Once the magic smoke comes out, things don't work any more.
John Kasunich
jmkasunich@fastmail.fm
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Sat, 26 Jul 2008
Last Saturday I confidently wrote "Tomorrow I'll bring in the rest of the pieces, clean everything, and put it back together". I should have known better.
The table ways are ball-bearing, and seem to be in good shape. Not so the cross-slide ways. They are dovetails, and have significant wear on the flat surfaces. Last Sunday I started scraping them flat. A business trip in mid-week cut into my time, but I finished today. It took 37 rounds of scraping. They are still far from perfect - I am not an experienced scraper hand - but they are much better than they were.
I took pictures before I started, and after every 5 rounds. I used GIMP to color enhance the photos, turning almost everything except the blue spotting dye to grey-scale. The image below is what I got when I first spotted the cross-slide on my surface plate. It made contact only on the front left corner, and on the two back corners. Sorry about the bad lighting, you have to look closely to see the nearly square patch in the back right. (Click on images to enlarge.)
The next six photos are after 5, 10, 15, 20, 25, and 30 rounds of scraping. In round 5, the initial patches grew a bit, but it wasn't until round 10 that I got contact on all four corners. From then on to round 30 I was mostly trying to bring the badly worn left center portion of the left way into contact. The last 1/4" or so is simply too badly worn, and I decided not to try to work the entire rest of the surface down to the level of the worn spot. Somewhere between rounds 20 and 30 I started to develop a low area on the near end of the right way. The last 7 rounds were mostly focused on fixing that, as well as improving the overall surface and breaking up any large areas.
After round 30, I stopped replenishing the spotting compound on the surface plate. That means the film on the plate got thinner after each round, and the readings became more sensitive. Large uniform areas in round 30 became collections of smaller spots in subsequent rounds, and I made smaller and smaller scrapes.
The round 37 photo below was taken with the slide rotated 90 degrees for more uniform lighting. The lighting was still a bit uneven - the photo shows much more blue on the right way, but in reality they are better balanced. There is still some uneveness on both ways, but when I go back and look at the starting photo, I don't feel too bad about saying "that is good enough". Especially since I still have to do the mating ways. I'm hoping they will be easier and faster.
One of the guys on IRC was wondering what a scraper looks like, so here is a photo of my scraper (given to me by my machinist father). It is carbide tipped, which saves a lot of honing. Behind it is my 12x18 surface plate.
(posted: 26 Jul 2008 23:03) (permalink)