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Making a straight edge from an old surface plate

Andrew Wilding

Aluminum
Joined
Jan 3, 2009
Location
nottinghamshire, uk
As part of my grinder rebuild I needed a dovetail straight edge. I was loathed to mess with one of the camelbacks (non dovetail type) that I have and finding one used was not happening, so I made one from an old surface plate. Here is a quick video showing the build:

 
I'm impressed. Something irrational makes me regret the sacrifice of a cast iron surface plate (actually a scraped bench plate) for the project. However, crafting a straightedge from the long side is probably a better second career for it. The remainder can be used for something else clever and original.

I think you made good use of your available materials and opportunities and the print you showed in the video had all the earmarks of a good job in progress. I would have liked to see the final print but that's just curiosity and superfluous to the point: posting a video of making what you need of what's handy and available for sacrifice.

My only suggestion would be to bevel the short webs back to meet the long web and radius the corners. Drill for handles? Sculpt on the long web a bas-relief panorama of Nelson's victory at Trafalgar?

Nice work.
 
Thanks Forrest. I did think about jazzing it up a bit with some nice curves and chamfers, but to be honest I just want to get on with the job I have in mind for it. I might make some insulating grips for it though. I will perhaps show the final spotting in another video
 
Wouldn't you be worried about the irregular form of the scupture distorting the accuracy of the straight edge? :D

Didn't think of that. Maybe for stress balance, a bas- relief on the other side - a series of three because of the webs? Scenes based on F S Remington's works? Nothing busy or complex. Just an area of equal stress for balance. I was thinking of the "Song of Hiawatha" illustrations? OTH Scrooge McDuck porposing in his money bin? Something quick befitting a tool well but quickly made.
 
This Old Tony had a 2 video series. I hate to admit, I was looking for a cast iron surface plate locally, as the price could be cheaper than getting a straight edge. I thought his looked pretty nice when he got done with it.

Yours looks fine to me also.

I saw this about a year ago and his use of the pull stroke scraper does seem to get a good amount of material off. I remember seeing a discussion about it here on PM, comparing it to the push scraper, but can't remember the details.

 
I'm starting to dabble or experiment with pull scraping and it's raised some questions for me too. I'd intended to just use the pull scraper for some decorative scraping (checkerboard) on some non-functional faces. As it happened I'd done some practice push scraping on those surfaces already. Now as I start a little pulling it becomes evident how scalloped the surface is since the blade now does a wider flat cut. This wasn't unexpected since Rich King talks about checking the depth between high and low on a scraped surface. However, this now starts me wondering if the pull scraped surface might have much less variation in depth. And is this a good or bad thing or is it indifferent? If flatter overall, it can still be flaked for oil retention.

Altogether, the more I explore the more unanswered questions seem to come up.
 
I would go by this mantra: "scrape first for alignment, then for bearing and flake for lubrication, not for decoration".
My interpretation of the problem is the following: if you need to rely on scraping also per lubrication (e.g. where it is practically impossible to flake), it's very important that your scraping marks are rather deep.
Another advantage of having deep scraping marks on a measuring/spotting tool is that they resist more wear, that is more time before you need to re-scrape it (if I recall correctly, Richard mentioned that they used to scraper their straightedges with 0.5 thousands deep marks in the final passes to improve the durability).

A characteristic of shallow scraping, which could be either an advantage or a disadvantage, depending upon the cases is that there is no much volume for air and fluids to be displaced.

Personally, I prefer to keep my scraping fairly deep in everything I scrape.

Paolo
 
I'm starting to dabble or experiment with pull scraping and it's raised some questions for me too. I'd intended to just use the pull scraper for some decorative scraping (checkerboard) on some non-functional faces. As it happened I'd done some practice push scraping on those surfaces already. Now as I start a little pulling it becomes evident how scalloped the surface is since the blade now does a wider flat cut. This wasn't unexpected since Rich King talks about checking the depth between high and low on a scraped surface. However, this now starts me wondering if the pull scraped surface might have much less variation in depth. And is this a good or bad thing or is it indifferent? If flatter overall, it can still be flaked for oil retention.

Altogether, the more I explore the more unanswered questions seem to come up.

I'd like to see what some of the seasoned scrapers and/or old timers say about this. Maybe Forrest has an opinion, but I'm pretty sure I've seen him say he uses a push...that might translate to a Biax. :)
 
I would go by this mantra: "scrape first for alignment, then for bearing and flake for lubrication, not for decoration".
My interpretation of the problem is the following: if you need to rely on scraping also per lubrication (e.g. where it is practically impossible to flake), it's very important that your scraping marks are rather deep.
Another advantage of having deep scraping marks on a measuring/spotting tool is that they resist more wear, that is more time before you need to re-scrape it (if I recall correctly, Richard mentioned that they used to scraper their straightedges with 0.5 thousands deep marks in the final passes to improve the durability).

A characteristic of shallow scraping, which could be either an advantage or a disadvantage, depending upon the cases is that there is no much volume for air and fluids to be displaced.

Personally, I prefer to keep my scraping fairly deep in everything I scrape.

Paolo

Yes, I've heard Rich tell the story (more than once) of his father rebuilding two machines, one with shallow strokes and one deeper. I can't gainsay his experience. So what's actually happening with the Swiss style pull scraping? Are there areas cut deeper than they appear? When you see the overlapping marks of the pull scraper, there shouldn't be clear rectangular areas if there are deeper spots between. Alternatively, the spots per inch should be way further apart. If that's so, have the Swiss been missing the opportunity for greater longevity of way surfaces all these years? It would seem like someone, somewhere would have figured that out and the new knowledge would have been incorporated into the trade. Or were they so hidebound in tradition that they couldn't adopt an improvement? That seems unlikely as well, hence my confusion.

There's at least a hint that SIP technicians did scrape for appearance, whether you call that decorative or not. That is, using what was most effective in material removal to first establish geometry and then contact, but pull scraping the last couple cycles for "the SIP look". Would they sacrifice functionality for appearance? I don't think so.

My project does separate functionality and appearance. I have good functional machine scraped surfaces then others that have to be something. They're either left as machined, painted, scraped for appearance or something else. The choice of what it will be is inevitable. Doing nothing to the machined surface is still a choice.
 
You have to find a balance between bearing points and scraping depth. You can scrape .0005 deep on a machine way with 10-15 points per inch. But, to get more points, you generally have to give up some of the depth. There is no silver bullet in scraping.
 
You have to find a balance between bearing points and scraping depth. You can scrape .0005 deep on a machine way with 10-15 points per inch. But, to get more points, you generally have to give up some of the depth. There is no silver bullet in scraping.

Given my very limited experience - I have to fully agree with this. I messed about with a small scraped standard I made for dovetail checks on y shaper - starting with deep scrapes (0.002") and a ppi of around 18. as I refined the ppi to get an average over 25ppi the measured variation in depth over the surface was at best 0.0005" but more frequently a bit below that. Inking then requires much care or you smudge and smear.... - I considered then 'flaking' the surface or a final pass of deeper scrapes with a small radius scraper - decided against it for fear of cocking up the ppi which had taken me some time to get even over the small surface - lots to learn by doing it many times.

Great thread this one.
 








 
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