Tool grinding woes

Trying to make a cutter from HSS to turn a single start 2 Module worm in silver steel and struggling woefully.......any tips ?

Helix angle is important for cutting some threads, have you made sure you have clearance suited to the helix angle? You can calculate the helix angle from the pitch and the diameter at the root of the cut.

Martin C

What aspect of grinding the tool are you struggling with?

A piece of small round HSS is often used for large lead threads as the tool can be turned around to the helix angle.

You can buy a threadcutting gauge for Acme thread that is the correct 29-degree angle for standard worm threads. Makes it easier to grind the tool to fit one of the notches in the gauge. It is a two-sided notch, so more useful than the one-sided notch on a standard threadcutting gauge that has BS, UN and Acme all in one gauge. I bought mine off the net.

That will get your angle right. Your exact tip width you'll probably need to measure with a micrometer, feeling just when the tip of the tool clicks into the gap between the pre-set mike anvils.

As said already, make sure the leading flank of the tool has the extra clearance ground on to clear the thread's helix angle. Finsih the tool grinding by rubbing it on a bench oil stone to get final fit and finish.

If you want to make a nicer job of it, grind some side rake on the top surface of the tool bit, angled back from the leading edge of the toolbit. Then set the topslide to 14 degrees and use this for your infeed. The cutting is then done almost all on the leading edge of the tool and the trailing edge just cleans up its surface a tad.

Alternatively, instead of angling the top slide, you can use the dodge of leaving the topslide in the normal position parallel with the lathe main axis. Then, for whatever depth of cut you take on the cross slide, advance the topslide by one quarter of that amount. EG, if taking a 1mm deep cut, advance the topslide 0.25mm. This move the toolbit position as close as dammit to a 14 degree path. This is my preferred way of doing it.

Why silver steel? HSS will work much better for you. It stands up to the forces of Acme/worm thread cutting without losing the edge so much better.

I read the post that you are using silver steel to make the component not the tool. Silver steel is not the nicest material to cut. Have you got a piece of say EN1A to practice the cut ? This will prove the tool geometry and method.

May be making a cutter to do the worm wheel so SS would be the metal to use

Sorry, I misread the silver steel as being for the tool, not the job as it in fact is. Carry on.

worm in silver steel

One of the toughest jobs you can do is a worm

plus silver steel, one of the toughest materials you will ever work with

Does it HAVE to be silver steel?

Many well known lathe makers of yesteryear outsourced leadscrews to a specialised firm instead of dealing with the hassles themselves

Silver Steel machines nicely as supplied in it's annealed state, both milling and turning, it's nicer to work with than Mild Steel.

I find it awkward to machine too even in its annealed state.