The Shop > Tools

Granite surface plate problem

<< < (4/4)

sparky961:
Yup, you still have a paradox.  You're comparing multiple unknown surfaces to one another.  You have no idea when the straight edges are being printed whether the surface plate or the straight edge isn't flat.  Even if three of the straight edges printed perfectly in multiple positions on the plate, as unlikely as it is you could still theoretically have a spherically concave or convex surface.  Desirable for optics, not desirable for machining.  Try printing a concave to a convex and you won't see it.  Take 3 concave/convex in any combination and you will.

While the chunks out of the edges are nasty, you've still got a nice chunk of quality granite there.  Of course, I'm going on the assumption that Mahr wouldn't put their name on crap, but I have no evidence for that.  Even it it has some nicks, it still has potential to be a very nice plate with some work.

If you haven't already, check out this video.  They're using diamond charged lapping plates, but I'll call your attention to a very interesting exchange at about 27 min into the video where the technician is asked how the laps are reconditioned.  He replies that they're doing it as they're reconditioning the plate.  "I'm making my equipment better and making your equipment better".  One wears the other - on a much smaller scale than most people are able to think.



(Direct link to time mentioned above)
=1591

PekkaNF:
RE: video...I was wondering that too, but I think that FIRST you must have pretty damn "perfect" lap to start with. I was thinking of buying three new disc brake rotors, lapping them against my lap and checking them against known good surface plate (probably have to buy new....thinking of ordering one today) and when I'm satisfied that they are close to charge one with coarse diamond, other finer and last even finer and attack the bad surface plate. if the surface plate is about 400*630mm in surface, about 300 mm rotor appears big enough to even out if you know where.

RE: contradiction....you are right comparing unknown to unknown is bit shot in the dark, but I had two 1000 camelbacks to compare with one 800 mm straight edge (two sides, both looks fine, but other one is more logical to other). I printed them against each others and they do agree close (not perfect). Now when I print them in order against surface plate, there should be same sort of print on each straight edge/camel back.  Right. If the straight edge is just a tad convex it should make the concave print cross the surface plate. Well, it did partially....And most straight camelback appears to be a bit convex and that should print whatever and it does but on the middle it just prints "better".

And same thing with two 600 mm camelbacks and 400 mm camelbacs. And dial indicator on height gauge shows that something is not quite right.

When I put another well kept 500 mm ULTRA brand straight edge on top of the 0,05 mm slip gauge strips on marks and slide 0,03 to 0,05 feeler gauge strip I can feel that not all over the plate feels the same. Far long side feels markedly most constant (knowing that this straight edge has a droop spesified) and on the middle "droop" seems to disapear....hastily I would conclude that at the measured point the "rock" has a valley close to droop.

I still does not KNOW how big the error is but I can say that I am pretty sure it not quite close enough to check all the camelbacks and straight edges.

pekka

leg17:

--- Quote from: PekkaNF on January 16, 2017, 08:00:03 AM ---.......
...... Nobody here seems to have heard of surface plate reconditioning for a private person. It's only 75 kg or such I could transport it easily at the back of my car some 200 km. But nooooo.
Pekka

--- End quote ---

Find out who does it and contact them directly.
Some of them are 'on the road' and do it on-site.
You might be able to work something out.

Navigation

[0] Message Index

[*] Previous page