Grizzly G0678 8x30: Repair, Scraping and Alignment

[AndySomogyi]

Made a variation of Nick Mueller’s dovetail alignment jig, all with hand tools (because my mill is broken and need this to fix it).

Confirmed my previous measurements of the knee on the mill.

This is a weird mill, because the surface ground parts are really pretty nice, but looks like the knee shifted when they were grinding the top ways, and the dovetails look like they were cut with an axe.

Now confirming how bad the dovetails are, I guess it’s a good thing I pulled the knee.

Got some work to do, but at least can confirm how much I need to cut off the dovetails.

 

[AndySomogyi]

Bought a no-name box level off eBay (hey, it’s what I can afford)

Inspected it and it’s dead nuts parallel, but way off in squareness, basically it’s a parallelogram.

Argh!@$!@& can’t anything go right with these POS tools I have ?!?!

Anyways, my options are (a) send it back and hope they send me another one that’s in-spec, or (b) try to get a partial refund, and scrape it square.

I’m sick of wasting time on this stupid mill, I just want to get back to making parts.

Note, by rules of geometry, squares are self-proving with a test indicator.

This one is about 0.006” out of square.

 

[Richard King 2]

Andy, If you setting the dovetail device on top on the clearance surface is the clearance surface co-planar to the scraped flats? If I were checking it I would set the device on the flats with the dowel pin pressed against the dove tail and reaching over the clearance surfaces and indicating the opposite dovetail.

 

[AndySomogyi]

Andy, If you setting the dovetail device on top on the clearance surface is the clearance surface co-planar to the scraped flats? If I were checking it I would set the device on the flats with the dowel pin pressed against the dove tail and reaching over the clearance surfaces and indicating the opposite dovetail.

Thanks for the info. As you point out, what matters is the alignment between the dovetails and the bearing flats, the top clearance surface doesn’t make contact with anything.

On the top flats, it’s easy because you just put a dowel pin between the dovetail and flats. On the back flats or column flats (sorry, I forget the correct term), you again need to measure dovetails relative to flats. That’s why I made the alignment jig, to position the dowel pin a fixed length relative to the bearing flats.

So I was using the jig on the back flats, indicating against a try square on a surface plate. I made sure the knee top flats and surface plate were co-planar and level. I built my workbench with an adjustable cast iron surf plate, and the entire thing is welded 2” box tube.

I also plan to flip it upside down, and set the top flats on 123 blocks on my granite surface plate and re-measure.

Then I plan to align the top dovetails by resting the knee on the back flats on the surface plate and measuring the top dovetails.

Just want to check, I’m making all these measurements with the knee on the bench, in a static, unloaded configuration. Basically making sure the knee itself is square and true by itself. Is that the right approach?

The back flats, you said they should be scraped so the front of the knee tips up about 0.0005, so I’ll try to shoot for that figure.

 

[Richard King 2]

You say it is taking so long. " reason in my opinion" You are re-inventing the wheel. Making things so complicated. I can scrape a bridgeport that is in terrible shape in 40 hours. Column, back of knee, top of knee, bottom of saddle, match fit all the gibs. I get the table ground and then match fit that to the saddle. I have re-scraped over 50 Bridgeport's and have been trying to advise you on "how to do it" I have taught thousands of people to not only rebuild machines, but have taught Bridgeport employee's, dozens of new machine building companies around the world. You have scraped 1 or 2 machines? Nick Muller is also self taught and also does not scrape as a professional, he is and electronics engineer. I am here to help and I recommended Hobby Machinist to you when you started to write on another forum. You came looking for help I thought, not show how your doing it with little to no experience, guessing as you go, reading the Connelly book helps, but it also was organized by Connelly, he was not a machine builder or rebuilder. Look at the front of the book where he acknowledges other people who wrote chapters in the book. I Never check the back of the knee like your showing. You need to scrape and check it on the column. I have to go teach another class today and I can write some more tonight. I hope this does not hurt your feelings, but how many hours do you have in the rebuild? 100 +? I hate to say it, but I am sure even the way it was off a mike, I could have the machine scraped in 30 hours. It's a mini Bridgeport.

 

[AndySomogyi]

You say it is taking so long. " reason in my opinion" You are re-inventing the wheel. Making things so complicated. I can scrape a bridgeport that is in terrible shape in 40 hours. Column, back of knee, top of knee, bottom of saddle, match fit all the gibs. I get the table ground and then match fit that to the saddle. I have re-scraped over 50 Bridgeport's and have been trying to advise you on "how to do it" I have taught thousands of people to not only rebuild machines, but have taught Bridgeport employee's, dozens of new machine building companies around the world. You have scraped 1 or 2 machines? Nick Muller is also self taught and also does not scrape as a professional, he is and electronics engineer. I am here to help and I recommended Hobby Machinist to you when you started to write on another forum. You came looking for help I thought, not show how your doing it with little to no experience, guessing as you go, reading the Connelly book helps, but it also was organized by Connelly, he was not a machine builder or rebuilder. Look at the front of the book where he acknowledges other people who wrote chapters in the book. I Never check the back of the knee like your showing. You need to scrape and check it on the column. I have to go teach another class today and I can write some more tonight. I hope this does not hurt your feelings, but how many hours do you have in the rebuild? 100 +? I hate to say it, but I am sure even the way it was off a mike, I could have the machine scraped in 30 hours. It's a mini Bridgeport.

Thanks Richard, I do appreciate your insight.

I’ll move it over to the column and try to measure it there also.

I fully admit, I have no idea what I’m doing here. At my day job, I’m a staff scientist, not a machinist. As such, I don’t have the experience in rebuilding to know what the right ‘feels’ or the generally accepted procedures, aside from the Connelly book.

I also don’t have all the fancy tools rebuilders have, and my salary is crap so I can’t afford top shelf tools. Got to make do.

One thing I do know from science is you need multiple different experiments to confirm something, you can’t trust just one. That’s why I’m using different measurement approaches to measure the same thing, so that they confirm each other. Because I know I don’t have any experience here, I’m trying to be careful with my measures, as I can’t be sure I’m doing it right.

I have no idea how many hours I have in this, have a day job so only spend maybe 2-3 hours an day, so maybe 50 hours? And a lot of that was making things like a brazed scraper and jig.

 

[AndySomogyi]

I’m a total noob at scraping these kind of instruments (I’ve scraped babbitt bearings in engines and lathe saddle, about it), but I’ve got the sides flat and parallel to under a tenth and squareness to couple tenths. Using the method from Moore’s “Foundations of Mechanical Accuracy” pages 33 and 34 (attached).

Started with this cheap ass square almost 0.010 out of square. First got it close with a belt sander then switched to the hand scrapers (made both of them).

Going to tweak the squareness a bit more, see how good I can get it.

BTW, eBay seller is allegedly going to get me a refund.

 

[Richard King 2]

I purchased the Moore Book 40 or so years ago, the Connelly book 50 years ago. I always teach "Never assume anything, prove it" I understand your a scientist and need to prove things to. What I am afraid of and why I wrote what I wrote is because some rookie who has never scraped a machine reads your info and does it your way. I have offered you help and you read but still do it your way. You quote books, show you tube or quote them and not listen to me. Your making something so simple so complicated. Good Luck

 

[Rex Walters]

Hi, Richard. I suspect that, like me, Andy didn't "do it his way" because he disagreed with you or intentionally ignored what you wrote. I think he simply didn't understand (or misunderstood) what you were trying to say.

If you setting the dovetail device on top on the clearance surface is the clearance surface co-planar to the scraped flats? If I were checking it I would set the device on the flats with the dowel pin pressed against the dove tail and reaching over the clearance surfaces and indicating the opposite dovetail.

There's a lot to unpack there. It took me several reads to understand what you meant. Like almost everything I've learned from you about scraping and rebuilding, it's hard to understand in written words. It'd be simple enough to understand in person with our hands on a real machine and real tools, but it's hard to visualize in words. Sadly, it's not always feasible for you to provide photos or videos for every point, much less show things in person (which is why your classes are so valuable). So we have to struggle and communicate with written words.

Please try not to get so frustrated when we don't understand. It usually takes more than one attempt to get something across in words.

Andy: Unrelated to the mill, but one point about checking squareness. This photo shows you laying the dowel pin on its side:



I believe the better technique is to place the pin on end, registering in a vee at the front of the indicator base. You then sweep the indicator, looking for max deflection with base, pin, and square all remaining in contact while rotating the base. You can also use a steel ball in a vee, or simply attach a semicircular bearing plate to the front of the base. In other words, point contact is better than line contact. I'd also draw a line parallel to one edge of the square with a sharpie and ensure the dowel pin and indicator tip are both touching the same line. The surface of the square is a plane that can be tipped on two different axes. You want to use your indicator as squareness comparator of a single line on that surface. Think: points to establish a line that sits on the plane. The pin-on-end registering in a vee gives you three-point contact at the base of the line you're verifying, and the indicator tip establishes the point at the other end of that line.

I'm sure you fully understand, but for completeness: The process I'd use to check a precision square is to first verify that two opposing faces are truly parallel (checking all four corners and the center of the top face with the indicator referencing from the same plate, as you've done). Then I'd draw a line a fixed distance from the edge of an orthogonal face (one of the faces you're testing for squareness). I'd then adjust the indicator so the dowel pin and indicator tip both touch the same line, sweep to find max deviation, and zero the indicator. Finally, I'd turn the square upside down, reference points on the same line, and sweep for max deviation. Any non-zero measurement indicates double the error.

I doubt you'll measure very different results if it's out several thou (which is shocking, tbh) but it does matter when you are checking something that's gage quality (tenths).

 

[AndySomogyi]

Hi, Richard. I suspect that, like me, Andy didn't "do it his way" because he disagreed with you or intentionally ignored what you wrote. I think he simply didn't understand (or misunderstood) what you were trying to say.



There's a lot to unpack there. It took me several reads to understand what you meant. Like almost everything I've learned from you about scraping and rebuilding, it's hard to understand in written words. It'd be simple enough to understand in person with our hands on a real machine and real tools, but it's hard to visualize in words. Sadly, it's not always feasible for you to provide photos or videos for every point, much less show things in person (which is why your classes are so valuable). So we have to struggle and communicate with written words.

Please try not to get so frustrated when we don't understand. It usually takes more than one attempt to get something across in words.

Andy: Unrelated to the mill, but one point about checking squareness. This photo shows you laying the dowel pin on its side:

View attachment 341258

I believe the better technique is to place the pin on end, registering in a vee at the front of the indicator base. You then sweep the indicator, looking for max deflection with base, pin, and square all remaining in contact while rotating the base. You can also use a steel ball in a vee, or simply attach a semicircular bearing plate to the front of the base. In other words, point contact is better than line contact. I'd also draw a line parallel to one edge of the square with a sharpie and ensure the dowel pin and indicator tip are both touching the same line. The surface of the square is a plane that can be tipped on two different axes. You want to use your indicator as squareness comparator of a single line on that surface. Think: points to establish a line that sits on the plane. The pin-on-end registering in a vee gives you three-point contact at the base of the line you're verifying, and the indicator tip establishes the point at the other end of that line.

I'm sure you fully understand, but for completeness: The process I'd use to check a precision square is to first verify that two opposing faces are truly parallel (checking all four corners and the center of the top face with the indicator referencing from the same plate, as you've done). Then I'd draw a line a fixed distance from the edge of an orthogonal face (one of the faces you're testing for squareness). I'd then adjust the indicator so the dowel pin and indicator tip both touch the same line, sweep to find max deviation, and zero the indicator. Finally, I'd turn the square upside down, reference points on the same line, and sweep for max deviation. Any non-zero measurement indicates double the error.

I doubt you'll measure very different results if it's out several thou (which is shocking, tbh) but it does matter when you are checking something that's gage quality (tenths).

Thanks Rex

I think my pic was a bit misleading. Basically what I did was lay the dowel flat, but sweep using the ball end of the indicator, and look for maximum height. First scraped one opposite pair of sides parallel, then scraped the remaining sides perpendicular to them.

I like your idea of a bearing as a measuring probe, I’ll try that also.

I used the ball end as a sort of squareness comparator. The reason I used the dowel is this is a scraped surface, so the ball end of the surface gauge would bounce around too much (using an tenths indicator), used the dowel to get a line contact of the bearing surface.

And on the top, I used a lapped carbide insert to get a measure of the top bearing surface (tenths indicator bounces too much).

I just called up the instruments guys at work and they said I can come in and use the clean room instruments to measure it, so we’ll see how good my work is. My tenths indicator shows about 2 tenths when inverting the part, which is 1 tenth out of square. And yes, tested all 4 faces. Ha ha, when I started, the sides were all bowed by about 0.0005, and out of square by about 0.010, yes, about then thousands out of square. It was so bad, I did the rough work with a belt sander .

Note: interesting thing is now this scraped square is more flat than my surface plate, as I can test different spots on my surface plate, and hinging the square feels slightly different in different spots. Basically using the square as a sphereometer.