Tool height

On my lathe (a Portass PD5) the surface of the compound slide that tools are clamped to is about 8mm below the centre height. This seems to mean that I can't use a tool thicker than 8mm (or more precisely, whose cutting edge is more than 8mm above its base). So how can I use a tool like this:

where the cutting edge is 25mm above the bottom of the holder? Can I attach some sort of tool holder directly to the cross slide (i.e. remove the compound slide altogether)? But then there will be no fine resolution way to move the tool parallel to the axis. What is the correct way to solve this problem?

Thank you - Rowan

You need to use a holder for those type of parting off tools to suit your lathe, this sort of thing

Thank you.

But that doesn't answer how I get the tool low enough so the cutting edge is accurately aligned with the cenre line of the lathe.

Thanks - Rowan

The tool holder will hold the tool much lower, and should then need slight packing up to bring to centre height. Study the dimensions in the link Jason gave and it should be obvious. Noel.

As Noel says the holder I linked to means that the bottom of your blade will be a lot lower than the height of the part at the rear of the photo which is what is held in the toolpost, just find one that suits the heights you have

Further to what noel and jason say that T shaped toolholder can be fitted with the tool holding part overhanging the end of the top slide. Which should bring things low enough to make room for shims or a spacer to get the tip height just so.

That said mounting on the topslide commits you to a certain amount of faffing around to ensure that the tool is exactly perpendicular to the work before starting to part off. As your D5 has a longer Tee slotted cross slide than older Portass machines there should be room to arrange a permanently fitted rear tool post to carry and inverted tool.

Makes for a more rigid set up as the top slide and its sliding ways are no longer involved. Being essentially permanently mounted its worth taking the trouble to get the tool set up really right rather than the pretty close that all to often has to be accepted when chopping and changing on the top slide. Lighter lathes are, inevitably, sensitive to the details of parting tool set up as parting off is, enevitably, quite aheavy cut fro a small machine.

Clive

Edited By Clive Foster on 09/08/2022 16:57:24

just looked at that Portass, you would probably have been better off with a 2 x 19 parting insert holder than the 3 x 26 shown. Not only is the bottom higher up relative to the ctr height of the spindle the 2mm nominal width cut will be easier on the machine than 3mm

The solutiuon is to make a "dog leg" toolholder, that hangs the bottom of the tool lower, so that it can be shimmed to bring the cutting edge UP mto centre height.If your lathe has a T slooted Cros Slide, if you can make and fit a rear toolpost, it should be made so that the inverted tool needs to be shimmed to bring it DOWN to centre height.

Look at Photo 3 in my "4 Way Indexing Rear Toolpost" Album to see this.

Almost everyone who uses a rear toolpost finds parting off easier..

Howard

Do you know where I can get one of these? I suspect that the cutting edge of the tool will still be too high though (there is only 8mm between the top of the top slide and the centre line of the lathe).

Thanks - Rowan

This is my one the cutting edge of the insert is only 5.5mm above the surface that the tool would be clamped to (top slide)

It's by Glanze, I think this is the one