MAKING A PRISM STRAIGHT-EDGE OUT OF DURA-BAR

[Richard King]

my friend, interpreter, and student shows how easy it is to make a prism straight-edge out of some cast iron. I said Dura-Bar to get attention. I buy my cast iron from Dura bar in IL. They will saw it into a triangle for you. Just tell them the size. Or do as he did, shape it or you can mill it.

 

[Luke Rickert]

While for a one off project this approach is fine, proper castings are superior for a few different reasons. Years ago when Stefan made that video no one was making castings, this is no longer the case so buying a casting is a much better idea.

A sold prism will deform enough under its own weight. This means you should hollow out the back leaving ribs which is a lot of machine time.

Continuously cast iron doesn't scrape as nicely as conventional cast and will not produce the same fine finish possible with a high quality casting.

Continuously cast iron bar is not thermally stress relived and moves around much more than a normal castings.

If anyone in Europe needs a short properly designed prism (35cm) I have heat treated castings available for 120 euros. (220 for machined)

 

[Richard King]

I disagree. I used to make prism castings from a wood pattern and sand. Then I heard of Dura-Bar continuous cast iron. It is extruded like steel. I have been making prism straight edges, parallels, inserts and scraping plates and have NEVER had an issue. No porosity or voids experienced with poured castings. https://www.dura-bar.com/advantages

 

[Luke Rickert]

For many applications continuously cast iron (such as Durabar) is a good option Orange Vices use it for example. Milling from bar can be much cheaper than making patterns etc but straight edges are not one of those examples. A well designed and poured castings have no issues with inclusions and the material is not only better they are cheaper at the end of the day compared to fully machining a straight edge from bar.

I have made special straight edges from bar for one-off projects and it is definently better than no straight edge but when you can get a proper casting it is a much better option.

Disagree if you wish but it would be far better to do as an educated, scientific person would and do the research, run the analysis and make straight edges both from bar and from castings and see what is better.

If you don't know how to design the parts for casting and/or use a low quality foundry of course you will end up with poor quality parts but that is not the fault of the production process.

 

[Richard King]

I have been making them out of it for over 30 years. I have the credentials of being an expert in this field. Who are you? What qualifies you? Your opinion is meaningless to me. How many straightedge have you made? I've made hundreds from sand castings from a foundry, many with flaws or blow holes and they need to be high temp stress relieved 2 times. The continuous cast in small parts or prism straightedge don't need any. On longer then 24" i have high temp stress relieved 1 time. I can write my friend Professor Alex Slocum (retired) of MIT for his opinion. But the last time I did about a question some PM supposit expert asked he said it was laughable that anyone questioned my expert opinion. Some people on here like to stir the pot just so they can look like an expert and are fake in my opinion.

 

[Luke Rickert]

What Richard fails to understand is that I do not have an opinion. Opinions are as meaningless in science and engineering as self appointed experts. What I do is to evaluate mechanical problems based only testing, analysis and established theory. As an experienced engineer with a masters degree I am qualified to do just that and do this professionally every day for highly critical structures (aircraft, subsea oil etc). With an interest in machine rebuilding and a dislike of BS I do use that skill set to try to straight out the misinformed and produce a few high quality products to fill in some of the holes in the market which I sell more or less at cost.

Education and official qualifications do actually matter, it isn't that someone without education cannot evaluate things logically but those without that background are more likely to approach problems as Richard and react with emotion rather than reason and logic. There is no such thing as magic (ringing straight edges for example), and just because you have been doing something for a long time does not mean you are an expert. What also really matters is actually doing. When was the last time you rebuilt an entire machine? (not this century I bet) I rebuild machines, I make patterns and have straight edges cast, and I machine and scrape them. I do the engineering and run the analysis myself to optimize the designs.

Frankly if you have been having castings made for 30 years and they still show up with flaws in critical areas you are by definition not an expert. Those parts are not fit for purpose and should not be accepted. The foundry will either fix their process or refuse the to produce the parts do to their design. My castings have no flaws, because I took the time to design patterns and runners properly and hired a foundry that knows what they are doing. It really isn't that complicated.

 

[michiganbuck]

Richard based on your experience just by eyeball how much error do you think the shaper machining left on the rough part face? I am not a scraper hand, so likely I might have wet surface ground the part after the shaper, and before starting scraping.
I enjoyed the viedo.
Buck

 

[MCritchley]

While for a one off project this approach is fine, proper castings are superior for a few different reasons. Years ago when Stefan made that video no one was making castings, this is no longer the case so buying a casting is a much better idea.

A sold prism will deform enough under its own weight. This means you should hollow out the back leaving ribs which is a lot of machine time.

Continuously cast iron doesn't scrape as nicely as conventional cast and will not produce the same fine finish possible with a high quality casting.

Continuously cast iron bar is not thermally stress relived and moves around much more than a normal castings.

If anyone in Europe needs a short properly designed prism (35cm) I have heat treated castings available for 120 euros. (220 for machined)

Whidbey, if you go back and search my posts I describe my cast iron stress relief recipe for Dura bar. I tested a scraped part that went in the furnace a few times on Bessel points. The part did not move after the first cycle. My conclusion was the stress was out of the part.


Your statement about Dura bar not being stress relived is true. The same can also be said for castings, both are full of stress. It’s best to stress relief before and after machining. And Dura bar scrapes fine, each cast or extruded piece scrapes differently. Much like hand planing wood. If I need a one off shape to get into a feature I will always use a piece of Dura bar and get the exact shape.

 

[lucky7]

Whidbey, you mentioned making some machine rebuilding/scraping products yourself. What do you make? Links to website?

 

[Richard King]

Richard based on your experience just by eyeball how much error do you think the shaper machining left on the rough part face? I am not a scraper hand, so likely I might have wet surface ground the part after the shaper, and before starting scraping.
I enjoyed the viedo.
Buck

I used to grind both castings and Dura-bar. I found dura bar easier to work with. If one can't grind .0002" or mill .001" in 12" it's time to hang it up. I'm going put the PM expert who I believe is a fake on ignore as he is full of it. Take his no experience writers word or mine. I suspect he makes and sells straight edge castings.

 

[dgfoster]

Whidbey, you mentioned making some machine rebuilding/scraping products yourself. What do you make? Links to website?

Lucky, My thought exactly. Whidbey, it was interesting and informative to hear your experience-based and education-based comparison of cast products vs Durabar.

One other factor concerning Durabar is expense. In quantity, it can be purchased fairly reasonably, I think. But, I have looked to buy a couple individual pieces and have them shipped to me and the prices were actually amazingly high---considerably more than for a casting that is already close to net size and shape. A while back I posted the quotes I got. Has anyone here actually purchased an individual piece of Durabar lately? And what was the cost?

Denis

 

[michiganbuck]

I think he said this is my 20 or 21th passes @30:07..and pass 22 @ 30:44 looking very good. I was wondering about how much stock (likely) was taken(scraped) off in that many passes. just trying to get an idea of stock removal for an amount of time.

looks like each scraping pass is/was only a very short time..but one would also need to add the blue-up time for the whole job. and he said that he may go to video #2 so likely he wants it even better or for scraping the angle.

Yes, I can get to a few tenths with my surface grinder, or 1 or 2 thow on my mill.

 

[lucky7]

Stock removal isn’t as directly measured as on a surface grinder (or other machine tool). There isn’t a uniform flat surface from scraping- there’s points ie hills and valleys. I average measuring with a dti reading off an old gauge block run along the surface. I’ve measured depth of cut to try to learn consistency and can reliably rough with a wide radius carbide by hand at 3-4 tenths depth- in the individual divot. But the overall surface goes down a variable amount- until you get to (guessing here) 10-ish points per inch. Gentle picking of polished high spots on finish passes is something I haven’t measured (not sure I could with my gear) but guessing one tenth depth? Not sure if this helps or confuses?

 

[TGTool]

I think he said this is my 20 or 21th passes @30:07..and pass 22 @ 30:44 looking very good. I was wondering about how much stock (likely) was taken(scraped) off in that many passes. just trying to get an idea of stock removal for an amount of time.

looks like each scraping pass is/was only a very short time..but one would also need to add the blue-up time for the whole job. and he said that he may go to video #2 so likely he wants it even better or for scraping the angle.

Yes, I can get to a few tenths with my surface grinder, or 1 or 2 thow on my mill.

He could have sped up his process a bit, and I suspect a professional could be rather more efficient in getting there.

For instance, he takes his first print and shows the blued areas where it touches. And he knows it's high in the middle, both from his check with the indicator and his print. So he could have been much more aggressive in removing the material in the early stages. He took off ONLY the blue but he could have taken a wider area part way out towards the ends and reduced the number of passes.

He got where he was going, no problem, and got good results, but if you were working on the time clock I think you'd find ways of speeding that up.

 

[jaguar36]

Lucky, My thought exactly. Whidbey, it was interesting and informative to hear your experience-based and education-based comparison of cast products vs Durabar.

One other factor concerning Durabar is expense. In quantity, it can be purchased fairly reasonably, I think. But, I have looked to buy a couple individual pieces and have them shipped to me and the prices were actually amazingly high---considerably more than for a casting that is already close to net size and shape. A while back I posted the quotes I got. Has anyone here actually purchased an individual piece of Durabar lately? And what was the cost?

Denis

I've found this as well, particularly if you end up needing to machine alot away.
I needed some in a hurry recently and while Not Durabar per se, but continually cast ductile iron from McMaster was ~$4 a lb.

 

[memphisjed]

Lucky, My thought exactly. Whidbey, it was interesting and informative to hear your experience-based and education-based comparison of cast products vs Durabar.

One other factor concerning Durabar is expense. In quantity, it can be purchased fairly reasonably, I think. But, I have looked to buy a couple individual pieces and have them shipped to me and the prices were actually amazingly high---considerably more than for a casting that is already close to net size and shape. A while back I posted the quotes I got. Has anyone here actually purchased an individual piece of Durabar lately? And what was the cost?

Denis

I purchased dura bar retail amounts with a cut charge at 3$ +ups shipping a pound about two months ago. This was for less than three feet- man off street retail.
Which was not eye watering more than full retail for cold rolled round (if buying only 3 feet).
Casting to shape does have a different character about the material.

 

[dgfoster]

So, I just looked at McMaster. Here is a screen shot of their pricing

So a 1’ piece of 2 5/8 square by 1 foot is 118.44 plus shipping. That is the smallest size they sell from which an industrious person could whittle a prism similar to a Featherweight 8”. I sell my casting to PM members for $74 -10% and 9 bucks priority mail shipping.

You can get 1.25 by 2.25 for 77 a foot plus shipping. Maybe there are better deals out there. But that is one factual data point. FWIW.

Denis

 

[Richard King]

I prefer Dura-Bar - It doesn't have a rough finish like a sand casting. It doesn't have hard spots especially on this corners from heat treating. Here is the last order I made 2 years ago. I use these plates for my practice plates when teaching. I have the host mill them.

1 0.750"H X 3.625"W X 72.000"L 2 52.3 lbs 105 $137.644/EA $275.29 GRAYIRON G2 IRON CUT PLATE Offering plate Material finish .625"X3.5" Lead time 3 days (This size was approx.$2.00 a foot)

2 Shipping & Handling 1 0.0 lbs 0 $127.19/EA $127.19

I will order some square material and have them saw it corner to corner, mill them and sell it on here. I am sure I can sell them cheaper then one can have a casting made.

 

[dgfoster]

I prefer Dura-Bar - It doesn't have a rough finish like a sand casting. It doesn't have hard spots especially on this corners from heat treating. Here is the last order I made 2 years ago. I use these plates for my practice plates when teaching. I have the host mill them.

1 0.750"H X 3.625"W X 72.000"L 2 52.3 lbs 105 $137.644/EA $275.29 GRAYIRON G2 IRON CUT PLATE Offering plate Material finish .625"X3.5" Lead time 3 days (This size was approx.$2.00 a foot)

2 Shipping & Handling 1 0.0 lbs 0 $127.19/EA $127.19

I will order some square material and have them saw it corner to corner, mill them and sell it on here. I am sure I can sell them cheaper then one can have a casting made.

Richard,

If you are having trouble with castings having hard spots on the corners, you are using castings from an incompetent foundry. There are ways to use proper feedstock, melting, and casting techniques to prevent such problems. As part of my quality control I have three methods of testing for uniform softness. I use a Leeb Hardness Tester or a Wilson harness tester on every casting that leaves my foundry. In addition, I machine about 1/3 of my castings and can tell on the first cut if the casting is uniformly soft. That is the "final word" on uniformity.

Secondly, proper thermal stress relieving a casting does NOT induce corner hardness. The correct stress relieving temperature is 1150 F (I think some heat treaters might use 1200). To get to the transformation temperature of cast iron a person should have to raise its temperature to 1350F or greater and then quench it. I think it is unform practice by any heater to then slowly cool from 1150 (1200) to room temp. So, for stress relief, the part would not ordinarily be raised to the transformation temperature of iron and it sure wouldn't be quenched. And to anneal cast iron I follow the common practice of raising its temperature to 1750 and slowly cooling it. Done correctly, that guarantees the softest casting possible.

Today I will stress relieve my new Featherweight Parallel/Level casting pictures of which I posted in a parallel thread. When I do so, I will put in a scrap of iron and pull it from the oven and quench it to see if that will harden it. I don't think it will. But, let's answer the question---easy enough with the right equipment.

Rough finish is a relative term, of course. But, if a foundry is using good sand with proper additiives and proper pouring technique, a relatively smooth surface will result. Here is a pic of the casting I poured for the first time yesterday. I think you can see it has a fairly smooth surface as cast---enough so that you can see it glistens.

Denis

Added: Oh, since you mentioned the feel of a casting in the hand, the above casting with its oval "windows" really feels nice in the hand.

 

[lucky7]

Denis, do you have your own heat treat oven now? If yes, what type did you get?