Light special operation aluminum machining

I've been in and around engine shops for fifty years. In the balancing area, some pistons require the removal of a few grams to bring them to target weight. The usual method is to chuck the piston bottom end out in a standard light duty 10" lathe, often having a 4' bed. Sometimes the boss is right at the bottom of the piston; just a facing op.



Sometimes, on older engines with taller pistons having cylindrical skirts, it is necessary to reach in with a boring bar and face off a few thou off the pin bosses. This requires careful hand feeding. Remove, weigh, replace, repeat.



Since the workpiece is never more than 4" long and the working area is never more than 2.5" to 4.5" diameter and 2" deep, a long lathe has way more footprint than the operation requires. The cut taken is always in aluminum and always a light cut. The center of the piston, where the connecting rod small end rides, is always open, so the area being cut is usually less than 1" on each side and usually an interrupted cut.

What other machines and setups could:

1. Have a smaller footprint.
2. Position the piston vertically so the line of sight is more convenient.
3. Be inexpensive enough to not cost more than a light duty lathe.
4. Holding would be "drop in, clamp, cut, open, pull out."
5. Standard tooling
6. Make the cut without hand/eye moving the tooling across the area being cut. Ideally, set the tool, feed down-up or in-out, without having to eyeball the other axis.

I can imagine a small benchtop mill with a variety of flycutters being able to do the work, but to make sure we'd choose the most efficient and cost-effective machine and tooling for this operation, how would you go about replacing the lathe?

jack vines

hardinge HC chucker lathe . no tailstock, 6" chuck . about the size of a small desk. can be had under $1500

Look into "speed lathes" - might be too small, but at least some seemed applicable. (Not sure if any are made new...)
Vekto & Mecana Speed Lathes

Thanks for the suggestions.

A speed lathe would have a smaller footprint and can be mounted to have a better line of sight, but still requires eyeballing the end of the cut.

There was a Hardinge here on craigslist which had been converted to a bench grinder. I should have taken a closer look at it.

jack vines

Small footprint and, I would assume, reasonable cost?

How about a bench top drill press with a three jaw chuck on the table. I would suggest soft, aluminum jaws. A large sanding disk would do the first type of piston you describe and a selection of smaller diameter ones for the second type.

An easy to use and accurate depth stop would be a must. Threaded rod with a fine thread and a speed nut with a scale would work nicely.

Of course, I am assuming that this is a machine that will be dedicated to this task only.

EPAIII said:

Small footprint and, I would assume, reasonable cost?

How about a bench top drill press with a three jaw chuck on the table. I would suggest soft, aluminum jaws. A large sanding disk would do the first type of piston you describe and a selection of smaller diameter ones for the second type.

An easy to use and accurate depth stop would be a must. Threaded rod with a fine thread and a speed nut with a scale would work nicely.

Of course, I am assuming that this is a machine that will be dedicated to this task only.

Click to expand...

Yes, this would be a dedicated machine.

Yes, we've considered a drill press with some type cutter which would be plunge-only, as DP chucks don't care for side thrust.

FWIW, sanding discs clog too quickly on aluminum to remove any meaningful material.

jack vines

PackardV8 said:

Yes, this would be a dedicated machine.

Yes, we've considered a drill press with some type cutter which would be plunge-only, as DP chucks don't care for side thrust.

FWIW, sanding discs clog too quickly on aluminum to remove any meaningful material.

jack vines

Click to expand...

So use a small milling machine with a 3-jaw chuck clamped to the table.

So use a small milling machine with a 3-jaw chuck clamped to the table.

not to be a wise-ass here, but what is a "small milling machine" ?

the enco/jet mill-drill press- cross-vise style is not even allowed to be mentioned on
this forum.... its a POS anyway, and has little reference of repeatedly removing
mass from any piston. a burke/powermatic/clausing doesn't really take any
less footprint than a normal #1 bpt/clone... so why suffer? they are basement
machines that command a premium .....

a bpt step- head, r8 , is quiet and smooth ,, and not in demand as much as a
vari speed . could be your answer.............

PackardV8 said:

Thanks for the suggestions.

A speed lathe would have a smaller footprint and can be mounted to have a better line of sight, but still requires eyeballing the end of the cut.

Click to expand...

Not sure how you get around that, but a speed lathe is light enough to mount at a 45 degree angle.. or some other angle that lets the Mark One Eyeball - or a binocular 'scope - have an easier view.

Or maybe.. just add a drop-on fixture incorporating a DRO of its own and one or more decent electronic cameras to some OTHER machine so it need NOT be "dedicated", just "zeroed", each use?

Shade tree technique, I am sure, but we usta balance a piston by drilling large non-penetrating divots or smaller through-holes into/through the skirt of appropriate size and count, not by milling anything at all.

Precision balance or scale, drillpress and Vee-block work. No mill OR lathe required, and not really any significant money invested even in vee blocks or clamping, either.

"Bad idea?" Pass.

The engines were pushed, often to failure, but piston skirts with holes in them (below the bottom-most ring) never seemed to be any sort of issue.

2CW

thermite said:

Shade tree technique, I am sure, but we usta balance a piston by drilling large non-penetrating divots or smaller through-holes into/through the skirt of appropriate size and count, not by milling anything at all.

The engines were pushed, often to failure, but piston skirts with holes in them (below the bottom-most ring) never seemed to be any sort of issue. 2CW

Click to expand...

Yes, that expedient certainly removes weight. However, if/when the customer ever looked inside and saw random holes in his piston skirts, he'd probably not think too highly of our work. What works and what looks good to the customer are not always the same thing. What the customer is happy with always wins.

jack vines