Vertical Parting Tool

[jackary]

I have just made a vertical parting tool for my Stepperhead lathe. I first tried a normal parting tool mounted vertically but it suffered from scuffing on the parallel sides of the tool which is at the last part of contact with the metal being cut. So I made a one piece tool by silver soldering a small part of a high speed steel parting tool to a slightly thinner sheet of steel. Then I ground the high speed part to have clearance in both directions and it worked very well. It is nice and rigid in the cutting directions, with no bending for the parting tool. The mandrel rotates in a clockwise direction for a rear tool post which will be a problem for lathes with screwed on chucks so they would have to have the tool mounted at the front of the lathe. Here is a short video of it operating. It is only cutting off a 20mm dia. because I could not hold the camera and apply cutting oil with a brush at the same time but I will try it with larger diameters. But so far so good. Why has this not been tried before?
http://www.youtube.com/watch?v=S8HvS...lSWeYLoFlU2iA=

Alan

[Dr Stan]

Very nice job. Parting/grooving can be a real pain in the backside grabbing & tearing, but you have made it look quite easy. Any chance of posting drawings on the Shop Tools thread?

[jkilroy]

You might try making a tool out of a scrapped circular saw blade, comes with a nice brazed carbide insert ready to go.

[PixMan]

It's been done many times before, though usually the tool is upside down so that the spindle doesn't have to be run in reverse. Many can't be run that way because they have screw-on chuck and faceplates.

[jackary]

Hi Pixman, I realise a normal rear parting tool has the cutting tool mounted upside down and generally horizontal to use anticlockwise rotation, and one reason is to avoid the chuck unscrewing, but this also means that the cutting tool has a bending component rather than a compressive component that the vertical tool has.
Alan

[sasquatch]

Nice workmanship, and YUP!! You do make it look quite easy.

Thanks for posting this, interesting!!

[PixMan]

Hi Pixman, I realise a normal rear parting tool has the cutting tool mounted upside down and generally horizontal to use anticlockwise rotation, and one reason is to avoid the chuck unscrewing, but this also means that the cutting tool has a bending component rather than a compressive component that the vertical tool has.
Alan

I don't understand what you mean. It seems to me that the forces on the tool itself would be the same. It is only the forces transmitted through the tool blade and to the gib and ways of the cross slide that would be different if the tool was upside down.

If parting in the "downward force" orientation, I'd probably just stick with traditional insert parting blades in a quick-change holder. If the machine's cross slide is good and tight, the upside-down parting tools work well and can be used on machines with screw-on chucks.

[Dragons_fire]

The cutting forces would be more in line with the tool this way, so it may not chatter as much.

why dont you just rotate it and mount it in front and then youre spindle can run forwards?

[jackary]

Hi Pixman & Dragons Fire,
My reasoning for a vertical cutting tool is that in both cases front or rear mounted parting tools, the cutting tool is subjected mainly to bending stresses. The greater the cutting depth the bigger the cantilever and the greater the bending moment. I think that this bending moment applies a rotating force on its mounting components i.e. the cross slide and topslide which can be moved to enable the cutting tool to have a greater or lesser cut depth creating dig ins and chatter etc. In essence the extended cutting tool is just like a ruler in classroom; where kids love to hold it extended over their desk edge and flick it so that it vibrates. By mounting the cutting tool vertically it is supported from below and the cutting forces are mostly directly downwards putting the cutting tool in compression rather than bending, because the cutting edge is directly supported below with no cantilever. I suggest that this avoids resonance due to a cantilevered support and avoids the stress concentration where the cutting tool meets its support block. It also allows the cut swarf to freely exit over the top of the tool. All these advantages allow the cutting edge to be thinner which also reduces the cutting forces. The downside is that you have to have a lathe that can safely rotate the mandrel clockwise without the chuck unscrewing, so threaded mandrel noses are no good for this. Of course it could be mounted on the front side of the lathe but this would generally get in the way of the normal topside location. Parting off has always been a problem with model engineer size lathes which has been helped by the new insert parting tools which have an insert fitted into a very deep thin toolholder but the geometry still exists. I will have to do more experimentation to try to justify these claims but it is really just food for thought and worth a try.
Alan

[DR]

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Why has this not been tried before?

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Alan

What is it that you feel has not been tried before?

Rear part off? Brazing HSS onto a blank? Allowing side clearance on the tool?

All of those have been around for many decades.