Author Topic: Getting the most out of a drill grinding jig, or Perfect twist drills every time  (Read 17496 times)

Offline Graham Meek

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Further to a request from the Moderators I have been asked to share my modifications on the drill grinding jig.

These jigs can be obtained from various vendors and come in a wide range of colours. The newer jigs are a copy of an Original grinding jig marketed by Picador. I do not know for sure if this was manufactured under license in the UK from a firm in the USA or the other way around. The fundamental difference with these jigs to those that are currently on the market is that they grind the drill differently due to their construction. The Picador has a vertical pivot point which means the facet is ground with a cylindrical profile. On the more current versions this pivot post leans towards the grinding wheel, because of this lean  the drill facet is now ground with a conical form.

Depending on the approximate decade of manufacture this lean varies between 6 and 12 Deg. Those with a 6 Deg lean usually do not grind a drill with the correct included angle. I think the reason for this is the guy who moved the moulded scale to compensate for the change to the original vertical post moved the scale the wrong way. If you look at my photograph of the jig with an engineers square against the drill facet you will see there is an additional 7.5 Deg wedge inserted in the base to rectify this error.

These jigs are and have to be accepted as a compromise. They are trying to grind drills from nearly a flat bottom through to a 90 Deg countersink. The worst case is the last as it will soon be realised this drill  point is going to require a lot of relief on the heel of the drill to allow the drill to cut without it rubbing on the heel. The relief is inbuilt and constant and is based on the 90 Deg included angle, this is accomplished by an offset between the drill location vee and pivot point centre line, it is approximately 5 mm or 0.2". This is hard to tie down as this dimension also varies. It is this eccentricity that is the key to the modification and a broader understanding of the what is required when twist drill grinding.

What has never helped these jigs is the Instructions supplied with the jig, some instructions say the drill must project by one diameter, (D), while others say 1/2 D. Some say the cutting edges should be vertical while others say they should be over at an angle. I have also been told that the instructions do not even translate from the other languages to give the same sort of instructions. This is sorry state of affairs and small wonder why these jigs usually end up under the bench.

Having used a Picador jig from time to time I had always had a good drill, even though the process was a bit fiddly. I usually reserved it's usage for grinding my neighbours or relations drills which always seem to come by the sackful. Preferring to grind my own free hand. I was therefore a little curious when a poster said "these jigs are useless" knowing that I have had good results. The above is some of the things I have found out in the interim and goes to show that not all of them are useless.

The only object of the exercise was to make these jigs more user friendly, have a tool that was a valuable asset and that produced factory standard ground drills without the fiddle factor that was usually required to get a good result. As most of these jigs end up sold on, under the bench or in the scrap bin the outlay involved to procure a donor jig is minimal so the reader could have at the end of the day a very valuable asset if they follow my lead. The down side is once word gets out that these jigs are a valuable resource the price will go up.

I hope you have found this post informative, I will endeavour to give you follow-up reports, in the meantime the modified jig will grind drills from 1.5 mm (1/16") to 25 mm (1") diameter without fuss although the sub 3 mm (1/8") need an additional element made to cater for this size range.

My best regards
Gray,

« Last Edit: June 19, 2014, 08:14:03 PM by Graham Meek »

Offline Graham Meek

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Sorry forgot to load this photograph,

Gray,

Offline Jo

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 :thinking: You have now got me thinking I might have to go and check the angle on my one, it never seemed right. I also have the top end of a rather better quality drill grinding jig but not the bottom half I wonder if it could be made to mount on the Union T&CG :noidea:.

Jo
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P.S. That does not mean I am turning down trying out that Dormer drill cutter grinder  :naughty:
Enjoyment is more important than achievement.

Offline Jo

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Well I have found my Picador drill sharpening jig  :-\ but the fit of the top into the bottom has about 5 degrees of wobble  :facepalm: And it looked square for this drill at 68 degrees  :headscratch:

Then there are these other two which are made of slightly better quality metal, but both are missing their bases and I suspect neither heads are complete  :shrug:

Jo
Enjoyment is more important than achievement.

Offline Graham Meek

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Hi Jo,

The jig you have looks about the same vintage as my donor jig, and to me it looks like the pivot pin in the base is leaning. When you say there is a wobble are you referring to the free play in the joint where the angle detent is not firmly into the vee location on the mating part, if so there is a quick fix for this problem.

The Crackle black finished attachment that you have looks like the attachment for an early Deckel cutter grinder, but I am not sure. The last jig looks like another such attachment but for some long lost machine.

My best regards
Gray,

Offline pgp001

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The one on the right of Jo's photo is the upper part of a "Reliance" drill grinding jig

Phil


Offline Jo

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Gray it is the pin that is too small for the hole it mounts in  :headscratch: It would be nice to get that one working properly  :ThumbsUp:.

Thanks Phil, I found a couple of photos of the reliance sharpener. I think that the quality of that reliance head is more in keeping with the union but the problem is time: Nothing is going to get done this side of the rally  :wallbang: But I hear someone has time and is off to a :DrinkPint: garden party this weekend  8)

Jo
Enjoyment is more important than achievement.

Offline Steam Haulage

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Jo,
 I had one of those Picador drill grinding jigs, it came from Sarjents in Reading, which did reasonable service for nearly 20 years. It got left behind at some point in time. On mine and I think just visible in your first picture the main support was held in place by a piece of spring (originally) steel holding the stem upright and in good contact with the base casting when new. Eventually the spring went soft and the jig leaned over.
The base was intended to be fixed to the bench alongside the grinding wheel and the slot allowed the user to adjust the distance from the wheel to the jig.
Seeing Graham's work makes me wish I still had mine. :'(

Jerry
Dogs look up to you, cats look down on you, pigs treat you as equal.

Offline ths

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Thanks for putting this her Gray, it's much appreciated.

Cheers, Hugh.

Offline Edward

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I have one of the picador jigs, inherited from my late grandfather.

Having recently set it up I had the same issue as Jo with a wobbly stem - I found removing the screwed on plate that retained the stem in the base v-shape and packing behind it with some brass shims tightened it up perfectly.

Then I spent a happy few hours resurrecting all my old and broken drills. Beware,as word gets round you will find yourself doing the same for family and friends!!

Offline Graham Meek

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The problem with these jigs is that on their own they all look the same. It is not until you get a Picador next to a modern clone that the differences become obvious. As stated before the Picador unit can produce good results with a little fiddling, the modified clone will produce a ground drill as good as you can purchase from a reputable manufacturer. The Devil is in the detail, and it is the fact that these jigs are being asked to grind a multitude of angles that is there downfall.

My modification does not retract from the original jigs capabilities, they are still there but what it does do is make the results far easier to achieve by providing a means of adjusting the relief angle to suit the drill diameter. It is no longer one relief angle fits all.

My best regards
Gray,

Offline Jo

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ok so mine is a clone not a Picador  :(

So Gray where do I start trying to sort it out?

Jo
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Offline Graham Meek

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Hi Jo, & Edward

The modification to the base vee is shown in the opening post in the "close-up of the eccentricity scale", a piece of 20x20x3 mm BMS angle has been fixed into the existing vee and the original retaining plate replaced. The post nearest the camera stops the plate from moving when rotating the new eccentric. Hidden from view a spring is fitted between the plate and the base casting to provide a means of adjustment.

These mods can be done to a Picador unit with advantage, BUT the Picador unit grinds the drill Facet on a totally different principle, purely because the pivot stem is vertical.

Offline Baron

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Hi Gray,

A good write up.  There's a couple more of these at the scrapyard (or there were on Wednesday) !  I was tempted to grab them both.
Maybe next time...

Best Regards:  Baron.

I donít regret the things Iíve done, I regret the things I didnít do when I had the chance.

Offline Thor

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Hi Gray,
thanks for continuing the drill grinding jig "saga". Baron, thanks for the pictures showing the difference between clones and Picador. Could you tell us the angles of each with respect to the table?

Thor