Featherweight 8" Straight Edge/Prism/Level/Parallel New and Improved!

[dgfoster]

THe 8" Straight Edge I designed and started casting in January 2020 has been my top seller. Having looked at it countless times and trying to decide how it might be improved, I have just begun making new patterns for an 8 that is very similar to the original. But, I think it is a little better.

Here is an overall pic of the new CAD drawing of it.

[And, yes, I will cast it in gold on request at some slight increase in cost ;-) ]

Here are a few pics of the draft low resolution fast print for inspection purposesonly. (Drawing stuff in CAD is one thing. But I like to actually have a physical part in my hand before commiting to a design.) The actual print that will be used as a pattern will take 12 hours to print and will be much better in surface texture and the lettering will be nice and clean. That print is currently in progress and will be finished around supper time.

Here you can see that the inclined surface of the prism is a bit longer than before.

And the new casting will be a bit taller than the prior one.

I'd welcome comments and questions.

Thanks for all the support members of this forum have provided over the years. I started doing my own castings five years ago and have made hundreds of tweaks to the patterns and foundry process since. The whole system gets incrementally better and better.

Denis

 

[dgfoster]

And here is the mold-ready pattern printed in PETG and painted. I'll try molding it this afternoon. When trying a new pattern the sand will almost always point out some defect in the pattern that I overlooked. Usually, a bit of sanding and maybe a bit of Bondo will fix that.

Denis

 

[Mark Rand]

What angle should one grind on thescraper blade for scraping the gold option?

 

[dgfoster]

What angle should one grind on thescraper blade for scraping the gold option?

For your security, I wasn’t going to divulge the fact you ordered two (ostensibly as gifts for PM members). Please contact me offline.

Denis

 

[dgfoster]

Well, I have molded the new pattern twice and, amazing to me, it drew cleanly from the sand both times. It will require no rework though I expected it would. Over and above just pulling cleanly it pulled with no reluctance at all. That might be a little hard to explain. But patterns often seem to be a little sluggish to fully clear the sand. Not this one. I attribute that ease of withdrawal to the precision of the 3D printer. All the surfaces that need draft have it and are exactly as drawn. In the past, making wooden patterns, I was careful to cut, plane, and sand as accurately as possible. But I suspect the various surfaces that are supposed to be flat and look pretty good when checked against straight rules and levels are not a planar as the printed ones.

So, my printer will be humming tonight making a second pattern.

Tomorrow, if there is a break in the rainy eather we are having, I'll cast a couple new-pattern 8's and 4 old pattern 8's. Fingers crossed.

Denis

 

[michiganbuck]

You might put centers on the ends(?)
Being a grinder hand I would consider a crushable wheel and crushing the long form so as to get the angle, the concave and convex radius with one grinder pass.

Crushers could be homemade using a lathe or bought.
Ops, the raised letters area likely would not be finished with grinding.
Guess you might get the Angla and the one radius.

 

[dgfoster]

You might put centers on the ends(?)
Being a grinder hand I would consider a crushable wheel and crushing the long form so as to get the angle, the concave and convex radius with one grinder pass.

Crushers could be homemade using a lathe or bought.
Ops, the raised letters area likely would not be finished with grinding.
Guess you might get the Angla and the one radius.

I am not sure I follow your suggestion. I guess you are suggesting that the casting could be ground rather than scraped or maybe the casting could be ground in preparation for scraping?

Grinding would be relatively easy on this small casting. And I can see that centers could provide a means to get all the planes accurately oriented toward each other as well as very accurate prism angle grinding. If you place the castig between centers, what additional fixturing would a person best use to rotationally fix the orientation of the casting while grinding a face?

Denis

 

[michiganbuck]

Yes for a semi-finished part, the grinding might sell a few more.
Lay two on a 6-18 so grinding could be quick.
Centers would be difficult because grinding off the centers would be more difficult than grinding on the flat.

 

[dgfoster]

Actually, I mill them on the prism faces, back and top rail if a customer requests. The surfaces are flat to less than a thou and the top and sole are parallel within a thou. That is close enough for almost everyone for prep for scraping. Milling them is pretty straight forward and I have detailed in a prior thread a method I like.

 

[dgfoster]

I was able to wedge a melt in between rain showers yesterday. The new pattern made a good casting.

Here is a 30 second video of the casting:
Overview of the casting video

Here are a couple stills after wire brushing the casting and cutting off risers and gates.


This is a closeup of one of the lettering panels as it comes from the resin printer.


Added: My dad always said "Never trust a skinny cook." I would add "Never trust a foundryman with clean hands." ;-)

Denis

 

[TGTool]

Very clever in the last picture to make that sly comment about the cook's size.

But to each his own. I heard one comedian say he has nothing against a large woman - they're warmth in the winter and shade in the summer.

 

[dgfoster]

Very clever in the last picture to make that sly comment about the cook's size.

But to each his own. I heard one comedian say he has nothing against a large woman - they're warmth in the winter and shade in the summer.

Yup. The self-critical comment was made after I noticed my hands were in their usual grubby condition (actually pretty good for me) in the photo. Since I work daily with graphite, sooty foundry equipment, dirty cast iron, various adhesives like epoxy and cyano glues, greases, and well-used foundry sand, getting my hands to actually look "clean" is nearly impossible. If my wife and I are going to some social function, I have to spend ten to fifteen minutes with dish soap, hot water, and a scrub brush. Even then there is some retained dirt under my fingernails and around the edges. Oh well...

Denis