Qualifying large table question

small.planes · May 18, 2020

Hi all,
I own a 48x30 cast iron surface table. Visually it looks pristine, but I have no calibration data.
I need a smaller plate anyway, probably 18" square.
Given this one will be new and have a calibration can I use it to qualify my larger table as "good"?
I was thinking overlapping prints should work, but I've not had to do anything like this before.
I also have a very second hand 24" square plate that I would like to learn scraping on. It came with a machine, so was effectively free. Can I scrape in 18" of it, then move and do the last 6" to match? Sort of the same question, but I don't intend to touch the table, just understand it's flatness ( or not)

Dave

jmkasunich · May 18, 2020

small.planes said:
Hi all,
I own a 48x30 cast iron surface table. Visually it looks pristine, but I have no calibration data.
I need a smaller plate anyway, probably 18" square.
Given this one will be new and have a calibration can I use it to qualify my larger table as "good"?
I was thinking overlapping prints should work, but I've not had to do anything like this before.
I also have a very second hand 24" square plate that I would like to learn scraping on. It came with a machine, so was effectively free. Can I scrape in 18" of it, then move and do the last 6" to match? Sort of the same question, but I don't intend to touch the table, just understand it's flatness ( or not)

Dave

I suspect you could use the 18x18 to scrape in a 24x24 if you work carefully. A 48x30 is going to be a lot harder. The small plate can be used to check local flatness (holes and humps) but you'll need other techniques to check overall flatness. Precision levels, autocollimator, reference straight-edge, etc.

This post might get better answers in the machine reconditioning and scraping forum. I'd definitely like to hear Richard King's opinion.

dian · May 19, 2020

i once corrected a 40" straight edge on a 32" plate. it would not seem like a big deal, but was a total pain and took several times longer than on a larger plate and in the end i cant really be sure what the result is.

DMF_TomB · May 19, 2020

small.planes said:
Hi all,
I own a 48x30 cast iron surface table. Visually it looks pristine, but I have no calibration data.
I need a smaller plate anyway, probably 18" square.
Given this one will be new and have a calibration can I use it to qualify my larger table as "good"?
I was thinking overlapping prints should work, but I've not had to do anything like this before.
I also have a very second hand 24" square plate that I would like to learn scraping on. It came with a machine, so was effectively free. Can I scrape in 18" of it, then move and do the last 6" to match? Sort of the same question, but I don't intend to touch the table, just understand it's flatness ( or not)

Dave

Repeat O Meter used for checking before and after lapping, some use 100mm precision level .02mm/m but obviously need plate level or vial bubble will be off scale

Search

Largest Manufacturing Technology Community on the Web

Search

Qualifying large table question

small.planes

Aluminum

jmkasunich

Aluminum

dian

Titanium

DMF_TomB

Diamond

Attachments

Similar threads