Question - roundover bit for a micro lathe?

Machine Shop
#1

If I wanted to smoothly knock off the edge on a piece of brass round stock, is there such a bit for a sherline or taig micro lathe?

The bits I seem to come across over & over again make facing, cutoff, or plunge cuts, but I can’t find anything that’d mill in a clean consistent rounded edge of any dimension.

When I think round-over it’s always been for a router in woodworking in the past. So perhaps I’m just not using the right name for the bit you’d put into a lathe tool-post.

To be clear - I don’t want a flat beveled edge - I’d like a slight clean consistent round over.

#2

Usually when I see people use a radius tool in a hobby environment they’ve milled/hardened or ground their own.

#3

Yes, its a form tool. However the smaller lathes may not be able to take the forces.

Edit forgot about the radius tool

#4

We have a radius cutter for our sherlines here and that does the trick. There may be a cutter of some kind otherwise but it would be under a lot of stress if it were more than just a point.

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#5

https://www.mscdirect.com/product/details/84412089 is this what I’m looking for?

#6

Tim - suspect you might be right on it not being available in a 1/4 inch shank… finding bigger stuff - but so far it’s more than I want to spend…I might just have to try to make one myself…

#7

I mean… is it? That would put a corner radius on a part, but I don’t know if it fits in your lathe, is the radius you want, or if it’s in your price range (seems expensive imho).

As Tim and Jim mentioned, this is a form tool. Most tools only contact the work at a very small point when cutting, but this is designed to touch the part along the entire length of the cut (the arc), which means it’s prone to chatter. I’m not sure if a smaller lathe will be rigid enough to use something like this.

There are other options (ball turning setups) but that’s almost always more trouble than it’s worth.

#8

this would be to put the slightest of radius on round annealed brass - so the pressure would be minimal - only issue is finding a 1/4 shaft radius to fit my micro-lathe… can’t seen to find that

#9

In theory the cnc Sherline lathe should be able to do this - with a “regular” cutting tool / insert.

#10

I’ll second that. takes a little practice but should be able to add a radius to the edge.

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#11

If you’re willing to do this portion at DMS, we have a 3/8" tool holder for the Sherline lathes.

image

I’ll “third” what @hon1nbo and @nicksilva said about using the radius tool as a viable solution. It worked for me …

#12

I went down this path at home because this is a banned activity at the space. I.E production of firearm projectiles.

A larger tool post for a bigger bit would be a way to go, but between the bit and the tool post I’d be out another $150.

So I’ve decided to abandon a nice lil radius and just do a slight flat bevel.

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What I’ll be doing is knocking off the ejector ring and reducing the length of these jacketed hollow point rounds which I make myself out of 9mm brass.

I’m doing this as, in their current form, these projectiles occasionally deform the .40 brass during reloading. The overall length of the projectile is also sub-optimal for several different reasons.

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