Mounting odd shaped pieces

Curious how others mount odd shaped pieces on mill tables of lathe face plates.

Do most machinists have a large stock of shims to use with step blocks in multiple locations through lots of trial and error?

I realize that setup can take much more time than the actual machining and wanted to find out how the "pros" might do it.

On a mill I tend to use screwjacks, step blocks and finger clamps.

On a lathe I have a home made chuckable face plate with 100+ holes drilled and tapped in it. I can bolt most anything to it. that is a fixture for many jobs.

Some guys use strong two sided tape to hold a part down for light cuts.

Pros tend to machine a dedicated fixture just for the part, one that will stand up to heavy cuts like used in a production environment. The fixture might hold 1 to 100+ parts in one set up.

The only limit is your imagination.

Not a pro by any means, but your question is so very broad that it could take a whole book to answer some of your questions.

Mabye a few members will post some cool pics of their difficult set-ups.

Much depends upon how much force and heat you will be applying to the part once it is fixtured.

I have set up very odd-shaped cast iron parts in a 14" abrasive cutoff saw, which exerts fairly low forces on the casting. I put the castings in a rectangular plastic pan, oriented so that it could be sawed on the desired plane, and poured plaster of Paris around it. I popped it out of the plastic after the plaster set, and clamped the plaster block in the saw. Then I sawed the casting in half. The plaster did not mind the fact that the iron got red hot around the cut. The plaster was then removed in the blast cabinet.

For higher forces, like milling or turning, you can do similar fixturing using bismuth alloy with a melting point of 158 deg. F. The alloy is pretty hard and strong, but you have to be sure you don't heat the part much while machining it.

Another trick is to use Superglue to hold flat parts to a faceplate or adapter which is chucked or bolted in the usual way. Use tissue paper between the parts. Acetone will dissolve the glue when you are done with the machining operation. The paper helps the acetone to penetrate the glue layer. I have had good luck with this method when sawing several identical sheet metal parts at one time. Stack several flat sheetmetal blanks with tissue paper and Superglue between each layer. Quickly clamp the stack until the glue sets. Then you can use a drillpress, bandsaw, fretsaw or filing machine to finish several parts at once.

Another trick is to clamp a tapered part between two 1-2-3 blocks, using screws in the holes in the blocks. By shimming both sides of the thin end of the part, and using sheet copper as a deformable pad at both ends, you can create reference surfaces that let you clamp the part in a mill vise in several positions while keeping the part centerline square to the machine.

Sometimes you can just use the little Starrett screw jacks to support an odd part in a couple of places wile it is clamped to a mill table.

Larry

I guess I was saying that with pieces that have protrusions or pieces that cannot be easily removed on the mounting side, how can they be shimmed/braced up in order to have the side to be machined parallel to the table.

I'm imagining a casting that has rounded lobes on the bottom side that would cause the piece to easily rock. Maybe an occasional flat spot that would accept a step block or stack of shims.

I did like tattoomike68's reply regarding jack screws.

Pictures of particularly challenging setups would be fun to see. How many people would think about taking a picture of those afterwards?

Funjob:



Cheers Les H.

Not real difficult, but a PITA. Especially because we fixed it once as part of a larger job, then the customers's mechanics and fabricators changed it, so we had to fix it again different.

Yup. Too big a question. When realy odd shaped work has to be held on orientation and on axis any thing that works - works. I've cast stuff in Bendalloy, encapsulated it with epoxy and plaster, tack welded it to hunks of plate and premachined the assembles fabrication to ged an accurate reference before mounting the work on the machine table, machined soft jaws, as was said, too big a question.

I recently got one of those inexpensive Vertex brand (from Enco) dividing heads for my mill. The nice thing about it is the spindle on the dividing head has the same mount as the spindle of my lathe. I can start a piece of work on the lathe (or on the mill) and then unmount the chuck complete with work still clamped and mount it on the dividing head on the mill (or on the lathe) and back again. I can swap back and forth between mill and lathe without unclamping the work from the chuck. Not only does it add a huge range of work I can now do but it makes it MUCH quicker to change setups.

As others have said.... your question is way to broad. I have a 200 page book here written in 1913 called "Jigs and Fixtures". While it covers many areas in detail it admits that it is only an introductory work to give the tool designer a general idea of common practices.

In many respects ANY part can benefit from having special jigs and fixtures made in order to speed up the manufacturing process and also make it easier to produce accurate parts consistently. Even plain cylindrical parts for the lathe and rectangular parts on the mill benefit from jigs and fixtures. The basic mill vise and the basic lathe dog with the work held between centers are special fixtures, we just take them for granted.

The best tools you have are somewhere between your ears. What you can do is only limited by your imagination and how much time and/or money you are prepared to spend to make the part.

-DU-

Les,

That looks like you would have a heckuva time avoiding chatter on that cut. I wonder if an old style lantern tool post and tool holder might have been easier instead of the QC on the "special" compound.

-DU-

DU,

Had to reach around the elbow, to face the flange up to the elbow and hold a .190" radius runing off to a control dia with a +/-.010" tol; variable stock on the face, there is a piece of drill rod chucked up in the tailstock that I gaged the tool against to get in the ballpark.

There is a setscrew under the tool block extention that slides along the tube across the ways, to take the down thrust, lucked out it was flat within a thou. As it got into the .190"rad there was a tad of chatter. The next tool was a face groove for an "O" ring, ruffed out at 120 rpm had to finish at 60 rpm to get rid of chatter in the bottom of the "O" ring groove.





Cheers,
Les H.

I go for whatever can of castable or moldable goop is handy at the moment. Bondo is a perennial favorite, and given the number of old machines undergoing cosmetic rehab, is most likely always available. Epoxy from the boatbuilding/woodworking shop is handy sometimes, and the gunsmith bench can yield up some blobs of cerro-safe or some other low temp metal. Lead can be pretty handy too. Either poured around something, or sometimes just strips or chunks at the right place will conform long enough to do the deed.

Most of my work though is piecing back together broken machinery parts, and I need to hold something just long enough to locate the first alignment pin, screw, etc. I don't have the problems of jigging for production runs, or applying serious metal removal techniques. And oh, how I dream of the day when I have to figure out how to hold a nice new casting, not the 2 or 3 oil soaked pieces that are supposed to add up to one whole one.

Rob

Les,

Yowch! Thanks for posting the pics and the explanation. Very cool setup. I will have to remember that one in case I have to ever do something similar. Hopefully not though

-DU-

Sorry if the question was too broad ...

The pictures and several examples listed were enough to get me in the right direction.

Thanks!

Perhaps some ideas adaptable from here.

http://www.carrlane.com/Catalog/index.cfm/29625071F0B221118070C1C513906103E0B05543B0B012009083C3B2853514359482013180B041D1E173C3B2853524B5A5B

or here.

http://www.dragonworks.info/Metalworking/Milling%20Fixtures/Milling%20fixtures.htm

David Merrill

Can't resist...
How do you mount odd shaped pieces???
Couple more shots of tequila and keep the lights off...
Works for ugly pieces too...