Help!!! Poor man's Straight Edge for a scraping standard???

Cast iron will take a "set" and changes come slow. You can bolt the thing to the floor and true it all up, and eventually you could unbolt it and it would stay pretty straight. But until then, and it could be a long time, it won't "relax" back to the factory straightness.

I'm sure when Richard sees this, he will chime in with his thoughts, which are sure to be worth hearing.
 
Cast iron can warp considerably if it was not properly seasoned to begin with. I rebuilt a Rockwell lathe whose bed had bent upwards .010" since manufacture.
 
George's response gave me food for thought...

Last night I left the adjustment bolt REALLY tight to see if the bed would untwist any during the night. This morning: no change, not even a tenth. This afternoon: no change. Then I had an idea... Putting a bottle jack on the high corner, I jacked against the ceiling beams whilst looking the the twist with a dial indicator. The house was creaking and I saw no more than a few tenths of change! When pressure was removed, it came right back.

So, I learned a few things... One, the casting is really and truly warped. The theory is amongst the gurus at work is that the cutout for the hydraulic hoses on the right side of the base yielded unbalance with regard to internal stresses and the base turned up on the right side. Two: the casting is rigid as all heck.

Call me impetuous, but I knew I could correct the condition by scraping. As I had done a bit of scraping before, snagging castings and making small areas flat, I decided to have a go at it. If worse came to worse, I could always have the ways blanchard ground to be all coplanar along with the column mounting surface - which conveniently is also on the same plane.

I borrowed a cast iron surface/lapping plate from work (recently calibrated), stopped off for some prussian blue, reread a few sections from "Machine Tool Reconditioning and Applications of Hand Scraping", and re-watched a Youtube video on scraping. I already had a scraping tool I made from an old file.

I started scraping... 4 hours of work later: voila! Between scraping and knocking down small high spots by flat filing, I get a consistent bluing across all 4 ways except for a small low area that is always straddled. Best of all, the saddle no longer rocks! I can't get a 0.001 feeler gauge in between any way and the saddle, where before I could get a 0.008 gauge in!

I'm actually surprized at how flat and smooth the whacked out way became. Now, I just need to clean off all the stray blue from the machine and my hands, and the cast iron particles that are all over. I found bleach bathroom cleaner takes the bluing right off - stains too!

In addition, I need to scrape in some oil holding X's and reassemble the grinder.

The way doesn't look like an old school frosted way, but it's way smoother than the ways on my Chinese mill apart from a few scratches where I dug the scraper accidentally. These should be benign. You can tell I'm not a first rate scraper... But it works!

So all in all, some manual labor (sore muscles tomorrow for sure), I have a base that is flat without being forced (I scraped with the adjuster set to just bottom out). Because it's stress free, I'm guessing it'll stay that way. I assume 44 years has been long enough for the base casting to stabilize!!!

I wish Richard had chimed in sooner, but I had the time and "went for it..." knowing I had an "out" - having the base ways and column mount surface blanchard ground.

Maybe now I can finally get the chuck flat!

John
 
John, although you have already worked out the problem, it seems, I had a thought that might help someone else in a similar situation. Aging a casting is part and parcel of good machine tool building, but it isn't always done. I have heard of smaller casings being stress relieved by heat treaters, so I thought it might be worth considering. Even then, it likely wouldn't be perfect, and would still need some fine tuning. It was just a thought.

As far as a straight edge, old time auto machinists used a (well I have one) flat bar about 5/16" thick, 36" long and ground parallel and straight on the two edges. I have checked it on a surface plate and found it S & P within 0.0002. It might be something you could purchase cheaper than a regular camel-back straight edge.
 
Going back to the orginal question asked by John, I've used a piece of precision flat ground stock before for a straight edge. It's good within .001" per foot, most of the time.:biggrin:

I've also taken a piece of cast iron flat bar (Dura Bar) and milled it flat on my mill. Then scraped it reasonably flat to my surface plate. Not Richard King flat but good enough for the stuff I work on.
 
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