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Gundrill sharpening fixture - need advice on using it

crystalltiice

Aluminum
Joined
Jul 31, 2015
Hi Guys,

I just bought two old gun drill sharpening fixtures made by SIG (Schweizerische Industrie-Gesellschaft) (Typ: 37.096.006 and Typ: TBS 5-12) and I'm trying to figure out how to use them. I have no gun drills on hand to try but was hoping some one with a similar fixture could advise.

They look similar to this except for the chuck part: http://www.teco.net.au/wp-content/uploads/2010/05/gun-drill-sharpening-fixture.jpg

I'll post a picture of the actual one I have soon.

It has a rather peculiar chuck for holding the drill - a triangle piece inside the chuck rests in the V groove of the drill and then as you tighten the chuck, a finger presses the drill from the opposite side against the triangle piece so the drill, regardless of its size is always centered, at least much better than any other fixture I've seen.

It does not have any graduations for rotating around the drill axis but rather has some pins on a collar and another locking pin on the body to engage with them. Almost like a spin indexing fixture/ rotation stop.

Two pins are close together and as such when engaged with the taper locking pin, they will stop drill rotation, I assume this is when one is grinding the cutting edge. Engaging the locking pin in other places will allow a large but limited range of rotation between the pins.

I'm assuming it is for grinding the back relief? These pins are fixed and not adjustable, I think there are about 3-4 of them.

The actual spindle also runs eccentric and there are some graduations on it just behind the chuck head, the strange thing is that it is marked from I think 1-13 on both parts of the assembly? It looks to adjust the amount of eccentricity, locked in place by a knurled ring which I can't get loose.

The spindle part has a few knurled rings with holes for a C spanner. I'm not sure if they are used for locking the rotation or only adjusting end play. The only ones that are moveable seem to adjust end play/lock rotation. The others are stuck and I'll have to first make a spanner to be able to loosen them to see what they do.

I have no experience sharpening gun drills but saw a nice video but with another type of fixture, it does however show the various angles on the drill tip. I assume that once I put a drill in the thing and go through the motions it will make more sense but I was hoping that someone with experience with one of these SIG fixtures can shed some light on it.

I contacted UNISIG as they seem to be the new owners of this product line of the original company but have yet to receive any reply. Hours on google has not yielded any results either. I'm really hoping someone on here has some insight!
 
It has been a few years since using one of those , but basically use that triangle to lock the drill down,locks against the drill flute. Lock the base at the bottom on the desired drill point angle. Set your primary clearance relief angle. then rotate around maybe with those pins you spoke of for secondary relief and so on so your drill doesn't have a heel left on it to rub. The small drills we ground were run through a bushing so I can't remember if we actually ground those on center or not. I forgot to mention when you are ready to sharpen just traverse the drill against the side of preferably a cup wheel. Produces a straight grind with necessary relief and new drill point. If you have a drill that's not abused or broken you can visualize the lines and angles being ground. Look at some of the major players web sites to see what their drills look like. You may have to do some trial and error grinding to get things sorted out. Hope this helps.
 
DM-42 Sharpening Head for Gun Drills
This is a faceted grind fixture. Yours looks like it has the ability to roll the secondary, that is good/better.
I prefer a radial grind and it looks like your fixture will do that. Tickle feel the gun drill you need to sharpen to find the original angles is the best way, as you mentioned.

I would set the edge angle off the dull gun drill with 12* for primary to make the primary a faceted grind.. The turn upward to the next pin to provide the secondary clearance angle. Ignore that the secondary is a triangle to the primary because that is no problem. Increment in-feed to the land width you wish / or what was on the original. Then feed across as increment turning the drill upwards to make the heal a constant roll grind. But rolling with a small up feed and a serises of passes across/not rolling into the wheel..

This way you don’t have to reset the primary cutting-edge angle with each next gun drill to be sharpened.
Grinding two flutes you will need to figure how to get two flutes the same.

You can use your/or the customers gun drill to fabricate a holding bushing for that size CRS is fine for this and a drilled hole with a split dowel can be the edge locator, and haveing a counter bore for the colding set screw so becoming the locator to make the edge eueball horizontal.

Some such fixtures have an extended bar with a tail center.

Using a type S or a type 50 one might think to roll up into the wheel would be good...but they often put a hole in the wheel making it (the wheel) not flat, so going across is best with perhaps a tickle fonish gring with full wheel.
 








 
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