Straight Edge For Mill Touch Ups

sbx

sbx

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Hey all,

I am contemplating doing some scraping on my PM25-MV for touching up any obvious high spots while I break it down for my CNC conversion. In doing so, I'd like to scrape in a straight edge/Prism for practice and for a reference surface for the parts of the mill I can't move.

I plan on getting a 18x24" granite surface plate (enco most likely).

So, I was thinking of getting a piece of 28" 1"x2" cast iron bar stock. Face Milling it flatish, then milling a 45 degree angle on one side. Then scraping the rest in. Probably just scrape the one large 2" flat side, and the 45 degree side.

How does that sound as a starting point?

Any thoughts on source for the iron? Speedy metals cuts to order and seems reasonable. Couldn't find durabar priced out anywhere.

Thoughts?

PS. I have cobbled together a couple scrapers already to start with. One Anderson emt style, and one smaller detail scraper. I also have Connolley's Machine restoration guide for instruction.
 
Sounds like a start. Go for it!

Speedy metals is probably the easiest to purchase from. I'm sure someone sells Dura-Bar product in your area. Get a hold of Dura-Bar and see if they can suggest a dealer in your area you could buy from. I've machined a couple of straight edges from G-2 durabar. Both have been scraped in. One of them I'm redoing to remove some weight from it. So far, the material has been fairly stable for my straight edges. I would suggest stress relieving the material after machining to be on the safe side before scraping. If it moves on you while scraping you will catch on after fighting it for while.
Ken
 
As a reference, Mr. King suggested I rough machine, stress relieve, finish machine, stress relieve, then scrape a camel back casting. Richard also has a good beginners video on scraping technique. You might check ebay. Don't forget your straight edge angle is less than your dovetail so you can tip it in. The smaller member is spotted against the larger to match them up eliminating the need to build,prove, and use a prism.
 
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Richard knows his stuff, whack the machined part with a rubber mallet to help stress relieve more quickly. He sells straightedge castings, so stands to reason he recommends them :) But it's the same principle for scraping anything, really.
 
Andre said:
Richard knows his stuff, whack the machined part with a rubber mallet to help stress relieve more quickly. He sells straightedge castings, so stands to reason he recommends them :) But it's the same principle for scraping anything, really.
Click to expand...
I'm referring to the stress relieving process he recommended.
 
I've used the rubber hammer method, it some what works. Best method is theromo stress relieve with the straight edge hanging in the furnace.
I know having different angles on your straight edge is what Richard stresses so you can work the angle on the dove tail instead of working the dovetail to the straight edge. I've always made my dovetail straight edges to fit the dovetail being scraped. In 40+ years of doing scraping off and on it has not been an issue with anything I've worked on.
 
I use a straight edge that is a hollow, webbed V....A 36" long will work for everything on a Bridgeport except the table.
JOHN
but I can not post pictures here yet
 
I made my straight edge from 1" X 2" cast iron from enco. Machined one edge to 60deg and hollowed much of it out from the opposite side.
Scraped a lot of material and it just kept bowing as I worked. Yes, I did hang and ring it.
Finally put it in the oven for a few hours, 550deg, and let it cool slowly. This helped some with the warpage and with the varying hardness.
Still had warpage so I put it back in the oven and set it on broil for several hours.
That seemed to stablize it and when I finally started to get close, I knocked it to the floor and had to start over.
OK, theres a number of lessons here.....
Used it right away to scrape the cross-slide of the lathe but haven't since checked to see if its still flat. It's hanging and I ring it most days.
Still need to make a 50deg one to do the shaper. Am certain it will go much better but not yet looking forward to it.
If I had to start over I'd get a camel back casting.
 
I would say you would need something more like 1" x 4" in order to give it some stability.

But if you're going to use it in the 'flat' orientation it's going to be quite floppy still, and may bend to conform to a convex/concave way upon which it's laid.

Most manufactured camelback straight edges have the angled part sticking out, but then are 4-5x the height as what they are in width, in order to keep the reference surfaces flat.

What you're proposing would be like lying a piece of paper down. It will just bend. Stand it upright though with a 90 degree fold in the bottom, and it will stay straight.

Perhaps you could get something like 5" x 2" iron and machine it heavily so that it ends up like an L shape?

...Or just find a used camelback somewhere :)
 
I also use a cast iron I beam....parallel type
JOHN
 
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