Wedg1e
They call me Mr. Bodge-angles
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You'll be making @doubleboost jealous with talk like that
I've heard he likes to bash a cucumber about a bit, when the wife isn't looking
- Thread starter Pete.
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I've heard he likes to bash a cucumber about a bit, when the wife isn't looking
Pete.
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Armed with my new-found 'skill' it's time to tackle this bad boy.
A 24" square plate I bought recently which the seller aquired with an in-date calibration tag classifying it as A grade. Well, it ain't - it's got a big low spot in one corner and another couple of depressed areas. The surface gauge showed a high edge but that's because of the low spot right along side it.
I needed a bit of working space around the plate so I spun it 90 degrees and brought the support pad out to the edge of my little bench. I gave it a quick go over with the lap to show up the low spots
You can see the low spot is exactly where the surface checks said it should be.
Another couple of goes with the lap shows the biggest hole clearly. this is showing 10um on the dial.
A 24" square plate I bought recently which the seller aquired with an in-date calibration tag classifying it as A grade. Well, it ain't - it's got a big low spot in one corner and another couple of depressed areas. The surface gauge showed a high edge but that's because of the low spot right along side it.
I needed a bit of working space around the plate so I spun it 90 degrees and brought the support pad out to the edge of my little bench. I gave it a quick go over with the lap to show up the low spots
You can see the low spot is exactly where the surface checks said it should be.
Another couple of goes with the lap shows the biggest hole clearly. this is showing 10um on the dial.
Pete.
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More lapping working in both directions to avoid lapping a trough in it.
Still showing big holes so I re-charged the lap with 50um dust and rolled it in hard. Then I gave it a 15 minute session working both directions in turn.
Seems to have got most of the hole out
The plate cleaned up nice so I got the repeat gauge out and it was showing a consistant reading but high on the dial.
I knew what this meant from doing the previous plate - the plate now has no holes in it but it's dished which gives a continuously 'high' reading compared to a truly flat plate. So before continuing I checked it with the autocollimator and sure enough all four corners are high. I put the lap on it and used on each corner in an arc shape to bring those coerners down. Checked it again quickly and it's showing mostly flat with a bit of dish along one edge.
Packed it up for the evening, I cleaned the plate and it looks like this:
Still showing big holes so I re-charged the lap with 50um dust and rolled it in hard. Then I gave it a 15 minute session working both directions in turn.
Seems to have got most of the hole out
The plate cleaned up nice so I got the repeat gauge out and it was showing a consistant reading but high on the dial.
I knew what this meant from doing the previous plate - the plate now has no holes in it but it's dished which gives a continuously 'high' reading compared to a truly flat plate. So before continuing I checked it with the autocollimator and sure enough all four corners are high. I put the lap on it and used on each corner in an arc shape to bring those coerners down. Checked it again quickly and it's showing mostly flat with a bit of dish along one edge.
Packed it up for the evening, I cleaned the plate and it looks like this:
ronan
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I meant to buy a granite surface plate before brexit, but never got around to it. The work i would be using would be lapping gasket faces and general marking out with the height gauge. Surprisingly i priced a granite plate at one of the metrology places here and it was surprisingly cheap for a decent brand .
Wedg1e
They call me Mr. Bodge-angles
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Jesus, Ronan, don't use the L-word and 'granite surface plate' in the same sentence, Pete will have a fit
ronan
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Yes, i know, but the way i have done it in the past is not by applying abrasive directly to the plate and lapping the surface that way, but by sticking sheets of wet and dry to it with tape and using it that way. There should be no wear on the plate that way.
Wedg1e
They call me Mr. Bodge-angles
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Ever noticed that the edges of whatever you're rubbing always get rounded off? The paper never stays perfectly flat.
Kayos
Gone......
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I used to actively refuse paid photography work, upset a few people including one lunatic who was convinced I had a agreed to photograph her wedding and paid me a deposit! (She hadn't, think she was just delusional)
I gave up putting stuff online after that
pressbrake1
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Good to see my old chinesium surface plate is useful for something!
Milkybars
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This morning @Pete. very kindly popped over in to Essex to have a look at my granite plate & comparator
Main plate was suprisingly in very healthy condition, it must have been looked after / covered given it's 1985 vintage and well within at least A spec
My comparator was a different story and as Pete used the repeat-o-meter it was obvious it had a somewhat harder life.
Thankfully the column is detachable (bolted through the base with a socket cap) Given it is DoALL I suspect it came to blighty via J&L (now MSC) back in the day
So taking advantage of the weather (and keeping the diamond dust out of the workshop) Pete set up on the bench outside and charged his lap.
As the readings had shown there was an obvious "puddle" in the plate after the first go with the lap . After 3 goes with the lap and a clean, the "puddle/ dip" was no more
Thank you once again @Pete. a pleasure to meet you
Main plate was suprisingly in very healthy condition, it must have been looked after / covered given it's 1985 vintage and well within at least A spec
My comparator was a different story and as Pete used the repeat-o-meter it was obvious it had a somewhat harder life.
Thankfully the column is detachable (bolted through the base with a socket cap) Given it is DoALL I suspect it came to blighty via J&L (now MSC) back in the day
So taking advantage of the weather (and keeping the diamond dust out of the workshop) Pete set up on the bench outside and charged his lap.
As the readings had shown there was an obvious "puddle" in the plate after the first go with the lap . After 3 goes with the lap and a clean, the "puddle/ dip" was no more
Thank you once again @Pete. a pleasure to meet you
Pete.
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Yeah that needle was swinging about like a VU meter at a rock concert
Nice chatting to you this morning mate. That comparator was showing nearly a half thou dip right under the gauge but it didn't take long to grind out, being so small.
Grade A for your big plate would require better than 3.8um total flatness which it clearly achieved. Attaining grade A isn't too difficult but going one grade better is a lot more challenging especially with my small lapping plate so it didn't make sense to even touch it. A is plenty adequate for general scraping work.
Nice chatting to you this morning mate. That comparator was showing nearly a half thou dip right under the gauge but it didn't take long to grind out, being so small.
Grade A for your big plate would require better than 3.8um total flatness which it clearly achieved. Attaining grade A isn't too difficult but going one grade better is a lot more challenging especially with my small lapping plate so it didn't make sense to even touch it. A is plenty adequate for general scraping work.
@Pete. , it's about time I invited you to run your gauge over my 6 foot x four foot marking out table - I've no doubt you wouldn't have too much trouble finding it's highs and lows, though it actually doesn't look too bad - I don't think that the cover has been off it since the scraping class the other year!
Pete.
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Yes to the first question.
Dunno about the second. Cast iron pickes up diamonds like you wouldn't believe so I guess that if you tried to lap it with diamonds you might just create a lap. Perhaps you could do it with timesaver compound since that breaks down instead of embedding.
Dunno about the second. Cast iron pickes up diamonds like you wouldn't believe so I guess that if you tried to lap it with diamonds you might just create a lap. Perhaps you could do it with timesaver compound since that breaks down instead of embedding.
Pete.
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pressbrake1
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Yes you can lap cast iron . Where I worked in the last century we had big lapping plates for such work
