By hand, stroke by stroke. Also on ways that have worn far out of tolerance.
I scrape to the spotting, not by feel. The oil pockets in the photo are the state in which I hand a way over.
I scrape on the installed machine, clamped and set up the way it will work afterward. The spotting comes from this machine and not from a fixture.
Even a way that has worn far out of tolerance is brought back by hand. How many passes it needs is decided by the spotting after every pass, not by a fixed plan.
How are machine ways scraped?
The way is spotted, the spotting shows the high spots, and I take those off by hand until the spots are spread evenly across the surface.
Spotting
Before every pass the way is spotted again. The mating way or a straightedge gives the spotting, and the spotting decides the next stroke.
The scraper
I work with the hand scraper that lies on the bed in the photo below. What remains at the end is the pattern of oil pockets shown at the top of this page.
Measuring
After the last pass I measure the way with an electronic level and dial indicator. You get the readings and the spotting as an inspection report.
What the job includes
- Spotted before every pass, against the mating way or a straightedge
- Scraped by hand until the spots are spread evenly
- Oil pockets on the finished surface
- Measured with level and dial indicator, handed over as a report
When do machine ways need scraping?
Stick-slip
The saddle sticks and then jumps instead of starting smoothly, most clearly at slow feeds and small infeeds.
Chatter marks
Regular waves on the part, even though speed, feed and tool are right.
Scoring and galling
The way shows scoring in the direction of travel, or galling where the saddle spends most of its time.
Play in the gib
The gib is adjusted all the way in, and the saddle still has play.
Frequently asked questions
1. Why is the way scraped and not ground?
For grinding, the bed has to come out of the machine and go onto a grinding machine. I scrape it in the machine, the way it will work afterward, and the spotting is taken on this machine.
2. Do you also scrape a bed that is already out of the machine?
Yes. A bed that is out of the machine, or a single saddle, I scrape on stands in my workshop in Mühlacker. I measure there the same way as on the installed machine.
3. What do you measure with after scraping?
With an electronic level and dial indicator, plus the spotting. I don’t offer laser measurement. You get the readings as an inspection report.