Thread: Slot Drill Sharpening - A Case of Making Do ( or not really )

I had been whinging to Stuart the other day about the state of my very worn tool and cutter grinder. He suggested because only a small amount of its travel is required when sharpening the end of a cutter ( the flutes are something else ) why not use it as it is.

So this afternoon I had a go. My first attempt was on a 19mm slot drill, the set up, questionable, but the results were satisfactory. The indexing head is from the Hercus vertical milling attachment. Holding it in a vice was not really ideal. I had used the vice to hold a diamond wheel dresser while dressing the wheel. A purpose made holder would be a worthwhile exercise. I had to dismantle the vice to remove all the grit. And the grit goes everywhere. One of the photos below shows the exposed ways.
Hercus provided no way protection in their design of this grinder. Sixty years of grit on the ways have taken their toll. I covered them with a rag held in place with little Neodymium magnets. Should have covered the bloody vice!

I was toying with the idea of making an adapter that would enable the indexing head to be mounted onto the vertical milling attachment's swivel base. Would be less cumbersome than having the thing attached to the vertical slide.

To position the slot drill so the cutting edge was parallel with the grinder's spindle I just eyeballed it. Just like I eyeballed the cutting and relief angle. Seemed to work OK. But that was the easy stuff. There are a couple of aspects of sharpening a slot drill than I'm not sure about. Some of my cutters have an offset notch between the cutting edges. That will require a thin wheel which means I'd have to swap and redress the wheels. Then there's shallow undercut in front of the cutting edge. I'm wading into deep water. The final photo shows a few of my larger slot drills with a variety of relief grinds amongst them. Replicating those grinds might be a bit tricky with the gear I have at my disposal.

How do owners of other T and Cs get on? Probably easily with the right kit.

BT

Hi BT,

Got to be better than using a less than sharp slot drill.
You shouldn't have to worry about the center gashing until you have sharpened it a fair few times. Not sure what you mean by "shallow undercut in front of the cutting edge".

Now for your DTI air spindle

Stuart

Hi Bob,
Good to see you at least make the attempt. As Stu says, they have to be a lot better than blunt bits!

Some of my slot drills have a gash in the center that looks to have been made with the corner of a wheel, maybe you could try that with the same wheel.

As i have found out with the blohm, be sure not to dress the wheel and then turn it off and then back on. The sudden jolt from turning it back on will ruin the dress/balance ever so slightly. Unless your using a vfd with a nice ramp up time of course.

Cheers,
Ew

The gash between the cutting edges is just clearance so that the cutter is more easily sharpened (if it wasn't there you would have a very messy spot in the cutter where the cutting edge swaps from pointing in one direction to pointing in the other). If you put a thin disc in an angle grinder it could be done with that as its placement is not critical. As long as one of the cutting edges overlaps the centreline/ axis of the cutter everything will still work.

Michael

Two slot drills close up. The first is a Hydra, gashing is a separate operation. The other cutter is a Clarkson. the gashing on the latter is where the undercutting I mentioned is evident. On the Hydra there is no undercutting. The grind is parallel with the cutter's axial centreline.

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( A note about the photos for those who may be interested. I don't have a digital SLR but I do have a bunch of old glass lenses. I bought a Nikon J1 interchangeable lens mirrorless camera and a 30 dollar adapter that enables the use of the old Nikon lenses on the J1.
The photos were taken with a 45 year old 50mm lens perched on the end of a set of Nikon extension rings. Better than the Coolpix jammed up against the eyepiece of the Marcel Aubert scope.)


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BT

That undercut appears to have a radius on it as well, I wonder why they bothered? Still a few 0.1mm touch ups before you have to worry.

Nice pictures

Stuart

I had a play with my T&G grinder today.. first time

This is a 1/2" square WKE 45 bit .... not too bad a result for a first attempt .... I need to put a radius on the end and hone it yet

I used a coarse grade cup wheel because it was already on the grinder

Mike

Bob, as Michael and Ewan have already mentioned: the end slot is not critical in terms of size and placement, Just make sure it is NOT in the centre. Ideally, one edge of the slot is on the centreline or just off it. If it is across the centre line, you can no longer make plunge cuts.
I've see pros make that cut with a thin 1" disk in a Dremel or air die grinder free hand. Don't bother setting up the T&C grinder for the purpose.

Originally Posted by morrisman

I had a play with my T&G grinder today.. first time

This is a 1/2" square WKE 45 bit .... not too bad a result for a first attempt .... I need to put a radius on the end and hone it yet

I used a coarse grade cup wheel because it was already on the grinder

Mike

Mike,

How about a photo or two of your setup. I bet your close up was taken with a bloody mobile phone. I'm still using a Nokia brick.

Originally Posted by jhovel

Bob, as Michael and Ewan have already mentioned: the end slot is not critical in terms of size and placement, Just make sure it is NOT in the centre. Ideally, one edge of the slot is on the centreline or just off it. If it is across the centre line, you can no longer make plunge cuts.
I've see pros make that cut with a thin 1" disk in a Dremel or air die grinder free hand. Don't bother setting up the T&C grinder for the purpose.

Thanks Joe.

I do have a Dremel complete with thin cut off discs. Those thin discs that just evaporate. I've learned to stand clear.

BT

Hi BT

I admit to being a novice T&C grinder user ...

Its a Addison BRAND grinder , MADE IN India ...........it came with a lot of attachments, most of which I dont know much about

the camera is a 3 meg pixal MINOLTA .. a $10 job from the op shop

Originally Posted by morrisman

Hi BT

the camera is a 3 meg pixal MINOLTA .. a $10 job from the op shop

Ah! Now you are just rubbing it in!!

Originally Posted by morrisman

...........it came with a lot of attachments, most of which I dont know much about

Well you won't be needing those then. I can help you with your burden.