[sheldonlathe] Adding DRO to my SB vertical mill


Scott McGrath
 

All the chinese glass scales ive used have been more or less ok and meet accuracy specs based on the standards that i have (a set of gauge blocks) prefer the US made acu-rite but those are 10x the price.

As to touch vs button.   What the heck were designers thinking touch screens with lubricant and swarf covered hands….    Buttons are what I recommend and use.

The only real challenge is mounting scales absolutely parallel to the ways to minimize cosine error as much as possible.


From: sheldonlathe@groups.io <sheldonlathe@groups.io> on behalf of Nick Andrews via groups.io <nickjandrews@...>
Sent: Sunday, January 2, 2022 11:08:56 PM
To: sheldonlathe@groups.io <sheldonlathe@groups.io>; SouthBendLathe@groups.io <SouthBendLathe@groups.io>
Subject: [sheldonlathe] Adding DRO to my SB vertical mill
 
So I'm thinking that while the challenge of full manual operation with the dials can be a lot of fun, sometimes the added features of a DRO would make life a whole lot easier.  But I don't want to spend more than I paid for the machine,  so am thinking of trying one of the $300-600 units.  Anyone have advice on which might be good or more important,  to avoid?  And if the tft touch screen type is more usable than the old style discrete buttons type?


Rogan Creswick
 

The only real challenge is mounting scales absolutely parallel to the ways to minimize cosine error as much as possible.

I've seen this stated in a few places, and I don't understand the justification.  I do understand wanting everything to be perfect, but I don't believe spending hours tapping scales in and running indicators around to get with 1-2 thou is in any way worth the time and frustration.

First off, the surface of the scale that I see people measure off of is an aluminum extrusion that contains the actual scale.  We don't know the precision with which that scale is mounted inside the extrusion, and I'm not convinced that the extrusion is guaranteed to be within even +/- 0.005" of the extrusion.

But let's set that aside -- and assume that these $200 scales are made perfectly -- and run the numbers for a 12" scale (intended to be representative of what you'd put on a bridgeport clone y-axis).

If the scale is not perfectly aligned with the axis of motion, we have a right triangle where the hypotenuse is 12" and the short leg is the error from one end to the other.  Let's assume that error is an egregious 0.125". The other leg of the triangle is given by the Pythagorean formula:

adj = sqrt(hypo ^2 - opposite ^2)

adj = sqrt(144 - 0.015625)

adj = 11.9993489

So, *if* you manage to mount a 12" scale with a full 1/8" of error, it looks like the total error in reading across that 12" scale is less than 7 tenths.

Assume we get within a 1/32" (which I think is reasonable using some care and a machinist scale), then that error drops to 0.000040". That's *much* better than the scales are actually rated for at this price point.

--Rogan


On Mon, Jan 3, 2022 at 4:24 AM Scott McGrath <scott@...> wrote:
All the chinese glass scales ive used have been more or less ok and meet accuracy specs based on the standards that i have (a set of gauge blocks) prefer the US made acu-rite but those are 10x the price.

As to touch vs button.   What the heck were designers thinking touch screens with lubricant and swarf covered hands….    Buttons are what I recommend and use.

The only real challenge is mounting scales absolutely parallel to the ways to minimize cosine error as much as possible.

From: sheldonlathe@groups.io <sheldonlathe@groups.io> on behalf of Nick Andrews via groups.io <nickjandrews=gmail.com@groups.io>
Sent: Sunday, January 2, 2022 11:08:56 PM
To: sheldonlathe@groups.io <sheldonlathe@groups.io>; SouthBendLathe@groups.io <SouthBendLathe@groups.io>
Subject: [sheldonlathe] Adding DRO to my SB vertical mill
 
So I'm thinking that while the challenge of full manual operation with the dials can be a lot of fun, sometimes the added features of a DRO would make life a whole lot easier.  But I don't want to spend more than I paid for the machine,  so am thinking of trying one of the $300-600 units.  Anyone have advice on which might be good or more important,  to avoid?  And if the tft touch screen type is more usable than the old style discrete buttons type?


John
 

Precisely!

Thanks Rogan

Happy New Year

John

 

From: SouthBendLathe@groups.io <SouthBendLathe@groups.io> On Behalf Of Rogan Creswick
Sent: 04 January 2022 04:02
To: SouthBendLathe@groups.io
Subject: Re: [SouthBendLathe] [sheldonlathe] Adding DRO to my SB vertical mill

 

The only real challenge is mounting scales absolutely parallel to the ways to minimize cosine error as much as possible.

 

I've seen this stated in a few places, and I don't understand the justification.  I do understand wanting everything to be perfect, but I don't believe spending hours tapping scales in and running indicators around to get with 1-2 thou is in any way worth the time and frustration.

 

First off, the surface of the scale that I see people measure off of is an aluminum extrusion that contains the actual scale.  We don't know the precision with which that scale is mounted inside the extrusion, and I'm not convinced that the extrusion is guaranteed to be within even +/- 0.005" of the extrusion.

 

But let's set that aside -- and assume that these $200 scales are made perfectly -- and run the numbers for a 12" scale (intended to be representative of what you'd put on a bridgeport clone y-axis).

 

If the scale is not perfectly aligned with the axis of motion, we have a right triangle where the hypotenuse is 12" and the short leg is the error from one end to the other.  Let's assume that error is an egregious 0.125". The other leg of the triangle is given by the Pythagorean formula:

 

adj = sqrt(hypo ^2 - opposite ^2)

 

adj = sqrt(144 - 0.015625)

 

adj = 11.9993489

 

So, *if* you manage to mount a 12" scale with a full 1/8" of error, it looks like the total error in reading across that 12" scale is less than 7 tenths.

 

Assume we get within a 1/32" (which I think is reasonable using some care and a machinist scale), then that error drops to 0.000040". That's *much* better than the scales are actually rated for at this price point.

 

--Rogan

 

 

On Mon, Jan 3, 2022 at 4:24 AM Scott McGrath <scott@...> wrote:

All the chinese glass scales ive used have been more or less ok and meet accuracy specs based on the standards that i have (a set of gauge blocks) prefer the US made acu-rite but those are 10x the price.

 

As to touch vs button.   What the heck were designers thinking touch screens with lubricant and swarf covered hands….    Buttons are what I recommend and use.

 

The only real challenge is mounting scales absolutely parallel to the ways to minimize cosine error as much as possible.


From: sheldonlathe@groups.io <sheldonlathe@groups.io> on behalf of Nick Andrews via groups.io <nickjandrews=gmail.com@groups.io>
Sent: Sunday, January 2, 2022 11:08:56 PM
To: sheldonlathe@groups.io <sheldonlathe@groups.io>; SouthBendLathe@groups.io <SouthBendLathe@groups.io>
Subject: [sheldonlathe] Adding DRO to my SB vertical mill

 

So I'm thinking that while the challenge of full manual operation with the dials can be a lot of fun, sometimes the added features of a DRO would make life a whole lot easier.  But I don't want to spend more than I paid for the machine,  so am thinking of trying one of the $300-600 units.  Anyone have advice on which might be good or more important,  to avoid?  And if the tft touch screen type is more usable than the old style discrete buttons type?


tooluserkd
 

I've setup heidenhain scales on both lathes and mills, using a depth mic to get the scale parallel to a reference surface (the table, on the mill) within .001.
The scale on the lathe X axis has a resolution of .00005 and the alignment requirements were the same.
The actual instructions say to align within .005.
It's really not a big deal, and I spent less than 30 minutes on the alignment process.
The vendor wants to charge $300. to install these DRO's, and I already had the mounting holes in place.
I was surprised how easy the job really was.
After 5 years zero problems with either installation, and they are verifiably accurate.