ideas for fixturing a cylinder workpiece?

[SRT Mike]

I have a piece of 2.5" 6061 aluminum that gets turned on the lathe to a teardrop shape. I need to do a secondary operation on the mill (mill a flat in the side of the piece and tap a hole).

Any ideas on fixturing this piece? the outside is a teardrop shape but the interior is a straight cylinder and it's threaded near the front.

I really don't want to put any marks on the outside because it will be sent out for finishing and I get quite a nice finish off the lathe that I'd rather not mar up.

The ideas I have so far is either a threaded rod that the piece will screw onto but it may not be as rigid as i'd like. Second option is some sort of expanding thing inside (similar to the lathe jaws I use to machine the OD on the lathe). Third option is I could turn a negative of the outside shape in a square block, then mount that square block in the vise jaws. If I let the teardrop piece protrude from the holder then by closing it in the jaws (pushing the tapered piece of the teardrop into it's matching shape) it would grip it sort of like a morse taper and prevent it moving and I can machine the part through a hole I cut in the top of the fixture.

What is the best solution? Are there any other ideas?

[HuFlungDung]

Along the line of your 3rd option, can you simply use a couple of simple donuts (rings, short cylinders), bored to contact either end in the fashion of a collar? If you make these collars with the same OD, then you can lay them in the bottom of the vise or in V blocks to keep the part axis level.

To protect the part, the collars could be made of UHMW plastic.

[Geof]

Originally Posted by SRT Mike .....The ideas I have so far is either a threaded rod that the piece will screw onto but it may not be as rigid as i'd like. ....

Let me see if I can explain in words without resorting to pictures. This is the approach I would probably take with some extra features. Possibly your sizes are too small to make this feasible.

Make a mandrel, neat fit on the thread, neat fit in the bore.

The mandrel has a through hole with a taper at each end and is split.

You have a second mandrel that fits neatly inside the first and has a matching taper at one end and a thread at the other. This second mandrel has a base or something that allows it to be secured horizontally in the milling machine. The first mandrel is slid over this, the.

You have a tapered 'washer' that fits on the second mandrel and enters the tapered end of the first mandrel; and you have a nut.

The part is screwed onto the mandrel that has its thread.

The nut is tightened on the second mandrel pushing the first mandrel down on the taper and pushing the tapered washer in locking everything up solid. from the inside.

[SRT Mike]

Originally Posted by Geof Let me see if I can explain in words without resorting to pictures. This is the approach I would probably take with some extra features. Possibly your sizes are too small to make this feasible. Make a mandrel, neat fit on the thread, neat fit in the bore. The mandrel has a through hole with a taper at each end and is split. You have a second mandrel that fits neatly inside the first and has a matching taper at one end and a thread at the other. This second mandrel has a base or something that allows it to be secured horizontally in the milling machine. The first mandrel is slid over this, the. You have a tapered 'washer' that fits on the second mandrel and enters the tapered end of the first mandrel; and you have a nut. The part is screwed onto the mandrel that has its thread. The nut is tightened on the second mandrel pushing the first mandrel down on the taper and pushing the tapered washer in locking everything up solid. from the inside.

i can't quite picture this.... but couldn't I just use a single mandrel?

Mitee bike makes an expanding doohickey that looks like a collet - a round thing split into multiple segments. It comes in one flavor that will fit the ID of my part, and when you tighten a bolt down the middle the diameter expands - basically a screw-actuated version of an ID clamping hydraulic chuck. Is your suggestion similar?

I just wasn't sure if that was a good way to do it but I guess the way that mitee bite holds it is pretty much the same as on the lathe so it should be OK....

[SRT Mike]

Originally Posted by HuFlungDung Along the line of your 3rd option, can you simply use a couple of simple donuts (rings, short cylinders), bored to contact either end in the fashion of a collar? If you make these collars with the same OD, then you can lay them in the bottom of the vise or in V blocks to keep the part axis level. To protect the part, the collars could be made of UHMW plastic.

I could do that yep - the only thing would be I am going to need to make lots and lots of these parts in batches of maybe 100 at a time but I have a lot of parts I run, so it will have to be easy to setup and locate each time with minimal chance for error. The part is cylindrically symmetrical since its turned so where the flat goes on the circumference is not important but it must be located the same exact distance from front to back on each part... and being lazy we'd rather not take the steel soft jaws off the vice if we can help it

[Geof]

Originally Posted by SRT Mike i can't quite picture this.... but couldn't I just use a single mandrel? Mitee bike makes an expanding doohickey that looks like a collet - a round thing split into multiple segments. It comes in one flavor that will fit the ID of my part, and when you tighten a bolt down the middle the diameter expands - basically a screw-actuated version of an ID clamping hydraulic chuck. Is your suggestion similar?..

Yes.

The Mitee Bite thing must be similar if not identical.

You need a fixed (inner) mandrel to giveyou the repeatable location and the split mandrel to give the clamping between the the part and the fixed mandrel.

In hindsight I realize I was wrong in including the thread. All you need is a split mandrel (collet). You slide your part on up to a stop, tighten a nut which expands the mandrel and there you are.

[tauntdesigns]

I don't know how deep the bore is but I was thinking... yea I shouldn't do that, lol

They make expanding 5c collects ( I've never used any ) that could be used in a 5c collect indexer.

Maybe?

[One of Many]

You start with a 2.5" diameter? But you don't state what the internal dimension or the length is. It sounds like you do the internals and external profile cuts in one op and part off?

One option might re-sequence the operations to do the end face and internals as the reference. Then part it off and move it to the mill for the flat and tapped hole. Back to the lathe for the teardrop profile IF the mandrel could support it. Use the tailstock for roughing if need be, then finish with the tailstock backed off. That adds a lot of part handling. The interrupted cut isn't going to help much, but the finish pass may not even notice it.

By the description, the teardrop end of the part isn't really defined well.

Another option if the part were reasonable length to fit between the jaws of a Kurt style vise. Even if the part were clamped above the moving jaw(tall soft jaws) such that the back jaw had a stub mandrel and the front jaw had a shallow dish to sort of "tailstock" support it, that should hold it for the secondary operation.

In many of the odd shaped parts I have done in the past. In order to make it easier to hold the part and less complex fixtures. I would leave excess material to be removed later and use it as a means to grip and align.

Last suggestion is consider a bismuth(low temp alloy) bedding. This is where you fixture a part in a box, supported such that the part is located properly in all planes and the part centerline is at the top of the box. Melt some low temp alloy and fill the box there by creating a nest for the part. I have seen applications where this was used to make vice and lathe soft jaws too.

DC