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Discussion in 'METROLOGY - MEASURE, SETUP & FIT' started by Bob Korves, Jun 12, 2017.
Looks like a new channel.
I have a Rockwell T&C grinder that will do surface work too. I look for abused stones that are sometimes swaybacked to the max. I use a diamond wheel (I have several) to make the surface flat again. A little water mist coolant is in order as there is some heat generated. They appear to my gunsmith eye flat as a flitter (technical term) . Even hard Arkansas stones can be saved from the sad state of abuse they have suffered.
I wonder what effect that the heat generated by the grinding has on the flatness of the stones; I know that with grinding steel parallels dry that it is near impossible to keep them (parallel) and straight, at least on the parallels that I made about 50 years ago of 0-1 tool steel, hardened; the heat of the cut would bow them up in the middle, even with the magnetic chuck on full power. Originally, I did not worry about exact nominal size, just parallelism; this was on a grinder 16 X 72" and not in good alignment, so I thought it might be nice to grind them to nominal size, but my B&S Micromaster does not currently have coolant and the results were not so good. I do not know how much effect that the lightening holes had and how much different a solid parallel would act but assume that it would make a difference. So, with stones ground dry, how flat is flat?
Chips&More (Dave)'s comment earlier in the thread and yours puzzled me until I started reading about gage block stones.
Starrett still sells stones expressly for removing burrs from gage blocks, which is simply amazing to me. See page 408 of their current catalog:
The cheapest of them (for steel) appears to just be a small piece of granite that is precision ground. For ceramic or carbide they recommend their aluminum oxide stones (the larger one has serrations which apparently helps with the "feel" per Starrett). The granite stone is what has my attention, though.
I think Dave may have it exactly right. The cheapest option for a "precision ground stone" may be simply a small, cheap granite surface plate.
I'd be willing to bet that rubbing a hardened and ground part on a surface plate would burnish and identify high spots identically to what you see in Robin's video.
Anyone here ever used any of those Starrett stones?
Just a flat granite block will define and burnish the high spots but it won't shear them off or improve the surface like a flattened aluminum oxide stone.
Heard about Robin's channel while watching Tom Lipton. I hope he makes a LOT more videos.
That could be difficult to take to the work, depending on size, shape, and location. I also agree with Jon that it would only burnish, not remove burs.
Yes Rex, I have been using a granite surface plate for a very long time for such purposes. I didn’t mention it earlier, sorry, but I also apply some Starrett granite cleaner as I’m doing the deburring. It really helps keep the shiners/skid marks off the surface of the stone if nothing else. The stone I use is about 9” X 12”. That kind of real estate is another big advantage over the smaller examples. I’m seeing on fleaBay that a replacement, if I bought new, would be about 50 bucks. Both the surface plate and sharpening stone are a good solution to deburr. I’m not deburring every day in my shop. It’s not a priority. But, it is a needed capability in my shop from time to time…Dave
Hi Bob, after a surface has been blemished it can no longer be the same. So then what? Do you remove the high spot(s)? Or do you try and push them back to where they were? When I recondition my Bridgeport mill table, I DO NOT RUN A FILE OVER ITS SURFACE. Instead, I have a large flat and heavy piece of cast iron that I slide all over the top of the table. This method burnishes the table. I dislike the thought of filing metal off. That will only change the landscape forever. If my precision whatever has a blemish and I’m concerned about it. I’m not that eager to try and remove it. I would rather burnish it. This of course depends on many factors. But I would try and burnish first…Dave
Once a clamp, t-nut, 1-2-3 block, part or anything falls on or scratches a softer surface, then yes it's not the same. I can't see rubbing two cast iron surfaces together until both surfaces are free of raised material from scratches or dings. Looks like you would just be asking for them to gall each other and cause more damage.
Intuitively, I'd also think that a granite surface plate would be terrible for removing a burr after dinging a precision ground surface. My intuition says a granite plate would only be good for burnishing and not for removing a burr.
Yet Starrett sells a granite stone expressly for removing such burrs. Dave also reports success doing the same on a surface plate.
I'm inclined to believe (especially with my humiliating lack of a surface grinder) that a precision ground 2" wide granite parallel might make a passable replacement for a precision ground stone like Robin shows in his video. Robin's stones might work better or faster due to the porosity of an India stone, but a shop grade granite surface plate might actually be cheaper than the commercial $500 stones that Robin mentions (for those of us that can't make our own).
It might take some time and effort with an abrasive stone cutter or chisel, but a $30 surface plate could make a a half dozen or more small hand stones. I'm tempted to try it.
This sounds truly outrageous, but I'm also wondering if a granite plate couldn't also be used as the final step to make a "precision ground" India stone. I want to try flattening an India stone on a diamond plate to get it relatively flat, then lapping it on a granite surface plate directly! I'm probably missing something, but I just don't understand why a stone lapped like that would have a substantially different surface than an India stone ground with a diamond wheel.
This is all just a gedanken experiment for me at this point though. I have no experience at all with any of this.
If you are ever down in Montebello, go to Standridge Granite and talk them out of some cutoffs from making surface plates. Or any other surface plate maker, or tombstone maker, counter top maker or installer, or whatever. They should be free or dirt cheap. I would certainly not try cutting up granite myself. You will still need something like a surface grinder or similar to get the material flat enough so it will not damage the precision hardened steel surfaces when they are rubbed. I think the flattened India stones make the most sense over all, and the cost of the stones is negligible in the big picture. It is like the guys who want to make their own surface plates. By the time you get together all the stuff needed to make, calibrate, and qualify one, and work the learning curve, the couple/few hundred dollars one costs factory made pales when Standridge can whip out in a short time in a factory to a known and tested quantity. Why reinvent the wheel? At some point we should make the parts that all the fancy tooling is designed to help achieve. I know, life is a journey. Enjoy the ride. But, along the road, don't forget to also savor the fruits...
I certainly will not be rubbing hardened steel with burs onto my surface plate that is calibrated to .000030" repeatability and .00015" accuracy over the entire 24x36" surface, and I am sure I would not do so on a small cheap import surface plate, if I had one, either.
Sorry, Bob. I seem to have riled you.
I'm talking (out of at least one orifice) about breaking a cheap $30 or $40 surface plate into a few pieces to play with, not attempting to flatten granite to surface plate standards in my garage! I'm pretty sure those pieces will have a surface as flat as anything I could make with my (nonexistent) surface grinder and an India stone.
I wouldn't take a piece of hardened steel to anyone's expensive certified plate.
Those cheap offshore granite plates aren't up to standridge standards, but they are pretty flat and surely flatter than a surface ground piece of soft aluminum oxide, aren't they? They are also cheap enough to use as a stone to remove burrs.
Until you shut me up by sending me a couple of the stones you're making I'll keep thinking out loud since I don't have the means of making my own. ;-)
Sorry if it sounded like I was riled, I often write more passionately than I actually feel. A remnant of strict schooling...
I think I would leave any surface plate intact, even if it is destined for rubbing and lapping. A small cheap one would be fine for rubbing pieces on. Then I would find some granite remnants from a counter top installer for hand held stones for rubbing the parts. They should be flat enough for that (?)
Most stone counter tops are polished. That might defeat the purpose. Some stone counter tops are honed leaving a dull finish which might be more appropriate. I would be skeptical of the flatness.
Bob - I agree with you. I think if you want a rubbing or burnishing stone that is flat, polished granite isn't nearly flat enough; it's just shiny. However there is a cheap substitute that is long wearing and even very slightly abrasive.
Slate. I got several broken pieces of 2" thick slate from a pool table manufacturer. First it is ground, not polished. It is ground because that's the cheapest way to get really flat. Second it is open structured so it is very slightly abrasive. I'd put it in line with Jade sharpening stones - between 10,000 and 30,000. Besides broken pieces of pool table slate are free.
Now that all being said, I'm still going with a carborundum stone. Taking away the upended crater from a ding does NOT hurt your milling table in the least. I know it is counter-intuitive, but hear me out: You can rub a 400 grit precision ground carborundum stone on your milling table for years without removing a measurable amount of metal.
- There is science behind my comments, not just opinion or 30 years experience. In order for an abrasive to cut, there is a minimum pressure on each crystal that is required to begin or enter the cut. Think of a dull kitchen knife being dragged in the cutting direction at a 45 degree angle onto a lino tile. If you press, it will catch if you use enough pressure. Part 2 of this equation is that by diamond grinding the stone you are cutting off the sharp points of the crystals, effectively turning the large majority of them into the equivalent of negative rake lathe tools. You've greatly increased the needed threshold pressure required to enter the cut. Part 3 is that by flattening and evening the stone, there are 4 to 6 times the contact area.
By preparing the stones in this way, you've increased the required pressure to start taking material by 12 to 50 times that of a 'sharp' stone, and a flat stone won't have any high spots to score your table.
For those of us who want a pair and are without a surface grinder, I'm sure one of us with a surface grinder can work out a suitable deal with you.
Oh, and by the way, our equivalent of Harbor Fright, Princess Auto, is currently selling 2"X6" combination stones for 2.99 in their 'surplus' section.
Yes. They are looking for pretty, not flatness...
To Rex and others on touching up your gauge blocks:
I recently received as a gift some DoAll gauge blocks to use as shop setup blocks (my precisions ones stay in the case 99% of the time). I checked with my toolmaker friend and he told me about a marvellous way to recondition them without messing up their accuracy!
He suggests that the first thing to do is to take a fresh sheet of paper - (I found 20 or 30lb stock , heavier the better, works) and place it on your surface plate or flat plate of glass. Then rub the gauge block firmly on the paper, using it as a polishing medium. It took all but the worst rust off my gauge blocks!
He hasn't told me what to do next, but possibly the granite block might be step 2...
After reading this thread, it reminded me of this video:
Now we know yet another use for a high quality, high dollar Starrett Pink Granite surface plate - to flatten a $4.00 India stone. The surface plate is destroyed but hey, your oil stone is stainless steel ruler flat! It makes me wonder what the tuition is for this school because someone has to pay for that surface plate.
Of course, my post is tongue in cheek. I just use a 1/2" thick piece of tempered glass and wet/dry sandpaper to get my oil stones flat enough for my use. With a straight edge (straight to 0.8 microns), I get no light once its flat and that's good enough for me. Then again, I'm not honing my measuring tools. If I ever do, I'll go begging Bob Korves for some!