Welcome to my casting nightmare

[Zeus1050]

I have some particularly nasty castings that are not cooperating. Mat is 356-t6, they are thin an flimsy. Part was originally made in the 1940’s, and they at the time made a lot of them with dedicated tooling . Runs are 25 pcs. See pics.

It is my contention that these were probably put in a jig, cased in lead or something like it and Blanchard ground , this makes for one side flat.

Initially, I chuck these up face the front and bore a hole in them for a press fit plug. The casting is held in soft jaws which are lined with 90 durometer urethane. The jaws have a hole bored that the pressed plug gets clamped on and the urethane along the edges clamps the irregular part. The right side has eccentric knife edged screws which bite into the casting. Issue one, it of course chatters and when unclamped part is bowed, issue 2 , because this thing can float, I’m getting poor hole location. The square end is only 1/8 thick. Suggestions on how to better hold this thin irregular shape, or how it may have been originally done? This was first made 25 years before I was born, things were done differently then. Because it is so thin, things like mighty bites , I don’t see working. If the big side was known flat and ground to size, then it could be mounted to a plate with small clamps. Order of present opps are bottom and holes, in cnc lathe chucked from id bore and shoulder turned, flipped on lathe , mounted in pie jaws and the spherical radius cut, middle bores to size. Lots of clamping on a flimsy piece of aluminum.

Suggestions ?

 

[DanielG]

Would it be faster to skip the casting and make it from bar stock?

If you have to do the casting, how about an expanding ID clamp on the cast bore and a regular holddown clamp on the tab. Machine the front complete, including the holes in the tab. Machine a negative of the front as a fixture, bolt it on face down, machine the back except where your screws are. Move the screws, machine the rest.

 

[Zeus1050]

Would it be faster to skip the casting and make it from bar stock?

If you have to do the casting, how about an expanding ID clamp on the cast bore and a regular holddown clamp on the tab. Machine the front complete, including the holes in the tab. Machine a negative of the front as a fixture, bolt it on face down, machine the back except where your screws are. Move the screws, machine the rest.

Clamping on an irregular cast surface is going to bend the casting, moving clamps and screws will not result in a flat bottom surface or the +\- .002 thickness . Appreciate the ideas.

I am making them from solid at this point, I would like to figure out how it was originally done or how other folks handle this kinda stuff. My prior experience with castings was bellhousings and other trans parts. If you are hot rod guy with a Mopar or Gm JW ultra bell, that is the work of this at the time 25 year old kid. I built the patterns, wrote the programs, designed and built the tooling. That was easy, that stuff is thick....this , not so much.

 

[eKretz]

Maybe originally they melted it into pitch or something of that sort. Put it in a pitch pot with a machined outside and you could machine the entire flat side pretty easily, including some of the holes for clamping when it's flipped over. Then remove it from the pitch, flip it, locate with the big bore on a fixture with drilled and tapped holes and clamp down with those few holes you drilled in the first setup. Drill and counterbore the holes that aren't serving as clamps, then switch the clamping holes and counterbore the rest. Use those clamping screws to hold the part while you machine the rest of the faces/ODs.

If you get to spec the castings yourself, add some provisions for clamping like tabs below the finished surface for clamping outside the finished perimeter. Then you can just cut them off later. I'd go with 3 points to keep you from tweaking it while doing that first side.

 

[Zeus1050]

Maybe originally they melted it into pitch or something of that sort. Put it in a pitch pot with a machined outside and you could machine the entire flat side pretty easily, including some of the holes for clamping when it's flipped over. Then remove it from the pitch, flip it, locate with the big bore on a fixture with drilled and tapped holes and clamp down with those few holes you drilled in the first setup. Drill and counterbore the holes that aren't serving as clamps, then switch the clamping holes and counterbore the rest. Use those clamping screws to hold the part while you machine the rest of the faces/ODs.

If you get to spec the castings yourself, add some provisions for clamping like tabs below the finished surface for clamping outside the finished perimeter. Then you can just cut them off later. I'd go with 3 points to keep you from tweaking it while doing that first side.

At this point , all sides have agreed that making from solid is better. Forgive my ignorance, “ pitch” as in pine pitch? We all have our specialties, I’m not familiar... Castings I built the patterns for had tooling tabs,

 

[Booze Daily]

You’re running these in a CNC lathe?
In 1940 they ran them in an engine lathe where parts weren’t chucked nearly as tight. That could be part of the problem.

 

[eKretz]

At this point , all sides have agreed that making from solid is better. Forgive my ignorance, “ pitch” as in pine pitch? We all have our specialties, I’m not familiar... Castings I built the patterns for had tooling tabs,

Chaser's pitch - Wikipedia

en.m.wikipedia.org

 

[Zeus1050]

You’re running these in a CNC lathe?
In 1940 they ran them in an engine lathe where parts weren’t chucked nearly as tight. That could be part of the problem.

They are run in a mill and a lathe. Chucking pressure in pie jaws is under 75psi. They are initially held by a pressed in plug clamped in a vice with a cavity molded around the part with urethane resin. See pic.

 

[Zeus1050]

Chaser's pitch - Wikipedia

en.m.wikipedia.org

Thank you. I’d say they were held in a fixture on a Blanchard using this stuff. Safer then lead. The original fixture I’m sure is long gone, it’s not worth recreating it for 100 parts a year. I suspected something like this, just never ran into it.

 

[sfriedberg]

it’s not worth recreating it for 100 parts a year.

Actually, are you sure about that? If it turns a fussy, borderline-of-scrap process into a slam dunk, it might actually pencil out in favor. Especially since most of the fixture would just be a non-critical dimensioned recess for holding pitch.

 

[Limy Sami]

Stick it to a backing plate with hot melt glue (it's worked for me) and as others have said watch the chucking pressure!!! I used to do a lot of plastic work and you sure learn about chucking presures on that stuff

 

[Peter S]

Did they use to flatten one side of castings with something like this?

I have never seen one or used one, so could well be wrong.

 

[Limy Sami]

Good call PeterS, .......I'd forgotten all about Snow grinders, .......... back in the day, one place I moonlighted at used them a lot for facing castings (and weldments etc) before machining.

FWIW we used to call it ''doing the ironing''

 

[Zeus1050]

Actually, are you sure about that? If it turns a fussy, borderline-of-scrap process into a slam dunk, it might actually pencil out in favor. Especially since most of the fixture would just be a non-critical dimensioned recess for holding pitch.

If my customer insisted that the parts be made from the castings, I’d agree, they are alright with them being made from solid. It’s always been a problem part for them and anyone they had do it.
I’ve never seen a “ snow grinder” , they very well may have been faced on a machine like that. I’m in Florida and there isn’t a lot of this kind of work around, it’s just not what gets done here, I’ve never been exposed, I created this post for the sole reason of asking folks who are in places that do this kinda stuff. The one place I worked as a kid that did castings Blanchard ground them to qualify them, that what made me think my nightmare was some how fixtured on a Blanchard table, my first guess was lead, I also considered plaster. Pitch makes perfect sense, casting the casting in hard urethane isn’t to far off from the pitch idea. Thanks for sharing.

 

[dgfoster]

Besides pitch you might also consider Woods metal in one of its variations. You'd make up a jig as above and pour in the metal at about 170F and it solidifies instantly and is very rigid and stable. Once finished with machining operations, warm up the fixture in a toaster oven or with a torch. The metal pours out cleanly and then dunk the fixture in a tub of room temp water. Repeat.

I use Cerrobend (158F Melting) to fixture some straight edge casting I machine. Its low melting point, good flow charecteristics, and rigidity make it interesting to use.

Denis

 

[Zeus1050]

Besides pitch you might also consider Woods metal in one of its variations. You'd make up a jig as above and pour in the metal at about 170F and it solidifies instantly and is very rigid and stable. Once finished with machining operations, warm up the fixture in a toaster oven or with a torch. The metal pours out cleanly and then dunk the fixture in a tub of room temp water. Repeat.

I use Cerrobend (158F Melting) to fixture some straight edge casting I machine. Its low melting point, good flow charecteristics, and rigidity make it interesting to use.

Denis

Woods Metal is pretty nasty stuff, 10% Cadnium . Lead isn’t much better. Pitch sounds like the way to go.I remember pitch being called “ dopping compound “, we used it to glue rocks on sticks so they could be polished on a lapidary wheel. I wouldn’t have thought of it or known what to call it or to consider it as a mount for parts.

 

[dgfoster]

Woods Metal is pretty nasty stuff, 10% Cadnium . Lead isn’t much better. Pitch sounds like the way to go.I remember pitch being called “ dopping compound “, we used it to glue rocks on sticks so they could be polished on a lapidary wheel. I wouldn’t have thought of it or known what to call it or to consider it as a mount for parts.

Well, yes it can be a problem. But there are variants of Wood's metal that contain no cadmium which is why I suggested a variant as I knew it would scare off some potential users and I'd likely be criticized for suggesting it.

However, the key to its safe use, cadmium or no, is not to eat it or inhale it as a dust. Being a very soft alloy it does not dust easily and direct skin contact results in no absorbtion. Like most toxins, serious issues result from "prolonged and repeated" contact.

Interestingly, the greatest risk of cadmium toxicity occurs in smokes as cigarette smoke contains cadmium---for some reason that is not touted in cigarette ads.

Here is a fairly authoritative statement on cadmium:

"Commercially, Cd is used in television screens, lasers, batteries, paint pigments, cosmetics, and in galvanizing steel, as a barrier in nuclear fission, and was used with zinc to weld seals in lead water pipes prior to the 1960s. Approximately 600 metric tons are produced annually in the United States, and about 150 metric tons are imported [2].

Human exposure to Cd occurs chiefly through inhalation or ingestion. Ten to fifty percent of inhaled cadmium dust is absorbed, depending on particle size. Absorption through skin contact is negligible. About five to ten percent of ingested Cd is absorbed, also depending on particle size. Intestinal absorption is greater in persons with iron, calcium, or zinc deficiency [3].

Cigarette smoking is considered to be the most significant source of human cadmium exposure [4]. Blood and kidney Cd levels are consistently higher in smokers than nonsmokers. Inhalation due to industrial exposure can be significant in occupational settings. for example, welding or soldering, and can produce severe chemical pneumonitis [3].

Cadmium exposure occurs from ingestion of contaminated food (e.g., crustaceans, organ meats, leafy vegetables, rice from certain areas of Japan and China) or water (either from old Zn/Cd sealed water pipes or industrial pollution) and can produce long-term health effects. Contamination of drugs and dietary supplements may also be a source of contamination [5].

Here is a link to a table of variants of Wood's metal:
Wood's Metal Atricle

I would add that lathes, milling machines, boring mills, and other machines (TRBoatworks' drill press) pose a much more proximate risk to health than occasional and judicious use of cadmium-containing metals. And driving to work in an automobile poses greater risk than all of the above. Not trying to be a wise guy, really. It is just useful to me to put "risk" in perspective.

Denis

 

[Zeus1050]

Well, yes it can be a problem. But there are variants of Wood's metal that contain no cadmium which is why I suggested a variant as I knew it would scare off some potential users and I'd likely be criticized for suggesting it.

However, the key to its safe use, cadmium or no, is not to eat it or inhale it as a dust. Being a very soft alloy it does not dust easily and direct skin contact results in no absorbtion. Like most toxins, serious issues result from "prolonged and repeated" contact.

Interestingly, the greatest risk of cadmium toxicity occurs in smokes as cigarette smoke contains cadmium---for some reason that is not touted in cigarette ads.

Here is a fairly authoritative statement on cadmium:

"Commercially, Cd is used in television screens, lasers, batteries, paint pigments, cosmetics, and in galvanizing steel, as a barrier in nuclear fission, and was used with zinc to weld seals in lead water pipes prior to the 1960s. Approximately 600 metric tons are produced annually in the United States, and about 150 metric tons are imported [2].

Human exposure to Cd occurs chiefly through inhalation or ingestion. Ten to fifty percent of inhaled cadmium dust is absorbed, depending on particle size. Absorption through skin contact is negligible. About five to ten percent of ingested Cd is absorbed, also depending on particle size. Intestinal absorption is greater in persons with iron, calcium, or zinc deficiency [3].

Cigarette smoking is considered to be the most significant source of human cadmium exposure [4]. Blood and kidney Cd levels are consistently higher in smokers than nonsmokers. Inhalation due to industrial exposure can be significant in occupational settings. for example, welding or soldering, and can produce severe chemical pneumonitis [3].

Cadmium exposure occurs from ingestion of contaminated food (e.g., crustaceans, organ meats, leafy vegetables, rice from certain areas of Japan and China) or water (either from old Zn/Cd sealed water pipes or industrial pollution) and can produce long-term health effects. Contamination of drugs and dietary supplements may also be a source of contamination [5].

Here is a link to a table of variants of Wood's metal:
Wood's Metal Atricle

I would add that lathes, milling machines, boring mills, and other machines (TRBoatworks' drill press) pose a much more proximate risk to health than occasional and judicious use of cadmium-containing metals. And driving to work in an automobile poses greater risk than all of the above. Not trying to be a wise guy, really. It is just useful to me to put "risk" in perspective.

Denis

Info is power. I don’t smoke, no that’s kinda a non issue, and of course machines do eat people, at least the careless.. there is no lack of danger in the world.There was a time when “ radon crocks” were being touted as the cure all for everything, we figured out, such is not the case. I appreciate your input.

 

[boslab]

It’s funny, the ubiquitous “Wright finisher”, there were 2 types, the one shown was the cup wheel flat table face finisher, often used on cylinder heads, blocks but originally built to flatten cast valve bodies , manifolds etc. the other model was the same footprint with a flat circular platten to take an abrasive disk, centre nut clamped though several had perforated Ali plattens and a fan blade cast into the underside to suck the paper down, intended for casting dressing. I beleive Wright was absorbed by snow grinders in the 50s , they discontinued the cup wheel machine kept the circular disk machine going as it was popular in material testing labs and such to dress optical emission spectrometer samples and standards, there are many still going, including the one in my shop that was thrown out of my workplace when the motor gave up, I bought it for scrap, 1 cent per pound as an employee of British steel then, damn thing weighs over 300 so it cost me £3
Solid cast iron base 1/2 inch thick with a door.
A local garage still uses the cup wheel finisher, it will do a car head apparently , still on its first wheel, which is cracked or chipped by the look, dosent seem to matter , the mechanic who owns it is still getting good results so can’t be bad.
Mark

 

[MCritchley]

I’ve used bees wax to fixture some weird parts in the past.
Nontoxic and organic if your into organic machining. The bees wax leaves a residue on the part, the only solvent that works is canola oil.

A different option other than potting would be to make a gigantic ring around the part and hold the part with like 25 set screws set into the perimeter of the part.
We had some paper thin motor castings with a .0005 tolerance that was proving difficult to keep flat after unclamping. We pointed the set screws and clamped on the neutral plane of the part.