Grinding your own hss lathe tools. Tips & tricks?

Given that you're machining 304 stainless, I would start slow (with plenty of the best cutting oil that you own). With such a fine tool, the natural tendency is to be tentative with the feed and, on stainless, the result is likely to be that the tool rubs, hardens the surface and then, when you apply a little bit more pressure, digs in and breaks.

FWIW, my advice would be:

- Run slowly (a few hundred RPM, or less);

- Plenty of oil;

- Feed steadily 'through' the surface of the part (I.e. don't wind the tool until it touches the surface and then start feeding);

- When you see the curl of swarf appear keep feeding steadily until you're at your target depth. DON'T STOP.

On the tool: Make sure that the tip is the widest part - it looks from that photo that the tool may have tapered towards the tip (although the actual tip has gone) - you don't want the tool to wedge itself into the slot it has cut, or it will jam and break.

Difficult to tell from the photos, but it looks like there is quite a large relief angle on the front of the tool - if so, reduce this to the minimum possible (5° maybe?) to better support the cutting edge.

I am a heathen, and rough out any HSS tools I need with an angle grinder - much quicker than a wheel - and sharpen them on a belt sander. That said, 3/8" is a big chunk of HSS to start with if you want a 0.3mm wide blade. Broken centre drills, etc. will need less grinding, but you will need to make holder for them.

Exhibit A (set up for internal grooving):

(3mm grooving tool facing the camera; 1mm from a previous job on the other end.)

My 2p, anyway.

For a 0.3mm wide groove, you might consider using a piece of HSS hacksaw blade ground into a parting tool shape. There was a thread on here somewhere recently that showed a few examples, I think. Pieces out of a very thin HSS circular saw blade or slitting saw could be used too.

Lathe toolbits in hobby grade HSS are not really very good at being ground down that thin. They tend to crumble away as you have found.

I still use a bench grinder from time to time but more often use one of these. I’ve made a nice table and a few other jigs for it. Being able to change grits for anything from 40g to over 1000g in a few seconds is very handy. You can even get diamond belts and a leather strop for it. It is variable speed and has forward and reverse. It’s been designed to sharpen all kinds of tools from carpentry tools, woodturning tools and knives etc.

A couple of product shots from Axminster.

Nice machine Vic (I like the variable speed) - but so is the price (£450).

Not tried roughing tools on my 4" Warco belt sander, might give it a go when the weather warms up a bit. Keep meaning to improve the work table in (vertical mode) but generally I use it for shaping bits of dead tree at the moment, so it's less of a problem.

Regards,

IanT

I have a Record Power Belt and Disc sander that I used to use, I made a proper table and jigs etc for it. The only issue was the lack of availability of different sanding belts for it. I can get Alox, Ceramic, Zirconium, Trizact or even diamond for the Axminster machine. The arbor on the side has also been handy for using satin mops. I bought the machine when it was on special offer, think I paid £399 for it. Still expensive but it’s a handy machine to have.

Readiung that "It took hours to grind a 3/8 toolbit", out of tinterest roughly timed a tool grinding job.

The job was to grind an unused 1/4" HSS toolbit, to produce a double ended tool that can be used to produce either front or back chamfers.

A Worden Cutter grinder was used.

Set up time was approximately 5 minutes (Remove existing tool holder , set table square to grinding wheel, adjust table to give 7.5 degree clearance angle, fit appropriate tool holder,insert 1/4" toolbit, and set holder to 45 degrees )

The tool was advanced by 0.005" for each pass (Possibly rushing things? )

Grindi and inspect one end, invert tool and reverse, clamp, and grind.

Total time, just under 30 minutes from start to finish.

Cleaning up and putting away took almost as long!

Holding the toolbit in a suitable holder, and grinding freehand would be less precose, and probably more brutal, but quicker.

Howard

I don't have the cutter grinder, but if I did I would probably have roughed out the tool freehand, and done the final work on the Worden. That would probably halve the time by reducing a lot of the tedious 5thou at a time work.

5 thou at a time that's some grinding!

More to the point with using a tool & cutter grinder - the 'Worden' as I have built, or other - don't use it for the bulk metal removal at umpteen thou a pass.

You don't want to exchange a lot of fairly expensive, dressed wheel for a lot of waste steel; plus more wheel to dress its over-worked surface back to condition.

Free-hand grind the tool blank to shape first, by bench-grinder or angle-grinder, then use the T&C machine for finishing to geometry and surface. And then 0.001" would be a lot more appropriate depth of cut than a hefty great 0.005".

I to start using the angle grinder to roughly grind the shape in HSS. Then use the bench grinder (white HSS stone) for a better shape. Finally I use a small 80 mm diamond disk (€10,--) and jigs to grind and regrind the tools.

Drills, mills, slitting disks, roughing mills, rotary broaches and some form tools are ground on the CNC lathe.

I can regrind a HSS tool faster than replacing an insert. Nevertheless, most of the time I use carbide because they last longer than HSS tools. Sometimes HSS does a better job and small internal HSS threading tools cheap to make.

My HSS grinder (finish grinder) and some stackable holders.

Surely using diamond on HSS is counterproductive?

A diamond wheel gives a very fine finish on a HSS tool, after grinding with a pink, white or grey wheel.. Not much different, but a bit more precise than final honing with a diamond file.

I said that 5 thou "cuts" were puishing things a bit, but probably better than risking glazing the wheel by tiny licks.

As ever, there is more than one way of skinning a cat (Not that I am advocating that as an activity! )

The objective is to finish up with a cutter that does what is required.

Howard