How to Machine Lead Bars

That lead bar looks cast in a mold that was not jiggled and as a consequence has surface voids at the walls. It may also have other voids due to shrinkage in the interior.

I suspect this might cause problems when machining. Lead can be made with compression molds that reduce the voids.

One problem you will have is the softness of the lead that will interfere with gripping in the chuck unless you have a wide area, smooth chucking mechanism.

this search string will find some data. read a few pages and see if you are helped.

http://www.google.ca/search?hl=en&safe=off&q=lathe+%2B%22machining+soft+metals%22&btnG=Search&meta=

Get a copy of "Machinery handbook" and never lose it!

Try K20 bits and speed upto 400m/min and feed 0.4-0.8 mm/rev

BTW: never tried lead, but this is what we use for the soft metals like aluminium, white bearing metals, teflons etc.

The most important thing to remember machining lead is that your tool must be very sharp and have a lot of clearance angle and back rake angle to prevent galling. When machining soft materials you want your cutter to slice the material, not push it. You can experiment with the speeds and feeds to get the finish you want. Obviously you want to avoid generating too much heat. Also, if you take too large of a cut you can bend your part, knocking it off center so that on the next revolution it will clobber your tool holder and maybe you ass well. Be careful.

Thanks all you helpers.

Gabriel.

Good advice here, Garyceng

In order to prevent the soft chip from turning back under the tool, I would suggest chip curlers- This metal will be quite soft, so aggressive chip curler is called for IMHO. You want to move the chip out and away from the work, so it doesn't pressure weld or gall.

This won't require a heavy oil. I have cut this using kerosene (mineral spirits).

ALso, holding this is a problem. Leave extra length to grip in the chuck.
I used chuck jaws with big teeth and made sure they got well into the workpiece. So your Yield loss (per cent of product per raw material input) will be higher than your customer (boss) expects. (cant have parts with teeth marks!) But you have to hold it, as Garyceng correctly points out.

The maximum Depth of cut should be about equal to to the depth of your tool edge. This is soft metal.

I donot have any experience drilling it. I suspect that coolant will be even more important in that case, and that you may not want anywhere near as sharp of angles, based on my drilling of copper.

I have not been able to find recommended tool geometry for lead online, in metals handbook desk edition, nor the met cut books. Good luck, be sure to wash your hands before eating and no eating or drinking in the work area.

http://www.jtbaker.com/msds/englishhtml/l2347.htm

milo

I wonder if this material is better double end chucked, like a wood lathe does it. This would allow for good flat grippers that do not use much stock or hurtthe soft lead wood.. You can probably make them with flat curved surfaces that exactly match the OD of your work piece

It is my soft chuck , rule in mm

I don't know if this will help or not, but if you can work harden the lead, it will be much easier to machine.

The method I used to use with flat material was to simply squish it in a vise. We were making small flat parts. If you could make a tube to fit the casting in with a piston that you could use in a hydraulic press the lead would machine much better after it had been squished and work hardened. Your tube doesn't need to be any bigger than to just clear the part.

The other comments on high relief angle and very sharp cutters are dead on and feeds and speeds similar to aluminum are also right.

Good luck!

That's an interesting approach.

Youngs modulus for lead is 16Gpa; pine is 8; steel is 200.

There is a different structure to pine wood than lead metal.

I wouldn't try it. but I'm a Dig teeth in deep and it will hold kind of guy. I'm third generation steel mill guy- grandad- catcher on mill with tongs; dad- electrician- me shoveler, environmentaltester, lab supervisor machining and testing . I don't claim much finesse.

My "guess" is that the lead will not hold.

My experience is teeth held.

milo

My point of view is that lead is soft and ductile, so with teeth it will flow, tghten the teeth and they sink deeper.

The broad smooth jaws will have a large grip area with a low grip pressure. so cutting drag might now shift it was the peak stress of teeth will.

Of course, an experienced lead turner is needed now...

I'll wait for someone's report, To me the low elasticity means that those jaws will squeeze and the lead will move ... not fight back like steel. Teeth will get in beyond ability of material to move, and be held by the deformed metal surrounding them;

Like I said, no finesse from where I come from.

Nice discussing this with you.

lets see what comes up

milo

I agree with you Milo. You seem to also have had the misfortune of machining lead.

Lead has the same problems as soft aluminum only much worse. As with any questionable material you must hold your work rigid. Drills will grab very easily in lead and try to rip the part out of the holding device. Grind extra clearance on the drill so the chip has someplace to go and use short pecs to clear the chips. The pecks sholud be less than the diameter of the drill. Otherwise the drill will gall in the hole and rip the part into a mess.

If you can't use a chuck with agressive teeth then the example shown by another poster using a shim is a great idea.

Hello devitg;

Suggest you use the speeds and feeds calculated for machining Lucite as the characteristics are essentially similar.

A nitride coated carbide can be used but no benefit had over a titanium nitride coated high speed steel tool bit with at least 15% tungsten content.

I'm not able to provide specific speed and feed rates or tooling characteristics because I am not knowing the composition of this lead material; basic .006 per/rpm feed with tool grind at 11%+ positive rake.

Your holding adapter is fine in a three jaw or collet chuck too.

As previously stated the "Machinery Handbook" contains all the information you seek and then some...