As it turned out, I showed up on the appointed day with the split patterns, and they decided they couldn't risk them, that their "guys are on piece rate and they would break these up on the jolt-shake machines after a half dozen parts"

Took them home, intending to copy them onto a match board in urethane, (reprothane) and never got the proverbial round to-it.

Now I'm having qualms about the shape. Don't want to make a big effort, if the lower section is out of proportion or "too heavy".

Here is my question to those who have experience (Forrest???): Is there too much metal in the lower flat section, and would it be stable if cast as shown? Or would that big lump pull and distort for years to come? I don't want to go to the trouble of coring it out if it looks "ok". But if it is an obvious problem ("won't work") to those in the know, I'd rather hear it now before going through the effort again, and would either core it (what a job on that one!) or reduce the bottom section.

As it stands, the pattern is 31" long (for a 30" finished part), about 3-7/8" across the widest flat on the bottom (intended to yield up to 3-1/2" if desired),and the bottom is about 1-1/4" thick at the thickest part of the draft, intending to allow up to 1" thick finished.

The pattern is mahogany over 1/8" aluminum webs. It has match pins and striker holes.
The top curve is a true caternary, but I no longer remember what parameters I used or why.

thanks!
smt

I suggest you find a different foundry, one that serves the low volume end of the business. One that does art castings and sculpture might be a good choice.

One thing your pattern seriously needs is a couple of cast-in bosses about 1/4 of L from each end on the camelback so the straighedge is stable when set vertically upside-down. Look at Winchman's post third post down: http://www.practicalmachinist.com/ubb/Forum1/HTML/003959.html.

These bosses when machined greatly facilitate manufacture and scraping because it avoids the need to shim when roughing the casting.

Cast an extra one for me, especially if it has the "Steven Thomas" logotype on it. No logotype? Damn! Whip up one. Maybe the foundry's patter shop will sell you a set of the lead letters you need.

This doesn't pertain to your question but I too would be interested in getting a casting from you....actually, I think a lot of people would!

Is this something you might offer?

Thanks....Mike

I have a couple more Q's since the great and experienced gave not only approval, but a (can I assume?!?) benediction! (thanks Forrest)

The next questions are, I have a few of the old MLA parallel fitters straight edges that were discontinued. They are in class 45, and that seems to be a good iron for a tool. Harder to scrape than machine ways, but a bit more durable and tougher. Would this be a good spec, or something "better"?

And then to put someone really on the spot, What kind of reasonable life should be expected out of these, given the last foudry was afraid of breaking them? Does it look possible to get a couple dozen impressions, or is that rank optimism? Again, the patterns are wood (mahogany & walnut) on 1/8" aluminum webs, screwed and epoxied, and filleted with a pretty dense Foreman's product. Paint is PPG black epoxy primer.

Trying to answer some of the other Q's:

Forrest, the link doesn't work for me, so I'll guess here. If it is one with bosses let into the arch, it was a conscious decision on my part to forgo them, as i have those on a 4' straight edge Rich King sent me a while back, and I don't like the way they cut into the arch. Don't get me wrong, they obviously work, but I thought it would be better without. Now if the bosses are attached above, _onto_ the arch, like tabs, that is indeed an idea i hadn't considered, and it could be a good solution.

Bruce, I didn't quite follow the weight observation. Meaning "too heavy to work with", or addressing the concern "will this section be likely to retain excess stress"?

If machined to yield a section averaging 3.2" wide (mid way up the 60" angle) x 1' thick x 30" long, the bottom should weigh about (CI is variable) 25 - 28 lbs. My SWAG is that the rest of the structure contains barely 1/2 again as much volume, so add another 10 - 15 lbs. Call it 42lbs total for one machined to maximize every dimension. My aim is for about 36 lbs average.

This pattern, though was designed for a one size fits all application: The obvious potential is for a 60º dovetail on one edge, and a 90º on the other edge; as well as the option to machine and scrape the top of the 90 side for working under shallow ledges.

Certainly the bottom can be machined much smaller if those options are not needed, and weight could probably be gotten right down into the high 20's overall weight

The other "want" at the time it was made, is the section is deep enough to cut most of it away and form a 90º V ; or conversely to cut a fairly deep V into the tool for working inverted V-ways.

Does anyone remember the foundry in Ohio that solicited for small batch work, helps hobbiests, specs the iron, and does stress relief? (sounds like nirvana:^))I've lost the link since my old computer died a couple months ago. The owner used to post either here or on the old engins site. (I'll ask the same question there, later, if no one here has it)

I would like to find out some more info for myself before getting specific about selling castings. Then if it looks like something I can proceed with, (and Don allows me to keep posting on the subject) I'll consider doing a group subscription type thing, given the amount of interest. Something like send the patterns to the foundry, take orders, and have them drop shipped where ever from there, if it works out. But right now I need the foundry info and have to get pricing.

Winchman's Post

that is a reasonable observation, except this gage was visualized to fill some specific wants of mine, that are not usually incorporated in one casting.

For a pure "camel back" straight edge, the bottom surface (the reference surface) need not be much over 2" or 2.5" wide for this 30" size, and it could be little more than say 3/8" thick with suitable trussing (as this one has). I didn't so much need another plain straight edge, as i wanted a casting that could be machined and scraped to more conveniently accomodate some of the particular problems I was seeing re-habbing older machines. I wanted a longer stable dovetail edge than the one on my 18" fitters straight edge. A longer rightangle ledge. And the option to do inside and outside V-ways. most plain camelback straight edges won't go into a dovetail, even to finish the flat. One uses a straight edge in as far as it will go to prove linearity, and extapolates into the dovetail itself with a smaller angle straight edge. These angle (or "dovetail") straight edges are often a bit cumbersome and not altogether inflexible as they get longer. If one edge of the camel back were made as an extension, the whole flat surface can be indicated directly.

To be clear, Challenge makes (or used to) a sort of T section SE for that purpose. The vertical fin is almost straight on top, and has less pronounced webbing than my pattern includes for (what I hope is) lateral stability.

Another observation: it is likely that B & S , and most probably Challenge, have some at least cursorily "scientific" and "efficient" design behind the shape of their products. But the vast majority of straight edge castings seem to have been made more with an eye to ease and speed of patternmaking, and ease of ramming, than with any particular insight as to efficient shape other than loose tradition.

So, it is fully recognized that this pattern is not ideal as far as optimizing the weight-to-lenght equation if it were to be used soley for proving the major linear parameter of a flatness observation. But it should offer a range of useful options to make real world scraping tasks on many machine parts easier and more efficient.....if the casting is viable (stable) as designed.

I'm checking into a number of leads for foundries, including the Tod engine link (Thank, AndyF)

George, thanks for the correction on Winchmans, I should have realized what Forrest was linking me to, as reading that series of posts is what got me thinking of dragging these patterns down off the shelf again.

If these patterns can be used directly for a suitable number of impressions without rebuilding them on matchboards, i will probably not add tabs. If it proves necessary to do the matchboard, it will probably require a either few more years of round to-its; or else a whole bunch of quantifiable interest and encouragement, in which cast the pattern could also be modified at that time.

PS. I just realized why B & S cast their name along the spine: makes is non-trivial for any would be casual forgers to copy directly! sure, just fill in the logo with a layer of body putty and fair it out, and you're more or less good to go if you want a few extra shop copies on a slightly shrunk scale. But Joe's foundry and refuge for homeless bar rats won't be passing "genuine" B & S product with the correct logo out the back door on rainy days.

The "from" on your header isn't filled in, but somehow I remember you being in Connecticutt.

Have you though of taking your patterns over to Taylor and Fenn's foundry?

They are a big, modern outfit but they go 'way back. At one time they made specialized machine tools, I imagine they know their iron.

The Economy isn't exactly in High Gear, they might talk to you about short run castings.

Thanks for the foundry option, I'm adding it to the growing source list!

Thanks for the foundry option, I'm adding it to the growing source list!

I had real good success dealing with Wells Foundry in London Ontario Canada. They don't mind dealing with one off's and the quality is terrific (almost as good as their service)
If you call them ask for Steve Wells

I love your design
http://www.angelfire.com/sc3/shapeaholic/straightedge.html

I remember your website, partly because of the straight edge, but mostly because of the very neat Alba shaper you restored.

(Just came in from running my rockford, trimming some A2 that was beating up bandsaw blades)

I believe I met the guys from Wells maybe 4 or 5 years ago at Eastech. If it was them I remember, yes, the personality and the capabilities are encouraging. I guess they are close enough to give a call. And My wife is always ready for a trip to Canada. But wonder how customs treats iron castings going back and forth across the border?

Jeremy, I'm on the ATIS stationary engine list, so remember when Rick Rowland, Dave Rotigel, Arnie Fero, and some others started retrieving that engine. It's a remarkable project, and some have a lot of time and money in it. Mr. Rowland acknowleged my email, so I'll wait to see what he says.