30" Precision Square Iron Casting completed. 55 Pounds.

I am posting notice of completion of a project I have been working on for a while. I had a request from a precision CNC equipment manufacturer to design and cast a casting that could be machined and scraped or ground into a precision square and that would be portable weighing less than 60 pounds.
Such squares are finished to a tenth or so flatness and extreme squareness as well. The manufacturer said there are lots of granite squares available in that size, but their weight makes transport of them particularly by air difficult and expensive.

So here is what I came up with. I cast it yesterday and came within ounces, literally, of pouring short as the casting required more iron than I estimated.




I did get some fins where wood sand supports (I called them ceiling bolts) charred and vaporized spreading the cope from drag a bit and allowing iron finning. Those supports will be steel next time.


Denis

 

Here are the "ceiling bolts in the cope.
The 2X4's screw into a backing plywood board that covers the cope during molding of the drag.


This is my only image of the ceiling bolts in place and was made when I did a trial ram of the cope before there was drag in the cope pattern. Just needed to see if they would actually support the sand---they did.


Denis

 

How do you get the pattern out with that undercut around the edge of the casting, is there removable bits on the pattern?.

 

Mark,

Oh, someone is actually looking at the pictures! ;-)

Loose pieces that fit in the groove around the edge of the pattern. 16 pcs to be exact. 3 for each long side and one for each end.

Denis

 

Very nice Denis. Pretty impressive planning and pattern work too.
Will the precision tools ever need maintenance as they age? Meaning are they subject to warping over time or anything like that, or does their low mass prevent that?

Pete

 

I am sure that even after these casting are properly thermally stress relieved they may move a little. But I think usually we are talking tenths. So the thinner part of the faces at an expected .250 and more likely .300 should have plenty of room for rescraping or grinding. My straight edges have been very stable over the years moving undetectably over 6 year’s time. No guarantees though I suppose.

Denis

 

very cool. Dennis, you really like the big stuff.

 

I bet you're glad you don't have to machine that monster!

 

Jason,

Well, yes and no. It would be pretty demanding as the 4” sides need to be straight, square or parallel with each other, and vertical with respect to the open face. In addition, the casting has some slight wonkiness as cast. It measures within a 32nd of squareness from corner to corner—-I am surprised it is that good. But laid on my table saw it will rock about 1/8.” That I do not consider bad, but still a person would have to a have a well-thought-out plan of cuts to minimize material removal on all faces and it up with all faces “plumb, true, and perpendicular” as my grandpa used to say.

Doing it on my Bridgeport would be possible but would require two setups per long face—-tedious for sure. I’ve done 36” straight edges that way. Not my fave.

But, for machining my 36” straight edge, I have access to a 1950’s era 15 ton horizontal mill that would make the whole process much easier. The setups would still need to be carefully planned, but each face could be done with a single setup. Running that horizontal is a pleasure as it is incredibly powerful and true-running. So, yah, I’d like to try it sometime and would not doubt someone will want a casting machined before shipping. The reward would be the opportunity to see the casting gleaming in its glory with all external surfaces shiny and smooth!

I hope to cast another in the next week or so less. Glutton for punishment, I guess. But, having done this one, I’ll refine the process a bit.

Denis

 

I milled cast iron for the first time yesterday. I was shocked how soft that stuff is and I was black as hell when finished. Safe to say, Most people will never understand the work that goes into making something, "plumb, true and perpendicular" It truly is an art. A black art! lol

 

It's abrasive to machine tool ways, some shops keep their old machines for machining castings. I keep a stack of newspaper and use those small round magnets to cover the lathe ways and keep the dust off. Whatever you do, do not use cloth rags to catch the chips: too much risk of it getting caught and wrapping round something spinning with you in between. An old beater vacuum cleaner is handy too for these jobs but keep in mind some machines suck the fine dust past the filter and over the motor, bearings and commutator.

 

Oh, I love your pattern making Dennis!

Really nice work,

Cheers Charlie

 

Thank you all of you folks for all of your encouragement and positive comments. I do appreciate it!

Denis

 

A shop I used to work at has a Toshiba Blanchard style grinder with a 200 Hp motor and a 72" rotary table. They would trim a 1/4" off the top of bathtub size base castings faster than any mill could do it!

 

Sounds like a beast! It would be challenging to fixture this square, to not just shatter it, to avoid distortion due to torsional forces and heat. I have no doubt that an experienced operator could do that. It would be fun to see such a machine in action.

No, the mold filled on the first pour, to my surprise and delight. It took 23 seconds pour time. The sprue diameter was .625”. I have turned a form for a .75” sprue that should result in a ten second fill time.

But I did notice some winding of the flasks when I went to reassemble them for a second pour. This is despite having used carefully cut half-lap corner joints and Timberlok fasteners. I think this winding was the result of me setting up the molds for pour with asymmetric leveling supports. I should have been more careful. But I should not be surprised I guess since the iron heats the wood quite hot and steams it to some extent due to heating of sand water. Heat and steam are the standard formula I use when intentionally bending wood, so I should hardly be surprised that the flask might wind, warp, or rack. And this particular flask system is quite spread out compared to most I use that aren’t so picture-frame like. Any way, I want to get at least one more pour out of them. So, I got out my hand planes and took about a quarter inch off opposite corners to get them back to flat. It will be interesting to see how they fare the next pour. But, read on for mor on that.

And I also noticed some bulging of the bottom board. This 3/4 plywood board is screwed to the bottom of the flask with 8 sizable screws. But it too is subjected to gravity forces induced by 250 pounds of sand and 55 pounds of iron. In addition, it is exposed to moisture of the sand and steam on only one side. So, that it might bulge is not surprising.

In most cases, this winding and bulging of the flask would not matter. But I am using a split pattern of that is relatively spindly and will bend if it encounters much force. And I want the castings to be as close to perfect as possible.

SO, I started making a steel bottom board from 1” square tubing in a ladder-like configuration and 16 ga sheet. I am taking pains to weld it up without winding, warping, or racking. It will be very rigid and should go a lomg way to holding the flask in a true rectangular shape despite heat, steam, and gravity.

I also bought steel to make steel flasks. They will be done by Thursday or Friday. I use steel for my 36 and 48” straight edges already and would have gone straight (so to speak) to it, had I known that the pattern itself would pull properly—-that was an open question in my mind—-and had I known that it would fill which which was an even bigger question. Knowing that the pattern can be pulled and poured makes me more willing to invest the needed time and money for metal flasks.

I hope to pour metal by tomorrow getting one last use out of these wood flasks. They won’t go to waste, I can use the wood in them for less critical items.

Denis

 

I just welded up the 38" X 20" bottom board for the flasks. It starts out on the bottom of the cope and I place one half of the pattern on it and ram it up. Then the cope flips and off comes the metal board. I ram up the drag and the bottom board is attached to it. The whole mold is flipped and the bottom board ends up on the bottom firmly attached and holding everything flat (hopefully). It is quite rigid. So I think it will be able to hold the mold/flask combo in good alignment. Time will tell.

The tubing is 1" square .100 wall and the sheet is 16 ga.

Denis

 

Nice work Dennis.

I wondered if you have considered casting the moulding boxes?

I have had some trouble with my 3mm steel ones flexing a bit, with the result that the sand would drop out sometimes on a particular pattern. I thought about heavier steel but the expense and time to make them put me off, plus I still didn't think that they would be rigid enough, without more reinforcement.

This reminded me of a cast aluminium one I had seen years ago, so I made the pattern and used it for the exterior shape and also as a core-box.

I will cast the handles separately and fix them with screws. The draught on the boxes will be used to stop the sand dropping out, which should work as long as I support the top with a board when removing the pattern,

Cheers Charlie

 

Your cast flask looks very sturdy and certainly equal to the task---as you have proven.

I sure have considered it. I have seen modular ones that bolt together at the corners. But it turns out that I think just making up a dedicated set of non-modular flasks works best for me. Dropout might be a problem for the ones I am about to fabricate. My plan is to use 1X1" square tubing welded to a gusset of 2" x 1/8" flat bar to make what would be like an I-beam except the top and bottom flanges will be square tubing. The 4 sides will be welded at the corners with the idea that if I no longer am using them for my current casting, I will just saw them apart at the corner and resize them. Not exactly modular, but with a welder and angle grinder at hand, they can be resized pretty handily. I think they will have enough rigidity with the two stringers of sq tubing per side. And I am hopeful that the square tubing will hold the sand in place. I'll be welding them soon---within the next week.

Denis