When the surface plate is just too small ..

[Richard King 2]

Here is another one. Your question is answered around min 15 -

 

[Richard King 2]

Richard-That is a most interesting and educational article! After reading it twice, I am still fuzzy on the difference between flatness and repeatability? What am I missing? It it because flatness is indicated at single points and repeatability is based on a larger area of the plate?

 

[graham-xrf]

Wow - I never thought the thread would so quickly become the filtered pure wisdom from the most experienced guys we know! It's now about getting the best from the primary reference one can have in a shop if we aspire to some precision.

It does not take much (distraction) to come across Robin Renzetti's Repeat-O-Meter, and it looks like something many of us might aspire to try and make. We know our effort would have to go some long way to approach Robin's extraordinary skill, and we might have to adapt to using one of those millionths dial guages in place of the electronic transducer, but it looks possible. There are other examples of DIY repeat-o-meters to be found on YT.

Since a Repeat-O-Meter does not measure flatness, there is also his auto-collimator. That kit, I agree, is probably out of reach for most of us, but then again, I am constantly surprised at what folk here can do! Robin does share all about his design and construction.

Without the benefit of autocollimator optics, there is always Connelly Section 9.12. which can be done with more simple equipment. One can use a straight-edge, which need not be perfect, but nor can it be "any old bit of iron". So long as one end stays constant relative to the other, and there is enough of reasonably good parts to spot on, there is a method to use it anyway. Basically, the flatter it is, the fewer spottings are needed.

[Edit - I have just seen from the description that @Richard King 2 helped ThunderDog do this check on his surface plate].

 

[graham-xrf]

I get it’s really easy to come up with an alt solution and go with it. But I understand this one parameter and without it I see no way to properly do a very basic check that will keep from down the wrong track. Which once you get off just goes further into the weeds.

But I’m certainly nobody and not an expert so shouldn’t have responded in the first place.

I disagree .. you are well ahead of me in your accumulated experience of working with this kit, and I do value your opinion.

 

[C-Bag]

I disagree .. you are well ahead of me in your accumulated experience of working with this kit, and I do value your opinion.

Being an old guy who spent a lot of time with my grandfather when young I got used to taking seemingly simple ideas to heart. Some guys when an old guy tells them you shouldn't do something because it's a waste of time and won't work see it as a challenge. Most of the old hands I've learned from(not scraping unfortunately) spent more time telling me what not to do, than what to do. They knew the pitfalls of the noob. Those pearls of wisdom were not discounted or wasted on me because of my special connection to my grandfather. That's not to say I took everything as gospel. I asked a lot of questions to make sure their wisdom had a foundation and they understood why they were telling me it. That's why it took longer than how to do it. It also made it "stick". This is what I most got from Connolly. He spends so much time telling and explaining what and why not to do something. I have very little actual time scraping but I've approached it like I do most things, I read and study long before I actually "do". Being an autodidact has it's pitfalls in that you have to be careful to not learn bad habits because they are the hardest to break.

So I'm not sure I have more accumulated experience than you do, but thanks for not completely discounting me.

 

[graham-xrf]

OK - I have shelled out for a used Windley camelback, 48" x 5". I might have tried for something narrower (lighter), but this one I got for £340. It looks OK to use as is, so far as my needs go, but there is a scratch to one side, near one end. Actual detail condition I will only discover when I get it here.

To use, I will have to contrive some sort of hoist. The business of actually setting a thing like this down on a lathe ways without dinging anything is a little practical detail usually glossed over in the texts, which are content with a compact phrase like "spot the surface ".

No question - the nice 18 x 18 surface plate is looking too small to have much role in helping this SE along - unless the method @Richard King 2 mentioned lets us up work our way up to a reasonable, possibly improved somewhat, straightedge. I reckon, in the future, I will likely try for a granite about big enough on the diagonal to check it against.

I think, for a while, I am going to get back to XRF electronics - that will be after I finish fitting polyurethane insulation boards to the metal garage door. It is mundane stuff, I know, but it snowed on Monday, and I absolutely have to plug the heat leaks in this place. At least the new brush-strip draught (draft?) excluders have worked well. Not cozy, but reasonable comfortable. I am sure the surface plate will like it!

 

[Weldingrod1]

You will like the garage door insulation: it makes the door much quieter and minimizes what your neighbors have to listen to!

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