Hand scraping

https://www.youtube.com/watch?v=xHT-uzKQM6U

compound slide
https://www.youtube.com/watch?v=MLrJxh3G3t4 In this video,I use scraping to repair the Mini Lathe Compound Slide and Improve accuracy.No milling machine needed.

https://www.youtube.com/watch?v=QJXqHpSh3SE

an engineers's findings
https://www.youtube.com/watch?v=YanlyahWDOw straight edge

https://www.youtube.com/watch?v=FgxjiEBhKvM&t=605s hand scraping carbon steel

gibb
https://www.practicalmachinist.com/vb/general/lathe-gibbs-make-buy-206251/ I would recommend making your own gib. If you buy one, it will likely be quite over size and you will need to fit it anyway. I would not make the gib harder than the casting it slides against you may end up galling the ways. If I was to go through the trouble of making a gib, I would make it out of a good bearing bronze. Make sure the gib is flat on the back side where it is not against the sliding part. The tendency with gibs is to be bowed in the middle giving you a false bearing. After it is fitted properly, put way oil on both sides of the gib. This will give a better feel for when you adjust it.

It seems like the need to "scrape it in" is overtaking the basic function...which is an adjustment to make the sliding way free moving without binding, but close fitting without rocking. Its sort of a conundrum but its what makes machine tools what they are.

The gib is just the opposite side of the dovetail, so the gib is acutally a sliding surface, but its also an adjustment. The super long skinny taper makes it so a small adjustment in the screws (like 1/8 turn for example) leads to a thousandth-level adjustment in the side-to-side fit. So another part of the challenge is to get the length correct so the spot you want to run is controlled by the adjustment screws with some takeup for wear in oncoming years.

I'd say you can probably almost file one to fit using the same surface-contact assessment (bluing, sharpie markers, etc as scraping), the idea is that you want solid contact all along the length so the slide doesn't rock. Scraping happens to be nice and controllable (meaning a slow-moving metal removal process) and won't make it into a banana as fast as machining.

The way I like to work on a slide is to completely disassemble the leadscrew/nut and just work on the slide itself. Clean up everything with solvent, remove burrs, cleanup some more, and generously oil. So I start moving the slide back and forth controlling the gib with my fingers only. One way it will want to wedge so just stop and work thru that by releasing it. You will eventually arrive at an area of handheld adjustment where it will just move freely but not wedge, and I suggest marking that spot and then putting the adjustment screws back at that point, and then continue from there. Important note is the screws are dainty delicate adjusters. Cranking down or high torque on the screws is neanderthal. So now you have an idea of where to cut it off, how much you need to add, etc. For me there's no shame in adding to the length of the gib, after all it has the right shape it just needs some more stroke. Cast iron would typically be joined with blue flux brazing rod in my shop. So when you are satisfied with your ability to move the slide freely by hand, then clean and oil the screw and nut and install and try some metal cutting to see if further adjustments are needed to tighten it up.

There's a bit more to it than "it must be scraped" but if you think conceptually about what's happening then for me its much less intimidating. It is a challenge to get a long skinny piece fitted along its length but just like anything some trials and errors will lead you to a working solution.

scraping in a tapered gib https://www.youtube.com/watch?v=LUEQhgGazAo This shows what you maybe were missing in the "Scraping in a lathe's top slide" video. https://www.youtube.com/watch?v=esAqz6bCVyQ

'https://www.youtube.com/watch?v=nT5O1szEG9k Keith Rucker'' Now that I have made the new tapered gib for the Monarch lathe, it is time to scrape it in to match the dovetails in the lathe cross slide using a Biax power scraper. I go through the process and finish up with some testing to make sure that the finished cross slide is running perpendicular to the lathe ways.

links
Machine design

Lathe youtube section for xy table