Gallery, Projects and General > How do I??
How to measure "square" for scraping? Angle plate
PekkaNF:
Hello,
I'm going to have a go scraping and need to proceed on baby steps, because ultmate goal is to get my old and tired milling machine closer to acpetable level than it is. Not perfect of über accurate, but closer to HMS standard.
I have a small granite surface plate and standard equuipment. So far I have used good known square and geeler gages to check other square pieces. I have also used a DTI and parallel to indicate dips and walleys.
But how do I check error on two planes that are supposed to be square to ecah others. I can spot each plane indvidually and I now that both of the planes are about 0,02 mm concave in the middle....but how to indicate which corner to scrape more to bring both planes closer to square?
Is there any other way than:
1. true DTI on master square
2. get comparison readings from the angle plate (plane that is expected to be most off)
3. Scrape offending corner down
4. Spot of flatnes and race for next offending bigger spot
5. Indicate again and cycle until "square" enough
6. Scrape flat
I don't have a master square, I have two pretty good flat squares.
This is probably a daft question, but I had pieces on small granite surface plate and was wondering "how on earth I make it sure that I know which way these planes are skewed without making assumptions I can't verify?".
Pekka
PekkaNF:
OK, found better search word for google and found this on YouTube:
How To Check A Block For Squareness
Modified surface gauge and DTI. Looks like a project.
Pekka
sparky961:
Someone posted a link to this a little while ago, maybe it was even you - but I don't recall. Here is is again:
http://www.totallyscrewedmachineshop.com/documents/FoundationsofMechanicalAccuracy.pdf
My take is that this book starts to become a bit of an advertisement for their measuring machine as the book goes on. However, along the way they do provide some very useful tips for achieving a high degree of accuracy with relatively simple tools, lots of time, and even more patience.
I have little experience in this area, but have decided that you can't really "measure" square. You can only compare it. Perhaps this is an over-simplification, but that's the way I've been looking at it. Have you used a "squaring gauge" before?
My thought is that you can zero the gauge on the most square item you have; be it your angle plate, square, or cylinder square. I like the idea of the cylinder square because you can verify the accuracy by checking the consistency of the diameter, finding one position that is truest to square, then turning it 180 degrees to verify you get the same reading with your squaring gauge.
After you know the gauge is set to read "0" when two surfaces are truly square, you use that to check your machine ways and such. Unfortunately you can't change the height of the gauge as you're measuring a surface. Instead, you'd have to mark off the height increments of interest and go back and forth with the gauge to check the various heights. Record the data and what you should end up with is a map of the highs and lows, indicating where you should be concentrating your scraping efforts.
A bit tedious, but you didn't expect this to be an evening project, did you? :)
(Edit: Seems you beat me to the post...)
sparky961:
Here are some pictures of the gauge I made from scratch. I have a SolidWorks model and dimensioned drawings that I'll share if anyone's interested. I haven't made the clamp for holding an indicator yet, and have just been using another one that's offset a bit too much for my liking.
Manxmodder:
Sparky,I really like the look of the gauge stand you've made. I'd be very gratefull to see some dimensioned drawings if it's not too much trouble.
Pekka,I'm following along and watching here as I'm very interested in how you resolve this problem.
Any chance you could post some images to get a better idea of exactly what you're looking at?....OZ
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