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36X24 'surface plate' -- Peterborough, ON

trlvn

trlvn

Ultra Member
No idea how flat this is anymore but maybe somebody is interested?

5607_891_5.jpg

www.govdeals.ca

Industrial Table with heavy stone top - govdeals.com

GovDeals' online marketplace provides services to government, educational, and related entities for the sale of surplus assets to the public. Auction rules may vary across sellers.
www.govdeals.ca www.govdeals.ca

Currently awaiting an opening bid ($10). Note the two dingleberries on the edges.

Craig
 
For up to $150 it is worth the risk, but only if you're local. Surface plates can be reconditioned...
 
I have one from a friend (retired at 80) who gave me an extremely good deal and I know its history and how little it was used. Looking at this one, be careful as it does have chipped edges and a few gouges on the surface. I'm with @Dabbler on the price (as the stand alone is worth it).

By the way a new plate that size starts at about $500.00. The stands at about $1000.00
 
Dabbler said:
Surface plates can be reconditioned...
Click to expand...
I have a used surface plate of unknown flatness that I would love to get reconditioned so that I have more confidence in it. I have looked into doing it myself and while the process seems straight forward, it seems to require some expensive equipment that just isn't worth it for a one off job. Is there an economical way of doing this yourself?
 
van123d said:
I have a used surface plate of unknown flatness that I would love to get reconditioned so that I have more confidence in it. I have looked into doing it myself and while the process seems straight forward, it seems to require some expensive equipment that just isn't worth it for a one off job. Is there an economical way of doing this yourself?
Click to expand...
Only if you already have the autocollimator or interferometer. If I tripped over one of those that was cheap enough I'd have a go at it, otherwise they're basically scrap if worn.
 
Well, coincidentally I do. Machining is just a hobby for me that I have just started. My career is in Cameras and I have an autocollimator in my lab that I have not used in a while. It was used to look at lens barrel tilt in an autofocus actuator. I could easily borrow this, and then would just need to make up a target.

www.edmundoptics.com

Edmund Optics® Autocollimator

Edmund Optics® Autocollimator used to measure small angles or calibrate and align assorted optical instruments and components is available at Edmund Optics.
www.edmundoptics.com

That would still leave me with finding a lapping plate that was large and flat enough? Not that I know the first thing about scraping, but wouldn't you need a known reference surface to scrape your lapping plate to before using it to lap in your surface plate?
 
Check out Rob Renzetti's YouTube channel. He has some ongoing surface plate re-surfacing projects & discusses related measurement/instrumentation.
 
Looks like old high school shop class stuff. There are four standard modern lathes up on there from the same seller.
 
Most larger plates like that one are worn in places and have flat places. For hobby work, using a bright *incandescent* light and a 200$ straight edge can find low and high spots with a resolution of 2 ten thousandths of an inch. The highs and lows can be marked with a sharpie, and using a cast plate flattened using the 3 plate method, you can 'touch up' the surface plate to abut C grade easily. Anything better that would require $$$$$$ equipment.

If people are interested, I can go into the details, but it takes a few pages of explanation.
For research, look up 'three plate method' and 'lapping surface plates' on the 'net'
 
van123d said:
Well, coincidentally I do. Machining is just a hobby for me that I have just started. My career is in Cameras and I have an autocollimator in my lab that I have not used in a while. It was used to look at lens barrel tilt in an autofocus actuator. I could easily borrow this, and then would just need to make up a target.

www.edmundoptics.com

Edmund Optics® Autocollimator

Edmund Optics® Autocollimator used to measure small angles or calibrate and align assorted optical instruments and components is available at Edmund Optics.
www.edmundoptics.com

That would still leave me with finding a lapping plate that was large and flat enough? Not that I know the first thing about scraping, but wouldn't you need a known reference surface to scrape your lapping plate to before using it to lap in your surface plate?
Click to expand...
You don't need a big lapping plate; its done with laps much smaller than the plate. I don't think it would be accurate that way, a large plate, and you would need a plate more accurate than the one you are trying to fix. You map the surface, lap concentrating on the high spots, repeat. The lap needs to be very flat and is charged and washed - no loose abrasive! I've done lapping but not a surface plate so am not in a position to tell you how....but there's lots of material out there on it.
 
If you can get a large enough sheet of abrasive and a somewhat flat surface you can flatten the stone that is seriously out of true. Close enough for what most need it for. See how to flatten heads with sandpaper

 
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