Considering Casting Simple Grey Iron Prism Shapes for Dovetail References.
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    Default Considering Casting Simple Grey Iron Prism Shapes for Dovetail References.

    Given the fact that Durabar is not available, so far I can tell, in a shape approximating a prism, I am considering making a simple prism-shaped grey cast iron 18" casting available. Since I will be making the pattern and casting it myself, the dimensions are negotiable. I'd be interested in some input as to optimal length, prism angles and face width. I think a very simple prism shape could be supplied ready to machine at a cost competitive with a Durabar rectangular shape. the prism-shaped casting would be far more convenient for the user as only facing would be required. I could also supply the casting with two milled faces. Such a casting (actually four of them) would fit in a a large USPS FRB. Such a casting would weigh something like 15 pounds.

    Denis

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    Hi Denis, I would think 2-3 inch face would be a good place to start for the width. Most of the prisms I have are from closed machine tool rebuilders and they are all around 22 inches in length. The common angles are 30, 45 and 60 degrees. Sounds like a good project. Daryl
    Last edited by Other Brother; 05-26-2019 at 10:55 AM. Reason: one "n" Sorry

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    Quote Originally Posted by Other Brother View Post
    Hi Dennis, I would think 2-3 inch face would be a good place to start for the width. Most of the prisms I have are from closed machine tool rebuilders and they are all around 22 inches in length. The common angles are 30, 45 and 60 degrees. Sounds like a good project. Daryl
    Thanks, Daryl. That is very useful information. And 22” still fits a large USPS FRB.

    Denis

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    Hi dgfoster,
    If it's a solid, why not take a square or rectangular Durabar and split it on a lengthwise angle? I've done that with rounds, making a cradle from 2 x 4s to support the material while it's fed though a bandsaw shouldn't be too hard.

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    Quote Originally Posted by Milland View Post
    Hi dgfoster,
    If it's a solid, why not take a square or rectangular Durabar and split it on a lengthwise angle? I've done that with rounds, making a cradle from 2 x 4s to support the material while it's fed though a bandsaw shouldn't be too hard.
    I guess the only reasons I can think of are:
    1) Convenience. Starting with a near-sized piece is certainly convenient.
    2) Economy. I think it would be possible to sell a cast piece at a price equal to or likely less than the Durabar option
    3) Warpage. Not having to deal with the warpage induced by sawing. (I have cut gibs from durabar and you can be sure though my cuts were straight, the pieces resulting were not.) The part I would supply would be thermally stress relieved and pretty straight as cast and quite straight (.002 or better flatness) if i machined it.

    Denis

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    Denis I do not have a picture, but where I do my scraping work there are several cast prisms there that might be helpful to you for the design process. How much of a hurry are you in? I should be over there in the next two weeks and will snap some pics of the features and post them here. I have made them from Durabar and yeah they sure move around a but when you cut things. 18-22" would be a handy size for sure

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    Stefan G wrote on Facebook, Forrest sent him a hand written book called "everything is made of Rubber" or something like that. I have never had issues in Iron that I can't bend back and scrape. All things move. Just have to deal with that as it's natural.. Forrest where are you??? come and tell us about your book.

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    Quote Originally Posted by Warren View Post
    Denis I do not have a picture, but where I do my scraping work there are several cast prisms there that might be helpful to you for the design process. How much of a hurry are you in? I should be over there in the next two weeks and will snap some pics of the features and post them here. I have made them from Durabar and yeah they sure move around a but when you cut things. 18-22" would be a handy size for sure
    Warren,

    Now you have me curious about the “features” those prisms include. If pics are not possible or a couple weeks, are the features hard to describe? I would very much appreciate any ideas you can throw into the mix.

    In some ways the project I was envisioning at this time was a sort of super -simple and relatively featureless casting aimed at providing a cheap, convenient, high quality alternative to a hunk of Durabar. This is in contrast to my 4-in-1 prism/level/parallel/straight edge Featherweight 18” casting that involves a lot more time to mold and machine but is also more versatile but also necessarily more expensive. My idea is that the basic casting is what some folks want and some want a more capable tool. I am happy to provide both.

    To my simple mind, on this casting, the angle for the faces was one question and length another. But I am willing to consider other simple “features” that don’t add (much) to production labor.

    Denis

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    You might consider casting in some features to make the shape easier to machine. Possibly a cavity to allow toe clamping or even tabs that can be cut off after machining. I think a prism is a very difficult shape to hold onto and achieve any kind of tolerance.

    I have used some "prisms" that are more like trapezoids. Basically it would be more like a plate say 3" or 4" wide and maybe 1-1/2 thick. A 45 degree bevel is milled on one edge and the opposite edge is hollowed out to reduce weight. The widest face is the reference surface.

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    Quote Originally Posted by ewlsey View Post
    You might consider casting in some features to make the shape easier to machine. Possibly a cavity to allow toe clamping or even tabs that can be cut off after machining. I think a prism is a very difficult shape to hold onto and achieve any kind of tolerance.

    I have used some "prisms" that are more like trapezoids. Basically it would be more like a plate say 3" or 4" wide and maybe 1-1/2 thick. A 45 degree bevel is milled on one edge and the opposite edge is hollowed out to reduce weight. The widest face is the reference surface.
    Tabs for holding are easy. Most likely, round tabs protruding from the ends and parallel to the long axis of the prism would be best. Then they could be mounted on vee-blocks and rotated to the desired position. I will say I have had good luck drilling holes in the ends and mounting on shop-made angle-iron reinforced angle plates for milling. Whatever method is used, the danger of clamping-induced flexion in the prism must be very carefully avoided. (Maybe that is too obvious to mention). Otherwise, spring back occurs on unclamping and that nice straight face is now a nice smooth curve.

    Denis

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    Denis the Castings have a pockets cast in the back side. I assume to lighten things up and perhaps they would sort of make a bridge type structure. Plus they would make a great place to hold things down. They were evenly spaced in along the back 3 or four inches long, leaving about a half inch of wall space on either side and were approx 3/4 or an inch deep. I am going by memory here, so I might be a bit off on things. I will try to get over there if I can this week. No guarantees. I am busy with work and happy about it.

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    Quote Originally Posted by dgfoster View Post
    ..the project I was envisioning at this time was a sort of super -simple and relatively featureless casting aimed at providing a cheap, convenient, high quality alternative to a hunk of Durabar.
    Breaking radio-silence twice now... You shouldn't bother.

    Anyone who NEEDS these minor goodies can get Durabar sawed cheaply enough, correct for any induced distortion well-enough, later, and isn't even limited to Durabar. Salvaged CI or even Ignorant steel and most any milling machine can get to the simple end "conveniently enough".

    "Most anyone" anyway.. think about it.. simpler by far than MANY "parts" as are made every day, yah?


    This is in contrast to my 4-in-1 prism/level/parallel/straight edge Featherweight 18” casting that involves a lot more time to mold and machine but is also more versatile but also necessarily more expensive.
    Stick to your esteemed and admirable dovetail. It is NOT expensive for what it is.

    MANY can do a good-enough simple prism. No one else is matching your light, clever, and versatile dovetail. Did I fail to mention "enduring"? A lifetime investment that can be handed-down for more than just the ONE lifetime.

    I could be wrong, but AFAIK, Antonio Stradivari left guitar picks to others, focused on what HE did best, too,

    "Life is too DAMNED short to..." etc.


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    Quote Originally Posted by thermite View Post
    Breaking radio-silence twice now...

    "Life is too DAMNED short to..." etc.

    Thermite: Good to see you break radio silence, if only a little


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    Quote Originally Posted by Warren View Post
    Denis the Castings have a pockets cast in the back side. I assume to lighten things up and perhaps they would sort of make a bridge type structure. Plus they would make a great place to hold things down. They were evenly spaced in along the back 3 or four inches long, leaving about a half inch of wall space on either side and were approx 3/4 or an inch deep. I am going by memory here, so I might be a bit off on things. I will try to get over there if I can this week. No guarantees. I am busy with work and happy about it.
    The pocketing sounds sort of like a a reduced execution of the 18" combination SE/Prism/Level/Parallel that I make. Making the pockets deep means that casting is trickier as molding deep pockets in green sand is a dicey proposition with a certain failure rate inevitable---part of the price of doing business. Shallow pockets, not so much.

    18se-1-.jpg
    18se-3-.jpg
    18stredgevial-8-.jpg

    Quote Originally Posted by thermite View Post
    Breaking radio-silence twice now... You shouldn't bother.

    Anyone who NEEDS these minor goodies can get Durabar sawed cheaply enough, correct for any induced distortion well-enough, later, and isn't even limited to Durabar. Salvaged CI or even Ignorant steel and most any milling machine can get to the simple end "conveniently enough".



    Stick to your esteemed and admirable dovetail.

    MANY can do a good-enough simple prism. No one else is matching your dovetail.

    I could be wrong, but AFAIK, Antonio Stradivari left guitar picks to others, focused on what HE did best, too,

    "Life is too DAMNED short to..." etc.

    Glad to see you back too, Bill. One thing I have always admired about your posts is your penchant for understatement. Like comparing me to Stradivari! But I do appreciate the positive comments....

    My problem is that I love to cast iron. So, I look for any excuse. ;-)

    Denis

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    Quote Originally Posted by dgfoster View Post
    My problem is that I love to cast iron. So, I look for any excuse. ;-)

    Denis
    Ummmhhh... Monarch 10EE's notoriously missing/cracked rear covers might be an excuse many would surely welcome.

    Challenging, too.. "Consumables", even... unless a bit of revision were worked in to address what makes them so fragile...


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    A thought is a similar I-beam shape with bevels that the company Metal Lathe Acesories used to make. 18-24" long. I can measure mine and send the OP pics when I get home in a week. Also not so difficult to make out of durabar if a guy disn't want to make a casting. Would just take more time machining.

    Lucky7

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    Hi Denis,
    I was over where the prisms are yesterday and completely forgot to photograph those prisms, other things on my mind. However they are similar to what you have posted above except there is much more material around the edges and web thickness is greater. I dare say the slots were cast in to reduce weight some. Sorry about the brain fade, simply too much going on all at once lately.

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    Quote Originally Posted by Warren View Post
    Hi Denis,
    I was over where the prisms are yesterday and completely forgot to photograph those prisms, other things on my mind. However they are similar to what you have posted above except there is much more material around the edges and web thickness is greater. I dare say the slots were cast in to reduce weight some. Sorry about the brain fade, simply too much going on all at once lately.
    Thanks, for even thinking about it later. I suspect there may be a few more important things going on than my ruminations about a new prism design.

    I am still interested to see pics if you get the chance...

    I hear what you are saying bout the heavier build of the prisms you are thinking of. The Featherweight design I chose was intended to reduce weight as much as reasonable while maintaining or improving rigidity realizing that in many cases not having to hoist a needless heavy hunk of iron up to a vertical vee-way to blue it would be an real advantage.and a nicety on horizontal ways.

    Denis

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    Dammm I had written this and some how it disappeared...so frustrating.

    anyway hate to hack this thread. Years ago when teaching a class in Stockton CA I saw a set of triangle prism straight-edges. They were hollow. a Triangle casting with a triangle hole in the inside. It looked like 3 flat bars of steel welded at the 3 edges, but they were cast. They were light and strong. had a pate bolted to the end and a handle attached to it. I always was going to make some as I figure it would be easy to make a sand draft to center inside the mold. Denis you have the time and money. Make some if you can. I believe they were made by a company called Shamrock or Clover....I believe a green shamrock was their logo.

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    Richard's idea sounds similar to Moore Tools square section cored out straight edges. A guy in Pacific NW (Portland?) was casting this type recently. Richard's idea though (if I understand correctly) is a cored out equilateral triangle section. Perhaps useful for spotting larger dovetails. Not sure how easy it would be to hinge. And with hinging a dovetail, I find even a standard 48" SE difficult. I'm not a professional scraper obviously.

    Lucky7


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