DIY Milling Machine Part 2: Scraping the steel inlays for some extra precision! 

PS: Same reason for the big chamfer on the linear guide blocks.

You are right the chamfers are to small. I will make the bigger before final assembly 👍

No pain no glory

...Unless you marry the wrong girl. Then it's the other way around.

you can avoid scraping by processing on surface grinder (after milling)

I haven't done it on the column. The height of both pads is correct there. But I should have measured if they are parallel to the guides or leaning in one direction. The one on the bed is leaning quite a bit to the front.

Right. That was exactly how I did it. It was quite time consuming to mount the rails to measure but I think that was the most precise and easy way.

@@AlexCNCen Agreed, cheers!

Sounds like Wintergatan

@@bkofford I'm sure it is wintergatan. Recently he's been giving permission to use his music for video. Most of them are his timelapse music. Also isn't Alex part of the engineering team?

Right it's is from Wintergatan. Already used that in my earlier videos.

It is hot rolled mild steel. I have no comparison against scraping cast iron. With the right geometry of the scraping blade I had no problems to get good results.

I will try out Dychem the next time. It was quite difficult to see the print pattern during the finishing passes.

I know someone who did it like that. It was a lot of work. Do not use hardened steel. Normal steel is good enough. You need to be able to scrape it. The most difficult thing is to get the parts aligned during the concrete pour. And it will warp a little bit during the curing process. If you are doing it good you should be able to get the flatness within 0,1-0,2 mm/m. It is possible to scrape it flat than but it will be a lot of work.

Hi. I haven't measured the final ppi. Maybe I got around 20 or so. Definitely more than needed. I stopped scraping when I was satisfied wit the measurement against the straight edge. In general it shouldn't be to critical if the surface is only in fixed contact with another surface. It's much more critical for sliding surfaces because that will influence how fast they wear down.

@@AlexCNCen I agree that for sliding surfaces the ppi and percentage of points (pop) are important for oil retention and stick-slip friction. However as a mounting surface for a linear guide I think that two low ppi could contribute to distortion of the guideway. I was trying to decide at what point the surface would be “good enough” for a linear guideway surface. I have scraped a 2x2x30 inch mild steel bar to about 25 ppi using the geometry on the carbide tool as described in the Engineer’s Findings video. It worked quite well. Then I used a ground flat stone to increase the pop to about 50%. The surface has nice large flat sections that will support the linear guide quite nicely, but perhaps is not so good for a sliding surface. I need to verify the overall flatness and local flatness of this test piece to confirm how well the technique worked. I’m waiting on the delivery of some metrology equipment to for this. I suspect it’s quite good as the scraped bar will ‘float’ across the surface plate on a cushion of air. I’m doing a similar build as you have done. The approach I’m taking, however, is to cast the base, column, and table on top of the a 24x36 granite surface plate to ensure the rail mounting surfaces are co-planer. So I need to prepare the mounting surfaces in advance of the casting the machine parts. Anyway Alex I’ve enjoyed watching your videos on this mill. It has really helped out with my thought process on how to complete my project. Well done and thank you for answering my comments.

For the column I don't know. But the bed is nearly finished now and I have put 7 hours of work into it. 2-3 hours more and it should be finished.

It is about the same as steel.

I got that used from ebay. But they are very rare.

Found some on somet's site (under edges) and also Kinex got some. Somet is czech manufacturer, but that granite edge is from Schut.

Easy fix for everything 😅