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any suggestions on selecting a surface plate?

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pious_greek

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#1

Bob Korves

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#2
The Shars surface plate has two ledges. That is really useful for clamping things to the plate. The stated accuracy of Chinese surface plates is often quite good, but can never be trusted because of the lack of valid quality control and quality assurance programs. Still, more than good enough for shop work unless you get one made at the end of the shift, or whatever. The price is excellent, less than half that of an equivalent US made plate. You will probably never know if you got a good one or a bad one, that sort of testing is not able to be done in nearly all hobby shops. So the grades are pretty much meaningless. If you really want one that is tested and vetted by the book and better, look to a company like Standridge Granite and get ready to pay much more, but you will know for sure what you are getting.
 

mikey

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#3
I own the Woodcraft one and I agree with Bob, not sure about the accuracy. They do include a surface map of the plate and for whatever its worth, it is a grade A plate so good enough for the shop floor. I bought this in lieu of a certified plate because to ship something like that to Hawaii would leave me in shock. This will have to do unless Bob wants to send me a Standridge plate for free (hint, hint)! :)
 

HudsonMC

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#4
You can use the plate to scrape in a straight edge, and then use the straight edge, truly flat or not, to check the plate. They're "self proving" in that regard. The process is described in Connelly's Machine Tool Reconditioning book, but it essentially boils down to scraping the straight edge in using the plate, and then rotating it 180 deg and checking the bluing pattern. If the pattern repeats, then the plate is flat. If it doesn't, it's not. Almost impossible to tell where and by how much using this method, but it will at least get you some information.
 

Bob Korves

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#5
You can use the plate to scrape in a straight edge, and then use the straight edge, truly flat or not, to check the plate. They're "self proving" in that regard. The process is described in Connelly's Machine Tool Reconditioning book, but it essentially boils down to scraping the straight edge in using the plate, and then rotating it 180 deg and checking the bluing pattern. If the pattern repeats, then the plate is flat. If it doesn't, it's not. Almost impossible to tell where and by how much using this method, but it will at least get you some information.
That is indeed in Machine Tool Reconditioning, and surprised me. It is not really a proof, it is an ad hoc means to an end where the straight edge is "judged" accurate. There are multiple ways for that test to not give a true result, but is used for ad hoc adjustment in the workshop (section 9.11). It is no doubt useful enough for 'machine tool reconditioning' if done carefully, but not for some other uses of a surface plate.
 

Rockytime

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#6
For the work I do on my Sherline and MaxiMat7 I use a 1/4" glass and a granite floor tile from the big box store. If you are just fooling around that will be plenty good and cheap. If you are doing work for NASA get something more substantial.
 

Uglydog

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#7
pious,
Think about the work you do now, and hope to do in the future.
What tolerance do you need?
What size plate do you need?
How thick is your wallet?

I'm a Luddite. No DROs... Very Large Cast Iron plates. etc...
These work for me and can be very inexpensive.
However, granite may be the best for you.

Daryl
MN
 

pious_greek

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#8
Glad I asked, I appreciate all the responses... I'm leaning towards the Standbridge now. I figure it'll be worth spending a little extra for some confidence in some of the fundamental measuring equipment.
 

brav65

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#9
I got a used Sterret plate from a hobby friend with a plan to have it certified some day. It is a 3" x 24"x24", got it for $60. I have the Shars plate noted above as well. They work for my sad attempts at machining.
 

projectnut

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#11
There was a time when I was considering a surface plate from Shars. In my case I was looking for one a bit larger at 24" x 36". All the specs sounded good, but the shipping added considerably more to the price. In the end I purchased a used 24" x 36" Challenge cast iron plate locally for less than it would have cost to have the Shars plate shipped to my shop.

The Challenge plate came from a shop I worked at over 10 years ago. As it turned out when the shop closed they sold the plate along with most of the machinery and tools (which included 2 granite plates and the one cast iron plate) to a former fellow employee. He didn't need three 24" x 36" plates, so to give it a good home he sold me the Challenge for $100.00. The best part is that it was certified less than 3 years ago. I'm sure the certification cost more than I paid for the plate.

I guess my points are that there may be good plates available locally at minimum cost, and be sure to find out what the shipping charge is before committing to a specific seller. Often times the shipping can raise the price above a little more expensive one found locally. Shipping from the Chicago area to California could be pricey.

In our area there are currently 5 plates available on Craigslist. They range in size from 18" x24" to 36" x 48". There's even a 18" x 24" granite one with a built in height gauge for $140.00.

https://chicago.craigslist.org/nwc/tls/d/black-granite-surface-plate/6301371829.html
 
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