Hi. Here is a report on a substitute surface plate made from a discarded granite countertop offcut. Somebody who doesn't like to measure things gave me a 6 x 6" square of discarded that he probably picked up somewhere in his neighborhood. He told me that it's good, but wouldn't say how good. When he saw my expression, he said I could throw it away if I wanted since it wasn't costing me anything. I just threw it in a junk box and didn't think about it until today. Somebody else dropped my desoldering iron and broke the glass filter cartridge. I epoxied it together, but the glue was proud and needed to seal against a silicone ring. A good chance to use the ersatz surface plate, but how good was it? I ran a DTI with a base over it and noticed two things. First, the surface is very smooth. No needle jiggling was observed. Second, there was about 0.004" of variation over the area. Not so good, huh? This is a good lesson for those who don't like to measure. Despite the obvious error, I used it to sand the sealing surface. The error will be much less than the 0.004" I measured. It will probably be as good as a newly calibrated Starrett. It should seal just fine. This is better than using a block of wood or sanding the sealing surface freehand. And it keeps grit away from the real surface plate.
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Countertop granite surface plate substitute
- Thread starter ericc
- Start date
- Joined
- Feb 13, 2017
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- 2,138
Been using one for years for model train building. That useage doesn't require that much accuracy for the most part. When it was given to me, I used a straight edge and a 0.002 feeler gauge and it was satisfactory for my project at the moment. I never did check any closer, just never had a round tuit.
The accuracy of what you are doing will determine what accuracy is needed for the surface plate. A 10:1 ratio is minimum. We had one in the shop at a steel mill, to calibrate a measuring device for production. Now, that required the accuracy. But, my models don't. It's a call you must make for yourself.
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The accuracy of what you are doing will determine what accuracy is needed for the surface plate. A 10:1 ratio is minimum. We had one in the shop at a steel mill, to calibrate a measuring device for production. Now, that required the accuracy. But, my models don't. It's a call you must make for yourself.
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- Joined
- Jul 2, 2014
- Messages
- 7,594
ericc, it is obvious you are guessing. A newly professionally calibrated surface plate would be a couple orders of magnitude more accurate than .004" over 6". I have a surface plate that is recently certified accurate to .00015" over the entire 18x24" area (class A). The repeat reading is .000030". It has been entirely in my control since calibration. If you would like to test your plate against mine, we can do that, come on over some day...
- Joined
- Jul 29, 2014
- Messages
- 2,846
I have a thick piece of plate glass that I use for rough stuff. I’ve been thinking of putting it on my real surface plate and looking for Newton’s rings. That ought to be a meaningful experiment, don’t you think?
I have a piece I payed at one end of my workbench. 1 1/4 thick I use for taping sandpaper to getting cutter marks out of a part or flattening something quickly. Not expecting to substitute my surface plates. Good to have around and usually free.
- Joined
- Dec 27, 2014
- Messages
- 4,093
I was given a sink cut out, about 30 inches long and 15 wide. With a .0005 indicator I could find no variation lengthwise, but it was hollow about .001 in the middle. I've cut it in two, planning on lapping the two tops and one of the bottoms until all three are flat.
I loaned my round tuit out, it hasn't come back, so I may never lap these pseudo surface plates.
I loaned my round tuit out, it hasn't come back, so I may never lap these pseudo surface plates.
That's a great idea and comes at the favorite price of most home workshops. I have a metal surface plate out of a friends scrap pile that I ran thru the Atlas shaper to get reasonably accurate and find that it's very helpful. I used just the other day to true an epoxy repaired thermostat housing from a diesel motor.
I can't weld, turn, mill, shape, glue or 3d print anything better than a couple decimals anyway.....But I sure have fun.
I can't weld, turn, mill, shape, glue or 3d print anything better than a couple decimals anyway.....But I sure have fun.
Hi Bob. It is your reports that have really inspired me. Every time I see a used name brand surface plate on craigslist, I remember your post about the plates with depressions worn in the middle. You mean that I am guessing about the flatness if a swept DTI shows 0.004" variation? Yes, but this granite offcut is clearly worse than the lowest grade of surface plate bought new. I don't think that I need to calibrate this plate any better to sand a little glass cylinder.
By the way, my little project got derailed temporarily. After fixing the desoldering filter, the Weller station vacuum gauge didn't budge. Something else is wrong. In fact, the filter media went the wrong direction, towards the nozzle, when the pump was actuated. This means positive pressure, not vacuum, when the pump was running. I checked the venturi tube, and the PO seems to have jammed a screw in the outlet. This is very dangerous, since it could cause the unit to spit liquid solder if it were allowed to warm up. I removed the screw and it was still weak, but at least it was a vacuum. Any leaks could not have been a problem because I put my finger over the inlet fitting and vacuum was still poor. Probably, the little airbrush pump was not enough. Next step, use the main compressor or try a vacuum pump th test. This thing is becoming a realigning princess.
By the way, my little project got derailed temporarily. After fixing the desoldering filter, the Weller station vacuum gauge didn't budge. Something else is wrong. In fact, the filter media went the wrong direction, towards the nozzle, when the pump was actuated. This means positive pressure, not vacuum, when the pump was running. I checked the venturi tube, and the PO seems to have jammed a screw in the outlet. This is very dangerous, since it could cause the unit to spit liquid solder if it were allowed to warm up. I removed the screw and it was still weak, but at least it was a vacuum. Any leaks could not have been a problem because I put my finger over the inlet fitting and vacuum was still poor. Probably, the little airbrush pump was not enough. Next step, use the main compressor or try a vacuum pump th test. This thing is becoming a realigning princess.
