle changing X/Y location when the head is raised or lowered.

 

[Tomc938]

@YYCHM i‘ve been wondering if a DRO makes the round column issue disappear. What’s your experience?

I'm afraid not. The DRO measures travel along a specific axis. X and Y and Z. You can set up a part in the mill, zero the DRO in all three axis. Then you can turn the head 360" to the back side of the mill. The X,Y and Z points will not change. All will still be 0. But in this configuration you will not get much milling done!

Now if someone could come up with a very accurate rotational sensor, you could get back to where you started within the error of the sensor. (Hmm. Maybe that would be a good project!)

 

[Tomc938]

So you can purchase rotational sensors. Might be interesting to try. There are several at Digi-key in the $50-80 range.

They say they are accurate to 20 minutes of arc - at 500 rpm. (I'm guessing most of us would not move the head at anything near that speed) so it would be interesting to see how that would translate into accuracy on the table. I guess you would need a way to move the head around the column with reasonable accuracy.

 

[Tomc938]

So I decided to do the math. Assuming I still remember how, 20' = 0.3333 degrees. The spacing on my mill from quill to column is 400 mm - you would have to add column and quill radius to get to the centre points. I didn't.

tan (0.33333)=O/400. Do the math (again, assuming I did it right) and the error could be 2 mm. I guess the question would be: Can you zero the rotational sensor and return it to zero with any accuracy?

Now I should go do what I should be doing. ;o)

 

[PeterT]

Ya I suspect its a no-go for reasons you mention. The device would have to be highly accurate (expensive) & even so, the radial distance from post center to quill center exaggerates the discrepancy. Every time I get a bright idea about how to remedy the round column positioning issue, I realize someone else has already thought about & extinguished it. Or worse yet I realize its the same idea I had 4 years ago & already forgot about it so it seems new again. Sorry round posters, the mechanical alignment constraints are probably still the way to go.

Or... a graduated series of long center finders. (There I go again )

 

[DPittman]

Or worse yet I realize its the same idea I had 4 years ago & already forgot about it so it seems new again.

Hee hee, I can TOTALLY relate to that!

 

[Tom Kitta]

They sadly do not seem to make a square column more expensive drill mill. The RF40 / RF45 are both gear head drilling machines. RF35 is a round column mini baby radial arm drill.

There is no RF35 machine that would be just like RF30/31 but with a square column and step pulley.

Gear heads are pita as you cannot run them fast. Top speed of 1500 rpm may be only exceeded by a bit, maybe 1800 tops. That is ... kind of slow.

 

[Dusty]

I don't think so John. The work is DRO registered in XY but the mill head has no idea where it is relative to spindle axis once its been raised or lowered around the post & potentially swiveled round it. That's why the stabilizing arms or other mechanical fixes.

But you know.... assuming the head can only drift by pivoting around the post (vs any nod or tram change as a function of being raised or lowered) - if you could hook up a sensitive 'radial' displacement DRO so the mill head knows where it was relative to the post, that might work. Click zero/null before raising head, raise head, display says drifted 1.2345 degrees. This time, rather than kick the cat, rotate back to 0.000 readout, lock head. Theoretically its back inline relative to table XY work which hasn't changed. The trick is you need some kind of zero reference encoder strip up the entire column that wont interfere with normal movement.

Looking at Peter's photo, lets say you could scribe a true line up and down the column to the right side when facing the mill. True the mill head then put a matching mark to marry up with the column scribe. As long as the head mark matches the scribe you should be in business whenever the head is raised or lowered. Or did I miss something with this thinking???

Of course the column and spindle need be on the same plane which one assumes they are from factory.

 

[DPittman]

Looking at Peter's photo, lets say you could scribe a true line up and down the column to the right side when facing the mill. True the mill head then put a matching mark to marry up with the column scribe. As long as the head mark matches the scribe you should be in business whenever the head is raised or lowered. Or did I miss something with this thinking???

Of course the column and spindle need be on the same plane which one assumes they are from factory.

That would be accurate enough for a drill press but not a milling machine... at least in my opinion.

 

[Johnwa]

I’m not sure that I agree. For example if you always re-zero to a corner of your workpiece then any x/y dimension from that corner should be correct. Even if you rotate the head once you re-zero it should work. Am I missing something?

 

[Dusty]

That would be accurate enough for a drill press but not a milling machine... at least in my opinion.

We've all seen the home made remedies to cure the round column mill raise/lower issue. In my view they are basically identical as to what I suggest for anyone without DRO equipment and running manual. What say you!

I believe this is what Johnwa means? I don't own a round column so someone would need advise me.

 

[Janger]

I think you're right Johnwa. As long as you don't move the part and the part zero is a good place to measure off of. You need a DRO or handwheels you can set the position (ie zero positon) for it to be convenient. But even without adjustable position handwheels if you kept track of the Delta X, Y, and Z it could still work. a PITA but possible. I think that would be easier than trying to get the head angle back to exactly where it was. But I don't have a round column mill so others with experience can set us straight. The video Bill shared makes it look pretty easy. Maybe the round column problem is not really much of an issue?

 

[Tomc938]

I’m not sure that I agree. For example if you always re-zero to a corner of your workpiece then any x/y dimension from that corner should be correct. Even if you rotate the head once you re-zero it should work. Am I missing something?

I believe you are correct. With the added step of re-zeroing to the same corner, I believe you would have the same starting reference point - within the accuracy of your edge finding. I like it!

 

[PeterT]

But you don't need a DRO for that. You could attach 123 block on table, zero quill with edge finder. Raise head up column, now its rotated somewhere about the post. But you still have to mate edge finder to 123 block assuming the prior DRO setup was to be preserved? The inconvenient part is the head is elevated or different tool in spindle so that it might be more difficult to reach the block. Unless I'm missing your point.

 

[YYCHM]

This is the sort of thing I have run into.

Have found the center of something I need to drill with a center finder, I zero my DRO. Now I go to mount the drill bit only to find that the work piece is too tall to accommodate the drill bit. The only solution is to raise the head. So I raise the head to accommodate the drill bit but now my zero might be out and I have to relocate zero with the center finder. The head is now too high to accommodate milling and have to lower it again and go through the same zeroing process. PITA. Doesn't happen often but does occur from time to time. Getting a stubby set of drill bits has eliminate a lot of that nonsense but not always.

 

[Dusty]

This is the sort of thing I have run into.

Have found the center of something I need to drill with a center finder, I zero my DRO. Now I go to mount the drill bit only to find that the work piece is too tall to accommodate the drill bit. The only solution is to raise the head. So I raise the head to accommodate the drill bit but now my zero might be out and I have to relocate zero with the center finder. The head is now too high to accommodate milling and have to lower it again and go through the same zeroing process. PITA. Doesn't happen often but does occur from time to time. Getting a stubby set of drill bits has eliminate a lot of that nonsense but not always.

Hey Craig, like having a pimple on one's rear and every time you move its a pain!

 

[Johnwa]

This is the sort of thing I have run into.

So I raise the head to accommodate the drill bit but now my zero might be out and I have to relocate zer The head is now too high to accommodate milling and have to lower it again and go through the same zeroing process. PITA. .

I see where that would be another problem!