07-16-2012, 09:12 PM
Hello All,
When I did my trade (Fitter and Machinist) I did an advanced machine assembly course, eight or so weeks forty hours a week, specifically focused on machine assembly, flat surface scraping, bearing scraping, white metaling of bearings, alignment of shafts bearing blocks and roller tables, etc.
To answer the question raised earlier, when to scrape and when to machine, the answer is really simple when you think about it, Machime as much as possible get the part as near to perfect as you can with the machine tools at hand, and then scrape to perfection, It is just a matter of time usage and efficiency, machine tools are designed to work to very accurate tolerances and do it quickly, scraping is very slow so use it where required but save your time and fingers where you can by accurate setup and machining.
DA did almost exactly as I was trained to do, by machining the 0.003" off of the back of the slide block and then hand finishing, the only difference I was taught would have been to use a flycutter, trammed in as good as is possible and then take 0.001" cuts until the smallest witness mark of the original surface remains, then hand finish, as a flycutter would leave a more uniform finish there would be less hand finishing and by leaving a tiny witness you would guarantee that the smallest possible amount of material was removed.
But I have to say, my hat is off to you DA for getting stuck in and using your logic to come up with the right answers.
Probably the best lesson here is that machine tools are just big ole hunks of iron, and we shouldn't be too precious about the "black arts of the machine builder" if it needs squaring up just stick it on the mill and square it up, I have seen some folks go all "forum rage-y" about someone using a file to remove burrs on a vice, the simple facts are that no matter what, a piece that is 0.002" out of square needs fixing, so just fix it, if it has a burr knock it off either with a fine file, a scraper or a stone, but get rid of it.
Best Regards
Rick
When I did my trade (Fitter and Machinist) I did an advanced machine assembly course, eight or so weeks forty hours a week, specifically focused on machine assembly, flat surface scraping, bearing scraping, white metaling of bearings, alignment of shafts bearing blocks and roller tables, etc.
To answer the question raised earlier, when to scrape and when to machine, the answer is really simple when you think about it, Machime as much as possible get the part as near to perfect as you can with the machine tools at hand, and then scrape to perfection, It is just a matter of time usage and efficiency, machine tools are designed to work to very accurate tolerances and do it quickly, scraping is very slow so use it where required but save your time and fingers where you can by accurate setup and machining.
DA did almost exactly as I was trained to do, by machining the 0.003" off of the back of the slide block and then hand finishing, the only difference I was taught would have been to use a flycutter, trammed in as good as is possible and then take 0.001" cuts until the smallest witness mark of the original surface remains, then hand finish, as a flycutter would leave a more uniform finish there would be less hand finishing and by leaving a tiny witness you would guarantee that the smallest possible amount of material was removed.
But I have to say, my hat is off to you DA for getting stuck in and using your logic to come up with the right answers.
Probably the best lesson here is that machine tools are just big ole hunks of iron, and we shouldn't be too precious about the "black arts of the machine builder" if it needs squaring up just stick it on the mill and square it up, I have seen some folks go all "forum rage-y" about someone using a file to remove burrs on a vice, the simple facts are that no matter what, a piece that is 0.002" out of square needs fixing, so just fix it, if it has a burr knock it off either with a fine file, a scraper or a stone, but get rid of it.
Best Regards
Rick
Whatever it is, do it today, Tomorrow may not be an option and regret outlasts fatigue.