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From the Chaski HSM forum-
Bump method of frosting ?
Posted By: MDM February 2002
Anyone care to explain the bump method of frosting a lathe bed as shown in Brett's pictorial on his Southbend lathe? Thanks!
Reply By: Forrest Addy
Here's one of the best kept secrets of the machine tool rebuilding racket: that pretty frosting pattern so much admired on exposed hand scraped ways is strictly for appearance and it works against the owner shortening the life of the machine.
I've heard old hands sincerely speak in glowing terms of a "proper frosting job" as though it was both the crowning glory of a machine's appearance and a conscienciously applied means of retraining oil and reducing friction. Given a free hand a master scraper would apply an artistic scraping pattern to all exposed bare metal surfaces mush as a prideful bosun's mate applies fancy ropework to all quarterdeck fittings and appurtinances.
The master surface plates at Hunter's Point Shop 31 scraping bench had a handsome logos scraped in the center of their reference faces and the logos and all had near perfect bearing.
I've seen case haedened machine tool purchaser of vast experience be so takes with a beautifully frosted way surface they completely ignore the hazard it represents to machine tool longevity. They admire its glistening irredescent surface, run their hands over it'shypnotic indentations and breathe "It takes a master srraping hand to do this>"
I think BS, I used to do that by the acre with a Biax half moon power scraper and the brilliance of the scraping came from lapping the scraping edge with 9 micron diamond compound to a mirror finish. You can cover up a multitude of machine discrepancies with pretty frosting. It's eyecatching and beautiflu. It's also the used machine tool sales equivalent of putting a banana in the rear axle of a used car to silence failing gears.
Most machine tools feature way wipers either of felt or sophisticated molder rubber designed to exclude grit and chips plus retain oil at the ended of the ways. Frosting doen with a heavy hand may go as deep as 0.002 below the scraped surface and if done for maximum effect the frosted depressions are abrupt intersections ideally configured to trap dirt.
I'm a firm believer of frosting as much as 5% of the area in any fully housed way bearings as a means of lubricant retention and reduceing "stiction" but never in ways intended to be exposed to chipflow or airborne dust. There the ways should remain scraped smooth so the way wipers can better conform to the surface, excluding dirt and retaining oil. When the hand scraping pattern fades from the exposed ways in a few years, it's time for a re-scrape.
My suggestion to MDM is to consider my above remarks with his application.
Push frosting is easy to describe but it requires a great deal of practice if a good appearance is desired. You select a sharp scraper with only a little crown, apply the edge firmly to the work, and give the heel of the scraper handle a sharp bump eoght with the heel of the hand or a rubber mallet. Ideally the frosted depressions should be oriented alternately 90 degrees and be near perfect squares.
Acvocates of hand frosting frequently make a "mushroom" consisting of a knurled aluminum handle of normal proportions having a 1 3/4 dia mushroom knob on the heel. There is a #1 Morse internal taper in the business end designed to take the welded on shanks of a selection of frosting scrapers having end radii suited for each of a variety of frosting paterns.
Masters of the skill can produce a perfect checker board in alternating bearing points where the frosting is of uniform size and its orientation is in alternating direction. If done correctly any percentage of original bearing can be attained.
For half moon frosting, imagine the mushroom end of the scraper handle as a clock dial. The tool is used by gently striking the clock dial with a soft rubber maul or the heel of the hand. A right hander firmly grasps the scraper by the snak of the blade (not the handle) and applies it to the work with the left edge held firmly down. He strikes the mushroom at about 4 o'clock with a repeated slightly down handed blows. A series of half moons progress with each blow. The blows have to be absolutely consistant in force and direction.
You have to experiment. Individual anatomy has a pronounced effect. I have a muashroom handle and some odds and ends of frosting scraper. While I've acquired the knack many time it has to be maintiained through frequent practice.
Reply By: John White
I am surely no expert on the subject of either scraping or frosting let alone the longevity of machine tools. But It has been my opinion all along that a smooth, unscraped surface has got to be longer-lived than a scraped one. As the poster above mentioned, it must surely be tough on wipers. But, I agree, it is pretty. Sort of like engine turning on a rifle bolt.
[This message has been edited by Admin5 (edited 02-15-2002).]
Bump method of frosting ?
Posted By: MDM February 2002
Anyone care to explain the bump method of frosting a lathe bed as shown in Brett's pictorial on his Southbend lathe? Thanks!
Reply By: Forrest Addy
Here's one of the best kept secrets of the machine tool rebuilding racket: that pretty frosting pattern so much admired on exposed hand scraped ways is strictly for appearance and it works against the owner shortening the life of the machine.
I've heard old hands sincerely speak in glowing terms of a "proper frosting job" as though it was both the crowning glory of a machine's appearance and a conscienciously applied means of retraining oil and reducing friction. Given a free hand a master scraper would apply an artistic scraping pattern to all exposed bare metal surfaces mush as a prideful bosun's mate applies fancy ropework to all quarterdeck fittings and appurtinances.
The master surface plates at Hunter's Point Shop 31 scraping bench had a handsome logos scraped in the center of their reference faces and the logos and all had near perfect bearing.
I've seen case haedened machine tool purchaser of vast experience be so takes with a beautifully frosted way surface they completely ignore the hazard it represents to machine tool longevity. They admire its glistening irredescent surface, run their hands over it'shypnotic indentations and breathe "It takes a master srraping hand to do this>"
I think BS, I used to do that by the acre with a Biax half moon power scraper and the brilliance of the scraping came from lapping the scraping edge with 9 micron diamond compound to a mirror finish. You can cover up a multitude of machine discrepancies with pretty frosting. It's eyecatching and beautiflu. It's also the used machine tool sales equivalent of putting a banana in the rear axle of a used car to silence failing gears.
Most machine tools feature way wipers either of felt or sophisticated molder rubber designed to exclude grit and chips plus retain oil at the ended of the ways. Frosting doen with a heavy hand may go as deep as 0.002 below the scraped surface and if done for maximum effect the frosted depressions are abrupt intersections ideally configured to trap dirt.
I'm a firm believer of frosting as much as 5% of the area in any fully housed way bearings as a means of lubricant retention and reduceing "stiction" but never in ways intended to be exposed to chipflow or airborne dust. There the ways should remain scraped smooth so the way wipers can better conform to the surface, excluding dirt and retaining oil. When the hand scraping pattern fades from the exposed ways in a few years, it's time for a re-scrape.
My suggestion to MDM is to consider my above remarks with his application.
Push frosting is easy to describe but it requires a great deal of practice if a good appearance is desired. You select a sharp scraper with only a little crown, apply the edge firmly to the work, and give the heel of the scraper handle a sharp bump eoght with the heel of the hand or a rubber mallet. Ideally the frosted depressions should be oriented alternately 90 degrees and be near perfect squares.
Acvocates of hand frosting frequently make a "mushroom" consisting of a knurled aluminum handle of normal proportions having a 1 3/4 dia mushroom knob on the heel. There is a #1 Morse internal taper in the business end designed to take the welded on shanks of a selection of frosting scrapers having end radii suited for each of a variety of frosting paterns.
Masters of the skill can produce a perfect checker board in alternating bearing points where the frosting is of uniform size and its orientation is in alternating direction. If done correctly any percentage of original bearing can be attained.
For half moon frosting, imagine the mushroom end of the scraper handle as a clock dial. The tool is used by gently striking the clock dial with a soft rubber maul or the heel of the hand. A right hander firmly grasps the scraper by the snak of the blade (not the handle) and applies it to the work with the left edge held firmly down. He strikes the mushroom at about 4 o'clock with a repeated slightly down handed blows. A series of half moons progress with each blow. The blows have to be absolutely consistant in force and direction.
You have to experiment. Individual anatomy has a pronounced effect. I have a muashroom handle and some odds and ends of frosting scraper. While I've acquired the knack many time it has to be maintiained through frequent practice.
Reply By: John White
I am surely no expert on the subject of either scraping or frosting let alone the longevity of machine tools. But It has been my opinion all along that a smooth, unscraped surface has got to be longer-lived than a scraped one. As the poster above mentioned, it must surely be tough on wipers. But, I agree, it is pretty. Sort of like engine turning on a rifle bolt.
[This message has been edited by Admin5 (edited 02-15-2002).]