Center drills

Find a junk printer - dot matrix, laser, or inkjet. They all have precision ground rods within. That's what I use.

Also, for the best precision in drilling holes with my minimill, I use a collet to hold the drill. The chuck that came with it isn't very good.

Yeah! Even when they already have broken packages on the shelf.

Also remembered another good tool: Piston wristpins from large diesel engines. I have 3 that are about 3" dia x 6" tall. They are accurately ground and make great squares. You can set one on the table alongside the spindle and look at the gap angle between the two.

Maybe a bit large for a mini mill but the rod used on car damper struts could be of use and readily available. Last dampers that came out of my VW I kept and were 22mm OD chromed ground bar and while I could see the wear area by the finish the difference in size from the unworn sections was almost indistinguishable with a 0.01mm graduated non digital micrometer, maybe in the order of 0.001 mm to 0.002mm.

IIRC Rollie's Dad used a shock absorber rod.

jsw

John wrote in rec.crafts.metalworking on Wed, 10 Nov 2010 21:25:39 -0500:

Are you sure that's not 90 degree spotting drills that work that way?

[ ... ]

Same thing -- different terminology.

Enjoy, DoN.

So, here is the result of 3 hours' work:

1) I found a dowel pin. At least I am pretty sure it is a dowel pin. It is pretty and shiny, 0.5" x 6", it has those black caps either end and on it it says USA made, 1/2". I do not know how I got it.

2) In the chuck, using a different indicator from last time, the TIR

================== different problem -- from what you describe in the complete post you are doing better than expected. For ultra precise work you need to go to a jig borer or grinder $$$$$$$. Google on SIP and Moore for examples

some discussion see

for one less expensive solution see

and the one I have and like Key is to use a very light hammer and just a tap to mark the metal, and then enlarge with a more robust punch and hammer. A mighty blast on the punch with the optical center finder will destroy the tip.

For high precision layout invest in a surface plate, a right angle plate, and a space block set and use this with a flat scribe (make from HSS lathe tool) for example

?PARTPG=INSRAR2&PMAKA=630-4050&PMPXNO=950511?PARTPG=INLMKD&PMPXNO=948885&PMAKA=418-4525 Bright light at the machine tool will help.

Also consider

you are set up to do precision layout. Problem with smaller machines is quill to table/workpiece distance. cheaper

-- Unka George (George McDuffee) .............................. The past is a foreign country; they do things differently there. L. P. Hartley (1895-1972), British author. The Go-Between, Prologue (1953).

[...]

I find Fastenal problematic at best.

There are two branches within reach of here. One I will not use at all. The other is more helpful but it tends to be a continuing struggle to get what one wants without having to have 100 units of it.

Furthermore, what it shows in their on-line catalog bears no relation to what is available from or through the local branches at least quantity-wise.

Not so long ago one was able to walk into a branch and pick up common stock like mild steel square rods of several dimensions etc. Now the shelves stand empty, still labeled with the items they previously contained. Yet the manager blames lack of stock on "shortage of storage space". BTW this particular branch is housed in a space the size of a small hangar with a few shelves huddled round the middle. The rest is completely wasted.

Having said that, I had good luck there yesterday, they had all the stuff I wanted including metric lock washers (at $3 I did not mind getting a 100) and a retaining compound they told me last week they would not have.

One has to count one's blessing when one finds them especially now that McMaster-Carr will not ship to new customers in Canada.

Michael Koblic, Campbell River, BC

That branch may have low sales, resulting in lower acceptable stock levels. I have never found an empty slot for steel rod or angle at the store I use.

I buy most small hardware by the 100 package. Only oddball threads or very rarely used sizes are bought in small quantities. It isn't worth the trouble to pick up the exact quantity of something you need, when you'll need more in a couple weeks.

Canada! Well, what do you expect? Those polar bears never where reliable at delivering packages, anyway. ;-)

Reamers (assuming a chucking reamer instead of one with a square tap wrench drive on the end) have a soft shank which can bend, so you can't trust that for indicating runout away from the chuck.

Weird.

Again weird. This is in the chuck, or in the collet?

Still using the chuck -- or the collet?

One of the little pocket sized gooseneck LED illuminators is nice for dealing with this. It has a magnetic base so you can stick it nearby and bend the neck so it illuminates the cross scribe.

O.K. but note that you will have a chisel point on the tip of the center drill (like on the normal jobber's length drill bits), while the spotting drill comes to a sharp point.

O.K. The machine screw length drills may have split points, so they can start more accurately even without a dimple or a spotting drill.

O.K. The axis is pretty perpendicular to the table, then. Did you have a light behind the square and pin?

Yes. And this can cause a drift in Y-axis position with different length drills or mills.

You had been using a digital one? I don't remember you saying this. *Some* digital ones are more accurate than some mechanical ones. The Starrett "Last Word" mechanical if the bias spring is not applying bias throughout the range. (A bump on the side of the point can cause it to skip in the spiral, so there is a major deadband in the range.)

How about *buy* at least one, so you know what it needs to look like? I recently got (from a sale flyer from MSC) a couple of 1/4" x 60 degree spotting/centering drills (MSC #FJ71332167). If the sale from that flyer is over, the "FJ" won't do any good, and the price will be back up to whatever it was.)

Probably -- especially with a drill with split points. For larger standard bits, the chisel point may be wider than the dimple left with the optical punch, in which case the drill is likely to walk away from the punched center point.

Consider acquiring at least one or two proper spotting drills, so you can compare them with what else you have and what you make later.

Yes!

It is certainly a source of error.

Good Luck, DoN.

================== different problem -- from what you describe in the complete post you are doing better than expected. For ultra precise work you need to go to a jig borer or grinder $$$$$$$. Google on SIP and Moore for examples

some discussion see

for one less expensive solution see

and the one I have and like Key is to use a very light hammer and just a tap to mark the metal, and then enlarge with a more robust punch and hammer. A mighty blast on the punch with the optical center finder will destroy the tip.

For high precision layout invest in a surface plate, a right angle plate, and a space block set and use this with a flat scribe (make from HSS lathe tool) for example

?PARTPG=INSRAR2&PMAKA=630-4050&PMPXNO=950511?PARTPG=INLMKD&PMPXNO=948885&PMAKA=418-4525 Bright light at the machine tool will help.

Also consider

you are set up to do precision layout. Problem with smaller machines is quill to table/workpiece distance. cheaper

-------------------------------------------------------------------------------- REPLY: (sorry this is WML and *still* will not format properly)

1) I have the optical punch. I think I mentioned it passing in my conclusion. I certainly prefer it, more so now after I tried the hard way :-) 2) I have *two* bright lights at the machine but still could not see the damn lines! I think the surface of the scrap piece of metal had something to do with it. Still, I would not have had a problem with the optical punch... 3) Wow! $40 for the co-axial indicator! I have been eyeing them for a while. And he ships to Canada! Now that dollar is at parity...Duly bookmarked! 4) For the stuff I do I like the cheaper options. However, one has to pick one's spots.

Thanks again,

Are you using layout dye [dykem]? This makes a big difference when trying to see the fine layout lines. Also for precision work you will need a smooth flat machined surface. for some examples see

?PMAKA=505-1392&PMPXNO=941830&PARTPG=INLMK3?PMPAGE=310&PARTPG=INSRIT

Most shops use blue but red traditionally was supposed to work better on brass. I have used red and blue on aluminum, brass and steel and can't see any difference.

Most any mill supply should stock. The thinner the coat of layout dye and the thinner the layout lines [i.e. the sharper the scriber] the better.

-- Unka George (George McDuffee) .............................. The past is a foreign country; they do things differently there. L. P. Hartley (1895-1972), British author. The Go-Between, Prologue (1953).

--------------------------------------------------------------------------------

I couldn't resist, ordered it. Then I saw the link for the $28 US-made one on Amazon. except it was not the full kit.

George, thanks for the information and the links.

Rex

...

I use a fine-tipped prick punch (home-made from a broken tap) to make a very small dimple at the line crossing, followed by a center punch ground somewhat sharper than the angle of a drill bit. Usually the drilled hole position is within 0.005".

jsw

By taking the MT arbor out of the spindle and rotating it 180 degrees (required for arbors with tangs, obviously), one could take comparison measurements. Differences may reveal where the inaccuracies are.

I would be switching arbors and substituting a different chuck, too. After switching tooling, and another set of measurements, it should become clear where all of the runout is coming from.

One of those MT arbor blanks with just a 1" (or other size) head/stub on them, could be very helpful in checking out the MT socket relative to the spindle's center axis. I'd make a durable mark on the spindle and start checking runout on the stub, which would be located cloe to the end of the spindle at this time. The arbor stub OD might not be perfectly concentric with the centerline of the MT taper, but it should be very close if the arbor was finish ground between centers.

If the stub doesn't have a center hole, then it probably wasn't finish ground between centers, so a little touchup may be required. I'd then make a durable mark on the arbor in line with the previous mark on the spindle, and touch the stub with a die grinder stone (held by a rigid fixture mounted to the machine table) to make a small zone/pathway that's concentric to the spindle's centerline.

Measurment of the newly ground path should show nearly perfect concentricity. If the error is excessive, I'd probably suspect a very poor grade of bearings.

I suppose this procedure could also be used on a drill chuck arbor, since the grinding zone only needs to be small, and could be outside of the taper where the chuck body seats.

The previous steps would verify if the bore of the MT spindle socket is good, but won't help with the head/spindle-to-base perpendicularity issue.

[snip]

What I do is to use an optical centering scope that mounts in the 3-jaw or collet chuck of the spindle, followed by a large spotting drill.

I have found that with this scope, it's more accurate to not center-punch the workpiece. I just center on the scribed lines and use the spotting drill to make the initial dimple. A center-punch dimple tends to pull the spotting drill sideways, reducing accuracy.

The other thing the scope is good for is locating zero-reference features on a workpiece, subsequently using the DRO to move to places where holes are desired. This is fast and accurate. I often scribe all the hole centers, to catch errors, but again I don't center punch the hole locations.

The only problem with the scope is that it was a bit expensive.

Joe Gwinn

[...]

Yes to the dye, no to the surface - it was awful.

[...]

Michael Koblic, Campbell River, BC