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| PekkaNF:
Hi I need to build something using hot rolled steel. I have heard that hot rolled steel is more stable and does nor warp too badly when skin is milled away. Planning to make top slide for a lathe. I need flat bar, something like 20-30 * 80-100 mm section. Q1: How I can tell difference between hot rolled and cold rolled steel at scrap yard? Specially if it is rusty? I know hot rolled should have mill scale, but how does it look? I tried to google and founf a lot of articles about removing it with an angle grinder. Q2: How do I remove mill scale? Piece is about 20*80*300 mm and I have time, but don't want to couge it with angle grinder Q3: Does it works if I make a dovetail rail of hot rolled steel and slide cast iron? What kind of finish I need here? Does milled (dove tail cutter) produce good enough finnish for sliding contact or do I need to grind or build a lap for it? Pekka |
| Lew_Merrick_PE:
--- Quote from: PekkaNF on July 31, 2014, 06:29:34 AM ---Q1: How I can tell difference between hot rolled and cold rolled steel at scrap yard? Specially if it is rusty? I know hot rolled should have mill scale, but how does it look? I tried to google and founf a lot of articles about removing it with an angle grinder. Q2: How do I remove mill scale? Piece is about 20*80*300 mm and I have time, but don't want to couge it with angle grinder Q3: Does it works if I make a dovetail rail of hot rolled steel and slide cast iron? What kind of finish I need here? Does milled (dove tail cutter) produce good enough finnish for sliding contact or do I need to grind or build a lap for it? --- End quote --- 1) Mill scale is a ranges from a dark brown to an almost black coating to the HRS material. CRS material will range from fairly bright silver-gray to all rusty. 2) Your choices for scale removal are: cut/grind or etch to remove it. Many people here will use a vinegar & salt soak. This is slow & steady. I almost never have the schedule time for such slow methods and typically use muriatic acid to remove scale. For a piece of the size you are quoting, my approach will take about 10-15 minutes. Be very careful of the fumes from muriatic acid -- do it outdoors. After you have etched off the scale, coat the part with a base. I use baking soda as it is inexpensive and readily available. Rinse thoroughly with water & dry it completely. Newly etched steel will rust in a heartbeat. I coat such parts with (wooden floor) wax to prevent that. 3) Unless you have an amazingly rigid spindle with very good bearings, you will almost certainly need to st/one out the resulting dovetail face to take it to a fine (but longitudinally scratched) finish. The alternative to this is to stone it to a mirror finish (the reflection will tell you how flat you got it) and flake a pattern of "oil catches" along the face with a scraper. Almost any decent book on scraping will give you a handle on the technique. |
| Meldonmech:
Hi Pekka When using your angle cutter, try out cut depths, and feed rates, preferably on an off cut of the actual material you will be using for your cast iron and hot rolled slides. You will the be able to assess the finishes you can obtain. The final cut should be very light several thou. using a very fine feed. Hard cast iron may need a deeper finishing cut. This should give you the best finish possible, and minimize final finishing. Lapping is a possibility, lapping the sliding part to the rail, and the gib strip to the rail. Again using scrap material to get a feel for the process. Lapping compound obtainable in varying grades can quickly ruin the surface. Try fine first to see if that will suffice. The final finish should be smooth and matt all over. Use plenty of oil, and make sure the mating surfaces are perfectly cleaned before assembly. The surfaces can then be scraped to provide oil retention as suggested by Lee. I believe that if things work on scrap, they will work on the job, and save a lot off heart ache. Good luck with your project it sounds interesting. Cheers David |
| Fergus OMore:
Ignoring the advice and whatever on steel, preferred top slide metal should be cast iron. The latter is so much more stable, easy to machine and then scrape. OK, I HAVE a set of slides on my little Stent tool and cutter grinder which are bright mild steel welded sections. Dead wrong as others will rush to comment but if you are prepared to normalise to get rid of the inbuilt stresses and scrape and whatever with way oil, you can do it. Me, I got the thing for a song as I bought it for the motor as the maker had died. Probably, the enormity of the task was too much. Again, as others will rush to point out, cast iron will move as well. I was making a Westbury mill head - not a Dore and it moved on splitting. Rude Anglo Saxon mutterings again. So think it out- carefully Norman |
| vtsteam:
Any blue-gray scale anywhere on it, even if mostly rust covered elsewhere is a giveaway. Scale tends to resist rust for quite awhile, and there is often a protected patch somewhere on a rusted piece. Also hot rolled tends to have rounded edges instead of neat clean square edges like cold rolled. Like a typical piece of angle iron -- the edge is often rounded/tapered, not perfect. |
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