Thread: Diamond Tool Holder

Hi Ben,
690rpm is your slowest speed?
What Diameter is that bar? I'm guessing your rpm is at least twice what it should be.

Stuart

G'Day Ben,
Do you have any way of dressing the wheels on on you POS grinder ?, if they are clogged or glazed they won't remove much material, just generate heat.
Regards,
Martin

P.S. Oops, didn't see Chris's post above.

As I said in my last post, ultimately this tool uses HSS and it still needs to be ground.

I have 2 good wheels on my Woodman 8" grinder, a Norton Blue #46 and a White Alox #120. Use the Norton mainly for HSS for the metal with a decent adjustable toolrest.

200 mm diam x 40 mm x 15.88 mm Classic 46 Grinding Wheel | The Sandpaper Man



I must say I never discolour the HSS, certainly nothing like you show in your photos.

Originally Posted by Stustoys

Hi Ben,
690rpm is your slowest speed?
What Diameter is that bar? I'm guessing your rpm is at least twice what it should be.

Stuart

Yep, too fast will explain all of that. He said it's 1". And half is about right.

I would turn that at 400rpm or so. Carbide I'd be up at 1500 or 1600.

It will not matter how hot you get your hss, there is no way you will temper it. If you want an interesting test, get a stick of 1/8", one end in vice. Heat it to cherry and then try to bend it with some pliers........

General rule I use is grind till its too hot to hold, then quench, repeat. But it won't matter if you blue the edge.

Cheers,
Ew

Originally Posted by Bryan

He said it's 1".

You had me thinking I was going blind!
The first piece of MS bar was 1"

Thats a Hercus 260 right? Spindle bore of 1"?
Now normally the chuck bore will be bigger than spindle bore(say 20%?)
The work piece appears to be bigger than the chuck bore.
So I'm thinking 1.5" maybe a litte more?
So the chart would say more around the 275rpm range.

Stuart

Originally Posted by Ueee

..It will not matter how hot you get your hss, there is no way you will temper it. If you want an interesting test, get a stick of 1/8", one end in vice. Heat it to cherry and then try to bend it with some pliers........

Sure, HSS will not temper... I was more worried about what happens to the red hot cutting edge when quenched in water. I believe it is best practice not letting the tool not get more than straw whilst grinding.

Originally Posted by cba_melbourne

Ben,

>I also found it hard not to discolour the HSS when grinding, went pretty slow and cooled it in water often

you probably apply too much pressure when grinding. The HSS should NOT change color. Overheating it and quenching does not make for a good cutting edge.

> Also, my grinder is a Chinese POS that I know regret buying.

It needs some TLC (Tender Loving Care). You can turn a cheap POS Chinese grinder into a reasonably good grinder, but it takes time and some extra outlay. First thing, toss away the grinding wheels. Good quality brand name grinding wheels cost often more than the complete brand new Chinese grinder. Then toss away the two ball bearings, buy good brand name ball bearings instead. Try to run it without wheels - it should not vibrate, else the rotor is unbalanced and needs fixing (some constant 100Hz hum is normal). Check the metal discs that support the grinding wheels - on cheap grinders these are often ugly pressings. Try to file off burrs and make the sides flat and parallel, if too bad make new parts (you have a lathe). Now install grinding wheels, using proper paper blotter. You may try several times, see if there is a position with minimal wheel runout. Now you need to dress the wheels, there are various tools to do this, but for occasional use there are rectangular blocks of some hard material (do that outside, lots of grit dust that is not good for any precision machine or tool nearby). Now you can already do some freehand grinding. Next step is improving the rests, make them more rigid and adjustable tilt in both axes to accurately guide the tool to be ground. Its lots of work, but you may end up with a usable grinder at a fraction the cost of a good grinder. Chris

I will agree with all Chris has said. I have done all of this to my POS chinese grinder and have made it work far better. H&F had a sale on with Abbot & Ashby 8 inch grinders at a great price when I was I was in Melbourne so one came home with me LOL.

The POS chinese grinder is waiting to be fitted with wire wheel and maybe buffing wheel. I think I paid less than $30 for the POS (Autocheap). The mounting disks were pressed steel and they were restrained by circlips. Now I ask you? Precision? Cast sleeves (I already had) and turned sleeves instead of circlips etc etc and it was improved, but a long way from good.

No looking back now.

Dean

Dean did you happen to look where the Abbot and Ashby grinders was made?

Originally Posted by Big Shed

Dean did you happen to look where the Abbot and Ashby grinders was made?

When I said "No looking back now" I meant it!

The original chinese POS vibrated like hell and I tried everything to fix it. It was mounted on a solid stand alo0ng with all the fixes and still vibrated.

The A & A is "sitting" on a desk near by and runs smooth without being secured! I am happy.

Cheers.

Dean

Just as an idea what can be made of a cheap and nasty grinder:

IMAG0919.jpg

I bought this in 86, could not afford a good grinder. Spent again as much as it did cost on bearings and good wheels, plus some hours to make rigid rests. But It has served me very well since. Where there is will, there is a way. Chris

Hi Guys, I was going to reply to some of the other points made about the Diamond Tool Holder but I'll start by trying to help Ben out.

As several posters have mentioned, the speed you are using is too fast for HSS when cutting steel.
As a general guide
HSS = low speed, low feed, heavy cuts.
Carbide = high speed, high feed, light cuts.

Heating up the HSS when grinding is no problem, it won't make a blind bit of difference to the temper.
What you don't want to do is keep dipping it into water, this will just cause thermal shock and is likely to leave micro cracks in the cutting edge. Just grind the tool bit and if it gets too hot to hold just leave it to air cool for a couple of minutes.
To change the temper in M42 HSS you would have to heat it to red and leave it at that temperature for several hours.

Try dropping your RPM by at least 1/2, put the lathe into it's lowest feed and take at least a 3mm deep cut (6mm on Diameter). The tool will cut that easily, even without coolant. Also, make sure to put a radius down the front of the tool bit, the easiest way is to use one of those diamond impregnated steel plates.
Once that's working, increase the feed rate in steps and see what the lathe is comfortable with, when you get the feed rate right you can try increasing the rpm too.

You mentioned the lowest speed was 690rpm, I assume that was not in back gear as the lowest speed on a Hercus 260 should be around 50rpm.
If you really want to run the lathe fast; use the Crobalt tool bit, that should be good for at least 1000rpm. Make sure you put that radius down the front corner to increase edge life and improve surface finish, and definitely don't cool the ground bit in water as cast alloy is more susceptible to thermal shock than HSS.

Cheers
Gary
Eccentric Engineering

Hi,

I've been a bit pre-occupied lately with family duties so I haven't been in the garage until tonight.

I did get to read everyone's posts and checked a few books. Definitely running my Hercus too fast for HSS. I also took my HSS and Crobolt bits to work and used the grinder there, much better result (and hopefully thanks to a OHS issue may have solved my grinder issues).

I had a quick turn tonight. Much better results.

Using HSS at 390RPM on a .2mm cut produced a really good finish on the bright bar stock.

I then moved onto the Crobolt bit. Running at 390RPM I took cuts at 0.1mm to 0.5mm on the slowest feed without any problems and a really good finish. I then a tried a 1mm DOC (2mm of the Diam) without success, but I think it's more to do with my lathe. Sounded like it was going to stall. It didn't damage the bit.

I then dropped the RPM's to 270, and took a 1mm cut, it worked but still sounded like it was straining the lathe. Reduced the cut to 0.7mm and ended up with another good finish and no stressful noise.

I read Gary's post earlier. I don't think my lathe is up to a 3mm cut. I will try again tomorrow night or on the weekend with the Crobolt bit at the higher speeds Gary recommended (will start with little cuts).

I may have confused some with my post the other night, I did start with 1" Blackbar then moved onto a approx. 2" bright bar.

I also tried the blackbar again, the Crobolt ate it up but still leaves a poor finish though it's probably better than the carbide. The face cut comes up pretty nice.

Cheers Ben.

Originally Posted by bwal74

I also tried the blackbar again, the Crobolt ate it up but still leaves a poor finish though it's probably better than the carbide. T

Hi Ben
Like you I cannot get a good finish on black mild steel...I get some steel supplies from a motor rewinder...I take the shafts

I get mixed results on this stuff...it seems to be going great and then the finish changes to bad and then goes good...all on the same bit of steel.....listening to the sound of DTH taking the cut it is definitely different qualities of steel an various points along the shaft....
next piece ( same make and model motor) could all be good or bad ...it just varies

On Bright MS its all good....so to me I use the black stuff for "training"