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Thread: Surface Plate Question
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25th Jul 2018, 03:46 PM #61Senior Member
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Yes, I forgot to say how big my working plate is: about 400 mm x 400 mm. Weighs a ton too!
As to how it is supported - on a fairly flat bit of softish old chipboard. Distributed support. Shock horror of course, but considering the very light loads I put on it, that is quite enough.
Yes, I do have a smaller genuine surface plate, but I rarely use it. I rarely work at the 1 micron level, so why bother? I also have some genuine broken tombstone plates, but haven't used them for ages either.
Cheers
Roger
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25th Jul 2018, 04:41 PM #62Most Valued Member
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Hi Roger,
Yep when its all said and done ultimately as long as you're happy with your setup and it achieves what you need then thats all that matters.
Simon
Sent from my SM-G900I using TapatalkGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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25th Jul 2018, 06:06 PM #63Philomath in training
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The 3 points are sometimes referred to as 'airy points' (or something similar). The idea is that they are the locations where the table has minimum total deflection (highest point to lowest), so it is likely to be flattest. A precision plate will be supported on the same three points when made (and measured) so it is all the same. Supporting a plate on a flat surface is not an issue but if plate is thin in metrological terms and the support is not flat or rigid then it could deflect. It depends on circumstance but deflections are not big and probably would not be noticable for typical workshop use.
I remember hearing a story about Mr Mitutoyo showing some people how to scrape an ultra precision surface plate. He'd take a swipe and then leave it for some minutes just so the heat from the cutting action did not affect the profile. Top grade plates have variation measured in the fractions of micron region. At this level it comes down to knowing that something is precise just so measurements made can be repeated without worrying that the surface is influencing the result.
Michael
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25th Jul 2018, 06:34 PM #64Senior Member
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CMM
went to an auction yesterday, and this went (I think) for c. $240
The plate was c 250mm, and the backing 150mm-200mm. Would be a bugger to move, but NICE granite.
CMM MACHINE, GIDDINGS & LEWIS
SHEFFIELD MEASUREMENT
MOD: CORDAX1808-MMEA
WITH MANUALS
(NOTE: RENISHAW HEAD NOT FOUND)
(POINTS ONLY)
SLAB SIZE: 163 x 74cM
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26th Jul 2018, 08:59 AM #65Most Valued Member
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26th Jul 2018, 10:00 AM #66Most Valued Member
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Girl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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27th Jul 2018, 10:23 AM #67Most Valued Member
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I hope thats not what I said
It all depends what you're trying to do (and also so, sometimes the "right" tools just make things easier. That doesn't mean they aren't possible without)(but you know that). I knew a guy that (if I recall correctly) used a setup like that to lap the head/block of early holden 6's so they could be run without head gaskets. Maybe even some of the first repco hipower* heads, I believe some the the records that car set still stand. I'd have to check.
Simon
I see I cover my points in the in the earlier thread. Wow its hard to make any sense of some of my posts without the pictures, or maybe its just me lol
Re the taper. The way I see it if you try and make a round socket there are 3* possible outcomes.
1. You get it "spot on". At the level I'm thinking would be required I think thats unlikely.
2. Your radius is to large. Now the bearing has a point contact on the bottom of the socket and can move in two axis.
3. Your radius is to small. Now the bearing has line contact around the top of the socket. Depending how deep you made your socket I'm thinking its POSSIBLE you'd end up with a selflocking taper.
No points for you
*ok there are at least 4 more outcomes, one of them possibly better than a straight taper, for the rest the result would be the same as 2 or 3, but my head starts to hurt lol. That doesnt include tool height effects on "shape"
See why I took the easy way yet?
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27th Jul 2018, 10:16 PM #68Most Valued Member
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28th Jul 2018, 08:08 AM #69Most Valued Member
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Thanks Stu. I see what you mean. And yes I read the post on your previous thread but without the pics it was missing 80% of the information!
In truth, you are quite good at explaining things but I'm very much a visual person.
So, welcome back Stu?
SimonGirl, I don't wanna know about your mild-mannered alter ego or anything like that." I mean, you tell me you're, uh, super-mega-ultra-lightning babe? That's all right with me. I'm good. I'm good.
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