What Size Surface Plate

I am just a hobbyist, and a newbie at that. In the Starrett literature I read early in my initial steps into this hobby it was made very clear to get the best that you can afford. I kept my eyes open and picked up a grade B Starrett 36 X 24 black plate for $200 Canadian (so like $130 US lol). I am a hobbyist as I said, but I have not once though to myself, "gosh I wish that this surface was smaller" (No I don't move it). My shop is only 12 x 14 so it does command a fair amount of real estate, but worth it, completely. I started with the Lee Valley plate and it was just fine. Happened across this Starrett and sold the LV for $50CAD. I did pick up a 12 X 18 Starrett for lapping, again on Kijiji (like Craig's list) for $90CAD. It is grade A and had I found it first would have made do, but again my point being that go as big as you can. Just my 2cents.


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With a used surface plate, Starrett, Lee Valley, or God's Only do not mean anything at all. It is just a rock until proven otherwise. If it is not in current calibration and certification to a specific grade within the last couple years, and then carefully taken care of under your supervision, it is a complete unknown. If you are using it for layout and other non precision work, then fine, don't sweat it. But if you are using it for accurate work, or calibrating other tooling that must be correct, or making parts that must meet accepted standards, then you are just guessing.
 
Like me and most of my stuff, my surface plate is rather ancient. Its a 12 x 18 cast iron plate with lifting handles on both ends, its easy for even this old coot to move around. Quite adequate for anything that I ever need it for. Picked it up from a precision machine shop that was shutting down to move elsewhere. Just happened to be in the right place at the right time. The surface is as close as I can measure to being perfect. No dings, dents, or major scratches. I think I paid $30 for it back in the '70's. Never really had need to use it until I finally started playing around with doing my own machining. It just occupies a spot on the back of my work bench with my stereo microscope and its accessories sitting on top of its well worn and oiled wood cover. Nary a spot of rust ever. Perfect size for all of my needs. I think that a 9 x 12 would just be too tight to easily use.
If it is adequate for whatever you need it for, then great. Just do not assume any accuracy level that is not proven and certified by a pro. You do not have the resources to assert it is "perfect," it is what it is...
 
I think a 12x18 was the handiest size that I have had, but now I have a 14x14 and an 24x24, I use the smaller one for layout, and the larger one seldom.
 
With a used surface plate, Starrett, Lee Valley, or God's Only do not mean anything at all. It is just a rock until proven otherwise. If it is not in current calibration and certification to a specific grade within the last couple years, and then carefully taken care of under your supervision, it is a complete unknown. If you are using it for layout and other non precision work, then fine, don't sweat it. But if you are using it for accurate work, or calibrating other tooling that must be correct, or making parts that must meet accepted standards, then you are just guessing.

I got both plates for "a song" so I paid the $300 to have the 24 X 36 calibrated. Fortunately it was above standard for toolroom grade so we calibrated and certified for toolroom grade. It will for my basement shop purposes be accurate enough and I don't see any need to have it rectified ever again. Cheers.


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Re-certified, not rectified..... stupid autocorrect.


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Good on the re-cert. Too bad it cost $300. A group of us in this area had Standridge Granite drop by on one of their road trips covering California and western Nevada shops. We had 5 plates in my shop from 4 owners, and that let us share the mileage fee and together we had a total larger than their minimum invoice amount. The plates were all calibrated to AA specs and certified to A grade (less costly.) They did put the actual achieved tolerances on the tags stuck to the plates. My 18x24" ended up costing me around $102 total by doing it this way. The 24x36" plates were more like $150-175, IIRC. I agree that a properly certified plate can go much further between certifications in a home shop where one person oversees all usage of the plate and uses it properly and carefully. OTOH, a plate bought used cannot be trusted even if it is in current calibration, because we do not know its history of care. A plate can be trashed in a short time if abused, and we have no way to properly vet it ourselves.
 
I would figure out your scope of work and then go a size larger.

I have an 18"x24"x3" and it is perfect 99.9% of the time but there are a few times when I wish it was just a tad larger. I picked mine up from a shop going out of business about 15 or so years ago and is a shop grade.

Mike
 
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