[Metrology] Which came first, chicken or egg? - As it pertains to scraping & flatness.

[Moderatemixed]

Hey all!

I will attest to generally being the guy who puts the Carriage “well ahead” of the horse. With that out of the way here goes.......

Note: I am also very much an amateur in the shop and my understanding of what exactly it is that my tools do is basic at best.

I have 3 surface plates, 2 Starrett Granite (24x36x4 and 12x18x3) and 1 Brown and Sharp Cast Iron (20x30). I wanted to measure their flatness so I bought a K&E Autocollimator and the associated mirrors.

I’ve just watched Kieth Ruckers video on the Repeat O Meter. I know that I need to get one, but I am going to fabricate one instead. I have both the Mahr Millimess and a Mahr Supremess indicators for said Repeat O Meter and the required materials (I think).

Once I have made all of the required measurements, with the autocollimator and Repeat O Meter I am going to have to “lap” the surfaces of the granite plates and dig out the Biax and scrape the cast plate.

Before I go further, yes my plates might be sufficiently flat for a hobby shop. I acknowledge that I am digging into the unnecessary and that my costs so far have been for the most part “ridiculous and wasteful” at best. If you are going to tell me that I’m wasting my time, I respect your opinion, but for some reason this stuff really interests me and I want to know more. I digress.

To my questions.

Objective: To get the lapping plate (10x14 Cast Iron) flat.

If none of my plates are flat, can I use the autocollimator to help me to locate highs and lows and then with the aid of the Biax “scrape” the cast plate flat? If so how, what’s the general procedure? To use an autocollimator alone to make a surface flat? I’ve seen the use of a reference flat and ink to identify high and low spots but thats the problem, I don’t have a reference flat, and I am trying to get one.

I need to come up with a reference surface in my shop that is flat, but how does one do so if your reference surfaces aren’t flat; hence the chicken/egg analogy.

With the equipment that I have already, can I produce a flat reference surface that I could use to make other surfaces flat? And what surface should that be?

Just to complicate things, I also have (got it with the autocollimator) a vertical alignment mirror which as I understand will allow me to level to .1 arc seconds of level and 90 degrees perpendicular to gravity. Should I use that mirror at all within the equation?

Any, and all comments and suggestions (of a positive nature) are appreciated. Those pointing out that I am in WAY over my head would be simply gilding the lilly.

Thanks everyone.

Cheers,

Derek.


Sent from my iPhone using Tapatalk

 

[Boswell]

This sounds like a deep rabbit hole. Looking forward to reading about your adventures. I fully understand

digging into the unnecessary and that my costs so far have been for the most part “ridiculous and wasteful” at best.

Good luck.

 

[Moderatemixed]

Having reread this, it might be simpler to ask, can I use the autocollimator as the master reference so I can scrape a reference surface out of Cast surface plate? And if so, how?

I don’t know if that is any more clear.....

Cheers.


Sent from my iPhone using Tapatalk

 

[Braeden P]

Hey @Richard King 2 what do you think about this.

 

[eeler1]

Hmmmmm, do you want a flat surface plate? Or do you want to learn a new skill? Maybe you could have it made flat by a pro for less than what you spend in equipment to do it yourself for a one time job.

Or enjoy the journey.

Just my thoughts.

 

[extropic]

Hey all!

I will attest to generally being the guy who puts the Carriage “well ahead” of the horse. With that out of the way here goes.......

Note: I am also very much an amateur in the shop and my understanding of what exactly it is that my tools do is basic at best.

I have 3 surface plates, 2 Starrett Granite (24x36x4 and 12x18x3) and 1 Brown and Sharp Cast Iron (20x30). I wanted to measure their flatness so I bought a K&E Autocollimator and the associated mirrors.

I’ve just watched Kieth Ruckers video on the Repeat O Meter. I know that I need to get one, but I am going to fabricate one instead. I have both the Mahr Millimess and a Mahr Supremess indicators for said Repeat O Meter and the required materials (I think).

Once I have made all of the required measurements, with the autocollimator and Repeat O Meter I am going to have to “lap” the surfaces of the granite plates and dig out the Biax and scrape the cast plate.

Before I go further, yes my plates might be sufficiently flat for a hobby shop. I acknowledge that I am digging into the unnecessary and that my costs so far have been for the most part “ridiculous and wasteful” at best. If you are going to tell me that I’m wasting my time, I respect your opinion, but for some reason this stuff really interests me and I want to know more. I digress.

To my questions.

Objective: To get the lapping plate (10x14 Cast Iron) flat.

If none of my plates are flat, can I use the autocollimator to help me to locate highs and lows and then with the aid of the Biax “scrape” the cast plate flat? If so how, what’s the general procedure? To use an autocollimator alone to make a surface flat? I’ve seen the use of a reference flat and ink to identify high and low spots but thats the problem, I don’t have a reference flat, and I am trying to get one.

I need to come up with a reference surface in my shop that is flat, but how does one do so if your reference surfaces aren’t flat; hence the chicken/egg analogy.

With the equipment that I have already, can I produce a flat reference surface that I could use to make other surfaces flat? And what surface should that be?

Just to complicate things, I also have (got it with the autocollimator) a vertical alignment mirror which as I understand will allow me to level to .1 arc seconds of level and 90 degrees perpendicular to gravity. Should I use that mirror at all within the equation?

Any, and all comments and suggestions (of a positive nature) are appreciated. Those pointing out that I am in WAY over my head would be simply gilding the lilly.

Thanks everyone.

Cheers,

Derek.


Sent from my iPhone using Tapatalk

Here's my take on your dilemma.
1) Survey the largest plate first because it's large enough to use your autocollimator (AC) on (the other plates are too small to mount the AC).
2) If the largest surface plate needs to be reworked, buy a cast iron lap (maybe 12" to 18" square) and have at it.
3) Rob Renz has a youtube series on lapping a granite surface plate (Watch).
4) After you get the largest plate up to snuff, use it as a base to survey the smaller granite plate. By "base" I mean set both the smaller granite and the AC on the larger plate.
5) Scrape the CI surface plate in using the larger granite as a reference surface to print it.
YMMV

 

[Moderatemixed]

Hmmmmm, do you want a flat surface plate? Or do you want to learn a new skill? Maybe you could have it made flat by a pro for less than what you spend in equipment to do it yourself for a one time job.

Or enjoy the journey.

Just my thoughts.

I want to learn a new skill, which would ultimately produce a flat surface plate. What is unclear to me is how you go about getting something flat when no reference flat exists. And can an autocollimator be used to facilitate the production of a reference flat surface, be it a surface plate or a straightedge like a Camelback.


Sent from my iPhone using Tapatalk

 

[Moderatemixed]

Perhaps what I will do is abandon this thread and replace it with one that is a bit more direct and simpler in nature.


Sent from my iPhone using Tapatalk