The Home Machinist!

I have a 9x20 chinese lathe, that I have been learning to use. I would like to know the best way to cut an o-ring slot, inside of a .3125" breach hole. The material for the breach, will be either aluminum or delrin.

Thank you

The very first tool in the pic should give you an idea for an internal grooving tool. For a groove inside a .312 hole I would probably start with a small boring bar.


While I'm at it here are some other turning tools.


My lathe tools are all machine ground.

Jim

I would make a boring bar, take a piece of 3/16 drill rod, and ream a .124" cross hole. Then grind a cutter from Carbide or hardened 1/8" drill rod. Press it into the hole, cut off the excess on the backside.

Since you probably have a thru hole, you could use a setscrew to hold the cutting tool in place.

Dave J.

Thanks for the info!

Silent wrote:I have a 9x20 chinese lathe, that I have been learning to use. I would like to know the best way to cut an o-ring slot, inside of a .3125" breach hole. The material for the breach, will be either aluminum or delrin.

Thank you

Here's a few tips that will make it easier for you.

Don't try for a tool that is the precise width. Use one that is narrower, allowing for the groove to be roughed, then you can step over to take a clean up cut on each side of the groove, using a long travel indicator for precise location and groove width. It's important to mic the grooving tool you will grind in order to be able to calculate the amount to move in each direction.

Rough the groove from its center point, stopping short of the desired diameter by a couple though. When you go for size, plunge the tool to proper depth on one shoulder, the one nearest the headstock, then retract the tool slowly, so as to face the cut a second time. You then move to proper location of the groove, the side towards the tailstock. Plunge to proper depth, then slowly advance the carriage until you reach the other side of the cut. Stay short a half a thou, and retract the tool. That will yield a precise groove with a good finish.

Cut Delrin dry, but lube aluminum with kerosene or WD-40.

You most likely will have best success hand grinding a tool rather than making one an insert type. It's not all that hard to do.

You will be drastically limited to bar size in this case, because of the small bore, and the relative depth of the grooving tool. Be mindful that you must be able to place the bar in the bore without the bar touching-----and it must be capable of generating the groove without touching, as well. The shank of the tool will likely have to be smaller than 3/16" in order to accomplish the task, so keep it short so it retains rigidity. A narrow grinding wheel can prove very useful for grinding the tool.

The picture, below, will give you a general idea of what your tool will look like. Keep in mind, yours will be much shorter, assuming the groove is near the end of the part.

Harold