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Budget DIY straight edge for hobbyist?

Mach_Zero

Plastic
Joined
Jul 25, 2022
Hey everyone, I'd like to make my own straight edge just because I'm interested in scraping and maybe scraping in a mini lathe. I have a grade B surface plate and will be using a hand scraper.

I've been looking around a lot and reading through countless forum posts on here of people with similar questions. I'd like to make my own straight edge just to learn and have some fun.

Is it worth buying a 12-24" piece of cast iron or something similar to scrape it in myself? I can buy some G2 cast iron from Alro. But I've seen some straight edges made of aluminum for sale online. I could get some aluminum I beam and scrape that in too but it doesn't seem as stable as cast iron.

Edit: Called Alro and they would have to ship from Michigan. It would be $160 for a 3/4" x 1.5" x 24" piece of G2 cast iron. Doesn't seem worth it to me. McMaster sells a piece gray cast iron 1.25" x 2.25" x 24" for $135 before shipping. Will that also work?

Thoughts? Is it foolish to even undertake a project like this? I'm not trying to be a professional machine reconditioner. I just want to make my own straight edge for fun and to have a usable straight edge in my home shop.
 
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Mark Rand

Diamond
Joined
Jul 9, 2007
Location
UK Rugby Warwickshire
It's a good project if you can machine the bar to clean it up and reduce the amount of work you need to do,

I made a set of three squares from cast iron bar stock using a scraper and surface plate as one of my first projects (three are needed to prove the 90° angle).

It won't end up any better than your surface plate, but it shouldn't be any worse either. :D
 

Mach_Zero

Plastic
Joined
Jul 25, 2022
It's a good project if you can machine the bar to clean it up and reduce the amount of work you need to do,

I made a set of three squares from cast iron bar stock using a scraper and surface plate as one of my first projects (three are needed to prove the 90° angle).

It won't end up any better than your surface plate, but it shouldn't be any worse either. :D
It really does seem like a fun project. I'm sure it wouldn't be great but I could always get a better surface plate in the future and scrape it in better. I just want to make sure the material I choose is suitable for a decent straight edge.

Right now I'm leaning towards the McMaster piece or maybe look for Versa bar. Would that be good for a straight edge? I'll try to get some fairly wide rectangular bar to increase the stiffness (second moment of area) like they do with camelbacks.
 

Mach_Zero

Plastic
Joined
Jul 25, 2022
Just called American Iron to ask about Versa bar and for a 1.5" x 3.25" x 24" piece it'll be less than 1/3 the price of the smaller McMaster piece. In fact, I'll have to buy 2 of them just to make it to their $75 order minimum. That will give me plenty of material to practice on. Seems like a great deal.
 

JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
I've made several smaller straight edges, as well as angles etc for use in scraping. It's good practice.

It's really a pain to try doing an SE that is larger than the corner-to-corner distance on your plate. (best if enough shorter to get most of the width of the SE onto the plate) And unless you are very good, you won't get it as good as one you can compare full length.

How big is the plate, and how long an SE do you need?
 

Richard King

Diamond
Joined
Jul 12, 2005
Location
Cottage Grove, MN 55016
I see your from Florida? I have 3 excellent students who live in FL... One in Lance Balyzley in Jacksonville, Adam Booth in Pensacola and John Perry in Santa Rosa Beach. I am sure all would help you learn to scrape if you asked. They all have professionally made straight-edges plus all the tools you would need. They all could machine it or grind it so the scraping would be simple.
 

Mach_Zero

Plastic
Joined
Jul 25, 2022
I've made several smaller straight edges, as well as angles etc for use in scraping. It's good practice.

It's really a pain to try doing an SE that is larger than the corner-to-corner distance on your plate. (best if enough shorter to get most of the width of the SE onto the plate) And unless you are very good, you won't get it as good as one you can compare full length.

How big is the plate, and how long an SE do you need?

I have a small 9 x 12" surface plate right now (don't laugh at me you guys with your huge 4ft x 4ft surface plates that weigh more than my car lol)

I'm planning to buy a larger plate soon, probably something like 18" x 24" or something like that.

I don't really need a straight edge right now. But I've always been fascinated with metrology and stuff like scraping and getting very flat surfaces. I think it'd be a cool experience and maybe it'll come in handy one day if I ever buy a used lathe or mill that could use reconditioning. So for now I'm ok with just making a 12 inch straight edge, though it would be awesome if I can make one that's closer to 18".

I see your from Florida? I have 3 excellent students who live in FL... One in Lance Balyzley in Jacksonville, Adam Booth in Pensacola and John Perry in Santa Rosa Beach. I am sure all would help you learn to scrape if you asked. They all have professionally made straight-edges plus all the tools you would need. They all could machine it or grind it so the scraping would be simple.
Richard you are a legend. I've been a subscriber of Adam's YouTube channel for quite some time now. I know he and pretty much every other prominent machinist youtuber speak very highly of your knowledge and teachings.
I wouldn't want to bother any of your students with questions or advice though. I'm just a hobbyist looking to learn some new skills.
 
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Luke Rickert

Hot Rolled
Joined
Oct 24, 2007
Location
OSLO
You will need to machine the bar before you can scrape it, I don't see any mention of a milling machine in your workshop. You can mill a bar that is longer than the machine's travel but it does make for more work.

Also a 24 inch straight edge that is just a bar without support structure can be useful but you need to be careful as they will deflect considerably under their own weight. Even a solid 12 inch straight edge will deflect when supported end to end enough to cause issues. I have a few 12 inch prism castings left if you are interested.
Poured castings are much nicer to work with than continuously cast bar and unlike a square solid bar, the design was optimized to minimize deflection.

Luke
 

Mach_Zero

Plastic
Joined
Jul 25, 2022
You will need to machine the bar before you can scrape it, I don't see any mention of a milling machine in your workshop. You can mill a bar that is longer than the machine's travel but it does make for more work.
I do have a mini mill at home but I have access to a Bridgeport at work.

I could mill the 12" bar at home but I doubt I could do the 24" unless I get really creative lol.
 

Luke Rickert

Hot Rolled
Joined
Oct 24, 2007
Location
OSLO
Haha thats awesome! How did you make sure the cuts were all aligned after moving the setup? Did you sweep it with an indicator and shim it or something?
I don't remember exactly but I do know I used the DRO and came back to the same Z for each setup. I think I might have done one side, flipped it and then done the other (and maybe back again) it turned out within easy scraping range in the end.
 

Richard King

Diamond
Joined
Jul 12, 2005
Location
Cottage Grove, MN 55016
During the training I ask my students to "pass-on what I taught them" So they will help you! Another possibility to get a straight-edge is to buy one from Gary Martin of martinmodel.com/collections/machining-scraping-project-castings. He sells his SE's retail for less then I can buy them, or check with any local machine rebuilders and see if they have any surplus straight-edges. I know Lance B was selling some surplus straight edges a few months ago.
 

lucky7

Stainless
Joined
Sep 6, 2008
Location
Canada
If it were me, I’d buy Denis Foster’s 18” prism casting. Will be easy to scrape on your new surface plate, can function as both a precision level and dovetail spotter. And if you need, he’ll machine it for you, giving you a head start. I have one and use it frequently.

Have fun!
 

Mach_Zero

Plastic
Joined
Jul 25, 2022
Hey everyone! It's been a few months now and I've been scraping a piece of durabar I bought. It's 12" x 1.5" and I will eventually cut a 45 degree angle on the other side. This is a practice piece to make sure I'm capable before I buy a casting.

Things I've learned so far:
  • Scraping is hard
  • The lighting in my garage is horrible
  • It is impossible to pinpoint a specific high spot with a 40mm radius hand scraper without completely missing and ruining your straight edge
  • Scraping is hard

I'm pretty happy with how it has turned out. I 3D printed one of those radius gauges with the 1" x 1" square cutout and I've been using that to check my points per square inch. I'm not sure if I'm counting correctly, but I think I have over 40 points in pretty much every part of the straight edge.

There is an area that seems a little light in one of the images below. I was trying to use the absolute minimum amount of prussian blue as possible to not artificially increase my points, but if I go any lighter I can't even see the paint when I print it.

What do you guys things? Any advice? Is this an appropriate place to stop and call it good?


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M.B. Naegle

Titanium
Joined
Feb 7, 2011
Location
Conroe, TX USA
Looks good!
What are you using for a hand scraper? Hand scraping takes some stamina and persistence, but the kind of scraper you use and how you do it can have a big effect on how tired you get.

One thing I learned in Richards class is If you're using one of the standard flat bar scrapers that has the plastic file handle on the end, it helps to add a plastic/rubber disc to the back (like what's used with angle grinder sanding discs) so you can brace it against your body, then scrap with your legs, not your arms, as it's easier to stay on point and you don't tire as quick.

Just to put a plug in for them, I took the class thinking I'll never be able to afford or justify a power scraper. Not long later I broke down and bought a used one and man it makes life easier! Hand scraping still has a place though if you're doing small surfaces or working in corners, like small cross-slide dove-tails, it can be easier than the Biax. But anything wider than 1", I pull out the Biax and move some metal.
 
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Luke Rickert

Hot Rolled
Joined
Oct 24, 2007
Location
OSLO
I think you need to shorten your strokes, that is one of the many things that a power scraper makes much easier. You want the width of the stroke about the same as the length.

Also a 60mm radius should be enough for now, 40mm is getting small which makes things more difficult and can cut too deep (the angle of the scraper also plays a role here) You don't need and actually don't want crazy deep scraping (no matter what some will say). At this point I would use an oil stone with oil and take the tops off everything and go back to a nice sharp 60mm radius and raise or lower the angle I am holding the scraper to adjust the width. All the high grade reference scraping and precision tools I have seen have no significant "depth" to their scraping marks, deep scraping is something the King loves to push but as a universal rule the concept fails to stand up to the most basic reasoning.

It is hard to see in the pictures but no matter the radius, make sure it is really sharp, the edge can't be too polished and just a diamond wheel really isn't fine enough, you need a lap as well.

Also you really don't want to machine the bar after you scrape it, it will move enough you need to re-mill the scraped face as well. Durabar has plenty of internal stresses, more than an heat treated casting for sure, but even heat treated castings move a little when you machine them. Just rough scraping one face of a straight edge will cause changes to the other so you need to go back and forth between them.
 

JST

Diamond
Joined
Jun 16, 2001
Location
St Louis
I think you need to shorten your strokes, that is one of the many things that a power scraper makes much easier. You want the width of the stroke about the same as the length.
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Usually it seems that length shortens as the surface "comes in". If you are doing a reference surface, such as a straight edge, by the time you are refining the surface toward the final surface, the scrapes may be down to mostly "square", as long as they are wide, and likely about 3-4 mm long.

Roughing would take forever that way, and longer strokes are fine then. Gradually shorten once you have scraping and marking all over the surface. Also start "splitting spots" at that point, rather than scraping them all off. Make sure to hit any "bull's eye spots".
 








 
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