Sharpening prick punch.

[BrooklynBravest]

Whats the cleanest way to sharpen these without a lathe and a tool post grinder?


I bought a nice brand new starret prick punch, took a couple pretty light shots into some 1018 steel flat and the tip chipped already.

I tried twirling it in my hand on the grinding wheel but that didn't come out too center.



Also side note, I asked in a previous thread but no one really directly answered the question. Do you guys use a center punch only on your layout marks or do you use a prick punch only at all? Or do you use a prick punch and center punch to widen the mark after?

[earlgo]

Chuck the prick punch up in the drill press, spin it and apply a stone to the end. It may take some time but you can get a good point this way.
Alternatively if your pistol drill is big enough, you can chuck the punch up in it and spin it against a spinning grinding wheel.
It is not required that the prick punch point be in the center. In fact, it helps alignment if you can see closer to the point, so grinding a flat on the taper next to the point, or an eccentric point, may be beneficial. Remember to keep the heat down by frequent cooling if required. A soft punch is aggravating.

--earlgo

[BadDog]

I've sharpened both by hand with no issue. If your not using an optical, there is really nothing to gain by (near) perfect concentricity, and as stated, you may be better served by off center points. I've converted pricks to center and back again with no complaints. However, I'm winging it here, but I suspect your prick punch is likely intended solely for such use and far too hard/brittle for anything more than light use. And that is not as a center punch for starting hand drill bits. Prick punches (as I know them) are for transferring "sanity check" layout from accurate drawings, or following scribed or layout lines so that you still have a reference you can see through coolant and other mess while working when the layout die washes (or is ground) away. If more than a tiny prick mark is needed, for instance to start a hand held drill, then following with a more robust center punch would be my choice. Also, if your strap material was hot roll with the mill scale remaining, the delicate point of the prick punch is certainly at risk. Heavy mill scale can be practically like trying to punch carbide. Prick punches (again, in my experience) are used in softer clean machined surfaces, so mill scale should be removed first.

[warmstrong1955]

Run of the mill center punches I sharpen on the grinder.
They hardly have to be perfect.

Transfer punches, I sharpen, and have built new, on the lathe.

They are not that hard, and either are center punches for that matter.
If you are particular and want to keep your center punch on center, chuck it up in the 3-jaw and have at it using the compound for the desired angle.

Bill

[BadDog]

Yeah, transfer punches (and screws) like optical centers are the only ones that require concentricity.

But this, and talk about turning in the lathe or drill motor, does bring up another question I've seen discussed before. And that is the direction for grinding the point. I've seen the argument made for grinding punches, and prick punches in particular, with a straight grind much like a GTAW tungsten. And that's the way I grind them. The general argument for this approach is that the inevitable grooves are along the path of displacment flow and penetration direction. Likewise there might tend to be less faceting (angle change) along that path when ground from point back as opposed to rotating horizontally across the wheel side or face. Given that prick punches are supposed to bite deeper for less pressure, I can see that more for the prick punch as opposed to the center punch, but I do them all that way.

[BrooklynBravest]

If the punch itself isn't center, will it throw off the drill bit when you go to center drill it before using the full size bit?

I'm going off how MrPete222 does it in his video. He uses a prick punch, very sharp homemade. Lightly makes a prick in the steel and then uses a micro drill press and a 1/16" bit or so to mark the spot deeper.

I have a center punch and a prick punch I really never use the center punch since its much wider and harder to place on my mark.

Mind you I am using layout lines and dykem to be as accurate as possible. Trying to be within 0.015 or.

Using drill press only.

[Harold_V]

Whats the cleanest way to sharpen these without a lathe and a tool post grinder?

If you have reasonable skill, spin it while it's in contact with a belt on a belt sander. You can generally create a respectable, quite near center, point.

I tried twirling it in my hand on the grinding wheel but that didn't come out too center.

I've always encouraged folks to use a grinding wheel for cutting tools, but for a scriber, a belt is far better. While a belt tends to round a cutting edge, your intention with a scriber is a round surface, unlike a cutting tool.

Also side note, I asked in a previous thread but no one really directly answered the question. Do you guys use a center punch only on your layout marks or do you use a prick punch only at all? Or do you use a prick punch and center punch to widen the mark after?

For those who work by hand, both can be a requirement, although work can be accomplished without either, assuming a drill press or mill is involved. Personally, unless I must drill a hole with a drill motor, I never use either item. I tend to use my mill (BP) for drilling, as I prefer to keep control of hole locations. That doesn't make my method of working right---just my preference. If you enjoy working by hand, I'd suggest both be used, as it's much easier to pick a proper location with a prick punch than a center punch, then the created location can be enlarged using a center punch. If that is your choice of habit, the center punch should be well centered, as well as quite round, otherwise you introduce inadvertent error in location, albeit generally quite small.

You are far better served, assuming you have at your disposal, a drill press, to simply use a wiggler, with work clamped on location, then start your holes using a center drill or spot drill. Disregard the notion that a center drill isn't suited for such work, as that's the opinion of those who have no experience and believe all the BS that is promoted on the internet. Those of us who were trained in manual machining have used center drills to locate holes as long as we've been in the trade and have yet to experience the supposed problems created by not using a spot drill.

Harold

[Harold_V]

If the punch itself isn't center, will it throw off the drill bit when you go to center drill it before using the full size bit?

The purpose of a center drill is to pick actual location. If you do so, it won't allow the drill to be drilled off location, but picking up a punch mark with a center drill offers a huge opportunity to introduce error. If you hope for close tolerance work, abandon the use of punches entirely. They are not preferred if close tolerance work is desired, and require a huge amount of skill and good fortune to be successful. Instead, do your layout work using a height gauge, then pick up your VERY fine lines using a wiggler.

And, if hole size is critical, don't shoot for final diameter in one shot. Drills have a way of not cutting round, straight, or on size. Drill your hole undersized, then open the hole with the proper sized drill, or ream if the tolerance demands that level of precision. Keep in mind, even reamers can yield bell mouthed holes, or out of round holes, although a reamed hole will almost always be superior to a drilled hole. Do take note that some materials respond poorly to double drilling, however. Brass or other copper alloys can be amongst them. In those cases, drills with zero rake are a good idea, to prevent self feeding.

I'm going off how MrPete222 does it in his video. He uses a prick punch, very sharp homemade. Lightly makes a prick in the steel and then uses a micro drill press and a 1/16" bit or so to mark the spot deeper.

He uses a small drill because it has little ability to do anything but follow the punch mark, but you are still battling the error that is introduced when you punch. Again, if you hope to do fine work, consider what I've said about the use of a wiggler, and not punching at all.

Mind you I am using layout lines and dykem to be as accurate as possible. Trying to be within 0.015 or.

Using drill press only.

If you use care, you can work to .005" tolerance reliably. Keep the wiggler sharp, and lines fine. Use magnification when you pick up the cross hair.

Note that the point of a wiggler need not be on dead center. So long as you get it running true, the shank can oscillate considerably and it makes no difference. That's why a wiggler is used in lieu of a rigid shank, which often doesn't run true due to error in chucking. Wigglers allow for compensation.

Harold

[Carm]

There was a time back in the dinosaur age when hand layouts were the norm, and still can be for large work done on machine tables too small to step off with the lead screw.
The prick punch is an intermediate tool between scribed lines and a center punch.
Prick punch has a far more acute angle than a center punch. It should be close to the scriber's.
All grinding on the above is radial to the point. True concentricity to the shank is unimportant.
The user feels the intersection between scribe marks and taps the prick punch at that point. Fussy work is verified with magnification and corrections are made with pool hall English.
The center punch follows for relatively rough work picked up with drills.
Prick punch is very good for needle wigglers.

To aid in accuracy, scribers and divider/trammel tools are often better sharpened to a radiused chisel shape to make a very fine line without throwing up a burr. The flat back picks up graduations by feel and transits straight edges without parallax.

[Conrad_R_Hoffman]

I've heard the technique BadDog describes as grinding a "bright point". The wheel direction is kept parallel to the axis of the punch. In theory the point should be stronger and the contact area will light up a tad better. I always grind them this way, more as a salute to history than a belief that it makes a huge difference.

[Mr Ron]

Here is the method I use; After blueing the work and scribing centerlines, I use a Starrett toolmakers hammer (it has a magnifying lens in it) and a prick punch to "lightly" punch a mark. I then check if the punch mark is indeed at the intersection of the scribed lines. If not, I angle the punch and tap to move the punch mark toward the intersection. Once I am satisfied that the punch mark is as close as I can get it, I use the center punch to enlarge the punch mark. I then use a center drill to start a hole. As Harold said, a wiggler should be used (I haven't used one, but maybe I should). It has been my experience that hammering the punch too aggressively creates an upset on the surface that acts to pull the drill off center.

[warmstrong1955]

Punching centers....is for +/- .030" at best, in my humble opinion.
Often, that's more than adequate.
Often, it's not.

For precesion I think of center punches as archaic things. Work great when drilling a hole that doesn't really matter if it's off a bit.
Same holds true to grinding the punch. If it's a bit off center, what difference will it make? (excluding transfer punches)
You are eyeballing the thing to scribe marks anyway.

Bill