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| SPiN Racing:
Howdy gents! Ok sooo I have been playing with things in the lathe here for a couple years now.. and have learned quite a few little tricks here and there. My issue I am having today is a methodology one.... I am certain there has to be a better method then I am using.. but I am not sure of it. I have a 6" diameter disk of 6061-T6, that is 1.5 inches thick. It was cut on a band saw, on both sides by the metal shop I bought it from.. so both sides are NOT true... but the perimeter is smooth. SO my issue is.... if I had one side that was true, and faces all perfect.. I could simply chuck it up with that face to the inside.. and then face the back side.. then move to the boring and other procedures I need to do. As both sides are not smooth.. when I put it in the 4 jaw independent chuck.. I am having a bear of a time getting it centered... and then again just as much of a hard time making sure that its in the chucks properly... so between the two different potential error in alignment issues... Im having a bear of a time. I have a dial indicator.. but if I get it centered at the chuck location.. its not centered at the far edge. And if I get the 4 jaw centered.. its all crooked. Is there some trick to this that old school machinists do? |
| Tony Wells:
Take a good machinist's square and map out the misalignment. Since both sides are out of square with the axis, you just need to know about how much. Depending on just how much, you can use gage pins, feeler gages...or whatever you can find to ascertain the amount out of square the face is, and where in what we'll call the "B" axis it peaks. In other words, where is the gap between the face and the square the greatest? Use a marker (Sharpie or similar) put a mark on the low spot, where the gap it greatest. Now to the lathe. Don't try to get it running axially true right off. Just close.......about 0.050 or so is good enough. Now move your indicator to the face, out near the edge, remembering it will be running out the 0.050 or so. With a soft mallet, tap the face towards the headstock until you see the same deviation on the indicator as you measured with the square. It won't have to be perfect, but of course, the closer the better. It all depends on how close it needs to run to the OD. Once you have replicated the out of square face with the mallet, now go back to the OD and indicate it in as normal. If you plan on machining the OD later, likely you ill be machining a feature at this stage that will be true and square to the face......since the first thing to do after you get the OD running true will be so skim cut the face to clean up the sawcut. At least, that's how I do it. There are other ways, but that always gets me by and isn't difficult now does it take a lot of time. |
| Fergus OMore:
Old time machinists didn't always have 4 jaws and three jaw chucks, they used faceplates. However, you should blue one side, rub it on a marking table of some sort to indicate the high spots, take a file or a scraper and knock the high spots off. Blue and start again-- until you are 'happy' that it will not rock about like a pea on a drum and clamp it to the face plate with the dressed side towards the faceplate. It can now be cleaned up! |
| Pete.:
If it's cut straight but not square I would go around the OD with a square and find the 'highest spot' of one face and mark that with a marker pen. Now put it in the 4-jaw with that high spot not quite touching the jaw face, indicate it in on the OD so you have a gentle grip then use a dial indicator on the saddle to clock off the OD as you run the saddle up and down until you get no/little movement on the dial. Now face it off and flip it over. |
| SPiN Racing:
Thank you so much gentlemen. I am going to use a combination of all of the techniques. As it turns out I cant take anything off the OD.. so I will be breaking out the square and starting with the high spots, and take them down some to get it closer to flat.. so that it is easier with less shims, to get it in the lathe correctly. Also indicating it with the chuck a measured amount out, that will make it a lot easier.. I hadnt thought to indicate it right at the jaw.. then duplicate it at the furthest distance, to get it square. I had always gone for 0. then re-adjust so the furthest distance is at 0.. then get a center on it to stabilise it. With this part its only 1.5 inches thick.. so its pretty thin, for being 6" diameter. |
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